Fig. 4: 2D PhPs of monolayer h-BN.

a, b Deceleration and confinement factors versus energy loss, respectively. Solid circles represent the experimental results of this work, empty squares represent the calculated results for a freestanding monolayer (ML), and empty rhombus represent the measured results of 10-nm-thick extracted from ref. ³⁵. The solid curves represent the fitting results to the corresponding data. c The calculated dispersion relation of the PhPs for various freestanding layers (Methods). \(t\) represents the number of layers of h-BN. d Spatial distribution of PhP transformed from 2D phonon spectra measured along Γ-K direction (0–0.4 Å⁻¹). Inset: calculated spatial distribution of PhPs for various layers using Eq. (1).