Surface charge dynamics on air-exposed ferroelectric Pb(Zr,Ti)O-3(001) thin films

Probing of the free surface ferroelectric properties of thin polar films can be achieved either by estimating the band bending variance under the top-most layer or by studying the extent of the extrinsic charge accumulated outside the surface. Photoemitted or incoming low-energy electrons can be used to characterize locally both properties in a spectromicroscopic approach. Thin ferroelectric lead zirco-titanate (PZT) is investigated by combining low energy/mirror electron microscopy (LEEM/MEM) with photoemission electron microscopy (PEEM) and high-resolution photoelectron spectroscopy (XPS). Significant extrinsic negative compensation charge is proven to accumulate on the surface of the outward polarized thin film, indicated by high MEM-LEEM transition values, up to 15.3 eV, and is correlated with the surface electrostatic potential, which can be partially screened either by electrons interacting with the sample or by soft X-rays through the ejection of secondary electrons and generation of positive charge under the surface. A radiation-induced surface charge compensation effect is observed. The study indicates that air-exposed high quality ferroelectric thin films show large negative surface potentials, determined locally on the surface, which are nevertheless sensitive to beam damage and molecular desorption. These values represent a confirmation of previously estimated surface potential energy values determined from the LEED data on clean surfaces.

Automated summary

The free surface ferroelectric properties of thin polar films can be studied by estimating band bending variance or by analyzing the extrinsic charge outside the surface. In this study, the ferroelectric lead zirco-titanate (PZT) is investigated using a combination of low energy/mirror electron microscopy (LEEM/MEM), photoemission electron microscopy (PEEM), and high-resolution photoelectron spectroscopy (XPS). The results show a significant accumulation of extrinsic negative compensation charge on the outward polarized thin film surface, indicating a correlation with the surface electrostatic potential. It is observed that air-exposed high-quality ferroelectric thin films have large negative surface potentials, which are sensitive to beam damage and molecular desorption.