Site selective inelastic electron tunneling spectroscopy probed by isotope labeling.

We study inelastic scattering in alkanethiol self-assembled monolayers using isotope labeling and unambiguously determine which molecular vibrations are active in the inelastic electron tunneling spectroscopy. The selective deuteration of the molecule also allows us to show that the different parts of the molecule contribute approximately equally to inelastic signal. Our first principles calculations confirm the experimental results and provide insights on electron transport through molecules.

Inelastic tunneling spectroscopy of alkanethiol molecules: high-resolution spectroscopy and theoretical simulations.

We investigate inelastic electron tunneling spectroscopy (IETS) for alkanethiol self-assembled monolayers (SAM) with a scanning tunneling microscope and compare it to first-principles calculations. Using a combination of partial deuteration of the molecule and high-resolution measurements, we identify and differentiate between methyl (CH3) and methylene (CH2) groups and their symmetric and asymmetric C-H stretch modes. The calculations agree quantitatively with the measured IETS in producing the weight of the symmetric and asymmetric C-H stretch modes while the methylene stretch mode is largely underestimated. We further show that inelastic intermolecular scattering is important in the SAM by plotting the theoretical current densities.

Inelastic electron tunneling spectroscopy of an alkanethiol self-assembled monolayer using scanning tunneling microscopy.

We report inelastic electron tunneling spectroscopy (IETS) of a C8 alkanethiol self-assembled monolayer using a scanning tunneling microscope (STM). High-resolution STM IETS spectra show clear features of the C-H bending and C-C stretching modes in addition to the C-H stretching mode, which enables a precise comparison with previously reported vibrational spectroscopy, especially electron energy loss spectroscopy data. Intensity variation of vibrational peaks with tip position is discussed with the STM IETS detection mechanism.