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.
Inelastic electron tunneling in 2H-Ta$_x$Nb$_{1-x}$Se$_2$ evidenced by scanning tunneling spectroscopy
本文报道了用低温扫描隧道显微镜测量的2 H-Ta $_x$ Nb $_{1-x}$ Se $_2$（$x=0\sim 0.1$）单晶的隧道谱。在长时间难以理解的突出的间隙状特征被发现伴随着一些“间隙”精细结构。通过研究二阶导数光谱及其温度和磁场依赖性，我们能够证明非弹性电子隧穿是这些特征的起源，并获得了原子尺度下2 H-Ta $_x$ Nb $_{1-x}$ Se $_2$的Eliashberg函数，为研究相关过渡金属二硫属化物的局域Eliashberg函数和声子谱提供了一种潜在的方法.
Non-equilibrium Effects in Vibrational Modes Pumped by Inelastic Tunneling
State Key Laboratory of Micro-nano Engineering Science, Tsung-Dao Lee Institute & School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院、李政道研究所微纳工程科学国家重点实验室）；SUPA, School of Physics and Astronomy, University of St Andrews（圣安德鲁斯大学物理与天文学院）；Department of Physics, King’s College London（伦敦国王学院物理系）；Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理研究所）；Physikalisches Institut, Universität Bonn（波恩大学物理研究所）
