Zhu Jiliang

RESEARCHES ON THE GROWTH BEHAVIOR OF PbTiO3 THIN FILMS AT THEIR INITIAL STAGES

ABSTRACT PbTiO3 thin films were prepared by RF magnetron sputtering with Ar gas, and the average growth rate was measured as 0.185 nm per minute by Scanning Electron Microscopy (SEM) measurement. PbTiO3 extra thin films at their early stages were deposited under same conditions with different deposition time as 1 min, 3 min and 6 min respectively; and the obtained extra thin films were observed by Atom Force Microscopy (AFM). The experimental results show that at their initial stages, PbTiO3 extra thin films grow through the formation and the diffusion of unit cells on the surface and the films grow with island mode. With the deposition time increasing, the size and the height of the islands increase and the number of islands decreases. The analysis of cross-view of the films sputtered for 1 min with AFM indicates that the height of islands is nearly 0.4 nm, and with increasing of the deposition time to 3 min and 6 min, the height of the islands increases with the integral time of the length of the PbTiO3 crystal unit cell. These results confirm further that the films grow through the diffusion of unit cells on the surface with island mode.

THE GROWTH SIMULATION OF ABO3 TYPE EPITAXIAL THIN FILMS

ABSTRACT A modified solid on solid (SOS) model for the simulation of epitaxial growth of ABO3 type thin films through cell-diffusion on the surface developed by using Monte Carlo (MC) method is presented in this paper. Two diffusion active energy parameters were assumed to be 0.6 eV, which is the diffusion potential barrier on the surface, and 0.8 eV, which is the diffusion potential barrier when a basic unit separates from other units. The results show that the ABO3 expitaxial thin films grow with layer by layer mode at the conditions of higher temperature and lower deposition rate. And with the conditions of lower temperature and higher deposition rate, it is the island mode; and even with same growth mode, the morphology pictures of thin films show that the growth process is different. The shape, size and number of islands are not only related to the growth temperature, but also related to the deposition rate. And the compact initial islands are more likely to develop into smooth thin films with layer-by-layer mode.

The First-Principle Calculation of La-doping Effect on Piezoelectricity in Tetragonal KNN Crystal

The La-dopping effect on the piezoelectricity in the K0.5Na0.5NbO3 (KNN) crystal with a tetragonal phase is investigated for the first time using the first-principle calculation based on density functional theory. The full potentiallinearized augumented plane wave plus local orbitals (APW-LO) method and the supercell method are used in the calculation for the KNN crystal with and without the La doping. The results show that the piezoelectricity originates from the strong hybridization between the Nb atom and the O atom, and the substitution of the K or Na atom by the La impurity atom introduces the anisotropic relaxation and enhances the piezoelectricity at first and then restrains the hybridization of the Nb-O atoms when the La doping content further increases.