Nanostructure research and electron microscopy

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Local structure of phase change materials and van der Waals-bonded chalcogenide-based heterostructures for memory application

In recent years, chalcogenide-based phase change materials attract much attention due to their important optical and electronic properties. The alloys exhibit unique materials properties and are used as active layer for data storage in phase change memory (PCM) technology (e.g. Intel Optane Memroy). Currently, the Phase Change Random Access Memory (PCRAM) relies on the reversible transition between amorphous and crystalline states. However, power consumption is a critical issue. Nanoscale engineering of phase change materials has been shown to be a promising approach for further development of the materials with lower power consumption. The approach is based on the synthesis of chalcogenide-based superlattices (SLs), also known as interfacial PCM (iPCM). These improved performances have been ascribed to the fact that the switching in iPCM cells is a melting-free mechanism. Moreover, storage devices based on solely crystalline structures will benefit of much stable resistance in addition. Theoretical models of the reversible switching and resistance contrast in SLs focus on the stacking sequence of particular layers. Consequently, the knowledge of the proper local atomic arrangement in chalcogenide-based materials is of paramount importance for understanding the switching mechanisms and their material properties as well as for designing of new materials with advance properties.

The research activity of the group aims at understanding the interplay between the growth, local structure and properties of chalcogenide-based phase change alloys. The materials under investigation are epitaxial chalcogenide-based thin films and SLs grown by pulsed laser deposition (in cooperation with the R&D Focus Non-thermal Thin Film Deposition and Nanostructures). The local structure is revealed by combination of state-of-the art transmission electron microscopy and theoretical image simulation.

Selected publications

  • A. Lotnyk, I. Hilmi, U. Roß, B. Rauschenbach
    Van der Waals interfacial bonding and intermixing in GeTe-Sb2Te3-based superlattices

    Nano Res. 11 (2018) 1676-1686
    doi.org/10.1007/s12274-017-1785-y

  • M. Behrens, A. Lotnyk, U. Roß, J. Griebel, P. Schumacher, J. W. Gerlach, B. Rauschenbach
    Impact of disorder on optical reflectivity contrast of epitaxial Ge2Sb2Te5 thin films

    CrystEngComm 20 (2018) 3688 – 3695
    10.1039/C8CE00534F

  • I. Hilmi, A. Lotnyk, J. W. Gerlach, P. Schumacher, B. Rauschenbach
    Epitaxial formation of cubic and trigonal Ge-Sb-Te thin films with heterogeneous vacancy structures
    Mater. Design 115 (2017) 138-146
    doi.org/10.1016/j.matdes.2016.11.003

  • N.S. Gunning, T. Dankwort, M. Falmbigl, U. Roß, G. Mitchson, D.M. Hamann, A. Lotnyk, L. Kienle, D.C. Johnson
    Expanding the concept of van der Waals heterostructures to interwoven 3D Structures
    Chem. Mater. 29 (2017) 8292-8298
    https://pubs.acs.org/doi/10.1021/acs.chemmater.7b02605

  • A. Lotnyk, U. Roß, S. Bernütz, E. Thelander, B. Rauschenbach
    Evaluation of local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures
    Sci. Rep. 6 (2016) 26724
    https://doi.org/10.1002/9783527808465.EMC2016.6108

  • U. Roß, A. Lotnyk, E. Thelander, B. Rauschenbach
    Microstructure evolution in pulsed laser deposited epitaxial Ge-Sb-Te chalcogenide thin films
    Journal of Alloys and Compounds 676 (2016) 582-590
    doi.org/10.1016/j.jallcom.2016.03.159

  • U. Roß, A. Lotnyk, E. Thelander, B. Rauschenbach
    Direct imaging of crystal structure and defects in metastable Ge2Sb2Te5 by quantitative aberration-corrected scanning transmission electron microscopy
    Appl. Phys. Lett. 104 (2014) 121904
    https://doi.org/10.1063/1.4869471