Nanosized allotropes of molybdenum disulfide

The present review provides an overview of the rich polymorphism encountered on different length scales within the very versatile material class of transition metal chalcogenides. On the mesoscopic to nanoscopic scale such compounds exhibit a wide variety of nanostructured allotropes with varying dimensionality and competing internal structure, such as nanorods, nanostripes, nanotubes, fullerene-like particles and fullerenes. On the atomistic scale, competing local atomic arrangements within one type of allotrope determine crucially the stability, the chemical potential, and the electronic properties. Thus, any modeling of such structures cannot be restricted to purely classical or quantum-mechanical approaches, but rather the development of classical models on the basis of electronic-structure calculations is required to fully account for all relevant nano- and meso-scale effects. The main part of this review is dedicated to the stability of such nanosystems in relation with the stable size regimes, with their electronic structure, and the derived analysis of the reactivity and application potential. The calculations explain, why the nano-scale properties of the MoS₂ allotropes can be quite different from the bulk ones, and predict novel effects both within and in addition to the established applications of MoS₂ compounds in catalysis, tribology, electronics and electrochemistry.     

Optical and resistivity studies of intercalated layer compounds

The optical absorption of three layered compounds has been studied at 4K between 0·1 and 3·0eV. The three compounds, TaS_1·6Se_0·4, TaS_1·6Se_0·4 (pyridine)_1/2, and TaS_1·6Se_0·4 (aniline)_3/4 have layer separations of 6·14, 12·09 and 18·07 A, respectively. Well-defined, free-carrier absorption edges exist near 1.0 eV in all three materials, from which values of the plasma frequency, the interband dielectric constant, and the optical scattering time were derived using the Drude theory. As the layer spacing increases both the plasma frequency and the dielectric constant decrease. The scattering time is short, 3 × 10^?15 sec, and almost independent of layer spacing. The calculated d.c. resistivity is consistent with the measured value in two of the three compounds.The variations of plasma frequency and dielectric constant with layer spacing are successfully interpreted in terms of a simple model which assumes the organic material acts as a dielectric separating metallic layers unchanged by its presence. Although a number of possibilities are put forward, no complete explanation is given for the short relaxation time in these compounds.     

Electrochemical performance of interspace-expanded molybdenum disulfide few-layer

Journal of Nanoparticle Research - Nanoalloys are bi- or multi-metallic nanoparticles with sizes in the range between 1 and 100 nm. They are the subject of intense research activity in the last...     

Phase conversion of chemically exfoliated molybdenum disulfide

Multilayer MoS₂ is exfoliated by Li treatment. A thin film of Li-treated MoS₂ contains a large portion of 1T phases. This is attributed to the atomic structural change caused by Li insertion, which is investigated using X-ray photoelectron spectroscopy (XPS). In a phase recovery via thermal annealing at 523 K in air, we observe another phase, referred to as the relaxed 1T phase, with a slightly larger binding energy than the 1T phase. After annealing at 523 K in air, the peak intensity of the relaxed 1T phase is reduced, accompanying a strong MoO_x peak and weak S 2s peak, according to XPS. This indicates that the annealing of Li-treated MoS₂ in air yields sulfur vacancies that induce the oxidation of Mo. However, after annealing at 523 K in vacuum, no MoO_x is observed, and the considerable peak intensity of the relaxed 1T phase remains, which starkly contrasts Raman-spectroscopy results supporting a full recovery from the 1T phase to the 2H phase. The absence of a gating effect of the Li-treated MoS₂ device supports the possibility of an incomplete phase change of Li-treated MoS₂ annealed in a vacuum.     

Electrical resistivity of NiAℓ

Resistivity-temperature measurements on annealed near stoichiometric NiA? showed the absence of a resistivity minimum and confirms that the reported anomalous transport properties are an extrinsic effect not observed in high purity NiA?. Thermal treatments on NiA? designed to effect the order did not produce a resistivity-temperature minimum.     

Electrical resistivity of Sm monochalcogenides

The resistivity of mixed valence compounds has been computed in a two band Hubbard-like model. It is shown that there is a transition from a semiconductor to a metallic conductivity and that an intermediate valence can be found in both phases.     

Electrical resistivity of antiferromagnetic GdP

The electrical resistivity of GdP single crystals has been measured between 4.2 and 300 K as function of the stoichiometry. The metallic type of resistivity exhibits critical scattering of electrons at the Néel temperature. Within the range of stoichiometries investigated, the type of scattering changes between “Ornstein-Zernike” like and “Fisher-Langer” like. The magneto-resistance is negative.     

