UO researchers learn to precisely control nanoparticle spacing

Langmuir article describes advance needed for nanoscale electronics and optics

EUGENE, Ore. - Another puzzle solved: University of Oregon researchers at the Oregon Nanoscience and Microtechnologies Institute (ONAMI) are now able to control precisely the spacing between nanoparticles, a key advance in the genesis of a new class of nanoscale electronics and optics.

An article published in Langmuir, the American Chemical Society's surface science journal, details the process developed by UO chemistry professor James E. ("Jim") Hutchison with two of his students, Gerd H. Woehrle and Marvin G. Warner.

"We care about the spacing between the particles because the interactions between them are distance-dependent," Hutchison says. "If they're too far apart, the interaction will be weaker, preventing the particles from passing electrons from one to another."

Using DNA as a template, the UO team has hit upon a convenient and reliable method to organize small gold nanoparticles into linear chains with precisely controlled interparticle spacing over a range of 1.5 to 2.8 nanometers. Controlling the magnitude and precision of the particle spacing is essential for creating electronic and optical applications of nanostructures.

Hutchison says the new technique goes a long way toward refining the biomolecular lithographic approach and gaining greater mastery over the patterning of features on the nanometer scale.

"This method fulfills a number of crucial requirements for its use in future applications," Hutchison says. "It is highly reproducible. The assembly process tolerates structural defects in the DNA template, and it enforces the interparticle spacing in nonlinear sections of the template. Also, the total coverage of DNA strands is greater than 90 percent, which demonstrates the high yield of the assembly process."

Hutchison says this process holds great promise as an alternative to current lithographic methods because it overcomes several limitations inherent in those methods.

"With further refinement, it should also be possible to realize more elaborate structures with the same degree of control by utilizing the structural versatility of more sophisticated DNA templates," he says.

The high degree of spatial control offered by this new approach, either in tandem with other lithographic forms or alone, "will prove exceedingly useful in patterning structures for use in nanoelectronics and nanophotonics, and for fabricating novel devices with tailored properties through controlling the interactions between adjacent particles," Hutchison explains.

This advance is the latest in a series of achievements coming out of the UO's Materials Science Institute.

Already known as the world leader in the application of green principles to the teaching of organic chemistry, Hutchison's group seeks to color the field of nanoscience green as well. In May, the University of Oregon received a patent on Hutchison's breakthrough technique for synthesizing nanoparticles using an environmentally benign process at room temperature. The scientific paper describing the process was published in the Journal of the American Chemical Society in 2000.

Hutchison's lab can turn out more nanoparticles in a few hours than can be made in a week using the standard approach. This faster, safer, cheaper way of making functionalized gold nanoparticles promises to accelerate the discovery of the scientific and commercial uses for nanotechnology.

Hutchison's process is versatile, rapid and reproducible--the first meaningful change in the way such material is made in 20 years. As a result, Oregon is staking its claim in what's shaping up to be this century's version of a gold rush. The National Science Foundation predicts that nanotechnology will be the basis of the next industrial revolution, a trillion-dollar market by 2015.

The Hutchison team is finding a variety of ways to harness the behavior of molecular "building blocks" so they can be employed in creating new medicines and products. They've learned to optimize or "tune" the properties of nanoparticles so they will dissolve in water or in solvents and exhibit specific reactivity, depending on the need. Other achievements include methods for forming well-ordered nanoparticle monolayers and multilayers on insulating surfaces for use in nanoelectronic devices.

All of these innovations have involved the application of green chemistry methods pioneered by Hutchison and UO chemistry professor Ken Doxsee. They established the world's first green organic chemistry lab at Oregon in 1997. Green chemistry is rapidly becoming the world standard as industry seeks cleaner and more resource-efficient manufacturing techniques.

09-jun-2004