Superlubricity & frictional anisotropy: why molecules choose a rough ride?

Igor Stanković, Institute of Physics Belgrade, Serbia

Viernes 26 de Octubre, 4:00 pm, Sala Luciano Laroze E-300

Superlubricity is a state in which friction vanishes almost entirely [1]. It is first measured in graphite where atoms are oriented in a hexagonal manner and form an atomic egg box landscape of periodic hills and valleys. When the two graphite surfaces are commensurate, i.e., in the registry, the friction force is high. When the two surfaces are rotated out of the registry, the friction is greatly reduced. This interplay of sliding direction and atomic-level energy landscape gives rise to so-called frictional anisotropy. So far, the frictional properties at the nanoscale have been studied by standard friction force microscopy [2]. However, lateral manipulation of nanoparticles is a more suitable method to study the dependence of friction on the crystallography of two contacting surfaces. In this talk, a combination of atomic force microscopy (AFM) based lateral manipulation results and molecular dynamics simulations are used to understand movements of organic needle-like nanocrystallites grown by van der Waals epitaxy on graphene [3]. The nanoneedle fragments – when pushed by an AFM tip – do not move along the original pushing directions. We use an experiment in conjunction with simulations to demonstrate that both, the significant friction anisotropy and preferential sliding directions are determined by the epitaxial relation and arise from the commensurate and incommensurate states between the organic nanocrystallites and the 2D materials.

[1] Martin Müser, Theoretical Studies of Superlubricity in Fundamentals of Friction and Wear on the Nanoscale, eds.   Enrico Gnecco and Ernst Meyer, Springer Int. Pub. (2015), 209-232.

[2] Ze Liu, Jiarui Yang, Francois Grey, Jefferson Zhe Liu, Yilun Liu, Yibing Wang, Yanlian Yang, Yao Cheng, and Quanshui Zheng,  Observation of Superlubricity in Microscale Graphite,  Phys. Rev. Lett. 108, 205503 (2012).

[3] Borislav Vasić, I. S., Aleksandar Matković, Markus Kratzer, Christian Ganser, Radoš Gajić, and Christian Teichert, Nanoscale, 2018, accepted