Papers by Keyword: MoS₂

Abstract: In this work, an investigation of the mechanically exfoliated MoS₂ under the influence of heat treatment was carried out. Optical and atomic force microscopy techniques were applied to determine the number of layers. Resonant Raman investigation was performed, which clearly showed systematic layer-dependent spectral features. The surface morphology of MoS₂ was investigated with the STM. Atomic-resolution images of MoS₂ is were obtained. Three types of atomic defects were identified as substitutions of donor and acceptor atoms in the Mo atomic layer below the topmost sulfur layer.

Abstract: In this work, the Fe-Cr-Mo-V-W-C-MoS₂ composites were fabricated using the powder metallurgy process. The uniaxial cold compaction was used to produce green specimens with the density of 6.3 g/cm³. Subsequently, the specimens were sintered at temperatures of 1150 and 1200 °C for 45 min in a vacuum furnace. Sintered specimens were cooled down in the furnace with N₂ at a cooling rate of 0.1 °C/s. The influence of MoS₂ addition on the density, hardness and microstructure were investigated. Density and hardness of composites were improved due to MoS₂ addition, especially, 5 wt.% MoS₂ addition and sintering at 1200 °C. The dissociation of MoS₂ contributed to the formation of sulfide phases and hard carbide particles within the composites. Sulfide phases such as FeS, CrS and other sulfides were detected by x-ray diffraction analysis. The reciprocating wear test was used to study the effect of MoS₂ addition on friction and wear resistance of composites. The synergy of FeS and CrS contained in the compacted layer and hard carbide particle formation within the matrix were expected to enhance tribological properties of composites by decreasing friction coefficient and improving wear resistance.

Abstract: In this paper, we report on the growth of highly uniform MoS₂ films, mostly consisting of monolayers, on SiC surfaces with different doping levels (n- SiC epitaxy, ~10¹⁶ cm^-3, and n⁺ SiC substrate, ~10¹⁹ cm^-3) by sulfurization of a pre-deposited ultra-thin MoO_x films. MoS₂ layers are lowly strained (~0.12% tensile strain) and highly p-type doped (<N_h>≈4×10¹⁹ cm⁻³), due to MoO₃ residues still present after the sulfurization process. Nanoscale resolution I-V analyses by conductive atomic force microscopy (C-AFM) show a strongly rectifying behavior for MoS₂ junction with n^- SiC, whereas the p⁺ MoS₂/n⁺ SiC junction exhibits an enhanced reverse current and a negative differential behavior under forward bias. This latter observation, indicating the occurrence of band-to-band-tunneling from the occupied states of n⁺ SiC conduction band to the empty states of p⁺ MoS₂ valence band, is a confirmation of the very sharp hetero-interface between the two materials. These results pave the way to the fabrication of ultra-fast switching Esaki diodes on 4H-SiC.

Abstract: In this study, we report that the thermal treatment effects on the Raman and photoluminescence (PL) spectra of mono and few-layer MoS₂ films by annealing in the vacuum and air at 300°C, respectively. The MoS₂ film samples were prepared on silicon substrate by exfoliating from a bulk MoS₂ crystal with a micromechanical exfoliation. For characterization of structural properties of the MoS₂ films and identification of the Raman active modes, Raman spectrometer equipped with a He-Ne laser source and an optical microscope has been used. The results show that the vacuum annealing 7L MoS₂ decreases the Full Width at Half Maximum (FWHM) of the Raman active modes as E¹_2g, A_1g and the vacuum annealing 1L MoS₂ increases the PL intensity and peak energy, for 60% and 13.3meV, respectively also air annealing bilayer MoS₂ increased the PL intensity (I_A) and peak energy (E_A), respectively for 85% and 15.4 meV (300°C for 40 min). After thermal annealing (vacuum and air), we observe that the indirect bandgap of the few-layer MoS₂ was changed.

Abstract: Upgrading of reinforcements with suitable combinations in Aluminum-based hybrid metal matrix composites became a key area of research in the current manufacturing era. These advanced materials have enriched Properties like specific strength, wear resistance, and low thermal expansion. With these perceptions, the current research paper was focused on AA-2024/MoS2/Al2O3 HMMCs. Taguchi L18 orthogonal array was adopted to design the experiments. Hybrid composites containing MoS2 and Al2O3 reinforcements were fabricated by the stir casting method. The pin on disk tribometer was used for finding the wear rate and coefficient of friction of prepared composites by considering sliding speed, applied load, and sliding time as wear parameters. Further, the influence of wear parameters on Wear Rate and Coefficient of Friction (COF) was presented. Consequently, the significance of the parameters on wear rate and COF are analyzed by analysis of variance (ANOVA).

