Piezoelectricity was discovered in 1880 by Jacques and Pierre Curie. This property allows materials to convert mechanical stress into electrical signals and vice versa. Piezoelectric devices have important applications in medicine, aerospace, transportation and consumer electronics. For example, piezoelectric elements are used as pressure sensors mobile phones and to monitor combustion in internal combustion engines. For future applications, sensors should operate at nanoscale or microscale level, be flexible and transparent, and easy to integrate with conventional electronics. This project will investigate piezoelectricity in novel two-dimensional (2D) materials, with the aim of realizing next generation devices. 2D materials are atomically thick and have unique optical and electrical properties. Their piezoelectric properties could be used realize mechanically powered transparent flexible charge-generating devices. This project will enable the fabrication of innovative devices at the microscale and nanoscale with unprecedented applications in medicine, industry, environmental engineering, and consumer electronics.
Piezoelectric properties in materials are due to non-centrosymmetric structure of the material crystal structure. It is also known that some materials are non-piezoelectric in their bulk structure. However, when they are thinned in monolayer or several layers, they show piezoelectricity properties. In this work the piezoelectric properties for 2D materials are studied. It presents a novel technique for enhancement of piezoelectric properties in weak piezoelectric two-dimensional materials. Surface Acoustic Waves (SAW) are used to enhance the piezoelectric properties of 2D materials. The SAW device will be built on an island of strong Piezoelectric material. The traveling acoustic wave would cause stress and strain on the two-dimensional materials placed on the substrate, which would increase the piezoelectric properties of the two-dimensional materials. The technique of using Surface Acoustic Waves (SAW) to activate acoustic waves that couple to the weak piezoelectric material and cause changes in the piezoelectric coefficient of the weak piezoelectric material is novel. In this work we are planning to apply this technique to several two-dimensional materials and measure improved piezoelectric coefficients and their applications, such as in sensors. The proposed method in this research greatly enhances the piezoelectric effect of 2D materials and eliminates the disadvantages of other techniques reported in the literature. The drawbacks in current methods include high demand of fabrication complexity and precision, high cost, and the limitation of the number of stacked layers of 2D materials. Different 2D materials such as molybdenum disulfide (MoS2) and indium selenide (InSe) will be tested and evaluated, including those commonly used and less-studied ones. The outcome of this proposed work will largely extend the utilization range of piezoelectricity of 2D materials, and will turn into more practical and novel devices in electronic, electromechanical, sensors, and optoelectronic fields.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
