The Characteristics And Applications Of Functionalized Molecules Surface Spectrum On Metal Nanoparticles

Surface-enhanced Raman scattering of p-aminothiophenol (PATP) molecules adsorbed on electrochemically roughened silver electrode and in an Au/PATP/Ag molecular junction assembled on indium-doped tin oxide electrode was investigated under near IR excitation. Contribution from chemical enhancement can be relatively amplified, due to the near IR excitation is far way from the surface plasmon resonance of the nanosized metal particles. For the Au/PATP/Ag molecular junction, the energy required for the charge transfer process is much lower than that of the PATP molecules adsorbed on the electrochemically roughened silver electrode. Coadsorption of chloride ions on the metal nanoparticles may result in an alteration of the local Fermi level of the metal nanoparticles, leading to a better energy matching between the energy level of the interconnecting PATP molecules and the Fermi level of the metal nanoparticles.Surface-enhanced Raman scattering (SERS) of the 4-mercaptopyridine (4-MPy) molecules adsorbed on the electrochemically roughened silver electrodes were investigated under practical electrochemical conditions. The adsorbed 4-MPy molecules are converted from a perpendicular orientation to a parallel orientation as the electrode potential is successively changed from 0 to -1.0 V. The coordination of the nitrogen atom of the pyridine ring to the silver metal weakens the ability of the 4-MPy molecules with a parallel orientation to capture the proton, due to the distribution of the electron density of the nitrogen to the silver metal. The applied potential has large effect on the protonation/deprotonation process of the adsorbed 4-MPy molecules. More adsorbed 4-MPy molecules are protonated as the electrode potential becomes more negative. This is ascribed to the increase in the charge density both on the electrode surface and the nitrogen atom of the pyridine ring at the negative potentials.