Molecular hydrogen evolution from bulk crystalline silicon pretreated withthermal hydrogen atoms

Temperature-programmed desorption (TPD) from Si(100), preexposed to gas-pha se atomic hydrogen at substrate temperatures (T-s) of 415 and 635 K, exhibi ts a new H-2 peak (alpha(1)) at 850 K in addition to the well-known beta(1) (780 K) and beta(2) (670 K) H-2 peaks. Dosing with D atoms after H atom ex posure shows that H in the beta(1) and beta(2) states, but not alpha(1), is replaced by D atoms, suggesting that the alpha 1 H-2 peak arises from the crystalline bulk. Large H exposures at T-s = 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 crystallin e bulk and surface etching. [S0163-1829(99)02120-7].