电子在圆柱孔和圆孔光阑中的退相干
Electron decoherence in cylindrical holes and circular apertures
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology（光子科学研究所，巴塞罗那科技与科学研究所）
- ICREA-Institució Catalana de Recerca i Estudis Avançats（加泰罗尼亚研究与高级研究学院）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
本文建立快电子在圆柱孔和圆孔光阑中退相干的定量理论，揭示退相干概率随温度、电导率等参数的变化规律，并指出大孔退相干对相干电子束仪器设计至关重要。
AI中文摘要：
自由电子的相干性对相敏电子显微镜的分辨率和对比度设定了基本极限，因为每当电子在其环境中留下可区分的激发时，相干性就会丧失。我们针对两种典型几何结构发展了快电子退相干的定量理论：穿过实际金属的圆柱孔以及薄完美导电薄膜中的圆孔光阑。通过将电磁格林张量表述与涨落-耗散定理相结合，同时完全保留延迟效应，我们获得了退相干概率和弹性相位作为电子轨迹、温度和材料响应的函数。对于圆柱孔，我们得到了一个闭合形式的、方位角分辨的表达式，该表达式将路径位置、温度和电导率的依赖关系分离开来。在高电导率和高温度极限下，该结果简化为一个普适表达式，该表达式与温度呈线性关系，且与电导率和电子速度均无关。对于圆孔光阑，我们使用柱面波模态展开进行求解，其能量损失概率在低频下以$1/\omega$形式发散，而退相干概率保持有限，并在孔径半径与相关电磁波长相当达到最大值。由于相互作用在空间上是局域的，孔径引起的退相干通常弱于圆柱孔产生的退相干，除非在高温下孔径足够大。最后，我们表明，对于足够大的孔，退相干可以主导聚焦电子探针的空间展宽，因此必须将其纳入相干电子束仪器的设计中。
英文摘要：
The coherence of free electrons sets fundamental limits on the resolution and contrast of phase-sensitive electron microscopy because coherence is lost whenever the electron leaves a distinguishing excitation in its environment. We develop a quantitative theory of fast-electron decoherence in two canonical geometries: a cylindrical hole drilled through a realistic metal and a circular aperture in a thin perfectly conducting film. By combining an electromagnetic Green-tensor formulation with the fluctuation--dissipation theorem while fully retaining retardation, we obtain the decoherence probability and elastic phase as functions of the electron trajectory, temperature, and material response. For the cylindrical hole, we obtain a closed-form, azimuthally resolved expression that separates the dependences on path position, temperature, and conductivity. In the high-conductivity and high-temperature limits, this result reduces to a universal expression that is linear in temperature and independent of both conductivity and electron velocity. For the circular aperture, which we solve using a cylindrical-wave modal expansion, the energy-loss probability diverges as $1/ω$ at low frequency, whereas the decoherence probability remains finite and reaches a maximum when the aperture radius is comparable to the relevant electromagnetic wavelength. Because the interaction is spatially localized, aperture-induced decoherence is generally weaker than that produced by a cylindrical hole, except for sufficiently large apertures at high temperature. Finally, we show that, for sufficiently large holes, decoherence can dominate the spatial broadening of a focused electron probe and must therefore be incorporated into the design of coherent electron-beam instruments.
