What is the Crystal Structure of Bismuth Selenide?

Among various topological insulators (TI) materials based on Bi compounds, bismuth selenide (Bi2Se3) is one of the most popular representative candidates for three-dimensional TI suitable for electronic applications because of its large bulk energy gap of 0.3 eV and Brillouin A single Dirac cone region. 

In addition, Bi2Se3 also exhibits excellent thermoelectric properties at room temperature and low temperature. For fundamental research and device applications, it is crucial to grow Bi2Se3 films with high quality and desired mechanical properties. This article will introduce the crystal structure of Bi2Se3 thin films^[1].

In above figure, XRD patterns show the dominant (0 0 3n) diffraction peaks of Bismuth Selenide(Bi2Se3) films in addition to a minor Bi2Se3 (0 1 5) peak and a Al2O3 (0 0 6) peak of the substrate, indicating the film growth along the [0001] direction. This is due to the rhombohedral crystal structure of Bi2Se3 (space group 𝐷53𝑑(𝑅3̲𝑚)), in which a hexagonal primitive cell consists of three layers of –(Se(1)–Bi–Se(2)–Bi–Se(1))–lamellae (called quintuple layers, QLs) stacking in sequence along the c-axis. The interaction between the neighboring QLs is mainly the Se(1)–Se(1) van der Waals bond (b). The interlayer Se(1)–Se(1) bonding not only is substantially weaker than the intralayer ionic-covalent bonds within individual QLs but also results in a lowest surface energy on the {001} planes, which leads to observed preferred (001)-oriented crystal growth behavior. 

As shown the inset of Figure a, the full width half maximum (FWHM) of the (0 0 6) peak from the XRD rocking curve was found to be 0.49°, which suggests the presence of certain disorientation between grains (see also b). This FWHM was comparable to that of bismuth selenide film grown on Al2O3 by PLD. Moreover, the in-plane orientation of the films were examined by XRD Ф-scan on {0 1 5} planes of the Bi2Se3 films at a tilt angle (χ) of 57.9°. The films did not show any diffraction peaks, indicating their in-plane polycrystalline characteristics.

Reference

[1] Lai, H.-D.; Jian, S.-R.; Tuyen, L.T.C.; Le, P.H.; Luo, C.-W.; Juang, J.-Y. Nanoindentation of Bi2Se3 Thin Films. Micromachines 2018, 9, 518. doi:10.3390/mi9100518

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