Investigation of Ball Milling Assisted Liquid-Phase Exfoliation of WS$_{\mathrm{2}}$ Crystals

With high surface area and exotic electronic properties, WS$_{\mathrm{2}}$ nanosheets are potentially useful for sensing, catalysis, and energy storage applications. The cost-effective and large-scale production of WS$_{\mathrm{2}}$ nanosheets is a fundamentally important step for its incorporation in future applications. The liquid phase exfoliation of WS$_{\mathrm{2}}$ nanosheets from its bulk counterpart using high-intensity ultrasound waves has proven to be a suitable method to produce a high yield of nanosheets. Here, we show that WS$_{\mathrm{2}}$ nanosheets' yield can be significantly increased if WS$_{\mathrm{2}}$ crystal is ball-milled prior to the ultrasonication in isopropyl alcohol. We find that the ball milling assisted sonication increases nanosheets' yield by 50{\%} compared to if the bulk crystal is solely ball milled or sonicated. The optical characterization shows the high quality of WS$_{\mathrm{2}}$ nanosheets with the yield as high as 6.4{\%}. We show that size selected nanosheets, prepared using repeated centrifugation and sedimentation method, are stable with no precipitation formation for more than two months.