Engineers Give Industry A Moth's Eye View

Source:

http://www.sciencedaily.com/releases/2007/11/071126115318.htm

ScienceDaily (Nov. 28, 2007) — When moths fly at night, their eyes need to capture all the light available. To do this, certain species have evolved nanoscopic structures on the surface of their eyes which allow almost no light to reflect off the surface and hence to escape.

Now scientists at MicroBridge, a project at Cardiff University's Manufacturing Engineering Centre (MEC), have adopted the model to create an industrial lens for use in a low light environment.
The structures on the surface of the new lens are less than 100 nanometres in height (a nanometre is one millionth of a millimetre). They need to be smaller than the wavelength of light to avoid disrupting the light as it enters the lens.
The tiny features of the lens mould were created using the MEC's Focused Ion Beam. The beam uses highly charged atomic particles to machine materials in microscopic detail.
Dr Robert Hoyle of the MEC said: "This was a particularly complicated challenge. Not only did the lenses have to be of very precise curvature but the nanoscopic structures on the lens surfaces had to be smaller than the wavelength of light so as to smooth out the sharp refractive index change as the light strikes the surface of the lens. This smoothing of the refractive index reduces the reflectiveness of the lens thus allowing it to capture more light. The end result has a number of highly practical uses for industry."
The research team is now looking at using the lens in optoelectronics and photovoltaic applications in semiconductors, including solar cells, where loss of light is a major problem. The lens also has potential uses in fibre optics, sensors and medical diagnostic devices.
Adapted from materials provided by Cardiff University.

Fausto Intilla

www.oloscience.com

High Performance Field-effect Transistors With Thin Films Of Carbon 60 Produced

Source:

http://www.sciencedaily.com/releases/2007/11/071126121735.htm

ScienceDaily (Nov. 27, 2007) — Using room-temperature processing, researchers at the Georgia Institute of Technology have fabricated high-performance field effect transistors with thin films of Carbon 60, also known as fullerene. The ability to produce devices with such performance with an organic semiconductor represents another milestone toward practical applications for large area, low-cost electronic circuits on flexible organic substrates.

