PULSED-LASER ABLATION OF A SINGLE-CRYSTAL CADMIUM TUNGSTATE (010) SURFACE STUDIED BY TIME-OF-FLIGHT MASS-SPECTROMETRY

Pulsed laser ablation of a cadmium tungstate (CdWO4)(010) surface was studied by time-of-flight mass spectrometric analysis at 532 and 266 n m. Single crystal CdWO4(010) surfaces with fewer defects than in previ ous work [J. Appl. Phys. 77. 6581 (1995)] are used, from which the kin etic energy (KE) of O-2(+) increased linearly with laser fluence. The KE observed at 266 nm was four times larger than that at 532 nm. This result can be explained by the difference between absorption coefficie nts of the plasma formed at the two laser wavelengths. This fact sugge sts an inverse bremsstrahlung process in which the desorbed species ar e accelerated in the flight path by the remaining part of the laser pu lse. The desorption process was studied by changing the temperature of the CdWO4 target from 100 to 900 K at a constant laser fluence. As th e temperature of the CdWO4 target increased, intensities of desorbed s pecies increased while their KEs were almost constant. These results c an be explained well in terms of a temperature dependence of the therm al desorption process of the photochemically formed desorption precurs ory state. The activation energy (0.3 eV) implies that the desorption precursory species are physisorbed on the surface. The data were analy zed with shifted Maxwell-Boltzmann velocity distributions, in which Ma xwell-Boltzmann temperatures and Mach numbers were elucidated as funct ions of both laser fluence and CdWO4 target temperature. (C) 1998 Amer ican Institute of Physics.