'Hot' Surface Activation of Molecular Complexes: Insight from Modeling Studies

摘要

The activation of gas-phase molecules on hot solid surfaces, a major issue for both fundamental research and technological applications, plays a key role in the fabrication of advanced materials supported on suitable substrates. The interest relates to the increasing requirement of attaining a deeper insight into the first molecular activation stages, a critical step in the bottom-up nucleation of functional nanostructures with specific size-structure relationships. While molecular activation is in general influenced by the surface chemical composition, in the harsh conditions typical of hot substrates, the surface-molecule energy transfer becomes crucial. As a consequence, physisorption competes with desorption, a diverse reactivity emerges, and novel activation mechanisms may be triggered, thus leading to products not attainable under mild conditions. Atomistic-level details of encounters between gas-phase molecules and hot surfaces are not easily available, owing to both the fast kinetics associated with high temperatures and the difficulties of performing experimental in situ analysis on a molecular scale. In this context, first-principles modeling studiesare of significant relevance in the design and tailoring of specific molecular routes to functional nanosystems, such as chemical vapor deposition (CVD) processes, in which surface temperature is a decisive factor. Herein, we report on how the multifaceted dynamical behavior of a CVD precursor on a hot substrate, captured by simulation, disclosed a novel general activation channel for high-temperature surface processes: the fast rolling motion of vibrationally excited molecules. This surface mobility regime, never reported to date, combines fast lateral transport of an adsorbent with excitation of its internal modes, thus suggesting that energetic collision of rolling species is actually one of the ways through which molecules are activated and react at a hot surface.