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]...

2D materials are considered promising candidates for developing next‐generation high‐performance energy efficient electronic, optoelectronic, and valley‐tronic devices. Though metal oxides are widely used in the fabrication of many advanced devices, very little work has been reported on their properties in 2D limit. This article reports the discovery of a new 2D materials system, 2D tin monoxide (SnO). Layer by layer growth of SnO on sapphire and SiO2 substrates is demonstrated using a pulsed laser deposition method. The number of SnO layers is controlled by controlling the number of laser shots during the deposition process. Raman spectroscopic and X‐ray photoelectron spectroscopic analysis confirms the formation of phase pure SnO layers. Field effect transistors (FETs) using few layer SnO channels grown on SiO2 substrates are successfully fabricated. These FETs show typical p‐channel conduction with field effect mobility ranging from 0.05 to 1.9 cm2 V−1 s−1. Field effect mobility varies with the number of SnO layers and decreases on either sides of the optimum layer numbers (12), which is explained based on charge screening and interlayer coupling in layered materials.

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p-type Cu 2 O thin films doped with trivalent cation boron are demonstrated for the first time as an efficient hole-selective layer for c-Si heterojunction solar cells. Cu 2 O and Cu 2 O:B films were deposited by rf magnetron sputtering, and the optical and electrical properties of the doped and undoped films were investigated. Boron doping enhanced the carrier concentration and the electrical conductivity of the Cu 2 O film. The band alignment of the Cu 2 O:B/ Si heterojunction was investigated using XPS and UPS measurements. The Cu 2 O:B/Si interface has a valance band offset of 0.08 eV, which facilitates hole transport, and a conduction band offset of 1.35 eV, which blocks the electrons. A thin SiO x tunnel oxide interlayer was also explored as the passivation layer. The initial trials of incorporating this Cu 2 O:B layer as a hole transporting layer in a single heterojunction solar cell with the structure, ITO/Cu 2 O:B/n-Si/Ag, and a cell area of 1 cm 2 yielded an open-circuit voltage of 370 mV, a short-circuit current density of 36.5 mA/cm 2 , and an efficiency of 5.4%. This p-type material could find potential applications in various optoelectronic applications like organic solar cells, TFTs, and LEDs.