3.2. Surface morphologies
The SEM surface micrographs of BaTiO3 thin films deposited under different pressures are shown in Fig. 2. It can be seen that the grain size becomes larger with increasing working pressure.
At 2.9 Pa, the grain boundaries are not clear. The film deposited at 3.5 Pa shows clear grain boundaries. But the grain size is not uniform. The film deposited at 4.0 Pa exhibits a smooth and densely packed structure with homogeneous grains. The average grain size is about 80 nm. However, when deposited at higher pressure, like 4.5 Pa, the film exhibits more pores compared with the film prepared at 4.0 Pa.
The surface morphologies of BaTiO3 thin films was examined by an atomic force microscope. Fig. 3 shows the results for the films deposited from 550 1C to 750 1C. The roughness in RMS with the different depoisiton tempera-tures is 3.0 nm, 5.1 nm, 2.4 nm, 8.5 nm and 11.4 nm, respectively. The roughness of the films significantly increases when deposited above 650 1C. This result can be attributed to the following: the energetic particle bombard-ment on the growing film that leads to the ejection of previously deposited atoms, and the formation of islands which grow large enough to touch and coalescence during nucleation and growth on the substrate [10]. For the substrate temperature from 650 1C to 750 1C, it is likely that the particles arrive in the substrate with high energy and cross the energy barrier of nucleation. These high energy particles are more likely to develop into films with high porosity and high roughness [11].