The new devices -- which have electron-mobility values higher than amorphous silicon, low threshold voltages, large on-off ratios and high operational stability -- could encourage more designers to begin working on such circuitry for displays, active electronic billboards, RFID tags and other applications that use flexible substrates.
"If you open a textbook and look at what a thin-film transistor should do, we are pretty close now," said Bernard Kippelen, a professor in Georgia Tech's School of Electrical and Computer Engineering and the Center for Organic Photonics and Electronics. "Now that we have shown very nice single transistors, we want to demonstrate functional devices that are combinations of multiple components. We have everything ready to do that."
Fabrication of the C60 transistors was reported August 27th in the journal Applied Physics Letters. The research was supported by the U.S. National Science Foundation through the STC program MDITR, and the U.S. Office of Naval Research.
Researchers have been interested in making field-effect transistors and other devices from organic semiconductors that can be processed onto various substrates, including flexible plastic materials. As an organic semiconductor material, C60 is attractive because it can provide high electron mobility -- a measure of how fast current can flow. Previous reports have shown that C60 can yield mobility values as high as six square centimeters per volt-second (6 cm2/V/s). However, that record was achieved using a hot-wall epitaxy process requiring processing temperatures of 250 degrees Celsius -- too hot for most flexible plastic substrates.
Though the transistors produced by Kippelen's research team display slightly lower electron mobility -- 2.7 to 5 cm2/V/s -- they can be produced at room temperature.
"If you want to deposit transistors on a plastic substrate, you really can't have any process at a temperature of more than 150 degrees Celsius," Kippelen said. "With room temperature deposition, you can be compatible with many different substrates. For low-cost, large area electronics, that is an essential component."
Because they are sensitive to contact with oxygen, the C60 transistors must operate under a nitrogen atmosphere. Kippelen expects to address that limitation by using other fullerene molecules -- and properly packaging the devices.
The new transistors were fabricated on silicon for convenience. While Kippelen isn't underestimating the potential difficulty of moving to an organic substrate, he says that challenge can be overcome.
Though their performance is impressive, the C60 transistors won't threaten conventional CMOS chips based on silicon. That's because the applications Kippelen has in mind don't require high performance.
"There are a lot of applications where you don't necessarily need millions of fast transistors," he said. "The performance we need is by far much lower than what you can get in a CMOS chip. But whereas CMOS is extremely powerful and can be relatively low in cost because you can make a lot of circuits on a wafer, for large area applications CMOS is not economical."
A different set of goals drives electronic components for use with low-cost organic displays, active billboards and similar applications.
"If you look at a video display, which has a refresh rate of 60 Hz, than means you have to refresh the screen every 16 milliseconds," he noted. "That is a fairly low speed compared to a Pentium processor in your computer. There is no point in trying to use organic materials for high-speed processing because silicon is already very advanced and has much higher carrier mobility."
Now that they have demonstrated attractive field-effect C60 transistors, Kippelen and collaborators Xiao-Hong Zhang and Benoit Domercq plan to produce other electronic components such as inverters, ring oscillators, logic gates, and drivers for active matrix displays and imaging devices. Assembling these more complex systems will showcase the advantages of the C60 devices.
"The goal is to increase the complexity of the circuits to see how that high mobility can be used to make more complex structures with unprecedented performance," Kippelen said.
The researchers fabricated the transistors by depositing C60 molecules from the vapor phase into a thin film atop a silicon substrate onto which a gate electrode and gate dielectric had already been fabricated. The source and drain electrodes were then deposited on top of the C60 films through a shadow mask.
Kippelen's team has been working with C60 for nearly ten years, and is also using the material in photovoltaic cells. Beyond the technical advance, Kippelen believes this new work demonstrates the growing maturity of organic electronics.
"This progress may trigger interest among more conventional electronic engineers," he said. "Most engineers would like to work with the latest technology platform, but they would like to see a level of performance showing they could actually implement these circuits. If you can demonstrate -- as we have -- that you can get transistors with good reproducibility, good stability, near-zero threshold voltages, large on-off current ratios and performance levels higher than amorphous silicon, that may convince designers to consider this technology."
Adapted from materials provided by Georgia Institute of Technology.

Fausto Intilla

www.oloscience.com

Powerful Microscope May Help Cancer Research

Source:

http://www.sciencedaily.com/releases/2007/11/071126100608.htm

ScienceDaily (Nov. 27, 2007) — The Centenary Institute unveiled a powerful microscope unlike any other in Australia. Representing the cutting edge in medical technology and microscopy, the unique imaging features of the multiphoton microscope will enable scientists at the Centenary Institute unprecedented access to the secret workings of living tissues at the cellular and molecular level.

The Centenary Institute is equally excited about the arrival of Austrian Professor Wolfgang Weninger, one of only a handful of people in the world who specialises in using the multiphoton microscope in the immunology field to view immune responses in real-time in living tissue.
At the Centenary, Professor Weninger will lead a team of researchers to study the dynamics of the immune system's response to cancer and infectious diseases.
Professor Weninger said, "Cancer is still a leading cause of death in Australia. There is a need to develop improved anti-cancer therapies based on the use of the body's own resources - namely our immune system. This type of microscope is an outstanding tool to study how our bodies fight cancer both in early and advanced stages. If we can learn more about how our immune system attacks cancer cells directly in the context of intact tissues, we hope to develop improved immuno-therapies."
Using the multiphoton microscope, Professor Weninger's team pioneered ground-breaking imaging models to record how the body's defences fight tumours and infectious diseases. He has made real-time videos of white blood cells invading and destroying cancer cells in living tissue.
I am confident that the results of his team's research will vastly improve our understanding of how the body's immune system fights cancer and infectious diseases. The multiphoton microscope will also support the research of other Centenary scientists particularly in autoimmune and liver diseases."
The multiphoton microscope at the Centenary Institute has two unique features, its imaging mode and laser. The unique imaging mode uses multiple laser beams and means fast moving objects and dynamic processes in living tissue can be viewed, for example, cells in the blood stream. The laser has been enhanced with a unit called an OPO that produces longer wavelengths of light than those used in other microscopes enabling researchers to potentially look deeper into living tissue than ever before.
Adapted from materials provided by Centenary Institute.

