Thermally Modulated Specular Phonon Transport in a High‐Debye‐Temperature Diamond Nanobeam

While the interplay between phonon and boundary dictates thermal transport at the nanoscale, the spectral manipulation of phonon-boundary scattering is insufficiently demonstrated yet. Here, we choose a single-crystal diamond nanobeam, a material with one of the highest Debye temperature materials, to investigate the impact of modulated phonon-boundary scattering with a temperature knob. The thermal conductivity of nanobeams is measured from room temperature down to ∼140 K, and we find that the value monotonically decreases scaling with T^∼1.07. Compared to the model prediction based on the Boltzmann transport equation combined with ab initio calculation, we find that the experimental data increasingly deviate from the model prediction with diffuse phonon scattering as the temperature decreases. The deviation indicates the increasing portion of non-diffuse phonon-boundary scattering. Our analysis indicates that specular phonon-boundary scattering is more sensitive to temperature in single-crystal diamond compared to that of silicon. This work suggests that the diamond is a potential material platform to manipulate wave-like phonon conduction above 100 K.