Role of acoustic phonon transport in near- to asperity-contact heat transfer

Acoustic phonon transport is revealed as a potential radiation-to-conduction transition mechanism for single-digit nanometer vacuum gaps. To show this, we measure heat transfer from feedback-controlled platinum nanoheater to laterally oscillating silicon tip the tip-nanoheater gap distance precisely controlled down bulk contact in high-vacuum shear force microscope. The measured thermal conductance shows dependence of ${d}^{\ensuremath{-}5.7\ifmmode\pm\else\textpm\fi{}1.1}$ near-contact regime, which good agreement with acoustic modeling based on atomistic Green's function framework. obtained experimental and theoretical results suggest that across nanoscale can be dominant near- asperity-contact regimes potentially by an external stimuli.