Menu
Modern science
Soil Microbes Accelerate Global Warming

Bold New Approach to Wind 'Farm' Design May Provide Efficiency Gains

Soft Memory Device Opens Door to New Biocompatible Electronics

Most Elliptical Galaxies Are 'Like Spirals'

New Planets Feature Young Star and Twin Neptunes

Editing the Genome: Scientists Unveil New Tools for Rewriting the Code of Life

High Social Rank Comes at a Price, Wild Baboon Study Finds

Fossil Forensics Reveals How Wasps Populated Rotting Dinosaur Eggs

Monitoring Cellular Interactions at Nano-Scale in More Detail Than Ever Before

Non-Africans Are Part Neanderthal, Genetic Research Shows

Making Blood Sucking Deadly for Mosquitoes

Rising Oceans: Too Late to Turn the Tide?

Newly Developed Fluorescent Protein Makes Internal Organs Visible

NASA's Dawn Spacecraft Returns Close-Up Image of Giant Asteroid Vesta

Bacteria Use Batman-Like Grappling Hooks to 'Slingshot' On Surfaces, Study Shows

Mysterious Fossils Provide New Clues to Insect Evolution

Twisted Tale of Our Galaxy's Ring: Strange Kink in Milky Way

Engineering Excitable Cells for Studies of Bioelectricity and Cell Therapy

Ancient Footprints Show Human-Like Walking Began Nearly 4 Million Years Ago

Memories May Skew Visual Perception

Movement of Black Holes Powers Quasars, the Universe's Brightest Lights

First Artificial Neural Network Created out of DNA: Molecular Soup Exhibits Brainlike Behavior

Dolphins' 'Remarkable' Recovery from Injury Offers Important Insights for Human Healing

Cosmological Evolution of Dark Matter Is Similar to That of Visible Matter

Exoplanet Aurora: An Out-Of-This-World Sight

New Photonic Crystals Have Both Electronic and Optical Properties
In an advance that could open new avenues for solar cells, lasers, metamaterials and more, researchers at the University of Illinois have demonstrated the first optoelectronically active 3-D photonic crystal.

"We've discovered a way to change the three-dimensional structure of a well-established semiconductor material to enable new optical properties while maintaining its very attractive electrical properties," said Paul Braun, a professor of materials science and engineering and of chemistry who led the research effort.

The team published its advance in the journal Nature Materials.

Photonic crystals are materials that can control or manipulate light in unexpected ways thanks to their unique physical structures. Photonic crystals can induce unusual phenomena and affect photon behavior in ways that traditional optical materials and devices can't. They are popular materials of study for applications in lasers, solar energy, LEDs, metamaterials and more.

However, previous attempts at making 3-D photonic crystals have resulted in devices that are only optically active that is, they can direct light but not electronically active, so they can't turn electricity to light or vice versa.

The Illinois team's photonic crystal has both properties.

"With our approach to fabricating photonic crystals, there's a lot of potential to optimize electronic and optical properties simultaneously," said Erik Nelson, a former graduate student in Braun's lab who now is a postdoctoral researcher at Harvard University. "It gives you the opportunity to control light in ways that are very unique to control the way it's emitted and absorbed or how it propagates."

To create a 3-D photonic crystal that is both electronically and optically active, the researchers started with a template of tiny spheres packed together. Then, they deposit gallium arsenide (GaAs), a widely used semiconductor, through the template, filling in the gaps between the spheres.

The GaAs grows as a single crystal from the bottom up, a process called epitaxy. Epitaxy is common in industry to create flat, two-dimensional films of single-crystal semiconductors, but Braun's group developed a way to apply it to an intricate three-dimensional structure.

"The key discovery here was that we grew single-crystal semiconductor through this complex template," said Braun, who also is affiliated with the Beckman Institute for Advanced Science and Technology and with the Frederick Seitz Materials Research Laboratory at Illinois. "Gallium arsenide wants to grow as a film on the substrate from the bottom up, but it runs into the template and goes around it. It's almost as though the template is filling up with water. As long as you keep growing GaAs, it keeps filling the template from the bottom up until you reach the top surface."

The epitaxial approach eliminates many of the defects introduced by top-down fabrication methods, a popular pathway for creating 3-D photonic structures. Another advantage is the ease of creating layered heterostructures. For example, a quantum well layer could be introduced into the photonic crystal by partially filling the template with GaAs and then briefly switching the vapor stream to another material.

Once the template is full, the researchers remove the spheres, leaving a complex, porous 3-D structure of single-crystal semiconductor. Then they coat the entire structure with a very thin layer of a semiconductor with a wider bandgap to improve performance and prevent surface recombination.

To test their technique, the group built a 3-D photonic crystal LED the first such working device.

Now, Braun's group is working to optimize the structure for specific applications. The LED demonstrates that the concept produces functional devices, but by tweaking the structure or using other semiconductor materials, researchers can improve solar collection or target specific wavelengths for metamaterials applications or low-threshold lasers.

"From this point on, it's a matter of changing the device geometry to achieve whatever properties you want," Nelson said. It really opens up a whole new area of research into extremely efficient or novel energy devices.

Для печати

New Material Lets Electrons 'Dance' and Form New State

Cod Resurgence in Canadian Waters

Fundamental Matter-Antimatter Symmetry Confirmed

First True View of Global Erosion

NASA's WISE Finds Earth's First 'Trojan' Asteroid

Engineers Fly World's First 'Printed' Aircraft

Scientist Converts Human Skin Cells Into Functional Brain Cells

Rainforest Plant Developed 'Sonar Dish' to Attract Pollinating Bats

Sea Level Rise Less from Greenland, More from Antarctica, Than Expected During Last Interglacial

How Bats Stay On Target Despite the Clutter

Fall of the Neanderthals: Volume of Modern Humans Infiltrating Europe Cited as Critical Factor

Largest-Ever Map of Plant Protein Interactions

Some Plants Duplicate Their DNA to Overcome Adversity

usb ip software

Menu
Diamonds Pinpoint Start of Colliding Continents

Researchers Identify Seventh and Eighth Bases of DNA

Fool's Gold Gives Scientists Priceless Insight Into Earth's Evolution

Astronomers Discover Largest and Most Distant Reservoir of Water Yet

Major Step Toward Creating Faster Electronics Using Graphene

New Photonic Crystals Have Both Electronic and Optical Properties

Epigenetic 'Memory' Key to Nature Versus Nurture

Climate Change to Increase Yellowstone Wildfires Dramatically

Retinal Cells Thoughts to Be the Same Are Not, Biologist Says

Minority Rules: Scientists Discover Tipping Point for the Spread of Ideas

Mitochondria Share an Ancestor With SAR11, a Globally Significant Marine Microbe

Drug Shown to Improve Sight for Patients With Inherited Blindness

Elliptical Galaxies Are Not Dead

Hubble Constant: A New Way to Measure the Expansion of the Universe

Enceladus Rains Water Onto Saturn

Engineers Develop One-Way Transmission System for Sound Waves

Researchers Graft Olfactory Receptors Onto Nanotubes

New Invisibility Cloak Hides Objects from Human View

Bionic Microrobot Mimics the 'Water Strider' and Walks On Water

How Memory Is Lost: Loss of Memory Due to Aging May Be Reversible

Reservoirs of Ancient Lava Shaped Earth

Wave Power Can Drive Sun's Intense Heat

Social Deficits Associated With Autism, Schizophrenia Induced in Mice With New Technology

Tundra Fires Could Accelerate Climate Warming

Chandra X-Ray Observatory Images Gas Flowing Toward Black Hole