NITROGEN ADSORPTION ON A W(100) SURFACE STUDIED BY AN ANALYSIS OF ELECTRON-ENERGY-LOSS FINE-STRUCTURE

The influences of annealing and electron bombardment on the adsorption states of nitrogen on a W(100) surface have been investigated by an a nalysis of electron energy-loss fine structure (EELFS). The nitrogen K -edge EELFS were measured, and converted into radial distribution func tions using the Fourier transform to obtain the atomic distance betwee n nitrogen and tungsten. Nitrogen adsorption on a tungsten surface at 400 K induces the formation of a stable beta(2) state, and less stable beta(1) state above 0.5 ML. The nearest-neighbor inter-atomic distanc e drastically increases from 0.167 nm to 0.187 nm, which corresponds t o distance between beta(2)-nitrogen and tungsten in the second layer, when the surface is exposed at 0.5 ML and annealed at temperatures bet ween 920 K and 1020 K where the beta(1)-nitrogen desorbs. The temperat ure-dependent increase in the atomic distance means that annealing ind uces a lateral reconstruction of tungsten atoms in the top layer, whic h is reasonably interpreted with the contracted-domain structure. Bomb ardment of 2 keV electrons at the dose of 10 A s/cm(2) on the surface annealed at 770 K after exposing above 0.5 ML at 400 K converts some o f the beta(2) State into the beta(1) state, which may result in the de crease in atomic distance between nitrogen and tungsten. (C) 1998 Else vier Science B.V.