title: Frictional transition from superlubric islands to pinned monolayers.
abstract: The inertial sliding of physisorbed submonolayer islands on crystal surfaces contains unexpected information on the exceptionally smooth sliding state associated with incommensurate 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 per cent, implying a hysteretic jump from superlubric free islands to a pressurized 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 phenomena will be essential in future applications of friction at crystal/adsorbate interfaces.
authors.affiliation: Dipartimento di Fisica e Astronomia G. Galilei, Università di Padova, via Marzolo 8, Padova 35131, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Pierno
authors.affiliation: CNISM Unità di Padova, via Marzolo 8, Padova 35131, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Bruschi
authors.affiliation: Dipartimento di Fisica e Astronomia G. Galilei, Università di Padova, via Marzolo 8, Padova 35131, Italy.
authors.forename: Giampaolo
authors.initials: G
authors.lastname: Mistura
authors.affiliation: CNR, Istituto Nanoscienze - Centro S3, via Campi 213/a, Modena 41125, Italy.
authors.forename: Guido
authors.initials: G
authors.lastname: Paolicelli
authors.affiliation: CNR, Istituto Nanoscienze - Centro S3, via Campi 213/a, Modena 41125, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: di Bona
authors.affiliation: 1] CNR, Istituto Nanoscienze - Centro S3, via Campi 213/a, Modena 41125, Italy [2] Dipartimento di Scienze Fisiche Informatiche e Matematiche, Università di Modena e Reggio Emilia, via Campi 213/a, Modena 41125, Italy.
authors.forename: Sergio
authors.initials: S
authors.lastname: Valeri
authors.affiliation: 1] International School for Advanced Studies (SISSA), via Bonomea 265, Trieste 34136, Italy [2] CNR-IOM Democritos, via Bonomea 265, Trieste 34136, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Guerra
authors.affiliation: 1] International School for Advanced Studies (SISSA), via Bonomea 265, Trieste 34136, Italy [2] CNR-IOM Democritos, via Bonomea 265, Trieste 34136, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Vanossi
authors.affiliation: 1] International School for Advanced Studies (SISSA), via Bonomea 265, Trieste 34136, Italy [2] CNR-IOM Democritos, via Bonomea 265, Trieste 34136, Italy [3] International Centre for Theoretical Physics (ICTP), Strada Costiera 11, Trieste 34151, Italy.
authors.forename: Erio
authors.initials: E
authors.lastname: Tosatti