Researchers watch a next-gen memory bit switch in real time
November 17, 2011
For the first time, engineering researchers have been able to watch in real time the nanoscale process of a ferroelectric memory bit switching between the 0 and 1 states.
Ferroelectric materials have the potential to replace current memory designs, offering greater storage capacity than magnetic hard drives and faster write speed and longer lifetimes than flash memory. Replacing dynamic random access memory – the short-term memory that allows your computer to operate – with ferroelectric memory can significantly decrease energy usage in computers. Ferroelectric memory doesn’t require power to retain data.
A paper on the research is published in the Nov. 18, 2011, edition of Science.
“This is a direct visualization of the operation of ferroelectric memory,” said principal investigator Xiaoqing Pan, a professor in the Department of Materials Science and Engineering and director of the U-M Electron Microbeam Analysis Laboratory.
“By following ferroelectric switching at this scale in real time, we’ve been able to observe new and unexpected phenomena. This work will help us understand how these systems work so one can make better memory devices that are faster, smaller and more reliable.”
The researchers were able to see that the switching process of ferroelectric memory begins at a different site in the material than they initially believed. And this switching can be sparked with a lot less power than they had hypothesized.
“In this system, electric fields are naturally formed at the ferroelectric/electrode interfaces and this lowers the barrier for switching – for free. That means you can write information with much lower power consumption,” Pan said.
Pan is leading the development of special hybrid materials that contain both ferroelectric and magnetic components and could lead to next-generation magnetoelectric memory devices. This new study reports the behavior of one such material. An advantage of using these hybrid materials in memories is that they combine the advantages of both electric and magnetic memory classes: the ease of writing ferroelectric memory and the ease of reading magnetic memory. The interactions between ferroelectric and magnetic orders allow these hybrid materials to be integrated into other novel designs such as spintronics, which harness the intrinsic “up” or “down” spin of electrons.
Researchers from Cornell University, Penn State University, the University of Washington, the University of Wisconsin and Peking University also contributed to the work. The paper is called “Domain Dynamics during Ferroelectric Switching.” The research is funded by the U.S. Department of Energy and the National Science Foundation.
Ferroelectrics, discovered about 90 years ago, are characterized by a spontaneous electric polarization that can be reoriented between different orientations by an applied electric field. This ability to form and manipulate the regions (domains) with different polarization orientations at the nanometer scale is key to the utility of ferroelectric materials for devices such as nonvolatile memories. The ferroelectric switching occurs through the nucleation and growth of favorably oriented domains and is strongly influenced by defects and interfaces with electrical contacts in devices. It is critical for memory devices to understand how the ferroelectric domain forms, grows and interacts with defects and interfaces.
Xiaoqing Pan:
www.mse.engin.umich.edu/people/faculty/pan
U-M College of Engineering:
www.engin.umich.edu
The University of Michigan College of Engineering is ranked among the top engineering schools in the country. At $180 million annually, its engineering research budget is one of the largest of any public university. Michigan Engineering is home to 11 academic departments, numerous research centers and expansive entrepreneurial programs. The college plays a leading role in the Michigan Memorial Phoenix Energy Institute and hosts the world-class Lurie Nanofabrication Facility. Michigan Engineering’s premier scholarship, international scale and multidisciplinary scope combine to create The Michigan Difference.
Contact: Nicole Casal Moore
ncmoore@umich.edu
734-647-7087
University of Michigan
Personal electronics’ next revolution: Home printers that make 3-D objects
November 16, 2011
Just imagine: Instead of sending Grandma a holiday photo of the family for her fridge, you call up the image on your computer monitor, click “print,” and your printer produces a three-dimensional plastic model ready for hanging on the holiday tree. Scenes like that – in which homes have 3-D printers that build solid objects on demand – are fast approaching reality, according to the cover story in the current edition of Chemical & Engineering News, the American Chemical Society’s weekly newsmagazine.
In the article, C&EN Associate Editor Lauren K. Wolf explains that 3-D printers are on the verge of a personal revolution akin to the one that began in the 1970s and transformed computers from room-size machines to devices that fit on tables and now in pockets. A similar transformation is taking place in the world of 3-D printing, where machines are shrinking and the ability to create detailed objects from a variety of materials is growing. Engineers are now able to create objects out of a number of plastics, metals, ceramics and even foods like chocolate, sometimes with details as fine as a human hair.
