Asymmetric Misfit Nanotubes: Chemical Affinity Outwits the Entropy at High-Temperature Solid-State Reactions

Asymmetric two-dimensional (2D) structures (often named Janus), like SeMoS and their nanotubes, have tremendous scope in material chemistry, nanophotonics, and nanoelectronics due to a lack of inversion symmetry and time-reversal symmetry. The synthesis of these structures is fundamentally difficult owing to the entropy-driven randomized distribution of chalcogens. Indeed, no Janus nanotubes were experimentally prepared, so far. Serendipitously, a family of asymmetric misfit layer superstructures (tubes and flakes), including LaX-TaX2 (where X = S/Se), were synthesized by high-temperature chemical vapor transport reaction in which the Se binds exclusively to the Ta atoms and La binds to S atoms rather than the anticipated random distribution.With increasing Se concentration, the LaS-TaX2 misfit structure gradually transformed into a new LaS-TaSe2-TaSe2 superstructure. No misfit structures were found for xSe = 1. These counterintuitive results shed light on the chemical selectivity and stability of misfit compounds and 2D alloys, in general. The lack of inversion symmetry in these asymmetric compounds induces very large local electrical dipoles. The loss of inversion and time-reversal symmetries in the chiral nanotubes offers intriguing physical observations and applications. © 2021 National Academy of Sciences. All rights reserved.ACKNOWLEDGMENTS. We thank Dr. Iddo Pinkas for the help with the Raman measurements. The support of the Israel Science Foundation (Grant 7130970101), Irving and Cherna Moskowitz Center for Nano and Bio-Nano Imaging, the Perlman Family Foundation, and the Kimmel Center for Nanoscale Science (Grant 43535000350000) are greatly acknowledged. Part of the TEM studies were conducted at the Laboratorio de Microscopias Avanzadas, Universidad de Zaragoza, Spain. S.H. and R.A. acknowledge funding by German Research Foundation (Deutsche Forschungsgemeinschaft project He 7675/1-1), by the Spanish Ministerio de Ciencia e Innovacion (PID2019-104739GB-100/AEI/ 10.13039/501100011033), and Government of Aragon (project DGA E13-20R [Fondo Europeo de Desarrollo Regional, European Union]). R.A. gratefully acknowledges the support from the European Union H2020 programs “ESTEEM3” (Grant 823717) and Graphene Flagship (881603)

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

Misfit layered compounds (MLCs) MX-TX2, where M, T = metal atoms and X = S, Se, or Te, and their nanotubes are of significant interest due to their rich chemistry and unique quasi-1D structure. In particular, LnX-TX2 (Ln = rare-earth atom) constitute a relatively large family of MLCs, from which nanotubes have been synthesized. The properties of MLCs can be tuned by the chemical and structural interplay between LnX and TX2 sublayers 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 relative newcomer 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. High-resolution 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 sublattices 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 5dz2 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. © 2022 The Authors. Published by American Chemical Society.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”

Line Defects in Molybdenum Disulfide Layers

Layered molecular materials and especially MoS2 are already accepted as promising candidates for nanoelectronics. In contrast to the bulk material, the observed electron mobility in single-layer MoS2 is unexpectedly low. Here we reveal the occurrence of intrinsic defects in MoS2 layers, known as inversion domains, where the layer changes its direction through a line defect. The line defects are observed experimentally by atomic resolution TEM. The structures were modeled and the stability and electronic properties of the defects were calculated using quantum-mechanical calculations based on the Density-Functional Tight-Binding method. The results of these calculations indicate the occurrence of new states within the band gap of the semiconducting MoS2. The most stable non-stoichiometric defect structures are observed experimentally, one of which contains metallic Mo-Mo bonds and another one bridging S atoms

Inorganic fullerenes and nanotubes: Wealth of materials and morphologies

It is already well established today that numerous materials form closed-cage structures, of which carbon fullerenes and nanotubes are a special case [1]. Inorganic fullerene-like nanoparticles (designated IF) and inorganic nanotubes (INT) have been produced by different routes and experimental techniques, achieving persistent growth of a variety of materials and structural wealth within them. The research in this area has focused on synthesizing new IF and INT materials and understanding their different properties as well as scaling up the synthetic process in order to make it suitable for industrial applications. In this review, the main synthetic procedures to obtain inorganic fullerene-like nanoparticles and nanotubes will be discussed alongside with the different mechanisms that affect the morphology of the final product. The main differences between the morphologies will be presented. Some general considerations relating the properties of the parent compound with the morphology of the product will be mentioned

Cathodoluminescence and Laser-Induced Fluorescence of Calcium Carbonate: A Review of Screening Methods for Radiocarbon Dating of Ancient Lime Mortars

Accurate radiocarbon (14C) dating of lime mortars requires a thorough mineralogical characterization of binders in order to verify the presence of carbon-bearing contaminants. In the last 20 years, cathodoluminescence (CL) has been widely used for the identification of geologic calcium carbonate (CaCO3) aggregates and unreacted lime lumps within the particle size fraction selected for carbon recovery. These components are major sources of older and younger carbon, respectively, and should be removed to obtain accurate age determinations. More recently, laser-induced fluorescence (LIF) has provided another means of investigating the preservation state and composition of CaCO3 binders. Considered the growing interest of the mortar dating community in the latest advancements of these analytical methods, here we review the principles of CL and LIF of CaCO3, their instrument setup, and their application to the characterization of ancient lime mortars used for 14C dating. In addition, we provide examples of SEM-CL and LIF analyses using high-resolution instrumentation, we discuss current issues and propose future lines of research

