| 156. | S Subramanian, Q T Campbell, S K Moser, J Kiemle, P Zimmermann, P Seifert, F Sigger, D Sharma, H Al-Sadeg, M Labella, D Waters, R M Feenstra, R J Koch, C Jozwiak, A Bostwick, E Rotenberg, I Dabo, A W Holleitner, T E Beechem, U Wurstbauer, J A Robinson Photophysics and Electronic Structure of Lateral Graphene/MoS2 and Metal/MoS2 Junctions Journal Article ACS Nano, 2020, ISSN: 1936-0851. Abstract | Links | Tags: Solid-Solid @article{, title = {Photophysics and Electronic Structure of Lateral Graphene/MoS2 and Metal/MoS2 Junctions}, author = {S Subramanian and Q T Campbell and S K Moser and J Kiemle and P Zimmermann and P Seifert and F Sigger and D Sharma and H Al-Sadeg and M Labella and D Waters and R M Feenstra and R J Koch and C Jozwiak and A Bostwick and E Rotenberg and I Dabo and A W Holleitner and T E Beechem and U Wurstbauer and J A Robinson}, url = {https://doi.org/10.1021/acsnano.0c02527}, doi = {10.1021/acsnano.0c02527}, issn = {1936-0851}, year = {2020}, date = {2020-11-16}, journal = {ACS Nano}, abstract = {Integration of semiconducting transition metal dichalcogenides (TMDs) into functional optoelectronic circuitries requires an understanding of the charge transfer across the interface between the TMD and the contacting material. Here, we use spatially resolved photocurrent microscopy to demonstrate electronic uniformity at the epitaxial graphene/molybdenum disulfide (EG/MoS2) interface. A 10× larger photocurrent is extracted at the EG/MoS2 interface when compared to the metal (Ti/Au)/MoS2 interface. This is supported by semi-local density functional theory (DFT), which predicts the Schottky barrier at the EG/MoS2 interface to be ∼2× lower than that at Ti/MoS2. We provide a direct visualization of a 2D material Schottky barrier through combination of angle-resolved photoemission spectroscopy with spatial resolution selected to be ∼300 nm (nano-ARPES) and DFT calculations. A bending of ∼500 meV over a length scale of ∼2\textendash3 μm in the valence band maximum of MoS2 is observed via nano-ARPES. We explicate a correlation between experimental demonstration and theoretical predictions of barriers at graphene/TMD interfaces. Spatially resolved photocurrent mapping allows for directly visualizing the uniformity of built-in electric fields at heterostructure interfaces, providing a guide for microscopic engineering of charge transport across heterointerfaces. This simple probe-based technique also speaks directly to the 2D synthesis community to elucidate electronic uniformity at domain boundaries alongside morphological uniformity over large areas.}, keywords = {Solid-Solid}, pubstate = {published}, tppubtype = {article} } Integration of semiconducting transition metal dichalcogenides (TMDs) into functional optoelectronic circuitries requires an understanding of the charge transfer across the interface between the TMD and the contacting material. Here, we use spatially resolved photocurrent microscopy to demonstrate electronic uniformity at the epitaxial graphene/molybdenum disulfide (EG/MoS2) interface. A 10× larger photocurrent is extracted at the EG/MoS2 interface when compared to the metal (Ti/Au)/MoS2 interface. This is supported by semi-local density functional theory (DFT), which predicts the Schottky barrier at the EG/MoS2 interface to be ∼2× lower than that at Ti/MoS2. We provide a direct visualization of a 2D material Schottky barrier through combination of angle-resolved photoemission spectroscopy with spatial resolution selected to be ∼300 nm (nano-ARPES) and DFT calculations. A bending of ∼500 meV over a length scale of ∼2–3 μm in the valence band maximum of MoS2 is observed via nano-ARPES. We explicate a correlation between experimental demonstration and theoretical predictions of barriers at graphene/TMD interfaces. Spatially resolved photocurrent mapping allows for directly visualizing the uniformity of built-in electric fields at heterostructure interfaces, providing a guide for microscopic engineering of charge transport across heterointerfaces. This simple probe-based technique also speaks directly to the 2D synthesis community to elucidate electronic uniformity at domain boundaries alongside morphological uniformity over large areas. |
| 155. | F Haase, B V Lotsch Solving the COF trilemma: towards crystalline, stable and functional covalent organic frameworks Journal Article Chemical Society Reviews, 2020, ISSN: 0306-0012. Abstract | Links | Tags: Foundry Organic @article{, title = {Solving the COF trilemma: towards crystalline, stable and functional covalent organic frameworks}, author = {F Haase and B V Lotsch}, url = {http://dx.doi.org/10.1039/D0CS01027H}, doi = {10.1039/D0CS01027H}, issn = {0306-0012}, year = {2020}, date = {2020-11-06}, journal = {Chemical Society Reviews}, abstract = {Covalent organic frameworks (COFs) have entered the stage as a new generation of porous polymers which stand out by virtue of their crystallinity, diverse framework topologies and accessible pore systems. An important \textendash but still underdeveloped \textendash feature of COFs is their potentially superior stability in comparison to other porous materials. Achieving COFs which are simultaneously crystalline, stable, and functional is still challenging as reversible bond formation is one of the prime prerequisites for the crystallization of COFs. However, as the COF field matures new strategies have surfaced that bypass this crystallinity \textendash stability dichotomy. Three major approaches for obtaining both stable and crystalline COFs have taken form in recent years: Tweaking the reaction conditions for reversible linkages, separating the order inducing step and the stability inducing step, and controlling the structural degrees of freedom during assembly and in the final COF. This review discusses rational approaches to stability and crystallinity engineering in COFs, which are apt at overcoming current challenges in COF design and open up new avenues to new real-world applications of COFs.}, keywords = {Foundry Organic}, pubstate = {published}, tppubtype = {article} } Covalent organic frameworks (COFs) have entered the stage as a new generation of porous polymers which stand out by virtue of their crystallinity, diverse framework topologies and accessible pore systems. An important – but still underdeveloped – feature of COFs is their potentially superior stability in comparison to other porous materials. Achieving COFs which are simultaneously crystalline, stable, and functional is still challenging as reversible bond formation is one of the prime prerequisites for the crystallization of COFs. However, as the COF field matures new strategies have surfaced that bypass this crystallinity – stability dichotomy. Three major approaches for obtaining both stable and crystalline COFs have taken form in recent years: Tweaking the reaction conditions for reversible linkages, separating the order inducing step and the stability inducing step, and controlling the structural degrees of freedom during assembly and in the final COF. This review discusses rational approaches to stability and crystallinity engineering in COFs, which are apt at overcoming current challenges in COF design and open up new avenues to new real-world applications of COFs. |
| 154. | T Banerjee, F Podjaski, J Kröger, B P Biswal, B V Lotsch Polymer photocatalysts for solar-to-chemical energy conversion Journal Article Nature Reviews Materials, 2020, ISSN: 2058-8437. Abstract | Links | Tags: Foundry Organic @article{, title = {Polymer photocatalysts for solar-to-chemical energy conversion}, author = {T Banerjee and F Podjaski and J Kr\"{o}ger and B P Biswal and B V Lotsch}, url = {https://doi.org/10.1038/s41578-020-00254-z}, doi = {10.1038/s41578-020-00254-z}, issn = {2058-8437}, year = {2020}, date = {2020-11-05}, journal = {Nature Reviews Materials}, abstract = {Solar-to-chemical energy conversion for the generation of high-energy chemicals is one of the most viable solutions to the quest for sustainable energy resources. Although long dominated by inorganic semiconductors, organic polymeric photocatalysts offer the advantage of a broad, molecular-level design space of their optoelectronic and surface catalytic properties, owing to their molecularly precise backbone. In this Review, we discuss the fundamental concepts of polymeric photocatalysis and examine different polymeric photocatalysts, including carbon nitrides, conjugated polymers, covalent triazine frameworks and covalent organic frameworks. We analyse the photophysical and physico-chemical concepts that govern the photocatalytic performance of these materials, and derive design principles and possible future research directions in this emerging field of ‘soft photocatalysis’.}, keywords = {Foundry Organic}, pubstate = {published}, tppubtype = {article} } Solar-to-chemical energy conversion for the generation of high-energy chemicals is one of the most viable solutions to the quest for sustainable energy resources. Although long dominated by inorganic semiconductors, organic polymeric photocatalysts offer the advantage of a broad, molecular-level design space of their optoelectronic and surface catalytic properties, owing to their molecularly precise backbone. In this Review, we discuss the fundamental concepts of polymeric photocatalysis and examine different polymeric photocatalysts, including carbon nitrides, conjugated polymers, covalent triazine frameworks and covalent organic frameworks. We analyse the photophysical and physico-chemical concepts that govern the photocatalytic performance of these materials, and derive design principles and possible future research directions in this emerging field of ‘soft photocatalysis’. |
| 153. | M Scheckenbach, J Bauer, J Zähringer, F Selbach, P Tinnefeld DNA origami nanorulers and emerging reference structures Journal Article APL Materials, 8 (11), pp. 110902, 2020. Links | Tags: Foundry Organic @article{, title = {DNA origami nanorulers and emerging reference structures}, author = {M Scheckenbach and J Bauer and J Z\"{a}hringer and F Selbach and P Tinnefeld}, url = {https://doi.org/10.1063/5.0022885}, doi = {10.1063/5.0022885}, year = {2020}, date = {2020-11-01}, journal = {APL Materials}, volume = {8}, number = {11}, pages = {110902}, keywords = {Foundry Organic}, pubstate = {published}, tppubtype = {article} } |
| 152. | Y Xiao, C Feng, J Fu, F Wang, C Li, V F Kunzelmann, C-M Jiang, M Nakabayashi, N Shibata, I D Sharp, K Domen, Y Li Band structure engineering and defect control of Ta3N5 for efficient photoelectrochemical water oxidation Journal Article Nature Catalysis, 3 (11), pp. 932-940, 2020, ISSN: 2520-1158. Abstract | Links | Tags: Solid-Liquid @article{, title = {Band structure engineering and defect control of Ta3N5 for efficient photoelectrochemical water oxidation}, author = {Y Xiao and C Feng and J Fu and F Wang and C Li and V F Kunzelmann and C-M Jiang and M Nakabayashi and N Shibata and I D Sharp and K Domen and Y Li}, url = {https://doi.org/10.1038/s41929-020-00522-9}, doi = {10.1038/s41929-020-00522-9}, issn = {2520-1158}, year = {2020}, date = {2020-11-01}, journal = {Nature Catalysis}, volume = {3}, number = {11}, pages = {932-940}, abstract = {Ta3N5 is a promising photoanode material with a theoretical maximum solar conversion efficiency of 15.9% for photoelectrochemical water splitting. However, the highest applied bias photon-to-current efficiency achieved so far is only 2.72%. To bridge the efficiency gap, effective carrier management strategies for Ta3N5 photoanodes should be developed. Here, we propose to use gradient Mg doping for band structure engineering and defect control of Ta3N5. The gradient Mg doping profile in Ta3N5 induces a gradient of the band edge energetics, which greatly enhances the charge separation efficiency. Furthermore, defect-related recombination is significantly suppressed due to the passivation effect of Mg dopants on deep-level defects and, more importantly, the matching of the gradient Mg doping profile with the distribution of defects within Ta3N5. As a result, a photoanode based on the gradient Mg-doped Ta3N5 delivers a low onset potential of 0.4 V versus that of a reversible hydrogen electrode and a high applied bias photon-to-current efficiency of 3.25 ± 0.05%.}, keywords = {Solid-Liquid}, pubstate = {published}, tppubtype = {article} } Ta3N5 is a promising photoanode material with a theoretical maximum solar conversion efficiency of 15.9% for photoelectrochemical water splitting. However, the highest applied bias photon-to-current efficiency achieved so far is only 2.72%. To bridge the efficiency gap, effective carrier management strategies for Ta3N5 photoanodes should be developed. Here, we propose to use gradient Mg doping for band structure engineering and defect control of Ta3N5. The gradient Mg doping profile in Ta3N5 induces a gradient of the band edge energetics, which greatly enhances the charge separation efficiency. Furthermore, defect-related recombination is significantly suppressed due to the passivation effect of Mg dopants on deep-level defects and, more importantly, the matching of the gradient Mg doping profile with the distribution of defects within Ta3N5. As a result, a photoanode based on the gradient Mg-doped Ta3N5 delivers a low onset potential of 0.4 V versus that of a reversible hydrogen electrode and a high applied bias photon-to-current efficiency of 3.25 ± 0.05%. |
| 151. | K Nisi, S Subramanian, W He, K A Ulman, H El-Sherif, F Sigger, M Lassaunière, M T Wetherington, N Briggs, J Gray, A W Holleitner, N Bassim, S Y Quek, J A Robinson, U Wurstbauer Light–Matter Interaction in Quantum Confined 2D Polar Metals Journal Article Advanced Functional Materials, n/a (n/a), pp. 2005977, 2020, ISSN: 1616-301X. Abstract | Links | Tags: Solid-Solid @article{, title = {Light\textendashMatter Interaction in Quantum Confined 2D Polar Metals}, author = {K Nisi and S Subramanian and W He and K A Ulman and H El-Sherif and F Sigger and M Lassauni\`{e}re and M T Wetherington and N Briggs and J Gray and A W Holleitner and N Bassim and S Y Quek and J A Robinson and U Wurstbauer}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202005977}, doi = {https://doi.org/10.1002/adfm.202005977}, issn = {1616-301X}, year = {2020}, date = {2020-10-15}, journal = {Advanced Functional Materials}, volume = {n/a}, number = {n/a}, pages = {2005977}, abstract = {Abstract This work is a systematic experimental and theoretical study of the in-plane dielectric functions of 2D gallium and indium films consisting of two or three atomic metal layers confined between silicon carbide and graphene with a corresponding bonding gradient from covalent to metallic to van der Waals type. k-space resolved free electron and bound electron contributions to the optical response are identified, with the latter pointing towards the existence of thickness dependent quantum confinement phenomena. The resonance energies in the dielectric functions and the observed epsilon near-zero behavior in the near infrared to visible spectral range, are dependent on the number of atomic metal layers and properties of the metal involved. A model-based spectroscopic ellipsometry approach is used to estimate the number of atomic metal layers, providing a convenient route over expensive invasive characterization techniques. A strong thickness and metal choice dependence of the light\textendashmatter interaction makes these half van der Waals 2D polar metals attractive for quantum engineered metal films, tunable (quantum-)plasmonics and nano-photonics.}, keywords = {Solid-Solid}, pubstate = {published}, tppubtype = {article} } Abstract This work is a systematic experimental and theoretical study of the in-plane dielectric functions of 2D gallium and indium films consisting of two or three atomic metal layers confined between silicon carbide and graphene with a corresponding bonding gradient from covalent to metallic to van der Waals type. k-space resolved free electron and bound electron contributions to the optical response are identified, with the latter pointing towards the existence of thickness dependent quantum confinement phenomena. The resonance energies in the dielectric functions and the observed epsilon near-zero behavior in the near infrared to visible spectral range, are dependent on the number of atomic metal layers and properties of the metal involved. A model-based spectroscopic ellipsometry approach is used to estimate the number of atomic metal layers, providing a convenient route over expensive invasive characterization techniques. A strong thickness and metal choice dependence of the light–matter interaction makes these half van der Waals 2D polar metals attractive for quantum engineered metal films, tunable (quantum-)plasmonics and nano-photonics. |
| 150. | B Tilmann, G Grinblat, R Berté, M Özcan, V F Kunzelmann, B Nickel, I D Sharp, E Cortés, S A Maier, Y Li Nanostructured amorphous gallium phosphide on silica for nonlinear and ultrafast nanophotonics Journal Article Nanoscale Horizons, 5 (11), pp. 1500-1508, 2020, ISSN: 2055-6756. Abstract | Links | Tags: Foundry Inorganic @article{, title = {Nanostructured amorphous gallium phosphide on silica for nonlinear and ultrafast nanophotonics}, author = {B Tilmann and G Grinblat and R Bert\'{e} and M \"{O}zcan and V F Kunzelmann and B Nickel and I D Sharp and E Cort\'{e}s and S A Maier and Y Li}, url = {http://dx.doi.org/10.1039/D0NH00461H}, doi = {10.1039/D0NH00461H}, issn = {2055-6756}, year = {2020}, date = {2020-09-30}, journal = {Nanoscale Horizons}, volume = {5}, number = {11}, pages = {1500-1508}, abstract = {Nanophotonics based on high refractive index dielectrics relies on appreciable contrast between the indices of designed nanostructures and their immediate surrounding, which can be achieved by the growth of thin films on low-index substrates. Here we propose the use of high index amorphous gallium phosphide (a-GaP), fabricated by radio-frequency sputter deposition, on top of a low refractive index glass substrate and thoroughly examine its nanophotonic properties. Spectral ellipsometry of the amorphous material demonstrates the optical properties to be considerably close to crystalline gallium phosphide (c-GaP), with low-loss transparency for wavelengths longer than 650 nm. When nanostructured into nanopatches, the second harmonic (SH) response of an individual a-GaP patch is characterized to be more than two orders of magnitude larger than the as-deposited unstructured film, with an anapole-like resonant behavior. Numerical simulations are in good agreement with the experimental results over a large spectral and geometrical range. Furthermore, by studying individual a-GaP nanopatches through non-degenerate pump\textendashprobe spectroscopy with sub-10 fs pulses, we find a more than 5% ultrafast modulation of the reflectivity that is accompanied by a slower decaying free carrier contribution, caused by absorption. Our investigations reveal a potential for a-GaP as an adequate inexpensive and CMOS-compatible material for nonlinear nanophotonic applications as well as for photocatalysis.}, keywords = {Foundry Inorganic}, pubstate = {published}, tppubtype = {article} } Nanophotonics based on high refractive index dielectrics relies on appreciable contrast between the indices of designed nanostructures and their immediate surrounding, which can be achieved by the growth of thin films on low-index substrates. Here we propose the use of high index amorphous gallium phosphide (a-GaP), fabricated by radio-frequency sputter deposition, on top of a low refractive index glass substrate and thoroughly examine its nanophotonic properties. Spectral ellipsometry of the amorphous material demonstrates the optical properties to be considerably close to crystalline gallium phosphide (c-GaP), with low-loss transparency for wavelengths longer than 650 nm. When nanostructured into nanopatches, the second harmonic (SH) response of an individual a-GaP patch is characterized to be more than two orders of magnitude larger than the as-deposited unstructured film, with an anapole-like resonant behavior. Numerical simulations are in good agreement with the experimental results over a large spectral and geometrical range. Furthermore, by studying individual a-GaP nanopatches through non-degenerate pump–probe spectroscopy with sub-10 fs pulses, we find a more than 5% ultrafast modulation of the reflectivity that is accompanied by a slower decaying free carrier contribution, caused by absorption. Our investigations reveal a potential for a-GaP as an adequate inexpensive and CMOS-compatible material for nonlinear nanophotonic applications as well as for photocatalysis. |
