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Ryuichi Arafune - One of the best experts on this subject based on the ideXlab platform.
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silicene on ag 1 1 1 geometric and electronic structures of a new honeycomb Material of si
Progress in Surface Science, 2015Co-Authors: Noriaki Takagi, Chunliang Lin, Kazuaki Kawahara, Emi Minamitani, N Tsukahara, Maki Kawai, Ryuichi ArafuneAbstract:Abstract Silicene, a two-dimensional honeycomb sheet consisting of Si atoms, has attracted much attention as a new Low-Dimensional Material because it gains various fascinating characteristics originating from the combination of Dirac fermion features with spin–orbit coupling. The novel properties such as the quantum spin Hall effect and the compatibility with the current Si device technologies have fueled competition to realize the silicene. This review article focuses on the geometric and electronic structures of silicene grown on Ag(1 1 1) investigated by scanning tunneling microcopy (STM), low energy electron diffraction (LEED) and density functional theory (DFT) calculations. The silicene on Ag(1 1 1) takes locally-buckled structure in which the Si atoms are displaced perpendicularly to the basal plane. As a result, several superstructures such as 4 × 4 , 13 × 13 R 13.9 ° , 4 / 3 × 4 / 3 , and etc. emerge. The atomic arrangement of the 4 × 4 silicene has been determined by STM, DFT calculations and LEED dynamical analysis, while the other superstructures remain to be fully-resolved. In the 4 × 4 silicene, Si atoms are arranged to form a buckled honeycomb structure where six Si atoms of 18 Si atoms in the unit cell are displaced vertically. The displacements lead to the vertical shift of the substrate Ag atoms, indicating the non-negligible coupling at the interface between the silicene layer and the substrate. The interface coupling significantly modifies the electronic structure of the 4 × 4 silicene. No Landau level sequences were observed by scanning tunneling spectroscopy (STS) with magnetic fields applied perpendicularly to the sample surface. The DFT calculations showed that the π and π ∗ bands derived from the Si 3p z are hybridized with the Ag electronic states, leading to the drastic modification in the band structure and then the absence of Dirac fermion features together with the two-dimensionality in the electronic states. These findings demonstrate that the strong coupling at the interface causes the symmetry breaking for the 4 × 4 silicene and as a result the disappearance of Dirac fermion features. The geometric and electronic structures of other superstructures are also discussed.
Noriaki Takagi - One of the best experts on this subject based on the ideXlab platform.
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silicene on ag 1 1 1 geometric and electronic structures of a new honeycomb Material of si
Progress in Surface Science, 2015Co-Authors: Noriaki Takagi, Chunliang Lin, Kazuaki Kawahara, Emi Minamitani, N Tsukahara, Maki Kawai, Ryuichi ArafuneAbstract:Abstract Silicene, a two-dimensional honeycomb sheet consisting of Si atoms, has attracted much attention as a new Low-Dimensional Material because it gains various fascinating characteristics originating from the combination of Dirac fermion features with spin–orbit coupling. The novel properties such as the quantum spin Hall effect and the compatibility with the current Si device technologies have fueled competition to realize the silicene. This review article focuses on the geometric and electronic structures of silicene grown on Ag(1 1 1) investigated by scanning tunneling microcopy (STM), low energy electron diffraction (LEED) and density functional theory (DFT) calculations. The silicene on Ag(1 1 1) takes locally-buckled structure in which the Si atoms are displaced perpendicularly to the basal plane. As a result, several superstructures such as 4 × 4 , 13 × 13 R 13.9 ° , 4 / 3 × 4 / 3 , and etc. emerge. The atomic arrangement of the 4 × 4 silicene has been determined by STM, DFT calculations and LEED dynamical analysis, while the other superstructures remain to be fully-resolved. In the 4 × 4 silicene, Si atoms are arranged to form a buckled honeycomb structure where six Si atoms of 18 Si atoms in the unit cell are displaced vertically. The displacements lead to the vertical shift of the substrate Ag atoms, indicating the non-negligible coupling at the interface between the silicene layer and the substrate. The interface coupling significantly modifies the electronic structure of the 4 × 4 silicene. No Landau level sequences were observed by scanning tunneling spectroscopy (STS) with magnetic fields applied perpendicularly to the sample surface. The DFT calculations showed that the π and π ∗ bands derived from the Si 3p z are hybridized with the Ag electronic states, leading to the drastic modification in the band structure and then the absence of Dirac fermion features together with the two-dimensionality in the electronic states. These findings demonstrate that the strong coupling at the interface causes the symmetry breaking for the 4 × 4 silicene and as a result the disappearance of Dirac fermion features. The geometric and electronic structures of other superstructures are also discussed.
