Add time:08/17/2019         Source:sciencedirect.com

Hydrogen desorption from two-dimensional (2D) and bulk-like (3D) erbium silicides on Si(111) has been investigated by means of thermal desorption spectroscopy (TDS) and high resolution electron energy loss spectroscopy (HREELS). By TDS, hydrogen is found to desorb as a single feature with a maximum in temperature located at 620 K on 2D silicide, whereas two desorption peaks at 460 K and 615 K, respectively, are measured on 3D silicide. These spectra are analyzed in the frame of the formulation developed by Redhead, and compared with hydrogen desorption from a monohydride Si(111) surface. On erbium silicide films, first-order kinetics is always observed in sharp contrast with the second-order kinetics measured for hydrogen desorption from the Si(111) surface. This remarkable behavior can be understood in terms of a pairing mechanism in which, for stability reasons, the H chemisorption sites appear in the form of pairs that contain either 0 (empty pair) or 2 (filled pair) H atoms. Using HREELS, two kinds of hydrogen chemisorption sites were identified prior to desorption. It is deduced that the features at 460 K on 3D and at 620 K on 2D erbium silicides are clearly related to concomitant hydrogen chemisorbed on the top layer silicon dangling bonds and in an interstitial site of the Er layer beneath. In contrast, the desorption peak at 615 K on bulk-like silicide is assigned to hydrogen absorption in bulk sites of the subsurface region.

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