yek567 - Science and Fiction: Nanotechnology

Showing posts with label Nanotechnology. Show all posts

Ultra-Thin Wires Could Revolutionize Computers

Atom-sized wires could lead to extremely small electronics and quantum computers.

Scientists said Thursday they have designed tiny wires, 10,000 times thinner than a human hair but with the same electrical capacity as copper, in a major step toward building smaller, more potent computers.

The advance, described in the US journal Science, shows for the first time that wires one atom tall and four atoms wide can carry a charge as well as conventional wires.

NEWS: Scientists Build Self-Replicating Robots

Scientists forged atom-sized wires in silicon using a technique called scanning tunneling microscopy.
Simmons et al., University of New South Wales
That could lead to even tinier electronic devices in the future as well as new steps toward quantum computing, an industry still in its infancy, which would create powerful computers that could sift through massive amounts of data faster than current digital computers which use binary code.

"Driven by the semiconductor industry, computer chip components continuously shrink in size allowing ever smaller and more powerful computers," said researcher Michelle Simmons of the University of New South Wales, in Sydney, Australia.

"We are on the threshold of making transistors out of individual atoms. But to build a practical quantum computer we have recognized that the interconnecting wiring and circuitry also needs to shrink to the atomic scale."

Scientists were able to forge atom-sized wires in silicon using a technique called scanning tunneling microscopy, whereby they placed chains of phosphorus atoms within a silicon crystal.

"This technique not only allows us to image individual atoms but also to manipulate them and place them in position," said researcher Bent Weber, the lead author of the study.

BLOG: How to Make Nano-Origami

The nano-wires they built this way ranged from 1.5 to 11 nanometers thick.

But even though the circuits were smaller, scientists observed no increased difficulty in coaxing an electric charge through them -- what has previously been considered a major obstacle to quantum computing.

In an accompanying Perspective article, David Ferry of the School of Electrical, Computer, and Energy Engineering at Arizona State University called the findings "good news for the semiconductor industry."

A Nanotech Teabag Delivers Potable Water for Less than a Cent

My hat goes off to the researchers at Stellenbosch University in South Africa, who developed this nano-fiber-filled tea bag. It can safely filter a liter of water, and it costs less than a cent.

The filter itself isn't reusable—or ready for mass production—and even at a fraction of a cent, it could be too expensive for those who need it most. However, it does have the potential to help deliver potable water in a scalable way.

In the following video you can see how it would work in conjunction with a reusable water bottle.

Creating Artificial Muscles More Powerful Than Anything In Nature

By observing the inner workings of an octopus's leg or an elephant's trunk, scientists have created muscles from carbon nanotubes that could one day power machines.
“Nature has been developing her technologies for many hundreds of millions of years," said Ray Baughman. “By looking at the way in which nature has solved problems like muscles, we can advance our own technologies.” Baughman is Director of the NanoTech Institute at the University of Texas at Dallas. His lab creates very tiny artificial muscles by spinning filaments of invisibly small carbon nanotubes into an extraordinary yarn. Pound per pound, this nano-yarn is stronger than steel, yet is so light it almost floats in air.

Penn Physicists Observe “Campfire Effect” in Blinking Nanorod Semiconductors

PHILADELPHIA — When semiconductor nanorods are exposed to light, they blink in a seemingly random pattern. By clustering nanorods together, physicists at the University of Pennsylvania have shown that their combined “on” time is increased dramatically providing new insight into this mysterious blinking behavior.

The research was conducted by associate professor Marija Drndic’s group, including graduate student Siying Wang and postdoctorial fellows Claudia Querner and Tali Dadosh, all of the Department of Physics and Astronomy in Penn’s School of Arts and Sciences. They collaborated with Catherine Crouch of Swarthmore College and Dmitry Novikov of New York University’s School of Medicine.

Their research was published in the journal Nature Communications.

When provided with energy, whether in the form of light, electricity or certain chemicals, many semiconductors emit light. This principle is at work in light-emitting diodes, or LEDs, which are found in any number of consumer electronics.

At the macro scale, this electroluminescence is consistent; LED light bulbs, for example, can shine for years with a fraction of the energy used by even compact-fluorescent bulbs. But when semiconductors are shrunk down to nanometer size, instead of shining steadily, they turn “on” and “off” in an unpredictable fashion, switching between emitting light and being dark for variable lengths of time. For the decade since this was observed, many research groups around the world have sought to uncover the mechanism of this phenomenon, which is still not completely understood.

“Blinking has been studied in many different nanoscale materials for over a decade, as it is surprising and intriguing, but it’s the statistics of the blinking that are so unusual,” Drndic said. “These nanorods can be ‘on’ and ‘off’ for all scales of time, from a microsecond to hours. That’s why we worked with Dmitry Novikov, who studies stochastic phenomena in physical and biological systems. These unusual Levi statistics arise when many factors compete with each other at different time scales, resulting in a rather complex behavior, with examples ranging from earthquakes to biological processes to stock market fluctuations.”

Drndic and her research team, through a combination of imaging techniques, have shown that clustering these nanorod semiconductors greatly increases their total “on” time in a kind of “campfire effect.” Adding a rod to the cluster has a multiplying effect on the “on” period of the group.

