Nanotubes from the Misfit Layered Compounds MS–TaS₂, Where M = Pb, Sn, Sb, or Bi: Synthesis and Study of Their Structure

Tubular structures of the MS–TaS₂ with (M = Pb, Sn, Sb, Bi) misfit layered compounds are reported. The lattice mismatch between the alternating MS and TaS₂ layers leads to a variety of chiral tubular structures. Such tubular structures are studied via scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). For the PbS–TaS₂ and SnS–TaS₂ tubules, relative in-plane orientations as well as folding vectors of the two subsystems can be determined. However, almost ring-like SAED patterns are obtained for SbS–TaS₂ nanotubes precluding exact determination of the relative in plane orientation. Also, very complex diffraction patterns were obtained for BiS–TaS₂ nanotubes

Study of Tubular Structures of the Misfit Layered Compound SnS₂/SnS

Tubular structures of the SnS₂/SnS misfit compound, which are currently prepared in large amounts, are reported. The lattice mismatch between the two alternating sublayers of SnS₂ and SnS leads to a variety of chiral tubular structures. Such tubular structures are studied via high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). The diversity of the structures manifests itself through different stacking orders of SnS₂ and SnS layers along their common <i>c</i>-axis and their relative in-plane orientation. Folding vectors and chiral angles of both subsystems can be determined

Quaternary Chalcogenide-Based Misfit Nanotubes LnS(Se)-TaS(Se)₂ (Ln = La, Ce, Nd, and Ho): Synthesis and Atomic Structural Studies

We have synthesized quaternary chalcogenide-based misfit nanotubes LnS­(Se)-TaS₂(Se) (Ln = La, Ce, Nd, and Ho). None of the compounds described here were reported in the literature as a bulk compound. The characterization of these nanotubes, at the atomic level, has been developed via different transmission electron microscopy techniques, including high-resolution scanning transmission electron microscopy, electron diffraction, and electron energy-loss spectroscopy. In particular, quantification at sub-nanometer scale was achieved by acquiring high-quality electron energy-loss spectra at high energy (∼between 1000 and 2500 eV). Remarkably, the sulfur was found to reside primarily in the distorted rocksalt LnS lattice, while the Se is associated with the hexagonal TaSe₂ site. Consequently, these quaternary misfit layered compounds in the form of nanostructures possess a double superstructure of La/Ta and S/Se with the same periodicity. In addition, the interlayer spacing between the layers and the interatomic distances within the layer vary systematically in the nanotubes, showing clear reduction when going from the lightest (La atom) to the heaviest (Ho) atom. Amorphous layers, of different nature, were observed at the surface of the nanotubes. For La-based NTs, the thin external amorphous layer (inferior to 10 nm) can be ascribed to a Se deficiency. Contrarily, for Ho-based NTs, the thick amorphous layer (between 10 and 20 nm) is clearly ascribed to oxidation. All of these findings helped us to understand the atomic structure of these new compounds and nanotubes thereof

Atomic Structural Studies on Thin Single-Crystalline Misfit-Layered Nanotubes of TbS-CrS₂

Various nanotubes from ternary misfit compounds have been reported in recent years. In the present work, the detailed atomic structure and chemical configuration of misfit-layered nanotubes based on the TbS-CrS₂ are reported. These analyses have been developed via different transmission electron microscopy techniques, including high-resolution scanning transmission electron microscopy, electron diffraction, and electron energy loss spectroscopy. These structural analyses show that two different kinds of nanotubes can be produced: a “regular” nanotube and a “wavy” one. Both kinds of nanotubes show the alternating arrangements of the TbS and CrS₂ subsystems; however, the wavy ones present a nearly periodically deficiency in terbium. In addition to the structural investigation, the chemical analyses have proved that the outer layer of both kinds of nanotubes is composed of the elements Cr and S. All these findings helped to understand the growth mechanism during the sulfurization reaction taking place in the synthesis process

Gold Nanoparticles as Surface Defect Probes for WS₂ Nanostructures

WS₂ inorganic nanotubes (INT) and inorganic fullerene-like nanoparticles (IF) are well-known for their high mechanical strength and as superior solid lubricants. The outermost WS₂ layer is considered to be fully bonded; thus, it was suggested that the interactions of these WS₂ nanostructures with their surroundings are governed by purely van der Waals (vdW) interactions. However, in the case of IF-WS₂ nanoparticles, the faceted surface may contain sites with nonsaturated coordination, which, in turn, react with the surrounding media. Gold nanoparticles (GNP) were used as probes for the IF-WS₂ surface defects, mapped by both scanning and transmission electron microscopy. The interaction between the GNP and the reactive surface was investigated using INT-WS₂ as a model and was characterized by atomic force microscopy (AFM)

Strontium Cobalt Oxide Misfit Nanotubes

Low-dimensional misfit layered compounds have been found to have ultralow thermal conductivity, which is attributed to their unique structure and the low dimensionality. There are a few studies reporting the preparation of sulfide-based misfit nanotubes but only one study on oxide-based analogs. In this investigation, we report a new oxide-based misfit nanotube derived from misfit layered strontium cobaltite. Thorough structural investigation by electron microscopy techniques, including electron diffraction, aberration corrected high-resolution (scanning) transmission electron microscopy, and electron energy-loss spectroscopy along with density functional theory calculations show that these nanotubes consist of alternating layers of SrCoO₂ and CoO₂. We have studied systematically the effect of base concentration on the structure and composition of the nanotubes, which reveals the importance of misfit stress to tightly roll the structure into tubular form and thus control the synthesis. Electronic structure calculations find that the structures are semiconducting with a ferrimagnetic ground state. Our studies further extend the family of bulk misfit layered oxides into the 1D realm with potential applications in thermoelectric and electronic devices

