Chemisorption and thermally activated etching of Si(100)-2×1 by iodine

Scanning tunneling microscopy (STM) and photoelectron spectroscopy were used to investigate the adsorption and thermally activated etching of Si(100)-2×1 by ${\mathrm{I}}_2$. STM indicated that adsorption at room temperature was dissociative on Si dangling bonds without dimer disruption. Surface bonding favored occupation of both dimer atoms, but steric hindrance prevented occupation of adjacent dimers in the initial stages of adsorption. Thus, c(4×2) domains were created at ∼0.5-ML coverage where alternate dimers within the same row were iodine terminated and adjacent rows were out of phase. These domains converted to a 2×1 structure when the exposure was increased. Exposure at temperatures in the range 700–900 K resulted in layer-by-layer etching with temperature-dependent morphologies and residual iodine coverages. The Si 2p photoemission spectra showed that Si-I bonds, ${\mathrm{Si}}^{+}$, represent the dominant chemisorption structure in all cases.