Open AccessAtomic scale chemical ordering in franckeite—a natural van der Waals superlattice
Author(s) -
Hannes Zschiesche,
Ayşe Melis Aygar,
Brian Langelier,
Thomas Szkopek,
Gianluigi A. Botton
Publication year - 2021
Publication title -
journal of physics. condensed matter
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 228
eISSN - 1361-648X
pISSN - 0953-8984
DOI - 10.1088/1361-648x/ac3451
Subject(s) - van der waals force , atomic units , stacking , characterization (materials science) , chemical physics , superlattice , scanning transmission electron microscopy , tetragonal crystal system , nanotechnology , van der waals radius , chemistry , materials science , crystallography , transmission electron microscopy , crystal structure , physics , optoelectronics , molecule , organic chemistry , quantum mechanics
The mineral franckeite is a naturally occurring van der Waals superlattice which has recently attracted attention for future applications in optoelectronics, biosensors and beyond. Furthermore, its stacking of incommensurately modulated 2D layers, the pseudo tetragonal Q-layer and the pseudo hexagonal H-layer, is an experimentally accessible prototype for the development of synthetic van der Waals materials and of advanced characterization methods to reveal new insights in their structure and chemistry at the atomic scale that is crucial for deep understanding of its properties. While some experimental studies have been undertaken in the past, much is still unknown on the correlation between local atomic structure and chemical composition within the layers. Here we present an investigation of the atomic structure of franckeite using state-of-the-art high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) and atom probe tomography (APT). With atomic-number image contrast in HAADF STEM direct information about both the geometric structure and its chemistry is provided. By imaging samples under different zone axes within the van der Waals plane, we propose refinements to the structure of the Q-layer and H-layer, including several chemical ordering effects that are expected to impact electronic structure calculations. Additionally, we observe and characterize stacking faults which are possible sources of differences between experimentally determined properties and calculations. Furthermore, we demonstrate advantages and discuss current limitations and perspectives of combining TEM and APT for the atomic scale characterization of incommensurately modulated von der Waals materials.