THE ROLE OF SURFACE-DEFECTS IN LASER-INDUCED THERMAL-DESORPTION FROM METAL-SURFACES

Laser-induced thermal desorption of Na dimers from rough sodium surfac es adsorbed on quartz substrates has been studied. For this purpose, l aser pulses with lambda=532 and 1064 nm and 7 ns duration were used. T he kinetic energy distribution and the integral desorption signal of t he dimers were determined as a function of the laser fluence. Measurem ents were also performed after reducing the surface roughness by annea ling at different temperatures. The fluence dependence of the integral desorption rate exhibits a plateau which follows and precedes a sharp increase. The results indicate that the Na dimers come off preferenti ally from special sites of low binding energy and low coordination num ber. Two of these sites can be distinguished. They exhibit different a nnealing behavior, different binding energies and can be depleted sele ctively by choosing the laser fluence appropriately. (C) 1997 Elsevier Science B.V.