The ferroelectricity in ultrathin HfO2 offers a viable alternative to ferroelectric memory. A reliable switching behavior is required for commercial applications; however, many intriguing features of this material have not been resolved. Herein, we report an increase in the remnant polarization after electric field cycling, known as the “wake-up” effect, in terms of the change in the polarization-switching dynamics of a Si-doped HfO2 thin film. Compared with a pristine specimen, the Si-doped HfO2 thin film exhibited a partial increase in polarization after a finite number of ferroelectric switching behaviors. The polarization-switching behavior was analyzed using the nucleation-limited switching model characterized by a Lorentzian distribution of logarithmic domain-switching times. The polarization switching was simulated using the Monte Carlo method with respect to the effect of defects. Comparing the experimental results with the simulations revealed that the wake-up effect in the HfO2 thin film is accompanied by the suppression of disorder.

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The phase transition through local strain engineering is an exciting avenue for controlling electronic, magnetic properties and catalyst activity of materials but complex phenomenon in nanoscience. Herein, we demonstrate the first combinations of bending strain and 2H/1T phase transition by rolling up MoS sheets for improving catalytic activity in relatively inert basal plane surfaces and promoting electron transfer from the less-conducting 2H MoS sheets to the electrodes. Furthermore, we generate various MoS@Pt nanoparticle hybrids nanomaterials and especially MoS@Pt scrolls containing the coverage of Pt NPs (8.3 wt%) have a high catalytic activity (39 mV per decade). The rolled up MoS@Pt sheets with bending strain (2.4%) provide an intra-layer plane gliding that allows the transversal displacement of an S plane from the 2H to the 1T phases (28%). This unique combination also allows us to maximize the intrinsic HER activity among molybdenum-sulfide based catalysts.

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