“If you put nanorods together, if each one blinks in rare short bursts, you would think the maximum ‘on’ time for the group will not be much bigger than that for one nanorod, since their bursts mostly don’t overlap,” Novikov said. “What we see are greatly prolonged ‘on’ bursts when nanorods are very close together, as if they help each other to keep shining, or ‘burning.’”

Drndic’s group demonstrated this by depositing cadmium selenide nanorods onto a substrate, shining a blue laser on them, then taking video under an optical microscope to observe the red light the nanorods then emitted. While that technique provided data on how long each cluster was “on,” the team needed to use transmission electron microscopy, or TEM, to distinguish each individual, 5-nanometer rod and measure the size of each cluster.

A set of gold gridlines allowed the researchers to label and locate individual nanorod clusters. Wang then accurately overlaid about a thousand stitched-together TEM images with the luminescence data that she took with the optical microscope. The researchers observed the “campfire effect” in clusters as small as two and as large as 110, when the cluster effectively took on macroscale properties and stopped blinking entirely.

While the exact mechanism that causes this prolonged luminescence can’t yet be pinpointed, Drndic’s team’s findings support the idea that interactions between electrons in the cluster are at the root of the effect.

“By moving from one end of a nanorod to the other, or otherwise changing position, we hypothesize that electrons in one rod can influence those in neighboring rods in ways that enhance the other rods’ ability to give off light,” Crouch said. “We hope our findings will give insight into these nanoscale interactions, as well as helping guide future work to understand blinking in single nanoparticles.”

As nanorods can be an order of magnitude smaller than a cell, but can emit a signal that can be relatively easily seen under a microscope, they have been long considered as potential biomarkers. Their inconsistent pattern of illumination, however, has limited their usefulness.

“Biologists use semiconductor nanocrystals as fluorescent labels. One significant disadvantage is that they blink,” Drndic said. “If the emission time could be extended to many minutes it makes them much more usable. With further development of the synthesis, perhaps clusters could be designed as improved labels.”

Future research will use more ordered nanorod assemblies and controlled inter-particle separations to further study the details of particle interactions.

This research was supported by the National Science Foundation.

Evan Lerner | elerner@upenn.edu | 215-573-6604
June 22, 2011

Speed of Light Lingers in Face of New Camera - Işık Hızında Çalışan Bir Fotoğraf Makinesi

More than 70 years ago, the M.I.T. electrical engineer Harold (Doc) Edgerton began using strobe lights to create remarkable photographs: a bullet stopped in flight as it pierced an apple, the coronet created by the splash of a drop of milk.

Di Wu and Andreas Velten, MIT Media Lab

SLOW DOWN M.I.T.'s camera captures light particles seemingly in motion by using repeated exposures, creating a “movie” of a nanosecond-long event.

Now scientists at M.I.T.’s Media Lab are using an ultrafast imaging systemto capture light itself as it passes through liquids and objects, in effect snapping a picture in less than two-trillionths of a second.

The project began as a whimsical effort to literally see around corners — by capturing reflected light and then computing the paths of the returning light, thereby building images coming from rooms that would otherwise not be directly visible.

“When I said I wanted to build a camera that looks around corners, my colleagues said, ‘Pick something that is more safe for your tenure,’ ” said Ramesh Raskar, an associate professor of media arts and sciences at the Media Lab. “Now I have tenure, so I can say this is not so crazy.”

Dr. Raskar enlisted colleagues from the chemistry department to modify a “streak tube,” a supersensitive piece of laboratory equipment that scans and captures light. Streak tubes are generally used to intensify streams of photons into streams of electrons. They are fast enough to record the progress of packets of laser light fired repeatedly into a bottle filled with a cloudy fluid.

The instrument is normally used to measure laboratory phenomena that take place in an ultra-short timeframe. Typically, it offers researchers information on intensity, position and wavelength in the form of data, not an image.

By modifying the equipment, the researchers were able to create slow-motion movies, showing what appears to be a bullet of light that moves from one end of the bottle to the other. The pulses of laser light enter through the bottom and travel to the cap, generating a conical shock wave that bounces off the sides of the bottle as the bullet passes.

The streak tube scans and captures light in much the same way a cathode ray tube emits and paints an image on the inside of a computer monitor. Each horizontal line is exposed for just 1.71 picoseconds, or trillionths of a second, Dr. Raskar said — enough time for the laser beam to travel less than half a millimeter through the fluid inside the bottle.

To create a movie of the event, the researchers record about 500 frames in just under a nanosecond, or a billionth of a second. Because each individual movie has a very narrow field of view, they repeat the process a number of times, scanning it vertically to build a complete scene that shows the beam moving from one end of the bottle, bouncing off the cap and then scattering back through the fluid. If a bullet were tracked in the same fashion moving through the same fluid, the resulting movie would last three years.

“You can think of it as slow motion,” Andreas Velten, a postdoctoral researcher who is a member of the design team, said during a recent technical presentation. “It is so much slow motion you can see the light itself move. This is the speed of light: there’s nothing in the universe that moves faster.”

Dr. Raskar says the technology has a variety of promising commercial applications. Last year, for example, one of his graduate students, Jaewon Kim, published a thesis envisioning portable CAT-scanning devices.

