Thermal conductivity engineering of bulk and one-dimensional Si-Ge nanoarchitectures

Ali Kandemir; Ayberk Ozden; Tahir Cagin; Cem Sevik

doi:10.1080/14686996.2017.1288065

Thermal conductivity engineering of bulk and one-dimensional Si-Ge nanoarchitectures

Sci Technol Adv Mater. 2017 Mar 13;18(1):187-196. doi: 10.1080/14686996.2017.1288065. eCollection 2017.

Authors

Ali Kandemir¹, Ayberk Ozden², Tahir Cagin^{3

4}, Cem Sevik⁵

Affiliations

¹ Department of Materials Science and Engineering, Izmir Institute of Technology, Izmir, Turkey.
² Faculty of Engineering, Department of Material Science and Engineering, Anadolu University, Turkey.
³ Department of Materials Science and Engineering, Texas A & M University, College Station, TX, USA.
⁴ Artie McFerrin Department of Chemical Engineering, Texas A & M University, College Station, TX, USA.
⁵ Faculty of Engineering, Department of Mechanical Engineering, Anadolu University, Eskisehir, Turkey.

Abstract

Various theoretical and experimental methods are utilized to investigate the thermal conductivity of nanostructured materials; this is a critical parameter to increase performance of thermoelectric devices. Among these methods, equilibrium molecular dynamics (EMD) is an accurate technique to predict lattice thermal conductivity. In this study, by means of systematic EMD simulations, thermal conductivity of bulk Si-Ge structures (pristine, alloy and superlattice) and their nanostructured one dimensional forms with square and circular cross-section geometries (asymmetric and symmetric) are calculated for different crystallographic directions. A comprehensive temperature analysis is evaluated for selected structures as well. The results show that one-dimensional structures are superior candidates in terms of their low lattice thermal conductivity and thermal conductivity tunability by nanostructuring, such as by diameter modulation, interface roughness, periodicity and number of interfaces. We find that thermal conductivity decreases with smaller diameters or cross section areas. Furthermore, interface roughness decreases thermal conductivity with a profound impact. Moreover, we predicted that there is a specific periodicity that gives minimum thermal conductivity in symmetric superlattice structures. The decreasing thermal conductivity is due to the reducing phonon movement in the system due to the effect of the number of interfaces that determine regimes of ballistic and wave transport phenomena. In some nanostructures, such as nanowire superlattices, thermal conductivity of the Si/Ge system can be reduced to nearly twice that of an amorphous silicon thermal conductivity. Additionally, it is found that one crystal orientation, [Formula: see text]100[Formula: see text], is better than the [Formula: see text]111[Formula: see text] crystal orientation in one-dimensional and bulk SiGe systems. Our results clearly point out the importance of lattice thermal conductivity engineering in bulk and nanostructures to produce high-performance thermoelectric materials.

Keywords: Molecular dynamics; alloy; interface roughness; nanowire; superlattices; thermal conductivity; thermoelectric.

Grants and funding

The work was supported from Scientific and Technological Research Council of Turkey (TUBITAK-113F096), Anadolu University (BAP-1306F281, 1407F335) and Turkish Academy of Sciences (TUBA-GEBIP). TC acknowledges partial support from the International Institute of Materials for Energy Conversion (IIMEC) at Texas A & M University, an NSF International Materials Institute (DMR 0844082).