Abstract
Two-dimensional (2D) molybdenum disulfide (MoS2) films with a tunable bandgap hold great promise for next-generation electronic and optoelectronic devices. Synthesis of large areas of high-quality MoS2 monolayers lacks experimental reproducibility. Moreover, the outcome of MoS2 growth by chemical vapor deposition is dependent on several interconnected growth parameters. In this study, we present results of MoS2 monolayer growth by strategically placing water droplets on the growth substrate and/or in the source prior to its loading in the growth chamber. The volume and distribution of water on the growth substrate and in the source had a direct impact on the morphology of the as-grown MoS2. Characterized by scanning electron microscopy (SEM), Raman microscopy, and atomic force microscopy (AFM), the number and size of MoS2 layers as well as its distribution on the growth substrate were found to have a strong dependence on the positioning of the water droplet. This study on MoS2 monolayer growth using water droplets as a promoter provides a simple and reproducible experimental technique enabling growth with high reliability.
Highlights
Since the celebrated discovery of graphene, intense research efforts have been directed towards developing twodimensional (2D) materials for electronic device applications [1, 2]
Based on the schematics and optical microscopy findings of the experiments that were described in Figure 2 and Table 1, the effect of the strategically placed water droplets was explained through a sequence of chemical reactions, Intensity (a.u.) Intensity (a.u.)
We present our results on the investigation into the role of strategically placed water droplets on the growth kinematics of MoS2 monolayers
Summary
Since the celebrated discovery of graphene, intense research efforts have been directed towards developing twodimensional (2D) materials for electronic device applications [1, 2]. Field-effect transistors made with 2D TMDs are expected to exhibit high performance with reduced feature sizes In this respect, monolayers of molybdenum disulfide (MoS2) are an attractive option for device applications since they have a direct bandgap of 1.8 eV and vertical thickness of 0.8 nm [5,6,7]. A series of well-controlled water-assisted experiments on growth showed that it was possible to control the areal coverage and numbers of layers of MoS2 films To explain these experimental results, this work presents a possible mechanism for monolayer growth based on chemical reactions between the various constituents involved in the growth process. The significance of this work is twofold. (i) It highlights the fact that though initially there was a very limited volume of water in the growth chamber, the reversible chemical reaction between H2O and MoO3 ensures that water vapor is continuously present near the growth substrates and protects source from poisoning. (ii) Monolayer MoS2 growth is critically dependent on a well-controlled balance between the partial pressure of MoO2(OH), MoO3, H2O, MoO2, and S
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