Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Of Friction and "The Da Vinci Code"

26.08.2005


Atoms are spaced periodically in one direction on a surface perpendicular to a quasicrystal’s 10-fold rotational axis. But at right angles they are spaced in a Fibonacci sequence, in which the ratio of short to long spacings is an irrational number like that of the Golden Mean. Friction is eight times greater in the periodic direction than in the aperiodic direction.


The Da Vinci Code, the best selling novel and soon-to-be-blockbuster film, may also be linked some day to the solving of a scientific mystery as old as Leonardo Da Vinci himself — friction. A collaboration of scientists from Lawrence Berkeley National Laboratory (Berkeley Lab) and the Ames Laboratory at Iowa State University have used Da Vinci’s principles of friction and the geometric oddities known as quasicrystals to open a new pathway towards a better understanding of friction at the atomic level.

In a paper published in the August 26 issue of the journal Science, a research collaboration led by Miquel Salmeron, a physicist with Berkeley Lab’s Materials Sciences Division, reports on the first study to measure the frictional effects of periodicity in a crystalline lattice. Using a combined Atomic Force Microscope (AFM) and Scanning Tunneling Microscope (STM), the researchers showed that friction along the surface of a quasicrystal in the direction of a periodic geometric configuration is about eight times greater than in the direction where the geometric configuration is aperiodic (without regularity).

Geometric periodicity was confirmed via rows of atoms that formed a Fibonacci sequence, a numerical pattern often observed in quasicrystals — and which was one of the clues to solving the Da Vinci code in the novel by Dan Brown.



"That we can get such a large difference in frictional force just by scratching the surface of a material in a different direction was a major surprise," says Salmeron. "Our results reveal a strong connection between interface atomic structure and the mechanisms by which frictional energy is dissipated."

Collaborating on the Science paper with Salmeron were Berkeley Lab’s Jeong Young Park and Frank Ogletree, and Raquel A. Ribeiro, Paul Canfield, Cynthia Jenks, and Patricia Thiel of the Ames Laboratory at Iowa State University.

The principles of friction, as described by Leonardo Da Vinci some 500 years ago, work fine for macroscale mechanics like keeping the moving parts in the engine of your car lubricated with oil. However, as mechanical devices shrink to nanosized scales (measured in billionths of a meter), a far better understanding of friction at the molecular level becomes crucial.

"Friction is difficult to characterize because there are so many different factors involved," says Park. "Scientific studies of frictional force were in limbo for such a long period of time because we simply didn’t have the tools we needed to study it at the atomic level."

The key tool deployed in this study was the combined AFM and STM. Both microscopes utilize a probe that tapers to a single atom at its tip. This tip is scanned across the surface of the sample to be studied, revealing atomic-level information. In the AFM mode, the tip actually touches the sample’s surface atoms like a phonograph needle making contact with a record — but with so little force that none of the scanned atoms are dislodged. In the STM mode, the tip never quite touches the sample atoms but is brought close enough that electrons begin to "tunnel" across the gap, generating an electrical current.

"We first used the STM mode to produce topographical images of our quasicrystals and ascertain which direction was periodic and which was aperiodic," says Salmeron. "We then switched to the AFM mode and gently scratched the crystals in each direction to measure and compare the frictional force."

At the atomic level, when two surfaces come in contact, the chemical bonds and clouds of electrons in their respective atoms create frictional force and cause energy to be dissipated. From Da Vinci’s studies it has long been known that friction is greater between surfaces of identical crystallographic orientation than between surfaces of differing orientation, because, says Salmeron, "commensurability leads to intimate interlocking and high friction."

However, some recent studies have reported higher frictional differences, or anisotropy, for incommensurate crystal surfaces when there were periodicity differences.

To measure the frictional effects due to periodicity alone, and not to other factors such as chemical differences, Salmeron, Park, and Ogletree worked with decagonal quasicrystals of an aluminum-nickel-cobalt alloy (Al-Ni-Co) prepared by their collaborators at Ames Laboratory, renowned experts on the surfaces of quasicrystalline materials.

Stacked planes of Al-Ni-Co crystals exhibit both ten-fold and two-fold rotational symmetry. By cutting a single Al‑Ni-Co quasicrystal parallel to its ten-fold axis, the researchers were able to produce a two-dimensional surface with one periodic axis and one aperiodic axis, separated by 90 degrees.

"Strong friction anisotropy was observed when the AFM tip slid along the two directions: high friction along the periodic direction, and low friction along the aperiodic direction," says Park. "We believe the source of this friction has both an electronic and a phononic contribution." Phonons are vibrations in a crystal lattice, like atomic sound waves.

The authors of the Science paper said that new theoretical models are needed to determine whether electrons or phonons are the dominant contributors to the frictional anisotropy they report.

"Our results finally give theorists a chance to be proactive in their modeling of friction," Salmeron says.

"High Frictional Anisotropy of Periodic and Aperiodic Directions on a Quasicrystal Surface," by Jeong Young Park, D. F. Ogletree, M. Salmeron, R. A. Ribeiro, P. C. Canfield, C. J. Jenks, and P. A. Thiel appears in the August 26, 2005 issue of Science magazine . For more information visit the Salmeron Group website, http://stm.lbl.gov/, and Jeong Park’s webpage, http://stm.lbl.gov/people/Jeong.htm.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Visit our Website at http://www.lbl.gov/.

Lynn Yarris | EurekAlert!
Further information:
http://www.lbl.gov

More articles from Physics and Astronomy:

nachricht Squeezing light at the nanoscale
18.06.2018 | Harvard John A. Paulson School of Engineering and Applied Sciences

nachricht The Fraunhofer IAF is a »Landmark in the Land of Ideas«
15.06.2018 | Fraunhofer-Institut für Angewandte Festkörperphysik IAF

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: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...

Im Focus: Photoexcited graphene puzzle solved

A boost for graphene-based light detectors

Light detection and control lies at the heart of many modern device applications, such as smartphone cameras. Using graphene as a light-sensitive material for...

Im Focus: Water is not the same as water

Water molecules exist in two different forms with almost identical physical properties. For the first time, researchers have succeeded in separating the two forms to show that they can exhibit different chemical reactivities. These results were reported by researchers from the University of Basel and their colleagues in Hamburg in the scientific journal Nature Communications.

From a chemical perspective, water is a molecule in which a single oxygen atom is linked to two hydrogen atoms. It is less well known that water exists in two...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Munich conference on asteroid detection, tracking and defense

13.06.2018 | Event News

2nd International Baltic Earth Conference in Denmark: “The Baltic Sea region in Transition”

08.06.2018 | Event News

ISEKI_Food 2018: Conference with Holistic View of Food Production

05.06.2018 | Event News

 
Latest News

Novel method for investigating pore geometry in rocks

18.06.2018 | Earth Sciences

Diamond watch components

18.06.2018 | Process Engineering

New type of photosynthesis discovered

18.06.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>