Tripathi Pragya - One of the best experts on this subject based on the ideXlab platform.
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Dielectric spectroscopy studies of low-disorder and Low-Dimensional Materials
Universitat Politècnica de Catalunya, 2016Co-Authors: Tripathi PragyaAbstract:In this thesis we employ dielectric spectroscopy (in different implementations) to study the dielectric properties of different Materials ranging from completely disordered supercooled liquids to low-disorder solids with only ratcheting reorientational motions, to Low-Dimensional systems such as thin films or needle-like crystals. The probed Material properties include the electrical conductivity, the space-charge processes due to sample heterogeneities, molecular dynamics, hydrogen-bond dynamics, and phase-transition temperature and kinetics. To study Materials in thin film form, we implement silicon-based interdigital electrode devices, which we calibrate to obtain their equivalent capacity in vacuum. We also probe two-dimensional samples obtained by intercalating (sandwiching) organic molecules between parallel graphite oxide sheets. We study both organic and hybrid (organic-inorganic) films, and compared the results with the bulk counterpart of the same Materials. Rhodamine films are deposited by two different procedures starting from rhodamine 6G chloride: solution-deposited films are ionic and ordered, while vacuum-deposited films consist of a different, neutral species, namely rhodamine19, due to decomposition of rhodamine 6G upon sublimation. Both types of films display variable-range hopping electronic conduction, and a conductivity-induced space-charge relaxation. Solution deposited films display a dipolar relaxation, absent in rhodamine 19 films. We assign the dipolar relaxation to some intramolecular motion involving the charged nitrogen of the Rhodamine and the chlorine counter-ion. We also performed studies on hybrid films of cadmium iodide covalently attached to ethylamine (CdI2EA), deposited by the Langmuir-Blodgett process. Bulk CdI2EA Material has a solid-to-solid (structural) phase transition, which in the Langmuir-Blodgett films occurs 5 degrees higher in temperature. The films displayed a dielectric relaxation dynamics absent in the bulk, and which is either due to the existence of molecular motions in the looser structure of the film, or to the motion of teh surfactant covalently attached to CdI2EA for Langmuir-Blodgett film deposition. Another example of Low-Dimensional Material is biclotymol, whose supercooled liquid form crystallizes into a metastable solid phase which consists of one-dimensional needle-like crystallites. The crystallization kinetics of bicotymol is a textbook example of the Avrami law with exponent n = 2 resulting from a temperature independent nucleation rate of the crystallites followed by unidimensional growth. The instability of the supercooled liquid phase may be related to the existence of fast secondary relaxation dynamics. The last two chapters of the thesis focus on ethane derivatives with distinct side groups, namely tetrachloroethane and ethanolamine. The solid phase of tetrachloroethane displays three distinct relaxation processes. We carry out molecular dynamic simulations to identify the three processes: the slowest is a cooperative reorientational dynamics whereby the molecules rotate by passing through an intermediate equivalent state; such collective relaxation is accompanied by a ¿precursor¿ single-molecule relaxation. The third process is a non-cooperative ratcheting motion between the equilibrium orientation and a high-energy orientation. In ethanolamine we observe the existence of a metastable solid phase besides the known stable one. A very prominent relaxation process is observed in both solid phases and in the liquid. The ubiquity of this relaxation indicates that it is related to local fluctuations of the hydrogen-bond network between the molecules. The same relaxation is also present when ethanolamine is sandwiched between graphite oxide sheets, but it is slower and characterized by a broader distribution of relaxation times due to the interaction with the graphite oxide matrix.En esta tesis utilizamos la espectroscopia dieléctrica para estudiar las propiedades dieléctricas de diferentes Materiales que van desde líquidos subenfriados completamente desordenados a sólidos de bajo desorden con movimiento de reorientación, hasta sistemas de baja dimensionalidad tales como películas delgadas o cristales casi unidimensionales. Las propiedades estudiadas incluyen la conductividad eléctrica, los procesos de carga espacial debido a las heterogeneidades de la muestra, la dinámica molecular, la dinámica de enlaces por puente de hidrógeno, y la cinética de cristalización. Para el estudio de Materiales en forma de película delgada, se han implementado nuevos dispositivos de electrodo interdigital a base de silicio. Muestras bidimensionales han sido obtenidas también por intercalación de moléculas orgánicas entre planos