Si(001) surface variation with annealing in ambient

Monohydride termination and surface variation of (Formula presented) by annealing in (Formula presented) ambient has been investigated with scanning-tunneling-microscopy (STM). A clean (Formula presented) surface was annealed and cooled to room temperature in (Formula presented) ambient with various partial pressure of (Formula presented) Hydrogen termination of the surface is observed when (Formula presented) exceeds (Formula presented) and complete monohydride termination is obtained with (Formula presented) The results are reproduced well by the calculation using the temperature-dependent sticking coefficient of molecular (Formula presented) on Si(001). [Kolasinski et al., J. Chem. Phys. 101, 7082 (1994)]. The surface obtained by (Formula presented) annealing shows characteristic (Formula presented)-step shape, which has a long kink-free portion connected by a long kink. It is shown that the etching of Si surface by (Formula presented) is not responsible for the determination of the shape of (Formula presented) steps. Instead, the presence of passivating hydrogen at the temperature above the frozen temperature of step motion on Si(001) is the origin of the characteristic step shape.