Tunable thermal conductivity in mesoporous silicon by slight porosity change

We report the thermal conductivity of photoelectrochemically synthesized mesoporous silicon (MPS), with ∼20-nm diameter pores and 52%–58% porosity. The thermal conductivity of MPS samples with a thickness of a few microns was measured using the three omega (3 ω) differential technique. We experimentally demonstrated that the thermal conductivity of MPS varies between 3 and 7 W/m K at room temperature and is dependent on the photoelectrochemical etching times used during the MPS synthesis, which induces a slight change in the MPS porosity. Calculations were conducted using the Boltzmann transport equation in the relaxation time approximation, with the results suggesting that the large thermal conductivity reduction in the MPSs was not entirely explained by the pore boundary scattering. Our findings indicate that elastic softening in the mesoporous structure may be responsible for the reduction in the thermal conductivity.