Fausto Intilla

www.oloscience.com

New T-ray Source Could Improve Airport Security, Cancer Detection

Source:

http://www.sciencedaily.com/releases/2007/11/071126121732.htm

ScienceDaily (Nov. 27, 2007) — Going through airport security can be such a hassle. Shoes, laptops, toothpastes, watches and belts all get taken off, taken out, scanned, examined, handled and repacked. But "T-rays", a completely safe form of electromagnetic radiation, may reshape not only airport screening procedures but also medical imaging practices.

Scientists at the U.S. Department of Energy's Argonne National Laboratory, along with collaborators in Turkey and Japan, have created a compact device that could lead to portable, battery-operated sources of T-rays, or terahertz radiation. By doing so, the researchers, led by Ulrich Welp of Argonne's Materials Science Division, have successfully bridged the "terahertz gap" – scientists' name for the range of frequencies between microwaves (on the lower side) and infrared (on the higher side) of the electromagnetic spectrum.
While scientists and engineers have produced microwave radiation using conventional electric circuits for more than 50 years, Welp said, terahertz radiation could not be generated that way because of the physical limitations of the semiconducting circuit components.
"Right around 1 terahertz, you have a range of frequencies where there have never been any good solid-state sources," he added. "You can make those frequencies if you are willing to put together a whole table full of expensive equipment, but now we've been able to make a simple, compact solid-state source."
Unlike far more energetic X-rays, T-rays do not have sufficient energy to "ionize" an atom by knocking loose one of its electrons. This ionization causes the cellular damage that can lead to radiation sickness or cancer. Since T-rays are non-ionizing radiation, like radio waves or visible light, people exposed to terahertz radiation will suffer no ill effects. Furthermore, although terahertz radiation does not penetrate through metals and water, it does penetrate through many common materials, such as leather, fabric, cardboard and paper.
These qualities make terahertz devices one of the most promising new technologies for airport and national security. Unlike today's metal or X-ray detectors, which can identify only a few obviously dangerous materials, checkpoints that look instead at T-ray absorption patterns could not only detect but also identify a much wider variety of hazardous or illegal substances.
T-rays can also penetrate the human body by almost half a centimeter, and they have already begun to enable doctors to better detect and treat certain types of cancers, especially those of the skin and breast, Welp said. Dentists could also use T-rays to image their patients' teeth.
The new T-ray sources created at Argonne use high-temperature superconducting crystals grown at the University of Tsukuba in Japan. These crystals comprise stacks of so-called Josephson junctions that exhibit a unique electrical property: when an external voltage is applied, an alternating current will flow back and forth across the junctions at a frequency proportional to the strength of the voltage; this phenomenon is known as the Josephson effect.
These alternating currents then produce electromagnetic fields whose frequency is tuned by the applied voltage. Even a small voltage – around two millivolts per junction – can induce frequencies in the terahertz range, according to Welp.
Since each of these junctions is tiny – a human hair is roughly 10,000 times as thick – the researchers were able to stack approximately 1,000 of them on top of each other in order to generate a more powerful signal. However, even though each junction would oscillate with the same frequency, the researchers needed to find a way to make them all radiate in phase.
"That's been the challenge all along," Welp said. "If one junction oscillates up while another junction oscillates down, they'll cancel each other out and you won't get anything."
In order to synchronize the signal, Argonne physicist Alexei Koshelev suggested that the stacks of Josephson junctions should be shaped into resonant cavities, which visiting scientist Lufti Ozyuzer of the Izmir Institute of Technology, Turkey, and graduate student Cihan Kurter then fashioned. When the width of the cavities was precisely tuned to the frequencies set by the voltage, the natural resonances of the structure synchronized the oscillations and thus amplified the T-ray output, in a method similar to the production of light in a laser.
"Once you apply the voltage," Welp said, "some junctions will start to oscillate. If those have the proper frequency, an oscillating electric field will grow in the cavity, which will pull in more and more and more of the other junctions, until in the end we have the entire stack synchronized."
By keeping the length and thickness of the cavities constant while varying their width between 40 and 100 micrometers, the researchers were able to generate frequencies from 0.4 to 0.85 terahertz at a signal power of up to 0.5 microwatts. Welp hopes to expand the range of available frequencies and to increase the strength of the signal by making the Josephson cavities longer or by linking them in arrays.
"The more power you have, the easier it is to adopt this technology for all sorts of applications," he said. "Our data indicate that the power stored in the resonant cavities is significantly larger than the detected values, though we need to improve the extraction efficiency. If we can get the signal strength up to 1 milliwatt, it will be a great success."
Collaborators on this research were Lutfi Ozyuzer, Alexei Koshelev, Cihan Kurter, Nachappa (sami) Gopalsami, Qing'An Li, Ken Gray, Wai-Kwong Kwok and Ulrich Welp of Argonne; Masashi Tachiki from the University of Tokyo; Kazuo Kadowaki, Takashi Yamamoto, Hidetoshi Minami and Hayato Yamaguchi from the University of Tsukuba; and Takashi Tachiki from the National Defense Academy of Japan.
The research was supported by DOE's Office of Basic Energy Sciences and by Argonne's Laboratory Directed Research and Development funds.
A scientific paper based on their research, "Emission of Coherent THz Radiation from Superconductors," appears in the November 23 issue of Science.
Adapted from materials provided by DOE/Argonne National Laboratory.