| 149. | V Sridhar, F Podjaski, J Kröger, A Jiménez-Solano, B-W Park, B V Lotsch, M Sitti Carbon nitride-based light-driven microswimmers with intrinsic photocharging ability Journal Article Proceedings of the National Academy of Sciences, 117 (40), pp. 24748, 2020. Abstract | Links | Tags: Molecularly-Functionalized @article{, title = {Carbon nitride-based light-driven microswimmers with intrinsic photocharging ability}, author = {V Sridhar and F Podjaski and J Kr\"{o}ger and A Jim\'{e}nez-Solano and B-W Park and B V Lotsch and M Sitti}, url = {http://www.pnas.org/content/117/40/24748.abstract}, doi = {10.1073/pnas.2007362117}, year = {2020}, date = {2020-09-21}, journal = {Proceedings of the National Academy of Sciences}, volume = {117}, number = {40}, pages = {24748}, abstract = {Light-driven microswimmers offer prospects for autonomous microsystems. Understanding their surface catalytic processes responsible for propulsion is essential in tailoring them for specific applications. So far, photocatalytic microswimmers have been limited by the requirement of continuous illumination. Here, we report light-driven 2D carbon nitride-based Janus microswimmers, which show efficient propulsion in aqueous media not only during but also after illumination for about 30 min after 30 s prior illumination, due to so-called solar battery swimming. Contrary to the mainstream reports, we reveal oxygen reduction rather than hydrogen evolution being responsible for propulsion with alcohol fuels. Balancing reaction conditions, we report the realization of light-induced intrinsic charging of a microswimmer, enabling sustained ballistic propulsion in the dark through discharge of accumulated energy.Controlling autonomous propulsion of microswimmers is essential for targeted drug delivery and applications of micro/nanomachines in environmental remediation and beyond. Herein, we report two-dimensional (2D) carbon nitride-based Janus particles as highly efficient, light-driven microswimmers in aqueous media. Due to the superior photocatalytic properties of poly(heptazine imide) (PHI), the microswimmers are activated by both visible and ultraviolet (UV) light in conjunction with different capping materials (Au, Pt, and SiO2) and fuels (H2O2 and alcohols). Assisted by photoelectrochemical analysis of the PHI surface photoreactions, we elucidate the dominantly diffusiophoretic propulsion mechanism and establish the oxygen reduction reaction (ORR) as the major surface reaction in ambient conditions on metal-capped PHI and even with TiO2-based systems, rather than the hydrogen evolution reaction (HER), which is generally invoked as the source of propulsion under ambient conditions with alcohols as fuels. Making use of the intrinsic solar energy storage ability of PHI, we establish the concept of photocapacitive Janus microswimmers that can be charged by solar energy, thus enabling persistent light-induced propulsion even in the absence of illumination\textemdasha process we call “solar battery swimming”\textemdashlasting half an hour and possibly beyond. We anticipate that this propulsion scheme significantly extends the capabilities in targeted cargo/drug delivery, environmental remediation, and other potential applications of micro/nanomachines, where the use of versatile earth-abundant materials is a key prerequisite.All data, materials, and associated protocols that support the findings of this study are shown in Materials and Methods and SI Appendix.}, keywords = {Molecularly-Functionalized}, pubstate = {published}, tppubtype = {article} } Light-driven microswimmers offer prospects for autonomous microsystems. Understanding their surface catalytic processes responsible for propulsion is essential in tailoring them for specific applications. So far, photocatalytic microswimmers have been limited by the requirement of continuous illumination. Here, we report light-driven 2D carbon nitride-based Janus microswimmers, which show efficient propulsion in aqueous media not only during but also after illumination for about 30 min after 30 s prior illumination, due to so-called solar battery swimming. Contrary to the mainstream reports, we reveal oxygen reduction rather than hydrogen evolution being responsible for propulsion with alcohol fuels. Balancing reaction conditions, we report the realization of light-induced intrinsic charging of a microswimmer, enabling sustained ballistic propulsion in the dark through discharge of accumulated energy.Controlling autonomous propulsion of microswimmers is essential for targeted drug delivery and applications of micro/nanomachines in environmental remediation and beyond. Herein, we report two-dimensional (2D) carbon nitride-based Janus particles as highly efficient, light-driven microswimmers in aqueous media. Due to the superior photocatalytic properties of poly(heptazine imide) (PHI), the microswimmers are activated by both visible and ultraviolet (UV) light in conjunction with different capping materials (Au, Pt, and SiO2) and fuels (H2O2 and alcohols). Assisted by photoelectrochemical analysis of the PHI surface photoreactions, we elucidate the dominantly diffusiophoretic propulsion mechanism and establish the oxygen reduction reaction (ORR) as the major surface reaction in ambient conditions on metal-capped PHI and even with TiO2-based systems, rather than the hydrogen evolution reaction (HER), which is generally invoked as the source of propulsion under ambient conditions with alcohols as fuels. Making use of the intrinsic solar energy storage ability of PHI, we establish the concept of photocapacitive Janus microswimmers that can be charged by solar energy, thus enabling persistent light-induced propulsion even in the absence of illumination—a process we call “solar battery swimming”—lasting half an hour and possibly beyond. We anticipate that this propulsion scheme significantly extends the capabilities in targeted cargo/drug delivery, environmental remediation, and other potential applications of micro/nanomachines, where the use of versatile earth-abundant materials is a key prerequisite.All data, materials, and associated protocols that support the findings of this study are shown in Materials and Methods and SI Appendix. |
| 148. | J Fu, F Wang, Y Xiao, Y Yao, C Feng, L Chang, C-M Jiang, V F Kunzelmann, Z M Wang, A O Govorov, I D Sharp, Y Li Identifying Performance-Limiting Deep Traps in Ta3N5 for Solar Water Splitting Journal Article ACS Catalysis, 10 (18), pp. 10316-10324, 2020. Abstract | Links | Tags: Solid-Liquid @article{, title = {Identifying Performance-Limiting Deep Traps in Ta3N5 for Solar Water Splitting}, author = {J Fu and F Wang and Y Xiao and Y Yao and C Feng and L Chang and C-M Jiang and V F Kunzelmann and Z M Wang and A O Govorov and I D Sharp and Y Li}, url = {https://doi.org/10.1021/acscatal.0c02648}, doi = {10.1021/acscatal.0c02648}, year = {2020}, date = {2020-09-18}, journal = {ACS Catalysis}, volume = {10}, number = {18}, pages = {10316-10324}, abstract = {Ta3N5 is a promising semiconductor for solar-driven photocatalytic or photoelectrochemical (PEC) water splitting. However, the lack of an in-depth understanding of its intrinsic defect properties limits further improvement of its performance. In this study, comprehensive spectroscopic characterizations are combined with theoretical calculations to investigate the defect properties of Ta3N5. The obtained electronic structure of Ta3N5 reveals that oxygen impurities are shallow donors, while nitrogen vacancies and reduced Ta centers (Ta3+) are deep traps. The Ta3+ defects are identified to be most detrimental to the water splitting performance because their energetic position lies below the water reduction potential. Based on these findings, a simple H2O2 pretreatment method is employed to improve the PEC performance of the Ta3N5 photoanode by reducing the concentration of Ta3+ defects, resulting in a high solar-to-hydrogen conversion efficiency of 2.25%. The fundamental knowledge about the defect properties of Ta3N5 could serve as a guideline for developing more efficient photoanodes and photocatalysts.}, keywords = {Solid-Liquid}, pubstate = {published}, tppubtype = {article} } Ta3N5 is a promising semiconductor for solar-driven photocatalytic or photoelectrochemical (PEC) water splitting. However, the lack of an in-depth understanding of its intrinsic defect properties limits further improvement of its performance. In this study, comprehensive spectroscopic characterizations are combined with theoretical calculations to investigate the defect properties of Ta3N5. The obtained electronic structure of Ta3N5 reveals that oxygen impurities are shallow donors, while nitrogen vacancies and reduced Ta centers (Ta3+) are deep traps. The Ta3+ defects are identified to be most detrimental to the water splitting performance because their energetic position lies below the water reduction potential. Based on these findings, a simple H2O2 pretreatment method is employed to improve the PEC performance of the Ta3N5 photoanode by reducing the concentration of Ta3+ defects, resulting in a high solar-to-hydrogen conversion efficiency of 2.25%. The fundamental knowledge about the defect properties of Ta3N5 could serve as a guideline for developing more efficient photoanodes and photocatalysts. |
| 147. | C Heshmatpour, P Malevich, F Plasser, M Menger, C Lambert, F Šanda, J Hauer Annihilation Dynamics of Molecular Excitons Measured at a Single Perturbative Excitation Energy Journal Article The Journal of Physical Chemistry Letters, 11 (18), pp. 7776-7781, 2020. Abstract | Links | Tags: Molecularly-Functionalized @article{, title = {Annihilation Dynamics of Molecular Excitons Measured at a Single Perturbative Excitation Energy}, author = {C Heshmatpour and P Malevich and F Plasser and M Menger and C Lambert and F \v{S}anda and J Hauer}, url = {https://doi.org/10.1021/acs.jpclett.0c02141}, doi = {10.1021/acs.jpclett.0c02141}, year = {2020}, date = {2020-09-17}, journal = {The Journal of Physical Chemistry Letters}, volume = {11}, number = {18}, pages = {7776-7781}, abstract = {Exciton\textendashexciton annihilation (EEA) is a ubiquitous phenomenon, which may limit the efficiency of photovoltaic devices. Conventional methods of determining EEA time scales rely on measuring the intensity dependence of third-order signals. In this work, we directly extract the annihilation rate of molecular excitons in a covalently joined molecular trimer without the need to perform and analyze intensity dependent data by employing fifth-order coherent optical spectroscopy signals emitted into ±2k⃗1 ∓ 2k⃗2 + k⃗3 phase matching directions. Measured two-dimensional line shapes and their time traces are analyzed in the framework of the many-body version of the Frenkel exciton model, extended to incorporate annihilation dynamics. Combining double-sided Feynman diagrams with explicit simulations of the fifth-order response, we identify a single peak as a direct reporter of EEA. We retrieve an annihilation time of 30 fs for the investigated squaraine trimer.}, keywords = {Molecularly-Functionalized}, pubstate = {published}, tppubtype = {article} } Exciton–exciton annihilation (EEA) is a ubiquitous phenomenon, which may limit the efficiency of photovoltaic devices. Conventional methods of determining EEA time scales rely on measuring the intensity dependence of third-order signals. In this work, we directly extract the annihilation rate of molecular excitons in a covalently joined molecular trimer without the need to perform and analyze intensity dependent data by employing fifth-order coherent optical spectroscopy signals emitted into ±2k⃗1 ∓ 2k⃗2 + k⃗3 phase matching directions. Measured two-dimensional line shapes and their time traces are analyzed in the framework of the many-body version of the Frenkel exciton model, extended to incorporate annihilation dynamics. Combining double-sided Feynman diagrams with explicit simulations of the fifth-order response, we identify a single peak as a direct reporter of EEA. We retrieve an annihilation time of 30 fs for the investigated squaraine trimer. |
| 146. | A Auer, M Andersen, E-M Wernig, N G Hörmann, N Buller, K Reuter, J Kunze-Liebhäuser Self-activation of copper electrodes during CO electro-oxidation in alkaline electrolyte Journal Article Nature Catalysis, 2020, ISSN: 2520-1158. Abstract | Links | Tags: Solid-Liquid @article{, title = {Self-activation of copper electrodes during CO electro-oxidation in alkaline electrolyte}, author = {A Auer and M Andersen and E-M Wernig and N G H\"{o}rmann and N Buller and K Reuter and J Kunze-Liebh\"{a}user}, url = {https://doi.org/10.1038/s41929-020-00505-w}, doi = {10.1038/s41929-020-00505-w}, issn = {2520-1158}, year = {2020}, date = {2020-09-07}, journal = {Nature Catalysis}, abstract = {The development of low-temperature fuel cells for clean energy production is an appealing alternative to fossil-fuel technologies. CO is a key intermediate in the electro-oxidation of energy carrying fuels and, due to its strong interaction with state-of-the-art Pt electrodes, it is known to act as a poison. Here we demonstrate the ability of Earth-abundant Cu to electro-oxidize CO efficiently in alkaline media, reaching high current densities of ≥0.35 mA cm−2 on single-crystal Cu(111) model catalysts. Strong and continuous surface structural changes are observed under reaction conditions. Supported by first-principles microkinetic modelling, we show that the concomitant presence of high-energy undercoordinated Cu structures at the surface is a prerequisite for the high activity. Similar CO-induced self-activation has been reported for gas\textendashsurface reactions at coinage metals, demonstrating the strong parallels between heterogeneous thermal catalysis and heterogeneous electrocatalysis.}, keywords = {Solid-Liquid}, pubstate = {published}, tppubtype = {article} } The development of low-temperature fuel cells for clean energy production is an appealing alternative to fossil-fuel technologies. CO is a key intermediate in the electro-oxidation of energy carrying fuels and, due to its strong interaction with state-of-the-art Pt electrodes, it is known to act as a poison. Here we demonstrate the ability of Earth-abundant Cu to electro-oxidize CO efficiently in alkaline media, reaching high current densities of ≥0.35 mA cm−2 on single-crystal Cu(111) model catalysts. Strong and continuous surface structural changes are observed under reaction conditions. Supported by first-principles microkinetic modelling, we show that the concomitant presence of high-energy undercoordinated Cu structures at the surface is a prerequisite for the high activity. Similar CO-induced self-activation has been reported for gas–surface reactions at coinage metals, demonstrating the strong parallels between heterogeneous thermal catalysis and heterogeneous electrocatalysis. |
| 145. | J Maschita, T Banerjee, G Savasci, F Haase, C Ochsenfeld, B V Lotsch Ionothermal Synthesis of Imide-Linked Covalent Organic Frameworks Journal Article Angewandte Chemie International Edition, 59 (36), pp. 15750-15758, 2020, ISSN: 1433-7851. Abstract | Links | Tags: Foundry Organic @article{, title = {Ionothermal Synthesis of Imide-Linked Covalent Organic Frameworks}, author = {J Maschita and T Banerjee and G Savasci and F Haase and C Ochsenfeld and B V Lotsch}, url = {https://doi.org/10.1002/anie.202007372}, doi = {https://doi.org/10.1002/anie.202007372}, issn = {1433-7851}, year = {2020}, date = {2020-09-01}, journal = {Angewandte Chemie International Edition}, volume = {59}, number = {36}, pages = {15750-15758}, abstract = {Abstract Covalent organic frameworks (COFs) are an extensively studied class of porous materials, which distinguish themselves from other porous polymers in their crystallinity and high degree of modularity, enabling a wide range of applications. COFs are most commonly synthesized solvothermally, which is often a time-consuming process and restricted to well-soluble precursor molecules. Synthesis of polyimide-linked COFs (PI-COFs) is further complicated by the poor reversibility of the ring-closing reaction under solvothermal conditions. Herein, we report the ionothermal synthesis of crystalline and porous PI-COFs in zinc chloride and eutectic salt mixtures. This synthesis does not require soluble precursors and the reaction time is significantly reduced as compared to standard solvothermal synthesis methods. In addition to applying the synthesis to previously reported imide COFs, a new perylene-based COF was also synthesized, which could not be obtained by the classical solvothermal route. In situ high-temperature XRPD analysis hints to the formation of precursor?salt adducts as crystalline intermediates, which then react with each other to form the COF.}, keywords = {Foundry Organic}, pubstate = {published}, tppubtype = {article} } Abstract Covalent organic frameworks (COFs) are an extensively studied class of porous materials, which distinguish themselves from other porous polymers in their crystallinity and high degree of modularity, enabling a wide range of applications. COFs are most commonly synthesized solvothermally, which is often a time-consuming process and restricted to well-soluble precursor molecules. Synthesis of polyimide-linked COFs (PI-COFs) is further complicated by the poor reversibility of the ring-closing reaction under solvothermal conditions. Herein, we report the ionothermal synthesis of crystalline and porous PI-COFs in zinc chloride and eutectic salt mixtures. This synthesis does not require soluble precursors and the reaction time is significantly reduced as compared to standard solvothermal synthesis methods. In addition to applying the synthesis to previously reported imide COFs, a new perylene-based COF was also synthesized, which could not be obtained by the classical solvothermal route. In situ high-temperature XRPD analysis hints to the formation of precursor?salt adducts as crystalline intermediates, which then react with each other to form the COF. |
