Down to the wire for silicon: Researchers create a wire four atoms wide, one atom tall

ScienceDaily (Jan. 5, 2012) — The smallest wires ever developed in silicon -- just one atom tall and four atoms wide -- have been shown by a team of researchers from the University of New South Wales, Melbourne University and Purdue University to have the same current-carrying capability as copper wires.

Experiments and atom-by-atom supercomputer models of the wires have found that the wires maintain a low capacity for resistance despite being more than 20 times thinner than conventional copper wires in microprocessors.

The discovery, which was published in this week's journal Science, has several implications, including:

For engineers it could provide a roadmap to future nanoscale computational devices where atomic sizes are at the end of Moore's law. The theory shows that a single dense row of phosphorus atoms embedded in silicon will be the ultimate limit of downscaling.For computer scientists, it places donor-atom based silicon quantum computing closer to realization.And for physicists, the results show that Ohm's Law, which demonstrates the relationship between electrical current, resistance and voltage, continues to apply all the way down to an atomic-scale wire.

Bent Weber, the paper's lead author and a graduate student in the Centre of Excellence for Quantum Computation and Communication Technology at the University of New South Wales, was thrilled with the finding.

"It's extraordinary to show that Ohm's Law, such a basic law, still holds even when constructing a wire from the fundamental building blocks of nature -- atoms," he says.

The innovation of the Australian group was to build the circuits up atom by atom, instead of the current method of building microprocessors, in which material is stripped away, says Gerhard Klimeck, a Purdue professor of electrical and computer engineering and director of the Network for Computational Nanotechnology.

"Typically we chip or etch material away, which can be very expensive, difficult and inaccurate," Klimeck says. "Once you get to 20 atoms wide you have atomic flucuations that make scaling difficult. But this experimental group built devices by placing atomically thin layers of phosphorus in silicon and found that with densely doped phosphorus wires just four atoms wide it acts like a wire that conducts just as well as metal."

The goal of the research is to develop future quantum computers in which single atoms are used for the computation, says Michelle Simmons, director of the Centre of Excellence for Quantum Computation and Communication Technology at the University of New South Wales and the project's principal investigator.

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

Hoon Ryu, a Purdue graduate who is now a senior researcher with the Korea Institute of Science and Technology's Supercomputing Center, said the practicality of the research is exciting.

"The metallic wire is in principle quite difficult to be scaled into one- to two-nanometer pitch, but in both experimental and modeling views, the research result is quite remarkable," Ryu says. "For the first time, this demonstrates the possibility that densely doping wire is a viable alternative for the next-gerenation, ultra-scale metallic interconnect in silicon chips."

To assist the Australian researchers, Klimeck's research team ran hundreds of simulations to study the variability of these nanoscale structures.

"Having the throughput capability for a highly scalable code is important for doing that, and we have that capability here at Purdue with http://nanoHUB.org," Klimeck says. "We ran hundreds of cases to understand the potential landscape of these devices, so this was computationally intensive work."

Klimeck says that in addition to the project's scientific and engineering implications, he found the collaboration the most rewarding aspect.

"It is an exciting collaboration," he says. "We were doing simulations of experimental work, which was based on a theoretical model. So we were bringing the three legs of modern science together in one project. Plus, our graduate students are able to stay in contact and work with each other despite working in various locations around the world. It's hard to think of a better example of how science is done today."

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The above story is reprinted from materials provided by Purdue University. The original article was written by Steve Tally.

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Journal Reference:

B. Weber, S. Mahapatra, H. Ryu, S. Lee, A. Fuhrer, T. C. G. Reusch, D. L. Thompson, W. C. T. Lee, G. Klimeck, L. C. L. Hollenberg, M. Y. Simmons. Ohm's Law Survives to the Atomic Scale. Science, 2012; 335 (6064): 64-67 DOI: 10.1126/science.1214319

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Researchers measure nanometer scale temperature

Atomic force microscope cantilever tips with integrated heaters are widely used to characterize polymer films in electronics and optical devices, pharmaceuticals, paints, and coatings. These heated tips are also used in research labs to explore new ideas in nanolithography and data storage, and to study fundamentals of nanometer-scale heat flow. Until now, however, no one has used a heated nano-tip for electronic measurements.

"We have developed a new kind of electro-thermal nanoprobe," according to William King, a College of Engineering Bliss Professor in the Department of Mechanical Science and Engineering at Illinois. "Our electro-thermal nanoprobe can independently control voltage and temperature at a nanometer-scale point contact. It can also measure the temperature-dependent voltage at a nanometer-scale point contact."

"Our goal is to perform electro-thermal measurements at the nanometer scale," according to Patrick Fletcher, first author of the paper, "Thermoelectric voltage at a nanometer-scale heated tip point contact," published in the journal Nanotechnology. "Our electro-thermal nanoprobe can be used to measure the nanometer-scale properties of materials such as semiconductors, thermoelectrics, and ferroelectrics."

The electro-thermal probes are different than thermal nanoprobes typically used in King's group and elsewhere. They have three electrical paths to the cantilever tip. Two of the paths carry heating current, while the third allows the nanometer-scale electrical measurement. The two electrical paths are separated by a diode junction fabricated into the tip. While the cantilever design is complex, the probes can be used in any atomic force microscope.