The technology promises to foster revolutions in venues ranging from kitchens to hospital operating rooms. Some surgeons, for instance, envision printing bone grafts or replacement blood vessels with embedded proteins and cells that will help them fuse naturally. Chefs could print designer chocolates and gourmet meals with unique textures and tastes. “In 20 years, many people will have a 3-D printer in their kitchen for printing designer foods and other products,” the article quotes one scientist as saying.
The American Chemical Society is a non-profit organization chartered by the U.S. Congress. With more than 163,000 members, ACS is the world’s largest scientific society and a global leader in providing access to chemistry-related research through its multiple databases, peer-reviewed journals and scientific conferences. Its main offices are in Washington, D.C., and Columbus, Ohio.
To automatically receive news releases from the American Chemical Society contact newsroom@acs.org.
Contact: Michael Bernstein
m_bernstein@acs.org
202-872-6042
American Chemical Society
Marines test new energy-efficient weapon in the war on trash
November 15, 2011
In partnership with the Office of Naval Research (ONR), Marines at Camp Smith, Hawaii, are testing a high-tech trash disposal system that can reduce a standard 50-gallon bag of waste to a half-pint jar of harmless ash.
Called the Micro Auto Gasification System (MAGS), the unit is currently undergoing evaluation by U.S. Marine Corps Forces, Pacific (MARFORPAC) as a possible solution to help Marines win their daily battle against the increasing trash at remote forward operating bases (FOB).
Lt. Col. Mike Jernigan, a Marine combat engineer who recently commanded a logistics battalion in Afghanistan, said waste disposal in the field is a problem.
“Right now, there are really only two solutions: burn it or bury it,” Jernigan said. “Any potential solution must reduce the security and logistics concerns of trash disposal, and help the environment that’s a good thing for the Marine Corps.”
MAGS is both environmentally friendly and fuel efficient. A controlled decomposition process, which thermally converts energy from biomass is the key to MAGS’ effectiveness. “The system essentially bakes the trash and recovers a high portion of combustible gas byproduct, which is used to fuel the process,” said Donn Murakami, the MARFORPAC science adviser who leads the Marine Corps’ evaluation team.
Developed under the Environmental Quality, Discovery and Invention program at ONR and in collaboration with the Canadian Department of Defence, MAGS was designed to meet the need for a compact, solid-waste disposal system for both ships and shore facilities.
“Decades ago, the idea of harvesting energy from trash was just a side show in the environmental movement,” said Steve McElvany, the MAGS program officer at ONR. “Now, the technology is mature enough to where the Department of the Navy is seriously evaluating its practical and tactical benefits.”
The energy-efficient and clean-burning properties of MAGS make it attractive to expeditionary units. It has a low carbon footprint, and emissions are not visible, which is a tactical plus. Waste heat can also be used for practical purposes, such as heating living quarters or water.
“What we are doing for FOBs can be applied to schools, hospitals or an office building,” Murakami said. “We are talking about disposing our waste in a different manner, rather than just sending it to the landfill.”
Testing of MAGS will continue through March. Next summer, phase three of the evaluation will address the system’s expeditionary aspect at the Pohakuloa Training Area, Hawaii.
MAGS is an example of how ONR energy programs are helping the Department of the Navy meet its ashore goal of producing 50 percent of installation energy requirements from alternative sources by 2020.
To view a video of MAGS in action, go to www.youtu.be/CyRNWeQNGO8.
About the Office of Naval Research
The Department of the Navy’s Office of Naval Research (ONR) provides the science and technology necessary to maintain the Navy and Marine Corps’ technological advantage. Through its affiliates, ONR is a leader in science and technology with engagement in 50 states, 70 countries, 1,035 institutions of higher learning and 914 industry partners. ONR employs approximately 1,400 people, comprising uniformed, civilian and contract personnel, with additional employees at the Naval Research Lab in Washington, D.C.