atómicos de óxido de grafito. Estudiamos películas orgánicas e híbridas orgánicas-inorgánicas depositadas mediante procedimientos diferentes, y comparamos los resultados con las fases puras de los mismos Materiales. Obtenemos películas ordenadas de rodamina 6G clorada por crecimiento desde solución, y películas amorfas de rodamina 19 por condensación de vapor en vacío. Ambos tipos de películas presentan una conducción electrónica por salto de electrones y una relajación de carga espacial. Las películas de rodamina 6G clorada muestran además una relajación dipolar, que se asigna a movimientos intramoleculares que involucran la carga asociada al nitrógeno de la rodamina 6G y al átomo de cloro. También se han estudiado películas híbridas de ioduro de cadmio covalentemente unido a etilamina (CdI2EA), depositadas mediante el método Langmuir-Blodgett. El Material en fase “bulk” presenta una transición estructural, que en la película delgada aparece a una temperatura superior de unos 5 K. Las películas presentan una relajación dinámica ausente en el Material puro y que es debida a la existencia de movimientos moleculares en la estructura de la película (menos densa), o bien al movimiento del surfactante que ha sido enlazado químicamente al CdI2EA para lograr la deposición. Otro ejemplo distinto de Material de baja dimensionalidad es el biclotymol, para el que el líquido subenfriado cristaliza en una fase sólida que consiste en cristales unidimensionales (en forma de aguja). La cinética de cristalización del bicotymol es un ejemplo perfecto de la ley de Avrami con exponente n = 2, resultante de una tasa de nucleación independiente de la temperatura, seguida por un crecimiento unidimensional. La inestabilidad de la fase líquida subenfriada puede estar relacionada con la existencia de dinámicas moleculares rápidas. Los dos últimos capítulos de la tesis se centran en dos derivados del etano con grupos laterales distintos, a saber, tetracloroetano y etanolamina. La fase sólida del tetracloroetano muestra tres procesos de relajación distintos. Mediante simulaciones moleculares se han podido identificar los tres procesos: el más lento es un proceso cooperativo en el que las moléculas “giran” sobre si mismas pasando por un estado equivalente intermedio; esta relajación colectiva se acompaña de una relajación "precursora", correspondiente al movimiento de una sola molécula. El tercer proceso es una rotación, no cooperativa, entre la orientación de equilibrio y una orientación de alta energía
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Dielectric spectroscopy studies of low-disorder and Low-Dimensional Materials
Universitat Politècnica de Catalunya, 2016Co-Authors: Tripathi PragyaAbstract:In this thesis we employ dielectric spectroscopy (in different implementations) to study the dielectric properties of different Materials ranging from completely disordered supercooled liquids to low-disorder solids with only ratcheting reorientational motions, to Low-Dimensional systems such as thin films or needle-like crystals. The probed Material properties include the electrical conductivity, the space-charge processes due to sample heterogeneities, molecular dynamics, hydrogen-bond dynamics, and phase-transition temperature and kinetics. To study Materials in thin film form, we implement silicon-based interdigital electrode devices, which we calibrate to obtain their equivalent capacity in vacuum. We also probe two-dimensional samples obtained by intercalating (sandwiching) organic molecules between parallel graphite oxide sheets. We study both organic and hybrid (organic-inorganic) films, and compared the results with the bulk counterpart of the same Materials. Rhodamine films are deposited by two different procedures starting from rhodamine 6G chloride: solution-deposited films are ionic and ordered, while vacuum-deposited films consist of a different, neutral species, namely rhodamine19, due to decomposition of rhodamine 6G upon sublimation. Both types of films display variable-range hopping electronic conduction, and a conductivity-induced space-charge relaxation. Solution deposited films display a dipolar relaxation, absent in rhodamine 19 films. We assign the dipolar relaxation to some intramolecular motion involving the charged nitrogen of the Rhodamine and the chlorine counter-ion. We also performed studies on hybrid films of cadmium iodide covalently attached to ethylamine (CdI2EA), deposited by the Langmuir-Blodgett process. Bulk CdI2EA Material has a solid-to-solid (structural) phase transition, which in the Langmuir-Blodgett films occurs 5 degrees higher in temperature. The films displayed a dielectric relaxation dynamics absent in the bulk, and which is either due to the existence of molecular motions in the looser structure of the film, or to the motion of teh surfactant covalently attached to CdI2EA for Langmuir-Blodgett film deposition. Another example of Low-Dimensional Material is biclotymol, whose supercooled liquid form crystallizes into a metastable solid phase which