Influence of Structural Dynamics on the Kinetics of Atomic Hydrogen Reactivity with Low-Temperature Alkanethiolate Self-Assembled Monolayers

Abstract

This study examines the impact of surface temperature on alkanethiolate self-assembled monolayer (SAM) reactivity with atomic hydrogen (H) as well as how the combined effects of temperature and alkanethiol chain length alter the reaction outcome. This is achieved using ultrahigh vacuum scanning tunneling microscopy (UHV-STM) to monitor the spatiotemporal evolution of the monolayer throughout the reaction. We find that with decreasing temperature, the reaction rate of alkanethiol SAMs with atomic H decreases monotonically. Furthermore, the kinetic profile of the low-temperature reaction differs from that at room temperature, indicating structural and dynamical fluctuations within the monolayer that influence reactivity. Chain length is also seen to significantly affect reactivity at reduced substrate temperature, with longer alkanethiols reacting more slowly than shorter ones. Finally, we observe a unique surface rearrangement of the SAM upon exposure to atomic H, including changes in the organization of close-packed thiol domains and the evolution of gold adatom islands not observed at elevated temperatures. Overall, this work provides both quantitative and nanoscopic insight into how substrate temperature influences the structural dynamics of thiolate monolayers and how these fluctuations influence chemical reactivity.

On-surface chemical dynamics of monolayer, bilayer, and many-layered graphene surfaces probed with supersonic beam scattering and STM imaging

“…STM studies of the chain-length and temperature-dependent reactivity of alkylthiolate self-assembled monolayers with incident beams of atomic hydrogen reveal the critical role that dynamic disorder in thiol chains and lm structure play in controlling surface passivation. 15,16 Sequential same-spot in situ visualization illustrated site-specic oxygen adsorption on Si(111)-(7 × 7) and showed how the oxidation of a given lattice site inuences subsequent and proximally located reactivity. 17 Additionally, STM visualization in combination with exposure to non-equilibrium uxes of N 2 allows the fate of individual adsorbed atoms originating from single impinging molecules to be tracked with Angstrom-level precision, 18 providing insights into energy dissipation pathways and the relative importance of non-adiabatic channels for this system.…”