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李言荣, Shiming He*, Yanrong Li, Xingzhao Liu, Bowan Tao, Dehong Li, Qingfang Lu
Thin Solid Films 478(2005)261-264,-0001,():
-1年11月30日
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.
Atomic force microscopy (, AFM), , Dielectric properties, Grain boundary, Growth mechanism, Ferroelectric materials, Pulse laser deposition, X-ray diffraction
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【期刊论文】Ab initio total energy study of ZnO adsorption on a sapphire (0001) surface
李言荣, Yang Chun, Li Yan-rong, Li Jin-shan
PHYSICAL REVIEW B 70, 045413 (2004),-0001,():
-1年11月30日
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.
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