J.F. Owen

Surface-enhanced Raman scattering of water adsorbed on silver electrodes

Abstract Temporal evolution of the Raman spectra of H2O, D2O and HDO during an oxidation-reduction cycle of a Ag electrode in aqueous 1 M KCl or KBr has been recorded with an optical multichannel analyzer. Surface enhanced Raman spectra of the adsorbed water are readily observable and are different from the Raman spectra of bulk water.

Irreversible loss of adatoms on Ag electrodes during potential cycling determined from surface enhanced Raman intensities

Abstract Surface enhanced Raman scattering of adsorbates (Ag0-Cl−, H2O and pyridine) on Ag electrodes in 1M KC1 and 1M KCl+0.05M pyridine electrolytes was monitored continuously with an optical multichannel analyzer system as the electrode potential was cycled over various ranges within nonfaradaic regions of the oxidation-reduction cycle. A systematic investigation was performed of the potential dependence of SERS of pyridine in 1M KX + 0.05M pyridine electrolytes, where X = F, Cl, Br and I. Since the surface coverage of the adsorbates is reversible with potential cycling within a potential range, it was possible to determine potential dependences of the irreversible loss in the SERS enhancement factor which occurs as the electrode potential is ramped toward the potential of zero charge (PZC). The results provide strong support for the role of adatoms on the electrode surface in the overall enhancement mechanism. There is evidence that the strongly bound adsorbates immobilize the adatoms at positive potentials but allow the adatoms to migrate and become lost at surface defects as the potential approaches the PZC where the adsorbates are less tightly bound.

Surface enhanced second-harmonic generation from Ag electrodes and adsorbates during electrochemical cycling

Second-harmonic generation from the Ag electrode surface and its adsorbate (AgCl or Ag2SO4) is measured. Temporal correlation of the second-harmonic intensity with the electro-chemical cyclic voltammogram is made and is compared with the evolution of the surface enhanced Raman scattering from the adsorbate during an oxidation-reduction cycle. The evolution of the diffused second-harmonic intensity from the Ag electrode and adsorbate from mechanically and etchant roughened surfaces to fully developed electrochemically roughened surfaces is presented. Laser radiation induced surface morphology changes of the silver electrode surface is noted from scanning electron micrographs.

Laser illumination effects on the surface morphology, cyclic voltammetry, and surface-enhanced raman scattering of Ag electrodes

Abstract Scanning electron microscopy reveals that the structure of the Ag electrode is notably altered by laser illumination during electrochemical oxidation and reduction in 1 M KX (X = 1, Br, Cl, and F) electrolytes. Laser illumination also influences the voltammogram in 1 M Kl, the intensities of the SERS of adsorbed H 2 O and pyridine, and the intensities of selected points in the featureless background of the SERS spectra.

Competition among adsorbed species for surface sites on Ag electrodes as determined by SERS

The surface enhanced Raman scattering intensity from halides (F−, Cl−, Br−, and I−), water, and pyridine adsorbed on a Ag electrode has been measured as a function of electrode potential. Competition is evident among the adsorbed species for surface sites on the Ag electrode during the electrochemical oxidation-reduction cycle. Furthermore, the presence of pyridine in the electrolyte influences the adsorption of halides and water.

The metal cation effect on the sers of interfacial D2O and H2O

Abstract The surface enhanced Raman scattering (SERS) line shape and potential dependence of interfacial water in electrolytes containing Cl− ions are dependent upon the hydration energy of the metal cation in the electrolyte. Two groups of cations, one with lower hydration energies (Cs+, Rb+, and K+), and one with higher hydration energies (Na+, Li+, Ba2+, Sr2+, Ca2+, and Mg2+), give rise to distinct SERS behavior. It is postulated that the cations influence the orientation of D2O and H2O molecules at the Ag electrode-electrolyte interface.

Raman scattering from Pt(CN)42− adsorbed on Pt colloids

Abstract Raman scattering from Pt(CN) 4 2− adsorbed on Pt colloids (average diameter of 16 A) is compared with the Raman signal from the same amount of Pt(CN) 4 2− in solution. The wavelength dependence of the adsorbate Raman intensity is measured from 308 to 647 nm and compared with a Lorenz/Mie calculation of the enhancement factor for the electromagnetic field intensity on the surface of a Pt sphere as a function of sphere radius and incident wavelength.

Increased enhancement in surface enhanced raman scattering from Ag electrodes with the addition of pyridine to the electrolyte

Abstract The addition of pyridine to a 1 M KCl electrolyte before the oxidation—reduction cycle (ORC) of a Ag electrode significantly increases the surface enhanced Raman scattering (SERS) intensities of the H 2 O and Ag 0 -Cl − stretching modes. The increase in the enhancement can be attributed to the fact that Ag 0 adatoms, formed during the ORC, are stabilized by adsorbed pyridine complexes. The addition of pyridine after the ORC does not affect the H 2 O and Ag 0 -Cl − SERS intensities.

Sers of H2O adsorbed on a Ag electrode: The role of high salt concentration

Abstract Surface enhanced Raman scattering (SERS) of H 2 O adsorbed on Ag electrodes has been investigated with the aim of distinguishing between the effect o

Sers of H2O, pyridine and halides adsorbed on Ag electrodes during electrochemical cycling

Abstract Recent investigations in this laboratory on surface enhanced Raman scattering (SERS) from H 2 O, Ag 0 −X − , and pyridine species adsorbed on Ag electrodes in 1 M KX (X=Cl, Br, I, and F) electrolytes are reviewed. Use of an optical multichannel analyzer has allowed simultaneous monitoring of the SERS peaks over a 1200 cm −1 range as the electrode potential is continuously cycled through the oxidation-reduction cycle (ORC) or is repeatedly cycled in a nonfaradaic region of the ORC. Laser-induced changes in the SERS intensities, electrode surface morphologies, and cyclic voltammograms are noted. The results indicate potential dependent competition among the adsorbates for sites on the Ag surface. The voltage dependence of the irreversible loss in the enhancement factor provides evidence for the role of adatoms in the SERS enhancement mechanism.