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 UI-IV conditions. The process of oxide removal was monitored by measuring the charge ui 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 mono/multilayer desorption phenomena. (C) 1998 Elsevier Science B.V.