Molecular hydrogen evolution from bulk crystalline silicon pretreated with thermal hydrogen atoms

Temperature-programmed desorption (TPD) from Si(100), preexposed to gas-phase atomic hydrogen at substrate temperatures (Tₛ) of 415 and 635 K, exhibits a new H₂ peak (α₁) at 850 K in addition to the well-known β₁ (780 K) and β₂ (670 K) H₂ peaks. Dosing with D atoms after H atom exposure shows that H in the β₁ and β₂ states, but not α₁, is replaced by D atoms, suggesting that the α₁ H₂ peak arises from the crystalline bulk. Large H exposures at Tₛ=635 and 415 K produce 3.2 and 4.2 ML hydrogen, respectively, in TPD, which in combination with LEED data supports a model involving concomitant H atom diffusion into the crystalline bulk and surface etching.