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 m ultilayer. We describe a method using a number of picosecond laser pul ses at 213 nm to achieve partial removal of the oxide overlayer on a p olycrystalline W substrate under UI-IV conditions. The process of oxid e removal was monitored by measuring the charge ui emitted photoelectr ons by using an appropriate anode (collector)-cathode (target) setup, and simultaneously, the surface reflectivity for each pulse, The tempo ral evolution of the photoelectric charge shows - as expected - an inc reasing tendency due to the lowering of the surface work function, but moreover - under certain experimental conditions - it shows the prese nce of several kinks, which are interpreted as a sign of changes in th e surface morphology. The results are discussed within the frame of a model describing mono/multilayer desorption phenomena. (C) 1998 Elsevi er Science B.V.