Dr. Raskar said he could also envision smartphone software that would capture and interpret reflections from, say, fruit. “Imagine if you have this in your phone about 10 years from now,” he said. “You will be able to go to your supermarket and tell if your fruit is ripe.”

Until now, picosecond speeds have largely been the province of an elite group of scientists clustered at the nation’s weapons laboratories.

At Lawrence Livermore National Laboratory, Gary Jones is an optical physicist who builds ultrafast imaging systems that help characterize the first microseconds of events like laser fusion and nuclear explosions. “To get a two-dimensional image within a picosecond means you have to have a lot of electronics moving really fast,” he said.

For Dr. Raskar — who optimistically calls the project “femto photography,” using the term for quadrillionths of a second — it is about more than just engineering or science. “We were inspired by looking at the world in a unique way just because we could,” he said.

The system allows the naked eye to see information that has until now been rendered as data and charts. The proper analogy is to the way astronomers use instruments like radiotelescopes to create images with “fake” colors to see things in new ways — or to the original inspiration of Eadweard Muybridge, the 19th-century British photographer who achieved a new understanding of a horse’s gait by creating a camera array with electromagnetic shutters set off by tripwires.

“We’re still trying to get our heads around what this means,” Dr. Raskar said, “because no one has been able to see the world in this way before.”

By JOHN MARKOFF

Published: December 12, 2011

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Massachusetts Teknoloji Enstitüsü'nün Medya Laboratuarındaki araştırmacılar, ışığı sıvıların ve objelerin içinden geçerken yakalamak için ultra hızlı bir görüntüleme sistemi kullanıyor. Bu teknikle saniyenin trilyonda ikisinden az bir sürede resim çekebiliyorlar. Proje aslında "görülemeyeni görmek" yönünde tuhaf bir çaba olarak başladı. Amaç, yansıyan ışığı yakalamak ve ardından ışığın geri dönüş yollarını hesaplayıp başka türlü görülemeyecek odalarda bulunanları görüntülemekti. Medya Laboratuarı'nda medya sanatları ve bilimleri doçenti Ramesh Raskar, "Görülemeyeni gören bir kamera yapmak istediğimi söylediğimde, meslektaşlarım 'Üniversitede sürekli bir pozisyon istiyorsan başka bir konu seç' dediler. Şimdi sürekli bir pozisyonum var ve bu yüzden yaptığımın o kadar da çılgınca olmadığını söyleyebilirim" diyor. Raskar ışığı tarayıp yakalayan süper hassas bir laboratuar gereci olan "ışın tüpü"nü modifiye etmek için kimya bölümünden yardım aldı. Işın tüpleri, genelde foton akımlarını elektron akımları halinde yoğunlaştırmak için kullanılıyor. Bu tüpler, bulanık bir sıvıyla doldurulmuş bir şişenin içine tekrar tekrar verilen lazer ışığının ilerlemesini kaydedecek kadar hızlı. Söz konusu gereç normalde, çok kısa bir zaman aralığında gerçekleşen laboratuar deneylerini ölçmek için kullanılıyor.

Tipik olarak, araştırmacılara yoğunluk, konum ve dalga boyuna dair veri sunuyor ancak görüntü sunmuyor. Araştırmacılar ısın tüpünü modifiye ederek şişenin bir ucundan diğer ucuna hareket eden bir ışık atımının nasıl göründüğünü gösteren ağır çekim filmler oluşturmayı başardılar. Lazer ışığı atımları şişenin içinden geçerek uca doğru ilerliyor, bu da atım geçerken şişenin yanlarına çarpıp seken konik bir şok dalgası üretiyor. Işın tüpü ışığı, bir katot ışın tüpünün görüntüyü çıkarıp bilgisayar ekranına çizmesiyle hemen hemen benzer şekilde tarıyor ve yakalıyor. Her bir yatay ışık çizgisi sadece 1.71 pikosaniye (saniyenin trilyonda biri) beliriyor. Raskar'a göre bu, lazer ışınının sıvı boyunca yarım milimetre gitmesi için yeterli zaman. Olayı görüntülemek için araştırmacılar bir nanosaniyenin (veya saniyenin milyarda birinin) biraz altında 500'e yakın kareyi kaydediyor.

Her filmin dar bir görüntü alanı olduğu için, süreci belli sayıda tekrarlayarak, ışının şişenin bir ucundan hareket ettiğini, diğer uca çarptığını ve gerisin geri sıvının içinde dağıldığını gösteren bütünlüklü bir sahne oluşturacak şekilde süreci şişe boyunca tekrarlıyorlar. Bir atım, sıvı boyunca hareket ederken takip edilseydi, ortaya çıkan film üç yıl uzunluğunda olurdu. Tasarım ekibinin üyesi olan Yardımcı Doçent Andreas Velten, "Bunu bir ağır çekim olarak düşünebilirsiniz. O kadar ağır bir çekim ki, bizzat ışığın hareketini görebiliyorsunuz. Evrende daha hızlı hareket eden başka bir şey yok" diyor.

