Crossing Thermal Lubricity and Electronic Effects in Friction: Vanadium Dioxide under the Metal–Insulator Transition

basic processes (e.g., phonon generation and electron–hole pair creation); thus, determining energy dissipation mechanisms offers the potential to control friction in new ways. [ 3–5 ] Theoretically, when an object is moving along an insulator surface, kinetic energy is dissipated solely through phonon emission (i.e., lattice vibration of the substrate). However, if the substrate is conductive, electronic channels can also be activated for energy dissipation. Friction force microscopy (FFM) enables us to investigate these issues at the nanoscale. [ 2,6 ] In FFM, the sample surface is scanned by a nanosized tip under a constant normal force while lateral distortions in the trace and retrace directions are detected, giving rise to the friction signal. [ 7 ] This provides a means to investigate how the friction force acts on the sharp tip. Indeed, FFM experiments have revealed phononic emissions dependent on the isotopic composition of the substrate [ 4 ] and electronic friction in p–n junctions. [ 5,8 ] Cannara et al. demonstrated that the vibration of lighter atoms could dissipate friction heat more effectively. [ 4 ] Park et al. showed that friction could be varied in a semiconductor by controlling carrier density. [ 6 ] To simultaneously demonstrate the relative magnitude of these two competing mechanisms, Kiesel utilized noncontact atomic force microscopy (AFM) and found that the superconductor state of Nb has less friction than its normal metal state [ 9 ] because friction energy cannot dissipate to paired electrons in the super-conducting state until these pairs are broken apart by the friction energy itself. Vanadium dioxide (VO 2) is a well-known material for its metal–insulator phase transition (MIT), which offers an interesting platform to study the infl uence of electronic structure on friction behavior. Particularly, because its transition temperature (T c) is near room temperature (T c = 68 °C for free-standing, stoichiometric VO 2 single crystals) and it has a high resistivity ratio and fast switching time, VO 2 attracts more attention than other materials with similar MIT characteristics. Here, we report the role of MIT on the friction properties of VO 2 at various temperatures. FFM combined with a current preamplifi er successfully resolves the metallic and insulating domains in the VO 2 by measuring its conductivity at nanoscale. We discovered that friction in the insulating phase decreases with increasing temperature, which is attributed to The remarkable turnover of friction on a vanadium dioxide (VO …