Probing the mysteries of nanoscale wear
Mechanical Engineering Assistant Professor Kevin Turner is working with Illinois-based Advanced Diamond Technologies (ADT) and collaborators at the University of Pennsylvania to design and fabricate high-performance, wear-resistant diamond probes for atomic-force microscopy, or AFM. AFM is a widely used research technique for measuring the nanoscale topography of surfaces. A sharp probe with a point that has a radius of 10 to 50 nanometers is attached to a cantilever beam and scanned across a surface. The probe follows the topography of the surface like a phonograph needle on a record, and a laser is reflected off the cantilever to create an image of the surface with nanoscale resolution.
Probe durability is crucial as AFM expands to industrial and manufacturing settings. ADT, which spun out of Argonne National Lab to commercialize a new type of ultrananocrystalline diamond material, developed a proposal with Turner and then-Engineering Physics Associate Professor Rob Carpick, now at the University of Pennsylvania. With a 2007 Small Business Technology Transfer grant from the National Science Foundation, the team created a new AFM diamond probe that performs better than almost any other type of probe and is by far more durable and wear-resistant than traditional probes made from silicon-based materials. ADT now sells a commercial version of the probe, for which the team received a 2009 R&D 100 Award.
“This project has been great as it not only led to a commercial AFM probe, but also required fundamental research into wear at the nanoscale,” says Turner. “The small-scale contact between AFM probes and samples is a unique platform to investigate the more fundamental mechanisms of wear.”
The original project examined probe performance in the contact mode of AFM, where the tip maintains constant contact with the surface during a scan. Turner’s team now is studying wear during the tapping mode of AFM, where a tip “taps” the surface billions of times to create an image. The researchers are also working to study better approaches to fabricate probes with sharper tips for imaging small-scale features.