Structure Of 1H Research Articles

Unsymmetrical ferrocene-based azines: Facile synthesis, investigation of spectral and electrochemical properties, and antibacterial activity

Ferrocenyl azines have been utilized in metal ion detection, as a ligand in the synthesis of metal complexes, in catalysis, in dye-sensitized solar cells, and in studies on antiparasitic, antitumor, and antileishmanial. However, most of the challenging synthesis routes require temperature control, expensive starting materials, and additional steps. In this research, a series of new unsymmetrical ferrocene-based azines (2a-j and 4a-j) were simply synthesized from the reaction of ferrocenecarboxaldehydehydrazone (1) and 1,1′-ferrocenedicarboxaldehydehydrazone (3) with various aryl aldehydes in moderate to good yield (40–80 %). All compounds were characterized using FT-IR, 1H and 13C NMR, and LC-MS. In addition, the molecular structure of 2b and 2h were determined by X-ray structure analysis. UV–Vis spectra of azines revealed weak absorbance in the 460–490 nm region for the d → d transition of Fe(II) and two strong absorbances in the range of 250–350 nm for π → π* and n → π* of aromatic rings and azine bridges. Cyclic voltammetry demonstrated higher half-wave potentials (E1/2) for all ferrocenyl azines in comparison to ferrocene as the internal standard, with a significant decrease of E1/2 for ferrocenyl-rich derivatives. The antibacterial activities of all synthesized ferrocenyl azines were also investigated against Staphylococcus aureus (gram-positive) and Escherichia coli (gram-negative) bacteria. Two ferrocene-rich compounds, 2i and 4j, have shown significant activity against Staphylococcus aureus.

Experimental investigation on the crystal structure and superconductivity of germanium-intercalated 2H–NbSe2 system

We report the structural and superconducting properties of Ge-intercalated 2H–NbSe2 polycrystals. GexNbSe2 samples with nominal 0 ≤ x ≤ 0.1 crystallize in the space group P63/mmc with Ge disorderedly occupying the interlayer Se6 octahedral interstices. Superconducting critical temperature Tc monotonically decreases from 7.2 K in NbSe2 to 4.9 K in Ge0.1NbSe2. Studies on resistivity, magnetization and specific heat derive the superconducting- and normal-state parameters, indicating that the suppression of the two-gap superconductivity is mostly caused by the lowered electron-phonon coupling parameter λe-p and density of states at the Fermi level N(EF). Surprisingly, the upper critical field Hc2 and irreversible field Hirr of the low Ge-level samples are enhanced compared with those of the undoped one, which may ascribe to the electron scattering and vortex pinning by nonmagnetic Ge. This study suggests the feasibility for improving high-field performance by slight impurity doping and advances the understanding of superconductivity in transition-metal dichalcogenides.

Probing the layer-dependent behavior of electronic properties and quantum capacitance in 2H MoS2: A computational analysis with emphasis on mechanical stability

The quest for clean, sustainable energy sources was prompted by the fast depletion of fossil fuels and the world's expanding energy requirements. To store renewable energy, it is important that effective energy storage devices such as supercapacitor (SCs) be manufactured. SCs offer a promising avenue for fast-charging, energy storage, and long-life cycles but maximizing their energy density remains a problem. This study theoretically explores the intrinsic Quantum capacitance (Cq) of MoS2 in the 2H phase with a few number of layers and how factors like electronic structure and density of states influence its capacitance behavior. In the present work, the first principles analysis utilizing computational modelling with Density Functional Theory (DFT) has been employed to investigate the Cq and surface charge density (σ) of MoS2. By explaining the connection between MoS2's electrical and structural properties with its Cq, valuable insights for optimizing it's SC performance were obtained. Both the density of states (DOS) and the Cq increase with the number of layers. Among the observed structures the highest value of Cq is observed for the three layered structure of 2H–MoS2 (2H3L-MoS2) at +1 V which is 1615.14 μF cm−2. Investigating the mechanical stability of optimized structure (2H3L-MoS2), a high Young's modulus of 180.46 GPa is observed for 2H3L structure. Hence, 2H-phase of MoS2 can be used as an excellent anode material for asymmetric SCs and flexible electronic devices.

