We investigate the structural and electronic properties of SiC nanotubes(NTs) with hexagonal cross sections by a first-principles calculation using plane-wave ultra-soft pseudo-potential technology based on the densit...We investigate the structural and electronic properties of SiC nanotubes(NTs) with hexagonal cross sections by a first-principles calculation using plane-wave ultra-soft pseudo-potential technology based on the density-functional theory.Our results reveal that surface-layer C and Si atoms relax significantly upon decreasing the tube-wall thickness because of surface-size and quantum-size effects.We also find that all relaxed SiC NTs stay stably on the nanoscale because of an admixture of sp2 and sp3 hybridization between C and Si atoms and a strong covalent,and that the band gap tends to decrease with increasing tube-wall thickness.Our calculations further indicate that both C and Si atoms on the inner and outer surface of SiC NTs contribute to defect states at the top of the valence band and at the bottom of the conduction band.These results provide reference information for a thorough understanding of the properties of SiC nanostructures and also enable more precise monitoring and control of the growth of SiC nanostructures.展开更多
Using the first-principles calculations, we studied the geometric structures, electronic structures and optical properties of the single-walled (n, 0) ZnO nanotubes (NTs). The calculated results show that all the bind...Using the first-principles calculations, we studied the geometric structures, electronic structures and optical properties of the single-walled (n, 0) ZnO nanotubes (NTs). The calculated results show that all the bind energies of the single-walled (n,0) ZnO NTs are of negative values, which indicate that the ZnO NTs can exist stably as single-walled NTs. While the calculated results of electronic structure indicate that the single-walled (n,0) ZnO NTs are a type of direct wide band-gap semiconductor materials, the whole valence bands are spread and drift to low-energy direction with the increase of the NT diameter. The defect energy levels caused by quantum size and surface effects emerge on the top of the valence bands. Furthermore, the calculated results of optical properties reveal that the dielectric peaks have a blue shift and the edge of absorption band corresponds to ultraviolet band with the decrease of the NT diameter. The single-walled (n, 0) ZnO NTs can be applied to ultraviolet semiconductor systems.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 60976069)Specialized Research Fund of Department of Education of Shaanxi Province (Grant No. 08jk487)+1 种基金Specialized Research Fund for Yan’an city (Grant Nos. 2008kg-08 and 2008ks-29)Specialized Research Fund of Key Disciplines of Signal and Information Processing for Yan’an University
文摘We investigate the structural and electronic properties of SiC nanotubes(NTs) with hexagonal cross sections by a first-principles calculation using plane-wave ultra-soft pseudo-potential technology based on the density-functional theory.Our results reveal that surface-layer C and Si atoms relax significantly upon decreasing the tube-wall thickness because of surface-size and quantum-size effects.We also find that all relaxed SiC NTs stay stably on the nanoscale because of an admixture of sp2 and sp3 hybridization between C and Si atoms and a strong covalent,and that the band gap tends to decrease with increasing tube-wall thickness.Our calculations further indicate that both C and Si atoms on the inner and outer surface of SiC NTs contribute to defect states at the top of the valence band and at the bottom of the conduction band.These results provide reference information for a thorough understanding of the properties of SiC nanostructures and also enable more precise monitoring and control of the growth of SiC nanostructures.
基金supported by the National Natural Science Foundation of China (Grant No. 60976069)the Scientific Research Program of the Educational Committee of Shaanxi Province, China (Grant No. 11JK0846)+1 种基金the Scientific Research Foundation for Doctors of Yanan University (GrantNos. YD2009-01 and YDZD2011-03)the Scientific and Technology Research and Development Program of Yanan Municipal (Grant No.2011ks-24)
文摘Using the first-principles calculations, we studied the geometric structures, electronic structures and optical properties of the single-walled (n, 0) ZnO nanotubes (NTs). The calculated results show that all the bind energies of the single-walled (n,0) ZnO NTs are of negative values, which indicate that the ZnO NTs can exist stably as single-walled NTs. While the calculated results of electronic structure indicate that the single-walled (n,0) ZnO NTs are a type of direct wide band-gap semiconductor materials, the whole valence bands are spread and drift to low-energy direction with the increase of the NT diameter. The defect energy levels caused by quantum size and surface effects emerge on the top of the valence bands. Furthermore, the calculated results of optical properties reveal that the dielectric peaks have a blue shift and the edge of absorption band corresponds to ultraviolet band with the decrease of the NT diameter. The single-walled (n, 0) ZnO NTs can be applied to ultraviolet semiconductor systems.
