X-ray induced electron stimulated desorption versus photon stimulated desorption: NH 3 on Ni(110)

Abstract

Abstract The X-ray induced desorption of H+ ions from NH3 layers adsorbed at T = 90 K on Ni(110) has been compared to the corresponding total electron yield (TY) in the photon energy range 390 to 900 eV. The H+ yield exhibits a jump at the N K-edge and the Ni L-edge which inversely varies with the NH3 layer thickness. The H+ Ni L-edge jump is closely correlated to the TY jump. Both vanish for the saturated NH3 multilayer, indicating that the observed Ni L-edge jump in the H+ yield is exclusively due to X-ray induced electron stimulated desorption (XESD). At the N K-edge, the near edge absorption fine structure of the H+ yield and TY of the saturated NH3 multilayer are distinctly different. This is interpreted as the H + yield being the superposition of direct photon stimulated ion desorption (PSID) and XESD. Based on the observed variation of the H+ yield near edge fine structure with varying NH3 layer thickness, a deconvolution of the PSID and XESD contributions is used to derive the relative contribution of PSID versus XESD to be 40% versus 60%, respectively. The relevance of this result for future PSID-SEXAFS studies is discussed. For monolayer NH3 on Ni(110) the polarization dependence of the N K-edge fine structure in the N(KVV) Auger yield indicates that the symmetry axis of NH3, is perpendicular to the surface.