Phonon‐Mediated Microfluidic Synthesis, Processing and Manipulation of Two‐Dimensional and Bulk Crystals
In this talk, we reveal a new direction in microfluidics we are currently exploring for the synthesis and assembly of novel materials. In particular, we demonstrate the intriguing possibility of harnessing phonon sources, more specifically high frequency (>10 MHz) surface acoustic waves (SAWs), for synthesizing and manipulating two-dimensional and bulk crystals. For example, the large surface acceleration associated with the SAW vibration—on the order of 10 million g’s—can be employed for micro/nanoscale material processing, in particular, for debundling carbon nanotube agglomerates. These large mechanical stresses, together with the high intensity electric field inherent in the electromechanical coupling of the acoustic wave during SAW microcentrifugation and nebulisation, can also be used for the rapid synthesis of organic and inorganic crystals, as well as those of metal–organic frameworks (MOFs). In the former, we obtained novel crystal morphologies—for example, of NaCl and glycine—that have yet to be reported to date, whereas in the case of the MOFs, simultaneously-activated freestanding crystals that are highly oriented akin to surface anchored MOFs (SURMOFs) but without the need for layer-by-layer deposition or self-assembled monolayers. Moreover, the same SAW microcentrifugation and nebulisation processes can be deployed to rapidly exfoliate bulk three-dimensional crystalline transitional metal dichalcogenides such as molybdenum disulphide (MoS2) and tungsten disulphide (WS2) into monolayer and few-layer nanosheets or quantum dots with high yield. Finally, the SAW can be exploited for the manipulation of quasiparticles in these two-dimensional materials. For example, we show the possibility for reversibly modulating trion to exciton transition, and their subsequent transport and hence spatial separation within the material.
Leslie Yeo is a Distinguished Professor at RMIT University, Australia. Following his PhD from Imperial College London in 2002, for which he was awarded the Dudley Newitt prize, he undertook a postdoctoral stint at the University of Notre Dame USA, after which he held a faculty position at Monash University. He also held the Australian Research Council’s Australian Research Fellowship and Future Fellowship from 2009 to 2017. Dr Yeo was the recipient of the Young Tall Poppy Science Award ‘in recognition of the achievements of outstanding young researchers in the sciences including physical, biomedical, applied sciences, engineering and technology’, and the Dean’s and Vice-Chancellor’s awards for excellence in early career research. He is co-author of the book Electrokinetically Driven Microfluidics & Nanofluidics, author of over 200 publications and 20 patent applications, Editor of Biomicrofluidics and an editorial board member of Interfacial Phenomena & Heat Transfer and Scientific Reports.