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 characterized by X-ray diffraction, transmission electron microscopy and high resolution electron microSCopy. PbTiO3 films deposited on (001) MgO under optimum conditions show a bilayer structure. The top layer of the films near the free surface is c axis oriented with (001)[100]PbTiO3 parallel-to (001)[100]MgO. The bottom layer of the films near the substrate 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 depends on the cooling rate and film thickness. It was found that the thickness 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 films with (101)[001]PbTiO3 parallel-to (110)[001]MgO. Highly (001)-textured PbTiO3 thin films were obtained on (111)-oriented Au/(001) MgO. This texture appears to be due to a number of small holes (< 1 mum) formed 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 other directions for PbTiO3, the resultant films are highly c axis oriented.