Observations of Island Structures at the Initial Growth Stage of PbZr_xTi_1-xO₃ Thin Films Prepared by Metalorganic Chemical Vapor Deposition

Abstract

Island structures of PbZr x Ti 1- x O 3 (PZT) ( x =0.26 and 0.74) were observed prior to formation of a continuous film at the initial growth stage on a Pt(111)/SiO 2 /Si substrate by metalorganic chemical vapor deposition (MOCVD). Triangular-shaped (111)-oriented PZT islands were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Transmission electron microscopy (TEM) observations revealed that PZT islands 80 to 100 nm wide and 20 to 30 nm high had a twin structure due to the presence of tetragonal or rhombohedral structures. Hence, small PZT islands could have spontaneous polarization. In piezoresponse measurements using scanning probe microscopy (SPM), the phase difference between the vibrational signal of the SPM cantilever and the applied ac voltage changed from 0 to 180°, resulting in a hysteresis loop due to polarization reversal by a dc bias voltage. From this piezoresponse result, it was found that PZT islands had ferroelectricity.