Unocic Kinga A, Walden Franklin S, Marthe Nelson L, Datye Abhaya K, Bigelow Wilbur C, Allard Lawrence F
Center for Nanophase Materials Sciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Rd, Oak Ridge, TN37831, USA.
Protochips Inc., 3800 Gateway Centre Blvd, Suite 306, Morrisville, NC27560, USA.
Microsc Microanal. 2020 Apr;26(2):229-239. doi: 10.1017/S1431927620000185.
Protocols for conducting in situ transmission electron microscopy (TEM) reactions using an environmental TEM with dry gases have been well established. However, many important reactions that are relevant to catalysis or high-temperature oxidation occur at atmospheric pressure and are influenced by the presence of water vapor. These experiments necessitate using a closed-cell gas reaction TEM holder. We have developed protocols for introducing and controlling water vapor concentrations in experimental gases from 2% at a full atmosphere to 100% at ~17 Torr, while measuring the gas composition using a residual gas analyzer (RGA) on the return side of the in situ gas reactor holder. Initially, as a model system, cube-shaped MgO crystals were used to help develop the protocols for handling the water vapor injection process and confirming that we could successfully inject water vapor into the gas cell. The interaction of water vapor with MgO triggered surface morphological and chemical changes as a result of the formation of Mg(OH)2, later validated with mass spectra obtained with our RGA system with and without water vapor. Integrating an RGA with an in situ scanning/TEM closed-cell gas reaction system can thus provide critical measurements correlating gas composition with dynamic surface restructuring of materials during reactions.
使用配备干燥气体的环境透射电子显微镜（TEM）进行原位透射电子显微镜反应的实验方案已经很成熟。然而，许多与催化或高温氧化相关的重要反应是在大气压下发生的，并且会受到水蒸气存在的影响。这些实验需要使用封闭细胞气体反应TEM样品杆。我们已经制定了实验气体中水蒸气浓度的引入和控制方案，范围从全大气压下的2%到约17托时的100%，同时使用原位气体反应堆样品杆返回侧的残余气体分析仪（RGA）测量气体成分。最初，作为一个模型系统，使用立方体形的MgO晶体来帮助制定处理水蒸气注入过程的方案，并确认我们能够成功地将水蒸气注入气室。由于形成了Mg(OH)₂，水蒸气与MgO的相互作用引发了表面形态和化学变化，随后通过我们的RGA系统在有水蒸气和无水蒸气情况下获得的质谱进行了验证。因此，将RGA与原位扫描/TEM封闭细胞气体反应系统集成，可以提供关键测量，将气体成分与反应过程中材料的动态表面重构联系起来。
