OPTICAL REFLECTION STUDY OF ADSORPTION OF NITROGEN ON A W(100) SURFACE

The process of nitrogen adsorption on a W(100) surface has been invest igated nondestructively by a surface photoabsorption method. Reflectan ce of p-polarized light incident near the Brewster angle was measured in the photon-energy range from 1.6 to 5.0 eV. Its exposure dependence up to 64 L (1 L = 1 x 10(-6) Torr s) is quite similar to that of the work function, which revealed two kinds of adsorption sites. The data are then converted into the variation of the surface dielectric functi on for an electric field tangential to the surface, which suggests tha t two optical transitions appear around 2.7 and 3.7 eV as the first ki nd of adsorption site is occupied, while the 2.7 eV transition shifts to higher energy as the second kind of adsorption proceeds. The induce d surface electronic states are briefly discussed with the aid of the published results of ultraviolet photoemission spectroscopy.