Contact: Peter Vietti
onrcsc@onr.navy.mil
703-588-2167
Office of Naval Research
A light wave of innovation to advance solar energy
November 10, 2011
Some solar devices, like calculators, only need a small panel of solar cells to function. But supplying enough power to meet all our daily needs would require enormous solar panels. And solar-powered energy collected by panels made of silicon, a semiconductor material, is limited — contemporary panel technology can only convert approximately seven percent of optical solar waves into electric current.
Profs. Koby Scheuer, Yael Hanin and Amir Boag of Tel Aviv University’s Department of Physical Electronics and its innovative new Renewable Energy Center are now developing a solar panel composed of nano-antennas instead of semiconductors. By adapting classic metallic antennas to absorb light waves at optical frequencies, a much higher conversion rate from light into useable energy could be achieved. Such efficiency, combined with a lower material cost, would mean a cost-effective way to harvest and utilize “green” energy.
The technology was recently presented at Photonics West in San Francisco and published in the conference proceedings.
Receiving and transmitting green energy
Both radio and optical waves are electromagnetic energy, Prof. Scheuer explains. When these waves are harvested, electrons are generated that can be converted into electric current. Traditionally, detectors based on semiconducting materials like silicon are used to interface with light, while radio waves are captured by antenna.
For optimal absorption, the antenna dimensions must correspond to the light’s very short wavelength — a challenge in optical frequencies that plagued engineers in the past, but now we are able to fabricate antennas less than a micron in length. To test the efficacy of their antennas, Prof. Scheuer and his colleagues measured their ability to absorb and remit energy. “In order to function, an antenna must form a circuit, receiving and transmitting,” says Prof. Scheuer, who points to the example of a cell phone, whose small, hidden antenna both receives and transmits radio waves in order to complete a call or send a message.
By illuminating the antennas, the researchers were able to measure the antennas’ ability to re-emit radiation efficiently, and determine how much power is lost in the circuit — a simple matter of measuring the wattage going in and coming back out. Initial tests indicate that 95 percent of the wattage going into the antenna comes out, meaning that only five percent is wasted.
According to Prof. Scheuer, these “old school” antennas also have greater potential for solar energy because they can collect wavelengths across a much broader spectrum of light. The solar spectrum is very broad, he explains, with UV or infrared rays ranging from ten microns to less than two hundred nanometers. No semiconductor can handle this broad a spectrum, and they absorb only a fraction of the available energy. A group of antennas, however, can be manufactured in different lengths with the same materials and process, exploiting the entire available spectrum of light.
When finished, the team’s new solar panels will be large sheets of plastic which, with the use of a nano- imprinting lithography machine, will be imprinted with varying lengths and shapes of metallic antennas.
Improving solar power’s bottom line
The researchers have already constructed a model of a possible solar panel. The next step, says Prof. Scheuer, is to focus on the conversion process — how electromagnetic energy becomes electric current, and how the process can be improved.
The goal is not only to improve the efficiency of solar panels, but also to make the technology a viable option in terms of cost. Silicon is a relatively inexpensive semiconductor, but in order to obtain sufficient power from antennas, you need a very large panel — which becomes expensive. Green energy sources need to be evaluated not only by what they can contribute environmentally, but also the return on every dollar invested, Prof. Scheuer notes. “Our antenna is based on metal — aluminium and gold — in very small quantities. It has the potential to be more efficient and less expensive.”
American Friends of Tel Aviv University (http://www.aftau.org) supports Israel’s leading, most comprehensive and most sought-after center of higher learning. Independently ranked 94th among the world’s top universities for the impact of its research, TAU’s innovations and discoveries are cited more often by the global scientific community than all but 10 other universities.
Internationally recognized for the scope and groundbreaking nature of its research and scholarship, Tel Aviv University consistently produces work with profound implications for the future.
Contact: George Hunka
ghunka@aftau.org
212-742-9070
American Friends of Tel Aviv University
Unique bipolar compounds enhance functionality of organic electronics
November 6, 2011
Researchers often work with a narrow range of compounds when making organic electronics, such as solar panels, light emitting diodes and transistors. Professor Tim Bender and Ph.D. Candidate Graham Morse of University of Toronto’s Department of Chemical Engineering and Applied Chemistry have uncovered compounds that exhibit unique and novel electro-chemical properties.
