OSU's Bharat Bhushan leads the research team studying lubrication of microdevices.           By Jo McCulty

Researchers pioneer lubrication of microdevices

Motor oil keeps car engines running smoothly, but what will grease tiny motors for the high-tech microdevices of the future? Ohio State researchers may have the answer.

Until now, scientists couldn't accurately measure the friction that plagues miniature motors, pumps and gears -- mechanisms that could one day move inside microscopic medical implants in the body, for example. Such devices, called microelectromechanical systems (MEMS), contain parts so small they are measured in nanometers, or billionths of a meter. Without knowing the friction present in these devices, scientists can't design the right micro-lubricants.

Led by Bharat Bhushan, Ohio Eminent Scholar and Howard D. Winbigler Professor of mechanical engineering, researchers here have pioneered the first direct method for measuring the friction of these tiny parts as they rub together -- with results twice as accurate as any previous indirect method could provide.

They also found a way to bake lubricant onto the surface of microdevices at temperatures as high as 150 degrees Celsius to oil the tiny moving parts.

"Before we can design microdevices that actually work, we must understand how friction, wear and other powerful forces operate on a tiny scale," Bhushan said.

Bhushan's cohorts on these projects include Ohio State mechanical engineering doctoral students Sriram Sundararajan and Huiwen Liu, and Wolfgang Eck and Volker Stadler, both physical chemists from the University of Heidelberg, Germany.

Normally, Bhushan's laboratory studies the texture of microthin coatings on computer hard disks and data tapes -- items for which friction, wear and lubrication dominate performance.

In 1999, scientists at the Laboratory for Analysis and Architecture of Systems in Toulouse, France, asked Bhushan to help lubricate a new silicon micromotor they were developing for biomedical applications. Friction was preventing the motor's tiny eight-arm rotor, a kind of miniature propeller, from spinning around its central hub.

For this work, Bhushan and his colleagues found a new application for a commercially available tool already sitting in their laboratory: an atomic force microscope (AFM), which records the shape of an object by dragging a tiny needle over its surface.

A typical AFM needle has a radius of only 50 to 100 nanometers -- a fraction of the width of a human hair. To the needle's sensitive touch, bumpy landscapes only a few atoms thick feel as expansive as mountains and valleys.

The AFM needle detected bumps on the surface of the rotor and the surrounding casing. The bumps, which ranged in size from 11 nanometers to 100 nanometers, were a normal result of the chemical process that shapes the tiny parts out of silicon, Bhushan said. Bumps on the rotor were rubbing against bumps on the casing, causing friction.

The researchers were also able to gauge the amount of friction inside the motor by measuring the force required for the needle to nudge the central rotor into motion. Other researchers have tried calculating friction from indirect measurements, such as the loss of electric current flowing over a MEMS structure, but this is the first time anyone has directly measured the frictional forces at play inside a working microdevice.

To grease the motor, Bhushan first tried flooding the device with Z-DOL, a commercially available synthetic lubricant that costs nearly $1,000 per pound. Bhushan had already purchased a supply of the material for his hard disk research.

Liquid Z-DOL only gummed up the motor, however, so the researchers tried something different -- they baked a 1-nanometer-thick coating of lubricant onto the surfaces of all the moving parts. At 400 degrees Celsius, the Z-DOL solidified into a smooth layer that allowed the components to move more freely. When the researchers again nudged the rotor into motion, they found that the solid Z-DOL coating reduced friction by half.

The Heidelberg researchers had already developed a thin coating of diamond-like carbon molecules to lubricate MEMS, and they were wondering whether a more complex -- and more expensive -- arrangement of molecules would result in a better coating. The arrangement is referred to as "cross-linked," since the atoms that form the molecules are linked together with strong bonds.

The Ohio State researchers found that the fancier coating wasn't better. By dragging the AFM needle across coated samples of silicon, they found that the simpler coating reduced friction twice as well as the cross-linked coating.

Bhushan's latest project involves measuring the amount of force tiny construction beams of silicon can withstand before they break. Such beams might support complex MEMS structures in the future.

This research is supported by NSF's Division of Electrical and Communications Systems.

Elder care can hurt work productivity, well-being

Employees who are caregivers for elder dependents report lower work and family performance and less well-being than those employees whose dependents are children, a new study has found. The worst situation was for employees who were caregivers for an elder dependent, took care of the adult at home, and who felt they couldn't share their concerns with co-workers or family, the findings showed. "Elder care has more negative impacts on workers than does child care, particularly for those who are the primary caretakers for an older adult," said Raymond Noe, co-author of the study and professor of management and human resources.

The study also showed that work climate and family climate both played a strong role in how well employees coped with their caregiving responsibilities. Specifically, workers reported higher levels of well-being and performance when they felt they could share their concerns and problems with both their co-workers and family members. "When employees feel they can discuss their caregiving concerns at work, it seems to relieve their stress and make them more effective on the job," Noe said.

www.acs.ohio-state.edu/units/research/archive/eldcare.htm