Prediction of large spin-valley polarization in the Janus 2H–WSSe monolayer on VN magnetic substrate

Two-dimensional heterostructures based on transition metal dichalcogenides (TMDs) exhibit broad application prospects in valleytronics due to the space-reversal symmetry breaking and strong spin–orbit coupling. In this work, the electronic structure, magnetic anisotropy and valley polarization of 2H–WSSe/VN van der Waals heterostructure under various interlayer spacings, magnetic angle and in-plane strain are investigated in detail by first-principles calculations. The stacked configuration of Se-C2-1 with most stable structure shows the largest valley polarization of 386.5[Formula: see text]meV. By adjusting the interlayer spacing of heterostructure, the largest valley polarization of 702.7[Formula: see text]meV appears in Se-C2-1 stacked configuration with interlayer spacing of 2.24 Å. The magnetic angle [Formula: see text] exhibits significant effects on valley polarization and magnetic anisotropy of 2H–WSSe/VN heterostructures. The stability and valley polarization of 2H–WSSe/VN heterostructure decrease after the in-plane biaxial strain is applied. The large and tunable valley polarization as well as magnetic anisotropy in the 2H–WSSe/VN heterostructures make it potential applications in valleytronic devices.

Effect of NM (B, C, N, O and F) doping and Fe[sbnd]NM co-doping on structure, electronic and magnetic properties of monolayer 2H[sbnd]MoTe[formula omitted] : A first principle investigation

Exploring magnetism in two-dimensional transition-metal dichalcogenides (TMDs) has gained a plethora of interest in recent times. Herein, employing spin-polarized density functional theory, we looked into the effect of non-metal doping (B, C, N, O, and F) and Fe-non metal co-doping on structure, electronic, and magnetic properties of 2HMoTe2 to identify new promising configurations for spin-based device applications. For non-metal doping, the results depict that B, N, and F-doped systems are magnetic, and the N-doped system shows magnetic-semiconducting behavior. The half-metallic Fe-doped MoTe2 transforms into a magnetic semiconductor upon co-doping. The structural distortion around the Fe atoms modifies the crystal field splitting, resulting in triply degenerate a1 and singly degenerate a2 and a3 states. Uncompensated electrons in the co-doped system and hybridization between Fe and NM atom modifies the magnetic properties of monolayer MoTe2. Competition between crystal field splitting and intra-atomic Hund’s exchange splitting determines the magnetic moment. Due to charge compensation, C-doped and FeC co-doped systems are non-magnetic. N-doped and FeN co-doped MoTe2 exhibit long-range magnetic ordering. Formation energy calculations revealed that the co-doped configurations are easily attainable in experiments compared to non-metal doped systems. The results open up a robust way to realize 2HMoTe2 based spintronic devices.

Controllable Valley Polarization and Strain Modulation in 2D 2H-VS2/CuInP2Se6 Heterostructures.

Two–dimensional (2D) transition metal dichalcogenides endow individually addressable valleys in momentum space at the K and K’ points in the first Brillouin zone due to the breaking of inversion symmetry and the effect of spin–orbit coupling. However, the application of 2H–VS2 monolayer in valleytronics is limited due to the valence band maximum (VBM) located at the Γ point. Here, by involving the 2D ferroelectric (FE) CuInP2Se6 (CIPSe), the ferrovalley polarization, electronic structure, and magnetic properties of 2D 2H–VS2/CIPSe heterostructures with different stacking patterns and FE polarizations have been investigated by using first–principles calculations. It is found that, for the energetically favorable AB–stacking pattern, the valley polarization is preserved when the FE polarization of CIPSe is upwards (CIPSe↑) or downwards (CIPSe↓) with the splitting energies slightly larger or smaller compared with that of the pure 2H–VS2. It is intriguing that, for the FE CIPSe↑ case, the VBM is expected to pass through the Fermi energy level, which can be eventually achieved by applying biaxial strain and thus the valleytronic nature is turned off; however, for the CIPSe↓ situation, the heterostructure basically remains semiconducting even under biaxial strains. Therefore, with the influence of proper strains, the FE polar reversal of CIPSe can be used as a switchable on/off to regulate the valley polarization in VS2. These results not only demonstrate that 2H–VS2/CIPSe heterostructures are promising potential candidates in valleytronics, but also shed some light on developing practical applications of valleytronic technology.

