Invited Paper HI+NS-ThM1
Tuning out-of-plane Piezoelectricity in 2D Materials using Ion Beams

Thursday, October 24, 2019, 8:00 am, Room B231-232

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have been extensively studied owing to their ultra-thin nature as well as superior material properties. In particular, after the experimental observation of intrinsic in-plane piezoelectricity in the 2D MoS₂, fundamental studies on the piezoelectricity as well as piezoelectric device applications of the 2D TMDs have attracted significant interest. However, their applications are strongly limited due to the fact that crystallographically only in-plane piezoelectricity exists in the 2D TMDs. In this presentation, I will summarize our recent effect on the realization of tunable out-of-plane piezoelectricity in the 2D TMDs using He ion beams. Among various 2D TMDs, we have chosen MoTe₂ because it is very sensitive to the external stimuli such as strain. We first examined the realization of the out-of-plane piezoelectriciy by local asymmtery breaking based on the surface corrugation to check its feasibility. Then, He ion irradiation as a function of dose were performed onto the MoTe₂ surface. It was found that the out-of-plane piezoelectricity was indeed induced by He ion beams and, further, the magnitude of the induced out-of-plane piezoelectricity was depedent on the dose level. The proposed strategy for modulation of tunable out-of-plane piezoelectricity can be easily applied to a broader class of 2D TMD materials that have not been used for applications with out-of-plane piezoelectricity. Accordingly, it can stimulate the expansion of practical energy device applications with 2D TMDs.