Fausto Intilla

www.oloscience.com

FED-TVs With Carbon Nanotube Technology Could Supersede Plasma And LCD Flat Screens

Source:

http://www.sciencedaily.com/releases/2007/11/071121094629.htm

ScienceDaily (Nov. 23, 2007) — Just as silicon is the wonder material for the computer age, carbon nanotubes will most likely be the materials responsible for the next evolutionary step in electronics and computing. Their extraordinary properties have identified them as having the potential to revolutionise many technologies.
In particular, it is widely believed that carbon nanotubes will take electronic devices to the next level. Many people expect the hugely popular LCD and plasma screens of today to be replaced by field emission flat screen displays (FED-TV). FED-TV's take all the best aspects of CRT's, LCD's and plasma TV's and roll them into a single package. While the technology exists, manufacturers are at present unable to compete with LCD's and plasma displays on a cost basis. However, carbon nanotubes have the ability to change all that.
In order to incorporate carbon nanotubes into devices like these field emission flat screen displays, an intimate knowledge of the properties of various forms of carbon nanotubes is invaluable. Researchers from University of Latvia, University College Cork, Trinity College Dublin, University of London and Mid Sweden University have just published work characterizing the conductive and field emission properties of single and multi walled carbon nanotubes.
In this research the conductive and field emission properties of individual single and multi-walled carbon nanotubes were assessed using an in-situ transmission electron microscope-scanning tunnelling microscope (TEM-STM) technique. The nanotubes were grown by chemical vapour and supercritical fluid deposition techniques.
Experimental field emission characteristics for all carbon nanotubes investigated fitted well to the Fowler-Nordheim equation when different work functions were applied. Differences in field emission and conductive properties are analysed and related to the structure of the carbon nanotubes. The method presented can be applied in order to make in situ selection of carbon nanotubes with desired properties for specific electronic applications.
The researchers found that conductivity and field emission properties were nanotube structure dependent. The structure of the outer layers and whether or not the nanotubes were filled with C60 molecules were key factors in determining the properties of the carbon nanotubes.
These findings make a significant contribution to the understanding of the structure/property relationships for carbon nanotubes, which in turn bring the next generation flat panel televisions and monitors a bit closer to our lounge rooms and offices.
Further details of the work by Jana Andzane, Joseph M. Tobin, Zhonglai Li, Juris Prikulis, Mark Baxendale, Håkan Olin, Justin D. Holmes and Donats Erts were published by AZoJono at http://www.azonano.com/Details.asp?ArticleID=2038.
Adapted from materials provided by AZoNetwork.