Electronic interactions and stability issues at the copper-graphene interface in air and in alkaline solution under electrochemical control

A micro-electrochemical cell is sealed with a polymer-free single-layer graphene (SLG) membrane to monitor the stability of Cu nanoparticles (NPs) attached to SLG, as well as the interfacial electronic interactions between Cu NPs and SLG both in air and in a mildly alkaline aqueous solution under electrochemical control. A combination of techniques, including in-situ Kelvin probe force microscopy (KPFM) and ex-situ electron microscopy, are applied. When Cu NPs are metallic at cathodic potentials, there is a relatively bias-independent offset in the SLG work function due to charge transfer at the Cu-SLG contact. When Cu NPs are oxidized at anodic potentials, on the other hand, the work function of SLG also depends on the applied bias in a quasi-linear fashion due to electrochemical gating, in addition to charge transfer at the CuOx-SLG contact. Furthermore, Cu NPs were found to oxidize and detach from SLG when kept under anodic potentials for a few hours, whereas they remain adhered to SLG at cathodic potentials. This is attributed to water intercalation at the CuO-SLG interface associated with the enhanced hydrophilicity of positively polarized graphene, as supported by the absence of Cu detachment following oxidation by galvanic corrosion in air

Cathodoluminescence in single and multiwall WS2 nanotubes: Evidence for quantum confinement and strain effect

[EN] For nanoparticles with sub-10 nm diameter, the electronic bandgap becomes size dependent due to quantum confinement; this, in turn, affects their electro-optical properties. Thereby, MoS2 and WS2 monolayers acquire luminescent capability, due to the confinement-induced indirect-to-direct bandgap transition. Rolling up of individual layers results in single wall inorganic nanotubes (SWINTs). Up to the present study, their luminescence properties were expected to be auspicious but were limited to theoretical investigations only, due to the scarcity of SWINTs and the difficulties in handling them. By optimizing the conditions in the plasma reactor, relatively high yields of WS2 SWINTs 3–7 nm in diameter were obtained in this work, compared to previous reports. A correlative approach, transmission electron microscopy coupled with a scanning electron microscope, was adapted to overcome handling obstacles and for testing individual nanotubes by low-temperature cathodoluminescence. Clear cathodoluminescence spectra were obtained from WS2-SWINTs and compared with those of WS2 multiwall nanotubes and the corresponding bulk material. Uniquely, the optical properties of INTs acquired from cathodoluminescence were governed by the opposite impact from quantum size effect and strain in the bent triple S-W-S layers. The experimental findings were confirmed by the Density Functional and Time-Dependent Density Functional theoretical modeling of monolayer and bilayer nanotubes of different chiralities and diameters. This study provides experimental evidence of the quantum confinement effect in WS2 SWINTs akin to WS2 monolayer. The ability to tune the electronic structure with morphology or number of layers may be exploited toward photoelectrochemical water splitting with WS2 catalysts, devising field effect transistors, photodetectors, and so on.The research of A.Z. was supported by a grant from the Israel Science Foundation (No. 330/16). The work of J.A.A. was supported by Junta de Castilla y León (Grant No. VA021G18) and the University of Valladolid (GIR Physics of Nanostructures). J.I.M. acknowledges financial support from Spanish MINECO (No. MAT2017-85089-C2–1-R, RYC-2015-17730), Comunidad de Madrid via Programa de Investigación Tecnologías 2018 (No. FOTOART-CM S2018/NMT-4367), and the innovation program under grant agreements 785219 and 881603 (GrapheneCore2 and GrapheneCore3-Graphene-based disruptive technologies, respectively). The authors are grateful to Dr. Alex Idelevich from HIT, who synthesized multiwall WS2 nanotubes. The authors thank Dr. A. Quade and A. Albrecht, of the Leibniz Institute for Plasma Science and Technology, who performed the XPS and XRD analysis, respectively.Peer reviewe

Large lattice distortions and size dependent bandgap modulation in epitaxial halide perovskite nanowires

Metal-halide perovskites have been shown to be remarkable and promising optoelectronic materials. However, despite ongoing research from multiple perspectives, some fundamental questions regarding their optoelectronic properties remain controversial. One reason is the high-variance of data collected from, often unstable, polycrystalline thin films. Here we use ordered arrays of stable, single-crystal cesium lead bromide (CsPbBr3) nanowires grown by surface-guided chemical vapor deposition to study fundamental properties of these semiconductors in a one-dimensional model system. Specifically, we uncover the origin of an unusually large size-dependent luminescence emission spectral blue-shift. Using multiple spatially resolved spectroscopy techniques, we establish that bandgap modulation causes the emission shift, and by correlation with state-of-the-art electron microscopy methods, we reveal its origin in substantial and uniform lattice rotations due to heteroepitaxial strain and lattice relaxation. Understanding strain and its effect on the optoelectronic properties of these dynamic materials, from the atomic scale up, is essential to evaluate their performance limits and fundamentals of charge carrier dynamics