Fan Xiangjun

First principles study on the charge density and the bulk modulus of the transition metals and their carbides and nitrides

A first principles study of the electronic properties and bulk modulus (B0) of the fcc and bcc transition metals, transition metal carbides and nitrides is presented. The calculations were performed by plane-wave pseudopotential method in the framework of the density functional theory with local density approximation. The density of states and the valence charge densities of these solids are plotted. The results show that B0 does not vary monotonically when the number of the valence d electrons increases. B0 reaches a maximum and then decreases for each of the four sorts of solids. It is related to the occupation of the bonding and anti-bonding states in the solid. The value of the valence charge density at the midpoint between the two nearest metal atoms tends to be proportional to B0.

Plasma Enhanced Chemical Vapor Deposition Synthesizing Carbon Nitride Hard Thin Films

Using plasma enhanced chemical vapor deposition and SiC and carbon buffer layers, we have obtained carbon nitride thin films on Si(100) and Si(111). The x-ray diffraction and x-ray photoelectron spectroscopy are used to characterize the thin films. The Vickers hardness of the carbon nitride thin films is more than 5100 kgf/mm2 and comparable to that of diamond.

In-situ measurements of ion implantation effects on YBCO superconducting films

Abstract This superconducting films of YBa2Cu3O7 have been deposited on SrTiO3 substrates using a home-made hollow cathode magnetron sputtering system. The samples were placed on a variable-temperature target stage of a 200 keV implanter and then bombarded by O+ to different doses. The electrical resistance of the samples and its dependence on both ion dose and temperature were measured in situ. Our experimental results reveal that the resistive behavior is extremely sensitive to ion dose, and the ion damage has a strong effect on the transport properties of these films.

Corrosion resistance properties and preparation of α-C3N4 thin films

Well adhered C3N4 films were prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD) on industrial pure iron substrates using ternary Si−N−C films as buffer layer. XRD measurement showed that the C3N4 films belong to the α-C3N4 phase. Electrochemical experiments showed that the corrosive resistance of the pure iron raised by two orders of magnitude after being covered with the α-C3N4 coating.

Low Energy H + Effects on the Photovoltaic and Optical Properties of Polycrystalline Silicon Solar Cells

Low energy hydrogen ion was used to passivate the electrically active defects existing in grains and grain boundaries of polycrystalline silicon solar cells. Short-circuit current of H+ implanted cells remarkably increased before and after preparing TiO2AR (antireflective) coating. The measurements (at λ=6328 Å) of the optical properties of H+ implanted silicon samples show that: the value of absorption coefficient reached the level of a-Si; refractive indexn and refłectivityR significantly decreased; the optical band gap increased from 1.1 eV to 1.3 eV. The results indicate that Si-H bonds have been formed after H+ implantation. The calculation shows that the optical thickness cycle of TiO2 AR coating will reduce correspondingly in order to obtain the optimum optical match between AR coating and implanted silicon since refractive index decreases after H+ implantation.

PREPARATION OF GAN THIN FILMS BY REACTIVE IONIZED CLUSTER BEAM TECHNIQUE

GaN thin films were prepared by reactive ionized cluster beam technique at relatively low substrate temperature about 400°C. The composition, structure and morphology of the films were characterized by x-ray photoelectron spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The binding energy of N 1s electron in the film is 397.85 eV which shows the formation of Ga-N bonding. The film has a polycrystalline structure revealed by the measurement results of TEM and SEM. It was found that raising nitrogen ion ratio in the beam is helpful to decrease oxygen content in the film.