Micro-optomechanical systems (MOMS) made using a CMOS compatible, direct patterning technique could help reduce the cost of space exploration say scientists from the University of Delaware, US. The team has used a combination of lithography, deposition and etching to create an array of lightweight, optically activated cantilevers from a sheet of carbon nanotube "paper" (Appl. Phys. Lett. 88 253107).

"Today's space-based telescopes use pneumatic or piezo actuation mechanisms to position the mirrors, which can be heavy and expensive to send into space," Balaji Panchapakesan of Delaware's Electrical and Computer Engineering department told Optics.org. "In contrast, lightweight optical actuators can be powered using compact semiconductor lasers."

Unfortunately, batch processing the actuator's optically sensitive carbon nanotube film into a fully formed device has proved to be a stumbling block for MOMS developers and presented the team with its biggest challenge.

"Direct patterning is only possible if there is zero stress in the nanotube film," explained Panchapakesan. "We firstly suspend and separate the nanotubes in solution and then create a film using vacuum filtration." Dubbed nanotube "paper", the 130 nm thick film can be bonded to silicon or oxide wafers by annealing at 75 °C and then patterned directly using photolithography.

The scientists found that they could successfully transfer high resolution features on to the carbon nanotube coated wafer to create cantilevers 300 µm long x 30 µm wide x 7 µm thick. By focusing 170 mW of laser emission (808 nm) at the base of the cantilever, the team was able to displace the tip by 23 µm, which Panchapakesan says compares well with electrostatic actuators.

According to the researchers, field emission displays and biomedical devices could also benefit from the work. They believe that it should be possible to make the cantilevers wavelength selective by refining the structure and physical properties of the carbon nanotubes. The team has a provisional patent for its technique and is now developing a series of micro- and nano-robotic mechanisms based on the actuator arrays.