The influence of phonon focusing on density of states and the Knudsen phonon gas flow in nanowires with different types of anisotropy of elastic energy

The influence of elastic energy anisotropy on phonon density of states (PDOS) and phonon mean free paths for acoustic modes in nanowires of cubic crystals with positive (Ge, Si, LiF, GaSb, GaAs, and GaN) and negative (CaF2, SrF2, and PbS) anisotropy of the second order elastic moduli has been investigated. The proposed calculation method allows one to determine angular distributions of the PDOS of fast and slow quasi‐transverse modes in elastically anisotropic crystals for phonon focusing and defocusing regions. It has been shown that the PDOS and the phonon mean free paths in the cubic crystals take maximum and minimum values in the directions of phonon focusing and defocusing, respectively. Moreover, the anisotropy of the crystals differs qualitatively: the maxima values for the type‐I crystals correspond to the minima for the type‐II crystals. The heat flux directions that provide the maximum and minimum phonon thermal conductivity in the nanowires have been identified.