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Innovative fusion of materials earns top award


September 18, 2008

An advance in nanotechnology that promises to improve the integration of nanoscale materials into the manufacture of microelectronics has earned a top research award for an Ira A. Fulton School of Engineering faculty member and three former Arizona State University students.

A 2008 Nano 50 award will be shared by Tom Picraux, a research professor in the School of Materials and chief scientist at the Center for Integrated Nanotechnologies at Los Alamos National Laboratory, former materials science and engineering graduate students Sarang Ingole and Pavan Aella, and Sean Hearne at Sandia National Laboratories, who earned a Ph.D. in physics at ASU.

The award recognizes “the top 50 technologies, products, and innovators that have significantly impacted, or will impact, the development of nanotechnology.” 

The Nano 50 honors are given by Nanotech Briefs, a monthly digital newsletter produced by the Tech Briefs Media Group, a leading publisher in the engineering and technology field. 

The awards winners are the “best of the best,” the innovators who are making the engineering advances that will move nanotechnology into mainstream markets, according to the publishing group. 

Picraux, Ingole, Aella and Hearne collaborated on work to find a more efficient method of fusing charge-carrying electrical contacts to tiny “nanowires” made of silicon. That accomplishment will help improve electronics technology, particularly chemical and biosensing devices and energy-collection systems. 

Fusing such metal-silicon connections has been difficult and costly, hindering the fabrication methods necessary for more advanced applications of nanoscale materials. 

The quality of these fusions can boost the effectiveness of solar energy systems because photovoltaic cells rely on the connections to carry energy generated from sunlight into homes, business and industrial operations. 

Current nano-manufacturing relies on ultra-high resolution patterns, or “masks,” to accurately engineer good electrical contact between metals and semiconductors – for example, nickel and silicon. The technique currently calls for electron beam lithography to separately connect the metal contacts to each nanowire. This process, in which the wire pattern is “written” with a beam of electrons to one nanowire at a time, has proven too slow for practical application. 

“From the microelectronics manufacturing approach, anything that takes a long time is just not cost effective,” said Tom Picraux, who works in the Los Alamos lab’s Center for Integrated Nanotechnologies, which was  formerly based at Arizona State University.

The research team designed a method that eliminates the final lithography step by first creating a set of planar gold electrodes. They then took advantage of an alternating electric field in a technique called dielectrophoresis. This pulls the silicon nanowires from a solution and places them between the electrodes. 

Again using an electric field, along with a mild acid bath, the researchers selectively electro-deposited the nickel only where the underlying gold electrodes were located until the ends of silicon nanowires were buried, and then heated them to several hundred degrees Celsius to establish good electrical contacts. 

Through the use of this “directed assembly” guided by the electric field to create the contacts, the process did not require lithography to connect the individual nanowires and all the connections are made at once in the parallel eletrodeposition process. The result is an increased potential for use in cost-effective nanotechnology manufacturing of existing technology, such as electronic switches. 

It may also increase the feasibility of larger-scale applications, including biological and chemical sensor networks to detect potential threats from dangerous substances, as well as the fabrication of nanowire solar cells for providing a greatly expanded source of clean solar energy. 

The team will receive its Nano 50 award at the NASA Tech Briefs National Nano Engineering Conference Nov. 12 and 13 in Boston. 

More information on the Nano 50 Awards and the conference is available at www.techbriefs.com/nano.

Aella is working as an engineer in the Advanced CVD Group of Micron Technology Inc. Ingole is a post-doctoral research associate in the School of Chemical Engineering at Purdue University.