Detall

Conferenciant: Prof. Leslie Yeo (RMIT University, Melbourne).

Resum: We demonstrate the intriguing possibility of harnessing phonon sources, in particular, high frequency (10 MHz order) surface and hybrid acoustic waves, for synthesizing and manipulating two-dimensional and bulk crystals. In particular, we show that the large mechanical stresses that arise from the extraordinary surface acceleration of the acoustic wave—on the order of 10 million g’s, together with the intense electric field inherent in its electromechanical coupling, are capable of facilitating rapid synthesis of organic and inorganic crystals, as well as those of metal–organic frameworks (MOFs), often yielding novel crystal morphologies and structures. Moreover, the same process can be deployed to rapidly exfoliate bulk three-dimensional crystalline transitional metal dichalcogenides (TMDs; e.g., MoS2) and carbides/nitrides (MXenes) into monolayer and few-layer nanosheets and quantum dots with high yield. Finally, the acoustic wave 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. In the case of the TMDs, we show with convincing evidence, that such novel phenomena can be attributed to their unique piezoelectric property, particularly when they exist in odd number of layers due to their broken crystallographic centrosymmetry.