Photoelectron diffraction imaging for C2H2 and C2H4 chemisorbed on Si(100)reveals a new bonding configuration

A new adsorption site for adsorbed acetylene on Si(100) is observed by phot oelectron imaging based on the holographic principle. The diffraction effec ts in the carbon Is angle-resolved photoemission are inverted (including th e small-cone method) to obtain an image of the atom's neighboring carbon. T he chemisorbed acetylene molecule is bonded to four silicon surface atoms. In contrast to the C2H2 case, the image for adsorbed C2H4 shows it bonded t o two Si surface atoms.