consists of one-dimensional needle-like crystallites. The crystallization kinetics of bicotymol is a textbook example of the Avrami law with exponent n = 2 resulting from a temperature independent nucleation rate of the crystallites followed by unidimensional growth. The instability of the supercooled liquid phase may be related to the existence of fast secondary relaxation dynamics. The last two chapters of the thesis focus on ethane derivatives with distinct side groups, namely tetrachloroethane and ethanolamine. The solid phase of tetrachloroethane displays three distinct relaxation processes. We carry out molecular dynamic simulations to identify the three processes: the slowest is a cooperative reorientational dynamics whereby the molecules rotate by passing through an intermediate equivalent state; such collective relaxation is accompanied by a ¿precursor¿ single-molecule relaxation. The third process is a non-cooperative ratcheting motion between the equilibrium orientation and a high-energy orientation. In ethanolamine we observe the existence of a metastable solid phase besides the known stable one. A very prominent relaxation process is observed in both solid phases and in the liquid. The ubiquity of this relaxation indicates that it is related to local fluctuations of the hydrogen-bond network between the molecules. The same relaxation is also present when ethanolamine is sandwiched between graphite oxide sheets, but it is slower and characterized by a broader distribution of relaxation times due to the interaction with the graphite oxide matrix.En esta tesis utilizamos la espectroscopia dieléctrica para estudiar las propiedades dieléctricas de diferentes Materiales que van desde líquidos subenfriados completamente desordenados a sólidos de bajo desorden con movimiento de reorientación, hasta sistemas de baja dimensionalidad tales como películas delgadas o cristales casi unidimensionales. Las propiedades estudiadas incluyen la conductividad eléctrica, los procesos de carga espacial debido a las heterogeneidades de la muestra, la dinámica molecular, la dinámica de enlaces por puente de hidrógeno, y la cinética de cristalización. Para el estudio de Materiales en forma de película delgada, se han implementado nuevos dispositivos de electrodo interdigital a base de silicio. Muestras bidimensionales han sido obtenidas también por intercalación de moléculas orgánicas entre planos atómicos de óxido de grafito. Estudiamos películas orgánicas e híbridas orgánicas-inorgánicas depositadas mediante procedimientos diferentes, y comparamos los resultados con las fases puras de los mismos Materiales. Obtenemos películas ordenadas de rodamina 6G clorada por crecimiento desde solución, y películas amorfas de rodamina 19 por condensación de vapor en vacío. Ambos tipos de películas presentan una conducción electrónica por salto de electrones y una relajación de carga espacial. Las películas de rodamina 6G clorada muestran además una relajación dipolar, que se asigna a movimientos intramoleculares que involucran la carga asociada al nitrógeno de la rodamina 6G y al átomo de cloro. También se han estudiado películas híbridas de ioduro de cadmio covalentemente unido a etilamina (CdI2EA), depositadas mediante el método Langmuir-Blodgett. El Material en fase “bulk” presenta una transición estructural, que en la película delgada aparece a una temperatura superior de unos 5 K. Las películas presentan una relajación dinámica ausente en el Material puro y que es debida a la existencia de movimientos moleculares en la estructura de la película (menos densa), o bien al movimiento del surfactante que ha sido enlazado químicamente al CdI2EA para lograr la deposición. Otro ejemplo distinto de Material de baja dimensionalidad es el biclotymol, para el que el líquido subenfriado cristaliza en una fase sólida que consiste en cristales unidimensionales (en forma de aguja). La cinética de cristalización del bicotymol es un ejemplo perfecto de la ley de Avrami con exponente n = 2, resultante de una tasa de nucleación independiente de la temperatura, seguida por un crecimiento unidimensional. La inestabilidad de la fase líquida subenfriada puede estar relacionada con la existencia de dinámicas moleculares rápidas. Los dos últimos capítulos de la tesis se centran en dos derivados del etano con grupos laterales distintos, a saber, tetracloroetano y etanolamina. La fase sólida del tetracloroetano muestra tres procesos de relajación distintos. Mediante simulaciones moleculares se han podido identificar los tres procesos: el más lento es un proceso cooperativo en el que las moléculas “giran” sobre si mismas pasando por un estado equivalente intermedio; esta relajación colectiva se acompaña de una relajación "precursora", correspondiente al movimiento de una sola molécula. El tercer proceso es una rotación, no cooperativa, entre la orientación de equilibrio y una orientación de alta energía.Postprint (published version
M I Salkola - One of the best experts on this subject based on the ideXlab platform.
