Initial stage of NO adsorption on Si(100)-(2 x 1) studied by synchrotron radiation photoemission and photodesorption

The NO adsorption on the Si(100)-(2 x 1) surface was investigated by synchr otron radiation photoemission and photodesorption in the energy ranges incl uding the valence band and the Si 2p, N 1s and O 1s core levels. The study was performed both ass function of NO exposure and as a function of tempera ture in the range 20-300 K. The photoemission experiments show clear eviden ce of a dissociative adsorption process both at room temperature as well as at temperatures as low as 20 K. Furthermore, the silicon surface states ar e involved in the adsorption process. The core level spectroscopy shows a c omplex adsorption pattern of the atomic species, which might involve a sub- surface migration of nitrogen atoms. The photodesorption yields only O+ in the Si 2p and O Is energy ranges. No nitrogen ion desorption is detected. I n the Si 2p energy range the O+ photodesorption pattern follows the enhance d secondary electron yield when crossing the ionization threshold. In the O Is energy range the O+ photodesorption pattern is interpreted in terms of a partial sub-surface migration of oxygen atoms. (C) 2000 Elsevier Science B.V. All rights reserved.