Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

’Tall’ crystals from tiny templates

21.07.2005


Ames Lab Researchers Modify Old Technique to Make 3-D Multilayered Structures



Achieving a first in the world of novel optical materials, researchers at the U. S. Department of Energy’s Ames Laboratory are making 3-D photonic band gap crystals four millimeters square (approximately one-eighth of an inch square) and 12 layers high without benefit of a “clean room” environment or the multimillion dollar equipment traditionally required to create such structures. The fundamental research, supported by the Basic Energy Sciences Office of the DOE’s Office of Science, holds potential for significantly reducing the costs associated with fabricating PBG crystals, devices that make it possible to route, manipulate and modify the properties of light.

PBG crystals can permit or block the transmission of light of certain frequencies in all directions. This characteristic makes them especially promising for applications in the field of optical communications, where the push is on to create a photonic crystal within a single computer chip.


The research path to that goal is an unbelievably expensive one. But Kai-Ming Ho, an Ames Laboratory senior physicist, and Kristen Constant, an Iowa State University associate professor of materials science and engineering, and their co-workers are easing the way by fabricating PBG crystal microstructures in the open air, something that has never been done before.

The project is based on Ho’s original 1990 research that theoretically demonstrated the existence of the first PBG crystal through his diamond lattice structure design.

That unique design is key to the multilayered PBGs that are being fabricated by members of Ho’s and Constant’s research groups. They have adapted a technique called microtransfer molding to make templates for the fabrication of multilayered photonic band gap crystals.

“The microtransfer mold technique is not new,” said Ho, who is also an ISU distinguished professor of physics and astronomy. “Modifying it to create multilevel lattice structures at micron- and submicron-length scales – that is the new advance.”

The modified technique involves meticulous work at the micron-scale level. (For size reference, the period at the end of this sentence equals approximately 615 microns.) First, an elastomer mold is created with more than 1,000 microchannels on its surface. The channels are filled by hand with a liquid polymer filler. The filler is then solidified by ultraviolet light. Next, the solidified polymer rods in the channels are coated with a second polymer that acts as a glue, bonding the filler to a silicon wafer substrate. Once hardened, the elastomer mold is peeled off, leaving a set of parallel polymer rods on the substrate – one layer of the polymer template. By repeating the procedure, in principle, any number of multilayer structures is achievable. To convert the template to a ceramic photonic crystal, the template is over-infiltrated with a titania slurry. The structure is fired to 550 degrees Celsius (1022 F) to remove the template and sinter the titania structure.

Ho and Constant credit many of the fabrication advances to the unique skills of the young scientists they mentor: postdoctoral fellow Chang-Hwan Kim; current graduate students Jae-Hwang Lee, Yong-Sung Kim, and Ping Kuang; and former graduate student Henry Kang, now at Hewlett Packard in Oregon. They are conquering what is perhaps the biggest challenge – aligning the multiple layers that make up the PBG crystals.

The 1,000 plus rods per layer in a four-millimeter-square PBG crystal are only 2.5 microns apart. “The placement of each rod is so precise,” said Constant. “It’s hard to imagine that we can put something down within a micron or half a micron.”

Ho added, “If you make a mistake in one layer, it will disrupt the next one and spoil the rest of the sample. In order to build multilayers, you need to get things right successively.”

Lee knows the kind of concentration that requires. He has constructed a 12-layer template for a PBG crystal and modestly admitted, “I can stack more than this; however, it will task my patience!”

To improve the alignment, Lee and Chang-Hwan Kim came up with an ingenious method based on diffracted moiré fringes that has proven indispensable. Ho explained, “Photonic crystals are periodic structures, so any shifts in periodicity will show up over a much larger area. Those shifts are called fringes,” he said. The better the alignment, the farther apart those fringes are spaced, so the fringe pattern tells you how good the alignment is.”

Constant praised the project’s blended research team of physicists and materials scientists. “We’ve established an expertise with microtransfer molding. When people hear that we’re doing this in open air, it really amazes them. It amazes me, too,” she admitted, “especially when you realize that a speck of dust can disrupt the whole structure.”

Ho noted that the care and expertise of the project’s team members was overcoming the open-air obstacles. “It’s a high-quality, low-cost process – that’s the key – and it’s achieved by a lot of engineering ingenuity,” he said.

Ames Laboratory is operated for the Department of Energy by Iowa State University. The Lab conducts research into various areas of national concern, including energy resources, high-speed computer design, environmental cleanup and restoration, and the synthesis and study of new materials.

Saren Johnston | EurekAlert!
Further information:
http://www.ameslab.gov

More articles from Materials Sciences:

nachricht Reliable molecular toggle switch developed
30.03.2017 | Karlsruher Institut für Technologie (KIT)

nachricht Researchers shoot for success with simulations of laser pulse-material interactions
29.03.2017 | DOE/Oak Ridge National Laboratory

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A Challenging European Research Project to Develop New Tiny Microscopes

The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.

To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

'On-off switch' brings researchers a step closer to potential HIV vaccine

30.03.2017 | Health and Medicine

Penn studies find promise for innovations in liquid biopsies

30.03.2017 | Health and Medicine

An LED-based device for imaging radiation induced skin damage

30.03.2017 | Medical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>