The inertial sliding of physisorbed submonolayer islands on crystal surfaces contains unexpected information on the exceptionally incommensurate smooth sliding state associated with superlubricity and on the mechanisms of its disappearance. Here, in a joint quartz crystal microbalance and molecular dynamics simulation case study of Xe on Cu (111), we show how superlubricity emerges in the large size limit of naturally incommensurate Xe islands. As coverage approaches a full monolayer, theory also predicts an abrupt adhesion-driven two-dimensional density compression on the order of several percent, implying a hysteretic jump from superlubric free islands to a pressurized √3 x √3 commensurate immobile monolayer. This scenario is fully supported by the quartz crystal microbalance data, which show remarkably large slip times with increasing submonolayer coverage, signalling superlubricity, followed by a dramatic drop to zero for the dense commensurate monolayer. Careful analysis of this variety of island sliding phenomenon will be essential in future applications of friction at crystal-adsorbate interfaces.

Frictional transition from superlubric islands to pinned monolayers

PIERNO, MATTEO AMBROGIO PAOLO;MISTURA, GIAMPAOLO;
2015

Abstract

The inertial sliding of physisorbed submonolayer islands on crystal surfaces contains unexpected information on the exceptionally incommensurate smooth sliding state associated with superlubricity and on the mechanisms of its disappearance. Here, in a joint quartz crystal microbalance and molecular dynamics simulation case study of Xe on Cu (111), we show how superlubricity emerges in the large size limit of naturally incommensurate Xe islands. As coverage approaches a full monolayer, theory also predicts an abrupt adhesion-driven two-dimensional density compression on the order of several percent, implying a hysteretic jump from superlubric free islands to a pressurized √3 x √3 commensurate immobile monolayer. This scenario is fully supported by the quartz crystal microbalance data, which show remarkably large slip times with increasing submonolayer coverage, signalling superlubricity, followed by a dramatic drop to zero for the dense commensurate monolayer. Careful analysis of this variety of island sliding phenomenon will be essential in future applications of friction at crystal-adsorbate interfaces.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11577/3157251
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