Papers by Keyword: Transition Metal Dichalcogenides

Abstract: The multi-layered MoS₂ with alkali metal intercalation was prepared on the transparent conductor by the sulfurization of MoO₃, followed by the subsequent electrochemical sodiation process. The layered structure of MoS₂ could endow the efficient electron/ion transport pathways for fast charge transfer. Together with the good ion storage and conductive behavior, the MoS₂ pursues its potential in electrochemical applications.

Abstract: We have investigated the magnetic properties of semiconducting molybdenum disulfide (MoS₂) monolayer (ML) using the plane wave self-consistent field (PWscf) method within the framework of density functional theory (DFT). The pristine semiconducting bulk MoS₂ is nonmagnetic (NM), due to the spin pairing of two electrons. We have indicated that the carrier-mediated ferromagnetism is available on the MoS₂ ML as both the hole and electron carriers. The ordinary neutral S (V_S⁰) vacancy creates the localized vacancy defect level and this level does not create the ferromagnetic (FM) state due to the spin pairing of two electrons by three Mo dangling bonds. While we have shown that the FM state is possible to create the FM state, due to the additional hole and electron carriers on the valency band and localized vacancy defect level by positively and negatively charged S (V_S¹⁺ and V_S^1- ) and positively charged Mo (V_Mo¹⁺) vacancies.

Abstract: The electronic structure of nickel iodide monolayer in NiI₂/ScX₂ (X = S, Se and Te) and NiI₂/NiTe₂ heterostructures was investigated by density functional theory (DFT). The spin-asymmetric semiconducting behavior of NiI₂ monolayer in these interfaces was observed. The width of the band gap of the NiI₂ monolayer practically does not change in heterostructures and remains at the level of 1.7 and 3.0 eV for minor and major spin channels, respectively. The NiI₂ layer can be p-doped by stacking with ScX₂ dichalcogenides. On the contrary, charge transfer (~0.01 |e| per f.u.) from NiTe₂ leads to n-doping of NiI₂. As a result, the Fermi level shifts up to the area of NiI₂ conduction band with spin down carriers only, which gives prospects of using this material in spin filter applications. The electronic structure of NiI₂/ScTe₂ under isotropic deformation in the plane remains the same under tension and compression within 5%, except for a small change in the band gap in the composite layers of NiI₂ within 25%. This allows one to conclude about the stability of the electronic properties under deformations, which gives possibility to use the heterostructures in flexible electronics devices.

Abstract: Solid solutions 1T-CrxTi1-xSe2 (x = 0-0,83) were synthesized. Single crystals in the concentration range x = 0-0.69 were grown. Structure of these materials was studied on single- and polycrystalline samples. It was determined that chromium atoms substitute for titanium atoms in the TiSe2 host lattice. XPS measurements of the core levels together with the resonance valence band spectra of the 1T-CrxTi1-xSe2, as well as absorption spectra of Ti and Cr were performed. According to the experimental XAS data and multiplet atomic calculation, titanium and chromium atoms have oxidation numbers of +4 and +3, respectively. The local magnetic moment of about 3 eV is detected at Cr atoms. A transition into the spin glass state is observed. The modeling calculations of chromium local density of states were carried out. These results are in a good agreement with the experimental ones and suggest that 3d density of electronic states of chromium that substitutes for titanium in the host lattice is spin polarized and has a half-metallic character.

Abstract: The intercalated compound Fe0.5TiSe2 has been studied by means of X-ray, neutron diffraction, electrical resistivity and magnetization measurements. This compound with Fe atoms located between Se-Ti-Se sandwiches has a monoclinic crystal structure and exhibits a long-range antiferromagnetic (AF) ordering below TN = 135 K. At T < TN, the Fe magnetic moments with a value ~ 3.0 µB are directed at an angle of (74.4±0.5)º to the layers and form a tilted antiferromagnetic structure with the propagation vector (½, 0, ½). It has been shown that application of magnetic field above 300 kOe may lead to transformations of the AF structure.

Abstract: In order to elucidate the origin of the interplay between charge density wave (CDW) and superconductivity in 1T-TaS2, we have synthesized powder samples of pure and C-intercalated 1T-CxTaS2 by means of a multi-anvil high-pressure synthesis method. We have found that single-phase samples are obtained in the 2-6 GPa range at 400 °C and for x=0-0.3. The structural, magnetic and transport properties of all samples have been investigated by means of neutron and x-ray diffraction, dc magnetization and dc electrical resistivity. For all x values including x=0, the data show that the CDW phase is suppressed concomitant to an abrupt onset of superconductivity, with Tc=3.2 K for x=0. The Tc value turns out to be weakly dependent on x, with a maximum Tc=3.8 K for x=0.2. This onset is accompanied by a crossover of magnetic behavior from paramagnetic Pauli-like to paramagnetic Curie-Weiss-like with effective moment  1.2 B/Ta, which suggests that a ionic picture is suitable for the superconducting phase, but not for the CDW phase. The analysis of the dependence of the a and c lattice parameters upon x as well as upon the synthesis conditions shows that the onset of superconductivity is mainly ascribed to unusual changes of the unit cell induced by the high-pressure synthesis. Specifically, the ex-situ lattice parameters exhibit a significantly larger c-axis parameter and a shrinking of the a-axis parameter stabilized by the high-pressure synthesis route. We argue that the above suppression of the CDW phase is induced by a broadening of the relevant 5d(t2g) band which stabilizes the metallic and superconducting phases. This scenario suggests that the strength of the electronic correlations are the main control parameter of the CDW-superconductivity competition in 1T-TaS2.

Abstract: Ultrahigh-resolution photoemission spectroscopy of 1T-Fe0.5TiSe2 was performed in order to study the changes in the density of states across the superconducting transition. We observed the gap about 2 meV in spectrum measured at 4.5 K.