Nanobelts coil up for piezoelectricity
19 August 2003
Researchers from the Georgia Institute of Technology, US, have made
single-crystal zinc oxide (ZnO) nanobelts that spontaneously rolled
themselves up into helical structures. The nanohelixes had piezoelectric
properties and could have applications in microsystems and the biomedical
"Piezoelectric and ferroelectric-based smart materials are just as important
as semiconductor nanostructures, because they are the transducers and
actuators for nanoscale machines and devices," researcher Zhong Lin Wang
told nanotechweb.org. "We have reported, for the very first time, the
successful synthesis of structurally controlled piezoelectric and
ferroelectric ZnO nanobelts 10-60 nm wide and 5-20 nm thick. The most
exciting result is the formation of single crystalline ZnO helical
nanosprings due to spontaneous polarization."
To grow the nanobelts, Wang and colleague Xiang Yang Kong used a
solid-vapour process. They heated ZnO powder in a horizontal tube furnace,
depositing ZnO nanostructures onto an alumina substrate. Most of the
nanostructures were nanobelts up to several hundreds of microns long, but
the scientists also saw nanobelts in a ring shape, and helical structures
consisting of coiled-up nanobelts. These helices, or nanosprings, had radii
of about 500-800 nm.
For the greatest piezoelectric effect, it's desirable to have ZnO
nanostructures with a large area of polarized (0001) zinc- and
oxygen-terminated surfaces. However, the (0001) surface has a high surface
energy and so its growth is energetically unfavourable. By carefully
controlling the experimental conditions, the Georgia team succeeded in
producing structures with surfaces dominated by (0001) facets. In fact,
electron diffraction studies indicated that more than 90% of the nanobelts
had top flat surfaces consisting of polar (0001) facets.
According to the scientists, the nanobelts and nanosprings are an ideal
system for understanding piezoelectricity and polarization-induced
ferroelectricity at the nanoscale. They could also have applications as
sensors, nanoinductors, transducers, actuators, and tunable functional
components for microelectromechanical systems (MEMS) and
nanoelectromechanical systems (NEMS). In addition, the different polar
surfaces - zinc- and oxygen-terminated - could find a use as selective
catalysts, and the helical nanosprings' tunable pitch distance could help to
separate DNA double-helix chains and tailor DNA structures via
"My future research will focus on two directions: application and
integration of piezoelectric nanobelt materials with microsystems, and
applications of nanobelts in biomedical science," added Wang. "We will work
on the emergence of the nanobelt structure for improving the performance of
MEMS and NEMS. We'd also like to use these materials for in-situ, real-time,
non-destructive and remote monitoring and detection of cancer cells."
The researchers reported their work in Nano Letters.
About the author
Liz Kalaugher is editor of nanotechweb.org.
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