The crystallinity and crystallographic orientation of $Ba_{1-x}Sr_xTiO_3$ (BST) films deposited by metal-organic chemical vapor deposition on (111) textured Pt/$SiO_2$/Si substrate have been studied with use of X-ray diffraction and transmission electron microscope (TEM).
In analysis results, we found 3 different crystallinities of BST films. One had an uniform amorphous layer at BST/Pt interface, another had a mixed interface with amorphous and crystalline and the other had a fully crystallized BST films at the interface. Each was certified by high resolution TEM micrographs and selected area electron diffraction patterns.
We investigated the crystallographic orientation relationships at BST/Pt interface in fully crystallized BST films. BST films had 2 preferred orientations which were (110) and (100) plane on (111) textured Pt electrode. These orientation relationships were that BST (110) ∥ Pt (111), BST [1\bar{1}0] ∥ Pt [1\bar{1}0] in BST (110) grain and BST (100) ∥ Pt (111), BST [010] ∥ Pt [1\bar{1}0] in BST (100) grain. Futhermore BST (110) and (100) grains had relationships which were BST (100)(100)grain ∥ BST (110)(110)grain, BST [001](100)grain ∥ [001](110)grain.
The BST films were heat-treated to reduce or remove amorphous layer existing at the interface with the condition - 750℃ 30min $N_2$, $O_2$, $N_2+O_2$ atmospheres. After heat treatments, interfacial structure of BST film was analyzed with X-ray diffraction and TEM. From X-ray diffraction results, amorphous layers were crystallized with (111) plane due to lattice match with (111) textured Pt electrode. Compared to normal lattices, heat treated BST lattices at interface were distorted about 4∼5°. These lattice distortions were observed by high resolution micrographs and selected area electron diffraction pattern. These were caused by strain influences of adjacent BST grains on Pt electrode.
The superlattice structure was observed in fully crystallized BST thin films. Selected area diffraction patterns showed satellite spots originated from the superlattice structure. Superlattice structures were clearly certified by high resolution micrographs showing clear lattice modulation. From these lattice modulations we found the repeated periodicity which was 3, 2, 3, 2,... BST (110) planes. There were well matched with satellite spots in selected area diffraction pattern. This periodicity of 5 BST (110) planes was continuously connected with 7 BST (200) planes. We could simulate this model of superlattice structure to obtain atomic arrangements and diffraction patterns with National Center for Electron Microscopy Simulation System (NCEMSS) software.
