Adsorption kinetics of n-alkyl thiols on gold studied by second harmonic generation and x-ray photoelectron spectroscopy

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Abstract
Optical second harmonic generation (SHG) was used to study the adsorption kinetics of self‐organizing n‐alkyl thiol films on polycrystalline gold substrates in situ and in real time. Thiols with carbon chains ranging from 1 to 22 were studied. SHG results showed that the average thiol coverage is constant for thiols longer than hexanethiol. The relation between the SHG signal change and the degree of thiol coverage was established by comparison with ex situ x‐ray photoelectron spectroscopy measurements. The temporal dependence of the adsorption is well described by Langmuir adsorption kinetics and the source of the SHG signal is found to be linearly related to the nonlinear susceptibility of the adsorbate–substrate interaction allowing a straightforward in situ determination of the coverage.