Fausto Intilla
www.oloscience.com

3-D Photonic Crystals Will Revolutionize Telecommunications

Source:

http://www.sciencedaily.com/releases/2007/11/071120104550.htm

ScienceDaily (Nov. 21, 2007) — Smaller, faster, more efficient: BASF research scientists are helping to revolutionize the future world of telecommunications – with the aid of three-dimensional photonic crystals. In a three-year project, BASF is researching into the development of these crystals together with partners such as Hanover Laser Center, Thales Aerospace Division, Photon Design Ltd., the Technical University of Denmark and the Ecole Nationale Supérieure des Télécommunications de Bretagne. By the end of 2008, the partners in the "NewTon" project expect to have developed the first functional components of this new technology. The long-term goal is to use three-dimensional photonic crystals as construction elements in telecommunication. Half of the project is being funded by the European Union.
Many times more information can be transmitted by light in the same time as has so far been possible with electricity. This is why telephone conversations, websites, photographs or music, for example, are now increasingly being transmitted in optical fibers. At present, however, this technology still has one drawback at the "network nodes". Indeed, at these nodes the routing of the information to the end-user is still done electrically, because no competitive, compact all-optical routing processor is yet available. This costs time and energy.
This is where the research activities of BASF and its partners come into the picture. They are developing a photonic crystal capable of reflecting only single colors of the white light depending on the observation angle. This phenomenon is known from nature: the splendid, shimmering colors on butterfly wings derive from the properties of photonic crystals.
"A structured three-dimensional photonic crystal could be the key component for a compact optical semiconductor or even for an all-optical routing processor", is the opinion of Dr. Reinhold J. Leyrer who is BASF’s project leader in Polymer Research division. "Converting optical signals into electrical signals would then be superfluous". But the scientists first have to develop a stable, structured three-dimensional photonic crystal. And exactly this is the goal of the EU project "NewTon". This kind of basic research projects are especially suited to activate the European scientific competence, in order to strengthen the competitiveness of the whole region and of all involved industrial branches.
The production of these crystals is based on aqueous dispersions, a key competence of BASF. These dispersions contain polymer spherical particles measuring about 200 nanometers which, when the fluid evaporates, are forming a homogeneous protective film as it is expected with the paints. Depending from the chemical structure of the polymer particles they can also arrange themselves into a regular lattice structure, forming a crystal.
The challenge facing the Ludwigshafen scientists is to enlarge the polymer particles contained in the dispersions to 1000 nanometers in such a way, that they all have exactly the same diameter. Using emulsion polymerization, they also apply an additional structure measuring less than 20 nanometers onto the polystyrene particles. The intention is to develop the most stable possible, large volume, three-dimensional crystal into which one of the project partners will then introduce the desired structure, the so called "defects".
Light at certain wavelengths then travels along these defects and even around sharp corners: the photonic crystal then acts as a photoconductor and takes the control over the propagation of light. The resulting structured crystal lattice is used in the further manufacturing process as a template, as the scientists call it. The spaces between the polymer spherical particles in the crystal lattice are filled with silicon. The researchers then "burn" the polymer particles out of the lattice. The result: a stable structure that is a mirror image of the original crystal. Crystals of this type could be used as components for an all-optical routing processor in telecommunications.
Manufacturers of components for telecommunication systems would benefit most from the use of photonic crystals. Since the crystals are smaller than electronic components, equipment would also become increasingly smaller and cheaper – while simultaneously offering improved performance. Components and equipment based on photonic crystals would also be more resistant and less vulnerable to electromagnetic radiation. End users will gain from these advances. In the long term, transmitting information through electrical signals will restrict speed and transmission capacity in telecommunications. The long-term goal is therefore to develop a communications technology based entirely on transmitting information by light waves. The research activities of the "NewTon" project are laying the foundations for this scenario.
Adapted from materials provided by BASF Aktiengesellschaft.

