The Metal-Insulator Transition in Vanadium Oxide Nanofilms Enables Microkelvin-Resolution Thermometry.

High-resolution thermometry is critical for probing nanoscale energy transport. Here, we demonstrate how high-resolution thermometry can be accomplished using vanadium oxide (VOx), which features a sizable temperature-dependence of its resistance at room temperature and an even stronger dependence at its metal-insulator-transition (MIT) temperature. We microfabricate VOx nanofilm-based electrical resistance thermometers that undergo a metal-insulator-transition at ∼337 K and systematically quantify their temperature-dependent resistance, noise characteristics, and temperature resolution. We show that VOx sensors can achieve, in a bandwidth of ∼16 mHz, a temperature resolution of ∼5 µK at room temperature (∼300 K) and a temperature resolution of ∼1 µK at the MIT (∼337 K) when the amplitude of temperature perturbations is in the microkelvin range, which, in contrast to larger perturbations, is found to avoid hysteric resistance responses. These results demonstrate that VOx-based thermometers offer a ∼10-50-fold improvement in resolution over widely used Pt-based thermometers.

Micro-kelvin temperature-stable system for biocalorimetry applications.

Achieving micro-kelvin (µK) temperature stability is critical for many calorimetric applications. For example, sub-nanowatt resolution biocalorimetry requires stabilization of the temperature of the calorimeter to µK levels. Here, we describe how µK temperature stability can be accomplished in a prototypical calorimetric system consisting of two nested shields and a suspended capillary tube, which is well suited for biocalorimetry applications. Specifically, we show that by employing nested shields with µTorr-levels of vacuum in the space between them as well as precise feedback control of the temperature of the shields (performed using high-resolution temperature sensors), the effect of ambient temperature fluctuations on the inner shield and the capillary tube can be attenuated by ∼100 dB. We also show that this attenuation is key to achieving temperature stabilities within ±1 and ±3 µK (amplitude of oscillations) for the inner shield and the capillary tube sensor, respectively, measured in a bandwidth of 1 mHz over a period of 10 h at room temperature (∼20.9 ± 0.2 °C). We expect that the methods described here will play a key role in advancing biocalorimetry.