| 144. | K Barthelmi, J Klein, A Hötger, L Sigl, F Sigger, E Mitterreiter, S Rey, S Gyger, M Lorke, M Florian, F Jahnke, T Taniguchi, K Watanabe, V Zwiller, K D Jöns, U Wurstbauer, C Kastl, A Weber-Bargioni, J J Finley, K Müller, A W Holleitner Atomistic defects as single-photon emitters in atomically thin MoS2 Journal Article Applied Physics Letters, 117 (7), pp. 070501, 2020, ISSN: 0003-6951. Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {Atomistic defects as single-photon emitters in atomically thin MoS2}, author = {K Barthelmi and J Klein and A H\"{o}tger and L Sigl and F Sigger and E Mitterreiter and S Rey and S Gyger and M Lorke and M Florian and F Jahnke and T Taniguchi and K Watanabe and V Zwiller and K D J\"{o}ns and U Wurstbauer and C Kastl and A Weber-Bargioni and J J Finley and K M\"{u}ller and A W Holleitner}, url = {https://doi.org/10.1063/5.0018557}, doi = {10.1063/5.0018557}, issn = {0003-6951}, year = {2020}, date = {2020-08-17}, journal = {Applied Physics Letters}, volume = {117}, number = {7}, pages = {070501}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } |
| 143. | H Y Qi, H Sahabudeen, B K Liang, M Polozij, M A Addicoat, T E Gorelik, M Hambsch, M Mundszinger, S Park, B V Lotsch, S C B Mannsfeld, Z K Zheng, R H Dong, T Heine, X L Feng, U Kaiser Near-atomic-scale observation of grain boundaries in a layer-stacked two-dimensional polymer Journal Article Science Advances, 6 (33), 2020, ISSN: 2375-2548. Abstract | Links | Tags: Foundry Organic @article{, title = {Near-atomic-scale observation of grain boundaries in a layer-stacked two-dimensional polymer}, author = {H Y Qi and H Sahabudeen and B K Liang and M Polozij and M A Addicoat and T E Gorelik and M Hambsch and M Mundszinger and S Park and B V Lotsch and S C B Mannsfeld and Z K Zheng and R H Dong and T Heine and X L Feng and U Kaiser}, url = {<Go to ISI>://WOS:000560465800030}, doi = {10.1126/sciadv.abb5976}, issn = {2375-2548}, year = {2020}, date = {2020-08-14}, journal = {Science Advances}, volume = {6}, number = {33}, abstract = {Two-dimensional (2D) polymers, hold great promise in the rational materials design tailored for next-generation applications. However, little is known about the grain boundaries in 2D polymers, not to mention their formation mechanisms and potential influences on the material's functionalities. Using aberration-corrected high-resolution transmission electron microscopy, we present a direct observation of the grain boundaries in a layer-stacked 2D polyimine with a resolution of 2.3 angstrom, shedding light on their formation mechanisms. We found that the polyimine growth followed a "birth-and-spread" mechanism. Antiphase boundaries implemented a self-correction to the missing-linker and missing-node defects, and tilt boundaries were formed via grain coalescence. Notably, we identified grain boundary reconstructions featuring closed rings at tilt boundaries. Quantum mechanical calculations revealed that boundary reconstruction is energetically allowed and can be generalized into different 2D polymer systems. We envisage that these results may open up the opportunity for future investigations on defect-property correlations in 2D polymers.}, keywords = {Foundry Organic}, pubstate = {published}, tppubtype = {article} } Two-dimensional (2D) polymers, hold great promise in the rational materials design tailored for next-generation applications. However, little is known about the grain boundaries in 2D polymers, not to mention their formation mechanisms and potential influences on the material's functionalities. Using aberration-corrected high-resolution transmission electron microscopy, we present a direct observation of the grain boundaries in a layer-stacked 2D polyimine with a resolution of 2.3 angstrom, shedding light on their formation mechanisms. We found that the polyimine growth followed a "birth-and-spread" mechanism. Antiphase boundaries implemented a self-correction to the missing-linker and missing-node defects, and tilt boundaries were formed via grain coalescence. Notably, we identified grain boundary reconstructions featuring closed rings at tilt boundaries. Quantum mechanical calculations revealed that boundary reconstruction is energetically allowed and can be generalized into different 2D polymer systems. We envisage that these results may open up the opportunity for future investigations on defect-property correlations in 2D polymers. |
| 142. | H A Vignolo-González, S Laha, A Jiménez-Solano, T Oshima, V Duppel, P Schützendübe, B V Lotsch Toward Standardized Photocatalytic Oxygen Evolution Rates Using RuO2@TiO2 as a Benchmark Journal Article Matter, 3 (2), pp. 464-486, 2020, ISSN: 2590-2385. Abstract | Links | Tags: Foundry Inorganic, Solid-Liquid @article{, title = {Toward Standardized Photocatalytic Oxygen Evolution Rates Using RuO2@TiO2 as a Benchmark}, author = {H A Vignolo-Gonz\'{a}lez and S Laha and A Jim\'{e}nez-Solano and T Oshima and V Duppel and P Sch\"{u}tzend\"{u}be and B V Lotsch}, url = {http://www.sciencedirect.com/science/article/pii/S2590238520303799}, doi = {https://doi.org/10.1016/j.matt.2020.07.021}, issn = {2590-2385}, year = {2020}, date = {2020-08-05}, journal = {Matter}, volume = {3}, number = {2}, pages = {464-486}, abstract = {Summary Quantitative comparison of photocatalytic performances across different photocatalysis setups is technically challenging. Here, we combine the concepts of relative and optimal photonic efficiencies to normalize activities with an internal benchmark material, RuO2 photodeposited on a P25-TiO2 photocatalyst, which was optimized for reproducibility of the oxygen evolution reaction (OER). Additionally, a general set of good practices was identified to ensure reliable quantification of photocatalytic OER, including photoreactor design, photocatalyst dispersion, and control of parasitic reactions caused by the sacrificial electron acceptor. Moreover, a method combining optical modeling and measurements was proposed to quantify the benchmark absorbed and scattered light (7.6% and 81.2%, respectively, of λ = 300\textendash500 nm incident photons), rather than just incident light (≈AM 1.5G), to estimate its internal quantum efficiency (16%). We advocate the adoption of the instrumental and theoretical framework provided here to facilitate material standardization and comparison in the field of artificial photosynthesis.}, keywords = {Foundry Inorganic, Solid-Liquid}, pubstate = {published}, tppubtype = {article} } Summary Quantitative comparison of photocatalytic performances across different photocatalysis setups is technically challenging. Here, we combine the concepts of relative and optimal photonic efficiencies to normalize activities with an internal benchmark material, RuO2 photodeposited on a P25-TiO2 photocatalyst, which was optimized for reproducibility of the oxygen evolution reaction (OER). Additionally, a general set of good practices was identified to ensure reliable quantification of photocatalytic OER, including photoreactor design, photocatalyst dispersion, and control of parasitic reactions caused by the sacrificial electron acceptor. Moreover, a method combining optical modeling and measurements was proposed to quantify the benchmark absorbed and scattered light (7.6% and 81.2%, respectively, of λ = 300–500 nm incident photons), rather than just incident light (≈AM 1.5G), to estimate its internal quantum efficiency (16%). We advocate the adoption of the instrumental and theoretical framework provided here to facilitate material standardization and comparison in the field of artificial photosynthesis. |
| 141. | B Li, Y C Rui, J L Xu, Y Q Wang, J X Yang, Q H Zhang, P Muller-Buschbaum Solution-processed p-type nanocrystalline CoO films for inverted mixed perovskite solar cells Journal Article Journal of Colloid and Interface Science, 573 , pp. 78-86, 2020, ISSN: 0021-9797. Abstract | Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {Solution-processed p-type nanocrystalline CoO films for inverted mixed perovskite solar cells}, author = {B Li and Y C Rui and J L Xu and Y Q Wang and J X Yang and Q H Zhang and P Muller-Buschbaum}, url = {<Go to ISI>://WOS:000533529500009}, doi = {10.1016/j.jcis.2020.03.119}, issn = {0021-9797}, year = {2020}, date = {2020-08-01}, journal = {Journal of Colloid and Interface Science}, volume = {573}, pages = {78-86}, abstract = {Inorganic p-type materials show great potential as the hole transport layer in perovskite solar cells with the merits of low costs and enhanced chemical stability. As a p-type material, cobalt oxide (CoO) has received so far not that level of attention despite its high hole mobility. Herein, solution-processed p-type CoO nanocrystalline films are developed for inverted mixed perovskite solar cells. The ultrafine CoO nanocrystals are synthesized via an oil phase method, which are subsequently treated by a ligand exchange process using pyridine solvent to remove the long alkyl chains covering the nanocrystals. From this homogeneous colloidal solution CoO films are obtained, which exhibit a smooth and pinhole free surface morphology with high transparency and good conductivity. The ultraviolet photoelectron spectrum also indicates that the energy levels of the CoO film match well with the mixed perovskite Cs-0(.05)(FA(0)(.)(83)MA(0)(.17))(0.95)(I0.83Br0.17)(3). Inverted solar cells based on crystalline Co0 films with ligand exchange show a reasonable energy conversion efficiency, whereas devices based on CoO films without ligand exchange suffer from a strong S-shape JV-characteristic. Thus, the crystalline CoO films are foreseen to pave a new way of inorganic hole transport materials in the fields of perovskite solar cells. (C) 2020 Elsevier Inc. All rights reserved.}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } Inorganic p-type materials show great potential as the hole transport layer in perovskite solar cells with the merits of low costs and enhanced chemical stability. As a p-type material, cobalt oxide (CoO) has received so far not that level of attention despite its high hole mobility. Herein, solution-processed p-type CoO nanocrystalline films are developed for inverted mixed perovskite solar cells. The ultrafine CoO nanocrystals are synthesized via an oil phase method, which are subsequently treated by a ligand exchange process using pyridine solvent to remove the long alkyl chains covering the nanocrystals. From this homogeneous colloidal solution CoO films are obtained, which exhibit a smooth and pinhole free surface morphology with high transparency and good conductivity. The ultraviolet photoelectron spectrum also indicates that the energy levels of the CoO film match well with the mixed perovskite Cs-0(.05)(FA(0)(.)(83)MA(0)(.17))(0.95)(I0.83Br0.17)(3). Inverted solar cells based on crystalline Co0 films with ligand exchange show a reasonable energy conversion efficiency, whereas devices based on CoO films without ligand exchange suffer from a strong S-shape JV-characteristic. Thus, the crystalline CoO films are foreseen to pave a new way of inorganic hole transport materials in the fields of perovskite solar cells. (C) 2020 Elsevier Inc. All rights reserved. |
| 140. | J Eichhorn, S E Reyes-Lillo, S Roychoudhury, S Sallis, J Weis, D M Larson, J K Cooper, I D Sharp, D Prendergast, F M Toma Revealing Nanoscale Chemical Heterogeneities in Polycrystalline Mo-BiVO(4)Thin Films Journal Article Small, 2020, ISSN: 1613-6810. Abstract | Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {Revealing Nanoscale Chemical Heterogeneities in Polycrystalline Mo-BiVO(4)Thin Films}, author = {J Eichhorn and S E Reyes-Lillo and S Roychoudhury and S Sallis and J Weis and D M Larson and J K Cooper and I D Sharp and D Prendergast and F M Toma}, url = {<Go to ISI>://WOS:000555446200001}, doi = {10.1002/smll.202001600}, issn = {1613-6810}, year = {2020}, date = {2020-08-01}, journal = {Small}, abstract = {The activity of polycrystalline thin film photoelectrodes is impacted by local variations of the material properties due to the exposure of different crystal facets and the presence of grain/domain boundaries. Here a multi-modal approach is applied to correlate nanoscale heterogeneities in chemical composition and electronic structure with nanoscale morphology in polycrystalline Mo-BiVO4. By using scanning transmission X-ray microscopy, the characteristic structure of polycrystalline film is used to disentangle the different X-ray absorption spectra corresponding to grain centers and grain boundaries. Comparing both spectra reveals phase segregation of V(2)O(5)at grain boundaries of Mo-BiVO(4)thin films, which is further supported by X-ray photoelectron spectroscopy and many-body density functional theory calculations. Theoretical calculations also enable to predict the X-ray absorption spectral fingerprint of polarons in Mo-BiVO4. After photo-electrochemical operation, the degraded Mo-BiVO(4)films show similar grain center and grain boundary spectra indicating V(2)O(5)dissolution in the course of the reaction. Overall, these findings provide valuable insights into the degradation mechanism and the impact of material heterogeneities on the material performance and stability of polycrystalline photoelectrodes.}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } The activity of polycrystalline thin film photoelectrodes is impacted by local variations of the material properties due to the exposure of different crystal facets and the presence of grain/domain boundaries. Here a multi-modal approach is applied to correlate nanoscale heterogeneities in chemical composition and electronic structure with nanoscale morphology in polycrystalline Mo-BiVO4. By using scanning transmission X-ray microscopy, the characteristic structure of polycrystalline film is used to disentangle the different X-ray absorption spectra corresponding to grain centers and grain boundaries. Comparing both spectra reveals phase segregation of V(2)O(5)at grain boundaries of Mo-BiVO(4)thin films, which is further supported by X-ray photoelectron spectroscopy and many-body density functional theory calculations. Theoretical calculations also enable to predict the X-ray absorption spectral fingerprint of polarons in Mo-BiVO4. After photo-electrochemical operation, the degraded Mo-BiVO(4)films show similar grain center and grain boundary spectra indicating V(2)O(5)dissolution in the course of the reaction. Overall, these findings provide valuable insights into the degradation mechanism and the impact of material heterogeneities on the material performance and stability of polycrystalline photoelectrodes. |
| 139. | C Courtois, C A Walenta, M Tschurl, U Heiz, C M Friend Regulating Photochemical Selectivity with Temperature: Isobutanol on TiO2(110) Journal Article Journal of the American Chemical Society, 142 (30), pp. 13072-13080, 2020, ISSN: 0002-7863. Abstract | Links | Tags: Solid-Liquid @article{, title = {Regulating Photochemical Selectivity with Temperature: Isobutanol on TiO2(110)}, author = {C Courtois and C A Walenta and M Tschurl and U Heiz and C M Friend}, url = {<Go to ISI>://WOS:000557854400021}, doi = {10.1021/jacs.0c04411}, issn = {0002-7863}, year = {2020}, date = {2020-07-29}, journal = {Journal of the American Chemical Society}, volume = {142}, number = {30}, pages = {13072-13080}, abstract = {Selective photocatalytic transformations of chemicals derived from biomass, such as isobutanol, have been long envisioned for a sustainable chemical production. A strong temperature dependence in the reaction selectivity is found for isobutanol photo-oxidation on rutile TiO2(110). The strong temperature dependence is attributed to competition between thermal desorption of the primary photoproduct and secondary photochemical steps. The aldehyde, isobutanal, is the primary photoproduct of isobutanol. At room temperature, isobutanal is obtained selectively from photo-oxidation because of rapid thermal desorption. In contrast, secondary photo-oxidation of isobutanal to propane dominates at lower temperature (240 K) due to the persistence of isobutanal on the surface after it is formed. The byproduct of isobutanal photo-oxidation is CO, which is evolved at higher temperature as a consequence of thermal decomposition of an intermediate, such as formate. The photo-oxidation to isobutanal proceeds after thermally induced isobutoxy formation. These results have strong implications for controlling the selectivity of photochemical processes more generally, in that, selectivity is governed by competition of desorption vs secondary photoreaction of products. This competition can be exploited to design photocatalytic processes to favor specific chemical transformations of organic molecules.}, keywords = {Solid-Liquid}, pubstate = {published}, tppubtype = {article} } Selective photocatalytic transformations of chemicals derived from biomass, such as isobutanol, have been long envisioned for a sustainable chemical production. A strong temperature dependence in the reaction selectivity is found for isobutanol photo-oxidation on rutile TiO2(110). The strong temperature dependence is attributed to competition between thermal desorption of the primary photoproduct and secondary photochemical steps. The aldehyde, isobutanal, is the primary photoproduct of isobutanol. At room temperature, isobutanal is obtained selectively from photo-oxidation because of rapid thermal desorption. In contrast, secondary photo-oxidation of isobutanal to propane dominates at lower temperature (240 K) due to the persistence of isobutanal on the surface after it is formed. The byproduct of isobutanal photo-oxidation is CO, which is evolved at higher temperature as a consequence of thermal decomposition of an intermediate, such as formate. The photo-oxidation to isobutanal proceeds after thermally induced isobutoxy formation. These results have strong implications for controlling the selectivity of photochemical processes more generally, in that, selectivity is governed by competition of desorption vs secondary photoreaction of products. This competition can be exploited to design photocatalytic processes to favor specific chemical transformations of organic molecules. |
