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Profs to Develop High-Speed Microscope Probe

Grant Will Help Measure Surfaces on Nanoscale

close-up of an early Atomic Force Microscope probe
This electron micrograph shows a close-up of an early Atomic Force Microscope probe developed by Asst. Profs. Joel Therrien and Daniel Schmidt. The probe measures approximately 70 micrometers long. (One micrometer is a millionth of a meter.)

By Edwin L. Aguirre

Asst. Prof. Joel Therrien of the Electrical and Computer Engineering Department and Asst. Prof. Daniel Schmidt of the Plastics Engineering Department have received a three-year $340,000 grant from the National Science Foundation to produce new, unconventional cantilevers for use in high-speed Atomic Force Microscopy (AFM).

The AFM is a type of scanning probe microscope capable of resolving surface features down to a fraction of a nanometer (billionth of a meter). It consists of a mechanical cantilever with a sharp tip, or probe, at its end that is used to “feel” the surface of a specimen.

“Much like the stylus of a record player senses the grooves in a vinyl record to produce sound, an AFM probe is a stylus that can sense the microscopic -- or even nanoscopic -- hills and valleys of a surface,” explains Therrien. “The key difference is that the tip of the AFM probe is far thinner than a human hair, and it can sense structures as tiny as individual molecules.”

However, high resolution comes with a price: speed.

“Current AFM probes are unable to rapidly scan over large areas,” he says. “To give an idea of how slow they are, it will take them a little over 2,200 years to scan a single 8½-by-11-inch sheet of paper! This is because the response of the probe -- determined by its shape and stiffness -- is simply not fast enough.”

The team’s research will look at ways to make AFM probes operate significantly faster. Therrien is the principal investigator for the project while Schmidt is the co-principal investigator.

“We are going to employ new techniques and materials so we can explore new AFM probes with shapes and properties that not only are highly appropriate for high-speed analysis but also difficult or impossible to make via conventional techniques,” says Therrien. “Such an increase in scan speed will allow AFMs to be used in nanomanufacturing processes, where they can fill a critical need in terms of product quality control.”

Therrien and Schmidt say the probe-making techniques they are developing can eventually be applied to a wider class of devices, known as Micro Electro-Mechanical Systems (MEMS), to enhance their functionality and durability. MEMS are commonly found in a wide range of consumer products, such as the air-bag sensors in cars and the position and pressure sensors in Nintendo Wii video game controllers and iPhones.

“Our process will result in tremendous cost savings,” says Therrien. “To give you an idea, in nanomanufacturing a typical probe costs anywhere from $15 to $100. It’s not unusual to go through a few probes a day if the use is very heavy, so picture spending a few hundred to a few thousand dollars a month if the facility is an industrial lab constantly doing analysis. In addition, the man-hours required are quite large due to the slow AFM scan speeds in use today. This is where our technology will help the most. In principle, we will be able to take a normal, five-minute scan and reduce that to a few seconds. The cost savings in analysis will potentially be quite large.”

Adds Schmidt: “With MEMS devices being used more and more these days, any way to make them with ‘better’ materials -- from the standpoint of durability and chemical stability, for instance -- and via a simpler, cheaper, cleaner process will be a pretty big deal. The combined performance advantages of higher scanning speed and the ability to make cantilevers using inexpensive molding techniques will be of substantial benefit to the nanomanufacturing, microelectronics and biomedical industries.”

Schmidt says that students involved in this project will be exposed to advanced MEMS fabrication techniques as well as to a unique range of expertise in the fields of electrical and plastics engineering, physics, chemistry and materials science.

“In particular, the development of new perspectives and creative problem-solving skills is integral to interdisciplinary research of this nature and will help foster student success,” he says.

Joel Therrien
Daniel Schmidt