X-ray exposure effects on carboxylic-terminated self-assembled monolayers and change in the interface electronic structure

Solid surfaces can be relatively easily modified and the surface properties can be tailored through functionalisation with self-assembled monolayers (SAMs). Degradation or damage of these layers can affect the surface properties introduced through the functionalisation with self-assembled monolayers, and hence the functionality of the respective surface in an application. In this study, we investigated the damage induced by X-ray exposure to the structure of carboxylic-terminated SAMs. The integrity of both the carboxylic and thiol groups, with thiol groups being essential for anchoring the monolayers to the gold substrate, was compromised through X-ray exposure. Analysis of ultraviolet photoelectron spectroscopy (UPS) and metastable impact electron spectroscopy (MIES) data shows that such damage leads to changes in the work function and affects the electronic distribution within the outermost layer. The change is caused by the alteration of the electronic structure at the interface, leading to a change of the dipole formed at this interface. Both changes can occur independent of each other. It can be expected that exposure to UV light has a similar influence on the structure of the SAMs to that of X-ray radiation.