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Synthesis and characterization of indium intercalation compound of MoS2, In x MoS2 (0?x?1)
... The optimized in-plane lattice constants a and out-of-plane interlayer distances d 0 of TMDC bilayers are summarized in Table 1. For MoS 2 bilayers, constants a under different methods are ranged from 3.16 to 3.20 Å, which agree with the experimental result (3.16 Å) [33,34]. However, d 0 values under different approaches are varied in a wide range (from 6.01 Å to 7.03 Å). ...
... The optimized in-plane lattice constants a and out-of-plane interlayer distances d 0 of TMDC bilayers are summarized in Table 1. For MoS 2 bilayers, constants a under different methods are ranged from 3.16 to 3.20 Å, which agree with the experimental result (3.16 Å) [33,34]. However, d 0 values under different approaches are varied in a wide range (from 6.01 Å to 7.03 Å). ...
... 10,14 However, partly we find few-layered 2D MoS2 with a molybdenum to molybdenum layer distance of 7 Å. This value is increased with respect to the bulk layer distance of 6.15 Å, 54,55 which is caused by the colloidal NSs having a twisted shape, therefore exhibitin non-optimal stacking. In samples with high molybdenum precursor concentration (240 mM, Figure 2d), few-layered NSs were found more frequently than in low molybdenum precursor synthesized NPLs. ...
2D semiconducting transition metal dichalcogenides (TMDCs) are highly promising materials for future spin- and valleytronic applications and exhibit an ultrafast response to external (optical) stimuli which is essential for optoelectronics. Colloidal nanochemistry on the other hand is an emerging alternative for the synthesis of 2D TMDC nanosheet (NS) ensembles, allowing for the control of the reaction via tunable precursor and ligand chemistry. Up to now, wet-chemical colloidal syntheses yielded intertwined/agglomerated NSs with a large lateral size. Here, we show a synthesis method for 2D mono- and bilayer MoS2 nanoplatelets with a particularly small lateral size (NPLs, 7.4 nm ± 2.2 nm) and MoS2 NSs (22 nm ± 9 nm) as a reference by adjusting the molybdenum precursor concentration in the reaction. We find that in colloidal 2D MoS2 syntheses initially a mixture of the stable semiconducting and the metastable metallic crystal phase is formed. 2D MoS2 NPLs and NSs then both undergo a full transformation to the semiconducting crystal phase by the end of the reaction, which we quantify by X-ray photoelectron spectroscopy. Phase pure semiconducting MoS2 NPLs with a lateral size approaching the MoS2 exciton Bohr radius exhibit strong additional lateral confinement, leading to a drastically shortened decay of the B exciton which is characterized by ultrafast transient absorption spectroscopy. Our findings represent an important step for utilizing colloidal TMDCs, for example small MoS2 NPLs represent an excellent starting point for the growth of heterostructures for future colloidal photonics.
... The optimized inplane lattice constants a and out-of-plane interlayer distances d 0 of TMDC bilayers are summarized in Table 1. For MoS 2 bilayers, constants a under different methods are ranged from 3.16 to 3.20 Å, which agree with the experimental result (3.16 Å) [33,34]. However, d 0 values under different approaches are varied in a wide range (from 6.01Å to 7.03 Å). ...
Atomically two-dimensional (2D) materials have out-of-plane van der Waals (vdW) interactions and in-plane covalent bonds, which enables the possibility to exfoliate and reassemble different 2D materials into arbitrarily stacked heterostructures. Here, we compare the atomic structures, binding energies, and dipole moments of transition-metal dichalcogenides (TMDCs) by different vdW-inclusive density functional theory (DFT) approaches. We found that the selection of the vdW-inclusive approaches largely affects the relaxed structure and the dipole moment of 2D systems. Specially, DFT-D3 takes chemical environments into account and reduces the double-counting effects at medium-range, and provides comparable binding energies for MoS2 with experimental results. This work highlights the importance of dispersion force and provides a guidance for selecting dispersion approaches in 2D device theoretical designs.
This study introduces iodine‐assisted thermal annealing of commercially sourced molybdenum disulfide (MoS₂) powders to significantly enhance their dispersion yield, exfoliation efficiency, and compatibility across a wide range of solvents. This method leverages iodine as a transport agent during annealing (800–1200 °C), leading to the removal of oxide and sulfide impurities that impede exfoliation and reduce swelling, such as those that bridge individual layers. Dispersions of the post‐treated MoS2 powder outperform alternative approaches such as surfactant‐assisted dispersion, redox dispersion, or lithium intercalation; here, stable colloidal solutions are produced with yields exceeding 50% where the dispersion is dominated by exfoliated single‐to‐few layer flakes. This is achieved without the need for surface additives or use of extreme mechanical forces that can degrade performance of MoS2 in electronic, sensor, and optical applications. These findings, which highlight the impact of composition and structural purity of the starting powders, offer a promising solution for expanding the use of layered transition metal dichalcogenide materials.
