Laser Strums Silicon 'Nanoguitar'

Daniel S. Burgess

A team of scientists at Cornell University in Ithaca, N.Y., has employed a laser to pluck the strings on a microscopic guitar. The demonstration illustrates the potential of optically driven actuation and detection schemes for future nanoelectromechanical devices in applications such as chemical and biological sensing and signal processing.

Researchers have used a laser to play a nanoscale instrument modeled on the Gibson Flying V electric guitar. The work demonstrates the potential of optical actuation and detection schemes for nanodevices. Sound files of two "songs" played on the guitar are available at www.news.cornell.edu/releases/nov03/
nemsguitar.ws.html. ©Cornell University.

Lidija Sekaric, who fabricated the "nanoguitar" while a graduate student at the university and who now is a researcher at IBM's Thomas J. Watson Research Center in Yorktown Heights, N.Y., explained that the team had previously reported using the optical technique with other nanoelectromechanical systems, but that the new demonstration has practical, public outreach purposes. "People can relate to a simple concept," she said. "They may not be able to grasp the full explanation and the subtleties of an optical driving scheme, but they can understand mechanical vibrations, even on the nanoscale."

Recalling the design of a Gibson Flying V electric guitar, the new device features freestanding "strings" of silicon 150 to 200 nm across and 6 to 12 µm in length. To produce the instrument, Sekaric and her colleagues in the Craighead Research Group employed high-voltage electron-beam lithography and wet chemical etching at the Cornell Nanofabrication Facility. The nanoguitar is five times larger than one shaped like a Fender Stratocaster that the group constructed six years ago, which was approximately the size of a red blood cell.

The researchers "pluck" a string on the crystalline silicon guitar by illuminating it with 632.8-nm light from a HeNe laser, which causes the string to oscillate at a resonant frequency determined by its length. To "hear" the guitar, they combine the light reflected from the vibrating string with that from the substrate below to produce interference patterns at a photodetector. Electrically down-converting the response from a spectrum analyzer connected to the receiver yields an audible tone.

Sekaric explained that the phenomenon suggests applications in chemical or biological sensing, in which the presence of a target molecule on a functionalized resonant nanomechnical device would produce specific changes in the signal at the detector. Nanostructures also could replace the radio frequency oscillators in various electronic devices, including cellular phones, offering ultralow-power operation and the ability to tune the stable resonance of the devices by the application of a DC voltage.

Fundamental research into the materials used to fabricate nanostructures and into the physical phenomena that affect such nanoscale devices is ongoing at Cornell, and Sekaric believes that future avenues of inquiry will consider the integration of such systems with other components in ways that will maximize their advantages. Nevertheless, she said, even if such designs never match the complexity of microscale devices, the work will be worthwhile. "If [nanoelectromechanical systems] stay only a good lab tool for studying mesoscopic physics, the rest of nanoscience has much to benefit."