In-Plane Thermal Conductivity of Radial and Planar Si/SiO_x Hybrid Nanomembrane Superlattices.

Abstract

Silicon, although widely used in modern electronic devices, has not yet been implemented in thermoelectric applications mainly due to its high thermal conductivity, κ, which leads to an extremely low thermoelectric energy conversion efficiency (figure of merit). Here, we present an approach to manage κ of Si thin-film-based nanoarchitectures through the formation of radial and planar Si/SiO_x hybrid nanomembrane superlattices (HNMSLs). For the radial Si/SiO_x HNMSLs with various numbers of windings (1, 2, and 5 windings), we observe a continuous reduction in κ with increasing number of windings. Meanwhile, the planar Si/SiO_x HNMSL, which is fabricated by mechanically compressing a five-windings rolled-up microtube, shows the smallest in-plane thermal conductivity among all the reported values for Si-based superlattices. A theoretical model proposed within the framework of the Born-von Karman lattice dynamics to quantitatively interpret the experimental data indicates that the thermal conductivity of Si/SiO_x HNMSLs is to a great extent determined by the phonon processes in the SiO_x layers.