Anomalous enhancement of atomic vibration induced by electronic transition in 2H-MoTe2 under compression

In this work, we explore the atomic vibration and local structure in 2H–MoTe2 by using high-pressure x-ray absorption fine structure spectroscopy up to ∼20 GPa. The discrepancy between the Mo–Te and Mo–Mo bond length in 2H–MoTe2 obtained from extended-XAFS and other techniques shows abnormal increase at 7.3 and 14.8 GPa, which is mainly due to the abrupt enhancement of vibration perpendicular to the bond direction. Ab initio calculations are performed to study the electronic structure of 2H–MoTe2 up to 20 GPa and confirm a semiconductor to semimetal transition around 8 GPa and a Lifshitz transition around 14 GPa. We attribute the anomalous enhancement of vibration perpendicular to the bond direction to electronic transitions. We find the electronic transition induced enhancement of local vibration for the first time. Our finding offers a novel insight into the local atomic vibration and provides a new platform for understanding the relationship between the electronic transition and atomic vibration.

Synthesis, characterization, DFT calculation, antifungal, antioxidant, CT-DNA/pBR322 DNA interaction and molecular docking studies of heterocyclic analogs

A series of heterocyclic analogs (2a-2l) was synthesized through condensation of 5-(4-aminophenyl)-1,3,4-oxadiazole-2-thiol and substituted aldehydes in ethanol and characterized by 1H, 13C NMR, IR, UV–visible spectroscopy and mass spectrometry. Optimization of the structure of heterocyclic analogs 2c, 2h and 2j was done by density functional theory (DFT) calculations. In vitro antifungal activity and growth pattern analyses of heterocyclic analogs (2a-2l) were evaluated against the Candida albicans. Results exhibited that analog 2c has significant antifungal potential with MIC value of 200 µg/ml comparable with standard drug fluconazole. In vitro hemolysis assay of the analog 2c showed 7.27% hemolysis at 200 µg/ml concentration indicating its nontoxic nature. The interaction of promising compound 2c with CT-DNA was carried out by UV-visible, fluorescence, Time-Resolved fluorescence spectrophotometry, cyclic voltammetry, circular dichroism and viscosity measurements. The UV-visible spectral analysis signifies the formation of complex between heterocyclic analog 2c and CT-DNA. The binding constant (Kb) and Gibb's free energy (ΔG) for 2c were found to be 6.34 × 105 and -33.1 KJmol−1, respectively. Further from fluorescence spectra, linear Stern–Volmer constant (KSV) for 2c was found to be 1.29 × 105. In silico molecular docking study of analog 2c with PDB: 1BNA confirmed the intercalation mode of binding which were corroborated with in vitro DNA binding results. The interaction study of analog 2c with supercoiled pBR322 plasmid DNA with varying concentration (3–20 mM) was carried out by Agarose gel electrophoresis. Antioxidant activity was also carried out for compounds 2a-2l using DPPH and H2O2 assay.

