Nanoelectronics

Rensselaer researchers are working toward harnessing carbon nanotubes to create advanced computing and electronics systems that are thousands of times faster than those in use today.

One challenge in making nanotubes work for electronics applications is to controllably place and grow nanotubes in multiple directions. Ganapathiraman Ramanath, assistant professor of materials science and engineering, and Ajayan are the first to grow nanotubes simultaneously in any set of predetermined directions. For example, they have simultaneously grown nanotubes in both horizontal and vertical directions on silicon-based substrates in a single process.

One nanoparticle that has been the focus of much attention is the carbon nanotube. Pulickel Ajayan, associate professor of materials science and engineering, is at the forefront of research surrounding these quirky “nanoscopic” cylinders. Photo: Gary Gold

Their work paves the way for making new nanoscale devices that depend on creating architectures consisting of tiny wires placed in many directions.

To allow the nanotubes to grow in different directions, Ramanath and Ajayan have devised a new selective growth process on chiseled silica blocks on a silicon substrate. In this process, a catalyst, called ferrocene, is introduced along with xylene, the hydrocarbon that serves as the carbon source. As a result, carbon nanotubes grow selectively on silica in a direction perpendicular to the surface, and leave the silicon substrate bare. The invention of this selective growth process, published last year in Applied Physics Letters, is key to achieving multidirectional nanotubes growth.

“By manipulating the topography of the silica blocks, and utilizing the selective and directional growth process,” Ramanath says, “we have been able to force nanotubes to grow in predetermined, multiple directions, with a very fine degree of control.”

For example, if a piece of silica is carved into a one-micrometer-thick cylindrical disc, the nanotubes will grow vertically on the silica’s top surface, while growing horizontally on its side.

“While other researchers have grown aligned nanotubes in either vertical or horizontal directions using similar catalysts and carbon sources,” Ramanath adds, “we are the first to combine several key strategies to controllably grow nanotubes in more than one direction, at different locations, at the same time, in a single process step.”

A Perfect Nano Model

The Rensselaer Nanotechnology Center and its NSF Center also draw on the Institute’s strengths in information technology and computer science. A group of researchers working in theoretical modeling and design is advancing the day when theorists will calculate, model, and design nanostructures for various applications. Headed by Pawel Keblinski, assistant professor of materials science and engineering and an expert in atomic modeling of materials, the team is using quantum mechanics calculations and molecular simulation methods to build and analyze computer models of nanostructures.

Pawel Keblinski, assistant professor of materials science and engineering, heads a team using quantum mechanics calculations and molecular simulation methods to build and analyze computer models of nanostructures. Photo: Thomas Griffin

“These models will assist the Nanotechnology Center’s researchers in all disciplines to understand experimental results, which provide information that can’t be seen with today’s instruments,” Keblinski says. “The models also test and verify theories, and allow researchers to develop and apply new methods.”

Keblinski’s work is strengthened by collaborations with Rensselaer’s Scientific Computation Research Center and Los Alamos National Laboratory.

Nano Impact

New technologies present challenges as well as opportunities for industry and society. Some fear that extraordinarily small biosensors could be used as weapons as well as tools in pollution control, disease diagnosis, and medical therapies. “Nanorobots” or drug delivery systems have the potential to lose control and cause unwanted damage.

For this reason, the Rensselaer Nanotechnology Center also has brought together a diverse group of faculty to examine what nanotechnology will do to the socioeconomic fabric of daily life.

“We need to be concerned with developing business models from breakthrough research that are aligned with societal values and goals,” says group leader Lois Peters, associate professor and director of the Lally School of Management and Technology doctoral program. “There is more to nanotechnology than just making a profit. Major societal benefits as well as dangers must be considered.”

Peters’ research team will focus on answering questions, such as: How do we prepare for developments in nanotechnology? What steps need to be taken to educate the work force? What management practices are required for nanotechnology to reach its full potential?

“Consideration of these questions will impact how we train and educate students, and will determine who will be the new corporate winners,” says Peters, one of the six Rensselaer authors of Radical Innovation: How Mature Companies Can Outsmart Upstarts (Harvard Business School Press).

The Next Frontier: Lowering the Walls To Explore Inner Space

Rensselaer is leading the way to the new frontier in nanotechnology. As the field continues to grow in the United States and abroad, it will further shrink borders among prominent researchers and disciplines, integrating knowledge and expertise that promise to change the world.

“It’s a real revolution in our ability to create and manipulate materials for new properties and functions to bring innumerable benefits that most of society hasn’t even dreamed of. The possibilities are endless,” Siegel says. “There is a wide range of disciplines contributing to the developments in nanostructure science and technology. Because of the ‘low walls’ and easy interaction at Rensselaer, we’ve been able to accelerate our work in nanotechnology.”

“That’s the really exciting part about nanotechnology,” Siegel adds. “It does not depend on one field; it transcends all disciplines and benefits from each of them.”