Proceedings of nanoGe Fall Meeting 2018 (NFM18)
DOI: https://doi.org/10.29363/nanoge.nfm.2018.133
Publication date: 6th July 2018
In recent years, monolayers of transition metal dichalcogenides have attracted a great deal of research interest. These two-dimensional (2D) materials typically have direct bandgaps in the visible or near-infrared, making them attractive for both classical and quantum optoelectronic applications [1]. Many different techniques have been developed to isolate monolayers from bulk; among them liquid assisted exfoliation is preferred by many, as it is simple, scalable, convenient and cost-effective [2]. However, the flakes produced using this class of technique are often not suitable for many applications, having poor uniformity and optical properties due to unintentional doping and other impurities.
In this work we employ ultrasonic bath sonication of bulk MoS2, starting with powders of grain sizes ranging from 6 to 40 µm, in an isopropanol/water mixture (70/30 vol %), following the procedure according to [3]. This produces suspensions of few-layer MoS2 flakes. Photoluminescence (PL) measurements from drop-cast samples on silicon substrates are found to have full widths at half maxima of 200 meV, indicating an average thickness of 2-3 layers. This agrees with independent atomic force microscopy measurements [4]. However, PL intensities are found to be weak – a typical result for flakes produced with this technique.
Super acid treatment of dry mechanically-exfoliated monolayers of MoS2 has been shown to vastly improve internal quantum efficiency, and with it, PL intensity [5] But it impractical to implement in a manufacturing process. In this work we will detail a new all-wet superacid treatment process for MoS2 flakes. We show that it enhances PL emission intensity by over 200 times. It thus represents a promising technique for the practical application of 2D inks for optoelectronics.
Reference:
1. Ryou et al. Scientific Reports 6, 29184 (2016)
2. Huo et al. Science Bulletin 60, 1994 (2015)
3. Bernal et al. 2D Materials, 3, 035014 (2016)
4. Bissett et al. ACS Omega, 2, 738 (2017)
5. Amani et al. Science, 350, 1065 (2015).
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