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Md Mohiuddin1 Nitu Syed1 Torben Daeneke1 Kourosh Kalantar-zadeh1

1, RMIT University, Melbourne, Victoria, Australia

The recent demonstration of piezoelectric phenomena in non-centrosymmetric molybdenum disulfide (MoS2) provides new opportunities for fast and efficient exfoliation processes [1, 2]. Here we demonstrate the exfoliation of MoS2 bulk crystals by utilizing the concomitant electric field and mechanical shear force produced in a microcentrifugation surface acoustic wave (SAW) device. We show that excellent exfoliation yields, containing around 60% monolayer MoS2, can be attained in only 25 minutes of SAW facilitated exfoliation. The short processing time and high monolayer yield are clear advantages of our method. We report that the SAW induced electric field is crucial for enhancing both the exfoliation yield and the fraction of monolayers. Our findings are supported by both experimental data and computational studies. The developed method provides many future opportunities since it is predicted to apply to all layered, non-centrosymmetric transition metal oxides and chalcogenides [3, 4]. Furthermore the method constitutes a direct pathway towards the integration of nanosheet exfoliation processes into complex microfluidic systems.

[1] Wenzhuo Wu, Lei Wang, Yilei Li, Fan Zhang, Long Lin, Simiao Niu, Daniel Chenet, Xian Zhang, Yufeng Hao, Tony F. Heinz, James Hone, and Zhong Lin Wang, Piezoelectricity of single-atomic-layer MoS2 for energy conversion and piezotronics. Nature, 514, 470-474 (2014).
[2] Hanyu Zhu, Yuan Wang, Jun Xiao, Ming Liu, Shaomin Xiong, Zi Jing Wong, Ziliang Ye, Yu Ye, Xiaobo Yin, and Xiang Zhang, Observation of piezoelectricity in free-standing monolayer MoS2. Nature Nanotechnology, 10, 151–155 (2015).
[3] Karel-Alexander N. Duerloo, Mitchell T. Ong, and Evan J. Reed, Intrinsic piezoelectricity in two-dimensional materials. Journal of Physical Chemistry Letters, 3, 2871-2876 (2012).
[4] Michael N. Blonsky, Houlong L. Zhuang, Arunima K. Singh, and Richard G. Hennig, Ab initio prediction of piezoelectricity in two-dimensional materials. ACS Nano, 9, 9885-9891 (2015).

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