Fausto Intilla
www.oloscience.com

Lung-on-a-chip Leads To New Insights On Pulmonary Diseases

Source:

http://www.sciencedaily.com/releases/2007/11/071119143651.htm

ScienceDaily (Nov. 20, 2007) — A new "lung-on-a-chip" developed at the University of Michigan mimics the fluid mechanics of the real thing on a plastic wafer just bigger than a quarter. It allows researchers to grow lung airway cells that act more like they're in a human body instead of a Petri dish.

Biomedical engineers used the device to show that the respiratory crackles stethoscopes pick up in patients with diseases including asthma, cystic fibrosis, pneumonia and congestive heart failure aren't just symptoms, but may actually cause lung damage.
"Our lung-on-a-chip causes the cells to really become lung-like in terms of function and protein secretion. They form the tight tissue connections that they do in the human lung. That doesn't happen in a dish. This device gives you the convenience and control of a dish but in physical conditions that are more like the body," said Shuichi Takayama, associate professor of biomedical engineering and principal investigator on this study.
Takayama believes this is the first lung-on-a-chip. It's the same size as the part of the lung it simulates, the smallest airway branches.
The researchers were able to recreate the sound of respiratory crackles on the chip. And they measured and watched the destruction associated with the crackling on the surrounding cells.
The crackling is the sound of a breath of air opening airways that are clogged with thick fluid plugs. The fluid plugs form more frequently in patients with lung diseases that block the production of a fluid-thinning protein or narrow the airways. The plugs burst when air expands the lungs during breathing.
Doctors have considered the crackling sound more as a symptom or red flag, explained Dr. James Grotberg, a co-author of the study who is a professor of biomedical engineering in the College of Engineering and the Medical School.
Now, the plugs that cause the crackles appear to be a cause in addition to an effect.
"We've shown that these liquid plugs are injurious, particularly when they rupture" Grotberg said. "The rupture sends a very strong stress wave onto the cells. What's interesting is that the forces from the rupture are large in one place and small in another and those two places are close to each other. So you have a very steep gradient in forces and that's what shreds the cells."
To the surrounding cells, the bursts are like little sticks of exploding dynamite, Grotberg said.
The lung-on-a-chip that allowed the scientists to demonstrate this is made of two rubber sheets with a groove etched across their length. Their grooved sides are stuck together, with a porous sheet of polyester between them. The polyester allows the device to function as two separate chambers.
Engineers flooded both chambers with nourishing liquid while they were growing the lung cells in the device. Then, they emptied the top chamber to simulate an airway. That's when the lung cells started to develop further than they do in a dish. They formed tighter tissue bonds and secreted airway proteins as if they were part of a real lung.
Once the cells were sufficiently developed on the chip, Takayama and his colleagues did the control part of the experiment. They ran liquid through the chip channels and then air before testing to see if the lung cells were still healthy. They were.
Then they turned on the "microfabricated plug generator," which was connected to the cell culture chamber on the same chip. The plug generator is a vial of liquid into which the scientists pump air in such a way that drops of liquid enter the mock airways of the chip and eventually burst. They tested for periods of 10 minutes and found that at least 24 percent of the cells had died after persistent exposure to bursting liquid plugs. They observed more cell damage with more frequent plug bursts.
Takayama is also an associate professor of macromolecular science and engineering. The paper is called "Acoustically detectable cellular-level lung injury induced by fluid mechanical stresses in microfluidic airway systems." Co-authors include Biomedical Engineering Research Fellow Dongeun Huh, Biomedical Engineering Senior Research Fellow Hideki Fujioka, Biomedical Engineering Research Fellow Yi-Chung Tung, Post-doctoral researcher Nobuyuki Futai, and Adjunct Professor of Internal Medicine Robert Paine III.
A paper on the findings is published in the Nov.12 early edition of the Proceedings of the National Academy of Sciences.
Adapted from materials provided by University of Michigan.

Fausto Intilla

www.oloscience.com