Nanotubes from the Misfit Layered Compound (SmS)1.19TaS2: Atomic Structure, Charge Transfer, and Electrical Properties

Misfit layered compounds MX-TX2, where M, T= metal atoms; X = S, Se or Te, (MLC) and their nanotubes are of significant interest due to their rich chemistry and unique quasi-1D structure. In particular, Ln-TX2 (Ln= rare-earth atom) constitute a relatively large family of MLC, from which nanotubes have been synthesized. The properties of MLCs can be tuned by the chemical and structural interplay between LnX and TX2 sub-layers and alloying of each of the Ln, T and X elements. In order to engineer them to gain desirable performance, a detailed understanding of their complex structure is indispensable. MLC nanotubes are a relatively new-comer and offer new opportunities. In particular, like WS2 nanotubes before, the confinement of the free-carriers in these quasi-1D nanostructures and their chiral nature offer intriguing physical behavior. Highresolution transmission electron microscopy in conjunction with a focused ion beam are engaged to study SmS-TaS2 nanotubes and their cross-sections at the atomic scale. The atomic resolution images distinctly reveal that Ta is in trigonal prismatic coordination with S atoms in a hexagonal structure. Furthermore, the position of the sulfur atoms in both the SmS and the TaS2 sub-lattices, is revealed. X-ray photoelectron spectroscopy, electron-energy loss spectroscopy and X-ray absorption spectroscopy are carried out. These analyses conclude that charge transfer from the Sm to the Ta atoms leads to filling of the Ta 5dz 2 level, which is confirmed by density functional theory (DFT) calculations. Transport measurements show that the nanotubes are semimetallic with resistivities in the range of 10-4 Ω⸳cm at room temperature and magnetic susceptibility measurements show a superconducting transition at 4 K.This work was partially supported by the Israel Science Foundation Grant No. 339/18 (Internal Grant No. 120924) (R.T.). The following foundations are acknowledged: Perlman Family Foundation; the Kimmel Center for Nanoscale Science Grant No. 43535000350000; and the Irving and Cherna Moskowitz Center for Nano and Bio-Nano Imaging. CzechNanoLab Project LM2018110 funded by MEYS CR is gratefully acknowledged for the financial support of the measurements and sample fabrication at the CEITEC Nano Research Infrastructure. This work was partially supported by Ceitec Nano+ (CZ.02.01/0.0./.0.0./16_013/0001728 under Program OPVVV) and the Horizon 2020 Research and Innovation Programme under Grant Agreement 810626 (SINNCE). Work at Ames Laboratory was supported by the Materials Sciences and Engineering Division of the Office of Basic Energy Sciences, Office of Science of U.S. Department of Energy. Ames Laboratory is operated for the U.S. DOE by Iowa State University of Science and Technology under Contract No. DE-AC02-07CH11358. A part of the work at Buffalo State was supported by the faculty startup fund from the Dean's Office, School of Arts and Sciences, State University of New York (SUNY), Buffalo State. We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities for XAS studies. Parts of this research were carried out at PETRA III, P23 "In-situ and X-ray imaging beamline"