Armchair graphene nanoribbons with different proportions of edge oxygen atoms are analyzed in this study using the crystal orbital method,which is based on density functional theory.Although buckled edges are present,...Armchair graphene nanoribbons with different proportions of edge oxygen atoms are analyzed in this study using the crystal orbital method,which is based on density functional theory.Although buckled edges are present,all the nanoribbons are energetically favorable.Unlike the adjacent edge oxygen atoms,the isolated edge oxygen atoms cause semiconductor-metal transitions by introducing edge states.For graphene nanoribbons with all oxygen atoms on the edges,band gap and carrier mobility vary with ribbon width.Furthermore,this behavior is different from that of hydrogen-passivated graphene nanoribbons because of different effective widths,which are pictorially presented with crystal orbitals.The carrier mobilities are as 18%~65% magnitude as those of hydrogen-passivated nanoribbons and are of the order of 10^3 cm^2·V^-1·s^-1.展开更多
Vanadium dioxides were fabricated on normal glass substrates using reactive radio frequency （RF） magnetron sputtering. The oxygen flow volume and annealed temperatures as growth parameters are systematically investi...Vanadium dioxides were fabricated on normal glass substrates using reactive radio frequency （RF） magnetron sputtering. The oxygen flow volume and annealed temperatures as growth parameters are systematically investigated. The electrical and opti- cal properties of VO2 and Au：VO2 thin films with different growth conditions are discussed. The semiconductor-metal phase transition temperature decreased by -10~C for the sample with Au doping compared to the sample without Au doping. How- ever, the optical transmittance of Au：VO2 thin films is much lower than that of bare VO2. These results show that Au doping has a marked effect on the electrical and optical properties.展开更多
In high temperature oxide superconductors, such as Sr-La-Cu-O,Ba-Y-Cu-O, there is a phase transition from semiconductor to metal as the composition changes under the same condition of heat treatment. Recently the theo...In high temperature oxide superconductors, such as Sr-La-Cu-O,Ba-Y-Cu-O, there is a phase transition from semiconductor to metal as the composition changes under the same condition of heat treatment. Recently the theoretical explanations are proposed, hut the research is still at an initial stage. Thus study in different ways on the cause of the phase transition and its relationship with high temperature superconductivity is one of the important current subjects.展开更多
The intricate correlation between charge degrees of freedom and physical properties is a fascinating area of research in solid state chemistry and condensed matter physics.Herein,we report on the pressureinduced succe...The intricate correlation between charge degrees of freedom and physical properties is a fascinating area of research in solid state chemistry and condensed matter physics.Herein,we report on the pressureinduced successive charge transfer and accompanied resistive evolution in honeycomb layered ruthenate AgRuO_(3).Structural revisiting and spectroscopic analyses affirm the ilmenite type R-3 structure with mixed valence cations as Ag^(+1/+2)Ru^(+4/+5)O_(3) at ambient pressure.In-situ pressure-and temperature-dependent resistance variation reveals a successive insulatormetal-insulator transition upon pressing,accompanied by unprecedented charge transfer between Ag and Ru under applied pressure,and a further structural phase transition in the insulator region at higher pressure.These phenomena are also corroborated by in-situ pressure-dependent Raman spectra,synchrotron X-ray diffraction,bond valence sums,and electronic structure calculations,emphasizing the dominated rare Ag2+,and near zero thermal expansion in the ab-plane in the metallic zone mostly due to the Jahn-Teller effect of d9-Ag2+.The multiple electronic instabilities in AgRuO_(3) may offer new possibilities toward novel and unconventionally physical and chemical behaviors in strongly correlated honeycomb lattices.展开更多
This paper is to report the temperature dependent electrical conductivity of single crystals of radical ion salt (RIS) potassium-TCNQ (K-tetracyanoquino- dimethane) in a wide range of temperatures from 30 to 500 K. Th...This paper is to report the temperature dependent electrical conductivity of single crystals of radical ion salt (RIS) potassium-TCNQ (K-tetracyanoquino- dimethane) in a wide range of temperatures from 30 to 500 K. This RIS is quasi-one-dimensional in nature. These single crystals of K-TCNQ are grown by different methods like electrochemical, solution growth and diffusion method. Activation energy is determined for the sample in different temperature regions and found different values. More than one semiconductor to metal phase transition is observed in the studied samples during electrical measurements below and above room temperature. All the features observed in the studied samples are analyzed in the framework of their molecular structure as well as under different effects like disorder, impurity, Coulomb interaction, charge density wave (CDW), scattering and 3-D effects etc.展开更多
Ga-doped ZnO nanowires have been synthesized by a pulsed laser chemical vapor deposition method. The crystal structure and photoluminescence spectra indicate that the dopant atoms are well integrated into the ZnO wurt...Ga-doped ZnO nanowires have been synthesized by a pulsed laser chemical vapor deposition method. The crystal structure and photoluminescence spectra indicate that the dopant atoms are well integrated into the ZnO wurtzite lattice. The photocurrent properties at different temperatures have been systematically investigated for nanowires configured as a three-terminal device. Among the experimental highlights, a pronounced semiconductor-to-metal transition occurs upon UV band-to-band excitation. This is a consequence of the reduction in electron mobility arising from the drastically enhanced Coulomb interactions and surface scattering. Another feature is the reproducible presence of two resistance valleys at 220 and 320 K upon light irradiation. This phenomenon originates from the trapping and detrapping processes in the impurity band arising from the native defects as well as the extrinsic Ga dopants. This work demonstrates that due to the dimensional confinement in quasi-one-dimensional structures, enhanced Coulomb interaction, surface scattering, and impurity states can significantly influence charge transport.展开更多
基金supported by the National Natural Science Foundation of China(No.21203127)the Beijing Higher Education Young Elite Teacher Project(YETP1629)the Scientific Research Base Development Program of the Beijing Municipal Commission of Education
文摘Armchair graphene nanoribbons with different proportions of edge oxygen atoms are analyzed in this study using the crystal orbital method,which is based on density functional theory.Although buckled edges are present,all the nanoribbons are energetically favorable.Unlike the adjacent edge oxygen atoms,the isolated edge oxygen atoms cause semiconductor-metal transitions by introducing edge states.For graphene nanoribbons with all oxygen atoms on the edges,band gap and carrier mobility vary with ribbon width.Furthermore,this behavior is different from that of hydrogen-passivated graphene nanoribbons because of different effective widths,which are pictorially presented with crystal orbitals.The carrier mobilities are as 18%~65% magnitude as those of hydrogen-passivated nanoribbons and are of the order of 10^3 cm^2·V^-1·s^-1.