In addition to Fletcher, co-authors of the paper include Byeonghee Lee, and William King. The research was performed in the Nanoengineering laboratory as well as the Micro and Nanotechnology Laboratory and the Materials Research Laboratory at Illinois.

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The above story is reprinted from materials provided by University of Illinois College of Engineering.

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Journal Reference:

Patrick C Fletcher, Byeonghee Lee, William P King. Thermoelectric voltage at a nanometer-scale heated tip point contact. Nanotechnology, 2012; 23 (3): 035401 DOI: 10.1088/0957-4484/23/3/035401

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Kilobots are leaving the nest: Swarm of tiny, collaborative robots will be made available to researchers, educators, and enthusiasts

The Kilobots are coming. Computer scientists and engineers at Harvard University have developed and licensed technology that will make it easy to test collective algorithms on hundreds, or even thousands, of tiny robots.

Called Kilobots, the quarter-sized bug-like devices scuttle around on three toothpick-like legs, interacting and coordinating their own behavior as a team. A June 2011 Harvard Technical Report demonstrated a collective of 25 machines implementing swarming behaviors such as foraging, formation control, and synchronization.

Once up and running, the machines are fully autonomous, meaning there is no need for a human to control their actions.

The communicative critters were created by members of the Self-Organizing Systems Research Group led by Radhika Nagpal, the Thomas D. Cabot Associate Professor of Computer Science at the Harvard School of Engineering and Applied Sciences (SEAS) and a Core Faculty Member at the Wyss Institute for Biologically Inspired Engineering at Harvard. Her team also includes Michael Rubenstein, a postdoctoral fellow at SEAS; and Christian Ahler, a fellow of SEAS and the Wyss Institute.

Thanks to a technology licensing deal with the K-Team Corporation, a Swiss manufacturer of high-quality mobile robots, researchers and robotics enthusiasts alike can now take command of their own swarm.

One key to achieving high-value applications for multi-robot systems in the future is the development of sophisticated algorithms that can coordinate the actions of tens to thousands of robots.

"The Kilobot will provide researchers with an important new tool for understanding how to design and build large, distributed, functional systems," says Michael Mitzenmacher, Area Dean for Computer Science at SEAS.

"Plus," he adds, "tiny robots are really cool!"

The name "Kilobot" does not refer to anything nefarious; rather, it describes the researchers' goal of quickly and inexpensively creating a collective of a thousand bots.

Inspired by nature, such swarms resemble social insects, such as ants and bees, that can efficiently search for and find food sources in large, complex environments, collectively transport large objects, and coordinate the building of nests and other structures.

Due to reasons of time, cost, and simplicity, the algorithms being developed today in research labs are only validated in computer simulation or using a few dozen robots at most.

In contrast, the design by Nagpal's team allows a single user to easily oversee the operation of a large Kilobot collective, including programming, powering on, and charging all robots, all of which would be difficult (if not impossible) using existing robotic systems.

So, what can you do with a thousand tiny little bots?

Robot swarms might one day tunnel through rubble to find survivors, monitor the environment and remove contaminants, and self-assemble to form support structures in collapsed buildings.

They could also be deployed to autonomously perform construction in dangerous environments, to assist with pollination of crops, or to conduct search and rescue operations.

For now, the Kilobots are designed to provide scientists with a physical testbed for advancing the understanding of collective behavior and realizing its potential to deliver solutions for a wide range of challenges.

Funding was provided by the National Science Foundation and the Wyss Institute.

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The perfect clone: Researchers hack RFID smartcards

ScienceDaily (Nov. 3, 2011) — Professional safecrackers use a stethoscope to find the correct combination by listening to the clicks of the lock. Researchers at the Ruhr-University Bochum have now demonstrated how to bypass the security mechanisms of a widely used contactless smartcard in a similar way. Employing so-called "Side-Channel Analysis" the researchers of the Chair for Embedded Security (Prof. Dr.-Ing. Christof Paar) can break the cryptography of millions of cards that are used all around the world.

Mathematically secure

RFID smartcards (Radio Frequency Identification) of the type DESFire MF3ICD40 are widely employed in payment and access control systems. The security of these cards is based on Triple-DES, a cipher that is unbreakable from a purely mathematic point of view. DESFire cards are for instance used by the public transport agencies in Melbourne, San Francisco and Prague. The DESFire MF3ICD40 is manufactured by NXP, the former semiconductor division of Philips Electronics.

Fluctuations of the magnetic field

A person is identified as a passenger, employee or customer when his RFID smartcard is placed in the proximity of a reader. To guarantee the necessary level of security, a secret key is stored on the integrated chip inside the card. But just like for the safe, the security mechanism produces the electronic equivalent of the clicks of a mechanic lock. "We measured the power consumption of the chip during the encryption and decryption with a small probe," says David Oswald. The fluctuations of the electro-magnetic field allow the researchers to conclude to the full 112-bit secret key of the smartcard.

