Bell Labs Develops 'Nanograss'

MURRAY HILL, N.J., March 16 -- Scientists at Bell Labs, the research and development arm of Lucent Technologies, have discovered a new method to control the behavior of tiny liquid droplets by applying electrical charges to specially engineered silicon surfaces that resemble blades of grass. The new technique of manipulating fluids has many potential applications, including thermal cooling of integrated circuits for powerful computers, novel photonic components for optical communications and small, low-cost "lab-on-a-chip" sensor modules.
David Bishop, vice president of nanotechnology at Bell Labs and president of the New Jersey Nanotechnology Consortium, said the techniques resulting from this research might be applied to fields from optical networking and advanced micro batteries to self-cleaning windshields and more streamlined boat hulls.
The advance resulted from a technique the team developed to process silicon surfaces to produce "nanograss" -- the surfaces resemble a lawn of evenly cut grass, with individual nanometer-size "blades."
This new capability lets liquids interact with surfaces in a novel way, providing a way to precisely control their effects. In everyday experience, fluids tend to wet surfaces and stick to them. For example, a raindrop sticks to a car's windshield; when water is spilled, it splatters every which way. Blades of the nanograss are so small, however, that liquid droplets sit on top and can be easily maneuvered.
Krupenkin and his team coated the nanograss with a nonstick, water-repellent material, and when the droplets are put on the surface, they can move about without wetting it. By applying a small voltage, however, the team could tailor the behavior of droplets, making them sink in and wet the surface as directed. The droplets also respond to a change in temperature, allowing for thermal cooling applications.
Such behavior may be harnessed to cool computer chips, Krupenkin said. "A droplet could be sent to a hot spot on the chip, where it would sink in and absorb the heat, and then go on its way, avoiding the expense and inefficiency of applying a coolant or a heat sink to an entire chip."
Another application for this technique may be in optical networking. For example, moving a droplet of fluid into a nanograss surface can alter the physical properties of the transmitting medium through which light signals are sent, and this may lead to better methods for optical switching. Novel optical components, such as filters, could be created by moving the fluid into and out of nanograss areas, Krupenkin said.
Details of the technique are being published in the May 11 issue of the American Chemical Society's journal, Langmuir.

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