Application of (e,2e) spectroscopy for studying surface states of W(001)

We applied the experimental technique of low energy (e,2e) spectroscopy in back-reflection geometry to measure the two-dimensional energy distribution s of correlated electron pairs excited by 20 eV primary electrons from a cl ean and oxygen covered W(001) surface. For the first time the contribution of correlated electron pairs originating from two different W(001) surface states S-1 and S-2 was identified in the (e,2e) spectra, thus demonstrating the high surface sensitivity of low energy (e,2e) spectroscopy. It was fou nd that the generation of electron pairs from W(001) surface states is cons iderably suppressed by the adsorption of 0.1 L of oxygen. The binding energ ies and the k(parallel to)-distributions of these states as determined in o ur measurements are in a reasonable agreement with the photoemission data, (C) 1998 Elsevier Science B.V. Ail rights reserved.