PHOTOEMISSION OF ADSORBED XENON STUDY OF SURFACE-DEFECTS GENERATED BY ION-BOMBARDMENT OF NI(111)

The surface defect density generated by 1.0 keV Ar+ ion bombardment of a Ni(111) crystal at 88 K is studied with photoemission of adsorbed xenon. (PAX). The defect sites are distinguished by the position of the Xe 3d5/2 peak. The peak position reflects the local electrostatic potential at the Xe adsorption site that is modified at a defect site from the terrace sites by the electron-density smoothing process. The PAX spectra of the ion bombarded surfaces have peaks at 669.3 eV from Xe adsorbed at terrace sites, 670.0 eV from Xe at step sites, and 671.0 eV. We ascribe the latter peak to Xe adsorbed at small vacancy islands or kink sites where the Xe atom can experience a larger electrostatic potential perturbation compared to Xe adsorbed at a step site producing the additional 1 eV shift to higher binding energy. The PAX spectra are acquired with two ambient Xe pressures, 7 X 10(-10) and 5 X 10(-6) Torr. At low Xe pressure, the total Xe coverage and step peak intensity rapidly increase with low ion fluence with initial rates of 3 Xe atoms/ion for the total Xe coverage and 1. 5 Xe atoms/ion for the step sites in the first 2.9 X 10(13) ions/cm2 fluence. In contrast, at high Xe pressure, the total Xe coverage, and the terrace peak intensity decrease rapidly in the same region of ion fluence with initial rates of - 3 Xe atoms/ion for the total Xe coverage and - 5 Xe atoms/ion for the terrace peak. The rate of decrease of the terrace peak intensity corresponds to 15 Ni terrace atoms uncovered per incident ion since the large Xe atom covers three terrace atoms. The loss of Xe coverage on terrace sites likely results from the destruction of the long-range order in the Xe two-dimensional solid on the ion bombardment roughened surface.