Adsorption and Stability of π-Bonded Ethylene on GaP(110)

We have investigated the structural and electronic properties of individual ethylene molecules on the GaP(110) surface by combining low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) with density functional theory (DFT) calculations. Isolated molecules were adsorbed on in situ cleaved GaP(110) surfaces through ethylene exposures at 300 K and 15 K. DFT calculations suggest two possible stable adsorption geometries for a single ethylene molecule on GaP(110) at low temperature. High-resolution STM images, however, reveal only one adsorption geometry for this system, consistent with the site having the largest computed binding energy. Unlike adsorption of ethylene on other metallic and semiconducting surfaces, ethylene physisorbs to GaP(110) through a weak hybridization of molecular pi-states with substrate surface states, leaving the frontier molecular orbitals largely unperturbed. Differential conductivity spectra acquired on single molecules are consistent with self-energy corrected DFT calculations.