Wafer Scale Synthesis and High Resolution Structural Characterization of Atomically Thin MoS₂ Layers

Abstract

Synthesis of atomically thin MoS2 layers and its derivatives with large‐area uniformity is an essential step to exploit the advanced properties of MoS2 for their possible applications in electronic and optoelectronic devices. In this work, a facile method is reported for the continuous synthesis of atomically thin MoS2 layers at wafer scale through thermolysis of a spin coated‐ammonium tetrathiomolybdate film. The thickness and surface morphology of the sheets are characterized by atomic force microscopy. The optical properties are studied by UV–Visible absorption, Raman and photoluminescence spectroscopies. The compositional analysis of the layers is done by X‐ray photo­emission spectroscopy. The atomic structure and morphology of the grains in the polycrystalline MoS2 atomic layers are examined by high‐angle annular dark‐field scanning transmission electron microscopy. The electron mobilities of the sheets are evaluated using back‐gate field‐effect transistor configuration. The results indicate that this facile method is a promising approach to synthesize MoS2 thin films at the wafer scale and can also be applied to synthesis of WS2 and hybrid MoS2‐WS2 thin layers.

Effect of hydrogen on the growth of MoS2 thin layers by thermal decomposition method

“…However, it is difficult to obtain continuous and uniform monolayer or bilayer MoS 2 film. The similar phenomena were also observed for reported MoS 2 film synthesized by thermolysis method [17,18]. It may be due to the M A N U S C R I P T…”

“…Figure 4a shows the XPS spectra of respectively; the peaks at 232.7 eV and 235.9 eV are attributed to Mo 6+ 3d 5/2 and Mo 6+ 3d 3/2 of MoO 3 respectively [17,24]. It is noted that there is a peak at the binding energy of 226.6 eV for all samples, which corresponds to S 2s [18]. The XPS studies reveal that the formation of MoO 3 accompanies with that of MoS 2 when H 2 flux is 0-70 sccm.…”

“…Recently, Liu et al [17] and George et al [18] have synthesized large-area MoS 2 thin layers, respectively, by thermolysis of ammonium tetrathiomolybdate ((NH 4 ) 2 MoS 4 ) precursor films. The synthetic approach for high-quality and uniform few-layer MoS 2 is facile, scalable and promising for future production of MoS 2 thin layers.…”

“…It is noted that for the thermolysis transformation process of (NH 4 ) 2 MoS 4 to MoS 2 [17][18][19][20], hydrogen (H 2 ) gas is introduced; however, the effect of H 2 gas on the growth process of MoS 2 thin layers is not clear. Brito et al suggest that H 2 can promote the thermal decomposition of (NH 4 ) 2 MoS 4 [20], whereas Liu et al think that H 2 may be devoted to avoid the Mo oxidation in the process [17].…”

Ohmic Contacts to 2D Semiconductors through van der Waals Bonding

“…3,4 MX 2 layers can be obtained via micromechanical cleaving, 5 by chemical vapor deposition (CVD), 6,7 or even by spin coating precursor molecules. 8 Important for applications in devices is the ability to have both electron (n-type) and hole (p-type) transport in these 2D materials. Charge carrier transport in MX 2 field-effect transistors (FETs) is usually dominated by electrons; p-type transport has only been demonstrated in WSe 2 .…”