THE ADSORPTION OF ALKANETHIOLS ON GOLD STUDIED QUANTITATIVELY BY XPS INELASTIC BACKGROUND ANALYSIS

Organic films of alkanethiols, CH3(CH2)n-1SH (n = 2, 6, 8, 11, 16, 18, 22), adsorbed from solution onto gold surfaces are investigated by quantitative XPS. Application of a recent formalism based on inelastic background analysis (the Tougaard method) to the XPS spectra allows information on the thiol film in-depth distribution to be extracted. For the analysis, a knowledge of the product of the inelastic mean free path-lambda and the inelastic scattering cross-section K(T) in the thiol film is needed. To examine the influence of the thiol lambda-K(T) function on the result of the analysis, the "universal cross-section" as well as the lambda-K(T) value for polyethylene evaluated from REELS spectra are applied in the present analysis. Our results show that the polyethylene lambda-K(T) function is superior to the universal function in describing the thiol lambda-K(T) function. In the present analysis of the thiol/gold system an in-depth distribution model assuming uniform overlayer growth with the thickness DELTA-x depending linearly on n was found to match the actual profile. For n = 22 the fractional thiol coverage of the gold surface is shown to be at least 90%.