Tunable thermal conductivity in mesoporous silicon by slight porosity change

Abstract

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 (3ω) 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.

Thermal conductivity of irradiated porous silicon down to the oxide limit investigated by Raman thermometry and scanning thermal microscopy

“…(3) we obtain the thermal conductivity for non-irradiated PSi at 56% which is found to be 6.3±0.2 W.m -1 .K -1 . It is difficult to find in literature the same PSi sample as the one we manufactured, but this non-IPSi thermal conductivity is in good agreement with already published results 14,19,20,22,24 . We now compare our results with the model that allows obtaining  as a function of the amorphous fraction developed by Newby et al 14 .…”

“…Other modified effective medium approaches (EMA) such as Maxwell-Garnett, Bruggeman and LLL, where the mean free paths in the crystalline phase can be considered further reduced due to confinement 47,48 , also predict low thermal conductivities, whatever the geometry of the crystallites (which can be asymptotically considered as spheres or cylinders). The impact of optical modes in confined structures might be significant 49 .The difficulty in matching the models derived from the Boltzmann transport equation with up-to-date mean free path distributions and the experimental results for crystalline porous samples has already been highlighted 24 .…”

“…Up to now, in most of the experimental studies of porous silicon only one thermal characterization technique was applied for the 3 technique for the same aim 14,23,24 . Using micro-Raman thermometry (µ-RT) and SThM, Newby et al showed a discrepancy between the two techniques in the thermal conductivity of irradiated PSi (IPSi) samples with = 41% 19 .…”

Controlling Thermal Conductivity in Mesoporous Silica Films Using Pore Size and Nanoscale Architecture

“…Such a positive correlation between pore size and thermal conductivity at a fixed porosity had been previously observed in porous crystals. − In crystals, the heat is carried by traveling phonons with a certain distribution of phonon MFPs. The scattering of phonons at the boundary between pores and the solid phase can reduce the effective phonon MFPs and thus the thermal conductivity.…”

Towards a Tuneable Thermal Conductivity Material via Low Voltage Ordering of CNT Networks

“…Materials with such a property are highly sought after and intensively researched, particularly in areas where thermal management actively improves efficiency, such as in the automotive sector. Methods which tune thermal conductivities employ various approaches, and may include: variations on the material density [1], atomic intercalations [2], mechanically induced lattice mismatching [3], phononic metamaterials [4] and multilayered graphene [5]. Voltage controlled changes in thermal conductivity at room temperature in a solid-state material has been demonstrated in Lead Zirconate Titanate [6], which was correlated to domain wall density.…”