Search

We have found that the polarization dependence of Raman scattering in organic crystals at finite temperatures can only be described by a fourth-rank tensor formalism. This generalization of the second-rank Raman tensor stems from the effect of off diagonal components in the crystal self-energy on the light scattering mechanism. We thus establish a novel manifestation of phonon-phonon interaction in inelastic light scattering, markedly separate from the better-known phonon lifetime., Funding Agencies|European Research Counsel [850041]; Swedish Research Council (VR) [2020-04630]; Belgian National Fund for Scientific Research (FNRS) [T.0072.18, T.0094.22, U.G001.19, O.005018F, O.00322]; French Community of Belgian (ARC) [20061]

We have found that the polarization dependence of Raman scattering in organic crystals at finite temperatures can only be described by a fourth-rank tensor formalism. This generalization of the second-rank Raman tensor stems from the effect of off diagonal components in the crystal self-energy on the light scattering mechanism. We thus establish a novel manifestation of phonon-phonon interaction in inelastic light scattering, markedly separate from the better-known phonon lifetime., Funding Agencies|European Research Counsel [850041]; Swedish Research Council (VR) [2020-04630]; Belgian National Fund for Scientific Research (FNRS) [T.0072.18, T.0094.22, U.G001.19, O.005018F, O.00322]; French Community of Belgian (ARC) [20061]

WS2 nanotubes present many new technologies under development, including reinforced biocompatible polymers, membranes, photovoltaic-based memories, ferroelectric devices, etc. These technologies depend on the aspect ratio (length/diameter) of the nanotubes, which was limited to 100 or so. A new synthetic technique is presented, resulting in WS2 nanotubes a few hundred micrometers long and diameters below 50 nm (aspect ratios of 2000-5000) in high yields. Preliminary investigation into the mechanistic aspects of the two-step synthesis reveals that W5O14 nanowhisker intermediates are formed in the first step of the reaction instead of the ubiquitous W18O49 nanowhiskers used in the previous syntheses. The electrical and photoluminescence properties of the long nanotubes were studied. WS2 nanotube-based paper-like material was prepared via a wet-laying process, which could not be realized with the 10 mu m long WS2 nanotubes. Ultrafiltration of gold nanoparticles using the nanotube-paper membrane was demonstrated.

We have found that the polarization dependence of Raman scattering in organic crystals at finite temperatures can only be described by a fourth-rank tensor formalism. This generalization of the second-rank Raman tensor stems from the effect of off diagonal components in the crystal self-energy on the light scattering mechanism. We thus establish a novel manifestation of phonon-phonon interaction in inelastic light scattering, markedly separate from the better-known phonon lifetime., Funding Agencies|European Research Counsel [850041]; Swedish Research Council (VR) [2020-04630]; Belgian National Fund for Scientific Research (FNRS) [T.0072.18, T.0094.22, U.G001.19, O.005018F, O.00322]; French Community of Belgian (ARC) [20061]

WS2 nanotubes present many new technologies under development, including reinforced biocompatible polymers, membranes, photovoltaic-based memories, ferroelectric devices, etc. These technologies depend on the aspect ratio (length/diameter) of the nanotubes, which was limited to 100 or so. A new synthetic technique is presented, resulting in WS2 nanotubes a few hundred micrometers long and diameters below 50 nm (aspect ratios of 2000-5000) in high yields. Preliminary investigation into the mechanistic aspects of the two-step synthesis reveals that W5O14 nanowhisker intermediates are formed in the first step of the reaction instead of the ubiquitous W18O49 nanowhiskers used in the previous syntheses. The electrical and photoluminescence properties of the long nanotubes were studied. WS2 nanotube-based paper-like material was prepared via a wet-laying process, which could not be realized with the 10 mu m long WS2 nanotubes. Ultrafiltration of gold nanoparticles using the nanotube-paper membrane was demonstrated.