“Organic solar cell need to absorb light, move electrons and transport holes. Normally you need one compound to do each function. Researchers have found compounds that can do two of the three. Our discovery leads to the potential of achieving all three with a single compound,” explains Bender.
During the summer of 2010, Bender gave Morse the very broad task of assessing new compositions of matter. Morse proposed a research hypothesis that led to the discovery of a new class of compounds with phthalimido molecular fragments. Along with fellow U of T collaborators, the pair have shown that their new compounds present the ability to move both holes and electrons in an organic light emitting diode (OLED). Given these compounds absorb sunlight as well, they have the potential to execute all three tasks needed for a functional organic solar cell. Bender and Morse are currently investigating this likelihood.
“Compounds with such electrochemical behaviour are very rare. The knowledge we developed will further an understanding of future compounds and synthesis strategies,” says Morse.
An important part of Bender and Morse’s work was the use of inexpensive raw materials and scalable synthetic methods so their research could transition smoothly into the next steps for materials development and conceivably a commercial product.
The detailed findings of their study were recently published in Applied Materials and Interfaces, an interdisciplinary journal designed to report on the function and development of new cutting-edge materials and their applications. The journal falls under the American Chemical Society – a top tier publisher in the field of chemistry and its application.
“Getting reported on by Applied Materials and Interfaces is an achievement in itself,” says Bender.
Contact: Liam Mitchell
liam.mitchell@utoronto.ca
416-978-4498
University of Toronto Faculty of Applied Science & Engineering
Major breakthrough improves software reliability and security
November 2, 2011
Anyone who uses multithreaded computer programs — and that’s all of us, as these are the programs that power nearly all software applications including Office, Windows, MacOS, and Google Chrome Browser, and web services like Google Search, Microsoft Bing, and iCloud, — knows well the frustration of computer crashes, bugs, and other aggravating problems. The most widely used method to harness the power we require from multicore processors, multithreaded programs can be difficult for programmers to get right and they often contain elusive bugs called races. Data races can cause very serious problems, like the software bug that set off the 2003 power blackout in the Northeast. Now there is a new system that will combat this problem.
Peregrine, a new software system developed by a team of researchers at Columbia Engineering School, led by Assistant Professor of Computer Science Junfeng Yang, will improve the reliability and security of multithreaded programs, benefiting virtually every computer user across the globe. Peregrine can be used by software vendors like Microsoft and Apple and web service providers like Google and Facebook, to provide reliable services to computer users. This new research was published in the 23rd ACM Symposium on Operating Systems Principles, considered to be the most prestigious systems conference held each year, and presented by Yang’s graduate student Heming Cui at Cascais, Portugal, on Oct. 26. The paper can be found at http://systems.cs.columbia.edu/archive/pub/2011/10/efficient-deterministic-multithreading-through-schedule-relaxation/.
“Multithreaded programs are becoming more and more critical and pervasive,” says Professor Yang.”But these programs are nondeterministic, so running them is like tossing a coin or rolling dice — sometimes we get correct results, and sometimes we get wrong results or the program crashes. Our main finding in developing Peregrine is that we can make threads deterministic in an efficient and stable way: Peregrine can compute a plan for allowing when and where a thread can “change lanes” and can then place barriers between the lanes, allowing threads to change lanes only at fixed locations, following a fixed order. This prevents the random collisions that can occur in a nondeterministic system.
“Once Peregrine computes a good plan without collisions for one group of threads,” adds Yang, “it can reuse the plan on subsequent groups to avoid the cost of computing a new plan for each new group. This approach matches our natural tendency to follow familiar routes so we can avoid both potential hazards in unknown routes and efforts to find a new route.”
Yang notes that in contrast to many earlier systems that address only resultant problems but not the root cause, Peregrine addresses nondeterminism — a system that is unpredictable as each input has multiple potential outcomes — and thus simultaneously addresses all the problems that are caused by nondeterminism.
Peregrine also deals with data races or bugs, unlike most previous efforts that do not provide such fine-grained control over the execution of a program. And it’s very fast — many earlier systems may slow down the execution of a program by up to ten times. Peregrine is also a practical system that works with current hardware and programming languages — it does not require new hardware or new languages, all of which can take years to develop. It reuses execution plans, whereas some previous work makes a different plan for each group of threads: as Yang points out, “The more plans one makes, the more likely some plans have errors and will lead to collisions.”
