Dai Zhen-Hong

Hydrogen Storage Capacity Study of a Li+Graphene Composite System with Different Charge States

Based on first-principles plane-wave calculations, we firstly reconfirm that the Li+graphene complex can be taken as a hydrogen storage medium with capacity of 12.8wt%. Then metal adsorption properties of this Li+graphene system with different charge states are investigated. Finally, the hydrogen storage ability of the charging system is calculated. Our calculations show that adding positive charge on a Li+graphene composite results in a conspicuous reduction of Li2s and Li2p orbital occupation with respect to the C2p state. As a result, a stronger bonding between Li and graphene is formed, and a special double-layer hydrogen adsorption structure has been found. Compared to the neutral system, utilizing the positive charged Li+graphene to store hydrogen molecules can solve the issue of clustering of metal atoms after releasing hydrogen, and can improve hydrogen storage capacity up to a gravimetric density of 20.4wt%, correspondingly one adsorbed Li atom can effectively absorb up to seven H2 molecules.

Quantum Statistical Calculation of Exchange Bias

The phenomenon of exchange bias of ferromagnetic (FM) films, which are coupled with an antiferromagnetic (AFM) film, is studied by Heisenberg model by use of the many-body Greens function method of quantum statistical theory for the uncompensated case. Exchange bias HE and coercivity Hc are calculated as functions of the FM film thickness L, temperature, the strength of the exchange interaction across the interface between FM and AFM and the anisotropy of the FM. Hc decreases with increasing L when the FM film is beyond some thickness. The dependence of the exchange bias HE on the FM film thickness and on temperature is also qualitatively in agreement with experiments.

Electronic Structure and Optical Properties in Uranium Dioxide: the First Principle Calculations

We report a study of the electronic structure and optical properties of uranium dioxide (UO2) based on the ab-initio density-functional theory and using the generalized gradient approximation. To correctly describe the strong correlation between 5f electrons of a uranium atom, we employ the on-site Hubbard U correction term and optimize the correlation parameter of the bulk uranium dioxide. Then we give the structural and electronic properties of the ground state of uranium dioxide. Based on the accurate electronic structure, we calculate the complex dielectric function of UO2 and the related optical properties, such as reflectivity refractive index, extinction index, energy loss spectra, and absorption coefficient.

Effect of Substrates on CuInSe2 Nanoparticle Thin Films by Radio Frequency Reactive Sputtering

CuInSe2 (CIS) nanoparticle thin films have been prepared by radio frequency reactive magnetron sputtering from compound ternary fan-shaped targets on low-temperature substrates with pure argon gas as the atmosphere. The stoichiometry of the ternary compound semiconductor quantum dots can easily be controlled by the ratios of the ternary elements and sputtering parameters. CIS nanoparticle thin films regularly shaped and distributed reasonably uniform in size on substrates of 7059 glass etc can be grown in this way. The average particle diameter can be varied between 40-80 nm by an appropriate choice of the substrate temperature, power density and total CIS coverage. The optical and electrical properties of the CIS films have also been studied.

Role of Vacancy in Trapping Impurity of Nitrogen in Molybdenum

Abstract Employing the first-principles simulation combined with the statistical model, we have investigated the interplay between impurity of nitrogen (N) and vacancy in molybdenum (Mo). Single N atom is energetically favorable for occupying the octahedral interstitial site. N atom is easily bonded at vacancy, and the trapping energy of N trapped by vacancy is 2.71 eV, in good agreement with the experimental result. Further, we predict vacancy concentration in the form of N 1 V complex in Mo, which notably increases due to the presence of N, despite the concentration of interstitial N is still higher than that of N 1 V complexes. The results demonstrate the key role of vacancy in N trapping in Mo.

Electronic Transport Through Three-Dimensional Metal Point Contact with Rough Boundaries*

We have studied numerically the electronic transport properties of metal point contact with rough boundaries. According to the forming process of the metal point contact, we add the roughness as stochastic variance on the cross-sectional radius of the metal point contact, the calculations are performed by making use of the mode matching technique and the transfer-matrix method. In this paper, we mainly study variation of the conductance with cross-sectional radius and length of the point contact. It shows that conductance quantization is influenced by the roughness of the metal point contact, when the roughness arrives at a certain degree, at the customary conductance plateaus, the conductance oscillates strongly with the variance of cross-sectional radius and length of the point contact.