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CrI3 is a layered ferromagnetic insulator that has recently attracted enormous interest as it was the first example of a stand-alone monolayer ferromagnet, paving the way towards the study of two-dimensional magnetic materials and their use as building blocks of hybrid van der Waals layered heterostructures. Here we go one step down in the dimensionality ladder and report the synthesis and characterization of a tubular one-dimensional van der Waals heterostructure where CrI3 nanotubes are encapsulated within multiwall carbon nanotubes, integrating a magnetic insulator and a conductor. By means of the capillary filling of multi-wall carbon nanotubes (MWCNT), we obtained single-wall CrI3 nanotubes with diameters ranging between 2 nm and 10 nm, with an average of 5.3 nm. Using aberration corrected electron microscopy in combination with spectroscopic techniques we confirm the structure and chemical composition of the nanotubes. SQUID measurements, combined with element-specific X-ray magnetic circular dichroism (XMCD) indicate unequivocally that the Cr atoms in encapsulated CrI3 nanotubes are magnetic with a collective state compatible with a radial magnetization state predicted both by first-principles calculations and a model Hamiltonian. Our results represent a step forward in establishing 1D van der Waals heterostructures as a playground for the exploration of non-collinear magnetic states arising from the interplay between magnetic anisotropy and curvature in tubular geometries., Comment: 19 pages with 5 figures

Various types of defects in MoS2 monolayers and their influence on the electronic structure and transport properties have been studied using the Density-Functional based Tight-Binding method in conjunction with the Green's Function approach. Intrinsic defects in MoS2 monolayers significantly affect their electronic properties. Even at low concentration they considerably alter the quantum conductance. While the electron transport is practically isotropic in pristine MoS2, strong anisotropy is observed in the presence of defects. Localized mid-gap states are observed in semiconducting MoS2 that do not contribute to the conductivity but direction-dependent scatter the current, and that the conductivity is strongly reduced across line defects and selected grain boundary models., Comment: 13 pages, 6 figures, submition to Phys. Rev. B

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.

The properties of MXenes, a new group of quasi-two-dimensional d-metal carbide or nitride nanomaterials derived by chemical exfoliation from the MAX phases, can be very sensitive to the presence of surface functional groups. Herein, the MXenes Ti2C and Ti3C2 functionalized by methoxy groups are considered by means of the density functional theory tight-binding method. Their structural, electronic properties, and relative stability are discussed in comparison with related and experimentally fabricated hydroxy derivatives of MXenes.

The phenomenon of a partial 2H\rightarrow1T phase transition within multiwalled WS2 nanotubes under substitutional Rhenium doping is discovered by means of high-resolution transmission electron microscopy. Using density-functional calculations for the related MoS2 compound we consider a possible origin of this phase transition, which was known formerly only for WS2 and MoS2 intercalated by alkali metals. An interplay between the stability of layered or nanotubular forms of 2H and 1T allotropes is found to be intimately related with their electronic structures and electro-donating ability of an impurity., Comment: submitted to JPC on 09th August 2011, still under revision!

We show that the magnetic properties of antiferromagnetic layered NiCl$_{2}$ can be altered under nano-sizing depending on dimensionality and morphology type of the corresponding nano-forms. By means of Monte-Carlo simulations within classical Heisenberg model, the spin ordering, magnetic part of heat capacity C$_{v}$ and N\'eel temperatures T$_{N}$ for multi-walled NiCl$_{2}$ nanotubes and a fullerene were calculated and analyzed in comparison with the bulk NiCl$_{2}$ and multilayered two-dimensional NiCl$_{2}$ crystals and nanostripes. We have found that the nano-structuring of NiCl$_{2}$ at the size reducing and at the formation of the closed structures can influence propitiously on the preservation of antiferromagnetic properties., Comment: 13 pages, 3 figures, 1 Table