M. Mallmann, R. Niklaus, T. Rackl, M. Benz, T. G. Chau, D. Johrendt, J. Minár, W. Schnick Chem. Eur. J., 25 , pp. 1-10, 2019, ISSN: 1521-3765. Abstract | Links | Tags: Foundry Inorganic @article{Mallmann2019, title = {Solid Solutions of Grimm\textendashSommerfeld Analogous Nitride Semiconductors II‐IV‐N2 (II=Mg, Mn, Zn; IV=Si, Ge): Ammonothermal Synthesis and DFT Calculations }, author = {M. Mallmann and R. Niklaus and T. Rackl and M. Benz and T. G. Chau and D. Johrendt and J. Min\'{a}r and W. Schnick}, doi = {https://doi.org/10.1002/chem.201903897}, issn = {1521-3765}, year = {2019}, date = {2019-09-17}, journal = {Chem. Eur. J.}, volume = {25}, pages = {1-10}, abstract = {Grimm\textendashSommerfeld analogous II‐IV‐N2 nitrides such as ZnSiN2, ZnGeN2, and MgGeN2 are promising semiconductor materials for substitution of commonly used (Al,Ga,In)N. Herein, the ammonothermal synthesis of solid solutions of II‐IV‐N2 compounds (II=Mg, Mn, Zn; IV=Si, Ge) having the general formula (IIa1−xIIbx)‐IV‐N2 with x≈0.5 and ab initio DFT calculations of their electronic and optical properties are presented. The ammonothermal reactions were conducted in custom‐built, high‐temperature, high‐pressure autoclaves by using the corresponding elements as starting materials. NaNH2 and KNH2 act as ammonobasic mineralizers that increase the solubility of the reactants in supercritical ammonia. Temperatures between 870 and 1070 K and pressures up to 200 MPa were chosen as reaction conditions. All solid solutions crystallize in wurtzite‐type superstructures with space group Pna21 (no. 33), confirmed by powder XRD. The chemical compositions were analyzed by energy‐dispersive X‐ray spectroscopy. Diffuse reflectance spectroscopy was used for estimation of optical bandgaps of all compounds, which ranged from 2.6 to 3.5 eV (Ge compounds) and from 3.6 to 4.4 eV (Si compounds), and thus demonstrated bandgap tunability between the respective boundary phases. Experimental findings were corroborated by DFT calculations of the electronic structure of pseudorelaxed mixed‐occupancy structures by using the KKR+CPA approach.}, keywords = {Foundry Inorganic}, pubstate = {published}, tppubtype = {article} } Grimm–Sommerfeld analogous II‐IV‐N2 nitrides such as ZnSiN2, ZnGeN2, and MgGeN2 are promising semiconductor materials for substitution of commonly used (Al,Ga,In)N. Herein, the ammonothermal synthesis of solid solutions of II‐IV‐N2 compounds (II=Mg, Mn, Zn; IV=Si, Ge) having the general formula (IIa1−xIIbx)‐IV‐N2 with x≈0.5 and ab initio DFT calculations of their electronic and optical properties are presented. The ammonothermal reactions were conducted in custom‐built, high‐temperature, high‐pressure autoclaves by using the corresponding elements as starting materials. NaNH2 and KNH2 act as ammonobasic mineralizers that increase the solubility of the reactants in supercritical ammonia. Temperatures between 870 and 1070 K and pressures up to 200 MPa were chosen as reaction conditions. All solid solutions crystallize in wurtzite‐type superstructures with space group Pna21 (no. 33), confirmed by powder XRD. The chemical compositions were analyzed by energy‐dispersive X‐ray spectroscopy. Diffuse reflectance spectroscopy was used for estimation of optical bandgaps of all compounds, which ranged from 2.6 to 3.5 eV (Ge compounds) and from 3.6 to 4.4 eV (Si compounds), and thus demonstrated bandgap tunability between the respective boundary phases. Experimental findings were corroborated by DFT calculations of the electronic structure of pseudorelaxed mixed‐occupancy structures by using the KKR+CPA approach. |
K Hübner, M Pilo-Pais, F Selbach, T Liedl, P Tinnefeld, F D Stefani, G P Acuna Directing Single-Molecule Emission with DNA Origami-Assembled Optical Antennas Journal Article Nano Letters, 19 (9), pp. 6629-6634, 2019, ISSN: 1530-6984. Abstract | Links | Tags: Molecularly-Functionalized @article{, title = {Directing Single-Molecule Emission with DNA Origami-Assembled Optical Antennas}, author = {K H\"{u}bner and M Pilo-Pais and F Selbach and T Liedl and P Tinnefeld and F D Stefani and G P Acuna}, url = {https://doi.org/10.1021/acs.nanolett.9b02886}, doi = {10.1021/acs.nanolett.9b02886}, issn = {1530-6984}, year = {2019}, date = {2019-09-11}, journal = {Nano Letters}, volume = {19}, number = {9}, pages = {6629-6634}, abstract = {Abstract Conventional surface enhanced Raman scattering (SERS) substrates are well known for their supreme electromagnetic enhancements and ultrahigh sensitivity in detecting molecules at low concentrations. However, large-area quasi-uniform SERS substrates are difficult to achieve by standard top-down nanofabrication techniques, resulting in fluctuant SERS responses and unwanted fluorescence interferences, which severely limit their performances in practical applications. To tackle these challenges, a large-scale quasi-uniform hybrid graphene fragmented-gold substrate with stable and reproducible SERS readouts as well as large enhancement factors over an ultrawideband spectrum is developed. The hybrid substrate is fabricated via cold-etching through a controllable break up of a thin gold film followed by a graphene transfer. The stimulated localized surface plasmons interact strongly with the graphene layer, leading to spectrally and spatially modified graphene-mediated surface enhanced Raman scattering (GSERS) responses. The perfect monolayer graphene of the GSERS substrate prevents adsorbates from the atmosphere and direct contact between bonded molecules and gold, thus reducing the catalytic activity of gold and producing clean, stable, and reproducible molecular Raman signals. The easy-fabricated hybrid GSERS substrate not only provides a powerful platform to collect robust molecular Raman spectra but also shows great potentials for future mass production of high-performance nanophotonic devices.