A novel technique to synthesize monolayers Of WS2: a low boiling point liquid exfoliation approach
Ravindra Kumar Jha, Raghubeer Singh, Debasree Burman, Sumita Santra, Prasanta
Volume 1, Issue 2, Page 125-130, Year 2016 | DOI: 10.5185/amp.2016/203
Keywords: Tungsten disulfide, sonication, TMDs, ball milling, exfoliation.
Abstract: We report herein exfoliation of WS 2 , which is one of the most promising but less investigated among 2D TMDs in binary mixture of diethyl ether (with boiling point=34.6°C) and water. The bulk WS 2 powder was first ball milled in toluene for few minutes and at low rpm. Subsequently the powder was kept at 4°C for 20 hours in binary mixture of diethyl ether and water with their volume fraction varying from 10% to 90%, before taking for the ultrasonication. It should be noted that neither diethyl ether nor water is capable of disperse WS 2 alone. Ultrasonic waves generate cavitation bubbles that collapse into high-energy jets, breaking up the layered crystallites and producing exfoliated nanoflakes. Hansen Solubility Parameters (HSP) for the binary mixture has been calculated and the mixture which minimizes the Hansen distance has been selected for further characterization of few layered nature of thin sheets. Field emission scanning electron microscopy (FESEM) has been utilized to monitor the progress in exfoliation at different stages. Atomic force microscopy (AFM) confirms the formation of <8nm thin sheets with lateral dimension of few hundred nm. Raman spectroscopy has been utilized for further confirmation. Transmission electron microscopy (TEM) has been utilized to show the crystallinity of nanosheets which agrees with the X-ray diffraction results. Ultra-violet-visible (UV-Vis) and Fourier transform infrared (FTIR) have been used as spectroscopy tools throughout the work. This exfoliation technique is unique in the sense of producing pristine nanosheets due to the involvement of very low boiling point solvents. Copyright © 2016 VBRI Press