Electronic properties and tunability of the hexagonal SiGe alloys

Hexagonal (2H) germanium is found to be a direct bandgap semiconductor, showing the potential of efficient light emission. Based on 2H–Ge, the structure and electronic properties of 2H–SiGe alloys are studied in detail by hybrid functional calculations. By varying the Si content of the 2H–SiGe alloys, the bandgap is found to be direct for Si contents smaller than 0.35. We find that the key factor in determining the indirect-to-direct transition of the band structures for 2H–SiGe alloys originates from the variation of lattice constant. Furthermore, the Si-rich 2H–SiGe alloy can be changed from indirect to direct bandgap by strain engineering. Furthermore, we consider the effective electron masses (me), band alignments with several oxides, optical absorption properties, and vacancy formation energies of 2H–SiGe alloys, which show that the direct-gap 2H–SiGe alloys have the potential for optoelectronic applications.

Discovery, semisynthesis and neurite outgrowth-promoting activity of novel merrillianone/cycloparviforalone based esters as neurotrophic agents

Natural products (NPs) are very important sources for the development of new drugs. Merrillianone and cycloparvifloralone, isolated from the roots, stems, and fruits of Illicium henryi Diels, are two natural sesquiterpene compounds. In continuation of our effort to discovery more effective neurotrophic compounds from NPs, a series of novel merrillianone/cycloparviforalone based esters 2a–i, 3a–g and 3i–q were prepared and their structures were characterized by 1H NMR, 13C NMR and IR spectral analyses. Furthermore, the spatial structure of compound 2h was unambiguously confirmed by X-ray crystallography. The neurite outgrowth-promoting activity results indicated that most of the target derivatives exhibited more potent neurite outgrowth-promoting activity than merrillianone and cycloparviforalone. Among all target derivatives, the neurite outgrowth-promoting activity of compounds 2a, 3a and 3b was about 2-fold stronger than that of their precursors merrillianone and cycloparviforalone, respectively. Besides, compounds 2a and 3a displayed relatively low cytotoxicity to normal GES-1 cells. Moreover, these derivatives had good hydrolytic stability. Finally, some interesting results of the structure–activity relationships (SARs) were also discussed. This work will pave the way for the development of merrillianone/cycloparviforalone derivatives as potential neurotrophic agents.

Isolation and Structural Elucidation of 15-Nuclear Copper Dihydride Clusters: An Intermediate in the Formation of a Two-Electron Copper Superatom.

Highly reactive copper-dihydride clusters, [Cu15 (H)2 (S2 CNR2 )6 (C2 Ph)6 ](PF6 ) {R= n Bu (1H ), n Pr (2H ), i Bu (3H )}, are isolated during the reaction of [Cu28 H15 {S2 CNn Bu2 }12 ](PF6 ) with ten equivalents of phenylacetylene. They are found to be intermediates in the formation of the earlier reported two-electron superatom [Cu13 (S2 CNR2 )6 (C2 Ph)4 ]+ . Better yields are obtained by reacting dithiocarbamate sodium salts, [Cu(CH3 CN)4 ](PF6 ), BH4- and phenylacetylene. The presence of two hydrides in the isolated clusters is confirmed by the synthesis and characterization of its deuteride analogue [Cu15 (D)2 (S2 CNR2 )6 (C2 Ph)6 ]+ , and a single-crystal neutron structure of 2H . Structural characterization of 1H reveals a new bicapped icosahedral copper(I) cage encapsulating a linear copper dihydride (CuH2 )- unit. Reaction of 3H with Au(I) salts yields a highly luminescent [AuCu12 (S2 CNi Bu2 )6 (C2 Ph)4 ]+ cluster.

Fabrication of rGO/CdS@2H, 1T, amorphous MoS2 heterostructure for enhanced photocatalytic and electrocatalytic activity