WS2 nanotubes present many new technologies under development, including reinforced biocompatible polymers, membranes, photovoltaic-based memories, ferroelectric devices, etc. These technologies depend on the aspect ratio (length/diameter) of the nanotubes, which was limited to 100 or so. A new synthetic technique is presented, resulting in WS2 nanotubes a few hundred micrometers long and diameters below 50 nm (aspect ratios of 2000-5000) in high yields. Preliminary investigation into the mechanistic aspects of the two-step synthesis reveals that W5O14 nanowhisker intermediates are formed in the first step of the reaction instead of the ubiquitous W18O49 nanowhiskers used in the previous syntheses. The electrical and photoluminescence properties of the long nanotubes were studied. WS2 nanotube-based paper-like material was prepared via a wet-laying process, which could not be realized with the 10 mu m long WS2 nanotubes. Ultrafiltration of gold nanoparticles using the nanotube-paper membrane was demonstrated.

We have found that the polarization dependence of Raman scattering in organic crystals at finite temperatures can only be described by a fourth-rank tensor formalism. This generalization of the second-rank Raman tensor ℛ stems from the effect of off-diagonal components in the crystal self-energy on the light scattering mechanism. We thus establish a novel manifestation of phonon–phonon interaction in inelastic light scattering, markedly separate from the better-known phonon lifetime., SCOPUS: ar.j, info:eu-repo/semantics/published

We have found that the polarization dependence of Raman scattering in organic crystals at finite temperatures can only be described by a fourth-rank tensor formalism. This generalization of the second-rank Raman tensor stems from the effect of off diagonal components in the crystal self-energy on the light scattering mechanism. We thus establish a novel manifestation of phonon-phonon interaction in inelastic light scattering, markedly separate from the better-known phonon lifetime., Funding Agencies|European Research Counsel [850041]; Swedish Research Council (VR) [2020-04630]; Belgian National Fund for Scientific Research (FNRS) [T.0072.18, T.0094.22, U.G001.19, O.005018F, O.00322]; French Community of Belgian (ARC) [20061]

We combine temperature-dependent low-frequency Raman measurements and first-principles calculations to obtain a mechanistic understanding of the order–disorder phase transition of 2,7-di-tert-butylbenzo[b]benzo[4,5]thieno[2,3-d]thiophene (ditBu-BTBT) and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) semiconducting amphidynamic crystals. We identify the lattice normal modes associated with the phase transition by following the position and width of the Raman peaks with temperature and identifying peaks that exhibit nonlinear dependence toward the phase transition temperature. Our findings are interpreted according to the “hardcore mode” model previously used to describe order–disorder phase transitions in inorganic and hybrid crystals with a Brownian sublattice. Within the framework of this model, ditBu-BTBT exhibits an ideal behavior where only one lattice mode is associated with the phase transition. TIPS-pentacene deviates strongly from the model due to strong interactions between lattice modes. We discuss the origin of the different behaviors and suggest side-chain engineering as a tool to control polymorphism in amphidynamic crystals., SCOPUS: ar.j, info:eu-repo/semantics/published

We have found that the polarization dependence of Raman scattering in organic crystals at finite temperatures can only be described by a fourth-rank tensor formalism. This generalization of the second-rank Raman tensor stems from the effect of off diagonal components in the crystal self-energy on the light scattering mechanism. We thus establish a novel manifestation of phonon-phonon interaction in inelastic light scattering, markedly separate from the better-known phonon lifetime., Funding Agencies|European Research Counsel [850041]; Swedish Research Council (VR) [2020-04630]; Belgian National Fund for Scientific Research (FNRS) [T.0072.18, T.0094.22, U.G001.19, O.005018F, O.00322]; French Community of Belgian (ARC) [20061]