}, keywords = {Molecularly-Functionalized}, pubstate = {published}, tppubtype = {article} } Abstract Conventional surface enhanced Raman scattering (SERS) substrates are well known for their supreme electromagnetic enhancements and ultrahigh sensitivity in detecting molecules at low concentrations. However, large-area quasi-uniform SERS substrates are difficult to achieve by standard top-down nanofabrication techniques, resulting in fluctuant SERS responses and unwanted fluorescence interferences, which severely limit their performances in practical applications. To tackle these challenges, a large-scale quasi-uniform hybrid graphene fragmented-gold substrate with stable and reproducible SERS readouts as well as large enhancement factors over an ultrawideband spectrum is developed. The hybrid substrate is fabricated via cold-etching through a controllable break up of a thin gold film followed by a graphene transfer. The stimulated localized surface plasmons interact strongly with the graphene layer, leading to spectrally and spatially modified graphene-mediated surface enhanced Raman scattering (GSERS) responses. The perfect monolayer graphene of the GSERS substrate prevents adsorbates from the atmosphere and direct contact between bonded molecules and gold, thus reducing the catalytic activity of gold and producing clean, stable, and reproducible molecular Raman signals. The easy-fabricated hybrid GSERS substrate not only provides a powerful platform to collect robust molecular Raman spectra but also shows great potentials for future mass production of high-performance nanophotonic devices. |
G Grinblat, I Abdelwahab, M P Nielsen, P Dichtl, K Leng, R F Oulton, K P Loh, S A Maier Ultrafast All-Optical Modulation in 2D Hybrid Perovskites Journal Article ACS Nano, 13 (8), pp. 9504-9510, 2019, ISSN: 1936-0851. Links | Tags: Solid-Solid @article{, title = {Ultrafast All-Optical Modulation in 2D Hybrid Perovskites}, author = {G Grinblat and I Abdelwahab and M P Nielsen and P Dichtl and K Leng and R F Oulton and K P Loh and S A Maier}, url = {https://doi.org/10.1021/acsnano.9b04483}, doi = {10.1021/acsnano.9b04483}, issn = {1936-0851}, year = {2019}, date = {2019-08-27}, journal = {ACS Nano}, volume = {13}, number = {8}, pages = {9504-9510}, keywords = {Solid-Solid}, pubstate = {published}, tppubtype = {article} } |
L Polavarapu, H Huang, Y Li, Y Tong, E-P Yao, M Döblinger, M W Feil, A F Richter, A L Rogach, J Feldmann Spontaneous Crystallization of Perovskite Nanocrystals in Nonpolar Organic Solvents: A Versatile Approach for their Shape-controlled Synthesis Journal Article Angewandte Chemie International Edition, 0 (ja), 2019, ISSN: 1433-7851. Abstract | Links | Tags: Solid-Solid @article{, title = {Spontaneous Crystallization of Perovskite Nanocrystals in Nonpolar Organic Solvents: A Versatile Approach for their Shape-controlled Synthesis}, author = {L Polavarapu and H Huang and Y Li and Y Tong and E-P Yao and M D\"{o}blinger and M W Feil and A F Richter and A L Rogach and J Feldmann}, url = {https://doi.org/10.1002/anie.201906862}, doi = {10.1002/anie.201906862}, issn = {1433-7851}, year = {2019}, date = {2019-08-21}, journal = {Angewandte Chemie International Edition}, volume = {0}, number = {ja}, abstract = {The growing demand of perovskite nanocrystals (NCs) for various applications has stimulated great research interest in the development of facile synthetic methods. They have often been synthesized by either ligand assisted reprecipitation (LARP) at room temperature or by hot-injection at high temperatures and inert atmosphere. However, the use of polar solvents in LARP effects their stability. Herein, we report on the spontaneous crystallization of perovskite nanocrystals in nonpolar organic media at ambient conditions by simple mixing of precursor-ligand complexes without applying any external stimuli. The shape of the NCs can be controlled from nanocubes to nanoplatelets by varying the ratio of monovalent (e.g. formamidinium+ (FA+) and Cs+) to divalent (Pb2+) cation-ligand complexes. The precursor-ligand complexes are stable for months, and thus perovskite NCs can be readily prepared prior to use. Moreover, we show that this versatile synthetic process is scalable and can be generally applicable for perovskite NCs of different compositions.}, keywords = {Solid-Solid}, pubstate = {published}, tppubtype = {article} } The growing demand of perovskite nanocrystals (NCs) for various applications has stimulated great research interest in the development of facile synthetic methods. They have often been synthesized by either ligand assisted reprecipitation (LARP) at room temperature or by hot-injection at high temperatures and inert atmosphere. However, the use of polar solvents in LARP effects their stability. Herein, we report on the spontaneous crystallization of perovskite nanocrystals in nonpolar organic media at ambient conditions by simple mixing of precursor-ligand complexes without applying any external stimuli. The shape of the NCs can be controlled from nanocubes to nanoplatelets by varying the ratio of monovalent (e.g. formamidinium+ (FA+) and Cs+) to divalent (Pb2+) cation-ligand complexes. The precursor-ligand complexes are stable for months, and thus perovskite NCs can be readily prepared prior to use. Moreover, we show that this versatile synthetic process is scalable and can be generally applicable for perovskite NCs of different compositions. |
J Gargiulo, R Berté, Y Li, S A Maier, E Cortés From Optical to Chemical Hot Spots in Plasmonics Journal Article Accounts of Chemical Research, 2019, ISSN: 0001-4842. Links | Tags: Molecularly-Functionalized @article{, title = {From Optical to Chemical Hot Spots in Plasmonics}, author = {J Gargiulo and R Bert\'{e} and Y Li and S A Maier and E Cort\'{e}s}, url = {https://doi.org/10.1021/acs.accounts.9b00234}, doi = {10.1021/acs.accounts.9b00234}, issn = {0001-4842}, year = {2019}, date = {2019-08-20}, journal = {Accounts of Chemical Research}, keywords = {Molecularly-Functionalized}, pubstate = {published}, tppubtype = {article} } |
