Direct observation of single domains in poled (111) PZT (PbZr0.25Ti0.75O3) films

Abstract

Films of (111) oriented poled ferroelectric lead zirconate titanate (PZT) crystallites on (100)Si/SiO2/(111) Pt were investigated by scanning tunneling microscopy (STM), atomic force microscopy (AFM) and small angle X–ray scattering (SAXS).SAXS investigations allowed to estimate a mean value of domain thickness of 17.5nm. Exertion of stress (5.1×104Nm−2) to the film resulted in an increase of domain width of ∼1%.After metallization of the PZT surface with a Cr–Ni film of 5.2nm or a Ti film of 5.0nm thickness, domains were visible by STM measurements as parallel stripes on the surface with a width of 15–20nm. A downward vertical corrugation of 1.0–1.5nm typically occurred at the intersection site of domain walls with the surface. Its presence is ascribed to shear strain originating from coherency defects in the interface.High resolution AFM with electron beam deposited supertips on unmetallized samples revealed areas of typically several micrometers in diameter showing crystallites with perfectly aligned domains of 10–15nm width. The domains formed parallel slabs of twinned-crystallites with their polarization c-axis changing alternately from [001] to [010] direction. For a fully poled (111) PZT film, the c-axis of each (90°) domain is inclined towards the surface by 35° and tilted against the surface normal by +45 or −45°, respectively. These results generally confirm the Speck–Streiffer–Pompe–Romanov domain model which predicts for a (111) PZT film of 500nm thickness a polyvariant with alternating (90°) domains of 16.4nm width.