Evidence of surface structural transformations during pulsed UV laser-induced oxide removal on polycrystalline W surfaces

A native oxide film on a metallic surface corresponds generally to a multilayer. We describe a method using a number of picosecond laser pulses at 213 nm to achieve partial removal of the oxide overlayer on a polycrystalline W substrate under UHV conditions. The process of oxide removal was monitored by measuring the charge of emitted photoelectrons by using an appropriate anode collector.–cathode target.setup, and simultaneously, the surface reflectivity for each pulse. The temporal evolution of the photoelectric charge shows – as expected – an increasing tendency due to the lowering of the surface work function, but moreover – under certain experimental conditions – it shows the presence of several kinks, which are interpreted as a sign of changes in the surface morphology. The results are discussed within the frame of a model describing monormultilayer desorption phenomena. q1998 Elsevier Science B.V.