“Today’s software systems are large, complex, and plagued with errors, some of which have caused critical system failures and exploits,” adds Yang. “My research is focused on creating effective tools to improve the reliability and security of real software systems. I’m excited about this area because it has the potential to make the cyberspace a better place and benefit every government, business, and individual who uses computers.”
Yang’s research was funded by the National Science Foundation, including an NSF CAREER award, the Defense Advanced Research Projects Agency (DARPA), the Air Force Research Laboratory (AFRL), and the Intelligence Advanced Research Projects Activity (IARPA).
Columbia Engineering
Columbia University’s Fu Foundation School of Engineering and Applied Science, founded in 1864, offers programs in nine departments to both undergraduate and graduate students. With facilities specifically designed and equipped to meet the laboratory and research needs of faculty and students, Columbia Engineering is home to NSF-NIH funded centers in genomic science, molecular nanostructures, materials science, and energy, as well as one of the world’s leading programs in financial engineering. These interdisciplinary centers are leading the way in their respective fields while individual groups of engineers and scientists collaborate to solve some of modern society’s more difficult challenges. http://www.engineering.columbia.edu/
Contact: Holly Evarts
holly@engineering.columbia.edu
212-854-3206
Columbia University
Researchers roll out a new form of lighting
November 1, 2011
In this month’s edition of Physics World, Paul Blom and Ton van Mol from the Holst Centre in Eindhoven describe a way of creating thin, flexible sheets of organic light-emitting diodes (OLEDs) using a cheap, newspaper-style “roll-to-roll” printing process.
These bendable materials could oust the conventional light bulb and revolutionize the way we illuminate our surroundings, being used for everything from lighting tiles and strips in homes and offices to windows that can simulate sunrise and sunset.
Rather than the traditional solid, “inorganic” LEDs that we are used to seeing in display signs, traffic lights and car indicators, OLEDs can be easily dissolved in a solvent and so sprayed onto a roll of thin, flexible, plastic foil in the same way that newspapers are printed.
“Many companies recognize the potential of OLEDs and are investing heavily in research and development in the hope that when this technology finally takes off, they will be in pole position to take advantage,” Blom and Van Mol write.
The bottom layer of an OLED, which acts as a support, is a flexible material such as a polymer foil that has the electrodes and the light-emitting layer sandwiched on top to make up the complete device. Each layer is between 5 and 200 nanometres thick.
Traditional LEDs have so far failed to become a viable alternative to light bulbs because, despite being highly efficient, they have to be fabricated in clean rooms and so are expensive to make. But with about 20 per cent of the electricity the world consumes going on lighting, Blom and Van Mol state that any new, more-efficient lighting technology could greatly reduce global energy consumption.
OLEDs are poised to take over from the light bulb as their spray-on production makes them a faster and cheaper alternative to traditional LEDs and can be produced en mass through the “roll-to-roll” newspaper technique.
There are, however, several hurdles that need to be overcome before OLEDs become a commercial commodity, such as depositing the materials onto a thin film sheet with high precision, managing the properties of the different materials and, most importantly, keeping water out of the device – OLEDs have a barrier requirement up to a thousand times more demanding that food packaging.
Blom and Van Mol describe how their institution, along with several other research institutes and commercial companies, is at the forefront of combating these problems and delivering OLEDs into the hands of the consumer.
Also in this issue:
- Current controversy – superluminal neutrinos split OPERA collaboration
- Mikhail who? – celebrating the 300th anniversary of the founding father of Russian science
Please mention Physics World as the source of these items and, if publishing online, please include a hyperlink to: http://physicsworld.com
Notes for editors:
1. Physics World is the international monthly magazine published by the Institute of Physics. For further information or details of its editorial programme, please contact the editor, Dr Matin Durrani, on tel +44 (0)117 930 1002. The magazine’s website physicsworld.com is updated regularly and contains physics news, views and resources. Visit http://physicsworld.com.
2. For copies of Physics World and copies of the articles reviewed here contact Michael Bishop, IOP Press Officer, tel +44 (0)117 930 1032, e-mail michael.bishop@iop.org.
