Thermal conduction in nano-porous silicon thin film

Abstract

Controlling the thermal conductivity of thermoelectric materials continues to be a goal for energy conversion applications. The Phonon Boltzmann Transport Equation is solved by using the Discrete Ordinates Method to numerically study the phonon thermal conductivity of nanostructured silicon thin film with pores in this study. The effects of the film thickness, film porosity, and porous structure are concerned. The numerical results show that the nano-pores are able to reduce the thermal conductivity of the silicon thin film sharply by the phonon boundary scattering, and the scattering boundary area has significant effect on the thermal conductivity. The method of local angle distribution between heat fluxes is introduced for the first time to optimize the pore placement for reducing the thermal conductivity. V

Photothermoelectric Effects in Nanoporous Silicon

“…[ 15 ] However, in the Si nanowires and nanoporous Si (NPSi), the value of ZT increases with signifi cantly decreasing the value of thermal conductivity [15][16][17][18][19] ( ZT = S 2 σT / κ , where T is the absolute temperature; S is the Seebeck coeffi cient; σ is the electrical conductivity; and κ is the thermal conductivity). NPSi has a thermal conductivity of up to three orders of magnitude smaller than bulk Si due to NPSi with more nanopore (less crystalline Si) introduces the phonon transfer of phonon-phonon or phonon-surface scattering [ 15 ] insignifi cantly compared with crystalline Si.…”

Crystal structure dependent thermal conductivity in two-dimensional phononic crystal nanostructures

“…Recently, Tang et al. performed numerical simulations and predicted that the placement of holes has a strong influence on thermal conduction 19 . Song and Chen studied thermal conductivity between PnC microstructures with a hole spacing of 4 m aligned in a square or triangular lattices 20 .…”

Thermal conductivity in nanostructured materials and analysis of local angle between heat fluxes

“…19,[22][23][24] little attention has been paid to the thermal conductivity of thin film with pores of other geometries, such as triangle and hexagon. In addition, we find that the effects of porosity and interface area on thermal conductivity are studied dependently in most previous studies 19,22,24 in which the interface area and the porosity changed at the same time. This paper reports the independent effect of porosity or interface area on thermal conductivity (crossplane) of the two-dimensional nanoporous silicon thin film by changing pore shapes.…”

“…We can see that the figure of merit ZT can be improved by reducing the thermal conductivity k. Work has been carried out on the reduction of the thermal conductivity of nanostructured materials. [9][10][11][12][13][14][15][16][17][18][19][20][21][22] Yu et al investigated the thermal conductivity of a 22-nm-thick film with a square array of pores by experimental measurement, and the obtained effective thermal conductivity (<10 W/mK) was reduced obviously compared with the bulk one (145 W/mK). 11 The thermoelectric properties of "holey silicon" (HS) structures, the thin silicon membranes decorated with high density of nanoscopic holes were investigated by Tang et al, 12 and the thermoelectric performance of HS is comparable with the best value recorded in silicon nanowire system.…”

“…The linearized PBTE was reformulated by incorporating the direction-dependent phonon boundary scattering to study the thermal conductivity of Si-Ge nanowires. 21 In our previous paper, 22 we numerically studied the thermal conduction in the two-dimensional nanoporous silicon thin film with the frequency-dependent model, and the local angle b, defined as the angle between the directions of heat flux component q x and the local heat flux q, is introduced for the first time to optimize the pore arrangement for reducing the thermal conductivity.…”