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Topic Name: Scientists may be one step closer to understanding the Atomic Forces that cause Friction
Category: Nuclear
Research persons: Robert Carpick, Anirudha Sumant
Location: University of Pennsylvania, United States
Details
Scientists may be one step closer to understanding the atomic forces that cause friction, thanks to a recently published study by researchers from the
University of Pennsylvania, the University of Houston and the U.S.
Department of Energy's Argonne National
Laboratory.
The 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.
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.
To investigate the latter, 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. They have also observed same trend on a silicon substrate, which is structurally similar to that of diamond.
Previous attempts to make hydrogen-terminated diamond surfaces relied on the use of plasmas, which tended to etch the material.
"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. "The nanoscale roughening of the diamond surface from the ion bombardment during the hydrogen or deuterium termination process, even though it was at very low level, remained one of our principal concerns."
Sumant and his collaborators had looked at a number of other ways to try to avoid etching, even going to such lengths as to soak the films in olive oil before applying the hydrogen layers. However, no method had provided a smooth, defect-free hydrogen layer with good coverage that would avoid generating background noise, he said.
However, while performing work at the University of
Wisconsin-Madison, Sumant developed a system for depositing diamond thin films. The technique, called hot filament chemical vapor deposition, involves the heating of a tungsten filament (like those found in incandescent light bulbs) to over 2000 degrees Celsius.
If the diamond film is exposed to a flow of molecular hydrogen while sitting within a centimeter 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. Since this method does not require the use of plasma, there is no danger of ion-induced etching.
"We've proved that this is a gentler method of terminating a diamond surface," Sumant said.
Sumant said that he hopes to use the knowledge gained from the experiment to eventually discover 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, one of Sumant's primary research interests at Argonne's Center for Nanoscale Materials.
The paper, "Nanoscale Friction Varied by Isotopic Shifting of Surface Vibrational Frequencies," appears in the November 2 issue of Science.
The research was supported by the National Science Foundation, an NSF Graduate Research Fellowship, the Air Force Office of Scientific Research and the Department of Energy's Office of Science, Office of Basic Energy Sciences.
About The Center for Nanoscale Materials
The Center for Nanoscale Materials at Argonne National Laboratory is a joint partnership between the U.S. Department of Energy (DOE) and the State of Illinois, as part of DOE'S Nanoscale Science Research Center program. The CNM serves as a user-based center, providing tools and infrastructure for nanoscience and nanotechnology research. The CNM's mission includes supporting basic research and the development of advanced instrumentation that will help generate new scientific insights and create new materials with novel properties. The existence of the CNM, with its centralized facilities, controlled environments, technical support, and scientific staff, enabled researchers to excel and significantly extend their reach.
Argonne National Laboratory, a renowned R&D center, brings the world's brightest scientists and engineers together to find exciting and creative new solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America 's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.
About Researcher:
Robert Carpick
Associate Professor
University of Wisconsin
543 Engineering Research Building
1500 University Ave.
Madison, WI 53706
Contact Information
Office: 543 Engineering Research Bldg.
Labs: 202 Engineering Research Bldg.
and 70/71/75 Computer Aided Engineering Bldg.
U.S. Mail: 1500 Engineering Dr., Madison WI 53706
E-mail: carpick_at_engr.wisc.edu
Office Phone: (608) 263-4891
Fax: (608) 263-7451
CAE Lab Phone: (608) 263-1403
ERB 202 Lab Phone: (608) 890-0261
Student Office: (608) 263-1622
About Funds:
National Science Foundation
The National Science Foundation (NSF) is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health. With an annual budget of about $5.91 billion (fiscal year 2007), NSF funds approximately 20 percent of all federally supported basic research conducted by the United States' colleges and universities. In some fields, such as mathematics, computer science, economics and the social sciences, NSF is the major source of federal backing.
The NSF's director, its deputy director, and the 24 members of the National Science Board (NSB)[1] are appointed by the President of the United States, and confirmed by the United States Senate. The director and deputy director are responsible for administration, planning, budgeting and day-to-day operations of the foundation, while the NSB meets six times a year to establish its overall policies. The current NSF director is Dr. Arden L. Bement, Jr., and the current deputy director is Dr. Kathie L. Olsen.
Air Force Research Laboratory
The Air Force Research Laboratory (AFRL) is a scientific research organization operated by the United States Air Force dedicated to the development of warfighting
technologies. The AFRL headquarters is at Wright-Patterson Air Force Base, Ohio. The laboratory was created in October 1997 through the consolidation of four former Air Force laboratories and the Air Force Office of Scientific Research
(AFOSR).
Office of Science
The Office of Science is the single largest supporter of basic
research in the physical sciences in the United States, providing more than 40
percent of total funding for this vital area of national importance. It oversees
– and is the principal federal funding agency of – the Nation’s research
programs in high-energy physics, nuclear physics, and fusion energy sciences.
The Office of Science manages fundamental research programs in
basic energy sciences, biological and environmental sciences, and computational
science. In addition, the Office of Science is the Federal Government’s
largest single funder of materials and chemical sciences, and it supports unique
and vital parts of U.S. research in climate change, geophysics, genomics, life
sciences, and science education.
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