We combine ab initio simulations and Raman scattering measurements to demonstrate explicit anharmonic effects in the temperature-dependent dielectric response of a NaCl single crystal. We measure the temperature evolution of its Raman spectrum and compare it to both a quasiharmonic and anharmonic model. Results demonstrate the necessity of including anharmonic lattice dynamics to explain the dielectric response of NaCl, as it is manifested in Raman scattering. Our model fully captures the linear dielectric response of a crystal at finite temperatures and may therefore be used to calculate the temperature dependence of other material properties governed by it., Funding Agencies|ISFIsrael Science Foundation [1861/17]; BSFUS-Israel Binational Science Foundation [2016650]; ERCEuropean Research Council (ERC)European Commission [850041-ANHARMONIC]; Swedish Research Council (VR)Swedish Research Council [2020-04630]

We combine ab initio simulations and Raman scattering measurements to demonstrate explicit anharmonic effects in the temperature-dependent dielectric response of a NaCl single crystal. We measure the temperature evolution of its Raman spectrum and compare it to both a quasiharmonic and anharmonic model. Results demonstrate the necessity of including anharmonic lattice dynamics to explain the dielectric response of NaCl, as it is manifested in Raman scattering. Our model fully captures the linear dielectric response of a crystal at finite temperatures and may therefore be used to calculate the temperature dependence of other material properties governed by it., Funding Agencies|ISFIsrael Science Foundation [1861/17]; BSFUS-Israel Binational Science Foundation [2016650]; ERCEuropean Research Council (ERC)European Commission [850041-ANHARMONIC]; Swedish Research Council (VR)Swedish Research Council [2020-04630]

Lead-based halide perovskite crystals are shown to have strongly anharmonic structural dynamics. This behavior is important because it may be the origin of their exceptional photovoltaic properties. The double perovskite, Cs2AgBiBr6, has been recently studied as a lead-free alternative for optoelectronic applications. However, it does not exhibit the excellent photovoltaic activity of the lead-based halide perovskites. Therefore, to explore the correlation between the anharmonic structural dynamics and optoelectronic properties in lead-based halide perovskites, the structural dynamics of Cs2AgBiBr6 are investigated and are compared to its lead-based analog, CsPbBr3. Using temperature-dependent Raman measurements, it is found that both materials are indeed strongly anharmonic. Nonetheless, the expression of their anharmonic behavior is markedly different. Cs2AgBiBr6 has well-defined normal modes throughout the measured temperature range, while CsPbBr3 exhibits a complete breakdown of the normal-mode picture above 200 K. It is suggested that the breakdown of the normal-mode picture implies that the average crystal structure may not be a proper starting point to understand the electronic properties of the crystal. In addition to our main findings, an unreported phase of Cs2AgBiBr6 is also discovered below approximate to 37 K., Funding Agencies|European Research Concil [850041 - ANHARMONIC]; Alexander von Humboldt FoundationAlexander von Humboldt Foundation; Department of Atomic Energy, Government of IndiaDepartment of Atomic Energy (DAE) [RTI 4007]; SERB IndiaDepartment of Science & Technology (India)Science Engineering Research Board (SERB), India [CRG/2020/003877]; Swedish Research Council (VR)Swedish Research Council [2020-04630, 2021-00486]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2018-05973]

Lead-based halide perovskite crystals are shown to have strongly anharmonic structural dynamics. This behavior is important because it may be the origin of their exceptional photovoltaic properties. The double perovskite, Cs2AgBiBr6, has been recently studied as a lead-free alternative for optoelectronic applications. However, it does not exhibit the excellent photovoltaic activity of the lead-based halide perovskites. Therefore, to explore the correlation between the anharmonic structural dynamics and optoelectronic properties in lead-based halide perovskites, the structural dynamics of Cs2AgBiBr6 are investigated and are compared to its lead-based analog, CsPbBr3. Using temperature-dependent Raman measurements, it is found that both materials are indeed strongly anharmonic. Nonetheless, the expression of their anharmonic behavior is markedly different. Cs2AgBiBr6 has well-defined normal modes throughout the measured temperature range, while CsPbBr3 exhibits a complete breakdown of the normal-mode picture above 200 K. It is suggested that the breakdown of the normal-mode picture implies that the average crystal structure may not be a proper starting point to understand the electronic properties of the crystal. In addition to our main findings, an unreported phase of Cs2AgBiBr6 is also discovered below approximate to 37 K., Funding Agencies|European Research Concil [850041 - ANHARMONIC]; Alexander von Humboldt FoundationAlexander von Humboldt Foundation; Department of Atomic Energy, Government of IndiaDepartment of Atomic Energy (DAE) [RTI 4007]; SERB IndiaDepartment of Science & Technology (India)Science Engineering Research Board (SERB), India [CRG/2020/003877]; Swedish Research Council (VR)Swedish Research Council [2020-04630, 2021-00486]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2018-05973]

