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Patterning defect-free nanocrystal films with nanometer resolution - Letter LED Display by icdenta icdenta
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Patterning defect-free nanocrystal films with nanometer resolution - Letter LED Display by ICDENTA ICDENTA
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| Article Posted: 08/28/2013 |
| Article Views: 82 |
| Articles Written: 1096 - MORE ARTICLES FROM THIS AUTHOR |
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Patterning defect-free nanocrystal films with nanometer resolution - Letter LED Display |
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Business,Business News,Business Opportunities
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Products Patterning defect-free nanocrystal films with nanometer resolution New process developed at MIT could enable better LED displays,solar cells and biosensors -- and foster basic physicsresearch. Films made of semiconductor nanocrystals -- tiny crystalsmeasuring just a few billionths of a meter across -- are seenas a promising new material for a wide range of applications.Nanocrystals could be used in electronic or photonic circuits,detectors for biomolecules, or the glowing pixels onhigh-resolution display screens. They also hold promise for moreefficient solar cells. The size of a semiconductor nanocrystal determines its electricaland optical properties. But it"s very hard to control theplacement of nanocrystals on a surface in order to makestructurally uniform films.
Typical nanocrystal films also havecracks that limit their usefulness and make it impossible tomeasure the fundamental properties of these materials. Now, researchers at MIT say they have found ways of makingdefect-free patterns of nanocrystal films where the shape andposition of the films are controlled with nanoscale resolution,potentially opening up a significant area for research and possiblenew applications. "We"ve been trying to understand how electrons move inarrays of these nanocrystals," which has been difficult withlimited control over the formation of the arrays, says physicistMarc Kastner, the Donner Professor of Science, dean of MIT"sSchool of Science and senior author of a paper published online in the journal Nano Letters . The work builds on research by Moungi Bawendi, the Lester WolfeProfessor of Chemistry at MIT and a co-author of this paper, whowas one of the first researchers to precisely control nanocrystalproduction. Such control made it possible, among other things, toproduce materials that glow, or fluoresce, in a range of differentcolors based on their sizes -- even though they are all madeof the same material.
In the initial phases of the new work, postdoc Tamar Mentzelproduced nanoscale patterns that emit invisible infrared light. Butworking on such systems is tedious, since each fine-tuning has tobe checked using time-consuming electron microscopy. So whenMentzel succeeded in getting semiconductor nanocrystal patterns toglow with visible light, making them visible through an opticalmicroscope, it meant that the team could greatly speed thedevelopment of the new technology. "Even though the nanoscalepatterns are below the resolution limit of the optical microscope,the nanocrystals act as a light source, rendering themvisible," Mentzel says. The electrical conductivity of the researchers" defect-freefilms is roughly 180 times greater than that of the cracked filmsmade by conventional methods.
In addition, the process developed bythe MIT team has already made it possible to create patterns on asilicon surface that are just 30 nanometers across -- aboutthe size of the finest features possible with present manufacturingtechniques. The process is unique in producing such tiny patterns ofdefect-free films, Mentzel says. "The trick was to get thefilm to be uniform, and to stick" to the silicon dioxidesubstrate, Kastner adds. That was achieved by leaving a thin layerof polymer to coat the surface before depositing the layer ofnanocrystals on top of it.
The researchers conjecture that tinyorganic molecules on the surface of the nanocrystals help them bindto the polymer layer. Such nanocrystal patterns could have many applications, Kastnersays. Because these nanocrystals can be tuned not only to emit butalso to absorb a wide spectrum of colors of light, they couldenable a new kind of broad-spectrum solar cell, he says. But Kastner and Mentzel"s personal interest has more to dowith basic physics: Since the minuscule crystals behave almost likeoversized atoms, the researchers aim to use the arrays to studyfundamental processes of solids, Mentzel says. The success of thistechnique has already enabled new research on how electrons move inthe films.
Such materials could also be used to develop sensitive detectorsfor tiny amounts of certain biological molecules, either asscreening systems for toxins or as medical testing devices, theresearchers say. Douglas Natelson, a professor of physics and astronomy at RiceUniversity who was not involved in this work, says, "Thechallenge in the past has been achieving thin, uniform films,patterned at high resolution, with good contact between thenanocrystals and no cracking." The MIT team"s approach,he says, "while deceptively simple in appearance,accomplishes all of these objectives." Natelson adds: "I think this is a very nice achievement. Thefluorescence images showing the nanopatterned films areeye-popping, particularly for those who know how tough thisis." The research was supported by the U.S Army Research Office, theDepartment of Energy and Samsung. Images of nanopatterned films of nano crystalline material producedby the MIT research team.
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