Studies of substituted hydrocarbon monolayers on platinum by means of auger electron spectroscopy with electrochemical calibration

Schoeffel, James Allan

Studies of substituted hydrocarbon monolayers on platinum by means of auger electron spectroscopy with electrochemical calibration

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uhm_phd_7801056_uh.pdf (2.19 MB)

Date

1977

Authors

Schoeffel, James Allan

Abstract

In electrode reactions and indeed in all chemical reactions involving solid reagents or catalysts, the electrode-solution interface is of principal importance. For this reason, information concerning the composition and the electronic and atomic structure of this interface should be helpful in understanding electrode reactions more fully. Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) can provide such information, and have begun to be applied to electrochemically interesting systems. A commercially available LEED/AES system has been interfaced to a PDP-ll/45 computer for digital data acquisition and storage of derivative spectra obtained by the conventional potential modulation/ second harmonic detection scheme of operation. The interface has been calibrated and an expression, for the collection efficiency of the retarding field analyzer, based on a layer model for the emitter, has been derived. In this way, absolute Auger electron yields can be extracted from the recorded data. Electrochemical oxidation studies of ethylene, allylamine, allylacetic acid, chlorotrifluoroethylene, and thiophene have been performed by potential-step coulometry utilizing an polycrystalline platinum thin layer electrode (TLE) to determine the number of electrons transferred per reactant molecule. Reaction mechanisms consistent with these results are proposed. Saturation coverages of the compounds adsorbed on the polycrystalline electrode, ɼp (sat), were determined, and the saturation of thiophene determined on a platinum (100) single crystal TLE, ɼ100 (sat), was used to calculate the ɼ100 (sat)'s of the other four compounds for use in the Auger calculations. Auger electron spectra of saturation coverages of the same five compounds on a platinum (100) single crystal surface have been obtained. K-1eve1 ionization cross-sections of carbon, nitrogen, oxygen, and fluorine, and the L23-1eve1 ionization cross-sections of sulfur and chlorine, calculated from the measured Auger electron yields, were studied. These are shown to agree reasonably well with those predicted by the theoretical model of Gryzinski when backscattering contributions and Coster-Kronig transition probabilities are taken into account. This good agreement for allylacetic acid, chlorotrif1ouroethylene, and thiophene was obtained only after normalization of the cross-sections to that determined for carbon in ethylene. The data imply that the saturation coverages of these compounds in the vacuum environment are less than in the solution environment of the TLE. Resolution of this matter requires further development of a vacuum compatible TLE so that the electrochemistry can be performed immediately following the Auger analysis on the same sample.

Description

Typescript.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1977.
Bibliography: leaves 100-102.
Microfiche.
x, 102 leaves ill

Keywords

Hydrocarbons, Platinum, Auger effect

URI

http://hdl.handle.net/10125/9483

Related To

Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Chemistry; no. 1031

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