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  • Characterisation and Defect Analysis of 2D Layered Ternary Chalcogenides
  • Characterisation and Defect Analysis of 2D Layered Ternary Chalcogenides

    Abstract number
    16
    Presentation Form
    Poster
    Corresponding Email
    [email protected]
    Session
    Poster Session 1
    Authors
    Mr. Tigran Simonian (1, 3, 4), Dr. Ahin Roy (1, 3, 4), Prof. Zdeněk Sofer (2), Prof. Valeria Nicolosi (1, 3, 4)
    Affiliations
    1. Advanced Microscopy Lab, Trinity College Dublin
    2. University of Chemistry and Technology Prague
    3. CRANN/AMBER, Trinity College Dublin
    4. School of Chemistry, Trinity College Dublin
    Keywords

    TlGaSe2, HRTEM, HRSTEM, EDX, EELS, DFT, Characterisation

    Abstract text

    TlGaX2 [X = Se, S, Te] is a family of layered 2-D ternary chalcogenides. These p-type semiconductors have band gaps within the green to ultraviolet range [1] [2] [3], which makes them ideal candidates for optoelectronic applications.

    Current examples of such applications, such as phototransistors [4] and detectors [5] [6], make use of multistep processes, such as mechanical exfoliation with a PMMA transfer [4], or thin film synthesis via thermal evaporation [6], which makes potential future scalability of these devices cumbersome. Liquid phase exfoliation (LPE) is a far more facile process that has been shown to work for a large number of layered van der Waals materials [7]. Herein, we demonstrate that these TlGaX2 materials can be exfoliated with a facile one step sonication in IPA, leaving behind little to no residue.

    While there have been a number of studies into the electronic structure of these materials, an exact description of their band structures has yet to be established [6]. Interestingly, despite defect quantification being an important structure-property relationship in semiconductors, none of its aspects, e.g. stoichiometry, charge states, structural defects, etc., have yet been fully addressed. For example, while it was reported that Se vacancies in TlGaSe2 can lead to a change in the nature and size of the bandgap, a quantitative relationship was not determined [2].

    In this work, we use high-resolution scanning transmission electron microscopy (HRSTEM), in combination with EDX/EELS, to experimentally address this aspect of defects in TlGaSe2. Our experiments clearly indicate the presence of stacking faults (as were seen previously in XRD studies with bulk TlGaSe2 [8], and with isostructural KInS2 [9]) and surface relaxation in LPE-TlGaSe2. Furthermore, we show a transient formation of a 1-D structure along the edges of TlGaSe2 flakes, catalysed by intense electron beam exposure in the microscope. Using complimentary density functional theory (DFT) simulations, we explore the effect of defects on the electronic structure, and rationalise the transient formation of the 1-D structure.

    References

    [1] A. T. Nagat, G. A. Gamal, and S. A. Hussein, “Growth and Characterization of Single Crystals of the Ternary Compound TlGaTe2,” Cryst. Res. Technol., vol. 26, no. 1, pp. 19–23, 1991.


    [2] A. Cengiz, Y. M. Chumakov, M. Erdem, Y. Şale, F. A. Mikailzade, and M. Y. Seyidov, “Origin of the optical absorption of TlGaSe2 layered semiconductor in the visible range,” Semicond. Sci. Technol., vol. 33, no. 7, 2018.


    [3] S. Duman and B. Gürbulak, “ Urbach Tail and Optical Absorption in Layered Semiconductor TlGaSe 2(1- x ) S 2 x Single Crystals ,” Phys. Scr., vol. 72, no. 1, pp. 79–86, 2005.


    [4] S. Yang et al., “Ultrathin ternary semiconductor TlGaSe2 phototransistors with Broad-spectral response,” 2D Mater., vol. 4, no. 3, 2017.


    [5] I. M. Ashraf et al., “Development and characterization of TlGaSe2 thin film-based photodetector for visible-light photodetector applications,” Opt. Mater. (Amst)., vol. 103, no. December 2019, p. 109834, 2020.


    [6] S. Johnsen et al., “Thallium chalcogenide-based wide-band-gap semiconductors: TlGaSe 2 for radiation detectors,” Chem. Mater., vol. 23, no. 12, pp. 3120–3128, 2011.


    [7] V. Nicolosi, M. Chhowalla, M. G. Kanatzidis, M. S. Strano, and J. N. Coleman, “Liquid exfoliation of layered materials,” Science (80-. )., vol. 340, no. 6139, pp. 72–75, 2013.


    [8] D. F. McMorrow, R. A. Cowley, P. D. Hatton, and J. Banys, “The structure of the paraelectric and incommensurate phases of TlGaSe 2,” J. Phys. Condens. Matter, vol. 2, no. 16, pp. 3699–3712, 1990.


    [9] L. Kienle, V. Duppel, A. Simon, M. Schlosser, and O. Jarchow, “Real structure of KInS2 polytypes,” J. Solid State Chem., vol. 177, no. 1, pp. 6–16, 2004.