The synthesis of high efficiency noble metal free catalysts is an important target for H2 production by water-splitting. In this work, rGO/CdS@MoS2 heterostructure with two catalytic paths was successfully synthesized and as the first applied the heterostructure in the field of electrocatalysis. The MoS2 structure is adjusted by controlling hydrothermal process. Moreover, the effects of structure and loading amount of 2H–MoS2, 1T-MoS2 and amorphous MoS2 (A-MoS2) on catalytic performance were also studied. The catalytic activity of rGO/CdS@MoS2 heterostructure has been improved obviously. Compared with 2H–MoS2, the distortion of 1T-MoS2 and the defect of A-MoS2 make it have more unsaturated S, so rGO/CdS@1T-MoS2 and rGO/CdS@A-MoS2 have better catalytic activity. For photocatalytic H2 evolution, loading MoS2 and rGO on catalysts changes the energy band structure, promotes the separation of electron-holes and provides a large number of active sites. Among them, the visible light photocatalytic H2 production rate of rGO/CdS@1T-MoS2 with 0.1 mol of 1T-MoS2 (CT0.1-G1) is 18.26 mmol/g/h. During the electrocatalytic H2 evolution, introducing MoS2 and rGO improves electronic structure and increases active sites. rGO/CdS@1T-MoS2 with 0.5 mol of 1T-MoS2 (CT0.5-G1) shows the low overpotential (312 mV) and Tafel slopes (85 mV/dec).

Discovery of the First Vitamin K Analogue as a Potential Treatment of Pharmacoresistant Seizures.

Despite the availability of more than 25 antiseizure drugs on the market, approximately 30% of patients with epilepsy still suffer from seizures. Thus, the epilepsy therapy market has a great need for a breakthrough drug that will aid pharmacoresistant patients. In our previous study, we discovered a vitamin K analogue, 2h, which displayed modest antiseizure activity in zebrafish and mouse seizure models. However, there are limitations to this compound due to its pharmacokinetic profile. In this study, we develop a new series of vitamin K analogues by modifying the structure of 2h. Among these, compound 3d shows full protection in a rodent pharmacoresistant seizure model with limited rotarod motor toxicity and favorable pharmacokinetic properties. Furthermore, the brain/plasma concentration ratio of 3d indicates its excellent permeability into the brain. The resulting data shows that 3d can be further developed as a potential antiseizure drug in the clinic.

Effect of fluorination on the crystal and electronic structure of organometallic cyclopentadienyl-phenylenediamino-cobalt complexes

The fluorinated half sandwich complex [CpCoLF] (Cp = cyclopentadiene; LF = o-perfluoro-phenylenediimine; 2F) shows a T-shaped geometry with the LF ligand coplanar with the metallocycle. The molecules are dimerized in a head-to-tail fashion and arranged in a herringbone manner in the crystal packing. The crystal structure of 2F is different from that of the corresponding hydrocarbon compound (2H). Moreover, the differences due to the presence of fluorine atoms are also highlighted by the analysis of the intermolecular contacts, which show that 2F exhibits several F⋯F contacts, as well as aromatic intra-dimer π … π interactions in addition to C–H … π and C–H⋯F contacts. No relevant π … π interactions are observed in the case of 2H. Hirshfeld Surface (HS) analysis also depicted well the differences in the solid state interactions between the different crystal structures. In particular, HS has been useful in highlighting the differences observed between the crystal structure of 2H obtained from Rietveld refinement and that measured on single crystal (2HP and 2HSCH, respectively). The effect of the fluorination on the electronic structure has been investigated also by CV measurements and Density Functional Theory calculations. Both are consistent with a lowering in energy of the molecular orbitals. Data Mining Force Field calculations clearly indicate that the 2HSCH structure is more stable than the 2HP one. These findings can be explained in terms of the energy of the intermolecular interactions. The enhanced stability of the fluorine substitute can be easily explained by the large number of strong interactions involving fluorine atoms.

Investigation of structural, optical and thermoelectric properties of 2H–MoTe2 and MoO3–TeO2 thin films

