ETHYLENE REACTIVITY WITH SILICON SURFACE

Abstract

The clean Si (111)(7×7) surface has been exposed to ethylene ( C 2 H 4) doses, up to 7000 L (1 L =10-6 Torr ×1 s ) at most, under ultrahigh vacuum. The structural and electronic property changes of the surface have been studied by low energy electron diffraction (LEED), Auger electron spectrometry (AES) and photoemission yield spectroscopy (PYS). The interaction presents two types of kinetic adsorption, where the first is produced below 3000 L of C 2 H 4. In the first step, the ethylene molecule is adsorbed molecularly and the initial sticking coefficient S 0 is very low (S0≈2×10-3). At the saturation (≈ 5000–6000 L), the valence band is fitted by a power law (E — 4.42)2.5 eV .1,2 The surface is then a stronger scattering for photoemitted electrons. We attribute this result, produced at the second step of adsorption, to the C 2 H 4-π orbital and hydrogen liberated by this molecule, which break the Si – Si surface bonds.