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Abstract

The adsorption of D₂ on Si(100) has been investigated by means of supersonic molecular beam techniques. We have succeeded in measuring the dependence of the molecular D₂ sticking coefficient S on surface temperature T_s and nozzle temperature T_n. The sticking coefficient increases gradually in the range 300≤T_n≤1040 K. The influence of increased v=1 population has not been deconvoluted from the effects of translational energy alone. The dependence on T_s is more interesting. With an incident translational energy of 65 meV, S rises from a value insignificantly different from the background level to a maximum value of (1.5±0.1)×10−5 at T_s=630 K. The decrease in the effective sticking coefficient beyond this T_s is the result of desorption during the experiment. Having established that S increases with both increasing molecular energy and increasing sample temperature, we have demonstrated directly for the first time that the adsorption of molecular hydrogen on Si is activated and that lattice vibrational excitations play an important role in the adsorption process.