Monday, November 28, 2005

"SECURITY: CMOS chip slashes time needed to ID flu strains"

CombiMatrix Corp. fabricated a smart CMOS chip for influenza identification that addresses a central criterion for containment of a potential pandemic: timeliness. The company says its microarray can be updated for new flu strains in less than 24 hours and can identify any known flu strain in as little as four hours, without requiring skilled technicians to operate it. The chip's CMOS format can electronically identify the binding events that represent a match between a sample of DNA and the DNA from a flu strain found in the body. An array of electrodes that are organized like memory cells in an SRAM determines where a binding event has occurred, eliminating the need for the fluorescent tags and optical scanners used with other methods. Current influenza identification tests require batch operations that must be run overnight. The conventional flu chips use dumb plastic or glass substrates that require skilled technicians to inspect the microarrays visually. And labs can't update the chips for new flu strains without waiting 18 months for Federal Drug Administration (FDA) approval. Laboratories with CombiMatrix chips in stock can repopulate them with any new DNA sequences they desire, literally overnight. By using CombiMatrix's desktop DNA synthesizer, any certified laboratory can populate the microarrays inside the CMOS chips with any predetermined DNA sequence. CombiMatrix's CMOS flu chips are disposable and can be ordered preloaded to identify DNA sequences for up to 12,000 strains of influenza. A forthcoming electrochemical detection system for the CombiMatrix chips will be packaged in a portable battery-operated unit. The array can be used as an adjunct to existing technology, to type difficult or ambiguous samples of flu or to study genetic drift in a flu strain as it migrates through a population. The system can process samples from animals as well as humans.

Monday, November 21, 2005

"NANOTECH: Nano transistors light the way to all-optical silicon chips"

An experimental light-emitting nanotube (LEN) transistor that's said to achieve 10,000 times the photon flux and over 1000 times the efficiency of LEDs could put researchers closer to the goal of "computing with light." By emitting thousands of photons for the same energy expenditure as one photon emission in an LED, the unipolar carbon nanotube transistor could lead to optical silicon chips, said its creator, IBM Corp. Light emission in solid-state LEDs occurs when separately injected electrons and holes recombine in an exotic material such as gallium arsenide. The resultant drop in energy causes a single photon to be emitted to compensate. IBM had earlier reported an ambipolar nanotube transistor, billed at the time as the world's smallest solid-state emitter, for which hot carriers — electrons and holes — were injected separately into the source and drain. The new technique induces electroluminescence from a single type of carrier — an exciton — using a unipolar nanotube transistor that the company says is three orders of magnitude more efficient than the ambipolar transistor. IBM believes light-emitting nanotube transistors will revolutionize the communications industry by enabling silicon devices to perform both electronic and optical signal processing operations. Eventually all-optical silicon chips could result, but in the meantime silicon chips could perform electrical-to-optical conversions, reducing the need for separate devices made from exotic materials, IBM researchers believe.

"SUPERCOMPUTERS: Big computers, little apps"

From realistic predictive modeling of natural and man-made disasters to atomic-level explorations of photosynthetic bacteria, supercomputers are enabling next-generation applications in science and technology. Increasingly, the machines' modeling muscle is even being applied to the design of consumer products. Supercomputing 2005, held here last week, reported on achievements and trends in the field. Simulations remain the most important supercomputer applications. At SC/05, researchers discussed the use of supercomputer simulations to forecast the course of disasters, such as modeling wave heights or predicting the drift of a plume from a so-called dirty bomb. But the era of big-application supercomputer simulations is giving way to small ones, said Thomas Lange, director of modeling and simulation for Procter & Gamble. Last week's conference continued a common practice in the supercomputing world: the smashing of records. Bragging rights to the world's largest full-electron calculation were claimed by a team that said it had successfully simulated every atom and every electron in the photosynthetic reaction center of the Rhodopseudomonas viridis bacterium. NASA, meanwhile, announced it had crafted the first complete simulation of a space shuttle flight from liftoff to re-entry, a feat achieved using its year-old Columbia supercomputer. While simulating a shuttle flight or a bacterial structure proceeds largely from known, fixed inputs, simulating the airborne drift of a contaminant plume depends on random inputs of incomplete and unreliable data. Simulation of a plume from a toxic contaminant requires a dynamic data-driven (DDD) approach to make sense of first responders' reports, which are subject to error, according to a team under the auspices of Sandia.

