Si and Ge allotrope heterostructured nanowires: experimental evaluation of the thermal conductivity reduction

Abstract

We have studied the thermal conductivity of Ge and Si allotrope heterostructured nanowires (NWs) synthesized by phase transformation. The NWs are composed of successive hexagonal 2H and cubic diamond 3C crystal phases along the 〈111〉 axis. Using 3ω-scanning thermal microscopy on NWs embedded in a silica matrix, we present the first experimental evidence of thermal conductivity reduction in such allotrope 2H/3C heterostructured NWs. In Ge heterostructured 2H/3C NWs, similarly to homogeneous 3C NWs, we show a thermal conductivity reduction when the NW diameter decreases. In addition, in Si and Ge NWs, we observe a reduced thermal conductivity due to the heterostructuration 2H/3C. We evidence that the temperature of phase transformation, which influences the size and the number of 2H domains, can constitute an efficient parameter to tune the thermal conductivity.

Imaging Thermoelectric Properties at the Nanoscale

“…The thermal conductivity of such NWs has already been evaluated using the previous system described in [ 28 ] and the thermal conductivity images can be found in [ 32 ]. We first checked that the thermal signal measured with the new experimental set-up was identical.…”

“…We can then evaluate the Ge NWs’ sample effective Seebeck coefficient to be around −800 ± 10 µV/K. The β coefficient is evaluated to be around 0.67 with a Ge NW thermal conductivity λ Ge = 16 W m −1 K −1 identified in [ 32 ]. Using the same simple model as for the Au/Si sample, we can deduce the Seebeck coefficient of Ge NWs/Ge substrate to be −240 ± 3 µV/K.…”

“…In addition to the thermal conductance, we can now image the electrical conductance and Seebeck voltage of nanostructured samples, such as nanolayers or embedded NWs on a substrate, paving the way to a quantitative measure- We can then evaluate the Ge NWs' sample effective Seebeck coefficient to be around −800 ± 10 µV/K. The β coefficient is evaluated to be around 0.67 with a Ge NW thermal conductivity λ Ge = 16 W m −1 K −1 identified in [32]. Using the same simple model as for the Au/Si sample, we can deduce the Seebeck coefficient of Ge NWs/Ge substrate to be −240 ± 3 µV/K.…”

“…We have previously developed a SThM set-up which offers the possibility to simultaneously image the thermal conductivity of several individual nanowires embedded in their matrix [28]. We have then studied the thermal conductivity of organic and inorganic NWs [29,30] and, more specifically, we have shown a reduction of the thermal conductivity which can be attributed to the reduction of the NW diameter [31] or to the size of polytype nanodomains in the case of Si 3C/2H heterostructured NWs [32].…”

Investigating the key role of carrier transport mechanism in SnSe nanoflakes with enhanced thermoelectric power factor

“…Systematic approaches to curb κ in materials are now well-established in the literature, e.g. introducing point defects and grain boundary through band modification techniques, creating structural disorders, manipulation of atomic ordering [4][5][6][7][8]. This is partly attributed to the active developments in the ab initio thermal transport theory [9][10][11][12].…”