S D Gennaro, Y Li, S A Maier, R F Oulton Nonlinear Pancharatnam−Berry Phase Metasurfaces beyond the Dipole Approximation Journal Article ACS Photonics, 2019. Links | Tags: Solid-Solid @article{, title = {Nonlinear Pancharatnam−Berry Phase Metasurfaces beyond the Dipole Approximation}, author = {S D Gennaro and Y Li and S A Maier and R F Oulton}, url = {https://doi.org/10.1021/acsphotonics.9b00877}, doi = {10.1021/acsphotonics.9b00877}, year = {2019}, date = {2019-08-12}, journal = {ACS Photonics}, keywords = {Solid-Solid}, pubstate = {published}, tppubtype = {article} } |
I Kaminska, J Bohlen, S Rocchetti, F Selbach, G P Acuna, P Tinnefeld Distance Dependence of Single-Molecule Energy Transfer to Graphene Measured with DNA Origami Nanopositioners Journal Article Nano Letters, 19 (7), pp. 4257-4262, 2019, ISSN: 1530-6984. Abstract | Links | Tags: Molecularly-Functionalized @article{, title = {Distance Dependence of Single-Molecule Energy Transfer to Graphene Measured with DNA Origami Nanopositioners}, author = {I Kaminska and J Bohlen and S Rocchetti and F Selbach and G P Acuna and P Tinnefeld}, url = {https://doi.org/10.1021/acs.nanolett.9b00172}, doi = {10.1021/acs.nanolett.9b00172}, issn = {1530-6984}, year = {2019}, date = {2019-07-10}, journal = {Nano Letters}, volume = {19}, number = {7}, pages = {4257-4262}, abstract = {Despite the thorough investigation of graphene since 2004, altering its surface chemistry and reproducible functionalization remain challenging. This hinders fabrication of more complex hybrid materials with controlled architectures, and as a consequence the development of sensitive and reliable sensors and biological assays. In this contribution, we introduce DNA origami structures as nanopositioners for placing single dye molecules at controlled distances from graphene. The measurements of fluorescence intensity and lifetime of single emitters carried out for distances ranging from 3 to 58 nm confirmed the d\textendash4 dependence of the excitation energy transfer to graphene. Moreover, we determined the characteristic distance for 50% efficiency of the energy transfer from single dyes to graphene to be 17.7 nm. Using pyrene molecules as a glue to immobilize DNA origami nanostructures of various shape on graphene opens new possibilities to develop graphene-based biophysics and biosensing.}, keywords = {Molecularly-Functionalized}, pubstate = {published}, tppubtype = {article} } Despite the thorough investigation of graphene since 2004, altering its surface chemistry and reproducible functionalization remain challenging. This hinders fabrication of more complex hybrid materials with controlled architectures, and as a consequence the development of sensitive and reliable sensors and biological assays. In this contribution, we introduce DNA origami structures as nanopositioners for placing single dye molecules at controlled distances from graphene. The measurements of fluorescence intensity and lifetime of single emitters carried out for distances ranging from 3 to 58 nm confirmed the d–4 dependence of the excitation energy transfer to graphene. Moreover, we determined the characteristic distance for 50% efficiency of the energy transfer from single dyes to graphene to be 17.7 nm. Using pyrene molecules as a glue to immobilize DNA origami nanostructures of various shape on graphene opens new possibilities to develop graphene-based biophysics and biosensing. |
J P Sabawa, A S Bandarenka Electrochimica Acta, 311 , pp. 21-29, 2019, ISSN: 0013-4686. Abstract | Links | Tags: Solid-Liquid @article{, title = {Degradation mechanisms in polymer electrolyte membrane fuel cells caused by freeze-cycles: Investigation using electrochemical impedance spectroscopy}, author = {J P Sabawa and A S Bandarenka}, url = {http://www.sciencedirect.com/science/article/pii/S0013468619307881}, doi = {https://doi.org/10.1016/j.electacta.2019.04.102}, issn = {0013-4686}, year = {2019}, date = {2019-07-10}, journal = {Electrochimica Acta}, volume = {311}, pages = {21-29}, abstract = {The performance of the polymer electrolyte membrane (PEM) fuel cells is sensitive to the exposure of these devices to subzero temperatures. In general, it is important to precondition the fuel cells prior to the shut-down preventing degradation after the start-up. Standard tests with conventional climatic chambers are nowadays costly and very time consuming. In this work, we introduce a method, which uses a simplified process with a PEM single-cell. The new design uses a Peltier-Element-Tempered (PET) single-cell with an active area size of 43.56 cm2. Now it is possible to achieve efficient and temperature controlled cold starts without a climate chamber or chiller plant. With the PET-controlled single cell, it was possible to do a series of complex accelerated freeze stress tests within the shortest time. To classify the performance change, polarization curves, cyclic voltammetry with the CV-CO-stripping method and Electrochemical Impedance Spectroscopy (EIS) at different current densities were performed. The measured impedance spectra were analyzed with a physical impedance model consisting of only 6 equivalent circuit elements. The charge-transfer resistance and the parameters of the Warburg diffusion element clearly reveal irreversible changes of the cathode during repeated freeze-cycles.