Selective resonance population in high resolution electron energy loss spectroscopy of 4-ethylbenzenethiol self-assembled monolayers on Au(1 1 1)

We have investigated the vibrational frequencies and excitation cross-section of self-assembled monolayers (SAMs) of 4-ethylbenzenethiol (CH3CH2(C6H4)SH) on Au(1 1 1) by high resolution electron energy loss spectroscopy (HREELS). Negative ion resonances were observed in the energy loss intensities as a function of the incident electron energy. Analysis of the C–H stretching modes indicates resonances of different energies are localised in both the ethyl and phenyl functional groups of the SAM molecules, which regulate the observed vibrational lineshape.