Thermal conductivity in porous silicon nanowire arrays

Abstract

The nanoscale features in silicon nanowires (SiNWs) can suppress phonon propagation and strongly reduce their thermal conductivities compared to the bulk value. This work measures the thermal conductivity along the axial direction of SiNW arrays with varying nanowire diameters, doping concentrations, surface roughness, and internal porosities using nanosecond transient thermoreflectance. For SiNWs with diameters larger than the phonon mean free path, porosity substantially reduces the thermal conductivity, yielding thermal conductivities as low as 1 W/m/K in highly porous SiNWs. However, when the SiNW diameter is below the phonon mean free path, both the internal porosity and the diameter significantly contribute to phonon scattering and lead to reduced thermal conductivity of the SiNWs.

High thermoelectric figure-of-merits from large-area porous silicon nanowire arrays

“…In fact, a much lower ZT value of SiNWAs are normally obtained, especially for the case of vertically aligned ones, this may be due to the arrays have low nanowire density or short length [32], large wire diameter [33] and polymer filler [34,35]. Also, recent research shows that bring nanopores into the nanomaterial can greatly decrease the thermal conductivity [36] and increase of the ZT value. For example, The theoretical and experimental results shows respectively that [37,38] the ZT value of $0.4 were achieved for nanoporous Si film at room temperature (RT) which is 2 orders of magnitude over that of the bulk Si.…”

Effects of vacancy defects and axial strain on thermal conductivity of silicon nanowires: A reverse nonequilibrium molecular dynamics simulation

“…This can enhance thermal transport in some devices based on nanostructures such as nano/microelectrical chips or improve efficiency of thermoelectric conversion. Besides some experimental attempts [21][22][23], theoretical modeling performs a significant role to predict the thermal conductivity of bulk silicon and also silicon nanostructures containing vacancies [24][25][26][27][28][29], impurities [30][31][32] and grain boundaries [33,34].…”

Silicon Porosification: Approaches to PSi Parameters Control

“…When the size of the Si nanocrystals become smaller than the phonon mean free path in c-Si (43 nm at room temperature), the classical Fourier heat conduction theory no longer holds (Chen 1996;Lysenko et al 1999a;Jean et al 2014), while disordered phonon scattering at nanocrystallites' boundaries play a major role. Recently, a detailed study of the different mechanisms involved in thermal transport occurring in PSi has been published (Weisse et al 2012), stating that for Si sizes larger than the phonon mean free path, the thermal conductivity steeply decreases with increasing porosity due to phonon scattering at the pore interfaces, whereas the dependence on the doping concentration and surface roughness is fair. In contrast, when the Si diameter is smaller than the phonon mean free path, the thermal conductivity strongly depends on both the external boundary-phonon scattering and the internal pore interface-phonon scattering, leading to a significant reduction in the thermal conductivity for such systems.…”