THE STRUCTURE OF HETEROEPITAXIAL LEAD TITANATE LAYERS GROWN BY ORGANOMETALLIC CHEMICAL-VAPOR-DEPOSITION

The structure of heteroepitaxial (001) lead titanate films on (001) st rontium titanate and (001) magnesium oxide grown by organometallic che mical vapour deposition has been investigated. PbTiO3 grows textured o n (001)MgO and heteroepitaxially on (001)SrTiO3. Details of the micros tructure are, however, comparable. Rutherford backscattering spectrome try (RBS) channelling experiments on heteroepitaxial PbTiO3 films on ( 001)SrTiO3 have shown that the microstructure is dominated by the laye r thickness. The cooling rate is found to have no influence on the mic rostructure. Very thin films to about 50 nm thickness show a relativel y large value of the minimum channelling yield which decreases with in creasing thickness. For film thicknesses between about 50 nm and 100 n m the minimum channelling yield is relatively low, down to a few perce nt, indicative of high-quality epitaxial films. If the him thickness e xceeds a critical value of about 100 nm the epitaxial quality deterior ates as can be concluded from the sharp increase in the value for the minimum yield. Changes in minimum yield are due to changes in the micr ostructure of the film which has been studied by transmission electron microscopy (TEM) and X-ray diffraction. TEM and {100}PbTiO3 pole-figu re measurements show the presence of a-axis oriented domains sharing { 101} twin planes with the c-axis matrix. The volume fraction has been estimated from theta-2 theta scans as a function of offset in theta. F or thick films the volume fraction scales with the minimum yield. This analysis is confirmed by rocking-width measurements. The presence of non-uniform residual strain in the film has been analyzed from broaden ing of the (001)PbTiO3 diffraction lines. Details of the microstructur e are correlated with the RES data. A tentative interpretation is pres ented.