基金supported by the Fundamental Research Funds for Central Universities of China (Grant No. 2009JBM098)the Natural Science Foundation of Beijing (Grant No. 2113050)
文摘Vanadium dioxides were fabricated on normal glass substrates using reactive radio frequency （RF） magnetron sputtering. The oxygen flow volume and annealed temperatures as growth parameters are systematically investigated. The electrical and opti- cal properties of VO2 and Au：VO2 thin films with different growth conditions are discussed. The semiconductor-metal phase transition temperature decreased by -10~C for the sample with Au doping compared to the sample without Au doping. How- ever, the optical transmittance of Au：VO2 thin films is much lower than that of bare VO2. These results show that Au doping has a marked effect on the electrical and optical properties.
文摘In high temperature oxide superconductors, such as Sr-La-Cu-O,Ba-Y-Cu-O, there is a phase transition from semiconductor to metal as the composition changes under the same condition of heat treatment. Recently the theoretical explanations are proposed, hut the research is still at an initial stage. Thus study in different ways on the cause of the phase transition and its relationship with high temperature superconductivity is one of the important current subjects.
基金supported by the National Science Foundation of China(grant nos.NSFC-22090041,21875287,U1932217,11974246,12004252,12025408,11921004,11974432,and 92165204)the Program for Guangdong Introducing Innovative and Entrepreneurial Teams(grant no.2017ZT07C069)NKRDPC-2017YFA0206203,NKRDPC-2018YFA0306001.
文摘The intricate correlation between charge degrees of freedom and physical properties is a fascinating area of research in solid state chemistry and condensed matter physics.Herein,we report on the pressureinduced successive charge transfer and accompanied resistive evolution in honeycomb layered ruthenate AgRuO_(3).Structural revisiting and spectroscopic analyses affirm the ilmenite type R-3 structure with mixed valence cations as Ag^(+1/+2)Ru^(+4/+5)O_(3) at ambient pressure.In-situ pressure-and temperature-dependent resistance variation reveals a successive insulatormetal-insulator transition upon pressing,accompanied by unprecedented charge transfer between Ag and Ru under applied pressure,and a further structural phase transition in the insulator region at higher pressure.These phenomena are also corroborated by in-situ pressure-dependent Raman spectra,synchrotron X-ray diffraction,bond valence sums,and electronic structure calculations,emphasizing the dominated rare Ag2+,and near zero thermal expansion in the ab-plane in the metallic zone mostly due to the Jahn-Teller effect of d9-Ag2+.The multiple electronic instabilities in AgRuO_(3) may offer new possibilities toward novel and unconventionally physical and chemical behaviors in strongly correlated honeycomb lattices.
文摘This paper is to report the temperature dependent electrical conductivity of single crystals of radical ion salt (RIS) potassium-TCNQ (K-tetracyanoquino- dimethane) in a wide range of temperatures from 30 to 500 K. This RIS is quasi-one-dimensional in nature. These single crystals of K-TCNQ are grown by different methods like electrochemical, solution growth and diffusion method. Activation energy is determined for the sample in different temperature regions and found different values. More than one semiconductor to metal phase transition is observed in the studied samples during electrical measurements below and above room temperature. All the features observed in the studied samples are analyzed in the framework of their molecular structure as well as under different effects like disorder, impurity, Coulomb interaction, charge density wave (CDW), scattering and 3-D effects etc.
文摘Ga-doped ZnO nanowires have been synthesized by a pulsed laser chemical vapor deposition method. The crystal structure and photoluminescence spectra indicate that the dopant atoms are well integrated into the ZnO wurtzite lattice. The photocurrent properties at different temperatures have been systematically investigated for nanowires configured as a three-terminal device. Among the experimental highlights, a pronounced semiconductor-to-metal transition occurs upon UV band-to-band excitation. This is a consequence of the reduction in electron mobility arising from the drastically enhanced Coulomb interactions and surface scattering. Another feature is the reproducible presence of two resistance valleys at 220 and 320 K upon light irradiation. This phenomenon originates from the trapping and detrapping processes in the impurity band arising from the native defects as well as the extrinsic Ga dopants. This work demonstrates that due to the dimensional confinement in quasi-one-dimensional structures, enhanced Coulomb interaction, surface scattering, and impurity states can significantly influence charge transport.