| 138. | B Kalinic, T Cesca, S Mignuzzi, A Jacassi, I G Balasa, S A Maier, R Sapienza, G Mattei All-Dielectric Silicon Nanoslots for Er3+ Photoluminescence Enhancement Journal Article Physical Review Applied, 14 (1), 2020, ISSN: 2331-7019. Abstract | Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {All-Dielectric Silicon Nanoslots for Er3+ Photoluminescence Enhancement}, author = {B Kalinic and T Cesca and S Mignuzzi and A Jacassi and I G Balasa and S A Maier and R Sapienza and G Mattei}, url = {<Go to ISI>://WOS:000553352700004}, doi = {10.1103/PhysRevApplied.14.014086}, issn = {2331-7019}, year = {2020}, date = {2020-07-28}, journal = {Physical Review Applied}, volume = {14}, number = {1}, abstract = {We study, both experimentally and theoretically, the modification of Er3+ photoluminescence properties in Si dielectric nanoslots. The ultrathin nanoslot (down to 5-nm thickness), filled with Er in SiO2, boosts the electric and magnetic local density of states via coherent near-field interaction. We report an experimental 20-fold enhancement of the radiative decay rate with negligible losses. Moreover, via modifying the geometry of the all-dielectric nanoslot, the outcoupling of the emitted radiation to the far field can be strongly improved, without affecting the strong decay-rate enhancement given by the nanoslot structure. Indeed, for a periodic square array of slotted nanopillars an almost one-order-of-magnitude-higher Er3+ PL intensity is measured with respect to the unpatterned structures. This has a direct impact on the design of more efficient CMOS-compatible light sources operating at telecom wavelengths.}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } We study, both experimentally and theoretically, the modification of Er3+ photoluminescence properties in Si dielectric nanoslots. The ultrathin nanoslot (down to 5-nm thickness), filled with Er in SiO2, boosts the electric and magnetic local density of states via coherent near-field interaction. We report an experimental 20-fold enhancement of the radiative decay rate with negligible losses. Moreover, via modifying the geometry of the all-dielectric nanoslot, the outcoupling of the emitted radiation to the far field can be strongly improved, without affecting the strong decay-rate enhancement given by the nanoslot structure. Indeed, for a periodic square array of slotted nanopillars an almost one-order-of-magnitude-higher Er3+ PL intensity is measured with respect to the unpatterned structures. This has a direct impact on the design of more efficient CMOS-compatible light sources operating at telecom wavelengths. |
| 137. | S S Yin, T Tian, K S Wienhold, C L Weindl, R J Guo, M Schwartzkopf, S V Roth, P Muller-Buschbaum Key Factor Study for Amphiphilic Block Copolymer-Templated Mesoporous SnO(2)Thin Film Synthesis: Influence of Solvent and Catalyst Journal Article Advanced Materials Interfaces, 2020, ISSN: 2196-7350. Abstract | Links | Tags: Foundry Inorganic, Solid-Liquid @article{, title = {Key Factor Study for Amphiphilic Block Copolymer-Templated Mesoporous SnO(2)Thin Film Synthesis: Influence of Solvent and Catalyst}, author = {S S Yin and T Tian and K S Wienhold and C L Weindl and R J Guo and M Schwartzkopf and S V Roth and P Muller-Buschbaum}, url = {<Go to ISI>://WOS:000550676200001}, doi = {10.1002/admi.202001002}, issn = {2196-7350}, year = {2020}, date = {2020-07-21}, journal = {Advanced Materials Interfaces}, abstract = {As a crucial material in the field of energy storage, SnO(2)thin films are widely applied in daily life and have been in the focus of scientific research. Compared to the planar counterpart, mesoporous SnO(2)thin films with high specific surface area possess more attractive physical and chemical properties. In the present work, a novel amphiphilic block copolymer-assisted sol-gel chemistry is utilized for the synthesis of porous tin oxide (SnO2). Two key factors for the sol-gel stock solution preparation, the solvent category and the catalyst content, are systematically varied to tune the thin film morphologies. A calcination process is performed to remove the polymer template at 500 degrees C in ambient conditions. The surface morphology and the buried inner structure are probed with scanning electron microscope and grazing-incidence small-angle X-ray scattering. Crystallinity is characterized by X-ray diffraction. The multi-dimensional characterization results suggest that cassiterite SnO(2)with spherical, cylindrical, and vesicular pore structures are obtained. The variation of the film morphology is governed by the preferential affinity of the utilized solvent mixture and the hydrogen bond interaction between the employed cycloether and H2O molecules in the solution.}, keywords = {Foundry Inorganic, Solid-Liquid}, pubstate = {published}, tppubtype = {article} } As a crucial material in the field of energy storage, SnO(2)thin films are widely applied in daily life and have been in the focus of scientific research. Compared to the planar counterpart, mesoporous SnO(2)thin films with high specific surface area possess more attractive physical and chemical properties. In the present work, a novel amphiphilic block copolymer-assisted sol-gel chemistry is utilized for the synthesis of porous tin oxide (SnO2). Two key factors for the sol-gel stock solution preparation, the solvent category and the catalyst content, are systematically varied to tune the thin film morphologies. A calcination process is performed to remove the polymer template at 500 degrees C in ambient conditions. The surface morphology and the buried inner structure are probed with scanning electron microscope and grazing-incidence small-angle X-ray scattering. Crystallinity is characterized by X-ray diffraction. The multi-dimensional characterization results suggest that cassiterite SnO(2)with spherical, cylindrical, and vesicular pore structures are obtained. The variation of the film morphology is governed by the preferential affinity of the utilized solvent mixture and the hydrogen bond interaction between the employed cycloether and H2O molecules in the solution. |
| 136. | C Courtois, M Eder, S L Kollmannsberger, M Tschurl, C A Walenta, U Heiz Origin of Poisoning in Methanol Photoreforming on TiO2(110): The Importance of Thermal Back-Reaction Steps in Photocatalysis Journal Article Acs Catalysis, 10 (14), pp. 7747-7752, 2020, ISSN: 2155-5435. Abstract | Links | Tags: Foundry Inorganic, Solid-Liquid @article{, title = {Origin of Poisoning in Methanol Photoreforming on TiO2(110): The Importance of Thermal Back-Reaction Steps in Photocatalysis}, author = {C Courtois and M Eder and S L Kollmannsberger and M Tschurl and C A Walenta and U Heiz}, url = {<Go to ISI>://WOS:000551549800025}, doi = {10.1021/acscatal.0c01615}, issn = {2155-5435}, year = {2020}, date = {2020-07-17}, journal = {Acs Catalysis}, volume = {10}, number = {14}, pages = {7747-7752}, abstract = {Alcohol photoreforming on titania represents a perfect model system for elucidating fundamental processes in the heterogeneous photocatalysis of semiconductors. One important but open question is the origin of poisoning during the photoreaction of primary alcohols on a bare, reduced rutile TiO2(110) crystal under ultrahigh vacuum conditions. By comparing the photocatalytic properties of methanol and 2-methyl-2-pentanol, it is demonstrated that the fading activity in methanol photoreforming does not originate from the often-assigned increase of trap states for photon-generated charge carriers. Instead, we attribute the apparent catalyst poisoning to an increased rate of thermal back reactions, particularly to that of the photochemical oxidation step. While overall back reactions are generally considered in photocatalysis, back reactions of individual steps are largely neglected so far. Our work shows that their inclusion in the reaction scheme is inevitable for the comprehensive modeling of photocatalytic processes.}, keywords = {Foundry Inorganic, Solid-Liquid}, pubstate = {published}, tppubtype = {article} } Alcohol photoreforming on titania represents a perfect model system for elucidating fundamental processes in the heterogeneous photocatalysis of semiconductors. One important but open question is the origin of poisoning during the photoreaction of primary alcohols on a bare, reduced rutile TiO2(110) crystal under ultrahigh vacuum conditions. By comparing the photocatalytic properties of methanol and 2-methyl-2-pentanol, it is demonstrated that the fading activity in methanol photoreforming does not originate from the often-assigned increase of trap states for photon-generated charge carriers. Instead, we attribute the apparent catalyst poisoning to an increased rate of thermal back reactions, particularly to that of the photochemical oxidation step. While overall back reactions are generally considered in photocatalysis, back reactions of individual steps are largely neglected so far. Our work shows that their inclusion in the reaction scheme is inevitable for the comprehensive modeling of photocatalytic processes. |
| 135. | K Gottschling, G Savasci, H Vignolo-Gonzalez, S Schmidt, P Mauker, T Banerjee, P Rovo, C Ochsenfeld, B V Lotsch Rational Design of Covalent Cobaloxime-Covalent Organic Framework Hybrids for Enhanced Photocatalytic Hydrogen Evolution Journal Article Journal of the American Chemical Society, 142 (28), pp. 12146-12156, 2020, ISSN: 0002-7863. Abstract | Links | Tags: Foundry Organic @article{, title = {Rational Design of Covalent Cobaloxime-Covalent Organic Framework Hybrids for Enhanced Photocatalytic Hydrogen Evolution}, author = {K Gottschling and G Savasci and H Vignolo-Gonzalez and S Schmidt and P Mauker and T Banerjee and P Rovo and C Ochsenfeld and B V Lotsch}, url = {<Go to ISI>://WOS:000551495700030}, doi = {10.1021/jacs.0c02155}, issn = {0002-7863}, year = {2020}, date = {2020-07-15}, journal = {Journal of the American Chemical Society}, volume = {142}, number = {28}, pages = {12146-12156}, abstract = {Covalent organic frameworks (COFs) display a unique combination of chemical tunability, structural diversity, high porosity, nanoscale regularity, and thermal stability. Recent efforts are directed at using such frameworks as tunable scaffolds for chemical reactions. In particular, COFs have emerged as viable platforms for mimicking natural photosynthesis. However, there is an indisputable need for efficient, stable, and economical alternatives for the traditional platinum-based cocatalysts for light-driven hydrogen evolution. Here, we present azide-functionalized chloro(pyridine)cobaloxime hydrogen-evolution cocatalysts immobilized on a hydrazone-based COF-42 backbone that show improved and prolonged photocatalytic activity with respect to equivalent physisorbed systems. Advanced solid-state NMR and quantum-chemical methods allow us to elucidate details of the improved photoreactivity and the structural composition of the involved active site. We found that a genuine interaction between the COF backbone and the cobaloxime facilitates recoordination of the cocatalyst during the photoreaction, thereby improving the reactivity and hindering degradation of the catalyst. The excellent stability and prolonged reactivity make the herein reported cobaloxime-tethered COF materials promising hydrogen evolution catalysts for future solar fuel technologies.}, keywords = {Foundry Organic}, pubstate = {published}, tppubtype = {article} } Covalent organic frameworks (COFs) display a unique combination of chemical tunability, structural diversity, high porosity, nanoscale regularity, and thermal stability. Recent efforts are directed at using such frameworks as tunable scaffolds for chemical reactions. In particular, COFs have emerged as viable platforms for mimicking natural photosynthesis. However, there is an indisputable need for efficient, stable, and economical alternatives for the traditional platinum-based cocatalysts for light-driven hydrogen evolution. Here, we present azide-functionalized chloro(pyridine)cobaloxime hydrogen-evolution cocatalysts immobilized on a hydrazone-based COF-42 backbone that show improved and prolonged photocatalytic activity with respect to equivalent physisorbed systems. Advanced solid-state NMR and quantum-chemical methods allow us to elucidate details of the improved photoreactivity and the structural composition of the involved active site. We found that a genuine interaction between the COF backbone and the cobaloxime facilitates recoordination of the cocatalyst during the photoreaction, thereby improving the reactivity and hindering degradation of the catalyst. The excellent stability and prolonged reactivity make the herein reported cobaloxime-tethered COF materials promising hydrogen evolution catalysts for future solar fuel technologies. |
| 134. | R M Kluge, N Saxena, W Chen, V Korstgens, M Schwartzkopf, Q Zhong, S V Roth, P Muller-Buschbaum Doping Dependent In-Plane and Cross-Plane Thermoelectric Performance of Thin n-Type Polymer P(NDI2OD-T2) Films Journal Article Advanced Functional Materials, 30 (28), 2020, ISSN: 1616-301X. Abstract | Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {Doping Dependent In-Plane and Cross-Plane Thermoelectric Performance of Thin n-Type Polymer P(NDI2OD-T2) Films}, author = {R M Kluge and N Saxena and W Chen and V Korstgens and M Schwartzkopf and Q Zhong and S V Roth and P Muller-Buschbaum}, url = {<Go to ISI>://WOS:000535017100001}, doi = {10.1002/adfm.202003092}, issn = {1616-301X}, year = {2020}, date = {2020-07-09}, journal = {Advanced Functional Materials}, volume = {30}, number = {28}, abstract = {Thermoelectric generators pose a promising approach in renewable energies as they can convert waste heat into electricity. In order to build high efficiency devices, suitable thermoelectric materials, both n- and p-type, are needed. Here, the n-type high-mobility polymer poly[N,N '-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5 '-(2,2 '-bithiophene) (P(NDI2OD-T2)) is focused upon. Via solution doping with 4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)-N,N-diphenylaniline (N-DPBI), a maximum power factor of (1.84 +/- 0.13) mu W K-2 m(-1) is achieved in an in-plane geometry for 5 wt% dopant concentration. Additionally, UV-vis spectroscopy and grazing-incidence wide-angle X-ray scattering are applied to elucidate the mechanisms of the doping process and to explain the discrepancy in thermoelectric performance depending on the charge carriers being either transported in-plane or cross-plane. Morphological changes are found such that the crystallites, built-up by extended polymer chains interacting via lamellar and pi-pi stacking, re-arrange from face- to edge-on orientation upon doping. At high doping concentrations, dopant molecules disturb the crystallinity of the polymer, hindering charge transport and leading to a decreased power factor at high dopant concentrations. These observations explain why an intermediate doping concentration of N-DPBI leads to an optimized thermoelectric performance of P(NDI2OD-T2) in an in-plane geometry as compared to the cross-plane case.}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } Thermoelectric generators pose a promising approach in renewable energies as they can convert waste heat into electricity. In order to build high efficiency devices, suitable thermoelectric materials, both n- and p-type, are needed. Here, the n-type high-mobility polymer poly[N,N '-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5 '-(2,2 '-bithiophene) (P(NDI2OD-T2)) is focused upon. Via solution doping with 4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)-N,N-diphenylaniline (N-DPBI), a maximum power factor of (1.84 +/- 0.13) mu W K-2 m(-1) is achieved in an in-plane geometry for 5 wt% dopant concentration. Additionally, UV-vis spectroscopy and grazing-incidence wide-angle X-ray scattering are applied to elucidate the mechanisms of the doping process and to explain the discrepancy in thermoelectric performance depending on the charge carriers being either transported in-plane or cross-plane. Morphological changes are found such that the crystallites, built-up by extended polymer chains interacting via lamellar and pi-pi stacking, re-arrange from face- to edge-on orientation upon doping. At high doping concentrations, dopant molecules disturb the crystallinity of the polymer, hindering charge transport and leading to a decreased power factor at high dopant concentrations. These observations explain why an intermediate doping concentration of N-DPBI leads to an optimized thermoelectric performance of P(NDI2OD-T2) in an in-plane geometry as compared to the cross-plane case. |
| 133. | S Strohmair, A Dey, Y Tong, L Polavarapu, B J Bohn, J Feldmann Spin Polarization Dynamics of Free Charge Carriers in CsPbI3 Nanocrystals Journal Article Nano Letters, 20 (7), pp. 4724-4730, 2020, ISSN: 1530-6984. Abstract | Links | Tags: Foundry Inorganic @article{, title = {Spin Polarization Dynamics of Free Charge Carriers in CsPbI3 Nanocrystals}, author = {S Strohmair and A Dey and Y Tong and L Polavarapu and B J Bohn and J Feldmann}, url = {<Go to ISI>://WOS:000548893200004}, doi = {10.1021/acs.nanolett.9b05325}, issn = {1530-6984}, year = {2020}, date = {2020-07-08}, journal = {Nano Letters}, volume = {20}, number = {7}, pages = {4724-4730}, abstract = {Lead halide perovskites (LHPs) exhibit large spin-orbit coupling (SOC), leading to only twofold-degenerate valence and conduction bands and therefore allowing for efficient optical orientation. This makes them ideal materials to study charge carrier spins. With this study we elucidate the spin dynamics of photoexcited charge carriers and the underlying spin relaxation mechanisms in CsPbI3 nanocrystals by employing time-resolved differential transmission spectroscopy (DTS). We find that the photoinduced spin polarization significantly diminishes during thermalization and cooling toward the energetically favorable band edge. Temperature-dependent DTS reveals a decay in spin polarization that is more than 1 order of magnitude faster at room temperature (3 ps) than at cryogenic temperatures (32 ps). We propose that spin relaxation of free charge carriers in large-SOC materials like LHPs occurs as a result of carrier-phonon scattering, as described by the Elliott-Yafet mechanism.}, keywords = {Foundry Inorganic}, pubstate = {published}, tppubtype = {article} } Lead halide perovskites (LHPs) exhibit large spin-orbit coupling (SOC), leading to only twofold-degenerate valence and conduction bands and therefore allowing for efficient optical orientation. This makes them ideal materials to study charge carrier spins. With this study we elucidate the spin dynamics of photoexcited charge carriers and the underlying spin relaxation mechanisms in CsPbI3 nanocrystals by employing time-resolved differential transmission spectroscopy (DTS). We find that the photoinduced spin polarization significantly diminishes during thermalization and cooling toward the energetically favorable band edge. Temperature-dependent DTS reveals a decay in spin polarization that is more than 1 order of magnitude faster at room temperature (3 ps) than at cryogenic temperatures (32 ps). We propose that spin relaxation of free charge carriers in large-SOC materials like LHPs occurs as a result of carrier-phonon scattering, as described by the Elliott-Yafet mechanism. |
