Abstract
Recently, two-dimensional monolayer molybdenum disulfide (MoS2), a transition metal dichalcogenide, has received considerable attention due to its direct bandgap, which does not exist in its bulk form, enabling applications in optoelectronics and also thanks to its enhanced catalytic activity which allows it to be used for energy harvesting. However, growth of controllable and high-quality monolayers is still a matter of research and the parameters determining growth mechanism are not completely clear. In this work, chemical vapor deposition is utilized to grow monolayer MoS2 flakes while deposition duration and temperature effect have been systematically varied to develop a better understanding of the MoS2 film formation and the influence of these parameters on the quality of the monolayer flakes. Different from previous studies, SEM results show that single-layer MoS2 flakes do not necessarily grow flat on the surface, but rather they can stay erect and inclined at different angles on the surface, indicating possible gas-phase reactions allowing for monolayer film formation. We have also revealed that process duration influences the amount of MoO3/MoO2 within the film network. The homogeneity and the number of layers depend on the change in the desorption–adsorption of radicals together with sulfurization rates, and, inasmuch, a careful optimization of parameters is crucial. Therefore, distinct from the general trend of MoS2 monolayer formation, our films are rough and heterogeneous with monolayer MoS2 nanowalls. Despite this roughness and the heterogeneity, we observe a strong photoluminescence located around 675 nm.
Highlights
As the dimensions of materials are reduced from three dimensions (3D), the fundamental physical properties change remarkably, allowing for novel applications, which are otherwise not possible [1, 2]
It is possible to form different few-layer transition metal dichalcogenides (TMDC) through colloidal synthesis techniques, which are beneficial in terms of high-yield and substratefree nanostructures [26]
chemical vapor deposition (CVD)-based synthesis was first reported in 2012 [21, 22], showing the potential of the method to realize high-quality, controlled growth of the MoS2 flakes, and other researches have revealed that monolayer flakes deposited by CVD can be used in different applications and devices such as phototransistors [30], photodetectors [31], memories [16], and so on
Summary
As the dimensions of materials are reduced from three dimensions (3D), the fundamental physical properties change remarkably, allowing for novel applications, which are otherwise not possible [1, 2]. CVD-based synthesis was first reported in 2012 [21, 22], showing the potential of the method to realize high-quality, controlled growth of the MoS2 flakes, and other researches have revealed that monolayer flakes deposited by CVD can be used in different applications and devices such as phototransistors [30], photodetectors [31], memories [16], and so on. We can shift from a rough surface with MoS2 flakes scattered at different angles to a smoother and more uniform surface composed of monolayer MoS2 formations Such single-wall MoS2 flakes, which for the most part are not flat on the surface, can be beneficial in applications including solar cells [35], energy storage [36], catalysis [11], and sensing [37] where large surface area of the flakes can increase the intended performance
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