title: Giant and Tunable Anisotropy of Nanoscale Friction in Graphene.
abstract: The nanoscale friction between an atomic force microscopy tip and graphene is investigated using friction force microscopy (FFM). During the tip movement, friction forces are observed to increase and then saturate in a highly anisotropic manner. As a result, the friction forces in graphene are highly dependent on the scanning direction: under some conditions, the energy dissipated along the armchair direction can be 80% higher than along the zigzag direction. In comparison, for highly-oriented pyrolitic graphite (HOPG), the friction anisotropy between armchair and zigzag directions is only 15%. This giant friction anisotropy in graphene results from anisotropies in the amplitudes of flexural deformations of the graphene sheet driven by the tip movement, not present in HOPG. The effect can be seen as a novel manifestation of the classical phenomenon of Euler buckling at the nanoscale, which provides the non-linear ingredients that amplify friction anisotropy. Simulations based on a novel version of the 2D Tomlinson model (modified to include the effects of flexural deformations), as well as fully atomistic molecular dynamics simulations and first-principles density-functional theory (DFT) calculations, are able to reproduce and explain the experimental observations.
authors.affiliation: Divisão de Metrologia de Materiais, Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO), Campus Xerém, Av. Nossa Senhora das Graças 50, Xerém, Duque de Caxias, RJ, 25250-020, Brazil.
authors.forename: Clara M
authors.initials: CM
authors.lastname: Almeida
authors.affiliation: Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, R. Marques de São Vicente 225, Rio de Janeiro, RJ, 22453-900, Brazil.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Prioli
authors.affiliation: Divisão de Metrologia de Materiais, Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO), Campus Xerém, Av. Nossa Senhora das Graças 50, Xerém, Duque de Caxias, RJ, 25250-020, Brazil.|Departamento de Física, Instituto de Ciências Exatas, Cidade Universitária, Juiz de Fora, MG, 36036-900, Brazil.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Fragneaud
authors.affiliation: Divisão de Metrologia de Materiais, Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO), Campus Xerém, Av. Nossa Senhora das Graças 50, Xerém, Duque de Caxias, RJ, 25250-020, Brazil.|Departamento de Física, Universidade Federal de Minas Gerais, Instituto de Ciências Exatas, Av. Antônio Carlos 6627, Belo Horizonte, MG, 31270-901, Brazil.
authors.forename: Luiz Gustavo
authors.initials: LG
authors.lastname: Cançado
authors.affiliation: Departamento de Física, Universidade Estadual Paulista, Campus Rio Claro, Av. 24A 1515, Rio Claro, SP, 13506-900, Brazil.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Paupitz
authors.affiliation: Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, R. Sérgio Buarque de Holanda, 777, Cidade Universitária, Campinas, SP, 13083-859, Brazil.
authors.forename: Douglas S
authors.initials: DS
authors.lastname: Galvão
authors.affiliation: Divisão de Metrologia de Materiais, Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO), Campus Xerém, Av. Nossa Senhora das Graças 50, Xerém, Duque de Caxias, RJ, 25250-020, Brazil.
authors.forename: Marcelo
authors.initials: M
authors.lastname: De Cicco
authors.affiliation: Instituto de Física, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos, 149-Cidade Universitária, Rio de Janeiro - RJ, 21941-590, Brazil.
authors.forename: Marcos G
authors.initials: MG
authors.lastname: Menezes
authors.affiliation: Divisão de Metrologia de Materiais, Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO), Campus Xerém, Av. Nossa Senhora das Graças 50, Xerém, Duque de Caxias, RJ, 25250-020, Brazil.
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Achete
authors.affiliation: Divisão de Metrologia de Materiais, Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO), Campus Xerém, Av. Nossa Senhora das Graças 50, Xerém, Duque de Caxias, RJ, 25250-020, Brazil.|Instituto de Física, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos, 149-Cidade Universitária, Rio de Janeiro - RJ, 21941-590, Brazil.
authors.forename: Rodrigo B
authors.initials: RB
authors.lastname: Capaz