| 132. | A M Pütz, M W Terban, S Bette, F Haase, R E Dinnebier, B V Lotsch Total scattering reveals the hidden stacking disorder in a 2D covalent organic framework Journal Article Chemical Science, 2020, ISSN: 2041-6520. Abstract | Links | Tags: Foundry Organic @article{, title = {Total scattering reveals the hidden stacking disorder in a 2D covalent organic framework}, author = {A M P\"{u}tz and M W Terban and S Bette and F Haase and R E Dinnebier and B V Lotsch}, url = {http://dx.doi.org/10.1039/D0SC03048A}, doi = {10.1039/D0SC03048A}, issn = {2041-6520}, year = {2020}, date = {2020-07-08}, journal = {Chemical Science}, abstract = {Interactions between extended π-systems are often invoked as the main driving force for stacking and crystallization of 2D organic polymers. In covalent organic frameworks (COFs), the stacking strongly influences properties such as the accessibility of functional sites, pore geometry, and surface states, but the exact nature of the interlayer interactions is mostly elusive. The stacking mode is often identified as eclipsed based on observed high symmetry diffraction patterns. However, as pointed out by various studies, the energetics of eclipsed stacking are not favorable and offset stacking is preferred. This work presents lower and higher apparent symmetry modifications of the imine-linked TTI-COF prepared through high- and low-temperature reactions. Through local structure investigation by pair distribution function analysis and simulations of stacking disorder, we observe random local layer offsets in the low temperature modification. We show that while stacking disorder can be easily overlooked due to the apparent crystallographic symmetry of these materials, total scattering methods can help clarify this information and suggest that defective local structures could be much more prevalent in COFs than previously thought. A detailed analysis of the local structure helps to improve the search for and design of highly porous tailor-made materials.}, keywords = {Foundry Organic}, pubstate = {published}, tppubtype = {article} } Interactions between extended π-systems are often invoked as the main driving force for stacking and crystallization of 2D organic polymers. In covalent organic frameworks (COFs), the stacking strongly influences properties such as the accessibility of functional sites, pore geometry, and surface states, but the exact nature of the interlayer interactions is mostly elusive. The stacking mode is often identified as eclipsed based on observed high symmetry diffraction patterns. However, as pointed out by various studies, the energetics of eclipsed stacking are not favorable and offset stacking is preferred. This work presents lower and higher apparent symmetry modifications of the imine-linked TTI-COF prepared through high- and low-temperature reactions. Through local structure investigation by pair distribution function analysis and simulations of stacking disorder, we observe random local layer offsets in the low temperature modification. We show that while stacking disorder can be easily overlooked due to the apparent crystallographic symmetry of these materials, total scattering methods can help clarify this information and suggest that defective local structures could be much more prevalent in COFs than previously thought. A detailed analysis of the local structure helps to improve the search for and design of highly porous tailor-made materials. |
| 131. | Al M F Fattah, M R Amin, M Mallmann, S Kasap, W Schnick, A Moewes Electronic structure investigation of wide band gap semiconductors—Mg2PN3 and Zn2PN3: experiment and theory Journal Article Journal of Physics: Condensed Matter, 32 (40), pp. 405504, 2020, ISSN: 0953-8984 1361-648X. Abstract | Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {Electronic structure investigation of wide band gap semiconductors\textemdashMg2PN3 and Zn2PN3: experiment and theory}, author = {Al M F Fattah and M R Amin and M Mallmann and S Kasap and W Schnick and A Moewes}, url = {http://dx.doi.org/10.1088/1361-648X/ab8f8a}, doi = {10.1088/1361-648x/ab8f8a}, issn = {0953-8984 1361-648X}, year = {2020}, date = {2020-07-06}, journal = {Journal of Physics: Condensed Matter}, volume = {32}, number = {40}, pages = {405504}, abstract = {The research on nitridophosphate materials has gained significant attention in recent years due to the abundance of elements like Mg, Zn, P, and N. We present a detailed study of band gap and electronic structure of M2PN3 (M = Mg, Zn), using synchrotron-based soft x-ray spectroscopy measurements as well as density functional theory (DFT) calculations. The experimental N K-edge x-ray emission spectroscopy (XES) and x-ray absorption spectroscopy (XAS) spectra are used to estimate the band gaps, which are compared with our calculations along with the values available in literature. The band gap, which is essential for electronic device applications, is experimentally determined for the first time to be 5.3 ± 0.2 eV and 4.2 ± 0.2 eV for Mg2PN3 and Zn2PN3, respectively. The experimental band gaps agree well with our calculated band gaps of 5.4 eV for Mg2PN3 and 3.9 eV for Zn2PN3, using the modified Becke\textendashJohnson (mBJ) exchange potential. The states that contribute to the band gap are investigated with the calculated density of states especially with respect to two non-equivalent N sites in the structure. The calculations and the measurements predict that both materials have an indirect band gap. The wide band gap of M2PN3 (M = Mg, Zn) could make it promising for the application in photovoltaic cells, high power RF applications, as well as power electronic devices.}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } The research on nitridophosphate materials has gained significant attention in recent years due to the abundance of elements like Mg, Zn, P, and N. We present a detailed study of band gap and electronic structure of M2PN3 (M = Mg, Zn), using synchrotron-based soft x-ray spectroscopy measurements as well as density functional theory (DFT) calculations. The experimental N K-edge x-ray emission spectroscopy (XES) and x-ray absorption spectroscopy (XAS) spectra are used to estimate the band gaps, which are compared with our calculations along with the values available in literature. The band gap, which is essential for electronic device applications, is experimentally determined for the first time to be 5.3 ± 0.2 eV and 4.2 ± 0.2 eV for Mg2PN3 and Zn2PN3, respectively. The experimental band gaps agree well with our calculated band gaps of 5.4 eV for Mg2PN3 and 3.9 eV for Zn2PN3, using the modified Becke–Johnson (mBJ) exchange potential. The states that contribute to the band gap are investigated with the calculated density of states especially with respect to two non-equivalent N sites in the structure. The calculations and the measurements predict that both materials have an indirect band gap. The wide band gap of M2PN3 (M = Mg, Zn) could make it promising for the application in photovoltaic cells, high power RF applications, as well as power electronic devices. |
| 130. | S Wakolbinger, F R Geisenhof, F Winterer, S Palmer, J G Crimmann, K Watanabe, T Taniguchi, F Trixler, R T Weitz Locally-triggered hydrophobic collapse induces global interface self-cleaning in van-der-Waals heterostructures at room-temperature Journal Article 2d Materials, 7 (3), 2020, ISSN: 2053-1583. Abstract | Links | Tags: Foundry Inorganic @article{, title = {Locally-triggered hydrophobic collapse induces global interface self-cleaning in van-der-Waals heterostructures at room-temperature}, author = {S Wakolbinger and F R Geisenhof and F Winterer and S Palmer and J G Crimmann and K Watanabe and T Taniguchi and F Trixler and R T Weitz}, url = {<Go to ISI>://WOS:000528571100001}, doi = {10.1088/2053-1583/ab7bfc}, issn = {2053-1583}, year = {2020}, date = {2020-07-03}, journal = {2d Materials}, volume = {7}, number = {3}, abstract = {Mutual relative orientation and well defined, uncontaminated interfaces are the key to obtain van-der-Waals heterostacks with defined properties. Even though the van-der-Waals forces are known to promote the 'self-cleaning' of interfaces, residue from the stamping process, which is often found to be trapped between the heterostructure constituents, can interrupt the interlayer interaction and therefore the coupling. Established interfacial cleaning methods usually involve high-temperature steps, which are in turn known to lead to uncontrolled rotations of layers within fragile heterostructures. Here, we present an alternative method feasible at room temperature. Using the tip of an atomic force microscope (AFM), we locally control the activation of interlayer attractive forces, resulting in the global removal of contaminants from the interface (i.e. the contaminants are also removed in regions several mu m away from the line touched by the AFM tip). By testing combinations of various hydrophobic van-der-Waals materials, mild temperature treatments, and by observing the temporal evolution of the contaminant removal process, we identify that the AFM tip triggers a dewetting-induced hydrophobic collapse and the van-der-Waals interaction is driving the cleaning process. We anticipate that this process is at the heart of the known 'self-cleaning' mechanism. Our technique can be utilized to controllably establish interlayer close coupling between a stack of van-der-Waals layers, and additionally allows to pattern and manipulate heterostructures locally for example to confine material into nanoscopic pockets between two van-der-Waals materials.}, keywords = {Foundry Inorganic}, pubstate = {published}, tppubtype = {article} } Mutual relative orientation and well defined, uncontaminated interfaces are the key to obtain van-der-Waals heterostacks with defined properties. Even though the van-der-Waals forces are known to promote the 'self-cleaning' of interfaces, residue from the stamping process, which is often found to be trapped between the heterostructure constituents, can interrupt the interlayer interaction and therefore the coupling. Established interfacial cleaning methods usually involve high-temperature steps, which are in turn known to lead to uncontrolled rotations of layers within fragile heterostructures. Here, we present an alternative method feasible at room temperature. Using the tip of an atomic force microscope (AFM), we locally control the activation of interlayer attractive forces, resulting in the global removal of contaminants from the interface (i.e. the contaminants are also removed in regions several mu m away from the line touched by the AFM tip). By testing combinations of various hydrophobic van-der-Waals materials, mild temperature treatments, and by observing the temporal evolution of the contaminant removal process, we identify that the AFM tip triggers a dewetting-induced hydrophobic collapse and the van-der-Waals interaction is driving the cleaning process. We anticipate that this process is at the heart of the known 'self-cleaning' mechanism. Our technique can be utilized to controllably establish interlayer close coupling between a stack of van-der-Waals layers, and additionally allows to pattern and manipulate heterostructures locally for example to confine material into nanoscopic pockets between two van-der-Waals materials. |
| 129. | D Yang, F C Lohrer, V Korstgens, A Schreiber, B Cao, S Bernstorff, P Muller-Buschbaum In Operando GISAXS and GIWAXS Stability Study of Organic Solar Cells Based on PffBT4T-2OD:PC71BM with and without Solvent Additive Journal Article Advanced Science, 2020. Abstract | Links | Tags: Foundry Organic, Molecularly Functionalized @article{, title = {In Operando GISAXS and GIWAXS Stability Study of Organic Solar Cells Based on PffBT4T-2OD:PC71BM with and without Solvent Additive}, author = {D Yang and F C Lohrer and V Korstgens and A Schreiber and B Cao and S Bernstorff and P Muller-Buschbaum}, url = {<Go to ISI>://WOS:000544597000001}, doi = {10.1002/advs.202001117}, year = {2020}, date = {2020-07-01}, journal = {Advanced Science}, abstract = {Solvent additives are known to modify the morphology of bulk heterojunction active layers to achieve high efficiency organic solar cells. However, the knowledge about the influence of solvent additives on the morphology degradation is limited. Hence, in operando grazing-incidence small and wide angle X-ray scattering (GISAXS and GIWAXS) measurements are applied on a series of PffBT4T-2OD:PC71BM-based solar cells prepared without and with solvent additives. The solar cells fabricated without a solvent additive, with 1,8-diiodoctane (DIO), and witho-chlorobenzaldehyde (CBA) additive show differences in the device degradation and changes in the morphology and crystallinity of the active layers. The mesoscale morphology changes are correlated with the decay of the short-circuit currentJ(sc)and the evolution of crystalline grain sizes is codependent with the decay of open-circuit voltageV(oc). Without additive, the loss inJ(sc)dominates the degradation, whereas with solvent additive (DIO and CBA) the loss inV(oc)rules the degradation. CBA addition increases the overall device stability as compared to DIO or absence of additive.}, keywords = {Foundry Organic, Molecularly Functionalized}, pubstate = {published}, tppubtype = {article} } Solvent additives are known to modify the morphology of bulk heterojunction active layers to achieve high efficiency organic solar cells. However, the knowledge about the influence of solvent additives on the morphology degradation is limited. Hence, in operando grazing-incidence small and wide angle X-ray scattering (GISAXS and GIWAXS) measurements are applied on a series of PffBT4T-2OD:PC71BM-based solar cells prepared without and with solvent additives. The solar cells fabricated without a solvent additive, with 1,8-diiodoctane (DIO), and witho-chlorobenzaldehyde (CBA) additive show differences in the device degradation and changes in the morphology and crystallinity of the active layers. The mesoscale morphology changes are correlated with the decay of the short-circuit currentJ(sc)and the evolution of crystalline grain sizes is codependent with the decay of open-circuit voltageV(oc). Without additive, the loss inJ(sc)dominates the degradation, whereas with solvent additive (DIO and CBA) the loss inV(oc)rules the degradation. CBA addition increases the overall device stability as compared to DIO or absence of additive. |
| 128. | K S Wienhold, V Korstgens, S Grott, X Y Jiang, M Schwartzkopf, S V Roth, P Muller-Buschbaum Solar Rrl, 4 (7), 2020, ISSN: 2367-198X. Abstract | Links | Tags: Foundry Organic, Molecularly-Functionalized @article{, title = {In Situ Printing: Insights into the Morphology Formation and Optical Property Evolution of Slot-Die-Coated Active Layers Containing Low Bandgap Polymer Donor and Nonfullerene Small Molecule Acceptor}, author = {K S Wienhold and V Korstgens and S Grott and X Y Jiang and M Schwartzkopf and S V Roth and P Muller-Buschbaum}, url = {<Go to ISI>://WOS:000527841700001}, doi = {10.1002/solr.202000086}, issn = {2367-198X}, year = {2020}, date = {2020-07-01}, journal = {Solar Rrl}, volume = {4}, number = {7}, abstract = {Printing of active layers for high-efficiency organic solar cells with the slot-die coating technique can overcome the challenge of upscaling, which will be needed for organic photovoltaics on its way to marketability. The morphology of a bulk-heterojunction organic solar cell has a very high impact on its power conversion efficiency. Therefore, it is of particular importance to understand the mechanisms of structure formation during printing of active layers to enable further optimization of the solar cell performance and upscaling of the production process. Meniscus-guided slot-die coating of the blend of a low bandgap conjugated polymer donor with benzodithiophene units PBDB-T-SF and the nonfullerene small molecule acceptor IT-4F is studied in situ with optical microscopy, Ultraviolet-visible spectroscopy, and grazing incidence small angle X-ray scattering. The structure formation is followed from the liquid to the final dry film state. Thereby, five regimes of morphology formation are determined. The morphological evolution in the printed active layer is correlated to changing optical properties of the thin film. In the final dry film, polymer domains of several tens of nanometers are observed, which will be favorable for application in high-efficiency organic solar cells.}, keywords = {Foundry Organic, Molecularly-Functionalized}, pubstate = {published}, tppubtype = {article} } Printing of active layers for high-efficiency organic solar cells with the slot-die coating technique can overcome the challenge of upscaling, which will be needed for organic photovoltaics on its way to marketability. The morphology of a bulk-heterojunction organic solar cell has a very high impact on its power conversion efficiency. Therefore, it is of particular importance to understand the mechanisms of structure formation during printing of active layers to enable further optimization of the solar cell performance and upscaling of the production process. Meniscus-guided slot-die coating of the blend of a low bandgap conjugated polymer donor with benzodithiophene units PBDB-T-SF and the nonfullerene small molecule acceptor IT-4F is studied in situ with optical microscopy, Ultraviolet-visible spectroscopy, and grazing incidence small angle X-ray scattering. The structure formation is followed from the liquid to the final dry film state. Thereby, five regimes of morphology formation are determined. The morphological evolution in the printed active layer is correlated to changing optical properties of the thin film. In the final dry film, polymer domains of several tens of nanometers are observed, which will be favorable for application in high-efficiency organic solar cells. |
| 127. | S Xue, R W Haid, R M Kluge, X Ding, B Garlyyev, J Fichtner, S Watzele, S J Hou, A S Bandarenka Enhancing the Hydrogen Evolution Reaction Activity of Platinum Electrodes in Alkaline Media Using Nickel-Iron Clusters Journal Article Angewandte Chemie-International Edition, 59 (27), pp. 10934-10938, 2020, ISSN: 1433-7851. Abstract | Links | Tags: Foundry Inorganic, Solid-Liquid @article{, title = {Enhancing the Hydrogen Evolution Reaction Activity of Platinum Electrodes in Alkaline Media Using Nickel-Iron Clusters}, author = {S Xue and R W Haid and R M Kluge and X Ding and B Garlyyev and J Fichtner and S Watzele and S J Hou and A S Bandarenka}, url = {<Go to ISI>://WOS:000529657400001}, doi = {10.1002/anie.202000383}, issn = {1433-7851}, year = {2020}, date = {2020-06-26}, journal = {Angewandte Chemie-International Edition}, volume = {59}, number = {27}, pages = {10934-10938}, abstract = {Herein, we demonstrate an easy way to improve the hydrogen evolution reaction (HER) activity of Pt electrodes in alkaline media by introducing Ni-Fe clusters. As a result, the overpotential needed to achieve a current density of 10 mA cm(-2) in H-2-saturated 0.1 m KOH is reduced for the model single-crystal electrodes down to about 70 mV. To our knowledge, these modified electrodes outperform any other reported electrocatalysts tested under similar conditions. Moreover, the influence of 1) Ni to Fe ratio, 2) cluster coverage, and 3) the nature of the alkali-metal cations present in the electrolyte on the HER activity has been investigated. The observed catalytic performance likely originates from both the improved water dissociation at the Ni-Fe clusters and the subsequent optimal hydrogen adsorption and recombination at Pt atoms present at the Ni-Fe/Pt boundary.}, keywords = {Foundry Inorganic, Solid-Liquid}, pubstate = {published}, tppubtype = {article} } Herein, we demonstrate an easy way to improve the hydrogen evolution reaction (HER) activity of Pt electrodes in alkaline media by introducing Ni-Fe clusters. As a result, the overpotential needed to achieve a current density of 10 mA cm(-2) in H-2-saturated 0.1 m KOH is reduced for the model single-crystal electrodes down to about 70 mV. To our knowledge, these modified electrodes outperform any other reported electrocatalysts tested under similar conditions. Moreover, the influence of 1) Ni to Fe ratio, 2) cluster coverage, and 3) the nature of the alkali-metal cations present in the electrolyte on the HER activity has been investigated. The observed catalytic performance likely originates from both the improved water dissociation at the Ni-Fe clusters and the subsequent optimal hydrogen adsorption and recombination at Pt atoms present at the Ni-Fe/Pt boundary. |