Raskar teknolojinin potansiyeli olan ticari uygulamaları olduğunu söylüyor. Sözgelimi geçen yıl yüksek lisans öğrencilerinden biri taşınabilir CAT tarama aygıtları tasarlayan bir tez yayınlamış. R askar, meyvelerden gelen yansımaları yakalayıp yorumlayacak akıllı telefon yazılımı da tasarlanabileceğini söylüyor. "10 yıl sonra telefonunuzda böyle bir şey olduğunu düşünün. Süpermarketinize gidip meyvenin olgun olup olmadığını anlayabileceksiniz."

Bugüne kadar pikosaniye hızları büyük oranda ülkenin silah laboratuarlarında çalışan seçkin bir bilim insanları grubunun alanıydı. Raskar için (ki projeyi, saniyenin kuadrilyonda biri için kullanılan terim üzerinden "femto fotoğrafçılık" diye adlandırıyor) bu mühendislikten veya bilimden öte bir konu. "Dünyaya eşi benzeri olmayan bir şekilde bakmak bize ilham verdi. Bu deneyi sadece yapabildiğimiz i çin y aptık" d iyor v e ekliyor: "Hâlâ bunun ne anlama geldiğini idrak etmeye çalışıyoruz, çünkü kimse daha önce dünyayı bu şekilde görebilme şansına sahip olmadı."

New Materials May Allow One-Way Light

Normally, a glass window doesn’t care where a ray of light came from. But special kinds of glass or plastic could be a bit pickier.

Nonlinear materials could distinguish between two rays of light coming from opposite directions, say two Italian physicists. Blocking a ray from one direction and allowing in a ray from the other could be useful for making a one-way street for light.

Textbook optics prohibits this kind of directional discrimination. Everyday linear materials are governed by the reciprocity theorem, which says that a beam of light coming from the left will pass through and reflect off a material in the same way as a beam of light coming from the right.
But nonlinear materials, which can change as light passes through them, play by different rules.

“Without nonlinearity this asymmetry would not be possible,” says Giulio Casati, a physicist at the University of Insubria in Como, Italy.

A textbook pendulum, for instance, swings with a steady frequency that can be calculated from equations. But a nonlinear pendulum’s frequency changes over time in a way that can be worked out only with a computer.

Casati mathematically modeled the behavior of light passing through two layers of nonlinear material. The light changes the properties of the materials as it passes through, which in turn changes the behavior of light in complex ways.

Thanks to this back-and-forth dance, the frequency of light that can pass through these materials depends on the direction of the light, he reports in the April 22 Physical Review Letters.
“Other people have used nonlinearity, but they use it in a different way,” says Panayotis Kevrekidis, a mathematical physicist at the University of Massachusetts Amherst who wasn’t involved in the research.
Previous attempts to break down the reversibility of light used photonic crystals. Those materials can only block a portion of the light that has been boosted to twice its original frequency.
Casati’s initial simulations describe a way to transmit about 80 percent of the light traveling in one direction while blocking about 70 percent of the light coming from the opposite direction.
This selectivity could be useful for making wave diodes. Just as a traditional diode allows electrical current to flow only one direction in a piece of electronics, a wave diode could guide the flow of light in quantum or optical computing.

“This simple model may also apply to more general situations, like acoustics or different kinds of waves,” says Stefano Lepri, a physicist at the Italian National Research Council Institute for Complex Systems in Florence and a coauthor of the study. Materials that respond to sound waves nonlinearly could, he suggests, be useful for one-directional soundproofing.

Image: A proposed wave diode would allow light coming from the left to pass through (image on left) but reflect light coming from the other direction (right). (Stefano Lepri/Physical Review Letters)

By Devin Powell, Science News
April 20, 2011

Bacterial Biofilms Beat Teflon in Repelling Liquids

Slimy mats of bacteria called biofilms may be the most liquid-repellent materials in nature, researchers have discovered.

“There are a few man-made materials that can perform better, and they have to be made in clean rooms. They’re incredibly expensive and brittle,” said materials scientist Alexander Epstein of Harvard University, co-author of the new study. “Making biofilm is as easy as growing bacteria.”
The goo secreted by Bacillus subtilis bacteria not only deflects water like a lotus leaf, but also repels concentrated alcohol, acetone and even vaporized liquid, according to a study published Jan. 18 in Proceedings of the National Academy of Sciences.

Biofilms are communities of bacteria that stick together using a mixture of sugars and proteins called the extracellular matrix, which takes on a wrinkled form under powerful microscopes (see image below). Since the discovery of bacteria in the late 1600s, most research has covered individual cells. It’s only since the 1990s that scientists have begun to understand the pervasiveness and importance of biofilms.

“We’re realizing more and more that almost all bacteria in nature are found as biofilms,” Epstein said. “It offers a lot of advantages for them, including better protection and increased chances they’ll stick to sources of food. It’s crazy stuff.”

While trying to map the internal structure of B. subtilis biofilm using a vaporized radioactive tracer that would show up in x-ray photos, the researchers found it couldn’t get inside. They were frustrated at first, but Epstein said his team soon realized the significance of the stubborn biofilm.
“We started to put different liquids on it. Concentrated alcohols just [beaded up],” Epstein said. For comparison, the researchers also tried a non-stick Teflon surface. “We found the biofilms substantially superior to Teflon,” he said.