The intercalation of layered materials offers a flexible approach for tailoring their structures and generating unexpected properties. This review provides perspectives on the chemical intercalation of layered materials, including graphite/graphene, transition metal dichalcogenides, MXenes, and some particular materials. The characteristics of the different intercalation methods and their chemical mechanisms are discussed. The influence of intercalation on the structural changes of the host materials and the structural change how to affect the intrinsic properties of the intercalation compounds are discussed. Furthermore, a perspective on the applications of intercalation compounds in fields such as energy conversion and storage, catalysis, smart devices, biomedical applications, and environmental remediation is provided. Finally, brief insights into the challenges and future opportunities for the chemical intercalation of layered materials are provided.
2D semiconducting transition metal dichalcogenides (TMDCs) are highly promising materials for future spin- and valleytronic applications and exhibit an ultrafast response to external (optical) stimuli which is essential for optoelectronics. Colloidal nanochemistry on the other hand is an emerging alternative for the synthesis of 2D TMDC nanosheet (NS) ensembles, allowing for the control of the reaction via tunable precursor and ligand chemistry. Up to now, wet-chemical colloidal syntheses yielded intertwined/agglomerated NSs with a large lateral size. Here, we show a synthesis method for 2D mono- and bilayer MoS2 nanoplatelets with a particularly small lateral size (NPLs, 7.4 nm ± 2.2 nm) and MoS2 NSs (22 nm ± 9 nm) as a reference by adjusting the molybdenum precursor concentration in the reaction. We find that in colloidal 2D MoS2 syntheses initially a mixture of the stable semiconducting and the metastable metallic crystal phase is formed. 2D MoS2 NPLs and NSs then both undergo a full transformation to the semiconducting crystal phase by the end of the reaction, which we quantify by X-ray photoelectron spectroscopy. Phase pure semiconducting MoS2 NPLs with a lateral size approaching the MoS2 exciton Bohr radius exhibit strong additional lateral confinement, leading to a drastically shortened decay of the A and B exciton which is characterized by ultrafast transient absorption spectroscopy. Our findings represent an important step for utilizing colloidal TMDCs, for example small MoS2 NPLs represent an excellent starting point for the growth of heterostructures for future colloidal photonics.
Two-dimensional (2D) materials and their heterostructures are useful in electronic applications, especially with the drive towards more and more miniaturization. Using first-principles calculations, we study the structural and electronic properties of some transition metal dichalcogenides and diselenides (MoS 2 , MoSe 2 , WS 2 , WSe 2 ). Our studies were based on density functional theory (DFT) as implemented in the Quantum ESPRESSO package. 2D layered materials present a huge challenge for DFT as a result of interlayer van der Waals (vdW) interaction which is absent from the typical DFT exchange-correlation functional. In order to account for the van der Waals interactions between layers, we applied the semi-empirical DFT-D2 method of Grimme and the revised Vydrov-Van Voorhis non-local correlation functional (rVV10). We show that the two approaches give similar structural properties. We also found that the size of the electronic band gap of these structures changes with respect to the number of layers stacked.
Employing the random phase approximation we investigate the binding energy and Van der Waals (vdW) interlayer spacing between the two layers of bilayer transition metal dichalcogenides MoS2, MoSe2, WS2, and WSe2 for five different stacking patterns, and examine the stacking-induced modifications on the electronic and optical/excitonic properties within the GW approximation with a priori inclusion of spin-orbit coupling and by solving the two-particle Bethe-Salpeter equation. Our results show that for all cases, the most stable stacking order is the high symmetry AA' type, distinctive of the bulklike 2H symmetry, followed by the AB stacking fault, typical of the 3R polytypism, which is by only 5 meV/formula unit less stable. The conduction band minimum is always located in the midpoint between K and Γ, regardless of the stacking and chemical composition. All MX2 undergo an direct-to-indirect optical gap transition going from the monolayer to the bilayer regime. The stacking and the characteristic vdW interlayer distance mainly influence the valence band splitting at K and its relative energy with respect to Γ, as well as, the electron-hole binding energy and the values of the optical excitations.
