Holograms to help nanotechnology
In a very short but intriguing article, Technology Research News (TRN) writes that researchers from Harvard University and New York University have found a way to use holographic optical traps (HOTs) to manipulate semiconductor nanowires. As this holographic approach to nano-assembly can allow for simultaneous independent manipulation of multiple nanowires, this could open the way for new forms of optical and electronic devices like fast, high-capacity computer memory chips.
Here are the opening paragraphs of the TRN article.
During the past few years scientists have gotten good at using holograms to move and manipulate microscopic objects. The methods, however, are usually limited to spherical objects, which include cells and microbes.
Researchers from Harvard University and New York University have found a way to use holographic optical traps to move and manipulate long, thin semiconductor nanowires. Holographic optical traps are computer-controlled holograms focused through a microscope onto objects floating in liquid.
On the pictures below, you can see as an example a rhombus constructed from semiconductor nanowires using holographic optical traps (Credit: Harvard University and New York University).
(a) A nanowire is translated towards an existing structure created earlier by trapping and fusing two nanowires. (b) The long nanowire is then cut with a pulsed optical scalpel. (c) The resulting free-floating nanowire piece then is brought back to the partially completed structure. (d) The structure is completed by fusing both ends of the fourth nanowire.
And below is how the HOT technology is trapping semiconductor nanowires (Credit: Harvard University and New York University).
(a) The light from a frequency-doubled solid-state laser is imprinted with a computer-generated hologram by a phase-shifting spatial light modulator (SLM) before being relayed to the input pupil of a high-numerical-aperture objective lens, which focuses the light into an array of optical traps, shown in (b). (c) An individual semiconductor nanowire can be localized by multiple optical traps, whose intersection with the wire typically is visualized by intense laser-induced fluorescence, as in (d).
The research work has been published by Optics Express under the title "Manipulation and assembly of nanowires with holographic optical traps" (Vol. 13, No. 22, Pages 8906 - 8912,) on October 31, 2005. Here is a link to the abstract
We demonstrate that semiconductor nanowires measuring just a few nanometers in diameter can be translated, rotated, cut, fused and organized into nontrivial structures using holographic optical traps. The holographic approach to nano-assembly allows for simultaneous independent manipulation of multiple nanowires, including relative translation and relative rotation.
And here are some of the conclusions of the full paper (PDF format, 5 pages, 257 KB), from which the above pictures and captions have been extracted.
In summary, the results presented here demonstrate that holographically projected arrays of optical traps can be used to manipulate and assemble semiconductor nanowires into precisely organized two-dimensional and three-dimensional structures. In the future, it should be possible to optimize this process by tuning the laser wavelength to enhance the optical trapping force.
The approach also will become substantially faster and more highly parallel with advances in holographic trapping technology. Optical assembly of functional subunits will facilitate hierarchical fabrication of larger systems, through processes that might exploit complementary techniques such as chemically-directed self-organization.
When will we see practical applications of these findings? Probably not before several years.
Sources: Technology Research News, November 7, 2005; and various web sites
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