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From the Lab: Nanotechnology

A new lens allows optical microscopy down to 60 nanometers and faster plastic electronics – using an ink-jet printer.

Superlens Crafters
Lens allows optical microscopy down to 60 nanometers

Results: A team from the University of California, Berkeley, has devised a silver “superlens” that could increase the resolution of light microscopy by about a factor of six. The lens doesn’t diffract light like conventional glass lenses. Instead, it uses evanescent waves, which are produced when light hits a lens at such an angle that it bounces off instead of passing through. Evanescent waves emerge on the other side of the lens and add optical information to normal “propagating” light waves, but they decay very quickly over short distances. By capturing and amplifying these weak waves, the researchers obtained images with 60-nanometer resolution.

Why it Matters: High-resolution imaging methods such as electron microscopy can’t image living tissue. Light microscopy can. Its resolution, however, is limited by the wavelength of the light used. And 400 nanometers is the shortest wavelength that doesn’t damage tissue. Evanescent waves allow researchers to get around this limitation. The technique could eventually allow researchers to watch, in real time, biological processes such as protein interactions in samples of living tissue – events that can now be studied only indirectly.

Previous research has used evanescent waves to construct images in piecemeal fashion. The Berkeley team, led by Xiang Zhang, has shown that it’s possible to take a clear and complete picture in one shot.

Methods: The researchers made a lens out of a 35-nanometer-thick film of silver. They chose a light source whose frequency matched the resonant frequency of the lens’s surface electrons. The light shone through the word “NANO,” inscribed in letters with a 40-nanometer line width on a piece of chromium through ion beam lithography. When the light hit the lens, the silver electrons resonated with the evanescent waves, boosting their energy. The superlens directed the waves onto light-sensitive material to capture the image.

Next Step: The superlens didn’t spread out the evanescent waves enough that the human eye could see the image directly; it had to be observed with an atomic force microscope. Future research will curve the lens so that it can further spread the waves and pass them into, say, a fiber-optic cable. Superlenses might then be integrated into light microscopes. – By Stu Hutson

Source: Fang, N., et al. 2005. Sub-diffraction-limited optical imaging with a silver superlens. Science 308:534-7.

Ink-jet manufacturing for faster plastic electronics

Results: Using conventional ink-jet printing equipment, Henning Sirringhaus of the University of Cambridge in England and colleagues built organic-polymer circuits with switching speeds more than 100 times greater than those of existing polymer circuits. They printed circuit features that they estimated to be smaller than 100 nanometers, less than one-one-hundredth the size of the smallest features previously produced through ink-jet printing.

Why it Matters: Thin, flexible, and cheap plastic electronics could have many applications, from solar cells to radio frequency identification labels in product packaging. Ink-jet printing is an attractive manufacturing option because it deposits materials quickly and cheaply over large areas. But so far, it has yielded features no smaller than 20 micrometers, while the features of typical integrated circuits measure tens of nanometers. The Cambridge team seems to have broken the resolution barrier, making ink-jet printing viable.

Methods: The researchers produced their ultrasmall features using a homebuilt ink-jet printer. They deposited a conducting polymer “ink” as droplets on glass. They then chemically modified the droplets’ surfaces so they would repel additional droplets. A second set of droplets was applied; these flowed off of the first set, landing a tiny distance away. That distance represents the smallest feature size this technique can achieve. The researchers laid out transistors: the closely spaced droplets formed electrodes, and an organic semiconductor filled the gap between them. The researchers estimated the width of this gap based on the performance of the transistors.

Next Step: The researchers are now using better-performing organic semiconducting materials. They are also producing circuits that involve hundreds of interconnected transistors. – By Corie Lok

Source: Sele, C. W., et al. 2005. Lithography-free, self-aligned inkjet printing with sub-hundred-nanometer resolution. Advanced Materials 17:997-1001.

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