Effects of oxygen pressure on lattice parameter, orientation, surface morphology and deposition rate of (Ba_(0.02)Sr_(0.98))TiO_3 thin films grown on MgO substrate by pulsed laser deposition

摘要

(Ba_(0.02)Sr_(0.98))TiO_3 thin films were grown on MgO substrate by pulsed laser deposition (PLD) techniques at various oxygen pressures from 40 to 10~(-3) Pa. Effects of oxygen pressure on lattice parameter, orientation, surface morphology and deposition rate of the thin films were investigated. X-ray diffraction patterns indicate that, with decreasing oxygen pressure, crystal orientation of the thin films develops from (110) preferred orientation to random orientation, and finally to perfectly (001) texture. Meantime, lattice parameter of the thin films increases with decreasing oxygen pressure. Especially, perfectly (001)-oriented (Ba_(0.02)Sr_(0.98))TiO_3 thin film was obtained under oxygen pressure of 10~(-3) Pa at substrate temperature of 850℃, in spite of the large lattice mismatch of about 8% between (Ba_(0.02)Sr_(0.98))TiO_3 and MgO. Atomic force microscopy images show that all the thin films have granular structure and the thin film grown at 10~(-3) Pa has much more homogeneous grain size distribution compared to all the other thin films. Moreover, the films grown at oxygen pressures of 1 and 10~(-1) Pa have more smooth surfaces, and the deposition rate of thin film increases with decreasing oxygen pressure.