Georgia Tech researchers display samples of materials on which ferroelectric nanostructures have been fabricated by thermochemical nanolithography. (left to right) Yaser Bastani with silicon, Nazanin Bassiri-Gharb with polyimide and Suenne Kim with glass.
ATLANTA, US: Using a technique known as thermochemical nanolithography (TCNL), researchers have developed a new way to fabricate nanometre-scale ferroelectric structures directly on flexible plastic substrates that would be unable to withstand the processing temperatures normally required to create such nanostructures.
The technique, which uses a heated atomic force microscope (AFM) tip to produce patterns, could facilitate high-density, low-cost production of complex ferroelectric structures for energy harvesting arrays, sensors and actuators in nano-electromechanical systems (NEMS) and micro-electromechanical systems (MEMS). The research was reported July 15 in the journal Advanced Materials.
“We can directly create piezoelectric materials of the shape we want, where we want them, on flexible substrates for use in energy harvesting and other applications,” said Nazanin Bassiri-Gharb, Co-author of the paper and an Assistant Professor in the School of Mechanical Engineering at the Georgia Institute of Technology.
The research was sponsored by the National Science Foundation and the US Department of Energy. In addition to the Georgia Tech researchers, the work also involved scientists from the University of Illinois Urbana-Champaign and the University of Nebraska Lincoln.
The researchers have produced wires approximately 30 nanometre wide and spheres with diameters of approximately 10 nanometre using the patterning technique. Spheres with potential application as ferroelectric memory were fabricated at densities exceeding 200 gigabyte per square inch - currently the record for this perovskite-type ferroelectric material, said Suenne Kim, the paper’s first Author and a Postdoctoral Fellow in laboratory of Professor Elisa Riedo in Georgia Tech’s School of Physics.
The thermochemical nanolithography process, which was developed at Georgia Tech in 2007, addresses many challenges. A computer controls the AFM writing, allowing the researchers to create patterns of crystallized material where desired.
To begin the fabrication, the sol-gel precursor material is first applied to a substrate with a standard spin-coating method. The researchers have used polyimide, glass and silicon substrates, but in principle, any material able to withstand the 250-degree heating step could be used.
“We still heat the precursor at the temperatures required to crystallize the structure, but the heating is so localized that it does not affect the substrate,” explained Riedo, a Co-author of the paper and an Associate Professor in the Georgia Tech School of Physics.
As a next step, the researchers plan to use arrays of AFM tips to produce larger patterned areas, and improve the heated AFM tips to operate for longer periods of time.
“Thermochemical nanolithography is a very powerful nanofabrication technique that, through heating, is like a nanoscale pen that can create nanostructures useful in a variety of applications, including protein arrays, DNA arrays and graphene-like nanowires,” Riedo explained. “We are really addressing the problem caused by the existing limitations of photolithography at these size scales. We can envision creating a full device based on the same fabrication technique without the requirements of costly clean rooms and vacuum-based equipment. We are moving toward a process in which multiple steps are done using the same tool to pattern at the small scale.”
In addition to those already mentioned, the research team included Yaser Bastani from the G W Woodruff School of Mechanical Engineering at Georgia Tech, Seth Marder and Kenneth Sandhage, both from Georgia Tech’s School of Chemistry and Biochemistry and School of Materials Science and Engineering, and Alexei Gruverman and Haidong Lu from the Department of Physics and Astronomy at the University of Nebraska-Lincoln.
©2011 Georgia Institute of Technology News