Graphene and tungsten disulfide nanosheets prepared using liquid phase exfoliation

Content Provider	Semantic Scholar
Author	Bagsican, Filchito Renee G.
Copyright Year	2014
Abstract	F.R. Bagsican, M. Ohshiro, K. Takayama, I. Kawayama, H. Murakami, A. Winchester, S. Kittu, S. Talapatra, M. Tonouchi Osaka University, SIU – Carbondale E-mail: bagsican-f@ile.osaka-u.ac.jp Atomically thin materials such as graphene and tungsten disulfide (WS2) have many possible applications like in flexible electronics and solar cell technologies. But production by micromechanical cleavage or physical vapor deposition is impractical for industrial applications because of low yield. This can be overcome by using methods that exploit the fact that graphene (graphite) and WS2 have structures with strong intraplanar forces but relatively weak interplanar interactions. In this study, we used liquid phase exfoliation to produce large quantities of graphene and WS2 nanosheets from bulk powder samples. The starting powder materials were annealed in argon atmosphere to remove any impurities present. Suspensions in isopropyl alcohol (IPA) of each of the powder materials were prepared and exfoliation was done using a sonic dismembrator at ~30W for 4 hours. The suspensions were centrifuged at 1500 rpm for 45 min to sediment any non-exfoliated particles. Supernatants were collected and subsequently used for drop casting on substrates with temperatures raised to ~80oC to evaporate IPA. For sample characterization, AFM and Raman mapping (using 532nm excitation laser) measurements were taken. AFM measurements of the films show features with sizes in the nanometer range (for graphene RMS roughness is ~70nm and height measurements are 50nm-300nm; for WS2 RMS roughness is ~14nm and height measurements are 3nm-20nm). Fig.1 are the Raman measurements at different spots in the films as indicated in the optical images (inset photos). Fig. 1A shows the characteristic peaks for graphene at ~1580 cm (G band), ~2700 cm (G' band), and the defect-induced D band at ~1350 cm. In Fig. 1B, the prominent peaks of WS2 are blue-shifted with respect to the observed peaks for bulk sample (E2g at 347 cm and A1g at 410 cm ) which might be stress-induced (because of substrate) or due to phonon confinement caused by the reduced crystal dimensions. THz-TDS data and estimated optical conductivities of samples will be also discussed.
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Resource Type	Article