Silicon is the workhorse among semiconductors in electronics. But in opto-electronics, where light signals are processed along with electronic signals, a semiconductor that is capable of emitting light is needed, which silicon can't do very well. Here gallium-arsenide (GaAs) is the workhorse, especially in the creation of light emitting diodes (LED) and LED lasers.
Scientists at the University of California, Berkeley have now grown GaAs structures into the shape of narrow needles which, when optically pumped, emit light with high brightness. The needles are approximately 3 to 4 microns long and taper at an angle of 6 to 9 degrees down to tips approximately 2 to 5 nanometers across.
These needles are not yet lasers; creating them will be the next step. This represents the first time a lab has been able to fashion GaAs into a defect-free crystal structure (technical name: wurtzite) exactly like this on a silicon substrate and without the use of catalysts.
Lead researcher Michael Moewe says that, in addition to optoelectronic devices, he expects the needles to be valuable in such applications as atomic force microscopy (AFM), where the sharp tips can be grown in arrays without further etching or processing steps. Some believe that AFM arrays, besides speeding up the recording of nearly atomic-resolution images of surfaces (allowing one to create atomic movies), might be used to create a new form of data storage by influencing the atoms in the sample. The needles also may be used in producing tip-enhanced Raman spectroscopy.
Raman spectroscopy is a process in which the energy levels of molecules are determined by shining light at a known frequency into the sample and then observing the frequency of the outgoing light. Delivering light from a sharp tip allows a much more targeted examination of the sample, possibly even permitting the spectroscopic study of single molecules.
The research will be presented at the 2008 Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference (CLEO/QELS) May 4-9 at the San Jose McEnery Convention Center in San Jose, Calif.
Source: Optical Society of America
Related stories:
3-D Imaging -- First Insights Into Magnetic Fields
3-D images are not only useful in medicine; the observation of internal structures is also invaluable in many other fields of scientific investigation. Recently, researchers from the Hahn-Meitner-Institute (HMI) in Berlin in cooperation with University of Applied Sciences have succeeded, for the first time, in a direct, three-dimensional visualisation of magnetic fields inside solid, non-transparent materials. This is announced by Nikolay Kardjilov and colleagues in the current issue of the journal
Nature Physics.
Light's Answer To Ultrasound
You have a tiny wound on your hand that doesn’t heal, a bad burn on your chest – or an injured retina. Your doctor cannot tell how serious the injuries are below the surface. He needs tissue samples. That means using a scalpel, which again equals pain, perhaps even a risk. Soon there may be hope for an improved and totally harmless method to peer under the surface of the skin: light.
Software Tool Finds 'Needles' in Data 'Haystacks'
When looking for a needle in a haystack, it's helpful to know what a needle looks like. A new software tool developed by researchers at the National Institute of Standards and Technology (NIST) makes it possible to find chemical 'needles' in data 'haystacks' without having to know anything about the 'needle' in advance.
The NIST software should be especially useful for analyzing ultrapure metals - recently shown to have superior strength, corrosion-resistance and other properties - and for monitoring nanoscale semiconductor fabrication. Commercial X-ray detector manufacturers already have included the method used in the software into their products.
Trench on Mars Ready for Next Sampling by NASA Lander
(PhysOrg.com) -- NASA's Phoenix Mars Lander has groomed the bottom of a shallow trench to prepare for collecting a sample to be analyzed from a hard subsurface layer where the soil may contain frozen water.
US fentanyl deaths topped 1,000 over 2 years
(AP) -- More than 1,000 people died over two years from an illegal version of the painkiller fentanyl, the government reported Thursday in its first national tally of those deaths.
Lenses galore -- Hubble finds large sample of very distant galaxies
By using the gravitational magnification from six massive lensing galaxy clusters, the NASA/ESA Hubble Space Telescope has provided scientists with the largest sample of very distant galaxies seen to date. Some of the newly found magnified objects are dimmer than the faintest ones seen in the legendary Hubble Ultra Deep Field, which is usually considered the deepest image of the Universe.
Slippery Customer: A Greener Antiwear Additive for Engine Oils
(PhysOrg.com) -- Titanium, a protean element with applications from pigments to aerospace alloys, could get a new role as an environmentally friendly additive for automotive oil, thanks to work by materials scientists from Afton Chemical Corporation (Richmond, Va.) and the National Institute of Standards and Technology.
90 billion tons of microbial organisms live in the deep biosphere
Biogeoscientists show evidence of 90 billion tons of microbial organisms—expressed in terms of carbon mass—living in the deep biosphere, in a research article published online by
Nature, July 20, 2008. This tonnage corresponds to about one-tenth of the amount of carbon stored globally in tropical rainforests.