ADSORPTION OF ATOMIC-HYDROGEN ON SI(100)-2X1 AT 400-K

At 400 K, the absolute coverage of hydrogen (deuterium) adsorbed on th e Si(100)-2 X 1 surface for different hydrogen-induced surface reconst ruction phases was determined by nuclear reaction analysis and low-ene rgy electron diffraction. The transition from a monohydride 2 X 1 phas e to a dihydride plus monohydride 3 X 1 phase results in a distinct pl ateau on the curve of coverage versus exposure. With increasing atomic hydrogen (deuterium) exposure the coverage increases to about 1.7 mon olayers with concomitant deterioration of the 3 X 1 phase, indicating etching of silicon backbonds. Prolonged exposure leads to an effective saturation coverage of 1.6 +/- 0.1 monolayers with further degradatio n of the 3 X 1 symmetry.