In Situ Scanning Tunneling Microscopy and X-ray Photoelectron Spectroscopy Studies of Ethylene-Induced Structural Changes on the Pt(100)-hex Surface

We have studied the structures of the Pt(100) surface in the presence of gas-phase ethylene at room temperature. High-pressure scanning tunneling microscopy shows that the hexagonal reconstruction on the clean Pt(100) surface is preserved under 1 Torr of C2H4, which produces an ethylidyne and di-sigma-bonded ethylene saturated surface. At 5 X 10(-6) Tort of C2H4, coadsorbed CO from the background gases lifts the reconstruction, with the excess Pt atoms from the hexagonal surface forming islands on the surface. The chemisorption of CO from background gases in the vacuum system, in the nominally pure C2H4, is revealed by ambient-pressure X-ray photoelectron spectroscopy.