In order to determine the structures of Si（111）-√7 √3-In surfaces and to understand their electronic properties, we construct six models of both hexagonal and rectangular types and perform first-principles calcula...In order to determine the structures of Si（111）-√7 √3-In surfaces and to understand their electronic properties, we construct six models of both hexagonal and rectangular types and perform first-principles calculations. Their scanning tunneling microscopic images and work functions are simulated and compared with experimental results. In this way, the hex-H3＇ and rect-T1 models are identified as the experimental configurations for the hexagonal and rectangular types, respectively. The structural evolution mechanism of the In/Si（lll） surface with indium coverage around 1.0 monolayer is discussed. The 4×1 and -√7× √3 phases are suggested to have two different types of evolution mechanisms, consistent with experimental results.展开更多
The solid-liquid equilibria of musk ketone + musk xylene, musk xylene +l,3-dimethyl-2,4-dinitro-5-tert-butyl benzene are measured by differential scanning calorimeter (DSC), these systems are proved to be simple eutec...The solid-liquid equilibria of musk ketone + musk xylene, musk xylene +l,3-dimethyl-2,4-dinitro-5-tert-butyl benzene are measured by differential scanning calorimeter (DSC), these systems are proved to be simple eutectics. Moreover the melting points and the fusion enthalpies of musk ketone, musk xylene and 1,3-dimethyl-2,4-dinitro-5-tert-butyl benzene are also measured by the DSC. These solid-liquid equilibrium data and the heats of fusion are reported for the first time. Then UNIFAC model is used to correlate the sofid-liquid equilibrium data. It is shown that the solid-liquid equilibria of musk systems can be predicted by the UNIFAC model.展开更多
Microstructural change of YBaCuO film/YSZ substrate with and without proton irradiation has been studied by scanning electron microscope and X- ray diffraction techniques. Structural analysis has shown that conversion...Microstructural change of YBaCuO film/YSZ substrate with and without proton irradiation has been studied by scanning electron microscope and X- ray diffraction techniques. Structural analysis has shown that conversion from tetragonal to orthorhombic phases, reduction of nonsuperconducting phase and preferential rearrangement of crystal grains are all favorable to the improvement of superconductivity in the YBaCuO film supported by YSZ substrate by proton beam bombardment.展开更多
We report the formation and local electronic structure of Ge clusters on the Si（111）-7×7 surface studied by using variable temperature scanning tunnelling microscopy （VT-STM） and low-temperature scanning tunn...We report the formation and local electronic structure of Ge clusters on the Si（111）-7×7 surface studied by using variable temperature scanning tunnelling microscopy （VT-STM） and low-temperature scanning tunnelling spectroscopy （STS）. Atom-resolved STM images reveal that the Ce atoms are prone to forming clusters with 1.0 nm in diameter for coverage up to 0.12 ML. Such Ce clusters preferentially nucleate at the centre of the faulted-half unit cells, leading to the ＇dark sites＇ of Si centre adatoms from the surrounding three unfaulted-half unit cells in filled-state images. Biasdependent STM images show the charge transfer from the neighbouring Si adatoms to Ce clusters. Low-temperature STS of the Ce clusters reveals that there is a band gap on the Ce cluster and the large voltage threshold is about 0.9 V.展开更多
The structures and stabilization of three crystal surfaces of TCNQ-based charge transfer complexes（CTCs） including PrQ（TCNQ） 2,MPM（TCNQ） 2,and MEM（TCNQ） 2,have been investigated by scanning tunneling microscop...The structures and stabilization of three crystal surfaces of TCNQ-based charge transfer complexes（CTCs） including PrQ（TCNQ） 2,MPM（TCNQ） 2,and MEM（TCNQ） 2,have been investigated by scanning tunneling microscopy（STM）.The three bulk-truncated surfaces are all ac-surface,which are terminated with TCNQ molecular arrays.On the ac-surface of PrQ（TCNQ） 2,the TCNQ molecules form a tetramer structure with a wavelike row behavior and a 纬 angle of about 18掳 between adjacent molecules.Moreover,the dimer structures are resolved on both ac-surfaces of MPM（TCNQ） 2 and MEM（TCNQ） 2.In addition,the tetramer structure is the most stable structure,while the dimer structures are unstable and easily subject to the STM tip disturbance,which results in changeable unit cells.The main reasons for the surface stabilization variation among the three ac-surfaces are provided by using the ＇蟺-atom model＇.展开更多
An effective near-field - far-field (NF - FF) transformation with spherical scanning for quasi-planar antennas from irregularly spaced data is developed in this paper. Two efficient approaches for evaluating the regul...An effective near-field - far-field (NF - FF) transformation with spherical scanning for quasi-planar antennas from irregularly spaced data is developed in this paper. Two efficient approaches for evaluating the regularly spaced spherical samples from the nonuniformly distributed ones are proposed and numerically compared. Both the approaches rely on a nonredundant sampling representation of the voltage measured by the probe, based on an oblate ellipsoidal modelling of the antenna under test. The former employs the singular value decomposition method to reconstruct the NF data at the points fixed by the