| 126. | L Nguyen, M Dass, M F Ober, L V Besteiro, Z M M Wang, B Nickel, A O Govorov, T Liedl, A Heuer-Jungemann Chiral Assembly of Gold-Silver Core-Shell Plasmonic Nanorods on DNA Origami with Strong Optical Activity Journal Article Acs Nano, 14 (6), pp. 7454-7461, 2020, ISSN: 1936-0851. Abstract | Links | Tags: Foundry Organic, Molecularly-Functionalized @article{, title = {Chiral Assembly of Gold-Silver Core-Shell Plasmonic Nanorods on DNA Origami with Strong Optical Activity}, author = {L Nguyen and M Dass and M F Ober and L V Besteiro and Z M M Wang and B Nickel and A O Govorov and T Liedl and A Heuer-Jungemann}, url = {<Go to ISI>://WOS:000543744100103}, doi = {10.1021/acsnano.0c03127}, issn = {1936-0851}, year = {2020}, date = {2020-06-23}, journal = {Acs Nano}, volume = {14}, number = {6}, pages = {7454-7461}, abstract = {The spatial organization of metal nanoparticles has become an important tool for manipulating light in nanophotonic applications. Silver nanoparticles, particularly silver nanorods, have excellent plasmonic properties but are prone to oxidation and are therefore inherently unstable in aqueous solutions and salt-containing buffers. Consequently, gold nanoparticles have often been favored, despite their inferior optical performance. Bimetallic, i.e., gold-silver core-shell nanoparticles, can resolve this issue. We present a method for synthesizing highly stable gold-silver core-shell NRs that are instantaneously functionalized with DNA, enabling chiral self-assembly on DNA origami. The silver shell gives rise to an enhancement of plasmonic properties, reflected here in strongly increased circular dichroism, as compared to pristine gold nanorods. Gold-silver nanorods are ideal candidates for plasmonic sensing with increased sensitivity as needed in pathogen RNA or antibody testing for nonlinear optics and light-funneling applications in surface enhanced Raman spectroscopy. Furthermore, the control of interparticle orientation enables the study of plasmonic phenomena, in particular, synergistic effects arising from plasmonic coupling of such bimetallic systems.}, keywords = {Foundry Organic, Molecularly-Functionalized}, pubstate = {published}, tppubtype = {article} } The spatial organization of metal nanoparticles has become an important tool for manipulating light in nanophotonic applications. Silver nanoparticles, particularly silver nanorods, have excellent plasmonic properties but are prone to oxidation and are therefore inherently unstable in aqueous solutions and salt-containing buffers. Consequently, gold nanoparticles have often been favored, despite their inferior optical performance. Bimetallic, i.e., gold-silver core-shell nanoparticles, can resolve this issue. We present a method for synthesizing highly stable gold-silver core-shell NRs that are instantaneously functionalized with DNA, enabling chiral self-assembly on DNA origami. The silver shell gives rise to an enhancement of plasmonic properties, reflected here in strongly increased circular dichroism, as compared to pristine gold nanorods. Gold-silver nanorods are ideal candidates for plasmonic sensing with increased sensitivity as needed in pathogen RNA or antibody testing for nonlinear optics and light-funneling applications in surface enhanced Raman spectroscopy. Furthermore, the control of interparticle orientation enables the study of plasmonic phenomena, in particular, synergistic effects arising from plasmonic coupling of such bimetallic systems. |
| 125. | C X Liu, S A Maier, G X Li Genetic-Algorithm-Aided Meta-Atom Multiplication for Improved Absorption and Coloration in Nanophotonics Journal Article Acs Photonics, 7 (7), pp. 1716-1722, 2020, ISSN: 2330-4022. Abstract | Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {Genetic-Algorithm-Aided Meta-Atom Multiplication for Improved Absorption and Coloration in Nanophotonics}, author = {C X Liu and S A Maier and G X Li}, url = {<Go to ISI>://WOS:000551497000018}, doi = {10.1021/acsphotonics.0c00266}, issn = {2330-4022}, year = {2020}, date = {2020-06-15}, journal = {Acs Photonics}, volume = {7}, number = {7}, pages = {1716-1722}, abstract = {For a repertoire of nanophotonic systems, including photonic crystals, metasurfaces, and plasmonic structures, unit cell with a single element is conventionally used for the simplicity of design. The extension of the unit cell with multiple meta-atoms drastically enlarges the parameter space and consequently provides potential configurations with improved device performance. Simultaneously, the multiplication does not induce additional complexity for lithography-based fabrications. However, the substantially increased number of parameters makes the design methodology based on physical intuition and parameter sweep impractical. Here, we show that expanding the number of meta-atoms in the unit cell significantly improves the performance of nanophotonic systems by the virtue of a genetic algorithm-based optimizer. Our approach includes physical intuition endowed in the geometry of meta-atoms, providing additional physical understanding of the optimization process. We demonstrate two photonic applications, including prominent enhancement of a broadband absorption and enlargement of the color coverage of plasmonic nanostructures. Not limited to the two proof-of-concept demonstrations, this methodology can be applied to all meta-atom-based nanophotonic systems, including plasmonic near-field enhancement and nonlinear frequency conversion, as well as a simultaneous control of phase and polarization for metasurfaces.}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } For a repertoire of nanophotonic systems, including photonic crystals, metasurfaces, and plasmonic structures, unit cell with a single element is conventionally used for the simplicity of design. The extension of the unit cell with multiple meta-atoms drastically enlarges the parameter space and consequently provides potential configurations with improved device performance. Simultaneously, the multiplication does not induce additional complexity for lithography-based fabrications. However, the substantially increased number of parameters makes the design methodology based on physical intuition and parameter sweep impractical. Here, we show that expanding the number of meta-atoms in the unit cell significantly improves the performance of nanophotonic systems by the virtue of a genetic algorithm-based optimizer. Our approach includes physical intuition endowed in the geometry of meta-atoms, providing additional physical understanding of the optimization process. We demonstrate two photonic applications, including prominent enhancement of a broadband absorption and enlargement of the color coverage of plasmonic nanostructures. Not limited to the two proof-of-concept demonstrations, this methodology can be applied to all meta-atom-based nanophotonic systems, including plasmonic near-field enhancement and nonlinear frequency conversion, as well as a simultaneous control of phase and polarization for metasurfaces. |
| 124. | M Gramlich, B J Bohn, Y Tong, L Polavarapu, J Feldmann, A S Urban Thickness-Dependence of Exciton-Exciton Annihilation in Halide Perovskite Nanoplatelets Journal Article Journal of Physical Chemistry Letters, 11 (13), pp. 5361-5366, 2020, ISSN: 1948-7185. Abstract | Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {Thickness-Dependence of Exciton-Exciton Annihilation in Halide Perovskite Nanoplatelets}, author = {M Gramlich and B J Bohn and Y Tong and L Polavarapu and J Feldmann and A S Urban}, url = {<Go to ISI>://WOS:000547468400064}, doi = {10.1021/acs.jpclett.0c01291}, issn = {1948-7185}, year = {2020}, date = {2020-06-14}, journal = {Journal of Physical Chemistry Letters}, volume = {11}, number = {13}, pages = {5361-5366}, abstract = {Exciton-exciton annihilation (EEA) and Auger recombination are detrimental processes occurring in semiconductor optoelectronic devices at high carrier densities. Despite constituting one of the main obstacles for realizing lasing in semiconductor nanocrystals (NCs), the dependencies on NC size are not fully understood, especially for those with both weakly and strongly confined dimensions. Here, we use differential transmission spectroscopy to investigate the dependence of EEA on the physical dimensions of thickness-controlled 2D halide perovskite nanoplatelets (NPIs). We find the EEA lifetimes to be extremely short on the order of 7-60 ps. Moreover, they are strongly determined by the NP1 thickness with a power law dependence according to tau(2) proportional to d(5.3). Additional measurements show that the EEA lifetimes also increase for NPIs with larger lateral dimensions. dimensions is critical for deciphering the fundamental laws governing These results show that a precise control of the physical the process especially in 1D and 2D NCs.}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } Exciton-exciton annihilation (EEA) and Auger recombination are detrimental processes occurring in semiconductor optoelectronic devices at high carrier densities. Despite constituting one of the main obstacles for realizing lasing in semiconductor nanocrystals (NCs), the dependencies on NC size are not fully understood, especially for those with both weakly and strongly confined dimensions. Here, we use differential transmission spectroscopy to investigate the dependence of EEA on the physical dimensions of thickness-controlled 2D halide perovskite nanoplatelets (NPIs). We find the EEA lifetimes to be extremely short on the order of 7-60 ps. Moreover, they are strongly determined by the NP1 thickness with a power law dependence according to tau(2) proportional to d(5.3). Additional measurements show that the EEA lifetimes also increase for NPIs with larger lateral dimensions. dimensions is critical for deciphering the fundamental laws governing These results show that a precise control of the physical the process especially in 1D and 2D NCs. |
| 123. | E Mitterreiter, B Schuler, K A Cochrane, U Wurstbauer, A Weber-Bargioni, C Kastl, A W Holleitner Atomistic Positioning of Defects in Helium Ion Treated Single-Layer MoS2 Journal Article Nano Letters, 20 (6), pp. 4437-4444, 2020, ISSN: 1530-6984. Abstract | Links | Tags: Foundry Inorganic @article{, title = {Atomistic Positioning of Defects in Helium Ion Treated Single-Layer MoS2}, author = {E Mitterreiter and B Schuler and K A Cochrane and U Wurstbauer and A Weber-Bargioni and C Kastl and A W Holleitner}, url = {<Go to ISI>://WOS:000541691200049}, doi = {10.1021/acs.nanolett.0c01222}, issn = {1530-6984}, year = {2020}, date = {2020-06-10}, journal = {Nano Letters}, volume = {20}, number = {6}, pages = {4437-4444}, abstract = {Structuring materials with atomic precision is the ultimate goal of nanotechnology and is becoming increasingly relevant as an enabling technology for quantum electronics/spintronics and quantum photonics. Here, we create atomic defects in monolayer MoS2 by helium ion (He-ion) beam lithography with a spatial fidelity approaching the single-atom limit in all three dimensions. Using low-temperature scanning tunneling microscopy (STM), we confirm the formation of individual point defects in MoS2 upon He-ion bombardment and show that defects are generated within 9 nm of the incident helium ions. Atom-specific sputtering yields are determined by analyzing the type and occurrence of defects observed in high-resolution STM images and compared with with Monte Carlo simulations. Both theory and experiment indicate that the He-ion bombardment predominantly generates sulfur vacancies.}, keywords = {Foundry Inorganic}, pubstate = {published}, tppubtype = {article} } Structuring materials with atomic precision is the ultimate goal of nanotechnology and is becoming increasingly relevant as an enabling technology for quantum electronics/spintronics and quantum photonics. Here, we create atomic defects in monolayer MoS2 by helium ion (He-ion) beam lithography with a spatial fidelity approaching the single-atom limit in all three dimensions. Using low-temperature scanning tunneling microscopy (STM), we confirm the formation of individual point defects in MoS2 upon He-ion bombardment and show that defects are generated within 9 nm of the incident helium ions. Atom-specific sputtering yields are determined by analyzing the type and occurrence of defects observed in high-resolution STM images and compared with with Monte Carlo simulations. Both theory and experiment indicate that the He-ion bombardment predominantly generates sulfur vacancies. |
| 122. | T Lochner, R M Kluge, J Fichtner, H A El-Sayed, B Garlyyev, A S Bandarenka Temperature Effects in Polymer Electrolyte Membrane Fuel Cells Journal Article Chemelectrochem, 2020, ISSN: 2196-0216. Abstract | Links | Tags: Solid-Liquid @article{, title = {Temperature Effects in Polymer Electrolyte Membrane Fuel Cells}, author = {T Lochner and R M Kluge and J Fichtner and H A El-Sayed and B Garlyyev and A S Bandarenka}, url = {<Go to ISI>://WOS:000546625300001}, doi = {10.1002/celc.202000588}, issn = {2196-0216}, year = {2020}, date = {2020-06-05}, journal = {Chemelectrochem}, abstract = {The behavior of proton exchange membrane fuel cells (PEMFCs) strongly depends on the operational temperatures. In mobile applications, for instance in fuel cell electric vehicles, PEMFC stacks are often subjected to temperatures as low as -20 degrees C, especially during cold start periods, and to temperatures up to 120 degrees C during regular operation. Therefore, it is important to understand the impact of temperature on the performance and degradation of hydrogen fuel cells to ensure a stable system operation. To get a comprehensive understanding of the temperature effects in PEMFCs, this manuscript addresses and summarizesin- situandex- situinvestigations of fuel cells operated at different temperatures. Initially, different measurement techniques for thermal monitoring are presented. Afterwards, the temperature effects related to the degradation and performance of main membrane electrode assembly components, namely gas diffusion layers, proton exchange membranes and catalyst layers, are analyzed.}, keywords = {Solid-Liquid}, pubstate = {published}, tppubtype = {article} } The behavior of proton exchange membrane fuel cells (PEMFCs) strongly depends on the operational temperatures. In mobile applications, for instance in fuel cell electric vehicles, PEMFC stacks are often subjected to temperatures as low as -20 degrees C, especially during cold start periods, and to temperatures up to 120 degrees C during regular operation. Therefore, it is important to understand the impact of temperature on the performance and degradation of hydrogen fuel cells to ensure a stable system operation. To get a comprehensive understanding of the temperature effects in PEMFCs, this manuscript addresses and summarizesin- situandex- situinvestigations of fuel cells operated at different temperatures. Initially, different measurement techniques for thermal monitoring are presented. Afterwards, the temperature effects related to the degradation and performance of main membrane electrode assembly components, namely gas diffusion layers, proton exchange membranes and catalyst layers, are analyzed. |
| 121. | M Isselstein, L Zhang, V Glembockyte, O Brix, G Cosa, P Tinnefeld, T Cordes Self-Healing Dyes—Keeping the Promise? Journal Article The Journal of Physical Chemistry Letters, 11 (11), pp. 4462-4480, 2020. Links | Tags: Foundry Organic @article{, title = {Self-Healing Dyes\textemdashKeeping the Promise?}, author = {M Isselstein and L Zhang and V Glembockyte and O Brix and G Cosa and P Tinnefeld and T Cordes}, url = {https://doi.org/10.1021/acs.jpclett.9b03833}, doi = {10.1021/acs.jpclett.9b03833}, year = {2020}, date = {2020-06-04}, journal = {The Journal of Physical Chemistry Letters}, volume = {11}, number = {11}, pages = {4462-4480}, keywords = {Foundry Organic}, pubstate = {published}, tppubtype = {article} } |
| 120. | S Vogler, J C B Dietschreit, L D M Peters, C Ochsenfeld Important components for accurate hyperfine coupling constants: electron correlation, dynamic contributions, and solvation effects Journal Article Molecular Physics, 2020, ISSN: 0026-8976. Abstract | Links | Tags: Solid-Liquid @article{, title = {Important components for accurate hyperfine coupling constants: electron correlation, dynamic contributions, and solvation effects}, author = {S Vogler and J C B Dietschreit and L D M Peters and C Ochsenfeld}, url = {<Go to ISI>://WOS:000543577500001}, doi = {10.1080/00268976.2020.1772515}, issn = {0026-8976}, year = {2020}, date = {2020-06-03}, journal = {Molecular Physics}, abstract = {The calculation of hyperfine coupling constants is a challenging task in balancing accuracy and computational effort. While previous work has shown the importance of electron correlation and molecular dynamic contributions, we present a systematic study simultaneously analyzing the influence of both effects on hyperfine coupling constants. To this end, we thoroughly study two organic radicals, namely the dimethylamino radical and ethanal radical cation, proving the need to account for conformational flexibility as well as the large influence of electron correlation. Based on these results, we analyse the effect of electron correlation and dynamic simulations on a set of 12 organic radicals, illustrating that both effects are vital for an accuratein silicodescription on the same scale. Furthermore, we study the influence of solvation using the efficient nuclei-selected algorithm to obtain hyperfine coupling constants with electron correlation for large systems, indicating the necessity to include explicit solvent molecules. Finally, we introduce a composite approach to incorporate all contributions for hyperfine coupling of radicals in solution at comparatively low computational cost. This is successfully tested on the hydroxylated TEMPO radical in aqueous solution, where we are able to compute aN-HFCC of 44.4 MHz compared to the experimentally measured 47.6 MHz. [GRAPHICS] .}, keywords = {Solid-Liquid}, pubstate = {published}, tppubtype = {article} } The calculation of hyperfine coupling constants is a challenging task in balancing accuracy and computational effort. While previous work has shown the importance of electron correlation and molecular dynamic contributions, we present a systematic study simultaneously analyzing the influence of both effects on hyperfine coupling constants. To this end, we thoroughly study two organic radicals, namely the dimethylamino radical and ethanal radical cation, proving the need to account for conformational flexibility as well as the large influence of electron correlation. Based on these results, we analyse the effect of electron correlation and dynamic simulations on a set of 12 organic radicals, illustrating that both effects are vital for an accuratein silicodescription on the same scale. Furthermore, we study the influence of solvation using the efficient nuclei-selected algorithm to obtain hyperfine coupling constants with electron correlation for large systems, indicating the necessity to include explicit solvent molecules. Finally, we introduce a composite approach to incorporate all contributions for hyperfine coupling of radicals in solution at comparatively low computational cost. This is successfully tested on the hydroxylated TEMPO radical in aqueous solution, where we are able to compute aN-HFCC of 44.4 MHz compared to the experimentally measured 47.6 MHz. [GRAPHICS] . |