Low cost, big damage

Having extracted the keys, an attacker can create an unlimited number of undetectable clones of a given card. The required time and effort are quite low: "For our measurements, we needed a DESFire MF3ICD40 card, an RFID reader, the probe and an oscilloscope to measure the power consumption," says Oswald. This equipment only costs a few thousand euros. Having obtained knowledge on the characteristic properties of the smartcard, the attack takes three to seven hours. The manufacturer NXP confirmed the security hole in the meanwhile and recommends his customers to upgrade to a newer version of the card.

Insufficient countermeasures

Already back in 2008, researchers around Prof. Dr.-Ing. Christof Paar used Side-Channel Analysis to break supposedly secure systems. Three years ago, garage and car doors "mysteriously" opened for the researchers of the Chair for Embedded Security. The employed KeeLoq RFID system -- which customers and manufacturers trusted blindly before -- turned out to be highly susceptible to Side-Channel Analysis, researchers said.

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A light wave of innovation to advance solar energy: Researchers adapt classic antennas to harness more power from the sun

ScienceDaily (Nov. 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."

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Feeding the five thousand -- or was it three? Researchers claim most crowd estimations are unreliable

ScienceDaily (Aug. 26, 2011) — The public should view crowd estimation with skepticism, say the authors of a study published in Significance, the magazine of the Royal Statistical Society and the American Statistical Association, as they suggest more reliable alternatives to current estimating methods.

Estimates of crowd sizes vary greatly, and the success of an event is often measured by the size of the crowd. Organizers of the 2007 "Stop the War" demonstration in London reported crowds of 60,000, whereas the police reported just 10,000. The US Government's estimate of the crowds at Obama's inauguration ceremony was 1.8 million, while other estimates were much less, closer to one million. "In the absence of any accurate estimation methods, the public are left with a view of the truth colored by the beliefs of the people making the estimates," claims Professor Paul Yip, of the University of Hong Kong, one of the authors of the study.

Such a huge discrepancy in estimates is currently not unusual and suggests the use of crowd sizes as a political tool. Larger crowd sizes are a means of recruiting others to the cause, and it is more difficult for the authorities to ignore demands. "The authorities are sometimes put in a difficult position," says Yip. "It is important to highlight the shortcomings of existing estimating methods."

In this latest study, the authors reveal several more accurate, more reliable methods of estimating crowd sizes. Currently, even when searching for the truth, there is a wide margin of error. The authors recommend organizers and authorities use an area x density estimating method for static crowds, which reduces the margin of error to less than 10%. Furthermore, they have devised an entirely new method of reliably estimating mobile crowds. Two inspection points are placed along the route where the number of participants is estimated, not too close together and with one near the end. In applying this two-inspection-point method to the Hong Kong 1st July march (a demonstration of widely-varying claimed size and of great political sensitivity) since 2003, more reliable estimates can then be obtained.

"It is important to rectify the myth of counting people. The public would be better served by estimates less open to political bias. Our study shows that crowd estimates with a margin of error of less than 10% can be achieved with the proposed method," Yip concludes.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Wiley-Blackwell, via AlphaGalileo.

Journal Reference:

Ray Watson, Paul Yip. How many were there when it mattered? Estimating the sizes of crowds. Significance, September 2011: 104-107 DOI: 10.1111/j.1740-9713.2011.00502.x

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Researchers use liquid crystal to replace space motors

ScienceDaily (Sep. 22, 2011) — Researchers at the Institute of Electronics, Communications and Information Technology (ECIT) and the Northern Ireland Semiconductor Research Centre (NISRC) at Queen's University Belfast have devised a way to eliminate the need for motors in space borne radiometers by incorporating liquid crystals in their Frequency Selective Surface (FSS) antenna arrays.

The project has attracted funding of £0.5 million from the European Space Agency (ESA) and £100,000 from economic development agency, Invest Northern Ireland. It is expected to result in significant weight savings in satellite payloads and greatly reduced power consumption in weather monitoring instruments.

The technology has other important potential applications as well. These include eradicating the attenuation of mobile phone signals passing through energy efficient glass and creating buildings that can be locked down to block radio signals at the flick of a switch.

The innovative ECIT project addresses frequencies ranging from millimeter wave up to 1 THz. Measuring radiation in this waveband is a key technique used to study Earth's atmosphere to improve global weather forecasting and understanding of climate change.

Current generation remote sensing radiometers that collect this data incorporate a turntable-mounted mirror operated by an electric motor to calibrate the instrument before each scan by directing their field of view between cold and ambient targets.

The ECIT/NISRC research team however has devised a technique for making such motors redundant. This involves sandwiching layers of liquid crystals between the FSS's metalized quartz layers to act as an electronically controlled shutter. Applying a small voltage to the structure then enables the radiometer to be switched from calibration mode to signal detection mode without mechanical components.

The team believes that using this technique to replace the motor and turntable could produce potential weight savings of 10 per cent per radiometer. It would also greatly reduce power consumption requirements as a motor represents a radiometer's single biggest power requirement.

Prototypes are being built at Queen's University's Northern Ireland Semiconductor Research Centre with ESA support and the devices are expected to be used in space missions from 2025 onwards.

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