Time dependence of surface enhanced Raman scattering at silver in the presence of underpotentially deposited lead and its implications for the roles of surface roughness

Abstract

sure (i.e., increasing the rate of the reaction) cannot alleviate this problem. The attainment of a limiting conversion due to isolation of active sites has been observed in many other solid-state polymerizations.23,24The dependence of conversion on polymerization pressure and annealing of the films prior to irradiation highlights the influence of morphology on gas-water interface polymerizations. The structural changes that occur in a monolayer of vinyl stearate upon polymerization can be understood by postulating the existence of crystallite "islands". This same model has been used to explain the morphology of a variety of monolayer films. 14'17,25'28 The distance between islands decreases with increasing surface pressure. The packing of the islands is pressure and time dependent. High surface pressures and long annealing times increase the effective crystallite size since these conditions permit neighboring islands to pack close to one another. Annealing removes defects which could be present in the film by providing enough time for the islands to pack closer and more efficiently.Electron microscopy studies by Ries and Walker have indicated the presence of crystallite islands in monomolecular films.26'28 An increase in surface pressure was shown to decrease the distance between adjacent islands.High surface pressures increased the effective crystallite size by causing neighboring islands to merge into one large island.

Metal Film over Nanosphere (MFON) Electrodes for Surface-Enhanced Raman Spectroscopy (SERS): Improvements in Surface Nanostructure Stability and Suppression of Irreversible Loss

“…The EM mechanism has several experimental signatures: (1) surface-enhanced Raman excitation spectra (SERES) that depend sensitively on surface nanostructure, the optical dielectric response functions of the metal, and the dielectric constant of the medium surrounding the roughened metal surface; − (2) the long-range (viz., a few nanometers) distance dependence; − (3) weak dependence of the EF on the chemical identity of the adsorbate; and (4) the existence of surface-enhanced second harmonic generation (SESHG), − surface-enhanced hyper-Raman scattering(SEHRS), , and other surface-enhanced spectroscopies (SES). In comparison, the involvement of the CHEM mechanism is manifested in a more subtle manner through (1) irreversible loss phenomena both in electrochemical-SERS (ECHEM-SERS) , and UHV-SERS; (2) laser excitation wavelength dependence in plots of SERS intensity vs electrode potential in ECHEM-SERS; , (3) observation of “first layer” SERS; , (4) strong dependence of the EF on the chemical identity of the adsorbate; (5) quenching of signals from “active sites” in UHV−SERS by submonolayer coverages of O 2 or Pd and in ECHEM-SERS by underpotential deposition (UPD) of submonolayer coverages of Tl, Cd, and Pb , on AgORC electrodes; and 6) thermal quenching of SERS of pyridine and H 2 O at AgORC electrodes. , …”

Adatom Hypothesis as a Predominant Mechanism of Surface Enhanced Raman Scattering: A Review of Experimental Argumentation

“…In general, these works had given the expected result: deposition of a less-SERS-active metal, specifically, lead [50,94,[152][153][154][155][156][157], aluminum [158], cadmium [152,159] (see also paper by Pettinger and Moerl in [34]), thallium [50,95,96,157,159,160], palladium [161][162][163], antimony (see paper by Liang et al in [36]), nickel and cobalt [164,165], and zinc [164] on SERS-active metals (in majority of cases, on silver) reduces SERS intensity on this metal or completely quenches it. However, deposition of a monolayer of thallium or lead on the surface of gold reduced SERS intensity by various adsorbates only by 2.5-4 times and deposition of a monolayer of mercury made practically no impact on SERS intensity of spectra for pyridine and ions of chloride, bromide, and thiocyanate, though it displaced line frequencies.…”