Inelastic Electron Tunneling Spectroscopy at High-Temperatures

TL;DR

This paper introduces the first high-temperature inelastic tunneling spectroscopy method, enabling real-time, high-resolution analysis of ion behavior in solid materials above room temperature, which was previously thought impossible.

Contribution

Development of high-temperature-stable tunnel junctions with ultrathin proton-conducting layers for inelastic tunneling spectroscopy above room temperature.

Findings

Achieved 20 meV spectral resolution at 400 K

Demonstrated detection of O-H vibrational modes in BaZrO3

Overturned previous spectral resolution limits at high temperatures

Abstract

Ion conducting materials are critical components of batteries, fuel cells, and devices such as memristive switches. Analytical tools are therefore sought that allow the behavior of ions in solids to be monitored and analyzed with high spatial resolution and in real time. In principle, inelastic tunneling spectroscopy offers these capabilities. However, as its spectral resolution is limited by thermal softening of the Fermi-Dirac distribution, tunneling spectroscopy is usually constrained to cryogenic temperatures. This constraint would seem to render tunneling spectroscopy useless for studying ions in motion. We report here the first inelastic tunneling spectroscopy studies above room temperature. For these measurements, we have developed high-temperature-stable tunnel junctions that incorporate within the tunnel barrier ultrathin layers for efficient proton conduction. By analyzing the vibrational modes of O-H bonds in BaZrO3-based heterostructures, we demonstrate the detection of protons with a spectral resolution of 20 meV at 400 K (FWHM). Overturning the hitherto existing prediction for the spectral resolution limit of 186 meV (5.4 kBT at 400 K), this resolution enables high-temperature tunneling spectroscopy of ion conductors. With these advances, inelastic tunneling spectroscopy constitutes a novel, valuable analytical tool for solid-state ionics.