|
Sci Tech
Heavier hydrogen on the atomic scale reduces friction
New research, led by Robert Carpick of the University of Pennsylvania, found a significant difference in friction exhibited by diamond surfaces that had been coated with different isotopes of hydrogen and then rubbed against a small carbon-coated tip.
It is hoped that the knowledge gained from the experiment will eventually lead to a way to manipulate the friction of surfaces on the atomic level.
Such a result would prove immensely valuable to the development of nanoelectromechanical systems, or NEMS, based on diamonds.
Previous attempts to make hydrogen-terminated diamond surfaces relied on the use of plasmas, which tended to etch the material.
Electronic interactions
Scientists lack a comprehensive model of friction on the nanoscale and only generally grasp its atomic-level causes, which range from local chemical reactions to electronic interactions to phononic, or vibrational, resonances.
Scientists may now be one step closer to understanding the atomic forces that cause friction, thanks to the recently published study by researchers from the University of Pennsylvania, and University of Houston and the U.S. Department of Energy’s Argonne National Laboratory.
Argonne scientist Anirudha Sumant and his colleagues used single-crystal diamond surfaces coated with layers of either atomic hydrogen or deuterium, a hydrogen atom with an extra neutron.
The deuterium-terminated diamonds had lower friction forces because of their lower vibrational frequencies, an observation that Sumant attributed to that isotope’s larger mass.
Silicon substrate
They have also observed the same trend on a silicon substrate, which is structurally similar to that of diamond.
“When you’re looking at such a small isotopic effect, an objectively tiny change in the mass, you have to be absolutely sure that there are no other complicating effects caused by chemical or electronic interferences or by small topographic variations,” Sumant said.
Principal concern
“The nanoscale roughening of the diamond surface from the ion bombardment remained one of our principal concerns.”
While performing work at the University of Wisconsin-Madison, Sumant developed a system for depositing diamond thin films.
The technique, called hot filament chemical vapour deposition, involves the heating of a tungsten filament to over 2,000 degrees Celsius, according to an Argonne National Laboratory press release.
Molecular hydrogen
If the diamond film is exposed to a flow of molecular hydrogen while sitting within a centimetre of the hot filament, the heat will cause the molecular hydrogen to break down into atomic hydrogen, which will react with the film’s surface to create a perfectly smooth layer.
“We’ve proved that this is a gentler method of terminating a diamond surface,” Sumant said. — Our Bureau
Printer friendly
page
Send this article to Friends by
E-Mail
Sci Tech
|
