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 eV͒. 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 photons͒ 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.

Positive ion emission from oxidized aluminum during ultraviolet excimer laser irradiation

“…The oxide associated with electropolishing actually forms during the brief air exposure during the time interval between electrochemical treatment and sample mounting (approximately 10 min) and is 1-2 nm thick. 18,19 This is as thin as one can normally achieve without careful in situ ion bombardment and annealing treatments. Figure 3 shows an Al þ TOF signal acquired during the first 100 pulses incident on a previously unexposed, electropolished surface at a fluence of only 10 mJ/cm 2 .…”

“…Electropolishing was performed in a 19:1 solution of room temperature acetic and perchloric acids for ten minutes at 40 V anode bias; these samples were briefly exposed to air after electropolishing, and therefore possess a thin oxide, typically 1-2 nm thick. 18,19 Anodization was performed in 0.05 M ammonium tartrate at room temperature for thirty minutes at 230 V bias; this treatment produces a dense barrier oxide about 300 nm thick. 20,21 After each treatment, the surfaces were cleaned with methanol to remove chemical residues.…”