We combine ab initio simulations and Raman scattering measurements to demonstrate explicit anharmonic effects in the temperature-dependent dielectric response of a NaCl single crystal. We measure the temperature evolution of its Raman spectrum and compare it to both a quasiharmonic and anharmonic model. Results demonstrate the necessity of including anharmonic lattice dynamics to explain the dielectric response of NaCl, as it is manifested in Raman scattering. Our model fully captures the linear dielectric response of a crystal at finite temperatures and may therefore be used to calculate the temperature dependence of other material properties governed by it., Funding Agencies|ISFIsrael Science Foundation [1861/17]; BSFUS-Israel Binational Science Foundation [2016650]; ERCEuropean Research Council (ERC)European Commission [850041-ANHARMONIC]; Swedish Research Council (VR)Swedish Research Council [2020-04630]

Lead-based halide perovskite crystals are shown to have strongly anharmonic structural dynamics. This behavior is important because it may be the origin of their exceptional photovoltaic properties. The double perovskite, Cs2AgBiBr6, has been recently studied as a lead-free alternative for optoelectronic applications. However, it does not exhibit the excellent photovoltaic activity of the lead-based halide perovskites. Therefore, to explore the correlation between the anharmonic structural dynamics and optoelectronic properties in lead-based halide perovskites, the structural dynamics of Cs2AgBiBr6 are investigated and are compared to its lead-based analog, CsPbBr3. Using temperature-dependent Raman measurements, it is found that both materials are indeed strongly anharmonic. Nonetheless, the expression of their anharmonic behavior is markedly different. Cs2AgBiBr6 has well-defined normal modes throughout the measured temperature range, while CsPbBr3 exhibits a complete breakdown of the normal-mode picture above 200 K. It is suggested that the breakdown of the normal-mode picture implies that the average crystal structure may not be a proper starting point to understand the electronic properties of the crystal. In addition to our main findings, an unreported phase of Cs2AgBiBr6 is also discovered below approximate to 37 K., Funding Agencies|European Research Concil [850041 - ANHARMONIC]; Alexander von Humboldt FoundationAlexander von Humboldt Foundation; Department of Atomic Energy, Government of IndiaDepartment of Atomic Energy (DAE) [RTI 4007]; SERB IndiaDepartment of Science & Technology (India)Science Engineering Research Board (SERB), India [CRG/2020/003877]; Swedish Research Council (VR)Swedish Research Council [2020-04630, 2021-00486]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2018-05973]

We combine ab initio simulations and Raman scattering measurements to demonstrate explicit anharmonic effects in the temperature-dependent dielectric response of a NaCl single crystal. We measure the temperature evolution of its Raman spectrum and compare it to both a quasiharmonic and anharmonic model. Results demonstrate the necessity of including anharmonic lattice dynamics to explain the dielectric response of NaCl, as it is manifested in Raman scattering. Our model fully captures the linear dielectric response of a crystal at finite temperatures and may therefore be used to calculate the temperature dependence of other material properties governed by it., Funding Agencies|ISFIsrael Science Foundation [1861/17]; BSFUS-Israel Binational Science Foundation [2016650]; ERCEuropean Research Council (ERC)European Commission [850041-ANHARMONIC]; Swedish Research Council (VR)Swedish Research Council [2020-04630]