nonredundant sampling representation and can be applied when the irregularly acquired samples lie on nonuniform parallels. The latter is based on an iterative technique and can be used also when such a hypothesis does not hold, but requires the existence of a biunique correspondence between the uniform and nonuniform samples, associ- ating at each uniform sampling point the nearest irregular one. Once the regularly spaced spherical samples have been recovered, the NF data needed by a probe compensated NF - FF transformation with spherical scanning are efficiently evaluated by using an optimal sampling interpolation algorithm. It is so possible to accurately compensate known posi- tioning errors in the NF - FF transformation with spherical scanning for quasi-planar antennas. Some numerical tests assessing the accuracy and the robustness of the proposed approaches are reported.展开更多
Graphene has been recognized as a promising 2D material with many new properties. However, pristine graphene is gapless which hinders its direct application towards graphene-based semiconducting devices. Recently, var...Graphene has been recognized as a promising 2D material with many new properties. However, pristine graphene is gapless which hinders its direct application towards graphene-based semiconducting devices. Recently, various ways have been proposed to overcome this problem. In this study, we report a robust method to open a gap in graphene via noncovalent functionalization with porphyrin molecules. Two type of porphyrins, namely, iron protoporphyrin (FePP) and zinc protoporphryin (ZnPP) were independently physisorbed on graphene grown on nickel by chemical vapour deposition (CVD) resulting in a bandgap opening in graphene. Using a statistical analysis of scanning tunneling spectroscopy (STS) measurements, we demonstrated that the magnitude of the band gap depends on the type of deposited porphyrin molecule.The π-π stacking of FePP on graphene yielded a considerably larger band gap value (0.45 eV) than physisorbed ZnPP (0.23 eV). We proposed that the origin of different band gap value is governed due to the metallic character of the respective porphyrin.展开更多
We report results from the investigation of the nonlinear refractive index and nonlinear absorption coefficient of {(1Z)-[4-(Dimethylamino)phenyl]methylene} 4-nitrobenzocarboxy hydrazone mono-hydrate (DMPM4NBCHM) solu...We report results from the investigation of the nonlinear refractive index and nonlinear absorption coefficient of {(1Z)-[4-(Dimethylamino)phenyl]methylene} 4-nitrobenzocarboxy hydrazone mono-hydrate (DMPM4NBCHM) solution using Z-scan technique with a continuous wave (CW) Argon ion laser. The results show that this type of organic material has a large nonlinear absorption and nonlinear refractive index at 488 nm and 514 nm. The origin of the nonlinear effects was discussed. We demonstrate that the light induced nonlinear refractive index variation, leads to limiting effect. The results indicated that DMPM4NBCHM could be promising candidates for application on nonlinear photonic devices and optical limiters.展开更多
基金V. ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.20603032, No.20733004, No.21121003, No.91021004, No.20933006）, the National Key Basic Research Program （No.2011CB921400）, the Foundation of National Excellent Doctoral Dissertation of China （No.200736）, the Fundamental Research Funds for the Central Universities （No.WK2340000006 and No.WK2060140005）, and the Shanghai Supercompurer Center, the USTC-HP HPC Project, and the SCCAS.
文摘In order to determine the structures of Si（111）-√7 √3-In surfaces and to understand their electronic properties, we construct six models of both hexagonal and rectangular types and perform first-principles calculations. Their scanning tunneling microscopic images and work functions are simulated and compared with experimental results. In this way, the hex-H3＇ and rect-T1 models are identified as the experimental configurations for the hexagonal and rectangular types, respectively. The structural evolution mechanism of the In/Si（lll） surface with indium coverage around 1.0 monolayer is discussed. The 4×1 and -√7× √3 phases are suggested to have two different types of evolution mechanisms, consistent with experimental results.
文摘The solid-liquid equilibria of musk ketone + musk xylene, musk xylene +l,3-dimethyl-2,4-dinitro-5-tert-butyl benzene are measured by differential scanning calorimeter (DSC), these systems are proved to be simple eutectics. Moreover the melting points and the fusion enthalpies of musk ketone, musk xylene and 1,3-dimethyl-2,4-dinitro-5-tert-butyl benzene are also measured by the DSC. These solid-liquid equilibrium data and the heats of fusion are reported for the first time. Then UNIFAC model is used to correlate the sofid-liquid equilibrium data. It is shown that the solid-liquid equilibria of musk systems can be predicted by the UNIFAC model.
文摘Microstructural change of YBaCuO film/YSZ substrate with and without proton irradiation has been studied by scanning electron microscope and X- ray diffraction techniques. Structural analysis has shown that conversion from tetragonal to orthorhombic phases, reduction of nonsuperconducting phase and preferential rearrangement of crystal grains are all favorable to the improvement of superconductivity in the YBaCuO film supported by YSZ substrate by proton beam bombardment.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 90406022 and 10674159）.
