Weak adsorption of ethylene on GaAs(100)

Hydrocarbon molecules are an important source of carbon contamination in semiconductor growth processes. We have investigated the adsorption of ethylene, ${\mathrm{C}}_2{\mathrm{H}}_4,$ on the As-terminated GaAs(100) surface at 100 K in ultrahigh vacuum with high-resolution electron-energy-loss spectroscopy. We find that the ethylene molecules are predominantly adsorbed weakly (physisorbed) on the surface with the $\mathrm{C}\mathrm{=}\mathrm{C}$ double bond parallel to the As surface dimers. This behavior differs significantly from the adsorption of ${\mathrm{C}}_2{\mathrm{H}}_4$ on Si(100), as predicted by recent theoretical calculation. When the surface temperature is increased from 100 to 300 K, some of the physisorbed ${\mathrm{C}}_2{\mathrm{H}}_4$ molecules convert to chemisorbed species.