}, keywords = {Solid-Liquid}, pubstate = {published}, tppubtype = {article} } The performance of the polymer electrolyte membrane (PEM) fuel cells is sensitive to the exposure of these devices to subzero temperatures. In general, it is important to precondition the fuel cells prior to the shut-down preventing degradation after the start-up. Standard tests with conventional climatic chambers are nowadays costly and very time consuming. In this work, we introduce a method, which uses a simplified process with a PEM single-cell. The new design uses a Peltier-Element-Tempered (PET) single-cell with an active area size of 43.56 cm2. Now it is possible to achieve efficient and temperature controlled cold starts without a climate chamber or chiller plant. With the PET-controlled single cell, it was possible to do a series of complex accelerated freeze stress tests within the shortest time. To classify the performance change, polarization curves, cyclic voltammetry with the CV-CO-stripping method and Electrochemical Impedance Spectroscopy (EIS) at different current densities were performed. The measured impedance spectra were analyzed with a physical impedance model consisting of only 6 equivalent circuit elements. The charge-transfer resistance and the parameters of the Warburg diffusion element clearly reveal irreversible changes of the cathode during repeated freeze-cycles. |
J Klein, M Lorke, M Florian, F Sigger, L Sigl, S Rey, J Wierzbowski, J Cerne, K Müller, E Mitterreiter, P Zimmermann, T Taniguchi, K Watanabe, U Wurstbauer, M Kaniber, M Knap, R Schmidt, J J Finley, A W Holleitner Site-selectively generated photon emitters in monolayer MoS2 via local helium ion irradiation Journal Article Nature Communications, 10 (1), pp. 2755, 2019, ISSN: 2041-1723. Abstract | Links | Tags: Foundry Inorganic @article{, title = {Site-selectively generated photon emitters in monolayer MoS2 via local helium ion irradiation}, author = {J Klein and M Lorke and M Florian and F Sigger and L Sigl and S Rey and J Wierzbowski and J Cerne and K M\"{u}ller and E Mitterreiter and P Zimmermann and T Taniguchi and K Watanabe and U Wurstbauer and M Kaniber and M Knap and R Schmidt and J J Finley and A W Holleitner}, url = {https://doi.org/10.1038/s41467-019-10632-z}, doi = {10.1038/s41467-019-10632-z}, issn = {2041-1723}, year = {2019}, date = {2019-06-21}, journal = {Nature Communications}, volume = {10}, number = {1}, pages = {2755}, abstract = {Quantum light sources in solid-state systems are of major interest as a basic ingredient for integrated quantum photonic technologies. The ability to tailor quantum emitters via site-selective defect engineering is essential for realizing scalable architectures. However, a major difficulty is that defects need to be controllably positioned within the material. Here, we overcome this challenge by controllably irradiating monolayer MoS2 using a sub-nm focused helium ion beam to deterministically create defects. Subsequent encapsulation of the ion exposed MoS2 flake with high-quality hBN reveals spectrally narrow emission lines that produce photons in the visible spectral range. Based on ab-initio calculations we interpret these emission lines as stemming from the recombination of highly localized electron\textendashhole complexes at defect states generated by the local helium ion exposure. Our approach to deterministically write optically active defect states in a single transition metal dichalcogenide layer provides a platform for realizing exotic many-body systems, including coupled single-photon sources and interacting exciton lattices that may allow the exploration of Hubbard physics.}, keywords = {Foundry Inorganic}, pubstate = {published}, tppubtype = {article} } Quantum light sources in solid-state systems are of major interest as a basic ingredient for integrated quantum photonic technologies. The ability to tailor quantum emitters via site-selective defect engineering is essential for realizing scalable architectures. However, a major difficulty is that defects need to be controllably positioned within the material. Here, we overcome this challenge by controllably irradiating monolayer MoS2 using a sub-nm focused helium ion beam to deterministically create defects. Subsequent encapsulation of the ion exposed MoS2 flake with high-quality hBN reveals spectrally narrow emission lines that produce photons in the visible spectral range. Based on ab-initio calculations we interpret these emission lines as stemming from the recombination of highly localized electron–hole complexes at defect states generated by the local helium ion exposure. Our approach to deterministically write optically active defect states in a single transition metal dichalcogenide layer provides a platform for realizing exotic many-body systems, including coupled single-photon sources and interacting exciton lattices that may allow the exploration of Hubbard physics. |
A Vogel, T Miller, C Hoch, M Jakob, O Oeckler, T Nilges Cu9.1Te4Cl3: A Thermoelectric Compound with Low Thermal and High Electrical Conductivity Journal Article Inorganic Chemistry, 58 (9), pp. 6222-6230, 2019, ISSN: 0020-1669. Abstract | Links | Tags: Foundry Inorganic @article{, title = {Cu9.1Te4Cl3: A Thermoelectric Compound with Low Thermal and High Electrical Conductivity}, author = {A Vogel and T Miller and C Hoch and M Jakob and O Oeckler and T Nilges}, url = {https://doi.org/10.1021/acs.inorgchem.9b00453}, doi = {10.1021/acs.inorgchem.9b00453}, issn = {0020-1669}, year = {2019}, date = {2019-05-06}, journal = {Inorganic Chemistry}, volume = {58}, number = {9}, pages = {6222-6230}, abstract = {Cu9.1Te4Cl3 is a new polymorphic compound in the class of coinage metal polytelluride halides. Copper is highly mobile, which results in multiple order\textendashdisorder phase transitions in a limited temperature interval from 240 to 370 K. Mainly as a consequence of thermal transport properties, the compound’s thermoelectric figure of merit reaches values up to ZT = 0.15 in the temperature range between room temperature and 523 K. Its structure is closely related to that of Ag10Te4Br3, another coinage metal polytelluride halide, which represents the first p\textendashn\textendashp-switchable semiconductor approachable by a simple temperature change. The title compound outperforms Ag10Te4Br3 in terms of thermoelectric properties by 1 order of magnitude and therefore acts as a link between the class of p\textendashn\textendashp compounds and thermoelectric materials.