Abstract: New porous films based on polyanionic cellulose with AlOOH nanoparticles have been developed. The morphology of the films has been studied by electron microscopy: the size of the formed pores is 1000-500 microns; the total surface porosity of the films is 30%. Using infrared microscopy, it was shown that during the formation of porous films, their chemical composition remains unchanged. Differential scanning calorimetry was used to determine the threshold for thermal destruction of porous films: 306 С. The possibility of using the obtained materials as antifriction coatings when filling the pores with solid lubricant MoS₂ is considered. It is shown that for a steel sample protected by a porous coating with MoS₂, the friction coefficient decreases by 50% compared to the friction coefficient for a steel surface under a load of up to 450 MPa.

Abstract: A new composite of graphene/MoS₂ is synthesized by co-exfoliation of graphite and MoS₂ in isopropanol (IPA) using the organic salt potassium sodium tartrate as the assistant. The composite is characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectra. The results of TEM, XPS, and Raman spectra all illustrate that the graphene/MoS₂ composite has been synthesized successfully. Furthermore, the composite is modified on glassy carbon electrode to fabricate a sensor to detect dopamine (DA). The sensor shows two linear detection ranges for DA. One is 1-45 μM and the other is 45-120 μΜ. The detection limit of the sensor (S/N=3) is 0.76 μM.

Abstract: In this study, We demonstrate mono and few layers MoS₂ samples on the SiO₂(270nm)/Si substrate from bulk MoS₂ crystal by micromechanical exfoliation technique. We have systematically studied Atomic Force Microscopy, Raman and PL properties of mono and few layer MoS₂ on the SiO₂(270nm)/Si substrate. First, we find that the number of layer values dependent the Raman and PL emission. First, Raman intensity area ratio of the MoS₂ E¹_2g, A_1g and 2LA modes to that area of the Si substrate increased linear with increasing number of layers MoS₂. Second, Normalized PL intensity area of the (A) peak decreased linear with increasing number of layers MoS₂. The value of those graphs is a method to understand the number of layers the exfoliated MoS₂.

Abstract: Since discovery of graphene, great attention had been paid to other two dimensional (2D) layered materials. As a graphene-like layered nanomaterial, molybdenum disulfide (MoS₂) had gained enormous attention from the materials fields which had been widely used in many areas such as solid lubricants, lithium ion batteries, photocatalysts, sensors or as conductive fillers in polymer composites. In this work, MoS₂ nanosheets were incorporated into polymer matrix as nanofillers by three typical preparation methods, including solvent blending, in situ polymerization and melt blending method. The MoS₂ nanosheets were dispersed well in the polymer matrices which improved the thermal stability, mechanical properties and reduced fire hazards of the composites obviously. The improvements in the thermal properties, fire resistance properties and mechanical properties of polymer/MoS₂ nanocomposites were mainly attributed to good dispersion of MoS₂, physical barrier effects of MoS₂ and catalytic char function of MoS₂ nanosheets.

Abstract: The two-dimensional material MoS₂ has attracted a growing attention due to its potential applications in electronic devices in recent years [1,2,3], and the monolayer MoS₂ is a direct gap semiconductor with a band gap of 1.8eV [4]. In the existing studies, it has indicated that MoS₂ can get an available magnetism with doping transition metal atoms [5], and is expected to be a new generation of diluted magnetic semiconductor (DMS) [6,7]. Moreover, we found that Fe-doped MoS₂ could present a strong magnetism but a semimetal characteristic, losing its original semiconductor properties while obtaining magnetism. Therefore, it is necessary to explore some methods to make monolayer MoS₂ exhibit both magnetic and semiconductor properties. In this paper, we propose the method of N, Fe atoms co-doping to achieve this objective. The structural, electronic and magnetic properties of MoS₂ doped with transition metal Fe and VA atoms have been investigated by first principle calculations based on density functional theory. The 3×3×1 supercell of monolayer MoS₂ as a calculation model has been used. The result shows that pure MoS₂ has no magnetism, while Fe-doped MoS2 exhibits a good magnetism about 1.849μB but a semimetal characteristic. This is due to that Mo-4d, S-2p, Fe-3d states has a strong coupling around the Femi energy for the introduction of Fe atom, and the Femi energy only pass through the spin-up density of states. For the co-doping with VA atoms and Fe atoms, it is found that the magnetic moment of Fe-N, Fe-P and Fe-As co-doped MoS₂ is 0.956μB, 0.775μB, 0.782μB. Moreover, the Fe-N co-doped MoS₂ presents semiconductor characteristics, in contrast, Fe-P and Fe-As co-doped MoS₂ appear semimetal properties. It indicates that the semimetal characteristic of Fe-doped MoS₂ could change into indirect band gap semiconductor due to the introduction of N atom. The band gap is 0.2eV. Our study demonstrate that the method of Fe, N co-doping could make MoS₂ have good magnetic and also semiconductor properties at the same time.