Reduction of thermal conductance in two-dimensional phononic crystals by coherent phonon scattering
The impact of lattice type, period, and filling fraction of two-dimensional silicon phononic crystals on thermal conductance at low temperatures is investigated systematically using the theory of elasticity and finite element method. Changes in the period and filling fraction of the phononic crystal significantly affect the group velocity and density of states of the phonons and, as a consequence, reduce the thermal conductance of the structure. The reduction does not depend significantly on the lattice type of phononic crystals, despite the differences in symmetry and geometry. The possibilities of experimental observation of this effect are discussed, and a mode of separating coherent from incoherent scattering is proposed. Moreover, the temperature dependence of coherent scattering is assessed, and our results demonstrate that coherent scattering plays an important role in realistic nanostructures only at relatively low temperatures.