Hydrogen evolution from atomically flat Si(111) surfaces exposed to 40% NH4F, oxygen-free water, or wet gas

Hydrogen evolved continuously when Si(111) wafers with atomically flat and hydrogen-terminated surfaces were immersed in aqueous 40% NH4F solution or oxygen-free water. The evolution of hydrogen was attributed to oxidative dissolution of silicon into the liquids. Although the dissolution rates were rather slow, the process could be sensitively traced by measuring the amount of hydrogen evolved. The rate of the hydrogen evolution was nearly proportional to the step densities existing on the Si(111) surface, suggesting that silicon dissolves from the step edges. On the basis of the rates of hydrogen evolution and the densities of steps, we determined the receding speeds of the monohydride steps to be about 39 and 7.5 nm min(-1) in 40% NH4F solution and in oxygen-free water, respectively, at room temperature. Continuous hydrogen evolution was also observed when atomically flat Si(111) wafers with dihydride steps were exposed to an inert gas containing water vapor. (c) 2006 The Electrochemical Society.