To analyze resistance to wetting, Epstein and his team measured the angle between droplets of liquid and the materials’ surfaces (right). At 10 percent alcohol, similar to wine’s concentration, Teflon started getting wet. Biofilms, however, balled up all concentrations of alcohol up to 80 percent (similar to Everclear). Liquids wetted biofilms only after sitting on them for minutes or hours.
Epstein isn’t suggesting we grow biofilms for frying pans or rain jackets, but thinks the research will inspire practical new applications. His team ultimately hopes to resolve biofilm’s molecular structure to develop new materials.
“We don’t fully understand it, but it’s broadly true that you need both protein and sugars for this repelling property,” Epstein wrote in an e-mail to Wired.com. “Sugars absolutely have to be there, but we don’t know why. We’re doing some followup research on that now,” he said.

Images: Courtesy of PNAS/Alexander Epstein et al. 1) A bead of 50 percent ethanol rests on a biolfilm of B. subtilis bacteria sliced from a Petri dish. 2) Wetness of a surface is determined by the contact angle of liquid droplets, and increases sharply when a droplet’s inner contact angle is less than 90 degrees. 3) A scanning electron micrograph of a mutant B. subtilis strain’s extracellular matrix, or ECM.

By Dave Mosher
January 31, 2011

Solar Cell Efficiency Could Be Boosted by Minimizing Defects

Nano-cones could help neutralize manufacturing defects in solar cells

A new advance in solar cells that tips the surface with minuscule cone structures could neutralize manufacturing defects, boosting efficiency up to 80 percent.

In conventional solar panels, more than 50 percent of the charges generated by sunlight are lost due to defects, said Jun Xu, a researcher at the Department of Energy's Oak Ridge National Laboratory. The irregularities in the formation of the crystalline structure of solar cells can trap electrons and limit the transfer of sunlight to electrical energy.

SOLAR FLAWS: Manufacturing defects impair solar cells ability to turn sunlight into electricity, but a new technique might help minimize the flaws. Image: Stephan Kambor via Wikimedia Commons

This is why Xu and his team are looking at how nanocones -- cone-shaped structures one-millionth of a meter long -- can neutralize the burden of defects.

The negative-polarity nanocones are made of zinc oxide, and surrounded by a positive-polarity cadmium telluride semiconductor that absorbs sunlight. The three-dimensional cone structure acts as a junction between the zinc oxide and cadmium telluride, making for a smoother conversion of the solar charge to electricity.

The idea, said Xu, is not to "fix" the defects, but to make them irrelevant. With the nanocone structure, the team was able to increase the overall electric charge to overcome the pitfalls of defects.
"If [manufacturers] make a defect with no way to solve it, we make the defect less relevant," he said. "You need to increase the efficiency ... you need to be able to increase change of transport. With a nanocone structure, you can do that."

On a small level, the efficiency gains are relatively minor -- rising to 3.2 percent, compared to 1.8 percent for panels without the nanocones. But Xu believes this will pay off on a larger scale.
"Our efficiency is moderate in generation, but the difference between the two platforms is huge," he said, referring to the models with and without nanocones. In the real world, even a much smaller percentage increase would be an important achievement for solar.

"If we can reduce the defective material, and we can increase the efficiency about 15 or 10 percent," he said, "that would be a huge success."

Zinc oxide and cadmium telluride serve as relatively cheap materials to create nanocones, as well, said Xu, with the potential to reduce the cost of commercial solar panels if applied to silicon -- the most common material used for solar panels.

The research will be published in the Institute of Electrical and Electronics Engineers' IEEE Proceedings.

From Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

Snowflakes Under an Electron Microscope

If you've ever wondered what snowflakes truly look like, spend a few moments with these images from the Electron Microscopy Unit of the Beltsville Agricultural Research Center in Beltsville, Maryland.

At the EMU, where other areas of focus include crop pathogens and livestock diseases, "studying the structure of snow is vital to several areas of science as well as to activities that affect our daily lives."
That's no doubt true. But for the rest of us, snow's structure is just beautiful. Enjoy!

The most complex snow-crystal classification system was devised in 1966 by Japanese meteorologists C. Magono and C.W. Lee. Entitled "Meteorological Classification of Natural Snow Crystals" (pdf), it describes more than 80 types of crystal. Above is P2b, or "stellar crystal with sectorlike ends."

The difference between what's seen under a light microscope — or would be seen by our eyes, were they a hundred times more powerful — and an electron microscope is shown in these two views of hoar crystals from a Wyoming snow pit.

For a near-instant, all-natural 3-D snowflake, cross your eyes and relax your vision until you can see three images. Then focus on the central image. Voila!

One more 3-D snowflake. If you dig this, there are six more available from the Electron Microscopy Unit.

Snow crystals often fall through supercooled cloud droplets, which can stay unfrozen down to -40 degrees Fahrenheit. The droplets coat snow crystals with still more crystals, and that frost is called rime.

Snowflake structure is visible at many levels, from a relatively coarse 100x magnification (top left) down to 1,800x (bottom right).

Falling snowflakes were collected at different temperatures on Bearden Mountain, West Virginia. At top left, 14 degrees Fahrenheit; top right, -4 degrees Fahrenheit; below, -22 degrees Fahrenheit.

