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 Pulses of electrons manipulate nanomagnets and store information
21.07.2017 | American Institute of Physics

nachricht Vortex photons from electrons in circular motion
21.07.2017 | National Institutes of Natural Sciences

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: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA looks to solar eclipse to help understand Earth's energy system

21.07.2017 | Earth Sciences

Stanford researchers develop a new type of soft, growing robot

21.07.2017 | Power and Electrical Engineering

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>