"MATERIALS: Carbon nanotube 'paper' stronger than steel"

Recent research using carbon nanotubes in place of conventional carbon fibers is revealing large gains in such critical material properties as tensile strength and electrical and thermal conductivity. A striking example is a paper product that is ultrathin, electrically conducting and 10 times lighter than steel while still being 250 times stronger. Called buckypaper by its developer, the Florida Advanced Center for Composite Technologies (FAC2T), the material could enable the development of stronger ultralight aircraft or of lighter-weight yet more-effective body armor. It might also find a role in vehicle armor or the construction of stiff, durable yet paper-thin computer displays, researchers said. Buckypaper is created from carbon nanotubes, which can be magnetically aligned during fabrication using the National High Magnetic Field Laboratory's 25 Tesla supermagnet, located at Florida State University. Carbon nanotubes have a high aspect ratio, measuring nanometers wide but extending tens or hundreds of microns in length. Carbon commonly forms into graphite, a flat sheet of carbon atoms bonded in a hexagonal, closely packed structure. Although the carbon-carbon bond is very strong, the two-dimensional sheets do not have much strength in any direction out of their plane. Carbon atoms can also bond into diamond, a three-dimensional crystal that is identical to crystalline silicon-a form that demonstrates the potential strength of carbon bonding. FSU has four U.S. patents pending for buckypaper. Among the smorgasbord of applications slated for development using the material, FAC2T predicts buckypaper will prove applicable as a large-scale electron-field emitter for flat-panel displays, as a thermal conductor for superefficient heat sinks and as high-current protective film for the exteriors of airplanes. Such film would allow lightning strikes to flow around a plane and dissipate without damaging it.

Thursday, November 17, 2005

"OPTICS: IBM claims to best venerable LED"

IBM Corp. unveiled the world's first unipolar electroluminescent nanotube transistor and claimed it glows over 1,000 times brighter with as much as 10,000 times more photon flux than a light-emitting diodes (LEDs). By emitting thousands of photons in silicon with the same energy expenditure as one photon in gallium arsenide, IBM predicted that carbon nanotube transistors will lead to integrated optics on silicon chips. According to IBM, integrated optics on silicon chips could lower costs, accelerate electronics and mitigate the need for exotic semiconductors like gallium arsenide. IBM said its technique achieves 1000-fold brighter emissions by electrically stimulating a carbon nanotube suspended over a doped silicon wafer. The resulting excitons are electrically neutral, yet emit infrared light when recombined. Other research groups have reported light emission by carbon nanotubes stimulated to photoluminescence with a laser. IBM claims its technique uses only electrical stimulation to create an exciton density that is 100-fold larger than photoluminescence in nanotubes. IBM claimed it achieved very high efficiency with its light-emitting technique, IBM through the extreme confinement within a 2-nm-diameter carbon nanotube suspended from each end over a silicon back gate. IBM fabricated the light-emitting transistor by etching trenches in a silicon dioxide film on a highly doped silicon wafer. The wafer substrate acted as a back gate to the carbon nanotube transistor.

Monday, November 14, 2005

"QUANTUM: dot technique builds 'better light bulb'"

Vanderbilt University researchers claim their quantum-dot approach to the generation of tunable broad-spectrum white light simplifies solid-state lighting. The quantum-dot light bulb, invented by professor Sandra Rosenthal uses a single size of nanocrystal to produce white light when irradiated with commercially available blue LEDs. The work shows that building a "better light bulb" does not require pumped lasers, exotically formulated phosphors or integrated quantum wells and nanocrystals, Rosenthal said: All you need to do is coat blue LEDs with her broad-spectrum quantum dots. The quantum-dot light bulbs are predicted to last as long as their LEDs-up to 50,000 hours, or 50 times as long as a normal light bulb. Usually the emitted light's wavelength is determined by the nanocrystal size-for example, a 10-nanometer diameter for red-but Rosenthal's group discovered a size and surface treatment combination that enables a single quantum dot to emit a full spectrum combination of light, resulting in warm yellowish white emission. The quantum dots used were half the size of normal nanocrystals and appeared to exhibit photonic surface emission. Rosenthal hopes that stimulating her photonic surface-emitting quantum dots electrically will yield an all-semiconductor white light bulb that does not rely on exotic compounds. The quantum dots theoretically could be sprayed on any surface to turn it into a light bulb producing a variable rainbow of shades.

Monday, November 07, 2005

"OPTICS: IBM controls speed of light in silicon"

Thomas Theis Photo Researchers at IBM Corp. have fabricated the world's first optical chip to electrically control the speed of light. Director of physical sciences at the T.J. Watson Research Center (Yorktown Heights, N.Y.) Thomas Theis (pictured above) describes IBM's demonstration of an optical silicon chip that can electrically alter the effective index of refraction of an integrated photonic-crystal waveguide. The experimental component could one day enable tunable optical delay-line chips, optical buffers, high-extinction optical switches and highly efficient wavelength converters, IBM said. Together with other optical components, such devices could also eliminate the telecommunications industry's reliance on bulky and costly optical-to-electrical and electrical-to-optical converters. The optical chip can variably slow light by a factor of 300x, under active control by a low-power (under 2-milliwatt), fast-changing (less than 100-nanosecond) electrical signal. It was constructed using normal silicon-on-insulator CMOS fabrication techniques, the team said. The active element is a 250-micron-long photonic-crystal waveguide formed with a nanoscale version of micromachining that perforated a 223-nm-thick membrane with holes 109 nm in diameter, spaced at a 437-nm pitch. As a result, the waveguide slows light passing through it in a 20-nm bandwidth at the communications wavelength of 1,620 nanometers.