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44


nanotimes News in Brief


12-02 :: February/March 2012


Nanotubes // Technique Allows User-defined Shapes, Location and Pattern Variation


© Based on Material by John Toon / Gatech R


esearchers at the Georgia Institute of Techno- logy and Oak Ridge National Laboratory (US)


have developed a “soft template infiltration” tech- nique for fabricating free-standing piezoelectrically active ferroelectric nanotubes and other nanostruc- tures from PZT – a material that is attractive because of its large piezoelectric response. 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 200nm in outer diameter with thickness ranging from 5 to 25nm, show a piezoelec- tric response comparable to that of PZT thin films of much larger dimensions. The technique could ulti- mately lead to production of actively-tunable photo- nic and phononic crystals, terahertz emitters, energy harvesters, micromotors, micropumps and nanoelec- tromechanical sensors, actuators and transducers – all made from the PZT material.


In fabricating the nanotubes, Bassiri-Gharb and gra- duate student Ashley Bernal (currently an assistant professor at the Rose-Hulman Institute of Techno- logy) began with a silicon substrate and spin-coated a negative electron-beam resist material onto it. A template was created using electron-beam lithogra- phy, and a thin layer of aluminum oxide was added on top of that using atomic layer deposition.


Next, the template was immersed under vacuum into an ultrasound bath containing a chemical precursor solution for PZT. The structures were pyrolyzed at 300° C (572° F), then annealed in a two-step heat trea- ting process at 600 and 800° Celsius (1,112 to 1,472° F) to crystallize the material and decompose the polymer substrate. The process produced free-standing PZT nanotubes connected by a thin layer of the original aluminum oxide. Increasing the amount of chemical infiltration allows production of solid nanorods or nanowires instead of hollow nanotubes.


Ashley Bernal, Alexander Tselev, Sergei Kalinin and Naza- nin Bassiri-Gharb: Free-Standing Ferroelectric Nanotubes Processed via Soft-Template Infiltration, In: Advanced Materials, Vol. 24(2012), Issue 9, March 2, 2012, Pages 1160-1165, DOI:10.1002/adma.201103993: http://dx.doi.org/10.1002/adma.201103993


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