Atomically thin layers of MoS₂via a two step thermal evaporation–exfoliation method

Abstract

Two dimensional molybdenum disulfide (MoS(2)) has recently become of interest to semiconductor and optic industries. However, the current methods for its synthesis require harsh environments that are not compatible with standard fabrication processes. We report on a facile synthesis method of layered MoS(2) using a thermal evaporation technique, which requires modest conditions. In this process, a mixture of MoS(2) and molybdenum dioxide (MoO(2)) is produced by evaporating sulfur powder and molybdenum trioxide (MoO(3)) nano-particles simultaneously. Further annealing in a sulfur-rich environment transforms majority of the excess MoO(2) into layered MoS(2). The deposited MoS(2) is then mechanically exfoliated into minimum resolvable atomically thin layers, which are characterized using micro-Raman spectroscopy and atomic force microscopy. Furthermore Raman spectroscopy is employed to determine the effect of electrochemical lithium ion exposure on atomically thin layers of MoS(2).

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

“…25). At the Γ-point, the bandgap transition is indirect for the bulk material, but gradually shifts to be direct for the monolayer 24,[73][74][75][76][77] . The direct excitonic transitions at the K-point remain relatively unchanged with layer number 32 .…”

“…For example, intercalation with Li + ions causes an upshift in the MoS 2 Raman A 1g and E 1 2g peak positions and a decrease in peak intensities, probably owing to strain introduced by the Li + entering interstitial sites 74,160 . The photoluminescence of monolayer MoS 2 also suggests applications in biosensing, where stable fluorescent markers are of importance for imaging and fluorometric assays.…”

“…These methods use different solid precursors heated to high temperatures: sulphur powder and MoO 3 powder vaporized and co-deposited onto a nearby substrate 71,74 ; a thin layer of Mo metal deposited onto a wafer heated with solid sulphur 72 ; and substrates dip-coated in a solution of (NH 4 ) 2 MoS 4 and heated in the presence of sulphur gas 73 . These CVD-related methods are summarized in Fig.…”

Controlled synthesis of high-quality crystals of monolayer MoS2 for nanoelectronic device application

“…Synthesis of large-area MoS 2 films have been reported in the past few years [22][23][24][25][26][27]. However, the preparation of large-size monolayer MoS 2 single crystals remain to be improved in view of its superior electronic and optoelectronic characteristics [28][29][30][31]. Furthermore, as the size of MoS 2 single crystals increased to hundreds of micrometers, the device fabrication and modulation process would be simplified greatly.…”

Growth of Large-Area and Highly Crystalline MoS2 Thin Layers on Insulating Substrates

“…3,4 Meanwhile, when the dimension of MoS 2 is reduced from a bulk form to a 2-d monolayer sheet, its optical properties change due to the transformation of the band gap from indirect to direct one. [5][6][7][8][9][10][11] Significant efforts have been devoted to prepare MoS 2 thin layers, including scotch tape assisted micromechanical exfoliation, [3][4][5]12 intercalation assisted exfoliation, [13][14][15][16][17][18][19][20] solution exfoliation, 15,16,[21][22][23] physical vapor deposition, 25,26 hydrothermal synthesis, 27 electrochemical synthesis, 28 sulfurization of molybdenum oxides 29,30 and thermolysis of the precursor containing Mo and S atoms. 23 However, MoS 2 tends to form zero-dimensional closed structures (fullerene-like nanoparticles) or one-dimensional nanotube structures during the synthesis.…”