University At Buffalo Engineer Develops Novel Method For Assembly Of Nanoparticles; Process May Lead To Manufacture Of Nanoscale Devices

The work could be an important step in fulfilling the immense potential of nanotechnology because it gives scientists and engineers improved control and flexibility in the creation of materials for the manufacture of many nanoscale devices, according to Paschalis Alexandridis, associate professor of chemical engineering in UB's School of Engineering and Applied Sciences.

Alexandridis and postdoctoral research associate Aristides Docoslis used non-uniform AC electric fields generated by microfabricated electrodes -- which create a motion known as dielectrophoresis -- to stack latex, silica or graphite microparticles into two- and three-dimensional structures of prescribed lengths and composition, held together by the electrical field.

The same process can be applied to nanoparticles, says Alexandridis, whose research is funded by a $100,000 Nanoscale Exploratory Research (NER) grant from the National Science Foundation, Division of Design, Manufacture and Industrial Innovation.

"This process enables you to guide particles to where you want them to go and then scale them up into ordered structures with desired electrical, optical or mechanical properties," explains Alexandridis. "You can use this process to create a well-defined object and assemble it on demand, which means these materials can actually be used to manufacture nanoscale tools or devices," he adds. "This may be particularly applicable for the manufacture of sensors and photonic devices."

Adaptability is an attractive feature of the process, Alexandridis says. The process can be used to direct and manipulate almost any particle, he explains, whether the particle has a net charge or not, or is suspended in an aqueous or non-aqueous medium. "Because of this flexibility, there's no limit to the applications of this process," Alexandridis says. "That's another advantage for the manufacturability of this method."

Focusing on the dielectrophoresis process, Alexandridis is developing models to predict how various particles, and combination of particles, will behave under the influence of different electrical fields, as a function of particle size and properties, electrode dimensions and pattern, and applied voltage and frequency. This information will help guide future nanomanufacturing applications, he says.

Alexandridis also is developing ways to glue particles together after the electrical field has assembled them. "The goal is to link the particles in a way that doesn't change the properties of the structure, but which makes the structure permanent and resilient," he says. "After you glue the particles together you can switch off the electrical field and have a free-standing, ordered structure."

"Or you can change the field frequency so that you can remove selectively the unglued particles," he adds. Results from Alexandridis' and Docoslis' research were published recently in Electrophoresis (2002, 23, 2174-2183).

Nanotechnology is a potentially revolutionary and lucrative scientific industry, with experts predicting manufacture and commercialization of microscopic products benefiting the fields of electronics, medicine, supercomputing, energy and environmental cleanup.