ANGLE-RESOLVED ANALYSIS OF DESORBED SPECIES IN PULSED-LASER ABLATION ON CADMIUM TUNGSTATE SINGLE-CRYSTAL SURFACES WITH DIFFERENT ORIENTATIONS STUDIED BY TIME-OF-FLIGHT MASS-SPECTROMETRY

Angular distributions of species desorbed by pulsed laser ablation wer e studied on three single crystal CdWO4 surfaces with different orient ations. Sharp angular distribution of desorbed species to surface norm al was analyzed with nth order of cos a dependency. The difference of n values of desorbed ionic O-2(+) species on the three different surfa ces was explained by a secondary thermal effect. However, the characte ristic sharp angular distribution was interpreted to be clued by an in itial photochemical process. The n values of desorbed O+, Cd+, W+ and WO2+ were simultaneously compared on the surfaces. The lighter-mass sp ecies showed sharper angular distributions than the heavier-mass speci es. The result was explained by a collision between them. Pseudo Mach numbers of ablated species were studied as a function of desorbing ang le a to evaluate both the flow velocity factor and the collision facto r. (C) 1998 Elsevier Science B.V. All rights reserved.