In the layer-by-layer growth regime of SrTiO3 films with pulsed laser molecular beam epitaxy, the relaxation behaviors of RHEED intensity after termination of growth were studied. From the characteristic relaxation times as a function of substrate temperatures, it was revealed that the surface relaxation occurred with low activity energy for diffusion of 0.3 eV and slow relaxation process, which was argued to be attributed to the diffusion of charge-neutral SrTiO3 units.

The effects of grain size on nonlinear dielectric properties of as-deposited SrTiO3 (STO) thin films were studied by using interdigital capacitor. C-axis-oriented STO thin films with different grain size were deposited onto interdigital electrodes made from YBa2Cu3O7 x thin films by pulsed laser deposition (PLD) technique. The grain size of as-eposited STO thin films increased with substrate temperature, and reached a maximum value at 700 8C. With further increase of substrate temperature, the grain size decrease rapidly because of the negative oxygen supersaturation and the high nucleation density. The nonlinear dielectric properties measurements showed to be highly correlated with the grain size of STO thin films; the zero-bias dielectric constant, the dielectric dissipation, and the tunability decreased with the decrease of the grain size.

The sapphire (0001) surface and the adsorption of ZnO are theoretically calculated by using a plane wave ultrasoft pseudo-potential method based on density functional theory. By comparing the PDOS of the Al and the O before and after the surface relaxation, we demonstrate different apphire (0001) surface states, and changes in surface chemical bonding resulting from Al and O are analyzed. The bonding processing of a ZnO molecule on the surface of Al2O3, adsorption energy and bonding orientation, and change in surface structure as well as the characters of surface chemical bonding are further investigated. We conclude that the surface inward relaxation in the first layer Al-O is weakened, even eliminated after the surface adsorption of the ZnO; chemical bonding energy achieved 4.4±0.4 eV. There is a deflected angle of 30° between the chemical bonding of the ZnO s0.185±0.01 nmd and the adjacent surface Al-O bonding; the stable chemical adsorption site of Zn is just about 30 deflected from the O-hexagonal symmetry of the a-Al2O3s0001d surface. Through analysis of the atomic populations, density of state, and bonding electronic density before and after the adsorption, it is revealed that the chemical bonding formed by the O2− of the ZnO and the surface Al3+ is characterized by strong ionic bonding, while the bond of the Zn2+ and the surface O2− has a covalent character, which mainly comes from the hybridization of the Zn 4s and the O 2p and partially from the hybridization of the Zn 3d and the O 2p, so as to facilitate the forming of tetrahedral coordination in the initial stage of the ZnO films growth. Hence it is favorable for the formation of the wurtzite structure.

ZnO adsorption on sapphire (0001) surface is theoretically calculated by using a plane wave ultrasoft pseudo-potential method based on ab initio molecular dynamics. The results reveal that the surface relaxation in the first layer Al-O is reduced, even eliminated after the surface adsorption of ZnO, and the chemical bonding energy is 434.3 (±38.6) kJ·mol−1. The chemical bond of ZnO (0.185±0.01nm) has a 30° angle away from the adjacent Al-O bond, and the stable chemical adsorption position of the Zn is deflected from the surface O-hexagonal symmetry with an angle of about 30°. The analysis of the atomic populations, density of state and bonding electronic density before and after the adsorption indicates that the chemical bond formed by the O2− of the ZnO and the surface Al3+ has a strong ionic bonding characteristic, while the chemical bond formed by the Zn2+ and the surface O2− has an obvious covalent characteristic, which comes mainly from the hybridization of the Zn 4s and the O 2p and partially from that of the Zn 3d and the O 2p.

Well-ordered self-assembled SrTiO3 thin film, as a template for complex oxide quantum wires, was fabricated on LaAlO3 (100) single-crystal substrates with laser molecular beam epitaxy. The self-assembled growth was in situ monitored by reflective high-energy electron diffraction. The morphology evolutions of the films as a function of thickness were studied by ex situ atomic force microscopy. As the thickness of the films increased from 3.875 to 46.5nm gradually, the compressive stress-induced SrTiO3 films exhibited a periodic well-ordered ripple structure, which formed a unique nanoassembled template for the fabrication of quantum wires. Small-angle X-ray scattering technique was employed to investigate the structure. Symmetric satellite peaks were discovered, indicating the well-ordered superstructure. In contrast, the similar superstructure was not observed duringthe growth of the tensile stress-induced LaAlO3 films on SrTiO3 substrates. The compressive stress was considered as the main reason of the self-assembled growth, and systematical elucidation about strain mechanism was discussed. These results might provide an efficient method for the controllable formation of well-aligned template of quantum wire for complex oxide with desirable structure via proper modulation of strains.