Oct 28, 2013
How does size affect the piezoelectric properties of ZnO nanowires?
Using state-of-the-art density functional theory calculations, researchers from the Politecnico di Torino and the CNR-IMEM in Italy, have studied how size affects the piezoelectric properties of nanostructured materials. In particular, by locally analysing the piezoelectric contributions of surface and bulk shells in hexagonal shaped wires, they demonstrate that surface effects are negligible for nanowire diameters larger than 15 Å.
ZnO nanowires with reduced diameters could make ideal building blocks for self-powered nanodevices thanks to their piezoelectric properties. We used density functional theory (DFT) calculations in conjunction with maximally localized Wannier functions (MLWFs) to study the piezoelectric properties of ZnO NWs with diameters smaller than 2.3 nm. Using this scheme, we were able to quantify both bulk and surface contributions. The close similarity between piezoelectric responses of bulk and nanostructure NWs reveals that piezoelectric constants are not enhanced at the nanoscale. This finding is different from previous observations.
On the contrary, the calculated effective strain energies of ZnO NWs are more sensitive to smaller nanowire size and are much lower compared to the bulk material. As such, our theoretical predictions indicate that the advantage of using NWs for energy harvesting comes thanks to their sensitivity to small mechanical agitation, thus making them ideal candidates for building efficient energy scavenging devices - irrespective of the fact that NW nanogenerators (which are typically around 40 nm in size) are expected to have piezoelectric properties similar to bulk ones.
More information can be found in the journal Nanotechnology (in press).
About the author
Kiprono Korir is PhD student in the Department of Applied Science and Technology at the Politecnico di Torino and CNR-IMEM, Italy. He works in the research group of Prof. Giancarlo Cicero and Prof. Alessandra Catellani who are currently working on understanding the properties of semiconducting nanostructured materials with applications in electronics, photonics and sensors by means of first principle simulations.