Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Friction Differences Offer New Tool in Carbon Nanotubes

16.09.2009
Nanotubes and nanowires are promising building blocks for future integrated nanoelectronic and photonic circuits, nanosensors, interconnects and electro-mechanical nanodevices. But some fundamental issues remain to be resolved – among them, how to position and manipulate the tiny tubes.

Publishing in the journal Nature Materials this week, researchers from four different institutions report measuring different friction forces when a carbon nanotube slides along its axis compared to when it slides perpendicular to its axis. This friction difference has its origins in soft lateral distortion of the tubes when they slide in the transverse direction.

The findings not only could provide a better understanding of fundamental friction issues, but from a more practical standpoint, offer a new tool for assembling nanotubes into devices and clarify the forces acting on them. Asymmetries in the friction could potentially also be used in sorting nanotubes according to their chirality, a property that is now difficult to measure with other means.

When an atomic force microscope (AFM) tip is scanned transversely across a multi-walled carbon nanotube, the amount of friction measured is twice as much as when the same tube is scanned longitudinally, along the length of the tube. The researchers attribute this difference to what they call “hindered rolling” – additional effort required to overcome the nanotube’s tendency to roll as the AFM tip strokes across it rather than along it.

“Because the energy required to move in one direction is twice as much as required to move in the other direction, this could be an easy way to control the assembly of carbon nanotubes for nanoelectronics, sensors and other applications,” said Elisa Riedo, co-author of the study and an associate professor in the School of Physics at the Georgia Institute of Technology. “To assemble nanotubes on a surface, you need to know how they interact and what force is needed to move them.”

The combined theoretical and experimental study was supported by the U.S. Department of Energy. Other institutions contributing to the project include the International Centre for Theoretical Physics, International School for Advanced Studies and CNR Democritos Laboratory – all in Trieste, Italy – and the University of Hamburg in Germany. The paper was published in advance online on September 13 by the journal Nature Materials.

Carbon nanotubes have exceptional thermal, mechanical and electrical properties that have generated considerable interest since they were first reported in 1991. Though friction has been studied before in nanotubes, this research is the first to provide detailed information about the frictional forces at work in both the longitudinal and transverse directions when the tubes interact with an AFM tip.

Friction is one of the oldest problems in physics and one of the most important to everyday life. It is estimated that the losses in the U.S. economy due to friction total about 6 percent of the gross national product. Friction is even more important to micro-electromechanical systems (MEMS) and nanoscale devices because these smaller systems are more affected by surface forces than large systems.

“As systems become smaller and smaller, it becomes more important to understand how to address friction,” said Riedo. “Surface forces can prevent micro and nano systems from operating at all.”

Experimentally, the researchers scanned an atomic force microscope tip longitudinally along a series of multiwalled carbon nanotubes held stationary on a substrate. They also conducted a series of similar scans in the transverse direction. The researchers applied a consistent force on the AFM tip in both scanning directions, and relied on powerful Van der Waals forces to hold tubes in place on the substrate.

“When you scan a nanotube transversely, you are probing something very different,” said Riedo. “You are also probing additional dissipation modes due to a kind of swaying motion in which energy is also dissipated through movement of the nanotube as it alters its cross section.”

The experiment showed that greater forces were required to move the tip in the transverse direction. Using molecular dynamics simulations, collaborators Erio Tosatti and Xiaohua Zhang at the International Centre for Theoretical Physics, International School for Advanced Studies and CNR Democritos Laboratory analyzed the phenomenon to understand what was happening.

“In principle, there seems to be no reason why the frictional forces required to move the AFM tip would be different in one direction,” Riedo noted. “But the theory confirmed that this ‘hindered rolling’ and soft mode movement of the nanotubes are the sources of the higher friction when the tip moves transversely.”

Because the nanotube-tip system is so simple, it offers an ideal platform for studying basic friction principles, which are important to all moving systems.

“This kind of system gives you the opportunity to explore friction using an ideal experiment so you can really probe the energy dissipation mechanism,” Riedo explained. “The system is so simple that you can distinguish between the dissipation mechanisms, which you can’t usually do well in macro-scale systems.”

Based on the molecular dynamics simulations, Riedo and Tosatti believe that the friction anisotropy will be very different in chiral nanotubes versus non-chiral – left-to-right symmetric – nanotubes.

“Because of the chirality, the tip moves in a screw-like fashion, creating hindered rolling even for longitudinal sliding,” Tosatti said. “Thus, the new measuring technique may suggest a simple way to sort the nanotubes; among the next steps in the research will be to show experimentally that this can be done.”

In addition to the researchers already mentioned, co-authors for this paper include Christian Klinke at the Institute of Physical Chemistry at the University of Hamburg, and Marcel Lucas and Ismael Palaci at Georgia Tech.

“Understanding the basic mechanism of friction in carbon nanotubes will help us in designing devices with them in the future,” Riedo added. “We have shown an anisotropy in the friction coefficient of carbon nanotubes in the transverse and longitudinal directions, which has its origin in the soft lateral distortion of tubes when the tip-tube contact is moving in the transverse direction. Our findings could help in developing better strategies for chirality sorting, large-scale self-assembling of nanotubes on surfaces, and designing nanotube adhesives and nanotube-polymer composite materials.”

Research News & Publications Office
Georgia Institute of Technology
75 Fifth Street, N.W., Suite 100
Atlanta, Georgia 30308 USA

John Toon | Newswise Science News
Further information:
http://www.gatech.edu

More articles from Materials Sciences:

nachricht Move over, Superman! NIST method sees through concrete to detect early-stage corrosion
27.04.2017 | National Institute of Standards and Technology (NIST)

nachricht Control of molecular motion by metal-plated 3-D printed plastic pieces
27.04.2017 | Ecole Polytechnique Fédérale de Lausanne

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Fighting drug resistant tuberculosis – InfectoGnostics meets MYCO-NET² partners in Peru

28.04.2017 | Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

 
Latest News

Wireless power can drive tiny electronic devices in the GI tract

28.04.2017 | Medical Engineering

Ice cave in Transylvania yields window into region's past

28.04.2017 | Earth Sciences

Nose2Brain – Better Therapy for Multiple Sclerosis

28.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>