Adsorption and desorption of deuterium on partially oxidized Si(100) surfaces

Abstract

Adsorption and desorption of deuterium are studied on the partially oxidized Si(100) surfaces. The partial oxygen coverage causes a decrease in the initial adsorption probability of D atoms. The observed ${\mathrm{D}}_{2}$ temperature-programmed-desorption (TPD) spectra comprise of multiple components depending on the oxygen coverage $({\ensuremath{\theta}}_{\mathrm{O}}).$ For ${\ensuremath{\theta}}_{\mathrm{O}}=0.1\mathrm{ML}$ the ${\mathrm{D}}_{2}$ TPD spectrum is deconvoluted into four components, each of which has a peak in the temperature region higher than the ${\mathrm{D}}_{2}$ TPD peaking at 780 K on the oxygen free surface. The highest TPD component with a peak around 1040 K is attributed to D adatoms on Si dimers backbonded by an oxygen atom. The other components are attributed to D adatoms on the nearest or second nearest sites of the O-backbonded Si dimers. D adatoms on the partially oxidized Si surfaces are abstracted by gaseous H atoms along two different abstraction pathways: one is the pathway along direct abstraction (ABS) to form HD molecules and the other is the pathway along indirect abstraction via collision-induced-desorption (CID) of D adatoms to form ${\mathrm{D}}_{2}$ molecules. The ABS pathway is less seriously affected by oxygen adatoms. On the other hand, the CID pathway receives a strong influence of oxygen adatoms since the range of surface temperature effective for CID is found to considerably shift to higher surface temperatures with increasing ${\ensuremath{\theta}}_{\mathrm{O}}.$ Gradual substitution of D adatoms with H atoms during H exposure results in HD desorption along the CID pathway in addition to the ABS one. By employing a modulated beam technique the CID-related HD desorption is directly distinguished from the ABS-related one.