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An equimolar mixture of hydrogen and iodine atoms adsorbed on the Si(100) surface is generated by adsorption of iodoethane and annealing to 570 K (which causes ethyl groups to undergo hydrogen elimination and ethylene to desorb). Multiple internal reflection-Fourier transform infrared spectroscopy (MIR-FTIR) shows that the adsorbed hydrogen is distributed among several configurations. After annealing to 700 K, the spectrum shows only a single configuration, which is assigned to surface dimers that are occupied by one hydrogen and one iodine atom. Density functional theory calculations indicate that these mixed-occupation dimers are not energetically favored over other doubly occupied configurations (two H atoms or two I atoms). This evidence indicates that, in contrast to other ordering phenomena in surface adlayers, the ordering in this case is a kinetic effect and is not driven by thermodynamics.

The adsorption and chemical transformation of iodoethane were studied on a Si(100)-2×1 surface using multiple-internal reflection Fourier-transform infrared spectroscopy (MIR-FTIR). The C–H and Si–H stretch vibrations served as fingerprints of all surface transformations. Although ethyl groups are stable on the Si(100)-2×1 surface at room temperature, thermal annealing studies suggest the reaction-limited formation of ethylene, a major hydrocarbon reaction product, accompanied by the loss of hydrogen, which is left on the surface until the temperature of recombinative H2 desorption is reached. Variable temperature studies indicate that ethyl groups are the only hydrocarbon entities on a surface up until the hydrogen elimination temperature. The positions of Si–H stretching bands suggest that a mixture of surface sites is formed at temperatures between 300 K and 600 K. However, the majority of surface hydrogen forms SiH–SiI surface species as the surface temperature reaches 700 K.