Ultra-sensitive nanodevice ‘wired’ by light

YALE (US)—In the push to detect motion on the atomic level—like the spin of a single electron—researchers from Yale University have proposed using silicon-based nanocantilevers that are smaller than the wavelength of light. The novel approach employs photonic principles, eliminating the need for electric transducers and expensive laser setups.

“The system we developed is the most sensitive available that works at room temperature. Previously this level of sensitivity could only be achieved at extreme low temperatures” says senior author Hong Tang, assistant professor of electrical and mechanical engineering in the Yale School of Engineering and Applied Sciences.

In nanoelectromechanical systems (NEMS), cantilevers are the most fundamental mechanical sensors. These tiny structures—fixed at one end and free at the other—act like nanoscale diving boards that “bend” when molecules “jump” on them and register a change that can be measured and calibrated.

An illustration of a nanocantilever multiplex array: electronmicrograph (top) and simulaton of wave flow (bottom).

Tang’s work suggests how NEMS can be improved by using integrated photonics to sense the cantilever motion. Their system can detect as little deflection in the nanocantilever sensors as 0.0001 Angstroms—one ten-thousandth the size of an atom.

To detect this tiny motion, the Yale team devised a photonic structure to guide the light wave through a cantilever. After exiting from the free end of the cantilever, the light tunnels through a nanometer gap and is collected on chip.

“Detecting the lightwave after this evanescent tunneling,” says Tang, “gives the unprecedented sensitivity.”

Tang’s work also details the construction of a sensor multiplex—a parallel array of 10 nanocantilevers integrated on a single photonic wire. Each cantilever is a different length, like a key on a xylophone, so when one is displaced it registers its own distinctive “tone.”

“A multiplex format lets us make more complex measurements of patterns simultaneously—like a tune with chords instead of single notes,” says postdoctoral fellow Mo Li, the lead author of the paper.

At the heart of this breakthrough is the novel way Tang’s group “wired” the sensors with light. Their technique is not limited by the bandwidth constraints of electrical methods or the diffraction limits of light sources.

“We don’t need a laser to operate these devices,” says study coauthor Wolfram Pernice. “Very cheap LEDs will suffice.”

Additionally, the LED light sources—like the million LED pixels that make up a laptop computer screen—can be scaled in size to integrate into a nanophotonicchip, an important feature for this application.

“This development reinforces the practicality of the new field of nanooptomechanics,” says Tang, “and points to a future of compact, robust, and scalable systems with high sensitivity that will find a wide range of future applications—from chemical and biological sensing to optical signal processing.”

Funding for the research was from a Yale Institute for Nanoscience and Quantum Engineering seed grant, a National Science Foundation career award, and the Alexander-von-Humboldt postdoctoral fellowship programs.

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