Easy synthesis of two-dimensional chalcogenide materials sach as MoTe2 and WTe2 is an important challenge for researchers. In this paper, we are showed that using Mo and Te oxides percursors as inexpensive initial materials and spray pyrolysis method, the MoO3–TeO2 thin film binary compounds, and the important two-dimensional structure of 2H–MoTe2 are prepared. . In this method, through the preparation of thin films of the MoO3–TeO2 binary composition by changing the molar concentration of Mo and Te in a solid-state reaction process, with molar ratios (a) MoO3 (0.05 M) -TeO2 (0.15 M), (b) MoO3 (0.1 M) -TeO2 (0.1 M) and (c) MoO3 (0.15 M) -TeO2 (0.05 M), we can obtain the 2H–MoTe2 phase. After synthesis of MoO3–TeO2 and 2H–MoTe2 compounds, structural and optical characterization of thin films, as well as thermoelectric properties of the prepared thin films were studied before and after annealing at T = 500 °C. X-ray diffraction results showed that the structure of thin films before annealing is amorphous structure, and after annealing at T = 500 °C for synthesis c: MoO3 (0.15 M) -TeO2 (0.05 M), the two-dimensional structure of 2H–MoTe2 was formed. The images of the field emittion scanning electron microscope (FE-SEM) showed that the morphology of the nanoparticles is the pseudo-spherical shape, rod and polygon, indicating the presence of particles in different phases at before annealing and flat – like form after annealing. The results of UV–Vis spectrometry showed that the energy gap of thin films varied in the range of 2.3–2.87 eV. The nanoparticle bonding structure was also studied by FT-IR spectroscopy. Studies on the thermoelectric properties of thin films before and after annealing showed that for synthsis (c): MoO3 (0.15 M) -TeO2 (0.05 M) with formation of the 2-H-MoTe2 phase, the seebeck coefficient was larger than other samples, and the majority carrier are holes. Also, ZT increases with decreasing molar concentration of TeO2 and reached to 1.32 at room temperature for synthesis c: MoO3 (0.15 M) -TeO2 (0.05 M).

Temperature dependence of thermodynamic properties of MoS2 monolayer and single-wall nanotubes: Application of the developed three-body force field

MoS2 nanostructures, especially mono-, multilayer nanothin films as well as single- and multiwall nanotubes are rather interesting popular objects in nanomaterials chemistry. The thermodynamic properties of inorganic nanotubes, and the temperature dependence of their properties can be efficiently investigated by first-principles and molecular mechanics methods in the framework of harmonic approximation. At the same time, only thin single-wall nanotubes are available for the first-principles calculations. The classical mechanics is suitable to simulate very large atomic systems and their phonon frequencies, but developing sufficiently accurate force field is rather tedious work. Herein, we report the force field fitted to the experimental and first-principles data on the structure of 2H- and 3RMoS2 polytypes of bulk crystal, structure of monolayer and several bilayers, vibrational frequencies of 2HMoS2 bulk and monolayer, relative energetic stability of polytypes experimental and first-principles data, elastic constants, strain energy of a (12, 12) MoS2 nanotube. The thermodynamic functions and their temperature dependence for the armchair and zigzag nanotubes are calculated within the formalism of molecular mechanics using elaborated interatomic potential. The results of molecular mechanics and first-principles method application to the thinnest nanotubes are compared.

Crystal structure of bis-{(S)-1-[2-(di-phenyl-phosphan-yl)ferrocen-yl]-(R)-eth-yl}ammonium bromide di-chloro-methane monosolvate.

During the synthesis of an FeBr2 complex with the PNP ligand (R,R,SFc,SFc)-[Fe2(C5H5)2(C38H35NP2)] (1), single crystals of the di-chloro-methane monosolvate of the Br- salt of the protonated ligand 1H+ were obtained serendipitously, i.e. [Fe2(C5H5)2(C38H36NP2)]Br·CH2Cl2. The crystal structure of 1H·Br·CH2Cl2 was determined by single-crystal X-ray diffraction. The mean bond lengths in the ferrocene units are Fe-C = 2.049 (3) Å and C-C = 1.422 (4) Å within the cyclo-penta-dienyl rings. The mean C-N bond length is 1.523 (4) Å. The inter-planar angle between the two connected cyclo-penta-dienyl rings is 49.2 (2)°. One ferrocene moiety adopts a staggered conformation, whereas the other is between staggered and eclipsed. The Br- ions and the CH2Cl2 mol-ecules are located in channels extending along <100>. One ammonium H atom forms a hydrogen bond with the Br- ion [H⋯Br = 2.32 (4) Å and C-H⋯Br = 172 (3)°]. The second ammonium H atom is not involved in hydrogen bonding.

