Johnson C W, Schmid A K, Mankos M, Röpke R, Kerker N, Wong E K, Ogletree D F, Minor A M, Stibor A
Lawrence Berkeley National Lab, Molecular Foundry, Berkeley, California 94720, USA.
Electron Optica Inc., Palo Alto, California 94303, USA.
Phys Rev Lett. 2022 Dec 9;129(24):244802. doi: 10.1103/PhysRevLett.129.244802.
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 ultranarrow distribution down to 16 meV due to tunable resonant tunneling field emission via localized band states at a nanoprotrusion's apex and a cutoff 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.
产生、操控和探测相干电子是未来量子显微镜和光谱技术的核心。利用并特别改变低温下电子束源的量子特性可以增强其发射特性。在此，我们描述了在5.9K温度下从单晶超导铌纳米尖端的场电子发射。发射的电子能谱显示，由于通过纳米突出顶端的局域能带态的可调谐共振隧穿场发射以及在低温下尖锐的费米边缘处的截止，能谱呈现出低至16meV的超窄分布。这比传统场发射电子源低一个数量级。尖端的自聚焦几何结构导致发射角度为3.7°，亮度降低至3.8×10⁸ A/(m² sr V)，并且在4.1nA束流和69meV能量宽度下可保持数小时的稳定性。这种源将减少透镜像差的影响，并在低能电子显微镜、电子能量损失谱和高分辨率振动光谱中实现新模式。
