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Search Results: 1 - 10 of 200392 matches for " Andrey N. Enyashin "
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Structural, elastic and electronic Properties of isotropic cubic crystals of carbon and silicon nanotubes : Density functional based tight binding calculations.
Andrey N. Enyashin,Alexander L. Ivanovskii
Carbon : Science and Technology , 2008,
Abstract: Atomic models of cubic crystals (CC) of carbon and graphene-like Si nanotubes are offered and their structural, cohesive, elastic and electronic properties are predicted by means of the DFTB method. Our main findings are that the isotropic crystals of carbon nanotubes adopt a very high elastic modulus B and low compressibility β, namely B = 650 GPa, β = 0.0015 1/GPa. In addition, these crystals preserve the initial conductivity type of their “building blocks”, i.e. isolated carbon and Si nanotubes. This feature may be important for design of materials with the selected conductivity type.
Modeling of Magnetic Properties of NiCl$_2$ Nanostripes, Nanotubes and Fullerenes
Andrey N. Enyashin,Alexander L. Ivanovskii
Physics , 2010, DOI: 10.1016/j.commatsci.2010.06.023
Abstract: 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.
Structural, electronic properties and stability of MXenes Ti2C and Ti3C2 functionalized by methoxy groups
Andrey N. Enyashin,Alexander L. Ivanovskii
Physics , 2013,
Abstract: 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.
Defect-induced conductivity anisotropy in MoS2 monolayers
Mahdi Ghorbani-Asl,Andrey N. Enyashin,Agnisezka Kuc,Gotthard Seifert,Thomas Heine
Physics , 2013, DOI: 10.1103/PhysRevB.88.245440
Abstract: 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.
Line Defects in Molybdenum Disulfide Layers
Andrey N. Enyashin,Maya Bar-Sadan,Lothar Houben,Gotthard Seifert
Physics , 2013, DOI: 10.1021/jp403976d
Abstract: 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.
Density-functional study of LixMoS2 intercalates (0<=x<=1)
Andrey Enyashin,Gotthard Seifert
Physics , 2012, DOI: 10.1016/j.comptc.2012.08.005
Abstract: The stability of Lithium intercalated 2H- and 1T allotropes of Molybdenum disulfide (LixMoS2) is studied within a density-functional theory framework as function of the Li content (x) and the intercalation sites. Octahedral coordination of Li interstitials in the van der Waals gap is found as the most favorite for both allotropes. The critical content of Lithium, required for the initialization of a 2H->1T phase transition is estimated to x ~ 0.4. For smaller Li contents the hexagonal 2H crystal structure is not changed, while 1T-LixMoS2 compounds adopt a monoclinic lattice. All allotropic forms of LixMoS2 - excluding the monoclinic Li1.0MoS2 structure - show metallic-like character. The monoclinic Li1.0MoS2 is a semiconductor with a band gap of 1.1 eV. Finally, the influence of Li intercalation on the stability of multiwalled MoS2 nanotubes is discussed within a phenomenological model.
New route for stabilization of 1T-WS2 and MoS2 phases
Andrey N. Enyashin,Lena Yadgarov,Lothar Houben,Igor Popov,Marc Weidenbach,Reshef Tenne,Maya Bar-Sadan,Gotthard Seifert
Physics , 2011, DOI: 10.1021/jp2076325
Abstract: 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.
Graphene allotropes: stability, structural and electronic properties from DF-TB calculations
A. N. Enyashin,A. L. Ivanovskii
Physics , 2010, DOI: 10.1016/j.cplett.2011.04.081
Abstract: Using the density-functional-based tight-binding method we performed a systematic comparative study of stability, structural and electronic properties for 12 various types of graphene allotropes, which are likely candidates for engineering of novel graphene-like materials.
Fluorographynes: Stability, Structural and Electronic Properties
A. N. Enyashin,A. L. Ivanovskii
Physics , 2012, DOI: 10.1016/j.spmi.2012.11.022
Abstract: The presence in the graphyne sheets of a variable amount of sp2/sp1 atoms, which can be transformed into sp3-like atoms by covalent binding with one or two fluorine atoms, respectively, allows one to assume the formation of fulorinated graphynes (fluorographynes) with variable F/C stoichiometry. Here, employing DFT band structure calculations, we examine a series of fluorographynes, and the trends in their stability, structural and electronic properties have been discussed as depending on their stoichiometry: from C2F3 (F/C= 1.5) to C4F7 (F/C= 1.75).
2D titanium carbonitrides and their hydroxylated derivatives: Structural, electronic properties and stability of MXenes Ti3C2-xNx and Ti3C2-xNx(OH)2
A. N. Enyashin,A. L. Ivanovskii
Physics , 2013, DOI: 10.1016/j.jssc.2013.09.010
Abstract: 3D titanium carbonitrides TiCxNy possess excellent physical, chemical, and mechanical properties, attractive for various industrial applications. Most recently, the uncommon nano-sized layers of 2D-like titanium carbonitrides were fabricated from MAX phases. Herein, the structural, electronic properties and stability of these new compounds as well as their hydroxylated derivatives - so-called MXenes Ti3C2-xNx and Ti3C2-xNx(OH)2 are probed by means of SSC-DFTB calculations. The genesis of the properties is discussed in the sequence: binary MXenes Ti3C2 (Ti3N2) -> their hydroxylated forms Ti3C2(OH)2 (Ti3N2(OH)2) -> pristine MXene Ti3C2-xNx -> hydroxylated Ti3C2-xNx(OH)2. Our results show that the examined materials are metallic-like. The most favorable type of OH-covering is presented by the occupation of the hollow sites between three neighboring carbon (nitrogen) atoms. The formation of 2D MXene carbonitrides with random distribution of C and N atoms was found to be thermodynamically more favorable.
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