Near-Monochromatic Tuneable Cryogenic Niobium Electron Field Emitter

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 • , a reduced brightness of 3.8 × 10 8 A/(m 2 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.

Highly Localized Optical Field Enhancement at Neon Ion Sputtered Tungsten Nanotips

“…Since the enhanced near-field is strongly confined to the nanotip, we expect the emission volume to be very small, which could result in highly coherent emission. , Nanotips can be utilized as sources for ultrashort electron pulses through photoemission since the mechanism of multiphoton photoemission and optical field emission is shown to be prompt within the duration of an optical cycle. ,, By combining these properties, an intriguing low-emittance electron emitter producing ultrashort electron pulses could be demonstrated in the future. Furthermore, at low temperatures, nanotips are known to have an extremely narrow transverse energy width in field emission . Provided that this property is conserved for photoemission, nanotips could prove to be highly interesting sources for applications such as ultrafast electron microscopy.…”

“…32 These properties were recently utilized to demonstrate a field emission source with extremely high brightness and narrow energy width. 33 In this Letter, we present the first observation of strong-field photoemission and rescattering at a nanotip, which we fabricated from tungsten needle tips via self-sputtering with neon ions. We investigate the expected high localization and enhancement of the near-field at the nanotip and compare the results with FDTD simulations and with the experimentally extracted near-field at a conventional needle tip.…”

“…Additionally, as the field enhancement is strongly spatially confined, the emission is also confined . These properties were recently utilized to demonstrate a field emission source with extremely high brightness and narrow energy width …”

“…Furthermore, at low temperatures, nanotips are known to have an extremely narrow transverse energy width in field emission. 33 Provided that this property is conserved for photoemission, nanotips could prove to be highly interesting sources for applications such as ultrafast electron microscopy. The fabrication method could also be applied to tips made from other materials in order to exploit specific material properties, such as the plasmonic response of gold or silver.…”

Enhanced Emission for Improved Electron Spectroscopy

“…The technique is still nascent, however, offering only limited energy resolution. To further improve the capabilities of electron spectroscopy, Alexander Stibor from the Lawrence Berkeley National Laboratory, California, and the University of Tübingen, Germany, along with his colleagues have developed a bright, highly collimated electron source with a narrow spectral width, promising record energy resolution [4]. This new technology could lead to high-resolution imaging in previously unmeasured "colors" that can also reveal molecular vibrational modes.…”