Imaging and atomic structure engineering of quasi-two-dimensional materials encapsulated between graphene sheets
Final Report Abstract
In this project we combined atomic imaging using low voltage spherical and chromatic aberration corrected (AC) HRTEM experiments and atomistic simulations. The project was carried out by two groups: the experimental microscopy team headed by Ute Kaiser at Ulm and the theory team headed by Arkady Krasheninnikov at HZDR. The teams studied the formation process, the structure, and the properties of novel two‐dimensional (2D) materials encapsulated between sheets of graphene and other 2D materials. Specifically, water, aqueous solutions of salts, and metals were encapsulated and studied using AC‐HRTEM in a wide range of temperatures and low electron voltages (20‐80 kV). Interestingly, we found from experiments with graphene‐encapsulated NaCl as well as for graphene‐encapsulated Li that only high‐quality graphene without defects is suitable for protecting ionic crystals from electron beam damage in TEM studies. On the other hand, since electron irradiation induces the formation of defects in the encapsulated materials through several mechanisms and chemical reactions, the electron beam was used to engineering new confined nanostructures and quasi‐2D crystals. To obtain complete understanding of the electron beam‐induced transformations and the role of radiation‐induced defects, multiscale atomistic simulations were carried out. A new computational approach based on the non‐adiabatic Ehrenfest dynamics combined with time‐dependent density‐functional theory was developed and implemented in a dedicated computer software and connected to the kinetic Monte‐Carlo schemes to describe the evolution of the system on a macroscopic time scale. A sophisticated sample platform for in‐situ TEM experiments developed in cooperation with colleagues at MPI Stuttgart (Dr. J. Smet) allowed to image the process of lithiation and delithiation between sheets of graphene under the influence of a biasing current for the first time. The discovered Li structures were investigated in atomic resolution and the resulting structure could be explained by first‐principles calculation. The project resulted in 12 publications (among them, 8 joint papers) including papers in prestigious journals like Nature, ACS Nano and Nano Letters. The COVID 19 pandemic slowed the project progress a little down because experimental work was prohibited at UUlm for a period of 10 weeks. The project meetings between the groups were mostly held using video conference. With respect to the benefits of the society, the results provided theoretical support to the ongoing fundamental experimental studies on 2D materials, and graphene‐encapsulated ionic crystal in the context of their future applications in electronics and energy storage, and in particular explained the development of irradiation damage in inorganic 2D materials under electron irradiation. We demonstrated our results to the public at science days at Ulm University in 2018, 2019, 2020. The results obtained within the project were also made available to the general public through online press releases.
Publications
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"Supported Two‐Dimensional Materials under Ion Irradiation: the Substrate Governs Defect Production", ACS Applied Materials & Interfaces 10 (2018) 30827
S. Kretschmer, M. Maslov, S. Ghaderzadeh, M. Ghorbani‐Asl, G. Hlawacek, and A. V. Krasheninnikov
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“Observation of charge density waves in free‐standing 1T‐TaSe2 monolayers by transmission electron microscopy”, Appl. Phys. Lett. 113 (2018) 173103
P. C. Börner, M. K. Kinyanjui, T. Björkman, A. V. Krasheninnikov, and U. Kaiser
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“Reversible superdense ordering of lithium between two graphene sheets “, Nature 564 (2018) 234
M. Kühne, F. Börrnert, S. Fecher, M. Ghorbani‐Asl, J. Biskupek, D. Samuelis, A. V. Krasheninnikov, U. Kaiser, and J.H. Smet
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“Effects of electron beam generated lattice defects on the periodic lattice distortion structure in 1T−TaS2 and 1T−TaSe2 thin layers” Phys. Rev. B 99 (2019) 024101
M. K. Kinyanjui, T. Björkman, T. Lehnert, J. Köster, A. Krasheninnikov, and U. Kaiser
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“Electron‐Beam‐Driven Structure Evolution of Single‐Layer MoTe2 for Quantum Devices” ACS Appl. Nano Mater. 2 (2019) 3262‐3270
T. Lehnert, M. Ghorbani‐Asl, J. Köster, Z. Lee, A. V. Krasheninnikov, and U. Kaiser
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“Alkali metals inside bi‐layer graphene and MoS2: insights from first‐principles calculations”, Nano Energy 75 (2020) 104927
I.V. Chepkasov, M. Ghorbani‐Asl, Z.I. Popov, J.H. Smet, and A. V. Krasheninnikov
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“Formation of defects in two‐dimensional MoS2 in the transmission electron microscope at electron energies below the knock‐on threshold: the role of electronic excitations” Nano Letters 20 (2020) 2865‐2870
S. Kretschmer, T. Lehnert, U. Kaiser, and A. V. Krasheninnikov
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“Defect Agglomeration and Electron Beam‐Induced Local Phase Transformations in Single‐Layer MoTe₂” J. Phys. Chem. C 125 (2021) 13601−13609
J. Köster, M. Ghorbani‐Asl, H.‐P. Komsa, T. Lehnert, S. Kretschmer, A. V. Krasheninnikov, and U. Kaiser
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“Layer‐Dependent Band Gaps of Platinum Dichalcogenides” ACS Nano 15 (2021) 13249−13259
J. Li, S. Kolekar, M. Ghorbani‐Asl, T. Lehnert, J. Biskupek, U. Kaiser, A. V. Krasheninnikov, and M. Batzill
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“Quasi‐Two‐Dimensional NaCl Crystals Encapsulated Between Graphene Sheets and their Decomposition under the Electron Beam”, Nanoscale 13 (2021) 19626
T. Lehnert, S. Kretschmer, F. Bräuer, A. V. Krasheninnikov, U. Kaiser
