Two-dimensional inorganic materials are emerging as a premiere class of materials for fabricating modern electronic devices. The interest in 2D layered transition metal dichalcogenides is especially high. Particularly, 2D MoS 2 is being heavily researched due to its novel functionalities and its suitability for a wide range of electronic and optoelectronic applications. In this article, the progress in mono/few layer(s) MoS 2 research is reviewed by focusing primarily on the layer dependent evolution of crystal, phonon, and electronic structure. The review includes extensive detail into the methodologies adapted for single or few layer(s) MoS 2 growth. Further, the review covers the versatility of 2D MoS 2 for a broad range of device applications. Recent advancements in the fi eld of van der Waals heterostructures are also highlighted at the end of the review. Unlike zero-band gap graphene (semimetal), [ 8 ] and large band gap hBN (insulator), [ 9 ] the 2D transition metal dichalcogenides (sulfi des and selenides) have band gaps comparable to conventional Si or GaAs, and thus present a tantalizing prospect of scaling all semiconductor science and technology down to a truly atomic scale. Although these transition metal dichalcogenides (TMDCs) are quite well known for the past few decades for their applications in solid state lubricants, [ 10 ] photovoltaic devices, [ 11,12 ] and rechargeable batteries, [ 13 ] the recent methodologies and concepts evolved from graphene research like exfoliation, transfer, and manipulation of 2D materials have driven interest toward the exploration of layered TMDCs. TMDCs possess hexagonal layers of transition metal atoms (M) sandwiched between two layers of chalcogen atoms (X) with an MX 2 stoichiometry. Depending on the different combinations of chalcogen (typically S, Se, or Te) and transition metal (mainly Mo and W) elements, several different kinds of TMDCs are possible. Among the various combinations of TMDCs, MoS 2 is the most promising 2D material as its elemental constituents are abundant, nontoxic, and amenable for easy mono/few layer(s) synthesis when compared to their analogous selenides and tellurides. DOIDespite graphene's exceptionally high carrier mobility, [ 14 ] fi eld-effect transistors (FETs) made from graphene cannot effectively function as electronic switches due to the absence of an electronic band gap. [ 15,16 ] 2D MoS 2 possesses a relatively high mobility up to 200 cm 2 (V-s) −1 with a high on/off current ratio of ≈10 8 at room temperature, [17][18][19][20] and has a layer dependent band gap with a crossover from indirect (1.2 eV) to direct (1.9 eV) at the bulk to monolayer transition, making this a promising material for effi cient electronic, [ 17,21 ] and optoelectronic devices. [22][23][24] The unique electronic band structure and optical properties of monolayer MoS 2 are suitable for a wide range of novel functional devices and hence has triggered exhaustive research on this nongraphene material during the last few years. [ 2,7,[25][26][27][28][29][30]...

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Thin films of ZnS with thicknesses ranging from 100 to 600 nm have been deposited on glass substrates by close spaced thermal evaporation. All the films were grown at the same deposition conditions except the deposition time. The effect of thickness on the physical properties of ZnS films has been studied. The experimental results indicated that the thickness affects the structure, lattice strain, surface morphology and optoelectronic properties of ZnS films significantly. The films deposited at a thickness of 100 nm showed hexagonal structure whereas films of thickness 300 nm or more showed cubic structure. However, coexistence of both cubic and hexagonal structures was observed in the films of 200 nm thickness. The surface roughness of the films showed an increasing trend at higher thicknesses of the films. A blue-shift in the energy band gap along with an intense UV emission band was observed with the decrease of film thickness, which are ascribed to the quantum confinement effect. The behaviour of optical constants such as refractive index and extinction coefficient were analysed. The variation of refractive index and extinction coefficient with thickness was explained on the basis of the contribution from the packing density of the layers. The electrical resistivity as well as the activation energy were evaluated and found to decrease with the increase of film thickness. The thickness had a significant influence on the optical band gap as well as the luminescence intensity.

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