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 nm. Single crystal CdWO4(010) surfaces with fewer defects than in previous work [J. Appl. Phys. 77. 6581 (1995)] are used, from which the kinetic 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 coefficients of the plasma formed at the two laser wavelengths. This fact suggests an inverse bremsstrahlung process in which the desorbed species are accelerated in the flight path by the remaining part of the laser pulse. The desorption process was studied by changing the temperature of the CdWO4 target from 100 to 900 K at a constant laser fluence. As the temperature of the CdWO4 target increased, intensities of desorbed species increased while their KEs were almost constant. These results can be explained well in terms of a temperature dependence of the thermal desorption process of the photochemically formed desorption precursory state. The activation energy (0.3 eV) implies that the desorption precursory species are physisorbed on the surface. The data were analyzed with shifted Maxwell-Boltzmann velocity distributions, in which Maxwell-Boltzmann temperatures and Mach numbers were elucidated as functions of both laser fluence and CdWO4 target temperature. (C) 1998 American Institute of Physics.