Images : Electron and Confocal Microscopy Laboratory, Agricultural Research Service, U. S. Department of Agriculture.

http://emu.arsusda.gov/snowsite/default.html

The Emergence of Holographic Video

Experimental networked display refreshes holograms every two seconds

An image of an F4 Phantom fighter jet created with the new 3D telepresence system.
Researchers at the University of Arizona (UA), Tucson, have developed a holographic system that can transmit a series of 3D images in near-real-time, a precursor to holographic videoconferencing.

The system incorporates a novel, photorefractive polymer--one that can rapidly refresh holographic images and is scalable for production--coupled to a unique system for recording and transmitting 3D images of individuals and objects via Ethernet.

Lead author Pierre-Alexandre Blanche and his colleagues from the university and Nitto Denko Technical Corp. of Oceanside, Calif., describe the breakthrough in the cover story of the Nov. 4, 2010, issue of Nature.

"This advance brings us a step closer to the ultimate goal of realistic holographic telepresence with high-resolution, full-color, human-size, 3D images that can be sent at video refresh rates from one part of the world to the other," says co-author and project lead Nasser Peyghambarian of UA and the Director of NSF's multi-institution Engineering Research Center for Integrated Access Networks (CIAN).

The researchers had previously demonstrated a refreshable polymer display system, but it could refresh images only once every four minutes. The new system can refresh images every two seconds; while not yet ideal for a display, the rate is more than one hundred times faster.

Additionally, using a single-laser system for writing the images onto the photorefractive polymer, the researchers can display visuals in color. While the current refresh rate for multi-color display is even slower than for monochromatic images, the development suggests a true 3D, multicolor system may be feasible.
"This breakthrough opens new opportunities for optics as a means to transport images in real time," says Lynn Preston, director of the NSF Engineering Research Centers program that supports CIAN. "Such a system can have an important impact on telepresence, telemedicine, engineering design and manufacturing, and other applications. This is an early and tremendously important outcome from this three-year old center."
More information is available in the UA press release.

Project lead Nasser Peyghambarian of the University of Arizona, who is also director of NSF's multi-institution Engineering Research Center for Integrated Access Networks (CIAN), explains the technology--a holographic system that can transmit a series of 3D images in near-real-time, a precursor to holographic videoconferencing.

Credit: National Science Foundation

A hologram of a member of Peyghambarian's lab appears in the photorefractive polymer screen. Moving the camera from side to side reveals what the researchers call parallax, one of the novelties of this research: The holographic image presents itself from different perspectives as the viewer moves his or her head from side to side or up and down.

Credit: N. Peyghambarian, University of Arizona

This holographic representation of a vase shows different colors capable with the new system and an effect known as parallax, which makes the image life-like: As the viewer moves his or her head from side to side or up and down, the holographic image presents itself from different perspectives.

Credit: N. Peyghambarian, University of Arizona

A pulsed 50-Hz Laser inscribes a holographic image of a F-4 fighter jet into the photo-refractive polymer screen.

Credit: N. Peyghambarian, University of Arizona

A laser inscribes a series of holograms into the photorefractive polymer screen. Each iteration of the writing process takes only two seconds.

Credit: N. Peyghambarian, University of Arizona

Study co-author and project lead Nasser Peyghambarian of the University of Arizona, Tucson, the director of NSF's multi-institution Engineering Research Center for Integrated Access Networks (CIAN).

Credit: University of Arizona

Team member Vivian Sieh holds up the photorefractive polymer that has enabled the new 3D telepresence system to achieve a two-second refresh rate.

Credit: University of Arizona

This material is based upon work supported by the Engineering Research Center Program of the National Science Foundation under NSF Cooperative Support Agreement Award No. EEC-0812072

-NSF-
November 3, 2010
Press Release 10-207

Carbon Nanotubes Boost Power of Lithium Battery

A new battery demonstrated a power output 10 times higher, for its size, than what is expected of a conventional rechargeable lithium battery.
Imagine that the same rechargeable battery in your cell phone could power a device that requires 10 times the energy. That possibility may be closer than you think.

A battery created by researchers at Massachusetts Institute of Technology demonstrated an increased capacity for charge by roughly a third and a power output 10 times higher, for its size, than what is expected of a conventional rechargeable lithium battery. The results were published yesterday in Nature Nanotechnology.

The research team, led by Yang Shao-Horn, an associate professor of materials science and mechanical engineering, and Paula Hammond, professor of chemical engineering at MIT, achieved this by creating an entirely new kind of electrode -- in this case, by modifying the positive end of the conventional battery, which is called the cathode.

The collaboration began through graduate student Seung Woo Lee, studying fuel cells, who was advised by both Shao-Horn and Hammond. Lee defended his doctoral dissertation this spring.

Using commercially available carbon nanotubes -- hollow cylinders 50,000 times thinner than a human hair but composed of carbon atoms -- the team fabricated the cathode entirely out of the nanotubes put down in layers.

The large surface area of a nanotube allows it to store more charge than other types of carbon, such as graphite, but previous battery fabrication methods tended to obscure these surfaces.

Using the exposed surfaces allows more charge to be stored -- increasing capacity -- while also letting those charges migrate more easily -- increasing power.

The findings of this research challenge the conventional wisdom about what materials could be used in the cathode of a battery. It also stimulates discussion about what such powerful batteries could be used for.

