Adsorption and desorption of deuterium on partially oxidized Si(100) surfaces
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Adsorption and desorption of deuterium are studied on the partially oxidized Si~100! surfaces. The partialoxygen coverage causes a decrease in the initial adsorption probability of D atoms. The observed D2temperature-programmed-desorption ~TPD! spectra comprise of multiple components depending on the oxygencoverage (u O). For u O50.1 ML the D2 TPD spectrum is deconvoluted into four components, each of whichhas a peak in the temperature region higher than the D2 TPD peaking at 780 K on the oxygen free surface. Thehighest TPD component with a peak around 1040 K is attributed to D adatoms on Si dimers backbonded by anoxygen atom. The other components are attributed to D adatoms on the nearest or second nearest sites of theO-backbonded Si dimers. D adatoms on the partially oxidized Si surfaces are abstracted by gaseous H atomsalong two different abstraction pathways: one is the pathway along direct abstraction ~ABS! to form HDmolecules and the other is the pathway along indirect abstraction via collision-induced-desorption ~CID! of Dadatoms to form D2 molecules. The ABS pathway is less seriously affected by oxygen adatoms. On the otherhand, the CID pathway receives a strong influence of oxygen adatoms since the range of surface temperatureeffective for CID is found to considerably shift to higher surface temperatures with increasing u O . Gradualsubstitution of D adatoms with H atoms during H exposure results in HD desorption along the CID pathway inaddition to the ABS one. By employing a modulated beam technique the CID-related HD desorption is directlydistinguished from the ABS-related one.
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