Electromechanical properties of graphene oxide as a two-dimensional actuator

2017-03-03T03:17:26Z (GMT) by Chang, Zhenyue
Fast growing miniaturization technologies in various fields have been facilitating the development of actuators in micro/nanoelectromechanical systems. Advanced futuristic actuator requires not only high in actuation performances, but also easy in designing, fabrication, monitoring and controlling at nanoscopic or even atomic scale. Many conventional electric and magnetic actuation materials are not suitable for miniaturization mainly due to the unfavourable scaling factor. Functional materials (or namely smart material), on the other hand, have received extensive attentions thanks to their inherent ability to deform at small scales upon an appropriate external stimulus. Piezoelectric materials, shape memory materials, and electro-active materials are three most widely used smart materials for actuation. Not surprisingly, these materials have been successfully employed in a myriad of applications at nanoscopic scales. For instance, many commonly studied atomically thin materials have been reported to exhibit piezoelectric effect, both theoretically and experimentally. Nanoscopic shape memory effect of traditional shape memory materials, like shape memory alloys and shape memory polymers, is observed. Additionally, quantum mechanical effect of nano electro-active materials, such as carbon nanotubes, has inspired many new opportunities in quantum mechanical actuation of graphene-based and two-dimensional materials. Here, we look at electromechanical properties of monolayer graphene oxide crystals that could potentially enable the possibility of designing two-dimensional actuators. In this thesis, three types of electromechanical properties of graphene oxide crystals (i.e. piezoelectric, shape memory, and quantum mechanical effects) are explored via Density Functional Theory calculations. Firstly, highly ordered graphene oxide crystals were found to exhibit a maximum in-plane strain of 0.12 % induced by piezoelectric response. Secondly, a two-dimensional shape memory graphene oxide was discovered. The recoverable strain is as large as 14.5 %. Lastly, some graphene oxide crystals can have two-way quantum mechanical actuation performances. Specifically, a single piece of graphene oxide crystal is capable of both expansion and contraction upon electron injection only, thanks to the existence of intrinsic bi-stable phases. Throughout this thesis, a case is made for monolayer graphene oxide crystals to be utilised in developing different types of electromechanical nano- or two-dimensional actuators.