We combine ab initio simulations and Raman scattering measurements to demonstrate explicit anharmonic effects in the temperature-dependent dielectric response of a NaCl single crystal. We measure the temperature evolution of its Raman spectrum and compare it to both a quasiharmonic and anharmonic model. Results demonstrate the necessity of including anharmonic lattice dynamics to explain the dielectric response of NaCl, as it is manifested in Raman scattering. Our model fully captures the linear dielectric response of a crystal at finite temperatures and may therefore be used to calculate the temperature dependence of other material properties governed by it., Funding Agencies|ISFIsrael Science Foundation [1861/17]; BSFUS-Israel Binational Science Foundation [2016650]; ERCEuropean Research Council (ERC)European Commission [850041-ANHARMONIC]; Swedish Research Council (VR)Swedish Research Council [2020-04630]

Lead-based halide perovskite crystals are shown to have strongly anharmonic structural dynamics. This behavior is important because it may be the origin of their exceptional photovoltaic properties. The double perovskite, Cs2AgBiBr6, has been recently studied as a lead-free alternative for optoelectronic applications. However, it does not exhibit the excellent photovoltaic activity of the lead-based halide perovskites. Therefore, to explore the correlation between the anharmonic structural dynamics and optoelectronic properties in lead-based halide perovskites, the structural dynamics of Cs2AgBiBr6 are investigated and are compared to its lead-based analog, CsPbBr3. Using temperature-dependent Raman measurements, it is found that both materials are indeed strongly anharmonic. Nonetheless, the expression of their anharmonic behavior is markedly different. Cs2AgBiBr6 has well-defined normal modes throughout the measured temperature range, while CsPbBr3 exhibits a complete breakdown of the normal-mode picture above 200 K. It is suggested that the breakdown of the normal-mode picture implies that the average crystal structure may not be a proper starting point to understand the electronic properties of the crystal. In addition to our main findings, an unreported phase of Cs2AgBiBr6 is also discovered below approximate to 37 K., Funding Agencies|European Research Concil [850041 - ANHARMONIC]; Alexander von Humboldt FoundationAlexander von Humboldt Foundation; Department of Atomic Energy, Government of IndiaDepartment of Atomic Energy (DAE) [RTI 4007]; SERB IndiaDepartment of Science & Technology (India)Science Engineering Research Board (SERB), India [CRG/2020/003877]; Swedish Research Council (VR)Swedish Research Council [2020-04630, 2021-00486]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2018-05973]

Lead-based halide perovskite crystals are shown to have strongly anharmonic structural dynamics. This behavior is important because it may be the origin of their exceptional photovoltaic properties. The double perovskite, Cs2AgBiBr6, has been recently studied as a lead-free alternative for optoelectronic applications. However, it does not exhibit the excellent photovoltaic activity of the lead-based halide perovskites. Therefore, to explore the correlation between the anharmonic structural dynamics and optoelectronic properties in lead-based halide perovskites, the structural dynamics of Cs2AgBiBr6 are investigated and are compared to its lead-based analog, CsPbBr3. Using temperature-dependent Raman measurements, it is found that both materials are indeed strongly anharmonic. Nonetheless, the expression of their anharmonic behavior is markedly different. Cs2AgBiBr6 has well-defined normal modes throughout the measured temperature range, while CsPbBr3 exhibits a complete breakdown of the normal-mode picture above 200 K. It is suggested that the breakdown of the normal-mode picture implies that the average crystal structure may not be a proper starting point to understand the electronic properties of the crystal. In addition to our main findings, an unreported phase of Cs2AgBiBr6 is also discovered below approximate to 37 K., Funding Agencies|European Research Concil [850041 - ANHARMONIC]; Alexander von Humboldt FoundationAlexander von Humboldt Foundation; Department of Atomic Energy, Government of IndiaDepartment of Atomic Energy (DAE) [RTI 4007]; SERB IndiaDepartment of Science & Technology (India)Science Engineering Research Board (SERB), India [CRG/2020/003877]; Swedish Research Council (VR)Swedish Research Council [2020-04630, 2021-00486]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [2018-05973]