3. The Institute of Physics is a leading scientific society promoting physics and bringing physicists together for the benefit of all. It has a worldwide membership of around 40 000 comprising physicists from all sectors, as well as those with an interest in physics. It works to advance physics research, application and education; and engages with policymakers and the public to develop awareness and understanding of physics. Its publishing company, IOP Publishing, is a world leader in professional scientific communications. Go to http://www.iop.org
Contact: Michael Bishop
michael.bishop@iop.org
44-117-930-1032
Institute of Physics
An important aspect of structural design of super-tall buildings and structures
October 31, 2011
Across-wind loads and effects have become increasingly important factors in the structural design of super-tall buildings and structures with increasing height. Although researchers have investigated the problem for over 30 years now, the research achievements of across-wind loads and effects and the computation methods of equivalent static wind loads are still not satisfactory. Professor GU Ming and his group from the State Key Laboratory of Disaster Reduction in Civil Engineering set out to tackle this problem. After more than 10 years of innovative research, they have obtained many results for across-wind loads on super-tall buildings and structures with various cross-sections and developed new methods for determining across-wind aerodynamic damping and across-wind equivalent static wind loads. These achievements have been adopted in national and local load codes and have been applied to the structural design of a large number of actual super-tall buildings and structures. Their work, entitled “Across-wind loads and effects of super-tall buildings and structures”, was published in Science China Technological Sciences.
Professor GU Ming and his group have performed a series of wind tunnel tests on models of typical tall buildings and structures for across-wind forces employing a wind pressure scanning technique and high-frequency force balance technique. There were a total of 121 general building models and dozens of real tall structure models. Twenty-five building models for wind pressure tests and 96 building models for direct measurements of wind forces were sampled employing the high-frequency force balance technique. The models had different cross-section shapes, namely a square, rectangular, triangle, Y shape, polygon, L shape, corner-modified square, ladder shape, twin-tower shape, and a shape with a continuously contracting cross section.
Formulas for across-wind aerodynamic forces were derived for practical use from many experimental results obtained in wind tunnel tests. As an example, a unified formula for the non-dimensional power spectra density of the across-wind force acting on rectangular buildings and square buildings with corner modifications was derived. The formula has better features than previous formulas.
Aeroelastic models were used to investigate the aerodynamic damping characteristics of buildings. A base for supporting the aeroelastic models of tall buildings was specially designed for the tests. The frequency, mass distribution, and damping of the aeroelastic models could be easily adjusted for parametric study. Three series of buildings, namely rectangular buildings, corner-modified square buildings, and buildings with continuously contracting cross sections, were modeled and tested under four categories of terrain conditions in the TJ-1 Boundary Layer Wind Tunnel at Tongji University. The effects of the cross-section shape and dynamic parameter of buildings as well as the terrain condition on the aerodynamic damping were thoroughly investigated. The time-averaging method of the random-decrease technique and the stochastic sub-space identification method were adopted in the current study to identify the aerodynamic damping ratio. On the basis of testing results and analyses, a formula for the aerodynamic damping ratio of a square building was derived for practical purposes.
A new method of determining the across-wind equivalent static wind load was also developed. The across-wind equivalent static wind load was firstly divided into mean, resonant and background components for separate computation, and these components were combined as the total equivalent static wind load. The resonant component is equal to the inertial force due to vibration of the structure and the background component is essentially the base-moment-based equivalent static wind load.
Since there is no corresponding guidance in the present Chinese code, the across-wind loads and responses have not been considered by structural engineers for many super-tall buildings and structures. As an important application, the above new formulas and methods have been adopted in the national code of China and a local load code and have also been directly applied to the structural design of many super-tall buildings and structures.
The recent trend of constructing higher buildings and structures implies that wind engineering researchers will face new challenges, even problems they are currently unaware of. Therefore, there needs to be more effort to resolve engineering design problems and to further the development of wind engineering.
see the article: GU Ming, Quan Yong. Across-wind loads and effects of super-tall buildings and structures. SCIENCE CHINA Technological Science, 2011, 54(10)
Contact: Gu Ming
minggu@tongji.edu.cn
86-021-659-81210
Science in China Press
New hybrid technology could bring ‘quantum information systems
October 29, 2011
The merging of two technologies under development – plasmonics and nanophotonics – is promising the emergence of new “quantum information systems” far more powerful than today’s computers.