}, keywords = {Foundry Inorganic}, pubstate = {published}, tppubtype = {article} } Cu9.1Te4Cl3 is a new polymorphic compound in the class of coinage metal polytelluride halides. Copper is highly mobile, which results in multiple order–disorder phase transitions in a limited temperature interval from 240 to 370 K. Mainly as a consequence of thermal transport properties, the compound’s thermoelectric figure of merit reaches values up to ZT = 0.15 in the temperature range between room temperature and 523 K. Its structure is closely related to that of Ag10Te4Br3, another coinage metal polytelluride halide, which represents the first p–n–p-switchable semiconductor approachable by a simple temperature change. The title compound outperforms Ag10Te4Br3 in terms of thermoelectric properties by 1 order of magnitude and therefore acts as a link between the class of p–n–p compounds and thermoelectric materials. |
B Garlyyev, K Kratzl, M Rück, J Michalička, J Fichtner, J M Macak, T Kratky, S Günther, M Cokoja, A S Bandarenka, A Gagliardi, R A Fischer Optimizing the Size of Platinum Nanoparticles for Enhanced Mass Activity in the Electrochemical Oxygen Reduction Reaction Journal Article Angewandte Chemie International Edition, 58 (28), pp. 9596-9600, 2019, ISSN: 1433-7851. Abstract | Links | Tags: Foundry Organic, Solid-Liquid @article{, title = {Optimizing the Size of Platinum Nanoparticles for Enhanced Mass Activity in the Electrochemical Oxygen Reduction Reaction}, author = {B Garlyyev and K Kratzl and M R\"{u}ck and J Michali\v{c}ka and J Fichtner and J M Macak and T Kratky and S G\"{u}nther and M Cokoja and A S Bandarenka and A Gagliardi and R A Fischer}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201904492}, doi = {10.1002/anie.201904492}, issn = {1433-7851}, year = {2019}, date = {2019-05-03}, journal = {Angewandte Chemie International Edition}, volume = {58}, number = {28}, pages = {9596-9600}, abstract = {Abstract High oxygen reduction (ORR) activity has been for many years considered as the key to many energy applications. Herein, by combining theory and experiment we prepare Pt nanoparticles with optimal size for the efficient ORR in proton-exchange-membrane fuel cells. Optimal nanoparticle sizes are predicted near 1, 2, and 3 nm by computational screening. To corroborate our computational results, we have addressed the challenge of approximately 1 nm sized Pt nanoparticle synthesis with a metal\textendashorganic framework (MOF) template approach. The electrocatalyst was characterized by HR-TEM, XPS, and its ORR activity was measured using a rotating disk electrode setup. The observed mass activities (0.87±0.14 A mgPt−1) are close to the computational prediction (0.99 A mgPt−1). We report the highest to date mass activity among pure Pt catalysts for the ORR within similar size range. The specific and mass activities are twice as high as the Tanaka commercial Pt/C catalysis.}, keywords = {Foundry Organic, Solid-Liquid}, pubstate = {published}, tppubtype = {article} } Abstract High oxygen reduction (ORR) activity has been for many years considered as the key to many energy applications. Herein, by combining theory and experiment we prepare Pt nanoparticles with optimal size for the efficient ORR in proton-exchange-membrane fuel cells. Optimal nanoparticle sizes are predicted near 1, 2, and 3 nm by computational screening. To corroborate our computational results, we have addressed the challenge of approximately 1 nm sized Pt nanoparticle synthesis with a metal–organic framework (MOF) template approach. The electrocatalyst was characterized by HR-TEM, XPS, and its ORR activity was measured using a rotating disk electrode setup. The observed mass activities (0.87±0.14 A mgPt−1) are close to the computational prediction (0.99 A mgPt−1). We report the highest to date mass activity among pure Pt catalysts for the ORR within similar size range. The specific and mass activities are twice as high as the Tanaka commercial Pt/C catalysis. |
C Ott, F Reiter, M Baumgartner, M Pielmeier, A Vogel, P Walke, S Burger, M Ehrenreich, G Kieslich, D Daisenberger, J Armstrong, U K Thakur, P Kumar, S Chen, D Donadio, L S Walter, R T Weitz, K Shankar, T Nilges Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems Based on SnIP Journal Article Advanced Functional Materials, 29 (18), pp. 1900233, 2019, ISSN: 1616-301X. Abstract | Links | Tags: Foundry Inorganic @article{, title = {Flexible and Ultrasoft Inorganic 1D Semiconductor and Heterostructure Systems Based on SnIP}, author = {C Ott and F Reiter and M Baumgartner and M Pielmeier and A Vogel and P Walke and S Burger and M Ehrenreich and G Kieslich and D Daisenberger and J Armstrong and U K Thakur and P Kumar and S Chen and D Donadio and L S Walter and R T Weitz and K Shankar and T Nilges}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.201900233}, doi = {10.1002/adfm.201900233}, issn = {1616-301X}, year = {2019}, date = {2019-03-13}, journal = {Advanced Functional Materials}, volume = {29}, number = {18}, pages = {1900233}, abstract = {Abstract Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core\textendashshell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting.}, keywords = {Foundry Inorganic}, pubstate = {published}, tppubtype = {article} } Abstract Low dimensionality and high flexibility are key demands for flexible electronic semiconductor devices. SnIP, the first atomic-scale double helical semiconductor combines structural anisotropy and robustness with exceptional electronic properties. The benefit of the double helix, combined with a diverse structure on the nanoscale, ranging from strong covalent bonding to weak van der Waals interactions, and the large structure and property anisotropy offer substantial potential for applications in energy conversion and water splitting. It represents the next logical step in downscaling the inorganic semiconductors from classical 3D systems, via 2D semiconductors like MXenes or transition metal dichalcogenides, to the first downsizeable, polymer-like atomic-scale 1D semiconductor SnIP. SnIP shows intriguing mechanical properties featuring a bulk modulus three times lower than any IV, III-V, or II-VI semiconductor. In situ bending tests substantiate that pure SnIP fibers can be bent without an effect on their bonding properties. Organic and inorganic hybrids are prepared illustrating that SnIP is a candidate to fabricate flexible 1D composites for energy conversion and water splitting applications. SnIP@C3N4 hybrid forms an unusual soft material core–shell topology with graphenic carbon nitride wrapping around SnIP. A 1D van der Waals heterostructure is formed capable of performing effective water splitting. |
E Pensa, J Gargiulo, A Lauri, S Schlücker, E Cortés, S A Maier Spectral Screening of the Energy of Hot Holes over a Particle Plasmon Resonance Journal Article Nano Letters, 19 (3), pp. 1867-1874, 2019, ISSN: 1530-6984. Links | Tags: Solid-Solid @article{, title = {Spectral Screening of the Energy of Hot Holes over a Particle Plasmon Resonance}, author = {E Pensa and J Gargiulo and A Lauri and S Schl\"{u}cker and E Cort\'{e}s and S A Maier}, url = {https://doi.org/10.1021/acs.nanolett.8b04950}, doi = {10.1021/acs.nanolett.8b04950}, issn = {1530-6984}, year = {2019}, date = {2019-03-13}, journal = {Nano Letters}, volume = {19}, number = {3}, pages = {1867-1874}, keywords = {Solid-Solid}, pubstate = {published}, tppubtype = {article} } |
B Doiron, M Mota, M P Wells, R Bower, A Mihai, Y Li, L F Cohen, N M Alford, P K Petrov, R F Oulton, S A Maier Quantifying Figures of Merit for Localized Surface Plasmon Resonance Applications: A Materials Survey Journal Article ACS Photonics, 6 (2), pp. 240-259, 2019. Links | Tags: Solid-Solid @article{, title = {Quantifying Figures of Merit for Localized Surface Plasmon Resonance Applications: A Materials Survey}, author = {B Doiron and M Mota and M P Wells and R Bower and A Mihai and Y Li and L F Cohen and N M Alford and P K Petrov and R F Oulton and S A Maier}, url = {https://doi.org/10.1021/acsphotonics.8b01369}, doi = {10.1021/acsphotonics.8b01369}, year = {2019}, date = {2019-02-20}, journal = {ACS Photonics}, volume = {6}, number = {2}, pages = {240-259}, keywords = {Solid-Solid}, pubstate = {published}, tppubtype = {article} } |
B Miller, J Lindlau, M Bommert, A Neumann, H Yamaguchi, A W Holleitner, A Högele, U Wurstbauer Tuning the Fröhlich exciton-phonon scattering in monolayer MoS2 Journal Article Nature Communications, 10 (1), pp. 807, 2019, ISSN: 2041-1723. Abstract | Links | Tags: Solid-Solid @article{, title = {Tuning the Fr\"{o}hlich exciton-phonon scattering in monolayer MoS2}, author = {B Miller and J Lindlau and M Bommert and A Neumann and H Yamaguchi and A W Holleitner and A H\"{o}gele and U Wurstbauer}, url = {https://doi.org/10.1038/s41467-019-08764-3}, doi = {10.1038/s41467-019-08764-3}, issn = {2041-1723}, year = {2019}, date = {2019-02-18}, journal = {Nature Communications}, volume = {10}, number = {1}, pages = {807}, abstract = {Charge carriers in semiconducting transition metal dichalcogenides possess a valley degree of freedom that allows for optoelectronic applications based on the momentum of excitons. At elevated temperatures, scattering by phonons limits valley polarization, making a detailed knowledge about strength and nature of the interaction of excitons with phonons essential. In this work, we directly access exciton-phonon coupling in charge tunable single layer MoS2 devices by polarization resolved Raman spectroscopy. We observe a strong defect mediated coupling between the long-range oscillating electric field induced by the longitudinal optical phonon in the dipolar medium and the exciton. This so-called Fr\"{o}hlich exciton phonon interaction is suppressed by doping. The suppression correlates with a distinct increase of the degree of valley polarization up to 20% even at elevated temperatures of 220 K. Our result demonstrates a promising strategy to increase the degree of valley polarization towards room temperature valleytronic applications.}, keywords = {Solid-Solid}, pubstate = {published}, tppubtype = {article} } Charge carriers in semiconducting transition metal dichalcogenides possess a valley degree of freedom that allows for optoelectronic applications based on the momentum of excitons. At elevated temperatures, scattering by phonons limits valley polarization, making a detailed knowledge about strength and nature of the interaction of excitons with phonons essential. In this work, we directly access exciton-phonon coupling in charge tunable single layer MoS2 devices by polarization resolved Raman spectroscopy. We observe a strong defect mediated coupling between the long-range oscillating electric field induced by the longitudinal optical phonon in the dipolar medium and the exciton. This so-called Fröhlich exciton phonon interaction is suppressed by doping. The suppression correlates with a distinct increase of the degree of valley polarization up to 20% even at elevated temperatures of 220 K. Our result demonstrates a promising strategy to increase the degree of valley polarization towards room temperature valleytronic applications. |
