In situ work function study of oxidation and thin film growth on clean surfaces

Abstract

Using a novel ultra high vacuum compatible Kelvin probe we have studied the work function ( φ) changes on semiconductors and metals occurring during basic surface processing, for example, surface cleaning, sputtering, oxidation and thin film growth. We show that damage of the 7×7 reconstruction due to Ar ion bombardment has a profound influence on the work function changes (Δ φ) during oxidation on the Si(111) surface, tending to decrease or even reverse the surface dipole. We have also followed the variable temperature oxidation kinetics of Si(111) in the range of 100–600 K and show that magnitude of the Δ φ peak during the initial adsorption curve decreases in a linear fashion with increasing substrate temperature. We interpret this as being due to the rapid onset of oxygen permeation through the surface layer at higher temperatures producing a reverse or zero net dipole. Combining work function data with a localized technique such as scanning tunnelling microscopy permits monitoring of surface processes at both microscopic and macroscopic levels. In conjunction with Professor Behm's group at Ulm University, Germany, we have monitored work function changes during evaporation of Al on Ru(0001) and show correlation between changes in φ with topographic features such as island growth mechanism, monolayer formation, etc.