Microscopic stringed instrument is plucked to study physics of vibrating systems

An electron microscope image of a nanoharp, used to study microscopic resonances. The "strings" are rods 50 nanometers thick.Dustin Carr/Cornell Nanofabrication Facility

By Bill Steele

From the folks who brought you the world's smallest guitar, now meet the nanoharp.

But while the microsopic guitar made by Cornell researchers two years ago was just a whimsical demonstration of new nanofabrication technology, this new "stringed instrument" plays the real music of science, serving as a platform to study the physics of very small vibrating systems.

"This is another use for our new ability to make microscopic mechanical systems," said Harold Craighead, Cornell professor of applied and engineering physics, who supervised the research. "By making things very small, you bring out properties that aren't evident in larger materials. We can combine this information with other types of measurements made by researchers in materials science to help understand how materials behave."

The new device, carved out of a single crystal of silicon with advanced versions of the methods used to build tiny electronic circuits, consists of two end pieces, one square and one triangular, with several "strings" of varying lengths stretching between them. The strings are actually silicon rods 50 nanometers (nm) in diameter, ranging from about 1,000 to 8,000 nm long. A nanometer is one billionth of a meter, making each string about 150 atoms thick. The entire device is about the size of a red blood cell.

Dustin Carr, a research support specialist at the Cornell Nanofabrication Facility and a graduate researcher in the Cornell physics department, described the tiny device at the American Physical Society centennial meeting in Atlanta. Carr and Craighead work with postdoctoral associate Stephane Evoy, graduate student Lidija Sekaric and Jeevak Parpia, Cornell professor of physics.

They built the device using electron-beam lithography and what's called "released silicon" technology, which refers to nanostructures that have been undercut to be freely suspended in space. The researchers are studying resonance effects in these microscopic systems. In the macroscopic world, plucking a string tuned to middle C, for example,will cause a nearby string tuned an octave higher to vibrate, responding to energy transmitted through the air. Nanodevices operate in a vacuum, but their vibrations can be transmitted through the silicon base.