Direct determination of absolute monolayer coverages of chemisorbed C2H2 and C2H4 on Si(100)

A convenient kinetic uptake method has been employed to determine the absolute saturation monolayer coverage of C2H2 and C2H4 on a Si(100)(2×1) surface. Such measurements are important for postulating the structure of the chemisorbed hydrocarbon species on this surface. The saturation surface coverage for both chemisorbed molecules at 105 K is 2.5(±0.2)×1014 molecules/cm2 . This number is consistent with 1 hydrocarbon molecule per Si dimer site at monolayer coverage when the role of surface defects on Si(100) is considered. A di-σ bonding model for both molecules is proposed at saturation coverage.