Imaging heat transport in suspended diamond nanostructures with integrated spin defect thermometers

TL;DR

This study uses nitrogen-vacancy centers in diamond to image heat transport in microstructures, revealing non-diffusive behavior and the influence of phonon scattering mechanisms, with implications for nanoscale thermal management.

Contribution

It introduces a novel temperature-imaging technique in diamond microstructures using spin defect thermometers, enabling detailed study of non-diffusive heat transport phenomena.

Findings

Thermal conductivity decreases as cantilever width shrinks.

First-principles simulations match experimental observations.

Non-diffusive heat transport is influenced by phonon scattering mechanisms.

Abstract

Among all materials, mono-crystalline diamond has one of the highest measured thermal conductivities, with values above 2000 W/m/K at room temperature. This stems from momentum-conserving `normal' phonon-phonon scattering processes dominating over momentum-dissipating `Umklapp' processes, a feature that also suggests diamond as an ideal platform to experimentally investigate phonon heat transport phenomena that violate Fourier's law. Here, we introduce dilute nitrogen-vacancy color centers as in-situ, highly precise spin defect thermometers to image temperature inhomogeneities in single-crystal diamond microstructures heated from ambient conditions. We analyze cantilevers with cross-sections in the range from about 0.2 to 2.6 $\mu$m$^2$, observing a strong reduction of the cantilevers' conductivity as the width decreases. We use first-principles simulations based on the linearized phonon Boltzmann transport equation and viscous heat equations to quantitatively predict the cantilevers' thermal transport properties, rationalizing how the interplay between intrinsic and extrinsic phonon scattering mechanisms determines the observed non-diffusive behavior. Our temperature-imaging method paves the way for the exploration of unconventional, non-diffusive heat transport phenomena in devices and nanostructures of arbitrary geometries.