The present work reports on the synthesis of indium intercalation compounds InxWS2 (0 ⩽ x ⩽ 1). The material has been characterized by X-ray studies for structure determination and particle size distribution, room temperature magnetic susceptibility, thermoelectric power experiments and conductivity measurements in the temperature range 150–300 K. These results have indicated that, like the host material WS2, the intercalated compounds also possess hexagonal symmetry and are diamagnetic p-type semiconductors. The activation energy for these compounds was determined from the conductivity data.
The present work reports a detailed investigation on crytal structure, electrical properties, and thermal stability for indium intercalation compounds of molybdenum disulphide. InxMoS2 (0⩽x⩽1). X-ray analyses show that intercalated compounds, like the host material 2HMoS2, also possess hexagonal symmetry with a small but continuous increase in interlayer spacing; there also exists a particle size anisotropy. Room temperature thermoelectric power experiments and low temperature (150 – 300 K) conductivity measurements indicate that intercalated compounds also exhibit n-type semiconducting behaviour similar to that of the base material MoS2. Thermal stability behaviour of these compounds in air and argon atmosphere has also been studied.
Polycrystalline molybdenum disulphide has been grown by high pressure (about 54.88 × 106 N m−2) reduction of molybdenum trisulphide and characterized by various physicochemical methods. The chemical analysis of the compound established a sulphur to molybdenum ratio of 2, which was also confirmed by thermogravimetric analysis in air. The X-ray data was found to be consistent with 2H-MoS2, n-type conductivity (S = −275 μV °C−1) and diamagnetic behaviour ( c.g.s. e.m.u.). It is a semiconducting material with a room temperature conductivity of of and an activation energy of 0.124 eV in the temperature range 150–300 K. A band gap of 0.95 ± 0.02 eV was found from optical absorption studies on a thin MoS2 film. Thermal studies of MoS2 in an argon atmosphere has shown its stability up to 1200 °C and thereafter it decomposes to Mo2S3. A model has been proposed which describes the thermal behaviour of MoS2 when heated at various temperatures up to 1200 °C and is based on the appearance of lines in X-ray powder diffractogram of the product resulting from the crystallization of MoS2. Scanning electron microscope studies have also been made.
The present work deals with an investigation on synthesis, structure and properties of indium intercalation compounds of tungsten diselenide ; InxWSe2 (0⩽x⩽1). X-ray analysis shows that these intercalated compounds like the host 2HWSe2 also possess hexagonal symmetry with a small but continuous increase in c-parameter. However, a new phase appeared in and InWSe2 diffractograms due to In2Se3. Room temperature magnetic susceptibility, thermoelectric power experiments and two-probe conductivity measurements in the temperature range 25 −225°C indicated that intercalated compounds also exhibit n-type semiconducting behaviour similar to the host WSe2 and results are explained on the basis of existing band model. Thermal stability behaviour of these compound in atmosphere has also been studied and based on X-ray data of oxidized product formation of tungsten bronzes has been proposed.
Single crystals of InxWSe2 (x=0, 0.33, 0.50) have been grown by direct vapour transport technique. These crystals are characterised by X-ray diffraction by determining their lattice parameters and particle size. The net effect of indium intercalation in WSe2 single crystals has been studied by measuring their electrical conductivity, Hall effect parameters, and thermoelectric power and the results are discussed in detail.
Tungsten dichalcogenides constitute a well defined family of compounds which crystallize in a layer type structure. These compounds find a wide range of applications in the field of catalysis and as a lubricant at high temperatures and pressures. They have also been investigated successfully as cathode and anode materials in photoelectrochemical cells for solar energy conversion. The layered tungsten dichalcogenides also exhibit superconducting behaviour when intercalated with alkali or alkaline earth metals and different divalent rare earth metals. In the present paper an attempt has been made to review the preparation, crystal structure and band models of tungsten dichalcogenides. Furthermore, we have tried to incorporate the physical, chemical, optical and electrical properties along with intercalation, thermal stability and uses of these compounds.
A detailed discussion on crystal structure of indium intercalated compounds of molybdenum disulphide, InxMoS2 (0⩽x⩽1) based on x-ray studies is reported. It shows that intercalated compounds, like the host 2HMoS2 also possess hexagonal symmetry with a small but continuous increase in c-parameter, unlike their alkali and alkaline earth metals analogs. This has been explained on the basis of the fact that there may be no increase in c-parameter at all in a given intercalation process and that this does not have purely geometric origin but also comes from electronic effects. Results of SEM study are also reported.
