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  5. Inspired by steel, nano-manufacturing gets wear-resistant carbide tip

Inspired by steel, nano-manufacturing gets wear-resistant carbide tip

University of Wisconsin-Madison researchers with scientists at the University of Pennsylvania, and IBM Research - Zürich have fabricated an extremely sharp, nanoscale tip made from silicon carbide that is thousands of times more wear-resistant than previous designs.

The new tip represents an important step toward creating new applications in nano-manufacturing, including biosensors and data storage. More specifically, scientists hope that the new tip can be used in sensors to manage glucose levels in diabetic patients or monitoring pollution levels in water.

Using plasma-based ion implantation, UW-Madison Distinguished Research Professor Kumar Sridharan and colleagues exposed surfaces of nanoscale silicon tips to carbon ions and then heat-treated them for short durations at more than 2,000 degrees Fahrenheit to form a super-strong silicon-carbide layer.

“It was very challenging,” says Sridharan. “When dealing with a plasma, it’s like trying to control lightning. We need to pull the ions from the plasma cloud and direct them to the lightning rod or tip without blunting the tip. If you strike the tip and blunt it, the whole thing is gone. We have to control the environment so that these tips can be made reliably en masse and we’ve achieved that.”

Although silicon carbide has long been known as an ideal candidate material for a tip, the unique process made it possible to harden the surface while maintaining the original shape and ensuring strong adhesion between the hardened surface of the tip and the underlying material­­–similar to how steel is treated to make it harder.

The new tip wears away at the rate of less than one atom per millimeter of sliding on a substrate of silicon dioxide, which represents 10,000 times further sliding distance than conventional silicon tips for the same wear volume, and more than 100-fold higher than that of silicon oxide-doped diamond-like carbon tips developed by the same collaboration last year.

Integrated on the end of a silicon microcantilever for use in atomic force microscopy, the development’s importance lies not just in its ability to maintain sharpness and wear resistance, but also in its endurance when sliding against a hard substrate, such as silicon dioxide. Because silicon—used in almost all integrated circuit devices—oxidizes in the atmosphere forming a thin layer of its oxide, this system is among the most relevant for emerging applications in nanolithography, thermomechanical data storage, biosensors, and nanomanufacturing applications. In addition, mechanical memory applications with very high density could be developed as an alternative to existing nonvolatile memory technologies.

This achievement may help make nanomanufacturing both practical and affordable, Sridharan says. The next step for the scientists is to begin testing the new tip for use in nanomanufacturing applications.

Collaborators on the study, published in the current issue of the peer-reviewed journal Advanced Functional Materials (INSERT DOI), include Mark A. Lantz and Bernd Gotsmann, IBM Research - Zurich; Tevis D. B. Jacobs, Papot Jaroenapibal and Robert W. Carpick, University of Pennsylvania; and Sean D. O’Connor and Sridharan, UW-Madison.

Jim Beal
2/16/2012