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Ute Kaiser1

1, University of Ulm, Ulm, , Germany

Recent advancements in transmission electron microscopy (TEM) have made it possible to directly visualise and determine sites of individual atoms in low-dimensional materials. Here we present recent results on in-situ dynamical, voltage-dependent behaviour after the interaction with 80kV-20kV electrons, using our recently developed high-resolution low-voltage SALVE instrument [1]. We discuss examples of interaction mechanisms in single-layer transition metal dichalcogenides, the study of their atomic and electronic structure, including charge density wave (CDW) materials at room temperature as well as at cryogenic temperatures in both reciprocal and real spaces. 1T-TaS2 in particular is investigated in its pristine form as well as intercalated with pyridine (C5H5N), and triethylenediamine (C6H12N2). Using momentum-resolved valence electron energy loss spectroscopy (MR-VEELS), we have determined the nature and dispersion of the plasmon and interband excitations.
As a second class of materials we report on in-situ studies about the atomic structure of, in-between graphene, encapsulated calcium sulfate solution. We found that only a few-layer thick crystalline anhydrite (CaSO4) in the so-called AII phase has been formed and we addressed the liquid-solid crystallization process to internal pressure inside the graphene pockets [2], similarly to the crystallization in [3,4].
We present another class of in-situ studies between two graphene layers, regarded as a fundamental unit of a graphite anode, and relate our results towards novel electrochemical energy storage solutions. In particular, a miniaturized electrochemical cell is presented. We reversibly lithiate single-crystalline bilayer graphene devices in controlled manner using an electrochemical gate confined to a device protrusion. Electron-beam stimulated chemical reaction inside carbon nanotubes are also presented for a wide range of transition metals and discussed in the light of nanocatalysis. [5]
[1] M. Linck, P. Hartel, S. Uhlemann, F. Kahl, H. Müller, J. Zach, M Haider, M. Niestadt M. Bischoff, J. Biskupek, Z. Lee, T. Lehnert, F. Börrnert, H. Rose, and U. Kaiser 117 (2016) 076101.
[2] T. Lehnert, M. Kinyanjui, A. Ladenburger, D. Rommel, K. Wörle, F. Börrnert, K. Leopold and U. Kaiser, ACS nano 11 (2017) 7967-7973.
[3] E. Khestanova, F. Guinea, L. Fumagalli, A.K. Geim and I.V. Grigorieva; Nature Communications, 7:12587, 2016
[4]K.S. Vasu, E. Prestat, J. Abraham, J. Di, R.J. Kashtiban, J. Beheshtian, J. Sloan, P. Carbone, M. Neek-Amal, S.J. Haigh, A.K. Geim and R.R. Nair; Nature Communications, 7:12168, 2016
[5] The authors greatly acknowledge funding from the German Research Foundation (DFG) and the Ministry of Science, Research and the Arts (MWK) of the federal state Baden-Württemberg, Germany in the frame of the SALVE project (www.salve-project.de).

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