As many homeowners know, when stacking firewood, pieces should be placed close enough to permit passage of a mouse, but not of a cat chasing the mouse.
Now, imagine a woodpile where all those mouse passageways are packed with ice, the wood carefully removed, and you have an idea of what the latest photonic structure built by researchers at the University of Illinois looks like.
It's called an inverse woodpile structure, and the U. of I. device is built of germanium, a material with a higher refractive index than silicon.
"Until now, all woodpile structures have been composed of solid or hollow rods in an air matrix," said Paul Braun, a University Scholar and a professor of materials science and engineering at the U. of I. "Our structure is composed of a germanium matrix containing a periodic array of tubular holes, made possible by a unique and flexible fabrication technique."
In a paper accepted for publication in the journal Advanced Materials, and posted on its Web site, Braun and his co-authors describe the fabrication and optical properties of their germanium inverse woodpile structure; a structure with one of the widest photonic band gaps ever reported.
"A wider band gap means there is a broader spectral range where you can control the flow of light," said Braun, who also is affiliated with the university's Beckman Institute, Frederick Seitz Materials Research Laboratory, and Micro and Nanotechnology Laboratory. "In many applications, from low-threshold lasers to highly efficient solar cells, photonic crystals with wide band gaps may be required."
To create their germanium inverse woodpile structure, the researchers first produced a polymer template by using a robotic deposition process called direct-write assembly.
The process employs a concentrated polymeric ink, dispensed as a filament to form the woodpile rods, from a nozzle approximately 1 micron in diameter (a micron is 1 millionth of a meter, approximately 50 times smaller than the diameter of a human hair).
The nozzle dispenses the ink into a reservoir on a computer-controlled, three-axis micropositioner. After the pattern for the first layer is generated, the nozzle is raised and another layer is deposited. This process is repeated until the desired three-dimensional structure is produced.
Next, the researchers deposited a sacrificial coating of aluminum oxide and silicon dioxide onto the entire structure. The coating enlarged the rods and increased the contact area between them. The space between the rods was subsequently filled with germanium.
The researchers then heated the structure to burn away the polymer template. Lastly, the sacrificial oxide coating was dissolved by acid, leaving behind a tiny block of germanium with an inner network of interconnected tubes and channels.
The finished structure - built and tested as a proof of concept - consists of 12 layers of tubes and measures approximately 0.5 millimeters by 0.5 millimeters, and approximately 15 microns thick."The direct-write template approach offers new design rules, which allows us to fabricate structures we otherwise could not have made,"
said co-author Jennifer Lewis, the Thurnauer Professor of Materials Science and Engineering and interim director of the Frederick Seitz Materials Research Laboratory."Our technique also can be adopted for converting other polymeric woodpile templates, such as those made by laser-writing or electro-beam lithography, into inverse woodpile structures,"
In addition to their potential as photonic materials, the interconnected, inverse woodpile structures could find use as low-cost microelectromechanical systems, microfluidic networks for heat dissipation, and biological devices.
With Braun and Lewis, co-authors of the paper are postdoctoral research associate Florencio García-Santamaria and graduate student Mingjie Xu, both at Illinois; electrical engineering professor Shanhui Fan at Stanford University; and physicist Virginie Lousse at the Laboratoire de Physique du Solide in Belgium.
The work was funded by the U.S. Department of Energy and the U.S. Army Research Office.
To reach Paul Braun, call 217-244-7293; e-mail: firstname.lastname@example.org To reach Jennifer Lewis, call 217-244-4973; e-mail: email@example.com.
James E. Kloeppel | University of Illinois
Scientists announce the quest for high-index materials
24.07.2017 | Moscow Institute of Physics and Technology
ADIR Project: Lasers Recover Valuable Materials
24.07.2017 | Fraunhofer-Institut für Lasertechnik ILT
3-D shape acquisition using water displacement as the shape sensor for the reconstruction of complex objects
A global team of computer scientists and engineers have developed an innovative technique that more completely reconstructs challenging 3D objects. An ancient...
Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.
For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...
What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.
To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...
The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....
A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...
21.07.2017 | Event News
19.07.2017 | Event News
12.07.2017 | Event News
24.07.2017 | Power and Electrical Engineering
24.07.2017 | Materials Sciences
24.07.2017 | Materials Sciences