Researchers from the Georgia Institute of Technology have created nanorings of single-crystal zinc oxide. Because of the semiconducting and piezoelectric properties of the material, these nanostructures could serve as nanometer-scale sensors, resonators and transducers, according to this article from nanotechweb.org.
Before going further, here is an example of these beautiful zinc-oxide circular nanorings (Credit: Georgia Tech).
"This is the first report on the growth of freestanding, single-crystal, complete nanorings, demonstrating the possibility of synthesizing extreme structures and offering a new nanostructure that was not previously thought possible," Zhong Lin (ZL) Wang told nanotechweb.org. "The growth mechanism is a spontaneous self-coiling process (the ‘slinky’ growth mechanism), which is fundamentally a new crystal growth process. It sets the foundation for understanding the formation of polar-surface-induced nanostructures."
How did they grow these nanorings which range in diameter from one to four microns and are 10-30 nanometers thick?
Wang and colleagues made the nanorings by a solid-vapour technique, starting with powders of zinc oxide, indium oxide and lithium carbonate in a horizontal tube furnace. Heating the materials to 1400° C in argon caused material to deposit on a silicon substrate. Around 20 to 40% of this material was made up of zinc-oxide nanorings with diameters of 1 to 4 microns and shells around 10 to 30 nm thick.
This news release from the Georgia Institute of Technology tells us more about the possible applications.
Nanorings offer new possibilities for fabricating unique nanoscale electromechanical systems, such as piezoelectric resonators for detecting single biomolecules, nanoscale elastic bearings and actuators.
"Nanorings offer a combination of many unique and attractive properties in one system," said Wang. "We want to build some unique devices that will test different electromechanical properties, particularly electro-mechanical coupling and applications in bio-detection. We want to fully use the piezoelectric properties, in addition to the semiconductor properties, because they will allow us to explore properties no other systems have."
Nanorings and nanosprings are candidates for building implantable sensors for real-time monitoring of such biomedical measures as blood pressure, blood flow rate and stress at the level of single cells, Wang said.
The research work was published by Science Magazine. Here is the abstract of the paper called "Single-Crystal Nanorings Formed by Epitaxial Self-Coiling of Polar Nanobelts."
Freestanding single-crystal complete nanorings of zinc oxide were formed via a spontaneous self-coiling process during the growth of polar nanobelts. The nanoring appeared to be initiated by circular folding of a nanobelt, caused by long-range electrostatic interaction. Coaxial and uniradial loop-by-loop winding of the nanobelt formed a complete ring. Short-range chemical bonding among the loops resulted in a single-crystal structure. The self-coiling is likely to be driven by minimizing the energy contributed by polar charges, surface area, and elastic deformation. Zinc oxide nanorings formed by self-coiling of nanobelts may be useful for investigating polar surface -- induced growth processes, fundamental physics phenomena, and nanoscale devices.
Sources: Liz Kalaugher, nanotechweb.org, February 27, 2004; John Toon, Georgia Institute of Technology, February 27, 2004; Science, Volume 303, Number 5662, February 27, 2004, pp. 1348-1351