Mun Junsik, Potemkin Daniel, Jang Houk, Park Suji, Mick Stephen, Petrovic Cedomir, Cheong Sang-Wook, Han Myung-Geun, Zhu Yimei
Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA.
Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, NY 11973, USA; Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794, USA.
Ultramicroscopy. 2024 Dec;267:114039. doi: 10.1016/j.ultramic.2024.114039. Epub 2024 Sep 7.
Fundamental quantum phenomena in condensed matter, ranging from correlated electron systems to quantum information processors, manifest their emergent characteristics and behaviors predominantly at low temperatures. This necessitates the use of liquid helium (LHe) cooling for experimental observation. Atomic resolution scanning transmission electron microscopy combined with LHe cooling (cryo-STEM) provides a powerful characterization technique to probe local atomic structural modulations and their coupling with charge, spin and orbital degrees-of-freedom in quantum materials. However, achieving atomic resolution in cryo-STEM is exceptionally challenging, primarily due to sample drifts arising from temperature changes and noises associated with LHe bubbling, turbulent gas flow, etc. In this work, we demonstrate atomic resolution cryo-STEM imaging at LHe temperatures using a commercial side-entry LHe cooling holder. Firstly, we examine STEM imaging performance as a function of He gas flow rate, identifying two primary noise sources: He-gas pulsing and He-gas bubbling. Secondly, we propose two strategies to achieve low noise conditions for atomic resolution STEM imaging: either by temporarily suppressing He gas flow rate using the needle valve or by acquiring images during the natural warming process. Lastly, we show the applications of image acquisition methods and image processing techniques in investigating structural phase transitions in CrGeTe, CuIrS, and CrCl. Our findings represent an advance in the field of atomic resolution electron microscopy imaging for quantum materials and devices at LHe temperatures, which can be applied to other commercial side-entry LHe cooling TEM holders.
凝聚态物质中的基本量子现象，从关联电子系统到量子信息处理器，主要在低温下展现其涌现特性和行为。这就需要使用液氦（LHe）冷却来进行实验观测。结合LHe冷却的原子分辨率扫描透射电子显微镜（低温扫描透射电子显微镜，cryo-STEM）提供了一种强大的表征技术，用于探测量子材料中局部原子结构调制及其与电荷、自旋和轨道自由度的耦合。然而，在低温扫描透射电子显微镜中实现原子分辨率极具挑战性，主要原因是温度变化引起的样品漂移以及与液氦冒泡、湍流气流等相关的噪声。在这项工作中，我们展示了使用商用侧入式LHe冷却支架在LHe温度下进行原子分辨率低温扫描透射电子显微镜成像。首先，我们研究了作为氦气流速函数的扫描透射电子显微镜成像性能，确定了两个主要噪声源：氦气脉冲和氦气泡泡。其次，我们提出了两种实现原子分辨率扫描透射电子显微镜成像低噪声条件的策略：要么使用针阀临时抑制氦气流速，要么在自然升温过程中采集图像。最后，我们展示了图像采集方法和图像处理技术在研究CrGeTe、CuIrS和CrCl结构相变中的应用。我们的研究结果代表了在LHe温度下量子材料和器件的原子分辨率电子显微镜成像领域的一项进展，可应用于其他商用侧入式LHe冷却透射电子显微镜支架。