The technology hinges on using single photons the tiny particles that make up light for switching and routing in future computers that might harness the exotic principles of quantum mechanics.
The quantum information processing technology would use structures called “metamaterials,” artificial nanostructured media with exotic properties.
The metamaterials, when combined with tiny “optical emitters,” could make possible a new hybrid technology that uses “quantum light” in future computers, said Vladimir Shalaev, scientific director of nanophotonics at Purdue University’s Birck Nanotechnology Center and a distinguished professor of electrical and computer engineering.
The concept is described in an article to be published Friday (Oct. 28) in the journal Science. The article will appear in the magazine’s Perspectives section and was written by Shalaev and Zubin Jacob, an assistant professor of electrical and computer engineering at the University of Alberta, Canada.
“A seamless interface between plasmonics and nanophotonics could guarantee the use of light to overcome limitations in the operational speed of conventional integrated circuits,” Shalaev said.
Researchers are proposing the use of “plasmon-mediated interactions,” or devices that manipulate individual photons and quasiparticles called plasmons that combine electrons and photons.
One of the approaches, pioneered at Harvard University, is a tiny nanowire that couples individual photons and plasmons. Another approach is to use hyperbolic metamaterials, suggested by Jacob; Igor Smolyaninov, a visiting research scientist at the University of Maryland; and Evgenii Narimanov, an associate professor of electrical and computer engineering at Purdue. Quantum-device applications using building blocks for such hyperbolic metamaterials have been demonstrated in Shalaev’s group.
“We would like to record and read information with single photons, but we need a very efficient source of single photons,” Shalaev said. “The challenge here is to increase the efficiency of generation of single photons in a broad spectrum, and that is where plasmonics and metamaterials come in.”
Today’s computers work by representing information as a series of ones and zeros, or binary digits called “bits.”
Computers based on quantum physics would have quantum bits, or “qubits,” that exist in both the on and off states simultaneously, dramatically increasing the computer’s power and memory. Quantum computers would take advantage of a strange phenomenon described by quantum theory called “entanglement.” Instead of only the states of one and zero, there are many possible “entangled quantum states” in between one and zero.
An obstacle in developing quantum information systems is finding a way to preserve the quantum information long enough to read and record it. One possible solution might be to use diamond with “nitrogen vacancies,” defects that often occur naturally in the crystal lattice of diamonds but can also be produced by exposure to high-energy particles and heat.
“The nitrogen vacancy in diamond operates in a very broad spectral range and at room temperature, which is very important,” Shalaev said.
The work is part of a new research field, called diamond photonics. Hyperbolic metamaterials integrated with nitrogen vacancies in diamond are expected to work as efficient “guns” of single photons generated in a broad spectral range, which could bring quantum information systems, he said.
Writer: Emil Venere, 765-494-4709, venere@purdue.edu
Sources: Vladimir Shalaev, 765-494-9855, shalaev@ecn.purdue.edu Zubin Jacob, zjacob@ualberta.ca
Related websites: Vladimir Shalaev: http://www.ece.purdue.edu/~shalaev Zubin Jacob: http://www.ece.ualberta.ca/~zjacob
IMAGE CAPTION
Structures called “metamaterials” and the merging of two technologies under development are promising the emergence of new “quantum information systems” far more powerful than today’s computers. The concept hinges on using single photons the tiny particles that make up light for switching and routing in future computers that might harness the exotic principles of quantum mechanics. The image at left depicts a “spherical dispersion” of light in a conventional material, and the image at right shows the design of a metamaterial that has a “hyperbolic dispersion” not found in any conventional material, potentially producing quantum-optical applications. (Zubin Jacob)
Contact: Emil Venere
venere@purdue.edu
765-494-4709
Purdue University
Amorphous diamond, a new super-hard form of carbon created under ultrahigh pressure
October 17, 2011
An amorphous diamond – one that lacks the crystalline structure of diamond, but is every bit as hard – has been created by a Stanford-led team of researchers.
But what good is an amorphous diamond?
“Sometimes amorphous forms of a material can have advantages over crystalline forms,” said Yu Lin, a Stanford graduate student involved in the research.