The inclusion concept in crystal chemistry arises because there exist a large number of crystal classes in which one can clearly identify a host structure that contains guest atoms, ions, or molecules. In these, geometric and topological effects are of very great importance, and the concept of inclusion is useful not only in determining whether a compound will form but also in predicting properties. The host is a crystal that can provide a tunnel, planar, or cagelike accommodation for a guest species, depending on whether these are found in one-, two-, or three-dimensional arrays. The restricted dimensionality of some of these systems often substantially affects their properties. The presence of the guest, typically over a variable concentration range, has little effect on the structure and lattice constants of the host in at least two dimensions. In layered compounds the third dimension increases to accommodate the guest, which is termed the “intercalate.” In all cases important aspects of the identity of both host and guest are preserved. The strength of the interaction between host and guest varies greatly. In the noble gas clathrates it is weak. At the other extreme it will be so great that the whole concept of guest and host loses intuitive value. Thus, there is no profit in considering TiS in the NiAs structure to be TiS2 in the CdI2 structure with Ti intercalated. There is obviously a high degree of arbitrariness as to what to include in this chapter.
The transition metal dichalcogenides of groups IVB, VB, and VIB exhibit considerable diversity in their physical properties, spanning the fields of metals, semiconductors, insulators, and superconductors [1]. An important feature of these materials is that they crystallize in a quasi two-dimensional type of layered structure which imparts substantial anisotrophy to many of their properties. In addition, the layered structure facilitates the process of intercalation, or insertion of foreign atoms and molecules into these process of intercalation, or insertion of foreign atoms and molecules into these materials, thus allowing a convenient method for altering the structure and electronic behavior.
The transition metal dichalcogenides are about 60 in number. Two-thirds of these assume layer structures. Crystals of such materials can be cleaved down to less than 1000 Å and are then transparent in the region of direct band-to-band transitions. The transmission spectra of the family have been correlated group by group with the wide range of electrical and structural data available to yield useful working band models that are in accord with a molecular orbital approach. Several special topics have arisen; these include exciton screening, d-band formation, and the metal/insulator transition; also magnetism and superconductivity in such compounds. High pressure work seems to offer the possibility for testing the recent theory of excitonic insulators.
Holes, photogenerated in d-energy bands of covalent semiconducting layer-type group VI-transition metal dichalcogenides react electrochemically differently from holes generated in semiconductors with valence bands based on p-orbitals (e. g. , CdS, ZnO, CdSe, GaAs). The chemical character of these holes as missing d-electrons, on the other hand, gives rise to very specific electrochemical surface reactions with electron donors such as I** minus , Br** minus , and even OH** minus , for example.
Layered intercalation compounds InxMCh2 (x = 0.67, 1.0) crystallize in an interesting 1T polymorph of the hexagonal structure in which the indium atoms adopt either a linear or a trigonal prismatic coordination with the chalcogens and the M atoms adopt a trigonal prismatic coordination. We measured the electrical resistivities and the Seebeck coefficients of systems of this type in the range 77–300 K. All the compounds were n type except InTaS2 which exhibited p-type metallic conductivity. No phase transitions were noted. The results are discussed in terms of charge transfer from the indium to the MCh2 layers.
Poly crystalline molybdenum disulphide was prepared by high-pressure (56 kg/cm2) reduction of molybdenum trisulphide at 200°C. The stoichiometry was tested by chemical analysis and the crystallinity by X-ray diffraction studies. The room-temperature ac conductivity measurement showed a value of 1 × 10−4Ω−1 cm−1. The material was diamagnetic with χ⊥ = 0.05 × 10−6 emu. A band gap of 1.18 eV was obtained and n-type conductivity found. SEM studies showed 10–20 μm grain size. Temperature effect on the grain size was also studied.
The MxZrS2 systems with M = Fe, Co, Ni have been investigated: nonstoichiometric phases are observed with M in the tetrahedral sites between ZrS2 layers. Electric measurements characterize a semiconducting behaviour and suggest the occurrence of trigonal zirconium + III clusters. Magnetic measurements seem to confirm also M-M bond formation.
We report the preparation of intercalation compounds of 2H☒TaS2 with post transition period elements. In general we find that elements to the left of the metalloid line in the periodic table will intercalate TaS2. Crystallographic lattice parameters, the maximum amount intercalated per Ta, magnetic susceptibility, and superconducting transition temperatures are also given.
Sulphide Catalysts, Their Properties and Applications”
- S O Weisser
- Landa
Treatise on Solid State Chemistry
- T F R H Gamble
- Gamball
Intercalated Layered Materials
- G V Subba
- M W Rao
- Schafer