Small scale experiments so far

Increased power output makes for a great capacitor as well, by efficiently storing charge and delivering that energy precisely when it is needed. Their work, Shao-Horn said, could "lead to a device with performance that bridges batteries and electrochemical capacitors."

So far, the thickest cathode the group has made for these experiments is only 3 micrometers -- 3 one-thousandths of a millimeter. This is tiny when compared to conventional lithium-ion batteries that have electrodes roughly 100 to 200 micrometers thick.

In their present form, Shao-Horn said, their cathode "could be ideal for microelectronic devices."
But these battery-capacitors are also useful in a number of other applications such as emergency power, "energy capture and power assist in cars, trucks and machinery requiring many start-stop cycles," said Shao-Horn. Successfully scaling up this design could dramatically reduce the inefficiencies in future lithium-ion batteries.

However, Shao-Horn preferred to err on the side of caution when peering into the future of this new technology, saying they are only just beginning to understand the underlying chemistry involved.
"Further work is required," said Shao-Horn, "to demonstrate that power and energy performance is maintained with thicker electrodes." A crucial next step of this research is to demonstrate an electrode with a thickness of 50 micrometers -- more than 10 times the size of what they made for their experiments.

The next phase is scaling it up

Doing so would allow the researchers to test whether the electrical properties of the carbon nanotubes can be successfully scaled up to greater and greater thicknesses. Potentially, Shao-Horn said, there is "no limit" on thickness. But in order to do this, Hammond's expertise in biomaterials will be essential.

The layer-by-layer fabrication technique used to make the 3-micrometer-thick carbon nanotube electrode described in the published paper was an extremely time-consuming process. For each layer of nanotubes, a sample had to be dipped into a solution awash with nanotubes.

Then, covered in the solution, the sample had to be left out for 15 to 20 minutes as gravity slowly pulled the nanotubes down through the liquid and onto the sample surface. This procedure had to be repeated about 400 times in order to pile up enough layers to reach a thickness of 3 micrometers.

To bring the layering process up to reasonable, commercially viable speeds, Hammond is appropriating an automatic spray technique she developed for producing layers of polymer materials.

"The spray method is 40 to 100 times faster," she said, taking only seconds to lay down each new layer of nanotubes rather than the 15 to 20 minutes it normally takes. The true test will come once much thicker electrodes are tested.
Other battery research from Shao-Horn's group has been highlighted in other ClimateWire stories.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500
By Darius Dixon and Climatewire | June 22, 2010

NanoCamo Is the Next Small Thing in Fashion

A new nanoassembly technique could make chameleon-like camouflage possible.

By using specially-designed proteins as nanomotors, Sandia National Laboratory researchers have created a system that can assemble quantum dots into bright, fluorescent rings. In this video, you can watch the formation of those rings, which are about five microns across, less than a tenth of the width of a human hair.
If these quantum dots were embedded on the surface of an object, the formation of the rings would cause the object to change color to the naked eye. Reverse the process and the color would change back. That raises the possibility of fast color changes of the sort that some animals use to blend in with their environments.
“Camouflage outfits that blend with a variety of environments without need of an outside power source — say, blue when at sea and then brown in a desert environment — is where this work could eventually lead,” George Bachand, the principal investigator at Sandia said in a press release.
But that’s probably a decade or more away, Bachand said.

Nobel Worthy: Best Graphene Close-Ups

Sorry diamond lovers, but graphene is the most awesome form of carbon out there. Evidence: Andre Geim and Konstantin Novoselov, the two scientists who isolated one-atom-thick sheets of the stuff in 2004, won the Nobel Prize this morning -- netting themselves a pot of 10 million Swedish kroner (about $1.49 million).
Despite its razor-thin makeup, graphene is one of the strongest, lightest and most conductive materials known to humankind. It’s also 97.3 percent transparent, but looks really cool under powerful microscopes. We’ve corralled some of the best shots here, with a bonus video of graphene being punished by an electron beam.

Mmmm... Graphene Cake

Theoretical physicist Philip Russell Wallace predicted graphene’s existence in 1947, but it wasn’t until the 1960s that scientists began looking for it in earnest. Forty years later, researchers practically wrote off isolating single-layer graphene. If the hexagonal layers didn’t roll up into buckeyballs or nanotubes, so the thinking went, they’d disintegrate entirely.
Geim and Novoselov persisted, however, and figured out how to isolate it using objects common to any office: Scotch tape and graphite, which is found in pencil leads.
At the top-right of this image is a 10-micron-wide, 30-layer-thick slice of graphene sheets.

Image: Science

Between the Graphene Sheets

The problem with seeing a single sheet of graphene is that it’s practically invisible.
To prove in 2004 that they’d isolated one using the tape-and-graphite method, Keim and Novoselov peeled off a single flake of graphene and stuck it onto silicon dioxide (the same stuff used to make semiconductors in electronics). Similar to how a sheen of oil becomes visible in a rainbow of colors on water, the combination of graphene on oxidized silicon revealed the flake in an electron microscope.

