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

The NO adsorption on the Si(100)-(2×1) surface was investigated by synchrotron radiation photoemission and photodesorption in the energy ranges including the valence band and the Si 2p, N 1s and O 1s core levels. The study was performed both as a function of NO exposure and as a function of temperature in the range 20–300 K. The photoemission experiments show clear evidence of a dissociative adsorption process both at room temperature as well as at temperatures as low as 20 K. Furthermore, the silicon surface states are involved in the adsorption process. The core level spectroscopy shows a complex 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 1s energy ranges. No nitrogen ion desorption is detected. In the Si 2p energy range the O+ photodesorption pattern follows the enhanced secondary electron yield when crossing the ionization threshold. In the O 1s energy range the O+ photodesorption pattern is interpreted in terms of a partial sub-surface migration of oxygen atoms.