Piezoelectric Actuation of Graphene-Coated Polar Structures.

Ferroelectric materials based on lead zirconate titanate (PZT) are widely used as sensors and actuators because of their strong piezoelectric activity. However, their application is limited because of the high processing temperature, brittleness, lack of conformal deposition, and a limited possibility to be integrated with the microelectromechanical systems (MEMS). Recent studies on the piezoelectricity in the 2-D materials have demonstrated their potential in these applications, essentially due to their flexibility and integrability with the MEMS. In this work, we deposited a few layer graphene (FLG) on the amorphous oxidized Si3N4 membranes and studied their piezoelectric response by sensitive laser interferometry and rigorous finite-element modeling (FEM) analysis. Modal analysis by FEM and comparison with the experimental results show that the driving force for the piezoelectric-like response can be a polar interface layer formed between the residual oxygen in Si3N4 and the FLG. The response was about 14 nm/V at resonance and could be further enhanced by adjusting the geometry of the device. These phenomena are fully consistent with the earlier piezoresponse force microscopy (PFM) observations of the piezoelectricity of the graphene on SiO2 and open up an avenue for using graphene-coated structures in the MEMS.

Domain Switching by Electron Beam Irradiation in SBN61:Ce Single Crystals Covered by Dielectric Layer.

The formation of the domain structure by electron beam irradiation in thermally depolarized Ce-doped strontium barium niobate single crystals with free surface and surface covered by a dielectric layer has been studied. The dependences of the domain sizes and domain depth on the irradiated dose have been measured. The circular shape of the isolated domains was obtained. The isotropic domain growth was attributed to step generation at the wall as a result of merging with the residual nanodomains which existed after thermal depolarization. The linear dose dependence of the switched area was attributed to the screening of the depolarization field by the injected charge. The electrostatic interaction of the approaching charged domain walls was revealed. The better quality of the domain patterns was achieved in the samples with electron localization in the dielectric layer. The obtained results can be applied for the creation of precise domain patterns with arbitrary orientation and shape to produce nonlinear optical devices with improved characteristics.