Modification of Alkanethiolate Self-Assembled Monolayers by Ultraviolet Light: The Effect of Wavelength

The effect of the wavelength upon the modification of the archetypical nonsubstituted alkanethiolate (AT) self-assembled monolayers (SAMs) on Au(111) by ultraviolet (UV) light was investigated. As a test system, the dodecanethiolate monolayer was selected, while the wavelength of the UV light was varied in two steps from 254 to 375 nm, which is a relevant range for a variety of inexpensive UV sources as well as custom-made and commercial lithography setups. The absolute cross sections of the most prominent and application-relevant UV-induced processes, above all photooxidation of the thiolate anchoring groups to sulfonates, were determined. They were found to decrease exponentially with increasing wavelength, with an effective wavelength attenuation parameter of similar to 24 nm. This behavior was rationalized within a model assuming the primary role of UV-induced hot electrons, originating from the substrate and triggering an excitation and subsequent oxidation of the sulfur atoms by their reaction with oxygen molecules, penetrating to the SAM-substrate interface across the SAM matrix. The observed behavior and the absolute values of the photooxidation cross sections represent a useful tool for the estimation of a proper dose or dose range in the applications involving modification of AT SAMs and thiolate SAMs in general by UV light.

Automated summary

The study investigated the effect of wavelength on the modification of archetypical nonsubstituted alkanethiolate self-assembled monolayers on gold surfaces by ultraviolet light. The results provided insights into the behavior of UV-induced processes under different wavelengths and offered a useful tool for estimating proper dosage ranges in applications involving modification of AT-SAMs and thiolate SAMs.