Suppressed Umklapp scattering ofβ-FeSi₂thin film and single crystalline nanowires

Abstract

Thermal conductivity is an intriguing physical property in the nanometer or quantum regime. In this study, we report the growth and thermal conductivity of β-FeSi thin film and single crystalline nanowires. The sample structures and chemical composition were identified by standard microscopy techniques. The temperature-dependent thermal conductivity of the thin film was measured by the 3ω method, whereas that of the nanowires was conducted by a suspended pattern technique. Temperature-dependent thermal conductivity was found to increase gradually from 300 to 500 K due to the effect of surface scattering. The experimental evidence presented herein is the suppression of Umklapp transport at the nanoscale near room temperature and the potential application of nanoengineered β-FeSi for future design of thermoelectric materials.

Silicon-based nanostructures for integrated thermoelectric generators

“…High power factors of as-deposited thin films of FeSi 2 , CrSi 2 and HMS were demonstrated in several works [118][119][120][121]. Moreover, potentially enhanced thermal properties in β-FeSi 2 thin films were suggested in the recent work of Hsin et al with a temperature dependence of κ that indicates a suppression of the Umklapp scattering (similar to NWs)-usually dominating in the bulk material [103].…”

“…However, despite their potential, only few works were devoted to characterize thermal and thermoelectric properties of silicide nanowires. In the recent work of Hsin et al, the thermal conductivity of a single β-FeSi 2 NW was measured from 300 to 500 K [103]. The results showed a reduction of κ, compared to a thin film counterpart with an inversion of the temperature dependence that indicates that thermal transport is not ruled by Umklapp scattering.…”

“…In the case of silicides, thin films were traditionally obtained in CMOS processes by sputtering or evaporating a metal on top of a silicon substrate and performing a high temperature annealing. However, lately other methods were developed, using magnetron-sputtering or pulsed laser deposition of both metal and silicon precursors followed by annealing (enabling finer composition/phase control) or MBE (enabling epitaxial growth) [103,118,119]. High power factors of as-deposited thin films of FeSi 2 , CrSi 2 and HMS were demonstrated in several works [118][119][120][121].…”

Lattice dynamics of β−FeSi2 nanorods

“…Promising approaches for the further improvement of the thermoelectric performance are doping [24][25][26] and reduction of the thermal conductivity by nanostructurization [27][28][29]. For instance, it was shown that the spatial confinement in β-FeSi 2 nanowires with diameters of about 100 nm has a significant impact on the thermal conductivity [30].…”

Thermoelectric properties of Zn- and Ce-alloyed In2O3 and the effect of SiO2 nanoparticle additives

“…Nevertheless, these materials are not routinely used owing to their high cost, environmental protection concerns, and oxidation resistance. To overcome the abovementioned problems, the idea of thermoelectric materials comprising the so-called earth-abundant elements has been proposed, such as nanoscale Si [10,11], metal silicides [12][13][14], copper sulfides [15], metal selenides [16,17], and Fe-Al-Si [18]. Although metal oxides typically provide a low ZT owing to both low electrical conductivity and high lattice thermal conductivity issues, they are still considered potential candidates.…”