Papers by Author: Cheng He

Abstract: The effects of external stress field f on band gap E_g(D, f) of ZnO nanowires (NWs) in a diameter range of D = 0.6 - 2.0 nm are investigated using first-principles density-function theory for the future application as nanogenerators. It is shown that the E_g(D,0) values decreases with the increasing diameter of ZnO NWs without the stress field. Moreover, E_g(D, f) decreases with increasing of f due to the rapid drop of conduction band maximum of ZnO NWs when D is constant. These findings imply that E_g(D,f) functions of ZnO NWs can be modulated by manipulating D and f, which may be help for design of ZnO nanogenerators with a higher generation output voltage.

Abstract: The geometric structure, band structure and density of state of pure and Ag-N, Ag-2N codoped wurtzite ZnO have been investigated by first-principles ultrasoft pseudopotential method in the generalized gradient approximation. These structures induce fully occupied defect states above the valence-band maximum of bulk ZnO. The calculation results show that the codoped structure Ag-N has better stability. Meanwhile, the carrier concentration is increased in the Ag-2N codoped configuration where the delocalized features are obvious. Our findings suggest that codoping of Ag-2N could efficiently enhance the N dopant solubility and is likely to yield better p-type conductivity.

Abstract: The most promising hydrogen storage materials are perhaps complex metal hydrides. Thus, a plausible first step in the rehydrogenation mechanism is proposed by simulating the reversible hydrogen storage in Zr-doped NaAlH₄. It provides insight into the catalytic role of Zr atoms on an Al surface in the chemisorptions of molecular hydrogen. It is found that the diffusion of hydride species on Al-metallic phase and formation of Al hydride species is probably the key to syntheses the next products in the rehydrogenation reaction.