Superconducting Niobium Tip Electron Beam Source

TL;DR

This paper investigates a superconducting niobium tip electron emitter that offers high current stability and ultra-narrow energy distribution, enhancing electron microscopy and spectroscopy resolution at various temperatures.

Contribution

It introduces a novel niobium tip electron emitter with tunable configurations, demonstrating improved energy width and current stability, suitable for advanced microscopy and quantum applications.

Findings

Energy width around 100 meV at 5.2 K

Energy width below 40 meV at 82 K with nano-protrusion

Beam current increased by two orders of magnitude with xenon adsorption

Abstract

Modern electron microscopy and spectroscopy is a key technology for studying the structure and composition of quantum and biological materials in fundamental and applied sciences. High-resolution spectroscopic techniques and aberration-corrected microscopes are often limited by the relatively large energy distribution of currently available beam sources. This can be improved by a monochromator, with the significant drawback of losing most of the beam current. Here, we study the field emission properties of a monocrystalline niobium tip electron field emitter at 5.2 K, well below the superconducting transition temperature. The emitter fabrication process can generate two tip configurations, with or without a nano-protrusion at the apex, strongly influencing the field-emission energy distribution. The geometry without the nano-protrusion has a high beam current, long-term stability, and an energy width of around 100 meV. The beam current can be increased by two orders of magnitude by xenon gas adsorption. We also studied the emitter performance up to 82 K and demonstrated the beam's energy width can be below 40 meV even at liquid nitrogen cooling temperatures when an apex nano-protrusion is present. Furthermore, the spatial and temporal electron-electron correlations of the field emission are studied at normal and superconducting temperatures and the influence of Nottingham heating is discussed. This new monochromatic source will allow unprecedented accuracy and resolution in electron microscopy, spectroscopy, and high-coherence quantum applications.