Book ChapterDOI
Raman Spectroscopy of Molecular Monolayers in Inelastic Electron Tunneling Spectroscopy Junctions
J. C. Tsang,J. R. Kirtley +1 more
- pp 499-508
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TLDR
In this paper, it has been shown that strong Raman scattering can be obtained from a monolayer of adsorbed molecules, which is known as Raman cross-sections of a pyridine molecule.Abstract:
The intensity of Raman scattering from molecules in solution suggests that the observation of Raman scattering from molecular monolayers should be very difficult given the small number of molecules involved. However, recent experimental work on Raman scattering from molecules adsorbed on the surface of metal electrodes in electrochemical cells has shown that strong Raman scattering can be obtained from a monolayer of adsorbed molecules.1,2,3 It has been estimated that the Raman cross section of a pyridine molecule adsorbed on an electrochemically prepared Ag surface in a KC1 solution is six orders of magnitude larger than for the same molecule in solution.2 Although this large enhancement has stirred considerable experimental and theoretical interest, its microscopic origins remain unknown.4,5,6read more
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Journal ArticleDOI
Liquid Wetting on Metal Surfaces and the Heat of Immersion/Adsorption in Lubrication
F. E. Lockwood,K. Bridger +1 more
TL;DR: In this paper, the authors collected persuasive qualitative experimental support to this effect and proposed a quantitative treatment deriving the friction or wear coefficients as functions of the heats of adsorption of boundary lubricant molecules.
Book ChapterDOI
Tunnel Junction Structures
Abstract: We have observed Raman scattering from molecular layers absorbed on the oxide layer in Al-Al2O3-metal tunnel junctions1-6. The observation of these signals was remarkable, since the molecular layers were present only in monolayer coverages, and were separated from the incident laser beam by a typically 20 nm thick metal film. In fact, the Raman scattering could be measured because the observed signal levels were up to ~ 5x104 times more intense per molecule than expected from similar measurements on bulk specimens. Therefore, surface enhanced Raman scattering, analogous to that observed in electrochemical cells and in vacuum (and discussed in other Chapters in this volume), can be present in tunnel junction structures as well. Our experiments conclusively demonstrated the role of electromagnetic resonances in surface enhanced Raman scattering: 1) Junctions with Ag second metal electrodes had the most intense spectra, with Cu and Au ~ 100 times weaker, and no signals were observed for Pb, Sn, In, or Al second metal electrodes. This is consistent with the fact that low imaginary parts of the dielectric response of the metals were required for strong electromagnetic resonances. 2) We found that the observed spectra were most intense for tunnel junctions evaporated on highly roughened substrates. Surface roughness was required to couple the surface electromagnetic resonances to external radiation.
References
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Journal ArticleDOI
Surface raman spectroelectrochemistry: Part I. Heterocyclic, aromatic, and aliphatic amines adsorbed on the anodized silver electrode
TL;DR: In this article, the authors verified the remarkable sensitivity of Raman spectroscopy for the study of adsorbed pyridine on a silver surface, and extended its applicability to other nitrogen heterocycles and amines.
Journal ArticleDOI
Surface roughness and the enhanced intensity of Raman scattering by molecules adsorbed on metals
TL;DR: In this article, the anomalous intensity arises from preresonant or resonant excitations of conduction electron resonances in adsorbate covered metal bumps on the surface, which form a two-dimensional colliodlike layer which displays a collective resonance at a frequency which depends on the bump density.
Journal ArticleDOI
Molecular Vibration Spectra by Inelastic Electron Tunneling
John J Lambe,R. C. Jaklevic +1 more
TL;DR: In this paper, an experimental and theoretical study has been carried out on the process of inelastic tunneling between metal films, which gives rise to the observation of vibrational spectra for molecules contained in the junction region.
Journal ArticleDOI
“Giant” Raman scattering by adsorbed molecules on metal surfaces
TL;DR: In this paper, the authors attributed the very large Raman scattering cross-section of adsorbed molecules, such as pyridine and CN-, on Ag is attributed to mechanisms involving either electron-hole pair excitations in the surface region of the metal or charge-transfer excitations between the metal substrate and the adsorbbed molecules.
Journal ArticleDOI
Effect of surface plasmons on transitions in molecules
TL;DR: In this article, a quantum theory of the coupling of excited molecules to the surface plasmon modes of a metal is described, and formulas for the separate decay into s photon, p photon, and surface PLAsmon channels valid for all molecule−metal separations are given.