Baoting Liu

ADSORPTION AND DISSOCIATION OF O2 ON Ti3Al (0001) STUDIED BY FIRST-PRINCIPLES

The adsorption and dissociation of oxygen molecule on Ti3Al (0001) surface have been investigated by density functional theory (DFT) with the generalized gradient approximation (GGA). All possible adsorption sites including nine vertical and fifteen parallel sites of O2 are considered on Ti3Al (0001) surface. It is found that all oxygen molecules dissociate except for three vertical adsorption sites after structure optimization. This indicates that oxygen molecules prefer to dissociate on the junction site between Ti and Al atoms. Oxygen atoms coming from dissociation of oxygen molecule tend to occupy the most stable adsorption sites of the Ti3Al (0001) surface. The distance of O–O is related to the surface dissociation distance of Ti3Al (0001) surface. The valence electron localization function (ELF) and projected density of states (DOS) show that the bonds of O–O are breakaway at parallel adsorption end structures.

Enhanced open circuit voltage in photovoltaic effect of polycrystalline La and Ni co-doped BiFeO3 film

Photovoltaic (PV) effect of polycrystalline Bi0.975La0.025Fe0.975Ni0.025O3 (BLFNO) film grown on Pt(111)/Ti/SiO2/Si(001) substrate using sol–gel method has been investigated. The BLFNO film possesses good ferroelectric property and large twice-remanent polarization. It is found that PV response exhibited a strong dependence on the potential of top indium tin oxide (ITO) and bottom Pt electrode. The open circuit voltage is -0.67 V when the potential of ITO electrode is higher than that of Pt electrode and 0.45 V when the potential of ITO electrode is lower than that of Pt electrode. This can be interpreted by the variation of barrier heights at both ITO/BLFNO and BLFNO/Pt interfaces.

Temperature dependence of rapidly thermally annealed Ba0.6Sr0.4TiO3 thin film fabricated on platinized Si substrate

Abstract Sol-gel prepared Ba0.6Sr0.4TiO3 (BST) thin films were prepared on platinized silicon substrate and annealed by rapid thermal annealing at temperatures ranging from 650 °C to 850 °C. X-ray diffraction, atomic force microscopy and electrical measurements were used to investigate the temperature dependence of the structural and physical properties of Ba0.6Sr0.4TiO3 thin film. The dielectric constants of BST samples annealed at 700 °C and 750 °C, measured at zero-bias electric field, are 166 and 193, respectively. It is found that all the prepared BST films show Ohmic-like conduction at low voltages except for the 650 °C annealed BST sample, for which Ohmic conduction covers the whole measured voltage range; BST films annealed at 700 °C, 750 °C and 800 °C demonstrate Poole–Frenkel emission conduction at high voltages, while BST film annealed at 850 °C presents Schottky emission behavior.

First-Principle Calculation of Elastic Compliance Coefficients for BiFeO3

The elastic compliance coefficients of PbTiO 3 with/without geometric optimization are firstly calculated by using density-functional theory (DFT) under different exchange correlation functions. It is found that the best results are not obtained by LDA/CA-PZ and optimized structure although these induce the nearest lattice constants to experimental ones, however, the results of PbTiO 3 without geometry optimization under GGA/PW91 function are in great consistent with the experimental data. Based on the same calculating method of PbTiO 3 , the elastic compliance coefficients for BiFeO 3 are obtained. And the data are compared with previous results predicted by fitting experimental data to Landau-type phenomenological theory, which possessing the difference of an order of magnitude with our data.

Contribution of Surface Defects to the Interface Conductivity of SrTiO3/LaAlO3

Based on the first-principles method, the structural stability and the contribution of point defects such as O, Sr or Ti vacancies on two-dimensional electron gas of n- and p-type LaAlO3/SrTiO3 interfaces are investigated. The results show that O vacancies at p-type interfaces have much lower formation energies, and Sr or Ti vacancies at n-type interfaces are more stable than the ones at p-type interfaces under O-rich conditions. The calculated densities of states indicate that O vacancies act as donors and give a significant compensation to hole carriers, resulting in insulating behavior at p-type interfaces. In contrast, Sr or Ti vacancies tend to trap electrons and behave as acceptors. Sr vacancies are the most stable defects at high oxygen partial pressures, and the Sr vacancies rather than Ti vacancies are responsible for the insulator-metal transition of n-type interface. The calculated results can be helpful to understand the tuned electronic properties of LaAlO3/SrTiO3 heterointerfaces.

Influence of growth temperature on the properties of Al-doped ZnO thin film fabricated by pulsed laser deposition

Al-doped ZnO thin film (AZO) is regarded as a potential candidate to replace the expensive ITO thin film and is the central issue in current research in the field of transparent conductive film because of its properties of high conductivity, low level of pollution, high transmittanceand and low fabrication cost. In this paper, c-axis preferred growth AZO films were fabricated on sapphire (0001) substrate by the pulsed laser deposition at different substrate temperatures (Ts). The scanning electron microscope (SEM), X-ray diffraction (XRD) and the four-point probe (FPP) were used to measure the thin film microstructure and electrical characteristics. SEM results show that the surfaces of all AZO films are very flat and have no droplets on them, expect the film grown at room temperature. The grain sizes of AZO gradually decrease with increse of Ts. X-ray diffraction spectra show that the quality of the crystallization of thin films gradually is improved with increase of Ts. The results measured by FPP show that with increase of temperature, sheet resistance first decreases then increases.

Effect of growth temperature on the properties of Al-doped ZnO thin film prepared by RF magnetron sputtering

Al-doped ZnO thin film(AZO) has become a type of material which is the first choice to replace the expensive ITO thin film and is the central issue in current research in the field of transparent conductive film because of its properties of high conductivity, high transmittance, low level of pollution, and cheap. In this paper, AZO films were produced by the RF magnetron sputtering under the different growth temperatures condition. The atomic force microscope (AFM), X-ray diffraction (XRD), visible-UV spectrophotometer and the four-point probe (FPP) were used to measure the thin film microstructure, optical properties and electrical characteristics. AFM results show that the film with the smoother surface and the more uniform size distribution grains are obtained by increasing substrate temperature. X-ray diffraction spectra show that with increase of the temperature, the quality of the crystallization of thin films gradually is improved and the the optimum growth temperature is 600 °C. Optical transmission spectra show that the AZO films have high transmittance and band gap of thin films decreases with increasing temperature. The results measured by FPP show that with increase of temperature, sheet resistance decreases.