We investigate molecular ${\mathrm{H}}_2$ interaction with $\beta -\mathrm{SiC}\left(100\right)3\times 2$ and β-SiC(100) $c(4\mathrm{}\times 2)$ surfaces and with Si atomic lines by atom-resolved scanning tunneling microscopy and ultraviolet photoemission spectroscopy. While the $3\times 2$ surface reconstruction remains totally inert, the $c(4\mathrm{}\times 2)$ is highly reactive to ${\mathrm{H}}_2$ with sticking probabilities up to eight orders of magnitude higher than for $\mathrm{Si}\left(100\right)2\times 1.$ ${\mathrm{H}}_2$ is initially dissociated at up-dimer adsorption sites influencing the two neighbor down dimers. At higher exposures, hydrogen induces a $2\times 1$ surface transformation. This very high reactivity difference between $3\times 2$ and $c(4\mathrm{}\times 2)$ reconstructions allows nonreacted Si atomic lines formation on a hydrogenated surface.

• Received 29 January 2001

DOI:https://doi.org/10.1103/PhysRevB.63.201305