Near-monochromatic tuneable cryogenic niobium electron field emitter

TL;DR

This paper reports on a cryogenic niobium nanotip electron emitter that produces ultra-narrow energy electron beams at low temperatures, promising advancements in quantum microscopy and spectroscopy.

Contribution

It introduces a superconducting niobium nanotip electron source with tunable, ultra-narrow energy distribution at cryogenic temperatures, enhancing electron emission properties for microscopy.

Findings

Energy spectrum with 16 meV width due to resonant tunneling

Emission angle of 3.7 degrees with stable operation

Reduced brightness and high stability over hours

Abstract

Creating, manipulating, and detecting coherent electrons is at the heart of future quantum microscopy and spectroscopy technologies. Leveraging and specifically altering the quantum features of an electron beam source at low temperatures can enhance its emission properties. Here, we describe electron field emission from a monocrystalline, superconducting niobium nanotip at a temperature of 5.9 K. The emitted electron energy spectrum reveals an ultra-narrow distribution down to 16 meV due to tunable resonant tunneling field emission via localized band states at a nano-protrusion's apex and a cut-off at the sharp low-temperature Fermi-edge. This is an order of magnitude lower than for conventional field emission electron sources. The self-focusing geometry of the tip leads to emission in an angle of 3.7 deg, a reduced brightness of 3.8 x 10exp8 A/(m2 sr V), and a stability of hours at 4.1 nA beam current and 69 meV energy width. This source will decrease the impact of lens aberration and enable new modes in low-energy electron microscopy, electron energy loss spectroscopy, and high-resolution vibrational spectroscopy.