The biggest drawback with using diamond for purposes other than jewelry is that even though it is the hardest material known, its crystalline structure contains planes of weakness. Those planes are what allow diamond cutters to cleave all the facets that help give a diamond its dazzle – they are actually breaking the gem along weak planes, not cutting it.
“With diamond, the strength depends on the direction a lot. It’s not a bad property, necessarily, but it is limiting,” said Wendy Mao, the Stanford mineral physicist who led the research. “But if diamond is amorphous, it may have the same strength in all directions.”
That uniform super-hardness, combined with the light weight that is characteristic of all forms of carbon – including diamond – could open up exciting areas of application, such as cutting tools and wear-resistant parts for all kinds of transportation.
Other researchers have tried to create diamond-like amorphous carbon, but have only been able to make extremely thin films that contain impurities such as hydrogen and do not have completely diamond-like atomic bonds. The amorphous diamond created by Mao and Lin can be made in thicker bulk forms, opening up more potential applications.
Lin is the lead author of a paper describing the research that will be published in Physical Review Letters. Mao, Lin’s adviser, is a coauthor. Colleagues at the Carnegie Institution of Washington contributed to the research and are also coauthors.
The researchers created the new, super-hard form of carbon using a high-pressure device called a diamond anvil cell. They did a series of experiments with tiny spheres of glassy carbon, an amorphous form of carbon which they compressed between the two diamond anvils. The spheres were a few tens of micrometers (millionths of a meter) in diameter.
They slowly cranked up the pressure on the spheres. When the pressure exceeded 40 gigapascals – 400,000 times atmospheric pressure – the arrangement of the bonds between the carbon atoms in the glassy spheres had completely shifted to a form that endowed the spheres with diamond-like strength.
The researchers detected the shift in internal bonding by probing the spheres with X-rays.
They also did experiments in which a glassy sphere was simultaneously subjected to different pressures from different directions, to further assess the strength of the new form of carbon. While the diamonds in the anvil pressed in on the sides of the sphere with a pressure of 60 gigapascals – about 600,000 times atmospheric pressure – the pressure on the tip of the sphere reached 130 gigapascals.
“The amorphous diamond survived a pressure difference of 70 gigapascals – 700,000 atmospheres – which only diamond has been able to do,” Mao said. “Nothing else can withstand that sort of stress difference.”
Although the bonds between atoms in the glassy spheres were altered by the extreme pressure, the amorphous, or disordered, structure of the spheres was unchanged.
“The material doesn’t get any more ordered as we compress it. It maintains its disorder,” Mao said. The outer form of the original material was also retained – if the researchers started with a sphere, then even at the highest pressures, the sphere was still a sphere. The only change was in the type of bonds between the carbon atoms.
One characteristic of the new amorphous diamond is that it is not always hard or always soft. The hardness of the amorphous carbon is tunable; it is soft at low pressure, but the greater the pressure, the harder it gets. Once the pressure of the anvil was released, it returned to its original form as simple glassy carbon, with strength no greater than it had to begin with.
For the amorphous diamond to find widespread application, Mao said, someone will have to find a way to either make the material at low pressure or figure out how to preserve it once the super-hard form is created under high pressure.
Even though the amorphous diamond returned to plain old glassy carbon when the pressure was released, there are still potential applications. The material could be used as a gasket in high-pressure devices where having a gasket that hardens with pressure would be beneficial. Or it could be used in further high-pressure experiments.
“We use a diamond anvil cell to compress samples for high-pressure research, but because this amorphous diamond phase hardens with pressure, it could be a second stage anvil inside the diamond anvil,” Lin said.
“Having another anvil in sequence would let us create even higher pressures at the very tip.”
Since the focus of Mao’s research group is to answer questions about the extreme environments in the deep Earth and other planetary interiors, a “double diamond” anvil could prove extremely useful. One can only speculate as to what exotic materials might be discovered with such an amped-up anvil.
Mao is an assistant professor with a joint appointment in Geological and Environmental Sciences at Stanford University and of Photon Science at the Department of Energy’s SLAC National Accelerator Laboratory. Lin is a graduate student in Geological and Environmental Sciences.
Contact: Louis Bergeron
louisb3@stanford.edu
650-725-1944
Stanford University