Development of a high-energy-, high-spatial-, and high-momentum-resolution electron energy loss spectrometer with liquid-Helium cooling stage (HR3-EEL spectrometer)

在过去的二十年里，光谱学技术在探测固体中的低能激发方面取得了长足的发展，在许多情况下，这导致了对基本固体效应的理解的重要突破。突出的例子是角分辨光电子能谱(ARPES)或扫描隧道谱(STS)，其中包括证明了拓扑绝缘体中存在无间隙表面态和高温超导体中存在各向异性带隙。这是可能的，因为这些技术探测表面的激发具有极好的能量分辨率(MEV范围或更低，取决于低温条件)以及高空间或角分辨率。然而，一种分析块体(和表面)中同时具有高能、高动量和高空间分辨率的电子和振动激发的光谱技术仍然缺乏，一直到深低温条件(液氦冷却)。例如，这样的工具将允许研究各种类型的低维结构(例如，界面、范德华材料)，在扩展维度上具有高动量分辨率，同时在非均匀方向上保持高空间分辨率。它将允许故意定制空间和动量分辨率，以研究复杂纳米结构(例如纳米光子器件和电子器件、有机半导体，但也包括缺陷)中的介电响应细节，包括非局部介电响应效应，如介电色散的空间变化。本项目的目标是通过建立一台全面改进的传输电子能损谱仪来实现这一雄心壮志。关键部件包括新开发的磁地电位单色仪、新的连续流动L-和样品台、改进的扇形磁铁能量过滤器和快速2DCMOSe电子探测器，这些都集成到了经过调整的最先进的瞬变电磁平台中，包括冷场发射枪和全面的、可自由配置的聚光器和投影光学元件等。该仪器将在鳗鱼光谱模式下达到低于10 meV的能量分辨率、极少的nm空间分辨率、小于1/µm的动量分辨率和低于10K的温度并行，以及在其他工作模式下的原子分辨率、电场和磁场传感。这一关键数字的突破大大拓宽了我们对各种主题材料中电荷密度响应函数的基本理解，这些材料包括高温超导体、拓扑绝缘体、Weyl和Dirac半金属、等离子体纳米结构、有机半导体、软生物物质或相关物质，从而深入了解它们特殊而普遍的基态和动力学性质(例如，电荷传输、介电响应、电子和声子能带结构、电荷有序)。

The last two decades have witnessed substantial development of spectroscopy techniques that probe low-energy excitations in solids, which, in many cases, lead to important breakthroughs in the understanding of fundamental solid-state effects. Prominent examples are Angular Resolved Photoemission Spectroscopy (ARPES) or Scanning Tunneling Spectroscopy (STS), which, amongst others, demonstrated the existence of gapless surface states in topological insulators and anisotropic gaps in high-temperature superconductors. That was possible because these techniques probe excitations at the surface with an excellent energy resolution (meV regime and below depending on cryogenic conditions) and high spatial or angular resolution. Nevertheless, a spectroscopic technique for analyzing electronic and vibrational excitations in the bulk (and surface) with simultaneous high-energy, high-momentum, and high-spatial resolution down to deep cryogenic conditions (liquid Helium cooling) is still missing. Such a tool would, for instance, allow studying the diverse class of low-dimensional structures (e.g., interfaces, van der Waals materials) with high momentum resolution in the extended dimensions, while maintaining high-spatial resolution in the inhomogeneous direction. It would allow deliberately tailoring spatial and momentum resolution for investigating the details of the dielectric response in complex nanostructures (e.g. nanophotonic and electronic devices, organic semiconductors, but also defects) including non-local dielectric response effects such as spatial variations in the dielectric dispersion. It is the aim of this project to realize this ambition by building a comprehensively improved Transmission Electron Energy Loss spectrometer. Crucial ingredients are a newly developed magnetic ground potential monochromator, a new continuous flow L-He sample stage, an improved sector magnet energy filter, and fast 2D CMOS electron detectors, which are integrated into an adapted state-of-the-art TEM platform including a cold field emission gun and a comprehensive, freely configurable condenser and projection optics, amongst others. The instrument will reach sub 10 meV energy resolution, few nm spatial resolution, sub 1/µm momentum resolution, and sub 10 K temperature in parallel in EEL spectroscopy mode as well as atomic resolution, electric and magnetic field sensing in other operation modes. This breakthrough in various key figures allows drastically widen our basic understanding of the charge density response function in various topical materials such as high-Tc superconductors, topological insulators, Weyl and Dirac semimetals, plasmonic nanostructures, organic semiconductors, soft biologic matter, or correlated matter, providing insight into their specific and universal ground state and dynamic properties (e.g., charge transport, dielectric response, electronic and phononic band structure, charge ordering).