Cooperative low-and high-frequency phonon dissipation in Penta-PdSe2: A key to structural superlubricity

MZ Wang and GL Ru and SB Cui and SS Xu and XQ Liu and WH Qi, SURFACES AND INTERFACES, 71, 106888 (2025).

DOI: 10.1016/j.surfin.2025.106888

Owing to its unique pentagonal crystal structure, PdSe2 is a promising candidate for achieving superlubricity in two-dimensional (2D) materials. However, the energy dissipation mechanisms during frictional processes remain unclear. This study investigated the interlayer frictional behaviour of pentagonal PdSe2 and the phonon dynamics during sliding. Fast Fourier transform (FFT) analysis of the friction forces reveals that the difference in frictional coefficients between commensurate and incommensurate contacts arises from resonant coupling at the washboard frequency under commensurate conditions, enabling efficient energy transfer between the probe and substrate. Phonon density of states (PDOS) spectra indicate that substrate atoms dissipate the acquired energy by vibrating in two distinct frequency regimes. Contact states influence the vibrational modes of the substrate atoms, leading to variations in friction. The normal load modulates the high- frequency modes, whereas the sliding speed alters both the low-frequency and high-frequency modes. The interplay between these modes determines the degree of macroscopic friction. These findings elucidate the phonon- mediated friction mechanisms in PdSe2 and provide theoretical insights into friction regulation.

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