Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Engineers point way to better use of nanotubes as measuring tips

13.10.2005


This image shows a carbon nanotube attached to a conventional silicon tip used on an instrument called an atomic force microscope, which is used to measure tiny features on the scale of nanometers. Forces between individual atoms called van der Waals’ forces cause the flexible, vibrating probe to stick to the sides of the tiny structures, producing "artifacts," or inaccuracies in the final image. Purdue researchers have shown how to avoid the sticking action and prevent certain artifacts so that nanotubes can be better used in the emerging field of "nanometrology." (Purdue School of Mechanical Engineering)


This image shows a comparison between an image taken with a conventional silicon tip (left) and a nanotube, both used on an atomic force microscope to scan the surface of an object to measure tiny contours on the scale of nanometers. While nanotubes are more slender and flexible than the silicon tips, making them ideal to reach into the nooks and crannies of nano-structures, the tubes have a tendency to stick to the sides of the structures because of forces between individual atoms called van der Waals’ forces. The sticking action results in "artifacts," or inaccuracies in the final image. The image on the left shows an image taken with a conventional tip, and the other image shows an example of artifacts caused by the sticking action. Purdue researchers have shown how to avoid the sticking action and prevent certain artifacts so that nanotubes can be better used in the emerging field of "nanometrology." (Purdue School of Mechanical Engineering)


Engineers at Purdue University have shown how researchers might better use tiny hollow fibers called "multi-walled carbon nanotubes" to more precisely measure structures and devices for electronics and other applications. Findings will appear in the November issue of the journal Nanotechnology.

Researchers attach the tubes to the ends of imaging instruments called atomic force microscopes. Because the tubes are long and slender, their shape is ideal for the emerging field of "nanometrology," which is precisely measuring structures on the scale of nanometers, or billionths of a meter.

Conventional silicon tips used on the microscopes are shaped like inverted traffic cones. They are fine for measuring relatively flat surfaces, but they do not readily penetrate crevices that often exist in tiny devices and structures, said Arvind Raman, an associate professor of mechanical engineering at Purdue. The silicon tips also wear out quickly, reducing image resolution, whereas the carbon nanotubes have been shown to retain their accuracy after many hours of use, said mechanical engineering doctoral student Mark Strus.



But while nanotubes better penetrate the nooks and crannies of nano-structures, the flexible tubes often stick to the sides of these structures due to attractive forces between individual atoms called van der Waals’ forces.

"An example I give students is that operating in a nanoscale environment is like having flypaper everywhere because of the attraction of van der Waals’ forces," Raman said. "These short-range, inter-atomic forces are very relevant on this size scale because a nanometer is less than 10 atoms wide."

Researchers use nanotubes as probes by inducing a vibration in a portion of the microscope assembly called a microcantilever.

"The microcantilever, which does all of the surface sensing, can be thought of as a very small oscillating diving board on which the silicon tip and nanotube are mounted to the free end," Strus said.

As the microcantilever vibrates, the nanotube tip comes close to the surface but never actually touches the object being imaged. The closer the tip comes to the surface, the more powerful the attractive van der Waals’ forces become. The increasing attraction causes changes in the vibration pattern of the oscillating microcantilever, and the changing pattern is carefully monitored to reveal precise changes in contours on the surface of the object, yielding an image.

The same forces that enable the technology to work, however, also cause the sticking action of the probe. The vibrating tip sticks to the sides of the object being imaged, producing "artifacts," or inaccuracies in the measurements and images.

Strus has led research aimed at oscillating the probes in a manner that prevents nanotubes from sticking to structures, and new findings could lead to more accurate measurements using the slender probes. The journal paper was written by Strus, Raman, C-S Han, senior research manager from the Nanomechanical Systems Research Center at the Korea Institute of Machinery and Materials, and C.V. Nguyen, a research scientists from the NASA Ames Research Center in Moffett Field, Calif.

Methods to precisely measure structures on the scale of nanometers will become essential as nanostructures are used more often in applications such as computer chips, advanced sensors, microscopic machines and the creation of new materials. Precision measurements will be critical for developing new standards needed to properly develop, study and manufacture products based on nanotechnology.

Although some researchers are using nanotube tips in place of conventional silicon tips, the technique is still being perfected and has not yet reached widespread commercial use.

"One of our points in this paper is that you can avoid getting these artifacts if you know how to set the parameters," Strus said. "For example, you can change your set point or your amplitude and still get a good image with your nanotube."

The researchers showed precisely how artifacts are created by the sticking nanotubes, which are about 25 nanometers thick. The researchers also have shown how to avoid these artifacts by adjusting operating parameters of the microscope to prevent the tube from sticking.

One way to decrease the sticking is to increase the amplitude, or how far the probe moves each time it vibrates across the surface. With each oscillation, the tube sweeps close to the surface of the object and then swings in the opposite direction, constantly repeating the motion. As the vibrating probe sticks to the sides of a structure, the microscope’s computerized controller pulls the tip farther from the surface. Then, after the tip is pulled away, it starts vibrating normally again, and the controller repositions it closer to the surface, again resulting in the sticking action. This cycle repeats, causing the image artifacts.

The researchers demonstrated how to prevent several specific types of artifacts while using nanotubes to take images of tiny tungsten posts about 100 nanometers in diameter and other nano-structures.

The research was funded by the Centre for Nanomechatronics and Manufacturing in South Korea, and the work is associated with Purdue’s Birck Nanotechnology Center, which is part of Discovery Park, the university’s hub for interdisciplinary research.

Writer: Emil Venere, (765) 494-4709, venere@purdue.edu

Sources: Arvind Raman, (765) 494-5733, raman@ecn.purdue.edu

Mark Strus, (765) 496-6416, mstrus@purdue.edu

Purdue News Service: (765) 494-2096; purduenews@purdue.edu

Emil Venere | EurekAlert!
Further information:
http://www.purdue.edu

More articles from Physics and Astronomy:

nachricht Further Improvement of Qubit Lifetime for Quantum Computers
09.12.2016 | Forschungszentrum Jülich

nachricht Electron highway inside crystal
09.12.2016 | Julius-Maximilians-Universität Würzburg

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Electron highway inside crystal

Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.

Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Researchers identify potentially druggable mutant p53 proteins that promote cancer growth

09.12.2016 | Life Sciences

Scientists produce a new roadmap for guiding development & conservation in the Amazon

09.12.2016 | Ecology, The Environment and Conservation

Satellites, airport visibility readings shed light on troops' exposure to air pollution

09.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>