Tuning thermal transport in Si nanowires by isotope engineering

Abstract

We study thermal transport in isotopically disordered Si nanowires, discussing the feasibility of phonon engineering for thermoelectric applications within these systems. To this purpose, we carry out atomistic molecular dynamics and nonequilibrium Green's function calculations to characterize the dependence of the thermal conductance as a function of the isotope concentration, isotope radial distribution and temperature. We show that a reduction of the conductivity of up to 20% can be achieved with suitable isotope blends at room temperature and approximately 50% at low temperature. Interestingly, precise control of the isotope composition or radial distribution is not needed. An isotope disordered nanowire roughly behaves like a low-pass filter, as isotope impurities are transparent for long wave-length acoustic phonons, while only mid- and high-frequency optical phonons undergo significant scattering.

Theoretical investigation of lattice thermal conductivity and electrophononic effects in SrTiO3

“…The thermal conductivity of a material must be high to keep a low thermal budget in a nanoscale device [3], for instance, while it should be as low as possible when it comes to the engineering of an efficient thermoelectric [4,5]. The thermal conductivity can be tuned to some extent by nanostructuring, adding defects [6,7], or designing periodic superstructures [8,9], but it would be desirable to be able to dynamically modify it. Besides an increased flexibility in materials design, this would also open the way to heat-based signal processing and computing [10].…”

Interface thermal behavior in nanomaterials by thermal grating relaxation

“…It provides a very efficient and robust method to investigate thermal properties in a wide range of system sizes. AEMD has been applied by several authors to the calculation of the thermal conductivity in c-Si,c-Ge and α-quartz [1], in Si/Ge nanocomposite [9], in Si nanowires [10] and in graphene-based structures [11,12]. Initially developed for classical Molecular Dynamics (MD) this technique has been recently implemented in ab-initio calculations as well [13].…”

Si and SiGe Nanowire for Micro-Thermoelectric Generator: A Review of the Current State of the Art

“…Furthermore, a curve of thermal conductivity vs. the concentration of doping isotope atom (x) is exhibited, which shows a similar tendency with Si x Ge 1−x and a plateau at 0.2 <x<0.8 (We will discuss this tendency in the next section). More simulations have been conducted for the isotope effect on thermal conductivity, like the isotopic core-shell Si NWs (Hattori and Uno, 2013) and isotope radial distribution (Royo and Rurali, 2016). The fabrication of Si isotope NWs is demonstrated in Mukherjee et al (2015) using the VLS method and a 30% decrease of thermal conductivity is shown in isotopically mixed 28 Si 30…”