Image: Science

There's a Hole in My Graphene

Graphene may be the strongest carbon-based material, period, but it can’t stop a beam of electrons.
In this video, Berkeley Lab scientists subject an unsuspecting sheet of graphene to the punishment of a powerful electron beam. The beam punched a hole in the graphene, causing individual carbon atoms to scramble for a spot to stick at the hole's edge.

Video/image: Lawrence Berkeley National Laboratory

Pounding the Graphene Skins

Graphene drum? Check. Laser microphone? Check. Rock on.

In a 2007 test of graphene’s ability to resonate, researchers at Pomona College in California and Cornell University in New York stretched a 2-nanometer-wide ribbon of graphene over a silicon dioxide trench, then used an electrode to vibrate the sheet.

Image: Science

Graphene Bubble

Graphene is made up of carbon arranged into chicken-wire-like hexagonal rings, yet the bonds between any carbon atoms can stretch up to 20 percent. The arrangement may seem innocuous, yet it paves the way for quantum mechanical weirdness to manifest itself.

Case in point: When scientists sandwiched graphene onto platinum, then popped out a microscopic bubble, electrons in the graphene sheet behaved as if they were being punished by a magnetic field stronger than any ever produced in a laboratory. No magnetic field was in sight, so the effect was called (naturally) pseudo-magnetism.

Image: Lawrence Berkeley National Laboratory

Ribbons 'O Graphene

To say graphene conducts electricity well is a gross understatement. The electrons buzzing around graphene’s carbon atoms are unusually free to roam and behave more like massless pieces of light called photons. This allows graphene to be used like a high-performance transistor capable of operating at speeds 100 to 1,000 times faster than silicon-based transistors.

Trouble is, graphene moves electrons around a little too well. The threshold between graphene’s on/off state is exceedingly small, causing it to conduct electricity even in an “off” state. By growing micron-thin ribbons of graphene (above) instead of full sheets, however, chemists like Hongjie Dai at Stanford University have raised that threshold more than 10,000 times. Further improvements could lead to high-speed graphene-powered electronics.

Image: Hongjie Dai/Stanford University

Graphene Transistor

Capitalizing on graphene’s electrical awesomeness, HRL Laboratories (owned by Boeing and General Motors) built the world’s first functional radio frequency (RF) transistor using graphene in 2008. The tiny device, known as an RF field-effect transistor, can pick up radio frequencies while hardly gobbling any electrical power.

The company has since scaled up a full-size chip of the transistors, but alleged practical uses in imaging and communications remain to be seen.

Image: HRL Laboratories
By Dave Mosher

October 5, 2010

New X-ray Camera Sees Through Melting Metal

A new high-speed X-ray video camera, now the fastest in the world, can see through molten metal and watch weld-weakening flaws form in real-time.

The $670,000 device successfully captured X-ray footage on Nov. 23 at 5,000 frames-per-second (fps), or five times faster than previous X-ray cameras (and 83 times faster than a consumer camcorder). The high-speed video above shows a laser welding solid aluminum in visible light, followed by the new X-ray-light welding clips.

“With visible light, we could only see the surface of the welding process. You couldn’t see what was happening inside,” said Felix Abt, one of the camera’s designers at the University of Stuttgart. “The only way to see pores that weaken weld seams was to cut the metal into pieces.”

Automotive companies use robots equipped with high-powered lasers to seam cars together with extreme speed and precision. As laser welding continues to get “more powerful, move faster, go deeper” and increase in use, Abt says, it’s increasingly important to understand the dynamics involved.

“Laser welding creates very high-pressure, high-velocity, fluctuating environments. You’re boiling metal that’s cooling almost instantly,” Abt said. “This leads to instabilities that weaken your weld.”

To capture the welding process in action, Abt and his colleague Rudolph Weber use an industrial-strength 4-kilowatt laser, which is roughly 400,000 times more powerful than a DVD drive’s beam. As their laser pummels a hunk of metal moving on a track, a tube fires X-rays through the weld and toward a high-speed video camera.

As a frame of reference, the first clip shows 10,000 fps visible light footage zoomed in on a small 10-by-5-millimeter frame. The fuzzy 1,000 fps and 5,000 fps clips that follow are the new ones filmed in X-ray light.
“The white structure on left is where the laser hits. That’s a capillary of metallic steam,” Abt said, noting aluminum boils at 4,400 degrees Fahrenheit. Whitish globules that break off the capillary are weld-weakening pores that cool in a matter of microseconds.

The new X-ray footage isn’t pretty, Abt says, but in a few months he and Weber will tune the camera to increase its clarity. They also plan to imbue welding samples with tracer materials, such as tungsten carbide, that absorb X-rays and improve image contrast.
“This is really only the beginning, but we now have the ability to watch processes that lead to porosity in real time while we’re welding,” Abt said.

Video: A 4-kilowatt laser melts solid aluminum. The first clip is 10,000 fps in visible light, followed by 1,000 fps and 5,000 fps in X-ray light. Credit: Felix Abt, Rudolph Weber/University of Stuttgart
Image: The device Abt and Weber constructed to record laser welding in X-ray light. The laser hangs from the ceiling, the X-ray cathode is on the left (as the welding itself doesn’t produce X-rays) and the digital video camera is on the right. An exhaust vent pulls fumes away from the rig during welding and a track below moves a metal sample during recording. Credit: Felix Abt/University of Stuttgart