Lead- and titanium-based oxide thin films were prepared by the metal-organic chemical vapor deposition technique (MOCVD) and the relationship between the film structures and the processing parameters, such as the ratio of Pb/Ti precursors in the gas phase, substrate materials, substrate surface orientation, and growth temperature, was systematically studied. It was found that whether a single-phase stoichiometric PbTiO3 film could be obtained depended on both the Pb/Ti precursor ratio in the gas phase and the deposition temperature. Under appropriate conditions, stoichiometric PbTiO3, films could be obtained on all the substrates including silicon, MgO, α-Al2O3, SrTiO3, and LaAlO3. The PbTiO3 films grown on silicon substrates were always polycrystalline, whereas epitaxial PbTiO3 films were obtainable on all the other substrates. For epitaxial PbTiO3 films, the epitaxial relationship, crystallinity, and domain structures were found to be a function of both the substrate materials and surface orientation as well as the deposition temperature. X-ray rocking curves (ω scan) of the (100) and (001) planes of PbTiO3 epitaxial film and PbTiO3 single crystal revealed the inherent nature of the domain structures in PbTiO3.

TiO2 thin films have been deposited on sapphire (0001) substrates under various conditions by metal-organic chemical vapor deposition. The structural properties of the deposited films were characterized by x-ray diffraction and transmission electron microscopy. The important growth parameters were found to be the deposition temperature and the deposition rate. The ranges studied for the two parameters were 400 to 850 °C and 10 to 120 Å/min, respectively. Depending on the growth conditions, most of the deposited films were either single-phase anatase or rutile, or a mixture of the two. These films were all epitaxial, but none of them were single-crystal films. Three distinct epitaxial relationships were observed between the films and the substrates, and, depending on the growth conditions, a deposited film can contain one, two, or all three of them. The fact that the films we obtained, although epitaxial, were never single crystal is explained based on the consideration of the difference in the rotational symmetries of the substrate surface and the film growth plane. We believe that it should be generally true that, in heteroepitaxial growth, a true single-crystal film can never be obtained as long as the point symmetry group of the substrate surface is not a subgroup of that of the film growth plane.

PbTiO3 thin films deposited on (001)MgO by the MOCVD technique have been characterized by x-ray diffraction and transmission electron microscopy (TEM). The PbTiO3 films grown at temperatures below Tc (~500 °C) are c-axis oriented polycrystals, while the PbTiO3 films grown at temperatures above Tc are single crystals with a bi-layer structure at room temperature. The top layers of the films near the free surface are c-axis oriented with the orientation relationship of (001)[100]PbTiO3||(001)[100]MgO. The bottom layers of the films near the substrate are a-axis oriented with the orientation relationship of The formation of the bi-layer microstructure of the PbTiO3 films will be discussed in terms of the effect of the cooling rate and the substrate on the phase transition of PbTiO3 from the cubic to the tetragonal phase. When the PbTiO3 films were grown with a large excess of the Pb precursor vapor in the vapor mixture, PbO and PbTiO3 coexisted in the films. Both PbO and PbTiO3 were grown epitaxially on (00l)MgO. The epitaxial orientation relationships were found to be (100) [001]PbO||(001) [100]MgO and (001)[100]PbTiO3||(001)[100]MgO. The 90° domains were observed in the PbTiO3 films deposited at temperatures above Tc. The domain walls are the ﹛101﹜ and ﹛011﹜ twin boundaries, which were formed during the phase transition from the cubic to the tetragonal phase.

Titanium dioxide thin films were grown on sapphire (11$\overline 1$0) substrates in a low-pressure metal-organic chemical vapor deposition system at temperatures ranging from 400 to 800 °C. Raman scattering, x-ray diffraction, transmission electron microscopy, and high resolution electron microscopy techniques were employed to characterize the structural properties of the deposited films. The resultant phases and structures of the deposited films depended on both the growth temperature and the substrate surface properties (surface imperfections, steps, etc.). At the growth temperature of 800 °C, single-crystal rutile films were obtained reproducibly with two possible epitaxial relationships. At lower temperatures (400 to 775 °C), the deposited films can be epitaxial or polycrystalline with highly oriented grains. The similarity between the atomic arrangements of the substrate and the film is discussed in detail to explain the observed epitaxial relationships and abruptness of the interfaces.

TiO2 rutile thin films grown on (110) sapphire (α−Al2O3) by the MOCVD technique have been characterized by transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). The TiO2 rutile thin films grew on the sapphire with two epitaxial orientations. The epitaxial orientation relationships between the rutile films (R) and the sapphire substrate (S) were found to be (1) (101)[010]R ‖ (110)[0001]s. Detailed atomic structures of near-interface regions have been investigated by HREM, providing a clear picture of the initial stage of film growth. HREM images show that about 70% of the nuclei at the interface are the (101) rutile, but most of them are very small, about 5 nm (or 2% of the film thickness) in the growth direction. The film growth was dominated by the (200) orientation. Nucleation and growth of the films will be discussed in terms of the lattice mismatch at the interface and growth rates along the two orientations. Planar defects such as twin boundaries and special grain boundaries are commonly observed in the films, especially in regions close to the substrate. The twin plane and twinning direction are {101} and 〈101〉, respectively. Special grain boundaries are found to be correlated with nucleation and twinning.

A four-circle diffractometry technique is used to determine the heteroepitaxial relations of VO2 and TiO2 thin films grown by an MOCVD technique on sapphire (0001) and (1120) surfaces. The use of a reflective geometry eliminates special sample preparation of the sample for the x-ray diffraction measurements. The distribution of epitaxial domains is found to depend strongly on the symmetry of the underlying substrate.