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https://hasegawa.issp.u-tokyo.ac.jp/nanosci-seminar-250411

Abstract:
Previous calculation [Guerra et al, Nature Materials, 9 634 (2010).] has predicted that gold nanocrystals slide on graphite with two radically different friction coefficients depending on their speeds. At low speeds (~µm/sec), nanocrystals on graphite are expected to possess higher friction, consistent with previous studies of thermal diffusion of gold on graphite and on graphene. At high sliding speeds in the range of 100 m/sec, nanocrystals are expected to behave radically differently, with a vanishing drag and, therefore, minimal friction. Such high speeds are not easily accessible by atomic force microscopy (AFM), a commonly used to measure nanoscale friction.

My research group has measured friction of gold nanocrystals with diameter ranging from 3 to 5 nm on graphene at speeds up to 35.6 cm/sec. We find the friction at high speeds to be an order of magnitude lower (!) than predicted previously by Guerra et al. I will discuss our measurement technique, the experimental results, and the origin of the observed friction (which is even lower than expected!) as well as recently ongoing efforts to understand this phenomenon further at individual nanocrystal levels. I will also briefly discuss other projects going on in my lab which includes magic angle graphene-based photodetectors, and application of machine learning to achieve high throughput scanning tunneling microscopy.