TOPOGRAPHIC AND SPECTROSCOPIC ANALYSIS OF ETHYLENE ADSORPTION ON SI(111)7X7 BY STM AND STS

A study of the adsorption of ethylene C2H4 on Si(111)7 X 7 at room tem perature by scanning tunneling microscopy and scanning tunneling spect roscopy is reported. No significant change in the surface reconstructi on is observed. The spatial distribution of the surface reaction has b een analyzed on an atom-by-atom basis. Reacted and unreacted sites hav e been selectively imaged. A higher reactivity of the adatoms in the f aulted subunits with respect to those in the unfaulted subunits is rep orted. Furthermore, the center adatoms are more reactive than the corn er adatoms. On the basis of this distribution of reacted atoms, the ad sorption site is assigned. The proposed bond model implies that an eth ylene molecule is bonded to a pair of adjacent Si adatom-rest atom. It is also shown that the adsorption process affects not only the surfac e atoms directly involved in the chemical bond with the ethylene molec ules, but also some of the neighboring adatoms.