“…Under frequencies of 319 MHz, 285 Hz, and 250 Hz, friction forces of the diamond tip reach the lowest. Fajardo [20] pointed out that, when vs/a ≤ f ≤ fp/ϒ , friction decreases under external vibration, where f is the vibration frequency, vs is the support velocity, a is the spatial periodicity, and fp is the resonance frequency. ϒ = γ/(2πfp), where γ is a microscopic friction coefficient describing the coupling with the phonon and the possible electron oscillations in the substrate.…”