Atomically Thin MoS₂: A Versatile Nongraphene 2D Material

Abstract

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]...

Atomic rearrangement of a sputtered MoS2 film from amorphous to a 2D layered structure by electron beam irradiation

“…The highest intensities of the E 1 2g and A 1g peaks for the 1 min EBI-treated sample indicated that the amount of Mo–S bonding may decrease with a longer irradiation time. The difference between the Raman shifts of the E 1 2g and A 1g peaks ( ∆k ) was ~25 cm −1 , which is typically shown for six atomic layers 5 or bulk MoS 2 29 .

Figure 1Raman spectra of as-deposited and EBI-treated MoS 2 films according to irradiation times of 1, 5, and 10 min.

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Photoluminescence Study of B‐Trions in MoS2 Monolayers with High Density of Defects

“…Among them, monolayers of transition metal dichalcogenides (TMDs), such as MoSe 2 , WSe 2 , and MoS 2 , are the most attractive having well‐defined semiconductor properties . MoS 2 is the most studied TMD atomic crystal, where an atomic plane of Mo atoms is found between two layers of S atoms in a trigonal prismatic structure forming a so‐called monolayer . In multilayer arrangements, monolayers are stacked together with weak van der Waals interactions between S atoms.…”

“…[3] MoS 2 is the most studied TMD atomic crystal, where an atomic plane of Mo atoms is found between two layers of S atoms in a trigonal prismatic structure forming a so-called monolayer. [4] In multilayer arrangements, monolayers are stacked together with weak van der Waals interactions between S atoms. While first MoS 2 monolayers were obtained by mechanical exfoliation, [1] other methods are proved to be more promising to produce large area and high quality 2D materials to enable their industrialization.…”

Near-infrared light triggered superior photocatalytic activity from MoS2–NaYF4:Yb3+/Er3+ nanocomposites

“…11 Recent studies have demonstrated that the geometry of photocatalyst has a significant effect on the photocatalytic activity. [16][17][18][19] MoS 2 with a narrow band gap of 1.8 eV has strong absorption in the visible region of solar spectrum; therefore it has been explored for photocatalytic applications. [13][14][15] 2D layered materials possess two main intrinsic advantages which can be utilized to enhance the photocatalytic efficiency.…”