Site-selective luminescence spectroscopy of bound excitons and local band structure of chlorine intercalated 2H- and 3R-MoS2 polytypes

Photoluminescence and X-ray diffraction are used to investigate 2H and 3R polytypes of MoS2 layered crystals intercalated with Cl2 molecules. The spectral structure of the observed bound excitons emission is individual for each polytype, which can be used for unambiguous identification of the 2H and 3R polytypes. The DFT band structure calculations have been done for three molecular layers of 2H-MoS2 and 3R-MoS2 polytypes with and without intercalation of Cl2 molecules. The spectroscopic experimental results confirmed theoretical calculations performed for both cases and it has been demonstrated that halogen intercalation completely changes the local band structure of both 2H- and 3R-MoS2 polytypes.

Structural and electrical properties of SnS2 thin films

The effect of substrate temperature on the structural and electrical properties, phase composition, and surface morphology of tin disulfide thin (SnS2) films obtained by the close-spaced vacuum sublimation (CSS) method was studied.Scanning electrical microscope (SEM) images of the samples showed that all of the films were polycrystalline with an average grain size of 0.7–1.2 μm. The average thickness of the thin films was 1 μm.Energy dispersive spectroscopy (EDS) analysis showed that all layers had close to stoichiometric atomic composition. Namely, the concentrations of tin and sulfur were 35 and 65% respectively.X-ray diffraction (XRD) study indicated that the samples obtained at 473–723 K mostly contained hexagonal phase SnS2 with high texture along the (002) crystallographic plane. The values of the lattice constants (a and c) of SnS2 thin films increase monotonically with substrate temperature from 0.3637 to 0.3647 nm and from 0.5703 to 0.5743 nm, respectively.Investigation of the SnS2 films by Raman spectroscopy confirmed the results of XRD studies, namely that the layers have single-phase hexagonal structure of 2H polytype.Studies of the electrical properties of SnS2 thin films showed that the conductivity of the films changed from 1.8 × 10−4 to 10−7 (Om⋅cm)−1. Analysis of the I–V characteristics in the space-charge limited current (SCLC) mode made it possible to define (Et1 = (0.52–0.55), Et2 = (0.46–0.49), Et3 = (0.43–0.45), and Et4 = (0.35–0.39) eV), the localized states energy depths in the band gap of the SnS2 thin films. The concentration of these localized states exceeds 1.31 × 1014 ≿m−3. Also, from the measurements of temperature dependent conductivity, several localized states with activation energies of 0.25 and 0.26 eV states were determined.

First-principles calculations on mechanical and elastic properties of 2H- and 3R-WS2 under pressure

The structure, mechanical stability and elastic properties of 2H- and 3R-WS2 under pressure have been investigated using first-principles calculations based on density functional theory (DFT). The equilibrium lattice parameters of 2H- and 3R-WS2 at 0GPa are consistent with experimental and other theoretical values. 2H-WS2 is more stable than 3R-WS2 when pressure is less than 5.8GPa whereas 3R-WS2 is more stable than 2H-WS2 when pressure is higher than 5.8GPa. According to the mechanical stability criteria, both 2H- and 3R-WS2 exhibit mechanical stability under the pressure range from 0 to 20GPa. With the increasing pressure, the elastic moduli (E, B, G), sound velocities (vs, vp, vm) and Debye temperatures of 2H- and 3R-WS2 increase monotonously whereas volume and specific heat decrease. Large elastic anisotropies in compressibility and in shear were demonstrated for 2H- and 3R-WS2 at 0GPa. As the pressure increases, anisotropies in compressibility and in shear become weak for 2H- and 3R-WS2. Moreover, 2H- and 3R-WS2 under pressure have higher hardness and better ductility than those at 0GPa.