E-P Yao, B J Bohn, Y Tong, H Huang, L Polavarapu, J Feldmann Exciton Diffusion Lengths and Dissociation Rates in CsPbBr3 Nanocrystal–Fullerene Composites: Layer-by-Layer versus Blend Structures Journal Article Advanced Optical Materials, 7 (8), pp. 1801776, 2019, ISSN: 2195-1071. Abstract | Links | Tags: Solid-Solid @article{, title = {Exciton Diffusion Lengths and Dissociation Rates in CsPbBr3 Nanocrystal\textendashFullerene Composites: Layer-by-Layer versus Blend Structures}, author = {E-P Yao and B J Bohn and Y Tong and H Huang and L Polavarapu and J Feldmann}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201801776}, doi = {10.1002/adom.201801776}, issn = {2195-1071}, year = {2019}, date = {2019-02-18}, journal = {Advanced Optical Materials}, volume = {7}, number = {8}, pages = {1801776}, abstract = {Abstract Solution-processable perovskite nanocrystals (NCs) are gaining increasing interest in the field of photovoltaics because of their enhanced stability compared to their thin-film counterparts. However, the charge transfer dynamics in perovskite NC based light-harvesting systems are not well understood. By applying femtosecond differential transmission (DT) spectroscopy the photoinduced charge transfer from inorganic perovskite CsPbBr3 NCs to the fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM) is investigated for two fundamentally different architectures, namely layer-by-layer heterostructures and blend structures. By varying the thickness of the NC layer on top of the PCBM in the layer-by-layer heterostructure, an exciton diffusion length of 290 ± 28 nm for CsPbBr3 NC is extracted. The diffusion process is followed by an ultrafast exciton dissociation (within 200 fs) at the CsPbBr3 NC/PCBM interface. In blend structures an overall faster charge transfer process is observed. Furthermore, photoconductivity measurements on a blend structure-based photodetector reveal an effective charge extraction from the active layer resulting in a high photosensitivity. DT measurements on this blend structure including adjacent electron- or hole-transport layers give insight into the extraction process and suggest a certain degree of phase segregation, which assists the charge collection.}, keywords = {Solid-Solid}, pubstate = {published}, tppubtype = {article} } Abstract Solution-processable perovskite nanocrystals (NCs) are gaining increasing interest in the field of photovoltaics because of their enhanced stability compared to their thin-film counterparts. However, the charge transfer dynamics in perovskite NC based light-harvesting systems are not well understood. By applying femtosecond differential transmission (DT) spectroscopy the photoinduced charge transfer from inorganic perovskite CsPbBr3 NCs to the fullerene derivative phenyl-C61-butyric acid methyl ester (PCBM) is investigated for two fundamentally different architectures, namely layer-by-layer heterostructures and blend structures. By varying the thickness of the NC layer on top of the PCBM in the layer-by-layer heterostructure, an exciton diffusion length of 290 ± 28 nm for CsPbBr3 NC is extracted. The diffusion process is followed by an ultrafast exciton dissociation (within 200 fs) at the CsPbBr3 NC/PCBM interface. In blend structures an overall faster charge transfer process is observed. Furthermore, photoconductivity measurements on a blend structure-based photodetector reveal an effective charge extraction from the active layer resulting in a high photosensitivity. DT measurements on this blend structure including adjacent electron- or hole-transport layers give insight into the extraction process and suggest a certain degree of phase segregation, which assists the charge collection. |
T Schröder, M B Scheible, F Steiner, J Vogelsang, P Tinnefeld Interchromophoric Interactions Determine the Maximum Brightness Density in DNA Origami Structures Journal Article Nano Letters, 19 (2), pp. 1275-1281, 2019, ISSN: 1530-6984. Abstract | Links | Tags: Molecularly-Functionalized @article{, title = {Interchromophoric Interactions Determine the Maximum Brightness Density in DNA Origami Structures}, author = {T Schr\"{o}der and M B Scheible and F Steiner and J Vogelsang and P Tinnefeld}, url = {https://doi.org/10.1021/acs.nanolett.8b04845}, doi = {10.1021/acs.nanolett.8b04845}, issn = {1530-6984}, year = {2019}, date = {2019-02-13}, journal = {Nano Letters}, volume = {19}, number = {2}, pages = {1275-1281}, abstract = {An ideal point light source is as small and as bright as possible. For fluorescent point light sources, homogeneity of the light sources is important as well as that the fluorescent units inside the light source maintain their photophysical properties, which is compromised by dye aggregation. Here we propose DNA origami as a rigid scaffold to arrange dye molecules in a dense pixel array with high control of stoichiometry and dye\textendashdye interactions. In order to find the highest labeling density in a DNA origami structure without influencing dye photophysics, we alter the distance of two ATTO647N dyes in single base pair steps and probe the dye\textendashdye interactions on the single-molecule level. For small distances strong quenching in terms of intensity and fluorescence lifetime is observed. With increasing distance, we observe reduced quenching and molecular dynamics. However, energy transfer processes in the weak coupling regime still have a significant impact and can lead to quenching by singlet-dark-state-annihilation. Our study fills a gap of studying the interactions of dyes relevant for superresolution microscopy with dense labeling and for single-molecule biophysics. Incorporating these findings in a 3D DNA origami object will pave the way to bright and homogeneous DNA origami nanobeads.