FisMat2017 - Submission - View

Abstract's title: Ballistic thermophoresis: a gold cluster on graphene
Submitting author: Emanuele Panizon
Affiliation: SISSA
Affiliation Address: Via Bonomea 265, 34136, Trieste
Country: Italy
Oral presentation/Poster (Author's request): Oral presentation
Other authors and affiliations: Roberto Guerra (Università di Milano), Erio Tosatti (SISSA, Trieste - CNR/IOM, Trieste - ICTP, Trieste)

The textbook thermophoretic force which acts on a body in a fluid is proportional to the local temperature gradient; the same could be assumed to hold for a diffusive nanometer sized object physisorbed on a 2D layer such as graphene. By means of a Non-Equilibrium Molecular Dynamics (NEMD) study of a test system - a gold nanocluster adsorbed on free - standing graphene clamped between two different temperatures - we find a phoretic force which for relatively large submicron lengths L is parallel to, but roughly independent of, the gradient magnitude. This signals a nonconventional thermophoresis that is ballistic in character. Analysis shows that the phoretic force is dominated by flexural phonons, whose flow is indeed known to be ballistic and distance-independent up to the relatively long scattering lengths that precede the standard diffusive regime. Interestingly, ordinary harmonic phonons only carry pseudomomentum and could not exert a force. Yet, the monolayer supports a specific anharmonic coupling between corrugation and 2D density which endow the flexural phonons with some real momentum, part of which is transmitted to the adsorbate through scattering. The resulting distance-independent thermophoretic force is not unlikely to possess practical applications.