Electronic structure of a cyclooctatetraene derivative COT-H on Ru( [formula omitted

Abstract

The electronic structure of a cyclooctatetraene derivative COT-H deposited on Ru( 1 0 1 ̄ 0 ) has been studied using ultra-violet photoemission spectroscopy (UPS). The highest occupied molecular orbital (HOMO) of COT-H and the other OCT-H derived features are located at about 1.8, 3.8, 5.6, 7.9 and 10.2 eV in binding energy, respectively. With increasing thickness of the COT-H layer, the work function decreases from a value of 4.3 eV on the Ru substrate to a COT-H bulk value of 3.3 eV at a COT-H thickness of 25 Å. The sharp decrease in work function at the beginning of COT-H deposition is attributed to dipole layer formed at the interface. Using the results from UPS spectra, and taking the optical band gap of 3.3 eV as the HOMO–LUMO band gap of COT-H, the ionization potential of COT-H is determined to be 5.1 eV, and the energy diagram at the COT-H/Ru interface is obtained.