The role of surface defects in laser-induced thermal desorption from metal surfaces

Abstract

Laser-induced thermal desorption of Na dimers from rough sodium surfaces adsorbed on quartz substrates has been studied. For this purpose, laser pulses with λ = 532 and 1064 nm and 7 ns duration were used. The kinetic energy distribution and the integral desorption signal of the dimers were determined as a function of the laser fluence. Measurements were also performed after reducing the surface roughness by annealing 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 preferentially from special sites of low binding energy and low coordination number. Two of these sites can be distinguished. They exhibit different annealing behavior, different binding energies and can be depleted selectively by choosing the laser fluence appropriately.