Field-Effect Transistors Based on WS₂ Nanotubes with High Current-Carrying Capacity

We report the first transistor based on inorganic nanotubes exhibiting mobility values of up to 50 cm² V^–1 s^–1 for an individual WS₂ nanotube. The current-carrying capacity of these nanotubes was surprisingly high with respect to other low-dimensional materials, with current density at least 2.4 × 10⁸ A cm^–2. These results demonstrate that inorganic nanotubes are promising building blocks for high-performance electronic applications

Nanotubes from Oxide-Based Misfit Family: The Case of Calcium Cobalt Oxide

Misfit layered compounds (MLCs) have generated significant interest in recent years as potential thermoelectric materials. MLC nanotubes could reveal behavior that is entirely different from the bulk material. Recently, new chemical strategies were exploited for the synthesis of nanotubular forms of chalcogenide-based MLCs, which are promising candidates for thermoelectric materials. However, analogous synthesis of oxide-based MLC nanotubes has not been demonstrated until now. Here, we report a chemical strategy for synthesis of cobalt-oxide-based misfit nanotubes. A combination of high-resolution (scanning) transmission electron microscopy (including image simulations), spatially resolved electron energy-loss spectroscopy, electron diffraction, and density functional theory (DFT) calculations is used to discover the formation of a phase within these nanotubes that differs significantly from bulk calcium cobaltite MLCs. Furthermore, DFT calculations show that this phase is semiconducting with a band gap in excess of 1 eV, unlike bulk calcium cobaltite MLCs, which are known to be metallic. Through systematic experiments, we propose a formation mechanism for these nanotubes that could also apply more generally to realizing other oxide-based MLC nanotubes

Nanotubes from Chalcogenide Misfit Compounds: Sn–S and Nb–Pb–S

Carbon fullerenes and nanotubes revolutionized understandingof the reactivity of nanoscale compounds. Subsequently, our group and others discovered analogous inorganic compounds with hollow, closed nanostructures. Such inorganic nanostructures offer many applications, particularly in the energy and electronics industries.One way to create inorganic nanostructures is via misfit layer-ed compounds (MLC), which are stacks of alternating two-dimensional molecular slabs, typically held together via weak van der Waals forces. They contain “misfits” in their <i>a</i>–<i>b</i> plane structures that can make them unstable, leading to collapse of the slabs into tubular nanostructures. For example, metal chalcogenide MLCs of the general formula (MX)_1+<i>y</i>/TX₂ (M = Sn, Pb, Bi, Sb, and other rare earths; T = Sn, Ti, V, Cr, Nb, Ta, etc.; X = S or Se) consist of a superstructure of alternating layers where the MX unit belongs to a (distorted NaCl) orthorhombic symmetry group (O), the TX₂ layer possesses trigonal (T) or octahedral symmetry, and the two layers are held together via both van der Waals and polar forces. A misfit in the <i>a</i> axis or both <i>a</i> and <i>b</i> axes of the two sublattices may lead to the formation of nanostructures as the lattices relax via scrolling. Previous research has also shown that the abundance of atoms with dangling bonds in the rims makes nanoparticles of compounds with layered structure unstable in the planar form, and they tend to fold into hollow closed structures such as nanotubes.This Account shows that combining these two triggers, misfits and dangling bond annihilation in the slab rims, leads to new kinds of nanotubes from MLCs. In particular, we report the structure of two new types of nanotubes from misfits, namely, the SnS/SnS₂ and PbS/NbS₂ series. To decipher the complex structures of these nanotubes, we use a range of methods: high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED) analyses, scanning electron microscopy (SEM), and Cs-corrected scanning transmission electron microscopy (STEM) in the high-angle annular dark-field mode (HAADF). In both new types, the lattice mismatch between the two alternating sublayers dictates the relative layer-stacking order and leads to a variety of chiral tubular structures. In particular, the incommensuration (a type of misfit) of the SnS₂/SnS system in both the (in plane) <i>a</i> and <i>b</i> directions leads to a variety of relative in-plane orientation and stacking orders along the common <i>c</i>-axis. Thus the SnS/SnS₂ nanotubes form superstructures with the sequence O–T and O–T–T, and mixtures thereof. We also report nanotubes of the misfit layered compound (PbS)_1.14NbS₂, and of NbS₂ intercalated with Pb atoms, with the chemical formula PbNbS₂. Thus, the possibility to use two kinds of folding mechanisms jointly offers a new apparatus for the synthesis of unique 1-D nanostructures of great complexity and a potentially large diversity of physicochemical properties

Spectroscopic Determination of Phonon Lifetimes in Rhenium-Doped MoS₂ Nanoparticles

We investigated the infrared vibrational properties of pristine and Re-substituted MoS₂ nanoparticles and analyzed the extracted phonon lifetimes in terms of multiple scattering events. Our measurements reveal both size- and doping-dependent changes that we attribute to grain boundary scattering and charge and mass effects, respectively. By contrast, Born charge is affected only by size. These findings illustrate the utility of reaching beyond traditional bulk semiconductors and quantum dots to explore how doping and confinement impact carrier-phonon interactions in low-dimensional semiconducting nanomaterials