Hypothesis: A scalable method for the production of low-dimensional semiconductor materials, such as tungsten diselenide (WSe2), is crucial for applications in flexible and transparent optoelectronic devices. Liquid exfoliation technique can be employed to fabricate a colloidal suspension of WSe2 nanosheets as a low-temperature and solution-processable route.
Experiments: The production of atomically thin WSe2 by liquid exfoliation is investigated, focusing the maximization of the concentration in the resulting suspension by selecting the most suitable solvent for this process. Three different strategies are compared: exfoliation in pure solvents, mixed solvent and aqueous solutions with surfactant.
Findings: N-methylpyrrolidone, previously reported as suitable solvent for suspension of other layered materials, results in the highest concentration among the pure solvents tested in this work; however a simple mixture of 30% of propan-2-ol in water surpasses its performance offering a low cost alternative. An optimal surface tension of 28 mN m(-1) is proposed and the influence of the molecular size of the solvent is also considered. The use of anionic surfactant in water makes feasible the exfoliation of WSe2 in aqueous solutions. The analysis of different exfoliation approaches under same processing conditions permits adequate comparison between different solvent systems and reveal optimal parameters for high yield liquid exfoliation of WSe2.
Keywords: Layered materials; Liquid exfoliation; Semiconductors; Surface properties; WSe(2).
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