Revealing the Atomistic and Electronic Structure of Irradiated Oxide Interfaces via DFT and 4D-STEM DPC

Le résumé fourni par la source

Next generation nuclear reactor metal alloy components are exposed to highly irradiating environments [1-6]; under these extreme conditions irradiation and corrosion may couple in unique ways, leading to nanoscale processes that differ from corrosion at ambient conditions [3-5, 7-16]. Gaining insight into this coupling is necessary to develop and apply corrosion mitigation mechanisms to extend the materials’ operational lifetime. Under oxidizing environments, protective oxide coatings can grow above metal underlayers [11, 17-25]. However, subsequent radiation damage in these coatings produces a high density of positively charged oxygen vacancy point defects, which are formed when oxygen atoms are displaced and carry along excess electrons. This process is explored in prior work where Fe2O3–Cr2O3 superlattice films grown epitaxially along the [0001] direction, exhibited interfacial electronic band offsets that were highly dependent on the atomic-scale structure of the interface [26]. Thus, the central question remains whether migration of charged point defects, a proxy for corrosion, can be controlled by the built-in interfacial electric fields present at oxide interfaces. This detailed study of irradiated Fe2O3–Cr2O3 thin film heterostructures explores the effects of irradiation-induced point defects on interfacial crystal structure by mapping their built-in interfacial electric fields. First-principles ab initio density functional theory (DFT) electronic structure modeling was performed to compute the effect of oxygen vacancies on electronic band offset. These calculations were paired with 4D-STEM differential phase contrast (DPC) imaging under a precessed beam and Electron Energy Loss Spectroscopy (STEM-EELS) technique to measure nanoscale changes in electric field on Fe2O3 / Cr2O3 heterostructures before and after Fe+ ion irradiation [27-29]. Our results show clear evidence that irradiation drives substantial modulation of interfacial electric fields corresponding to the atomistic structure of the interface. We demonstrate that irradiation selectively induces built-in electric fields, allowing for the manipulation of their direction; this suggests a method to electrically control the spatial distribution of defects by engineering oxide interfaces, which has significant implications for designing corrosion-resistant materials intended for extreme environments [30].

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