David Kirkpatrick

November 18, 2009

Moving nanoscale objects with light

This finding is important toward creating working nanoscale machines.

The release:

Nov. 16, 2009

Small optical force can budge nanoscale objects

By Bill Steele

dual rings
Scanning electron micrograph of two thin, flat rings of silicon nitride, each 190 nanometers thick and mounted a millionth of a meter apart. Light is fed into the ring resonators from the straight waveguide at the right. Under the right conditions optical forces between the two rings are enough to bend the thin spokes and pull the rings toward one another, changing their resonances enough to act as an optical switch.
Image from Cornell Nanophotonics Group

With a bit of leverage, Cornell researchers have used a very tiny beam of light with as little as 1 milliwatt of power to move a silicon structure up to 12 nanometers. That’s enough to completely switch the optical properties of the structure from opaque to transparent, they reported.

The technology could have applications in the design of micro-electromechanical systems (MEMS) — nanoscale devices with moving parts — and micro-optomechanical systems (MOMS) which combine moving parts with photonic circuits, said Michal Lipson, associate professor of electrical and computer engineering.

The research by postdoctoral researcher Gustavo Wiederhecker, Long Chen, Ph.D. ’09, Alexander Gondarenko, Ph.D. ’10, and Lipson appears in the online edition of the journal Nature and will appear in a forthcoming print edition.

Light can be thought of as a stream of particles that can exert a force on whatever they strike. The sun doesn’t knock you off your feet because the force is very small, but at the nanoscale it can be significant. “The challenge is that large optical forces are required to change the geometry of photonic structures,” Lipson explained.

But the researchers were able to reduce the force required by creating two ring resonators — circular waveguides whose circumference is matched to a multiple of the wavelength of the light used — and exploiting the coupling between beams of light traveling through the two rings.

A beam of light consists of oscillating electric and magnetic fields, and these fields can pull in nearby objects, a microscopic equivalent of the way static electricity on clothes attracts lint. This phenomenon is exploited in “optical tweezers” used by physicists to trap tiny objects. The forces tend to pull anything at the edge of the beam toward the center.

When light travels through a waveguide whose cross-section is smaller than its wavelength some of the light spills over, and with it the attractive force. So parallel waveguides close together, each carrying a light beam, are drawn even closer, rather like two streams of rainwater on a windowpane that touch and are pulled together by surface tension.

The researchers created a structure consisting of two thin, flat silicon nitride rings about 30 microns (millionths of a meter) in diameter mounted one above the other and connected to a pedestal by thin spokes. Think of two bicycle wheels on a vertical shaft, but each with only four thin, flexible spokes. The ring waveguides are three microns wide and 190 nanometers (nm — billionths of a meter) thick, and the rings are spaced 1 micron apart.

When light at a resonant frequency of the rings, in this case infrared light at 1533.5 nm, is fed into the rings, the force between the rings is enough to deform the rings by up to 12 nm, which the researchers showed was enough to change other resonances and switch other light beams traveling through the rings on and off. When light in both rings is in phase — the peaks and valleys of the wave match — the two rings are pulled together. When it is out of phase they are repelled. The latter phenomenon might be useful in MEMS, where an ongoing problem is that silicon parts tend to stick together, Lipson said.

An application in photonic circuits might be to create a tunable filter to pass one particular optical wavelength, Wiederhecker suggested.

The work is supported by the National Science Foundation (NSF) and the Cornell Center for Nanoscale Systems. Devices were fabricated at the Cornell Nanoscale Science and Technology Facility, also supported by NSF.

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July 16, 2008

The Casimir force and nanotechnology

Filed under: Science, Technology — Tags: , , , , — David Kirkpatrick @ 12:54 am

I first blogged on the Casimir force, stiction and nanotech a couple of weeks ago (find that post here and check out the first item) Here’s some updated news out of the University of Florida. Physicists there have found a way to reduce quantum stickiness.

From the second link:

What seems like magic is known as the Casimir force, and it has been well-documented in experiments. The cause goes to the heart of quantum physics: Seemingly empty space is not actually empty but contains virtual particles associated with fluctuating electromagnetic fields. These particles push the plates from both the inside and the outside. However, only virtual particles of shorter wavelengths — in the quantum world, particles exist simultaneously as waves — can fit into the space between the plates, so that the outward pressure is slightly smaller than the inward pressure. The result is the plates are forced together.

Now, University of Florida physicistshave found they can reduce the Casimir force by altering the surface of the plates. The discovery could prove useful as tiny “microelectromechanical” systems — so-called MEMS devices that are already used in a wide array of consumer products — become so small they are affected by quantum forces.

April 8, 2008

Argon/1-pentanol vapor to lubricate micromachines

Filed under: Technology — Tags: , , , , , — David Kirkpatrick @ 2:13 pm

A diluted gas may be the lubricant of choice for micromachines by creating a one molecule protective barrier.

From KurzweilAI.net:

Helping a micromachine to work
Nature News, April 7, 2008A dilute gas may soon become the lubricant of choice for microelectromechanical systems, or MEMS, devices.


(Sandia National Laboratories, SUMMiTTM Technologies)

By saturating devices with argon gas containing a small amount of 1-pentanol vapor, they can make microscopic machines run at least 100,000 times longer without failing.

The pentanol seems to adhere to silicon MEMS surfaces, creating a one-molecule-thick coating.

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