Thermal conductivity reduction in silicon fishbone nanowires

Jeremie Maire,Roman Anufriev,Masahiro Nomura,Sebastian Volz,Takuma Hori,Junichiro Shiomi

doi:10.1038/s41598-018-22509-0

Abstract

Semiconductor nanowires are potential building blocks for future thermoelectrics because of their low thermal conductivity. Recent theoretical works suggest that thermal conductivity of nanowires can be further reduced by additional constrictions, pillars or wings. Here, we experimentally study heat conduction in silicon nanowires with periodic wings, called fishbone nanowires. We find that like in pristine nanowires, the nanowire cross-section controls thermal conductivity of fishbone nanowires. However, the periodic wings further reduce the thermal conductivity. Whereas an increase in the wing width only slightly affects the thermal conductivity, an increase in the wing depth clearly reduces thermal conductivity, and this reduction is stronger in the structures with narrower nanowires. Our experimental data is supported by the Callaway-Holland model, finite element modelling and phonon transport simulations.

Highlights

Thermal transport in low dimensional and nanostructured materials has attracted high attention over the past decades, in particular with regards to promising prospects in thermoelectric energy generation[1], including the possibility of using the wave properties of phonons, which can be relevant at cryogenic temperatures[2,3]
We experimentally demonstrate that the transient behaviour of the fishbone NWs follow the mass contrast, and that thermal conductivity and thermal relaxation rates can be reduced at room temperature by more than 20% and 35%, respectively
The nanostructures are processed on the 145 nm-thick undoped upper single-crystalline silicon layer. 4 × 4 μm[2] squares are drawn by electron beam lithography and 125-nm-thick aluminum pads are deposited via electron beam assisted metal evaporation

Summary

OPEN Thermal conductivity reduction in silicon fishbone nanowires

Jeremie Maire[1,2], Roman Anufriev 1, Takuma Hori[3], Junichiro Shiomi[3,4], Sebastian Volz1,2 & Masahiro Nomura[1,5]. A few experimental works[21,22] have demonstrated a reduction of thermal conductivity in corrugated silicon NWs due to the limited phonon mean free path[21,22] To further enhance this surface scattering, theoretical works[23,24,25,26] proposed various diameter-modulated NWs and found that heat conduction is strongly suppressed in these structures. Is it possible to reduce thermal conductivity proportionally to the ratio between the corrugation and the central constriction, but this reduction can be larger than an order of magnitude at room temperature for structures of a couple of nanometers in width[25]. We experimentally demonstrate that the transient behaviour of the fishbone NWs follow the mass contrast, and that thermal conductivity and thermal relaxation rates can be reduced at room temperature by more than 20% and 35%, respectively

Fabrication and Measurements

Results and Discussion

Methods

Author Contributions

Additional Information