The effect of thermal oxidation on laser-induced photoelectron emission during tensile deformation of polycrystalline aluminum

Abstract

Many metals emit electrons when exposed to UV radiation (photon energies 4 to 8 eV). Deformation can significantly affect the intensity of these emissions. In the case of reactive metals, these emissions are also altered by the presence of surface oxides. We have characterized the effect of thermal oxides on laser-induced photoelectron emission from commercially pure polycrystalline aluminum with a view toward using these emissions as a probe of deformation processes. The thickness of oxides produced by a range of annealing treatments in air was determined by x-ray photoelectron spectroscopy. Time-of-flight measurements on photoelectrons from these surfaces under 248 nm irradiation (5 eV photons) show two peaks: a fast peak which we attributed to electrons from metallic aluminum, and a slower peak, which may be due to electrons from interface states. Surface oxide films of sufficient thickness attenuate both peaks. We show that the sensitivity of the photoelectron signals to deformation varies with thermal oxidation pretreatments and oxide film thickness and that with the appropriate oxide thickness the total photoelectron intensity becomes a sensitive probe of deformation-related processes during tensile testing.