Abstract
We report a unique in situ instrument development effort dedicated to studying gas/solid interactions relevant to heterogeneous catalysis and early stages of oxidation of materials via atom probe tomography and microscopy (APM). An in situ reactor cell, similar in concept to other reports, has been developed to expose nanoscale volumes of material to reactive gas environments, in which temperature, pressure, and gas chemistry are well controlled. We demonstrate that the combination of this reactor cell with APM techniques can aid in building a better mechanistic understanding of resultant composition and surface and subsurface structure changes accompanying gas/surface reactions in metal and metal alloy systems through a series of case studies: O2/Rh, O2/Co, and O2/Zircaloy-4. In addition, the basis of a novel operando mode of analysis within an atom probe instrument is also reported. The work presented here supports the implementation of APM techniques dedicated to atomic to near-atomically resolved gas/surface interaction studies of materials broadly relevant to heterogeneous catalysis and oxidation.
Highlights
The physics governing chemical reactions at surfaces and interfaces, involved in both heterogeneous catalysis and oxidation processes, share fundamental synergistic interactions between reactant gases and specific surface structures [1]
At Pacific Northwest National Laboratory (PNNL), significant effort has been dedicated to developing a suite of hardware and experimental protocols for the preparation and handling of environmentally sensitive materials centered around a unique environmental transfer hub (ETH) chamber [40]
The central hub chamber design allows the connection of ancillary chambers, such as an Environmental Chemical Reactor (ECR) for controlled gas-phase surface reaction studies and ultra-high vacuum (UHV) specimen transfer to the Local Electrode Atom Probe (LEAP) for atom probe tomography (APT) analysis
Summary
The physics governing chemical reactions at surfaces and interfaces, involved in both heterogeneous catalysis and oxidation processes, share fundamental synergistic interactions between reactant gases and specific surface structures [1]. The application of FET techniques in the field of surface science can reveal valuable insight into chemical reaction dynamics on nanoscale metal surfaces [12, 26, 27], non-linear dynamics such as the oscillatory water formation [28], and even be used to track the path of activated oxygen atoms from their surface formation to their subsurface penetration [29] During these studies, the specimen surfaces were directly imaged by FIM and FEM while exposed to reactive gases, allowing the observation of reaction dynamics in real time over a structurally complex hemispherical specimen surface. In the original work presented here, we detail the design and operating principles of an in situ reactor directly attached to a Local Electrode Atom Probe (LEAP) instrument for studying material structure and composition changes via correlative FEM and APT Results obtained using this capability are reported for a variety of material systems, including cobalt (Co), rhodium (Rh), and a zirconium (Zr) alloy. Tomographic data reconstruction and analysis were performed using CAMECA’s Integrated Visualization & Analysis Software (IVAS) version 3.6.14
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