EFFECTS OF SUBSTRATE ORIENTATION AND COOLING RATE ON MICROSTRUCTURE OF PBTIO3 THIN-FILMS GROWN BY METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITION

PbTiO3 thin films grown on (001) MgO, (110) MgO and (111)-textured Au/ (001)MgO by metal-organic chemical vapor deposition have been characte rized by X-ray diffraction, transmission electron microscopy and high resolution electron microSCopy. PbTiO3 films deposited on (001) MgO un der optimum conditions show a bilayer structure. The top layer of the films near the free surface is c axis oriented with (001)[100]PbTiO3 p arallel-to (001)[100]MgO. The bottom layer of the films near the subst rate is a axis oriented with (100)[001BAR]PbTiO3 parallel-to (001)[100 ]MgO. 90-degrees domains (or {101} twins) were observed only in the c- axis-oriented layers. The thickness of the a-axis-oriented layers depe nds on the cooling rate and film thickness. It was found that the thic kness of the a-axis-oriented layers near the substrate decreases with decreasing cooling rate and/or increasing film thickness. PbTiO3 films deposited on (110) MgO, however, are single-layer epitaxial thin film s with (101)[001]PbTiO3 parallel-to (110)[001]MgO. Highly (001)-textur ed PbTiO3 thin films were obtained on (111)-oriented Au/(001) MgO. Thi s texture appears to be due to a number of small holes (< 1 mum) forme d in the Au thin films during heating to the growth temperature. These holes seem to have acted as nucleation sites for (001)PbTiO3 on (001) MgO. Since the growth rate along {100} is much faster than along othe r directions for PbTiO3, the resultant films are highly c axis oriente d.