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  • Upgrading the precision of a nanopositioner

Photonics Spectra
Nov 2008
Rebecca C. Jernigan,

WEST LAFAYETTE, Ind. – The common laboratory nanopositioner moves very small items easily and precisely. Most nanomanipulators have a resolution of about 10 to 20 nm, resulting from thermally induced vibrations. Since single atoms are about a tenth of that resolution, this means that most nanopositioners have a positioning uncertainty of about 100 to 200 atoms in size.

But what if you are scanning for a particular surface atom? Jason Vaughn Clark, a professor of electrical and computer engineering and of mechanical engineering at Birck Nanotechnology Center at Purdue University in West Lafayette, Ind., has developed a monolithic comb drive with a resolution of about 0.1 nm that could have atomic-scale precision. The device is less than 1 mm in size, with the smallest feature measuring ~2 μm.


The monolithic comb drive could provide atomic-scale resolution. Image courtesy of Jason Vaughn Clark.

Clark said that the idea for the device developed from a lecture he gave on circuit analysis, during which he explained the concept of voltage division, describing how voltage changes continuously from one end of a resistive element to the other. “Knowing that MEMS [microelectromechanical systems] have both mechanical and electrical properties, I could immediately see how this concept could be a solution to the problem of extending the large deflection range of the comb drive from one to two degrees of freedom.” He credits the breakthrough to his experience in both electrical and mechanical engineering, which enabled him to approach the problem from multiple angles simultaneously.

Compared with traditional atomic force microscopes, the monolithic comb drive offers a greater range of motion, smaller uncertainty and electrostatically variable stiffness, and it does not require a bulky laser or piezoelectric stage. The device operates in modes including DC, tunable resonance, and various Lissajou patterns. Several monolithic drives may be used for multiplexed applications.

The comb drive also incorporates Clark’s electromicrometrology (EMM) technology, which uses the coupling between the microelectronics and -mechanics to electronically measure the mechanical properties of MEMS; i.e., it self-calibrates its comb drive force and displacement using EMM-based traceable measurements. Clark reduces the thermally induced vibrations using electrostatic force feedback.

Tools other than probe tips could be attached to the motorized positioner, including optical lenses, LEDs, biological molecules, and other materials and active devices. Clark expects that future research also will investigate the device’s potential for high-density data storage.

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