Degradation of octanethiol self-assembled monolayers from hydrogen-atom exposure: A molecular-scale study using scanning tunneling microscopy

Octanethiol self-assembled monolayers were exposed to gas-phase hydrogen atoms, and the resulting changes in the order and chemical structure of the surface were monitored using scanning tunneling microscopy (STM). Extensive damage to the monolayer was observed in the form of both dark and bright features in STM images. These changes began along domain boundaries and moved into close-packed regions of the monolayer as hydrogen-atom exposure time increased. Increasing exposure also results in an accelerated rate of observed surface changes, indicating that the reactivity of the surface increases as a result of initial gas-surface reactions. Complex restructuring of the alkanethiol monolayer is observed, including defect formation and the disordering of the alkanethiol monolayer. However, in some cases the monolayer demonstrates the capability of self-healing, with local annealing and reordering of close-packed domains. This annealing and reordering likely results from increased mobility of surface-bound alkanethiolates in the vicinity of monolayer defects, or from diffusion and readsorption of transiently formed alkanethiol molecules.