The dynamics of metal nanoparticles on a supporting interacting substrate.

The interaction strength of the nanoparticles (NPs) with the supporting substrate can greatly influence both the rate and selectivity of catalytic reactions, but the origins of these changes in reactivity arising from the combined effects of NP structure and composition, and NP-substrate interaction is currently not well-understood. Since the dynamics of the NPs is implicated in many NP-based catalytic processes, we investigate how the supporting substrate alters the dynamics of representative Cu NPs on a model graphene substrate, and a formal extension of this model in which the interaction strength between the NPs and the substrate is varied. We particularly emphasize how the substrate interaction strength alters the local mobility and potential energy fluctuations in the NP interfacial region, given the potential relevance of such fluctuations to NP reactivity. We find the NP melting temperature T progressively shifts downward with an increasing NP-substrate interaction strength, and that this change in NP thermodynamic stability is mirrored by changes in local mobility and potential energy fluctuations in the interfacial region that can be described as "colored noise." Atomic diffusivity, D, in the "free" and substrate NP interfacial regions is quantified, and observed variations are rationalized by the localization model linking D to the mean square atomic displacement on a "caging" timescale on the order of a picosecond. In summary, we find that the supporting substrate strongly modulates the stability and dynamics of supported NPs-effects that have evident practical relevance for understanding changes in NP catalytic behavior derived from the supporting substrate.