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observation of intrinsically localized modes in a discrete low dimensional Material
Physical Review Letters, 1999Co-Authors: Basil I Swanson, James A Brozik, Steven P Love, Geoffrey F Strouse, Andrew P Shreve, A R Bishop, Weizong Wang, M I SalkolaAbstract:We report the experimental observation of intrinsic dynamically localized vibrational states in crystals of the highly nonlinear halide-bridged mixed-valence transition metal complex {l_brace}[Pt(en){sub 2} ]thinsp[Pt(en ){sub 2}Cl{sub 2}]thinsp(ClO{sub 4}){sub 4}{r_brace} , where en=ethylenediamine . These states are identified by the distinctive structure and strong redshifts they impose upon the overtone resonance Raman spectra. Quantitative modeling of the observed redshifts is presented based on a nonadiabatic coupled electron-lattice model that self-consistently predicts strong nonlinearity and highly localized multiquanta bound states. {copyright} {ital 1999} {ital The American Physical Society}
Maki Kawai - One of the best experts on this subject based on the ideXlab platform.
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silicene on ag 1 1 1 geometric and electronic structures of a new honeycomb Material of si
Progress in Surface Science, 2015Co-Authors: Noriaki Takagi, Chunliang Lin, Kazuaki Kawahara, Emi Minamitani, N Tsukahara, Maki Kawai, Ryuichi ArafuneAbstract:Abstract Silicene, a two-dimensional honeycomb sheet consisting of Si atoms, has attracted much attention as a new Low-Dimensional Material because it gains various fascinating characteristics originating from the combination of Dirac fermion features with spin–orbit coupling. The novel properties such as the quantum spin Hall effect and the compatibility with the current Si device technologies have fueled competition to realize the silicene. This review article focuses on the geometric and electronic structures of silicene grown on Ag(1 1 1) investigated by scanning tunneling microcopy (STM), low energy electron diffraction (LEED) and density functional theory (DFT) calculations. The silicene on Ag(1 1 1) takes locally-buckled structure in which the Si atoms are displaced perpendicularly to the basal plane. As a result, several superstructures such as 4 × 4 , 13 × 13 R 13.9 ° , 4 / 3 × 4 / 3 , and etc. emerge. The atomic arrangement of the 4 × 4 silicene has been determined by STM, DFT calculations and LEED dynamical analysis, while the other superstructures remain to be fully-resolved. In the 4 × 4 silicene, Si atoms are arranged to form a buckled honeycomb structure where six Si atoms of 18 Si atoms in the unit cell are displaced vertically. The displacements lead to the vertical shift of the substrate Ag atoms, indicating the non-negligible coupling at the interface between the silicene layer and the substrate. The interface coupling significantly modifies the electronic structure of the 4 × 4 silicene. No Landau level sequences were observed by scanning tunneling spectroscopy (STS) with magnetic fields applied perpendicularly to the sample surface. The DFT calculations showed that the π and π ∗ bands derived from the Si 3p z are hybridized with the Ag electronic states, leading to the drastic modification in the band structure and then the absence of Dirac fermion features together with the two-dimensionality in the electronic states. These findings demonstrate that the strong coupling at the interface causes the symmetry breaking for the 4 × 4 silicene and as a result the disappearance of Dirac fermion features. The geometric and electronic structures of other superstructures are also discussed.