Electrical resistivity of alkali metals

The temperature variations of the electrical resistivity of alkali metals lithium, sodium, potassium, rubidium and caesium are calculated in the free electron approximation and using Krebs's model for the phonon spectrum. The double average over the Fermi surface is evaluated by an improved method due toBailyn and the separation between normal and Umklapp processes is affected in a more satisfactory manner. The results of the calculations are compared with the experimental data obtained at different temperatures. The theoretical resistivity curves for sodium, potassium, rubidium and caesium show satisfactory agreement with experiment, but not in the case of lithium.     

Direct insertion of polypyrrole into molybdenum disulfide

In this paper, we report on the direct intercalation of polypyrrole into MoS₂. This was achieved by first synthesizing LiMoS₂. The LiMoS₂ was exfoliated by reaction with deionized water. Addition of a colloidal suspension of polypyrrole in NMF to the single MoS₂ layers results in flocculation with entrapment of the polymer chain in the van der Waals gap of the layered structure. The sandwiched compound was characterized by powder X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry.     

Electrical resistivity of liquid cesium

The temperature dependences of liquid cesium resistivity are calculated using smooth nonlocal model pseudopotentials (SNMP). The calculations were performed for temperatures of 35, 150, 280, 310, 470, and 630°C, both with temperature-dependent SNMP parameter variations and without them. The SNMP parameters of liquid cesium were determined based only on the experimental values of free ion terms without applying any methods of adjustment to the electrical resistivity of cesium. Application of SNMP makes it possible to substantially improve the similarity of the temperature dependences for calculated and experimentally obtained electrical resistivities of liquid cesium as compared to the calculations based on local model potentials.     

Electrical resistivity of amorphous alloys

Amorphous alloys of Ga, Sn, Pb and Bi with Cu, Ag and Au are produced by evaporation on a cold substrate. The residual resistivity, the temperature dependence of the resistivity, the transition temperature of superconductivity and the temperature of the amorphous-crystalline transformation are measured. We observe e.g. that the residual resistivity increases with the noble metal concentration, and that the temperature coefficient of the resistivity of the Au alloys is always negative. In these two respects amorphous alloys differ in behaviour from the corresponding liquid alloys. These observations can be correlated with the atomic energy levels of the free atoms.     

Electrical resistivity of heusler alloys

The electrical resistivity of eight different Heusler alloys is discussed in terms of electron phonon and spin-disorder scattering. The systematics common to the alloys can be explained in the intermediate to high temperature range while the low temperature range still presents interpretation difficulties.     

Electrical resistivity of liquid Ag-Au alloy

Calculations of the dependence of the electrical resistivity in liquid Ag-Au binary alloy on composition are reported. The structure of the binary alloy is described as a hard-sphere system. A one-parameter local pseudo-potential which incorporates s-d hybridization effects phenomenologically, is employed in the resistivity calculation. A reasonable agreement with experimental trend is observed.     

Electrical resistivity of liquid gold-silicon alloys

The electrical resistivity of liquid Au_1?xSi_x alloys was measured in the gold-rich concentration range, 0.16 ? x ? 0.40, as a function of temperature and composition. In this region the temperature coefficients of the resistivity is negative. The resistivities and temperature coefficients are compared with recent data on amorphous sputtered films; for x ? 0.31 the resistivities of the films are in agreement with those of the liquids within the accuracy of the measurements. The results can be interpreted in terms of the Ziman theory.     

Electrical resistivity of K-based liquid binaries

The study of the electrical resistivity of alkali K-based liquid binaries, viz, K _1−x Na _x, K _1−x Rb _x, and K _1−x Cs _x have been made by well recognized model potential. The most recent local field correction functions due to Farid et al. (F) and Sarkar et al. (S) are used for the first time in the study of electrical resistivity of liquid binary mixtures and found suitable for such study. The results due to the inclusion of Sarkar et al.’s local field correction function are found superior to those obtained due to Farid et al.’s local field correction function. The present results compare well the experimental data. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 40–44, August, 2006.     

Electrical resistivity of amorphous Sn-Cu alloys

The residual resistivity of amorphous Sn-Cu alloys increases with the Cu-concentration. Both positive and negative temperature coefficients are observed. The positive temperature coefficient and the transition temperature of superconductivity depend linearly on the Cu-concentration and both vanish simultaneously.     

Electrical resistivity of metastable Ag-Ni alloys

We have successfully prepared solid solution metal films of Ag-Ni with Ni content to 23.4 at.%. Four-probe resistivity measurements were conducted between 2.5 and 300°K and while no anomalies of the magnetic type were observed, the temperature dependence of the resistivity indicates significant deviations from Matthiessen's rule.