According to a December 15 news release from the University of Basel, an international team of scientists has observed a considerable energy loss brought about by frictional effects around charge density waves, and may have practical applications to controlling nanoscale friction.
The research results appear online in Nature Materials, in an article entitled, “Giant frictional dissipation peaks and charge-density-wave slips at the NbSe2 surface.”
Although often viewed as an undesirable phenomenon due to its wearing effects on materials, too little friction can be a disadvantage. Therefore, a thorough understanding of frictional effects is essential, especially with respect to the field of nanotechnology.
In the 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 – researchers helped to give an enhanced understanding of how friction works in microscopic dimensions.
In the experiment led by Dr. Ernst Meyer, Professor of Experimental Physics at the University of Basel, the team vibrated the nanometer-sized tip of an atomic force microscope over the surface of a layered structure of niobium and selenium atoms. The team selected this combination because of its inimitable electronic properties, and in particular, the charge-density waves formed at extremely low temperatures. The electrons are no longer evenly distributed as in a metal; rather, they form areas where the electron density alternates between a high and low range.
The researchers observed high energy losses in the surrounding area of these charge density waves between the surface and the tip of the atomic force microscope, even at moderately 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,” said Meyer.
The team observed this energy loss only at temperatures below -203° C, and given that charge density waves do not occur at higher temperatures, the researchers interpreted this as substantiation that frictional forces between the probe tip and charge density waves are the cause of the energy loss.
The theoretical model illustrates that the high energy loss results from a succession of local phase shifts in the charge density waves. The researchers say that this newly discovered phenomenon may be of practical significance in the field of nanotechnology, particularly as the frictional effect can be adjusted as a function of distance and voltage.