Using scanning tunneling microscopy and spectroscopy, we have investigated the reaction of atomic hydrogen with the Si(111)-7×7 reconstructed surface. A simple picture evolves in which the reaction proceeds concurrently along two channels: a direct binding of the hydrogen atoms to the existing dangling bonds of the surface, and a slower removal of the uppermost Si layer and binding of the hydrogen atoms to the created dangling bonds of the next layer.

• Received 12 June 1990

DOI:https://doi.org/10.1103/PhysRevB.43.1816