}, keywords = {Molecularly-Functionalized}, pubstate = {published}, tppubtype = {article} } An ideal point light source is as small and as bright as possible. For fluorescent point light sources, homogeneity of the light sources is important as well as that the fluorescent units inside the light source maintain their photophysical properties, which is compromised by dye aggregation. Here we propose DNA origami as a rigid scaffold to arrange dye molecules in a dense pixel array with high control of stoichiometry and dye–dye interactions. In order to find the highest labeling density in a DNA origami structure without influencing dye photophysics, we alter the distance of two ATTO647N dyes in single base pair steps and probe the dye–dye interactions on the single-molecule level. For small distances strong quenching in terms of intensity and fluorescence lifetime is observed. With increasing distance, we observe reduced quenching and molecular dynamics. However, energy transfer processes in the weak coupling regime still have a significant impact and can lead to quenching by singlet-dark-state-annihilation. Our study fills a gap of studying the interactions of dyes relevant for superresolution microscopy with dense labeling and for single-molecule biophysics. Incorporating these findings in a 3D DNA origami object will pave the way to bright and homogeneous DNA origami nanobeads. |
T Wu, Y Luo, S A Maier, L Wei Phase-matching and Peak Nonlinearity Enhanced Third-Harmonic Generation in Graphene Plasmonic Coupler Journal Article Physical Review Applied, 11 (1), pp. 014049, 2019, (PRAPPLIED). Abstract | Links | Tags: Solid-Solid @article{, title = {Phase-matching and Peak Nonlinearity Enhanced Third-Harmonic Generation in Graphene Plasmonic Coupler}, author = {T Wu and Y Luo and S A Maier and L Wei}, url = {https://link.aps.org/doi/10.1103/PhysRevApplied.11.014049}, doi = {10.1103/PhysRevApplied.11.014049}, year = {2019}, date = {2019-01-24}, journal = {Physical Review Applied}, volume = {11}, number = {1}, pages = {014049}, abstract = {Strong nonlinear optical effects generally require giant optical fields interacting with the nonlinear media. Doped graphene hosts electrically tunable plasmons with long lifetimes that interact strongly with light. We investigate a graphene plasmonic coupler and explore two mechanisms to pursue highly efficient third-harmonic generation (THG): (1) phase matching of graphene plasmons at fundamental- and third-harmonic frequencies and (2) peak third-order nonlinear susceptibility of doped graphene. The third-harmonic wave is mainly converted from the evanescent mode of the incident light and the THG efficiency is found to be enhanced by over 10 orders of magnitude compared with a bare monolayer graphene. The significantly enhanced nonlinear optical responses in the graphene plasmonic coupler make this configuration an ideal platform for the development of alternative frequency generators and for signal processing at midinfrared and terahertz frequencies.}, note = {PRAPPLIED}, keywords = {Solid-Solid}, pubstate = {published}, tppubtype = {article} } Strong nonlinear optical effects generally require giant optical fields interacting with the nonlinear media. Doped graphene hosts electrically tunable plasmons with long lifetimes that interact strongly with light. We investigate a graphene plasmonic coupler and explore two mechanisms to pursue highly efficient third-harmonic generation (THG): (1) phase matching of graphene plasmons at fundamental- and third-harmonic frequencies and (2) peak third-order nonlinear susceptibility of doped graphene. The third-harmonic wave is mainly converted from the evanescent mode of the incident light and the THG efficiency is found to be enhanced by over 10 orders of magnitude compared with a bare monolayer graphene. The significantly enhanced nonlinear optical responses in the graphene plasmonic coupler make this configuration an ideal platform for the development of alternative frequency generators and for signal processing at midinfrared and terahertz frequencies. |
J Li, E Tan, N Keller, Y-H Chen, P M Zehetmaier, A C Jakowetz, T Bein, P Knochel Cobalt-Catalyzed Electrophilic Aminations with Anthranils: An Expedient Route to Condensed Quinolines Journal Article Journal of the American Chemical Society, 141 (1), pp. 98-103, 2019, ISSN: 0002-7863. Abstract | Links | Tags: Molecularly-Functionalized @article{, title = {Cobalt-Catalyzed Electrophilic Aminations with Anthranils: An Expedient Route to Condensed Quinolines}, author = {J Li and E Tan and N Keller and Y-H Chen and P M Zehetmaier and A C Jakowetz and T Bein and P Knochel}, url = {https://doi.org/10.1021/jacs.8b11466}, doi = {10.1021/jacs.8b11466}, issn = {0002-7863}, year = {2019}, date = {2019-01-09}, journal = {Journal of the American Chemical Society}, volume = {141}, number = {1}, pages = {98-103}, abstract = {The reaction of various organozinc pivalates with anthranils provides anilines derivatives, which cyclize under acidic conditions providing condensed quinolines. Using alkenylzinc pivalates, electron-rich arylzinc pivalates or heterocyclic zinc pivalates produces directly the condensed quinolines of which several structures belong to new heterocyclic scaffolds. These N-heterocycles are of particular interest for organic light emitting diodes with their high photoluminescence quantum yields and long exciton lifetimes as well as for hole-transporting materials in methylammonium lead iodide perovskites solar cells due to an optimal band alignment for holes and a large bandgap.}, keywords = {Molecularly-Functionalized}, pubstate = {published}, tppubtype = {article} } The reaction of various organozinc pivalates with anthranils provides anilines derivatives, which cyclize under acidic conditions providing condensed quinolines. Using alkenylzinc pivalates, electron-rich arylzinc pivalates or heterocyclic zinc pivalates produces directly the condensed quinolines of which several structures belong to new heterocyclic scaffolds. These N-heterocycles are of particular interest for organic light emitting diodes with their high photoluminescence quantum yields and long exciton lifetimes as well as for hole-transporting materials in methylammonium lead iodide perovskites solar cells due to an optimal band alignment for holes and a large bandgap. |
PublicationsPeter Sonntag2019-11-21T16:22:01+01:00