Nanotechnologists from Penn collaborate to form near-frictionless diamond material

February 25, 2010

PHILADELPHIA -- Researchers at the University of Pennsylvania, the University of Wisconsin-Madison and IBM Research-Zürich have fabricated an ultra sharp, diamond-like carbon tip possessing such high strength that it is 3,000 times more wear-resistant at the nanoscale than silicon.

The end result is a diamond-like carbon material mass-produced at the nanoscale that doesn't wear. The new nano-sized tip, researchers say, wears away at the rate of one atom per micrometer of sliding on a substrate of silicon dioxide, much lower than that for a silicon oxide tip which represents the current state-of-the-art. Consisting of carbon, hydrogen, silicon and oxygen molded into the shape of a nano-sized tip and integrated on the end of a silicon microcantilever for use in atomic force microscopy, the material has technological implications for atomic imaging, probe-based data storage and as emerging applications such as nanolithography, nanometrology and nanomanufacturing.

The importance of the discovery lies not just in its size and resistance to wear but also in the hard substrate against which it was shown to perform well when in sliding contact: silicon dioxide. Because silicon -- used in almost all integrated circuit devices -- oxidizes in atmosphere forming a thin layer of its oxide, this system is the most relevant for nanolithography, nanometrology and nanomanufacturing applications.

Probe-based technologies are expected to play a dominant role in many such technologies; however, poor wear performance of many materials when slid against silicon oxide, including silicon oxide itself, has severely limited usefulness to the laboratory.

Researchers built the material from the ground up, rather than coating a nanoscale tip with wear-resistant materials. The collaboration used a molding technique to fabricate monolithic tips on standard silicon microcantilevers. A bulk processing technique that has the potential to scale up for commercial manufacturing is available.

Robert Carpick, professor in the Department of Mechanical Engineering and Applied Mechanics at Penn, and his research group had previously shown that carbon-based thin films, including diamond-like carbon, had low friction and wear at the nanoscale; however, it has been difficult to fabricate nanoscale structures made out of diamond-like carbon until now.

Understanding friction and wear at the nanoscale is important for many applications that involve nanoscale components sliding on a surface.

"It is not clear that materials that are wear-resistant at the macroscale exhibit the same property at the nanoscale," lead author Harish Bhaskaran, who was a postdoctoral research at IBM during the study, said.

Defects, cracks and other phenomena that influence material strength and wear at macroscopic scales are less important at the nanoscale, which is why nanowires can, for example, show higher strengths than bulk samples.
The study, published in the current edition of the journal Nature Nanotechnology, was conducted collaboratively by Carpick and postdoctoral researcher Papot Jaroenapibal of the Department of Mechanical Engineering and Applied Mechanics in Penn's School of Engineering and Applied Science; Bhaskaran, Bernd Gotsmann, Abu Sebastian, Ute Drechsler, Mark A. Lantz and Michel Despont of IBM Research-Zürich; and Yun Chen and Kumar Sridharan of the University of Wisconsin. Jaroenapibal currently works at Khon Kaen University in Thailand, and Bhaskaran currently works at Yale University.

Research was funded by a European Commission grant and the Nano/Bio Interface Center of the University of Pennsylvania through the National Science Foundation.

University of Pennsylvania

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