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Group III monochalcogenides such as GaSe and GaS have attracted considerable interest as two-dimensional (2D) alternatives to the traditional transition metal dichalcogenides. The production of large-area films as well as the long-term ambient stability remains a challenge for scalable integration of these materials into the next generation of 2D circuitry and optoelectronic devices. In this report, a simple atmospheric-pressure chemical vapor deposition method is proposed to synthesize continuous monolayers of GaSe and GaS. The proposed method utilizes commercially available precursors and does not requires vacuum-sealed ampules or exfoliation. The optimal parameters for continuous monolayer self-limited growth were determined by systematically changing the growth time, the gas flow rate, and the amount of precursors. So far, the study of bare monolayer GaSe by Raman spectroscopy has been difficult due to the very low Raman signal and a rapid laser-induced oxidation of the material. A laser-scanning method that minimizes the cumulative laser damage and allows a reasonable signal-to-noise ratio was utilized to study the time-dependent ambient stability of bare and encapsulated monolayer samples by Raman spectroscopy. Our results reveal that bare GaSe monolayers can stand up to 6 h in air before complete degradation, and encapsulation with transparent polymeric films can delay this process for few days. These results open the door to produce large-area films of monolayer group III monochalcogenides and to consider film encapsulation with different transparent polymers that could further extend the long-term durability of these ambient sensitive 2D materials.
Afaneh et al. (Fri,) studied this question.