Nanoscale friction: High energy losses in the vicinity of charge density waves

December 15, 2013
An oscillating Atomic Force Microscope tip is shown in proximity to the Charge Density Wave (CDW) on NbSe2 surface. The yellow and blue spheres are the Selenium and Niobium atoms forming the lattice. A single CDW phase slip process is visible onto NbSe2 surface in the vicinity of the tip. Credit: University of Basel

In collaboration with the University of Basel, an international team of researchers has observed a strong energy loss caused by frictional effects in the vicinity of charge density waves. This may have practical significance in the control of nanoscale friction. The results have been published in the scientific journal Nature Materials.

Friction is often seen as an adverse phenomenon that leads to wear and causes . Conversely, however, too little friction can be a disadvantage as well – for example, running on an icy surface or driving on a wet road.

An understanding of frictional effects is therefore of great importance – particularly in the field of nanotechnology, where friction has to be controlled at a nanoscale. A recent study conducted by researchers from the University of Basel, the University of Warwick, the CNR Institute SPIN in Genoa and the International Centre for Theoretical Physics (ICTP) in Trieste has helped to give a better understanding of how friction works in microscopic dimensions.

In the experiment led by Prof. Dr. Ernst Meyer, Professor of Experimental Physics at the University of Basel, the team vibrated the nanometer-sized tip of an atomic force microscope above the surface of a layered structure of niobium and selenium atoms. They selected this combination due to its unique electronic properties, and in particular the charge- formed at extremely low temperatures. The electrons are no longer evenly distributed as in a metal, but instead form areas where the electron density fluctuates between a high and low range.

Energy losses in the vicinity of charge density waves

The researchers registered very high energy losses in the vicinity of these charge density waves between the surface and the tip of the , even at relatively large distances of several atomic diameters. "The energy drop was so great, it was as if the tip had suddenly been caught in a viscous fluid," says Meyer.

Graphical rendering of the “system” studied by Pellegrini, Santoro, Tosatti. Credit: SISSA)

The team observed this energy loss only at temperatures below 70° Kelvin (-203° C). Since charge density waves do not occur at higher temperatures, it interpreted this as evidence that frictional forces between the probe tip and charge density waves are the cause of the energy loss.

The theoretical model shows that the high energy loss results from a series of local phase shifts in the charge density waves. This newly discovered phenomenon may be of practical significance in the field of nanotechnology, particularly as the frictional effect can be modulated as a function of distance and voltage.

Explore further: Finnish researchers find explanation for sliding friction

More information: Markus Langer, Marcin Kisiel, Rémy Pawlak, Franco Pellegrini, Giuseppe E. Santoro, Renato Buzio, Andrea Gerbi, Geetha Balakrishnan, Alexis Baratoff, Erio Tosatti and Ernst Meyer, Giant frictional dissipation peaks and charge-density-wave slips at the NbSe2 surface, Nature Materials, published online, December 15, 2013. DOI: 10.1038/NMAT3836

Related Stories

Finnish researchers find explanation for sliding friction

May 29, 2012

Friction is a key phenomenon in applied physics, whose origin has been studied for centuries. Until now, it has been understood that mechanical wear-resistance and fluid lubrication affect friction, but the fundamental origin ...

At the nanoscale, graphite can turn friction upside down

October 17, 2012

(—If you ease up on a pencil, does it slide more easily? Sure. But maybe not if the tip is sharpened down to nanoscale dimensions. A team of researchers at the National Institute of Standards and Technology (NIST) ...

Physicists discover a new kind of friction in the nanoworld

May 15, 2013

Whether in vehicle transmissions, hip replacements, or tiny sensors for triggering airbags: The respective components must slide against each other with minimum friction to prevent loss of energy and material wear. Investigating ...

Controlling friction by tuning van der Waals forces

July 19, 2013

For a car to accelerate there has to be friction between the tire and the surface of the road. The amount of friction generated depends on numerous factors, including the minute intermolecular forces acting between the two ...

Recommended for you

Counting down to the new ampere

August 29, 2016

After it's all over, your lights will be just as bright, and your refrigerator just as cold. But very soon the ampere—the SI base unit of electrical current—will take on an entirely new identity, and NIST scientists are ...

Measuring tiny forces with light

August 25, 2016

Photons are bizarre: They have no mass, but they do have momentum. And that allows researchers to do counterintuitive things with photons, such as using light to push matter around.

Spherical tokamak as model for next steps in fusion energy

August 24, 2016

Among the top puzzles in the development of fusion energy is the best shape for the magnetic facility—or "bottle"—that will provide the next steps in the development of fusion reactors. Leading candidates include spherical ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.