Nanoscale characterization of bismuth telluride epitaxial layers by advanced X-ray analysis

Abstract

The surface properties of topological insulators are strongly correlated with their structural properties, requiring high‐resolution techniques capable of probing both surface and bulk structures at once. In this work, the high flux of a synchrotron source, a set of recursive equations for fast X‐ray dynamical diffraction simulation and a genetic algorithm for data fitting are combined to reveal the detailed structure of bismuth telluride epitaxial films with thicknesses ranging from 8 to 168 nm. This includes stacking sequences, thickness and composition of layers in model structures, interface coherence, surface termination, and morphology. The results are in agreement with the surface morphology determined by atomic force microscopy. Moreover, by using X‐ray data from a zero‐noise area detector to construct three‐dimensional reciprocal‐space maps, insights into the nanostructure of the domains and stacking faults in Bi2Te3 films are given.

Hybrid reflections from multiple x-ray scattering in epitaxial bismuth telluride topological insulator films

“…, 18) are clearly visible, as well as the 111 s and 222 s substrate reflections, labeled S1 and S2, respectively. As demonstrated in previous publications [16,32], spliting of peaks L3, L6, L12, and L18 in the Bi 2 Te 2.6 film ( Fig. 1a) are caused by the Te deficit that favours bilayers of Bi to form inside the van der Waals gap between two consecutive Bi 2 Te 3 quintuple layers (QLs).…”

Simulation of X-ray diffraction in Mn$_x$Bi$_2$Te$_{3+x}$ epitaxic films

“…Diffraction of X-rays in layered materials of large d-spacing can be exactly calculated by means of a set of recursive equations described in details elsewhere. 1,2 It is valid in grazing incidence specular reflection geometries, 3,4 as well as near strong Bragg reflections from the substrate lattice undergoind dynamical diffraction. In Fig.…”

“…A more detailed discussion on this subject can be found elsewhere. 1 This set of recursive equations that become very suitable for layered materials has emerged within a vast effort to advance X-ray diffraction methods for analyzing relevant materials, ranging from nanostructured devices to biological tissues. [5][6][7][8][9][10][11][12]…”

X-ray diffraction tools for structural modeling of epitaxic films of an intrinsic antiferromagnetic topological insulator

“…Composition fluctuation is related to the occurrence of distinct building blocks-sets of atomic monolayers sharing covalent bonds-randomly stacked along film thickness and bonded to each other by weak vdW forces. Figures 1a and 1b show the building blocks that have been used for modeling Bi 2 Te 3−δ films with deficit δ of tellurium [29], and in Figures 1d 1c, the blocks that are used here for modeling the MBT films.…”

“…Simulations of X-ray scattering and diffraction are well-established procedures for structural analysis at nanometer and subnanometer length scales of layered materials, ranging from amorphous films to crystalline ones such as epitaxial layers on single-crystal substrates [28,29]. Higher are the ordering in stacking sequences of the atomic layers, the more pronounced are the diffracted intensities at higher angles allowing more refined structure models.…”