Thickness dependent electron stimulated desorption of thin epitaxial films of alkali halides

Thin epitaxial NaCl layers of various thicknesses have been deposited on (100) GaAs substrates and subsequently desorbed with a 1 keV electron beam. The film thickness was monitored with a quartz crystal microbalance and verified by recording the substrate Ga2p1/2(111 eV) photoelectron peak attenuation due to overlayer growth. Electronic and structural properties of the freshly prepared films were subsequently investigated in the attached analytical chamber by means of LEED, LEELS, and AES. The signal intensities of desorbed alkali and halogen atoms were detected with a quadrupole mass spectrometer. For the first time the thickness dependence of the alkali halide electron stimulated desorption (ESD) yield was determined in absolute units. The experimental results are well described by a simple diffusion equation indicating that range dependent transport processes are involved in ESD of alkali halides.