Center for Nanophase Materials Sciences, Oak Ridge National Laboratory;
Center for Nanophase Materials Sciences, Oak Ridge National Laboratory.
J Vis Exp. 2021 Jul 24(173). doi: 10.3791/62174.
Gas reactions studied by in situ electron microscopy can be used to capture the real-time morphological and microchemical transformations of materials at length scales down to the atomic level. In situ closed-cell gas reaction (CCGR) studies performed using (scanning) transmission electron microscopy (STEM) can separate and identify localized dynamic reactions, which are extremely challenging to capture using other characterization techniques. For these experiments, we used a CCGR holder that utilizes microelectromechanical systems (MEMS)-based heating microchips (hereafter referred to as "E-chips"). The experimental protocol described here details the method for performing in situ gas reactions in dry and wet gases in an aberration-corrected STEM. This method finds relevance in many different materials systems, such as catalysis and high-temperature oxidation of structural materials at atmospheric pressure and in the presence of various gases with or without water vapor. Here, several sample preparation methods are described for various material form factors. During the reaction, mass spectra obtained with a residual gas analyzer (RGA) system with and without water vapor further validates gas exposure conditions during reactions. Integrating an RGA with an in situ CCGR-STEM system can, therefore, provide critical insight to correlate gas composition with the dynamic surface evolution of materials during reactions. In situ/operando studies using this approach allow for detailed investigation of the fundamental reaction mechanisms and kinetics that occur at specific environmental conditions (time, temperature, gas, pressure), in real-time, and at high spatial resolution.
通过原位电子显微镜研究气体反应可以用于捕获材料在原子尺度以下的实时形态和微观化学转变。使用（扫描）透射电子显微镜（STEM）进行的原位封闭腔气体反应（CCGR）研究可以分离和识别局部动态反应，这是使用其他表征技术极难捕捉到的。对于这些实验，我们使用了一种利用微机电系统（MEMS）加热微芯片（以下简称“E 芯片”）的 CCGR 支架。这里描述的实验方案详细介绍了在具有校正像差的 STEM 中进行干燥和湿气体原位气体反应的方法。这种方法在许多不同的材料系统中都有相关性，例如在大气压力下以及存在或不存在水蒸气的各种气体中进行的催化和结构材料的高温氧化。这里，描述了几种针对各种材料形态因素的样品制备方法。在反应过程中，带有或不带有水蒸气的残余气体分析仪（RGA）系统获得的质谱进一步验证了反应过程中的气体暴露条件。因此，将 RGA 与原位 CCGR-STEM 系统集成可以提供关键的见解，以在反应过程中根据气体组成与材料的动态表面演变相关联。使用这种方法进行的原位/操作条件研究允许在特定环境条件（时间、温度、气体、压力）下实时进行详细研究基本反应机制和动力学，具有高空间分辨率。