文摘We report the formation and local electronic structure of Ge clusters on the Si（111）-7×7 surface studied by using variable temperature scanning tunnelling microscopy （VT-STM） and low-temperature scanning tunnelling spectroscopy （STS）. Atom-resolved STM images reveal that the Ce atoms are prone to forming clusters with 1.0 nm in diameter for coverage up to 0.12 ML. Such Ce clusters preferentially nucleate at the centre of the faulted-half unit cells, leading to the ＇dark sites＇ of Si centre adatoms from the surrounding three unfaulted-half unit cells in filled-state images. Biasdependent STM images show the charge transfer from the neighbouring Si adatoms to Ce clusters. Low-temperature STS of the Ce clusters reveals that there is a band gap on the Ce cluster and the large voltage threshold is about 0.9 V.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.10804010,50772015,60977015,and 10974019)the National Basic Research Program of China(Grant No.2006CB932301)the Scientific Research Foundation for the Returned Overseas Chinese Scholars of Ministry of Education
文摘The structures and stabilization of three crystal surfaces of TCNQ-based charge transfer complexes（CTCs） including PrQ（TCNQ） 2,MPM（TCNQ） 2,and MEM（TCNQ） 2,have been investigated by scanning tunneling microscopy（STM）.The three bulk-truncated surfaces are all ac-surface,which are terminated with TCNQ molecular arrays.On the ac-surface of PrQ（TCNQ） 2,the TCNQ molecules form a tetramer structure with a wavelike row behavior and a 纬 angle of about 18掳 between adjacent molecules.Moreover,the dimer structures are resolved on both ac-surfaces of MPM（TCNQ） 2 and MEM（TCNQ） 2.In addition,the tetramer structure is the most stable structure,while the dimer structures are unstable and easily subject to the STM tip disturbance,which results in changeable unit cells.The main reasons for the surface stabilization variation among the three ac-surfaces are provided by using the ＇蟺-atom model＇.
文摘An effective near-field - far-field (NF - FF) transformation with spherical scanning for quasi-planar antennas from irregularly spaced data is developed in this paper. Two efficient approaches for evaluating the regularly spaced spherical samples from the nonuniformly distributed ones are proposed and numerically compared. Both the approaches rely on a nonredundant sampling representation of the voltage measured by the probe, based on an oblate ellipsoidal modelling of the antenna under test. The former employs the singular value decomposition method to reconstruct the NF data at the points fixed by the nonredundant sampling representation and can be applied when the irregularly acquired samples lie on nonuniform parallels. The latter is based on an iterative technique and can be used also when such a hypothesis does not hold, but requires the existence of a biunique correspondence between the uniform and nonuniform samples, associ- ating at each uniform sampling point the nearest irregular one. Once the regularly spaced spherical samples have been recovered, the NF data needed by a probe compensated NF - FF transformation with spherical scanning are efficiently evaluated by using an optimal sampling interpolation algorithm. It is so possible to accurately compensate known posi- tioning errors in the NF - FF transformation with spherical scanning for quasi-planar antennas. Some numerical tests assessing the accuracy and the robustness of the proposed approaches are reported.
文摘Graphene has been recognized as a promising 2D material with many new properties. However, pristine graphene is gapless which hinders its direct application towards graphene-based semiconducting devices. Recently, various ways have been proposed to overcome this problem. In this study, we report a robust method to open a gap in graphene via noncovalent functionalization with porphyrin molecules. Two type of porphyrins, namely, iron protoporphyrin (FePP) and zinc protoporphryin (ZnPP) were independently physisorbed on graphene grown on nickel by chemical vapour deposition (CVD) resulting in a bandgap opening in graphene. Using a statistical analysis of scanning tunneling spectroscopy (STS) measurements, we demonstrated that the magnitude of the band gap depends on the type of deposited porphyrin molecule.The π-π stacking of FePP on graphene yielded a considerably larger band gap value (0.45 eV) than physisorbed ZnPP (0.23 eV). We proposed that the origin of different band gap value is governed due to the metallic character of the respective porphyrin.
文摘We report results from the investigation of the nonlinear refractive index and nonlinear absorption coefficient of {(1Z)-[4-(Dimethylamino)phenyl]methylene} 4-nitrobenzocarboxy hydrazone mono-hydrate (DMPM4NBCHM) solution using Z-scan technique with a continuous wave (CW) Argon ion laser. The results show that this type of organic material has a large nonlinear absorption and nonlinear refractive index at 488 nm and 514 nm. The origin of the nonlinear effects was discussed. We demonstrate that the light induced nonlinear refractive index variation, leads to limiting effect. The results indicated that DMPM4NBCHM could be promising candidates for application on nonlinear photonic devices and optical limiters.