| 119. | H D Boggiano, R Berte, A F Scarpettini, E Cortes, S A Maier, A V Bragas Determination of Nanoscale Mechanical Properties of Polymers via Plasmonic Nanoantennas Journal Article Acs Photonics, 7 (6), pp. 1403-1409, 2020, ISSN: 2330-4022. Abstract | Links | Tags: Solid-Solid @article{, title = {Determination of Nanoscale Mechanical Properties of Polymers via Plasmonic Nanoantennas}, author = {H D Boggiano and R Berte and A F Scarpettini and E Cortes and S A Maier and A V Bragas}, url = {<Go to ISI>://WOS:000542931300008}, doi = {10.1021/acsphotonics.0c00631}, issn = {2330-4022}, year = {2020}, date = {2020-06-02}, journal = {Acs Photonics}, volume = {7}, number = {6}, pages = {1403-1409}, abstract = {Nanotechnology and the consequent emergence of miniaturized devices are driving the need to improve our understanding of the mechanical properties of a myriad of materials. Here we focus on amorphous polymeric materials and introduce a new way to determine the nanoscale mechanical response of polymeric thin films in the GHz range, using ultrafast optical means. Coupling of the films to plasmonic nanoantennas excited at their vibrational eigenfrequencies allows the extraction of the values of the mechanical moduli as well as the estimation of the glass transition temperature via time-domain measurements, here demonstrated for PMMA films. This nanoscale method can be extended to the determination of mechanical and elastic properties of a wide range of spatially strongly confined materials.}, keywords = {Solid-Solid}, pubstate = {published}, tppubtype = {article} } Nanotechnology and the consequent emergence of miniaturized devices are driving the need to improve our understanding of the mechanical properties of a myriad of materials. Here we focus on amorphous polymeric materials and introduce a new way to determine the nanoscale mechanical response of polymeric thin films in the GHz range, using ultrafast optical means. Coupling of the films to plasmonic nanoantennas excited at their vibrational eigenfrequencies allows the extraction of the values of the mechanical moduli as well as the estimation of the glass transition temperature via time-domain measurements, here demonstrated for PMMA films. This nanoscale method can be extended to the determination of mechanical and elastic properties of a wide range of spatially strongly confined materials. |
| 118. | F Fang, M J Liu, W Chen, H C Yang, Y Z Liu, X Li, J J Hao, B Xu, D Wu, K Cao, W Lei, P Muller-Buschbaum, X W Sun, R Chen, K Wang Atomic Layer Deposition Assisted Encapsulation of Quantum Dot Luminescent Microspheres toward Display Applications Journal Article Advanced Optical Materials, 8 (12), 2020, ISSN: 2195-1071. Abstract | Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {Atomic Layer Deposition Assisted Encapsulation of Quantum Dot Luminescent Microspheres toward Display Applications}, author = {F Fang and M J Liu and W Chen and H C Yang and Y Z Liu and X Li and J J Hao and B Xu and D Wu and K Cao and W Lei and P Muller-Buschbaum and X W Sun and R Chen and K Wang}, url = {<Go to ISI>://WOS:000528492300001}, doi = {10.1002/adom.201902118}, issn = {2195-1071}, year = {2020}, date = {2020-06-01}, journal = {Advanced Optical Materials}, volume = {8}, number = {12}, abstract = {Quantum dots (QDs) are promising for being used in advanced displays due to their outstanding emission properties. Herein, a novel encapsulation method for QDs is reported and ultra-stable QDs@SiO2@Al2O3 luminescent microspheres (QLuMiS) are obtained by combining a sol-gel method for the intermediate SiO2 layer with a fluidized powder atomic layer deposition (ALD) for the outer Al2O3 layer. The rich hydroxyl coverage on the QDs@SiO2 surface provides abundant chemisorption sites, which are beneficial for the deposition of Al2O3 in the ALD process. Simultaneously, the water-oxygen channels in the SiO2 layer are blocked by the Al2O3 layer, which protects the QDs against deterioration. Consequently, the QLuMiS exhibit an excellent stability with 86% of the initial light conversion efficiency after 1000 h of blue light aging under a light power density of 2000 mW cm(-2). Such stability is significantly better than that of QDs@Al2O3 and QDs@SiO2 samples. Moreover, under this strong irradiation aging condition with blue light, the extrapolated lifetime (L50) of QLuMiS is 4969 h, which is ten times longer than that of QDs@SiO2 and is the best record as far as is known. Finally, a prototype of a QLuMiS-based cellphone screen with a wide color gamut of 115% NTSC is demonstrated.}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } Quantum dots (QDs) are promising for being used in advanced displays due to their outstanding emission properties. Herein, a novel encapsulation method for QDs is reported and ultra-stable QDs@SiO2@Al2O3 luminescent microspheres (QLuMiS) are obtained by combining a sol-gel method for the intermediate SiO2 layer with a fluidized powder atomic layer deposition (ALD) for the outer Al2O3 layer. The rich hydroxyl coverage on the QDs@SiO2 surface provides abundant chemisorption sites, which are beneficial for the deposition of Al2O3 in the ALD process. Simultaneously, the water-oxygen channels in the SiO2 layer are blocked by the Al2O3 layer, which protects the QDs against deterioration. Consequently, the QLuMiS exhibit an excellent stability with 86% of the initial light conversion efficiency after 1000 h of blue light aging under a light power density of 2000 mW cm(-2). Such stability is significantly better than that of QDs@Al2O3 and QDs@SiO2 samples. Moreover, under this strong irradiation aging condition with blue light, the extrapolated lifetime (L50) of QLuMiS is 4969 h, which is ten times longer than that of QDs@SiO2 and is the best record as far as is known. Finally, a prototype of a QLuMiS-based cellphone screen with a wide color gamut of 115% NTSC is demonstrated. |
| 117. | K S Wienhold, W Chen, S S Yin, R J Guo, M Schwartzkopf, S V Roth, P Muller-Buschbaum Following in Operando the Structure Evolution-Induced Degradation in Printed Organic Solar Cells with Nonfullerene Small Molecule Acceptor Journal Article Solar Rrl, 2020, ISSN: 2367-198X. Abstract | Links | Tags: Foundry Organic, Molecularly Functionalized @article{, title = {Following in Operando the Structure Evolution-Induced Degradation in Printed Organic Solar Cells with Nonfullerene Small Molecule Acceptor}, author = {K S Wienhold and W Chen and S S Yin and R J Guo and M Schwartzkopf and S V Roth and P Muller-Buschbaum}, url = {<Go to ISI>://WOS:000538529300001}, doi = {10.1002/solr.202000251}, issn = {2367-198X}, year = {2020}, date = {2020-06-01}, journal = {Solar Rrl}, abstract = {Understanding the degradation mechanisms of printed bulk-heterojunction (BHJ) organic solar cells during operation is essential to achieve long-term stability and realize real-world applications of organic photovoltaics. Herein, the degradation of printed organic solar cells based on the conjugated benzodithiophene polymer PBDB-T-SF and the nonfullerene small molecule acceptor IT-4F with 0.25 vol% 1,8-diiodooctane (DIO) solvent additive is studied in operando for two different donor:acceptor ratios. The inner nano-morphology is analyzed with grazing incidence small angle X-ray scattering (GISAXS), and current-voltage (I-V) characteristics are probed simultaneously. Irrespective of the mixing ratio, degradation occurs by the same degradation mechanism. A decrease in the short-circuit current density (J(SC)) is identified to be the determining factor for the decline of the power conversion efficiency. The decrease in J(SC) is induced by a reduction of the relative interface area between the conjugated polymer and the small molecule acceptor in the BHJ structure, resembling the morphological degradation of the active layer.}, keywords = {Foundry Organic, Molecularly Functionalized}, pubstate = {published}, tppubtype = {article} } Understanding the degradation mechanisms of printed bulk-heterojunction (BHJ) organic solar cells during operation is essential to achieve long-term stability and realize real-world applications of organic photovoltaics. Herein, the degradation of printed organic solar cells based on the conjugated benzodithiophene polymer PBDB-T-SF and the nonfullerene small molecule acceptor IT-4F with 0.25 vol% 1,8-diiodooctane (DIO) solvent additive is studied in operando for two different donor:acceptor ratios. The inner nano-morphology is analyzed with grazing incidence small angle X-ray scattering (GISAXS), and current-voltage (I-V) characteristics are probed simultaneously. Irrespective of the mixing ratio, degradation occurs by the same degradation mechanism. A decrease in the short-circuit current density (J(SC)) is identified to be the determining factor for the decline of the power conversion efficiency. The decrease in J(SC) is induced by a reduction of the relative interface area between the conjugated polymer and the small molecule acceptor in the BHJ structure, resembling the morphological degradation of the active layer. |
| 116. | X B Tang, W Chen, D Wu, A J Gao, G M Li, J Y Sun, K Y Yi, Z J Wang, G T Pang, H C Yang, R J Guo, H H Liu, H Y Zhong, M Y Huang, R Chen, P Muller-Buschbaum, X W Sun, K Wang In Situ Growth of All-Inorganic Perovskite Single Crystal Arrays on Electron Transport Layer Journal Article Advanced Science, 7 (11), 2020. Abstract | Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {In Situ Growth of All-Inorganic Perovskite Single Crystal Arrays on Electron Transport Layer}, author = {X B Tang and W Chen and D Wu and A J Gao and G M Li and J Y Sun and K Y Yi and Z J Wang and G T Pang and H C Yang and R J Guo and H H Liu and H Y Zhong and M Y Huang and R Chen and P Muller-Buschbaum and X W Sun and K Wang}, url = {<Go to ISI>://WOS:000527687700001}, doi = {10.1002/advs.201902767}, year = {2020}, date = {2020-06-01}, journal = {Advanced Science}, volume = {7}, number = {11}, abstract = {Directly growing perovskite single crystals on charge carrier transport layers will unravel a promising route for the development of emerging optoelectronic devices. Herein, in situ growth of high-quality all-inorganic perovskite (CsPbBr3) single crystal arrays (PeSCAs) on cubic zinc oxide (c-ZnO) is reported, which is used as an inorganic electron transport layer in optoelectronic devices, via a facile spin-coating method. The PeSCAs consist of rectangular thin microplatelets of 6-10 mu m in length and 2-3 mu m in width. The deposited c-ZnO enables the formation of phase-pure and highly crystallized cubic perovskites via an epitaxial lattice coherence of (100)(CsPbBr3)parallel to(100)(c-ZnO), which is further confirmed by grazing incidence wide-angle X-ray scattering. The PeSCAs demonstrate a significant structural stability of 26 days with a 9 days excellent photoluminescence stability in ambient environment, which is much superior to the perovskite nanocrystals (PeNCs). The high crystallinity of the PeSCAs allows for a lower density of trap states, longer carrier lifetimes, and narrower energetic disorder for excitons, which leads to a faster diffusion rate than PeNCs. These results unravel the possibility of creating the interface toward c-ZnO heterogeneous layer, which is a major step for the realization of a better integration of perovskites and charge carrier transport layers.}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } Directly growing perovskite single crystals on charge carrier transport layers will unravel a promising route for the development of emerging optoelectronic devices. Herein, in situ growth of high-quality all-inorganic perovskite (CsPbBr3) single crystal arrays (PeSCAs) on cubic zinc oxide (c-ZnO) is reported, which is used as an inorganic electron transport layer in optoelectronic devices, via a facile spin-coating method. The PeSCAs consist of rectangular thin microplatelets of 6-10 mu m in length and 2-3 mu m in width. The deposited c-ZnO enables the formation of phase-pure and highly crystallized cubic perovskites via an epitaxial lattice coherence of (100)(CsPbBr3)parallel to(100)(c-ZnO), which is further confirmed by grazing incidence wide-angle X-ray scattering. The PeSCAs demonstrate a significant structural stability of 26 days with a 9 days excellent photoluminescence stability in ambient environment, which is much superior to the perovskite nanocrystals (PeNCs). The high crystallinity of the PeSCAs allows for a lower density of trap states, longer carrier lifetimes, and narrower energetic disorder for excitons, which leads to a faster diffusion rate than PeNCs. These results unravel the possibility of creating the interface toward c-ZnO heterogeneous layer, which is a major step for the realization of a better integration of perovskites and charge carrier transport layers. |
| 115. | J Skotnitzki, A Kremsmair, D Keefer, F Schuppel, B L De Bonneville, R De Vivie-Riedle, P Knochel Regio- and diastereoselective reactions of chiral secondary alkylcopper reagents with propargylic phosphates: preparation of chiral allenes Journal Article Chemical Science, 11 (20), pp. 5328-5332, 2020, ISSN: 2041-6520. Abstract | Links | Tags: Foundry Organic @article{, title = {Regio- and diastereoselective reactions of chiral secondary alkylcopper reagents with propargylic phosphates: preparation of chiral allenes}, author = {J Skotnitzki and A Kremsmair and D Keefer and F Schuppel and B L De Bonneville and R De Vivie-Riedle and P Knochel}, url = {<Go to ISI>://WOS:000537133000020}, doi = {10.1039/c9sc05982b}, issn = {2041-6520}, year = {2020}, date = {2020-05-28}, journal = {Chemical Science}, volume = {11}, number = {20}, pages = {5328-5332}, abstract = {The diastereoselective S(N)2 '-substitution of secondary alkylcopper reagents with propargylic phosphates enables the preparation of stereodefined alkylallenes. By using enantiomerically enriched alkylcopper reagents and enantioenriched propargylic phosphates as electrophiles anti-S(N)2 '-substitutions were performend leading to alpha-chiral allenes in good yields with excellent regioselectivity and retention of configuration. DFT-calculations were performed to rationalize the structure of these alkylcopper reagents in various solvents, emphasizing their configurational stability in THF.}, keywords = {Foundry Organic}, pubstate = {published}, tppubtype = {article} } The diastereoselective S(N)2 '-substitution of secondary alkylcopper reagents with propargylic phosphates enables the preparation of stereodefined alkylallenes. By using enantiomerically enriched alkylcopper reagents and enantioenriched propargylic phosphates as electrophiles anti-S(N)2 '-substitutions were performend leading to alpha-chiral allenes in good yields with excellent regioselectivity and retention of configuration. DFT-calculations were performed to rationalize the structure of these alkylcopper reagents in various solvents, emphasizing their configurational stability in THF. |
| 114. | A Dey, A F Richter, T Debnath, H Huang, L Polavarapu, J Feldmann Transfer of Direct to Indirect Bound Excitons by Electron Intervalley Scattering in Cs2AgBiBr6 Double Perovskite Nanocrystals Journal Article Acs Nano, 14 (5), pp. 5855-5861, 2020, ISSN: 1936-0851. Abstract | Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {Transfer of Direct to Indirect Bound Excitons by Electron Intervalley Scattering in Cs2AgBiBr6 Double Perovskite Nanocrystals}, author = {A Dey and A F Richter and T Debnath and H Huang and L Polavarapu and J Feldmann}, url = {<Go to ISI>://WOS:000537682300069}, doi = {10.1021/acsnano.0c00997}, issn = {1936-0851}, year = {2020}, date = {2020-05-26}, journal = {Acs Nano}, volume = {14}, number = {5}, pages = {5855-5861}, abstract = {Lead-free halide double perovskites have emerged as a nontoxic alternative to the heavily researched lead-based halide perovskites. However, their optical properties and the initial charge carrier relaxation processes are under debate. In this study, we apply time-resolved photoluminescence and differential transmission spectroscopy to investigate the photoexcited charge carrier dynamics within the indirect band structure of Cs2AgBiBr6 nanocrystals. Interestingly, we observe a high energetic emission stemming from the direct band gap, besides the previously reported emission from the indirect band gap transition. We attribute this emission to the radiative recombination of direct bound excitons. This emission maximum redshifts nearly 1 eV within 10 ps due to electron intervalley scattering, which leads to a transfer of direct to indirect bound excitons. We conclude that these direct bound excitons possess a giant oscillator strength causing not only a pronounced absorption peak at the optical band gap energy but also luminescence to occur at the direct band gap transition in spite of the prevailing intervalley scattering process. These results expand the understanding of the optical properties and the charge carrier relaxation in double perovskites, thus, facilitating the further development of optoelectronic devices harnessing lead-free perovskites.}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } Lead-free halide double perovskites have emerged as a nontoxic alternative to the heavily researched lead-based halide perovskites. However, their optical properties and the initial charge carrier relaxation processes are under debate. In this study, we apply time-resolved photoluminescence and differential transmission spectroscopy to investigate the photoexcited charge carrier dynamics within the indirect band structure of Cs2AgBiBr6 nanocrystals. Interestingly, we observe a high energetic emission stemming from the direct band gap, besides the previously reported emission from the indirect band gap transition. We attribute this emission to the radiative recombination of direct bound excitons. This emission maximum redshifts nearly 1 eV within 10 ps due to electron intervalley scattering, which leads to a transfer of direct to indirect bound excitons. We conclude that these direct bound excitons possess a giant oscillator strength causing not only a pronounced absorption peak at the optical band gap energy but also luminescence to occur at the direct band gap transition in spite of the prevailing intervalley scattering process. These results expand the understanding of the optical properties and the charge carrier relaxation in double perovskites, thus, facilitating the further development of optoelectronic devices harnessing lead-free perovskites. |
