Ultra-low thermal conductivity and acoustic dynamics of Si nanostructured metalattices probed using ultrafast high harmonic beams

Begoña Abad Mayor ,Disha Talreja,Venkat Gopalan,Pratibha Mahale,Weinan Chen,Joshua Knobloch,Yihuang Xiong,Travis Frazer,Jorge N Hernández-Charpak ,Noel C Giebink ,Henry C Kapteyn ,Ismaïla Dabo ,John V Badding ,Alex J Grede ,Tom Mallouk,Vincent H Crespi ,Hiu Yan Cheng ,Margaret M Murnane

doi:10.1051/epjconf/201920504006

Abstract

We extend optical nanometrology capabilities to smaller dimensions by using tabletop coherent extreme ultraviolet (EUV) beams. Specifically, we characterize thermal transport and acoustic wave propagation in 3D periodic silicon inverse metalattices with <15nm characteristic dimensions. Measurements of the thermal transport demonstrate that metalattices may significantly impede heat flow, making them promising candidates for thermoelectric applications. Extraction of the acoustic wave dispersion down to ~100nm shows good agreement with finite element predictions, confirming that these semiconductor metalattices were fabricated with a very high-quality. These results demonstrate that EUV nanometrology is capable of extracting both dispersion relations, and thermal properties of 3D complex nano-systems, with applications including informed design and process control of nanoscale devices.

Highlights

Nanoscale metamaterials make it possible to engineer the transport, electronic and magnetic properties of materials, which is critical for nanoelectronics, thermoelectric and data storage devices [1]
We extend ultrafast short wavelength high harmonic nanometrology to probe thermal and acoustic dynamics in novel silicon metalattices - which are polycrystalline silicon infiltrated into a self-assembled 14-30nm face-centered cubic silica nanosphere templates to form a nanoscale inverse opal (Fig. 1)
In our extreme ultraviolet (EUV) nanometrology (Fig. 1), we monitor the change in diffraction efficiency as a function of pump-probe time delay to extract these surface dynamics

Summary

Introduction

Nanoscale metamaterials make it possible to engineer the transport, electronic and magnetic properties of materials, which is critical for nanoelectronics, thermoelectric and data storage devices [1]. Nanoscale inverse opal metalattices combine precise nanostructuring with long range order by infiltrating various materials into nanosphere opal templates (see Fig. 1). This enables unique properties not accessible otherwise [2]. We extend ultrafast short wavelength high harmonic nanometrology to probe thermal and acoustic dynamics in novel silicon metalattices - which are polycrystalline silicon infiltrated into a self-assembled 14-30nm face-centered cubic silica nanosphere templates to form a nanoscale inverse opal (Fig. 1). The short wavelength (≈30 nm) and pulse duration (≈10 fs) of the tabletop high harmonic generation source match the intrinsic length- and time-scales of the relevant nanoscale dynamics, making it an ideal probe of nanostructured systems [3, 4]

Experimental section

Thermal transport and acoustic dynamics of Si metalattices