Memristive devices – electronic components that can change their resistance depending on their history of operation – offer a new approach in various fields of digital computing.  This advancement in information technology is being pursued in order to satisfy the ever increasing need for computing power on the one hand and to enable the imitation of neuronal networks like the hippocampus on the other. The conductive properties in memristive devices are typically governed by atomistic effects like cation or anion movement: the change of resistance state is dependent on the nanoscopic layout. The mechanisms, however, behind a non-binary, remanent, reversible and repeatable change of electrical resistance are not well understood. In this work we present the results of dedicated transmission electron microscopy (TEM) analysis involving highly precise electron energy loss spectroscopy (EELS) methods in a complex oxide multilayer stack of only about ten nanometer total thickness. The layer sequence Nb/Al/Al2O3/NbxOy/Au (from bottom to top; Fig. 1 a) was deposited onto a Si/SiO2 substrate. The memristive properties of such junctions were recently investigated. 
Combined energy dispersive X-ray spectroscopy (EDX) and EELS experiments allow for analyses of both light and heavy metals as well as the reliable detection of oxygen. In contrast to the deposited layer sequence we observe an entire oxidation of the metallic Al and even a partial oxidation of the Nb bottom electrode. (Fig. 1 b) and Fig. 2) Furthermore, the results imply the abundant presence of oxygen vacancies apparent from the O K-peak in the spectrum of the amorphous Al oxide layer which acts as a tunnel barrier. (Fig. 1 c) These puzzling results will be discussed in the framework of former studies on the Nb-Al overlayer technique. 
Different conduction mechanisms are being discussed based on the findings and an outlook onto further research by electronic structure calculation is given. The results shed light on the fundamentals of tunnel barrier-based memristive devices which are compatible to state-of-the-art CMOS technology and were already built into integrated circuits.
Acknowledgements: The research was conducted within the DFG program FOR2093 “Memristive devices for neuronal networks”. This research has received funding from the European Union within the 7th Framework Program (FP7/2007-2013) under Grant Agreement no. 312483 (ESTEEM2).
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To cite this abstract:Julian Strobel, Mirko Hansen, Georg Haberfehlner, Gerald Kothleitner, Martin Ziegler , Hermann Kohlstedt, Lorenz Kienle; Combined EELS-EDX analysis of nanoscale memristive NbOx and AlOx layers. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/combined-eels-edx-analysis-of-nanoscale-memristive-nbox-and-alox-layers/. Accessed: December 12, 2018
EMC Abstracts - https://emc-proceedings.com/abstract/combined-eels-edx-analysis-of-nanoscale-memristive-nbox-and-alox-layers/