| 113. | B Garlyyev, S Xue, J Fichtner, A S Bandarenka, C Andronescu Prospects of Value-Added Chemicals and Hydrogen via Electrolysis Journal Article Chemsuschem, 13 (10), pp. 2513-2521, 2020, ISSN: 1864-5631. Abstract | Links | Tags: Foundry Inorganic, Solid-Liquid @article{, title = {Prospects of Value-Added Chemicals and Hydrogen via Electrolysis}, author = {B Garlyyev and S Xue and J Fichtner and A S Bandarenka and C Andronescu}, url = {<Go to ISI>://WOS:000520259100001}, doi = {10.1002/cssc.202000339}, issn = {1864-5631}, year = {2020}, date = {2020-05-22}, journal = {Chemsuschem}, volume = {13}, number = {10}, pages = {2513-2521}, abstract = {Cost is a major drawback that limits the industrial-scale hydrogen production through water electrolysis. The overall cost of this technology can be decreased by coupling the electrosynthesis of value-added chemicals at the anode side with electrolytic hydrogen generation at the cathode. This Minireview provides a directory of anodic oxidation reactions that can be combined with cathodic hydrogen generation. The important parameters for selecting the anodic reactions, such as choice of catalyst material and its selectivity towards specific products are elaborated in detail. Furthermore, various novel electrolysis cell architectures for effortless separation of value-added products from hydrogen gas are described.}, keywords = {Foundry Inorganic, Solid-Liquid}, pubstate = {published}, tppubtype = {article} } Cost is a major drawback that limits the industrial-scale hydrogen production through water electrolysis. The overall cost of this technology can be decreased by coupling the electrosynthesis of value-added chemicals at the anode side with electrolytic hydrogen generation at the cathode. This Minireview provides a directory of anodic oxidation reactions that can be combined with cathodic hydrogen generation. The important parameters for selecting the anodic reactions, such as choice of catalyst material and its selectivity towards specific products are elaborated in detail. Furthermore, various novel electrolysis cell architectures for effortless separation of value-added products from hydrogen gas are described. |
| 112. | J W Borchert, U Zschieschang, F Letzkus, M Giorgio, R T Weitz, M Caironi, J N Burghartz, S Ludwigs, H Klauk Flexible low-voltage high-frequency organic thin-film transistors Journal Article Science Advances, 6 (21), 2020, ISSN: 2375-2548. Abstract | Links | Tags: Foundry Organic, Molecularly Functionalized @article{, title = {Flexible low-voltage high-frequency organic thin-film transistors}, author = {J W Borchert and U Zschieschang and F Letzkus and M Giorgio and R T Weitz and M Caironi and J N Burghartz and S Ludwigs and H Klauk}, url = {<Go to ISI>://WOS:000537235300049}, doi = {10.1126/sciadv.aaz5156}, issn = {2375-2548}, year = {2020}, date = {2020-05-20}, journal = {Science Advances}, volume = {6}, number = {21}, abstract = {The primary driver for the development of organic thin-film transistors (TFTs) over the past few decades has been the prospect of electronics applications on unconventional substrates requiring low-temperature processing. A key requirement for many such applications is high-frequency switching or amplification at the low operating voltages provided by lithium-ion batteries (similar to 3 V). To date, however, most organic-TFT technologies show limited dynamic performance unless high operating voltages are applied to mitigate high contact resistances and large parasitic capacitances. Here, we present flexible low-voltage organic TFTs with record static and dynamic performance, including contact resistance as small as 10 Omega.cm, on/off current ratios as large as 10(10), subthreshold swing as small as 59 mV/decade, signal delays below 80 ns in inverters and ring oscillators, and transit frequencies as high as 21 MHz, all while using an inverted coplanar TFT structure that can be readily adapted to industry-standard lithographic techniques.}, keywords = {Foundry Organic, Molecularly Functionalized}, pubstate = {published}, tppubtype = {article} } The primary driver for the development of organic thin-film transistors (TFTs) over the past few decades has been the prospect of electronics applications on unconventional substrates requiring low-temperature processing. A key requirement for many such applications is high-frequency switching or amplification at the low operating voltages provided by lithium-ion batteries (similar to 3 V). To date, however, most organic-TFT technologies show limited dynamic performance unless high operating voltages are applied to mitigate high contact resistances and large parasitic capacitances. Here, we present flexible low-voltage organic TFTs with record static and dynamic performance, including contact resistance as small as 10 Omega.cm, on/off current ratios as large as 10(10), subthreshold swing as small as 59 mV/decade, signal delays below 80 ns in inverters and ring oscillators, and transit frequencies as high as 21 MHz, all while using an inverted coplanar TFT structure that can be readily adapted to industry-standard lithographic techniques. |
| 111. | T Deilmann, M Rohlfing, U Wurstbauer Light-matter interaction in van der Waals hetero-structures Journal Article Journal of Physics-Condensed Matter, 32 (33), 2020, ISSN: 0953-8984. Abstract | Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {Light-matter interaction in van der Waals hetero-structures}, author = {T Deilmann and M Rohlfing and U Wurstbauer}, url = {<Go to ISI>://WOS:000536663700001}, doi = {10.1088/1361-648X/ab8661}, issn = {0953-8984}, year = {2020}, date = {2020-05-15}, journal = {Journal of Physics-Condensed Matter}, volume = {32}, number = {33}, abstract = {Even if individual two-dimensional materials own various interesting and unexpected properties, the stacking of such layers leads to van der Waals solids which unite the characteristics of two dimensions with novel features originating from the interlayer interactions. In this topical review, we cover fabrication and characterization of van der Waals hetero-structures with a focus on hetero-bilayers made of monolayers of semiconducting transition metal dichalcogenides. Experimental and theoretical techniques to investigate those hetero-bilayers are introduced. Most recent findings focusing on different transition metal dichalcogenides hetero-structures are presented and possible optical transitions between different valleys, appearance of moire patterns and signatures of moire excitons are discussed. The fascinating and fast growing research on van der Waals hetero-bilayers provide promising insights required for their application as emerging quantum-nano materials.}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } Even if individual two-dimensional materials own various interesting and unexpected properties, the stacking of such layers leads to van der Waals solids which unite the characteristics of two dimensions with novel features originating from the interlayer interactions. In this topical review, we cover fabrication and characterization of van der Waals hetero-structures with a focus on hetero-bilayers made of monolayers of semiconducting transition metal dichalcogenides. Experimental and theoretical techniques to investigate those hetero-bilayers are introduced. Most recent findings focusing on different transition metal dichalcogenides hetero-structures are presented and possible optical transitions between different valleys, appearance of moire patterns and signatures of moire excitons are discussed. The fascinating and fast growing research on van der Waals hetero-bilayers provide promising insights required for their application as emerging quantum-nano materials. |
| 110. | S Xue, B Garlyyev, A Auer, J Kunze-Liebhauser, A S Bandarenka How the Nature of the Alkali Metal Cations Influences the Double-Layer Capacitance of Cu, Au, and Pt Single-Crystal Electrodes Journal Article Journal of Physical Chemistry C, 124 (23), pp. 12442-12447, 2020, ISSN: 1932-7447. Abstract | Links | Tags: Foundry Inorganic, Solid-Liquid @article{, title = {How the Nature of the Alkali Metal Cations Influences the Double-Layer Capacitance of Cu, Au, and Pt Single-Crystal Electrodes}, author = {S Xue and B Garlyyev and A Auer and J Kunze-Liebhauser and A S Bandarenka}, url = {<Go to ISI>://WOS:000541745800029}, doi = {10.1021/acs.jpcc.0c01715}, issn = {1932-7447}, year = {2020}, date = {2020-05-09}, journal = {Journal of Physical Chemistry C}, volume = {124}, number = {23}, pages = {12442-12447}, abstract = {In this work, we have investigated the influence of alkali metal cations on the electrical double-layer (EDL) properties for various metal electrodes. Using electrochemical impedance spectroscopy, we demonstrate that those cations significantly affect the EDL capacitance in the case of single-crystalline Cu(111), Cu(100), Au(111), Pt(111), stepped Pt(775), and kinked Pt(12 10 5) electrodes in 0.05 M MeClO4 (Me+ = Li+, Na+, K+, Rb+, and Cs+) electrolytes. For all the electrodes, the capacitance always linearly increases with decreasing hydration energy of Me+ in the following order: Li+ < Na+ < K+ < Rb+ < Cs+. Moreover, we estimate the effective concentrations of the alkali metal cations near the electrode surfaces by correlating the capacitances with the relative permittivity. For all the electrodes, the concentrations near the electrode surface were calculated to be similar to 60 to 80 times higher than in the bulk solutions.}, keywords = {Foundry Inorganic, Solid-Liquid}, pubstate = {published}, tppubtype = {article} } In this work, we have investigated the influence of alkali metal cations on the electrical double-layer (EDL) properties for various metal electrodes. Using electrochemical impedance spectroscopy, we demonstrate that those cations significantly affect the EDL capacitance in the case of single-crystalline Cu(111), Cu(100), Au(111), Pt(111), stepped Pt(775), and kinked Pt(12 10 5) electrodes in 0.05 M MeClO4 (Me+ = Li+, Na+, K+, Rb+, and Cs+) electrolytes. For all the electrodes, the capacitance always linearly increases with decreasing hydration energy of Me+ in the following order: Li+ < Na+ < K+ < Rb+ < Cs+. Moreover, we estimate the effective concentrations of the alkali metal cations near the electrode surfaces by correlating the capacitances with the relative permittivity. For all the electrodes, the concentrations near the electrode surface were calculated to be similar to 60 to 80 times higher than in the bulk solutions. |
| 109. | A Singldinger, M Gramlich, C Gruber, C Lampe, A S Urban Nonradiative Energy Transfer between Thickness-Controlled Halide Perovskite Nanoplatelets Journal Article Acs Energy Letters, 5 (5), pp. 1380-1385, 2020, ISSN: 2380-8195. Abstract | Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {Nonradiative Energy Transfer between Thickness-Controlled Halide Perovskite Nanoplatelets}, author = {A Singldinger and M Gramlich and C Gruber and C Lampe and A S Urban}, url = {<Go to ISI>://WOS:000535176100006}, doi = {10.1021/acsenergylett.0c00471}, issn = {2380-8195}, year = {2020}, date = {2020-05-08}, journal = {Acs Energy Letters}, volume = {5}, number = {5}, pages = {1380-1385}, abstract = {Despite showing great promise for optoelectronics, the commercialization of halide perovskite nanostructure-based devices is hampered by inefficient electrical excitation and strong exciton binding energies. While transport of excitons in an energy-tailored system via Forster resonance energy transfer (FRET) could be an efficient alternative, halide ion migration makes the realization of cascaded structures difficult. Here, we show how these could be obtained by exploiting the pronounced quantum confinement effect in two-dimensional CsPbBr3-based nanoplatelets (NPls). In thin films of NPls of two predetermined thicknesses, we observe an enhanced acceptor photoluminescence (PL) emission and a decreased donor PL lifetime. This indicates a FRET-mediated process, benefitted by the structural parameters of the NPls. We determine corresponding transfer rates up to k(FRET) = 0.99 ns(-1) and efficiencies of nearly eta(FRET) = 70%. We also show FRET to occur between perovskite NPls of other thicknesses. Consequently, this strategy could lead to tailored energy cascade nanostructures for improved optoelectronic devices.}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } Despite showing great promise for optoelectronics, the commercialization of halide perovskite nanostructure-based devices is hampered by inefficient electrical excitation and strong exciton binding energies. While transport of excitons in an energy-tailored system via Forster resonance energy transfer (FRET) could be an efficient alternative, halide ion migration makes the realization of cascaded structures difficult. Here, we show how these could be obtained by exploiting the pronounced quantum confinement effect in two-dimensional CsPbBr3-based nanoplatelets (NPls). In thin films of NPls of two predetermined thicknesses, we observe an enhanced acceptor photoluminescence (PL) emission and a decreased donor PL lifetime. This indicates a FRET-mediated process, benefitted by the structural parameters of the NPls. We determine corresponding transfer rates up to k(FRET) = 0.99 ns(-1) and efficiencies of nearly eta(FRET) = 70%. We also show FRET to occur between perovskite NPls of other thicknesses. Consequently, this strategy could lead to tailored energy cascade nanostructures for improved optoelectronic devices. |
| 108. | P Alexa, J M Lombardi, P Abufager, H F Busnengo, D Grumelli, V S Vyas, F Haase, B V Lotsch, R Gutzler, K Kern Enhancing Hydrogen Evolution Activity of Au(111) in Alkaline Media through Molecular Engineering of a 2D Polymer Journal Article Angewandte Chemie International Edition, n/a (n/a), 2020, ISSN: 1433-7851. Abstract | Links | Tags: Solid-Liquid @article{, title = {Enhancing Hydrogen Evolution Activity of Au(111) in Alkaline Media through Molecular Engineering of a 2D Polymer}, author = {P Alexa and J M Lombardi and P Abufager and H F Busnengo and D Grumelli and V S Vyas and F Haase and B V Lotsch and R Gutzler and K Kern}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201915855}, doi = {10.1002/anie.201915855}, issn = {1433-7851}, year = {2020}, date = {2020-05-05}, journal = {Angewandte Chemie International Edition}, volume = {n/a}, number = {n/a}, abstract = {Abstract The electrochemical splitting of water holds promise for the storage of energy produced intermittently by renewable energy sources. The evolution of hydrogen currently relies on the use of platinum as a catalyst\textemdashwhich is scarce and expensive\textemdashand ongoing research is focused towards finding cheaper alternatives. In this context, 2D polymers grown as single layers on surfaces have emerged as porous materials with tunable chemical and electronic structures that can be used for improving the catalytic activity of metal surfaces. Here, we use designed organic molecules to fabricate covalent 2D architectures by an Ullmann-type coupling reaction on Au(111). The polymer-patterned gold electrode exhibits a hydrogen evolution reaction activity up to three times higher than that of bare gold. Through rational design of the polymer on the molecular level we engineered hydrogen evolution activity by an approach that can be easily extended to other electrocatalytic reactions.}, keywords = {Solid-Liquid}, pubstate = {published}, tppubtype = {article} } Abstract The electrochemical splitting of water holds promise for the storage of energy produced intermittently by renewable energy sources. The evolution of hydrogen currently relies on the use of platinum as a catalyst—which is scarce and expensive—and ongoing research is focused towards finding cheaper alternatives. In this context, 2D polymers grown as single layers on surfaces have emerged as porous materials with tunable chemical and electronic structures that can be used for improving the catalytic activity of metal surfaces. Here, we use designed organic molecules to fabricate covalent 2D architectures by an Ullmann-type coupling reaction on Au(111). The polymer-patterned gold electrode exhibits a hydrogen evolution reaction activity up to three times higher than that of bare gold. Through rational design of the polymer on the molecular level we engineered hydrogen evolution activity by an approach that can be easily extended to other electrocatalytic reactions. |
| 107. | W Chen, H D Tang, N Li, M A Scheel, Y Xie, D P Li, V Korstgens, M Schwartzkopf, S V Roth, K Wang, X W Sun, P Muller-Buschbaum Colloidal PbS quantum dot stacking kinetics during deposition via printing Journal Article Nanoscale Horizons, 5 (5), pp. 880-885, 2020, ISSN: 2055-6756. Abstract | Links | Tags: Foundry Inorganic, Solid-Solid @article{, title = {Colloidal PbS quantum dot stacking kinetics during deposition via printing}, author = {W Chen and H D Tang and N Li and M A Scheel and Y Xie and D P Li and V Korstgens and M Schwartzkopf and S V Roth and K Wang and X W Sun and P Muller-Buschbaum}, url = {<Go to ISI>://WOS:000531354100007}, doi = {10.1039/d0nh00008f}, issn = {2055-6756}, year = {2020}, date = {2020-05-01}, journal = {Nanoscale Horizons}, volume = {5}, number = {5}, pages = {880-885}, abstract = {Colloidal PbS quantum dots (QDs) are attractive for solution-processed thin-film optoelectronic applications. In particular, directly achieving QD thin-films by printing is a very promising method for low-cost and large-scale fabrication. The kinetics of QD particles during the deposition process play an important role in the QD film quality and their respective optoelectronic performance. In this work, the particle self-organization behavior of small-sized QDs with an average diameter of 2.88 +/- 0.36 nm is investigated for the first time in situ during printing by grazing-incidence small-angle X-ray scattering (GISAXS). The time-dependent changes in peak intensities suggest that the structure formation and phase transition of QD films happen within 30 seconds. The stacking of QDs is initialized by a templating effect, and a face-centered cubic (FCC) film forms in which a superlattice distortion is also found. A body-centered cubic nested FCC stacking is the final QD assembly layout. The small size of the inorganic QDs and the ligand collapse during the solvent evaporation can well explain this stacking behavior. These results provide important fundamental understanding of structure formation of small-sized QD based films prepared via large-scale deposition with printing with a slot die coater.}, keywords = {Foundry Inorganic, Solid-Solid}, pubstate = {published}, tppubtype = {article} } Colloidal PbS quantum dots (QDs) are attractive for solution-processed thin-film optoelectronic applications. In particular, directly achieving QD thin-films by printing is a very promising method for low-cost and large-scale fabrication. The kinetics of QD particles during the deposition process play an important role in the QD film quality and their respective optoelectronic performance. In this work, the particle self-organization behavior of small-sized QDs with an average diameter of 2.88 +/- 0.36 nm is investigated for the first time in situ during printing by grazing-incidence small-angle X-ray scattering (GISAXS). The time-dependent changes in peak intensities suggest that the structure formation and phase transition of QD films happen within 30 seconds. The stacking of QDs is initialized by a templating effect, and a face-centered cubic (FCC) film forms in which a superlattice distortion is also found. A body-centered cubic nested FCC stacking is the final QD assembly layout. The small size of the inorganic QDs and the ligand collapse during the solvent evaporation can well explain this stacking behavior. These results provide important fundamental understanding of structure formation of small-sized QD based films prepared via large-scale deposition with printing with a slot die coater. |
Publications2020-08-21T17:11:33+02:00