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Thursday, 23 February 2012

Ferroelectric Nanotubes: “Soft Template Infiltration” Technique Fabricates Free-Standing Piezoelectric Nanostructures from PZT Material

Georgia Tech 
Feb 23, 2012
Composite scanning electron microscope (SEM) image of PZT nanotube arrays and their piezoelectric response as measured by band-excitation PFM (BE-PFM). (Click image for high-resolution version. Image courtesy of Ashley Bernal and Nazanin Bassiri-Gharb)

Researchers have developed a “soft template infiltration” technique for fabricating free-standing piezoelectrically active ferroelectric nanotubes and other nanostructures from PZT – a material that is attractive because of its large piezoelectric response. Developed at the Georgia Institute of Technology, the technique allows fabrication of ferroelectric nanostructures with user-defined shapes, location and pattern variation across the same substrate.

The resulting structures, which are 100 to 200 nanometers in outer diameter with thickness ranging from 5 to 25 nanometers, show a piezoelectric response comparable to that of PZT thin films of much larger dimensions. The technique could ultimately lead to production of actively-tunable photonic and phononic crystals, terahertz emitters, energy harvesters, micromotors, micropumps and nanoelectromechanical sensors, actuators and transducers – all made from the PZT material.

Using a novel characterization technique developed at Oak Ridge National Laboratory, the researchers for the first time made high-accuracy in-situ measurements of the nanoscale piezoelectric properties of the structures.

“We are using a new nano-manufacturing method for creating three-dimensional nanostructures with high aspect ratios in ferroelectric materials that have attractive piezoelectric properties,” said Nazanin Bassiri-Gharb, an assistant professor in Georgia Tech’s Woodruff School of Mechanical Engineering. “We also leveraged a new characterization method available through Oak Ridge to study the piezoelectric response of these nanostructures on the substrate where they were produced.”

The research was published online on Jan. 26, 2012, and is scheduled for publication in the print edition (Vol. 24, Issue 9) of the journal Advanced Materials. The research was supported by Georgia Tech new faculty startup funds.

Ferroelectric materials at the nanometer scale are promising for a wide range of applications, but processing them into useful devices has proven challenging – despite success at producing such devices at the micrometer scale. Top-down manufacturing techniques, such as focused ion beam milling, allow accurate definition of devices at the nanometer scale, but the process can induce surface damage that degrades the ferroelectric and piezoelectric properties that make the material interesting.

Until now, bottom-up fabrication techniques have been unable to produce structures with both high aspect ratios and precise control over location. The technique reported by the Georgia Tech researchers allows production of nanotubes made from PZT (PbZr0.52Ti0.48O3) with aspect ratios of up to 5 to 1.
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