Ultrafast dynamics of the dipole moment reversal in a polar organic monolayer.

Pyridine layers on Cu(110) possess a strong electric field due to the large dipole of adsorbed pyridine. This electric field is visible as an enhanced sum frequency response from both the copper surface electrons and the aromatic C-H stretch of pyridine via a third order susceptibility. In response to a visible pump pulse, both surface electron and C-H stretch sum frequency signals are reduced on a subpicosecond time scale.

Detection of Metal-Molecule-Metal Junction Formation by Surface Enhanced Raman Spectroscopy.

Vibrational modes play a key role in characterizing metal-molecule-metal junctions, but their detection currently either requires single-molecule sensitivity or the generation of defect-free large-scale junctions. Here we demonstrate that surface-enhanced Raman scattering (SERS) on nonideal surfaces can provide a significant amount of information despite many defects in the layer. We determine the vibrational signature of the molecular electronic junction for palladium ions complexed and reduced on 4-mercaptopyridine adsorbed on rough gold and gold nanoparticles using SERS and density functional theory.

Discrimination between hydrogen bonding and protonation in the spectra of a surface-enhanced Raman sensor.

We investigate the surface-enhanced Raman spectra of 4-mercaptopyridine on gold in a variety of acids. 4-Mercaptopyridine is a known pH sensor which exhibits characteristic spectral changes when the pH is changed. Here we show with the help of experiment and density functional calculations that the ring breathing mode is also highly sensitive to hydrogen bonding.