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2013-07-31

Controlling contagion by restricting mobility: In the face of an epidemic, even moderate travel restrictions would slow contagion

July 30, 2013 — In an epidemic or a bioterrorist attack, the response of government officials could range from a drastic restriction of mobility -- imposed isolation or total lockdown of a city -- to moderate travel restrictions in some areas or simple suggestions that people remain at home. Deciding to institute any measure would require officials to weigh the costs and benefits of action, but at present there's little data to guide them on the question of how disease spreads through transportation networks.

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However, a new MIT study comparing contagion rates in two scenarios -- with and without travel restrictions -- shows that even moderate measures of mobility restriction would be effective in controlling contagion in densely populated areas with highly interconnected road and transit networks. The researchers called the difference between infection rates in the two scenarios the "price of anarchy," a concept from game theory that's frequently used as a metric in studies of the controlled use of transportation networks.

The study, published online July 31 in the Journal of the Royal Society Interface, is the first to link the concept of price of anarchy to the spread of contagion. It assumes that transmission of the news of the epidemic (which influences how people select travel routes) and the epidemic itself follow the same mobility network, and uses standard epidemiological models to simulate the flow of contagion.

The researchers -- Ruben Juanes, the ARCO Associate Professor in Energy Studies in MIT's Department of Civil and Environmental Engineering, graduate student Christos Nicolaides and research associate Luis Cueto-Felgueroso -- used data from the 2000 U.S. census to establish the aggregate daily flux of people commuting between counties.

Previous research had shown that when individuals become aware of an epidemic, they travel not by taking the shortest route, but by taking the shortest route that avoids infected areas -- even if they're already infected -- a strategy that exposes people in uninfected areas to disease. Such "selfish behavior," as it's called in game theory, is in direct opposition to the strategy of policymakers, who presumably would act in the benefit of the greater social good by routing infected individuals through areas where infection rates were already high.

The MIT study shows that the price of anarchy in some regions of the United States, such as along Interstate 95 in the Northeast, would be considerable. For a moderately contagious disease -- one in which every infected person infects, on average, two others -- restricting individuals to specific travel routes would decrease infection rates by as much as 50 percent.

"In an area with high connectivity, the outcome of action coordinated by officials is going to be better than selfish action, but the economic and social costs of disruption could sometimes be too high," Juanes says. "In other cases, there would be an enormous benefit to having authorities impose travel restrictions. The price of anarchy is a quantitative measure that identifies areas where intervention might pay off."

"Although the study is an idealized scenario, it does give insight to authorities about when and where it would be important to impose route restrictions on human mobility in the case of an emergent outbreak or in the extreme case of bioterrorism," says Nicolaides, the paper's first author, who was funded by a Vergottis Fellowship from the MIT School of Engineering. "But you have to take into account the structure of the underlying mobility network and its traffic properties. Imposing policy-initiated action in areas with low traffic would not render substantial benefits for the containment of an epidemic."

In their models, the researchers tracked an infectious disease as it spread via commuting networks in the contiguous United States, and found that the price of anarchy for contagion varies depending on the proximity of a network to major commuting corridors.

"A commuting network may be very local, but some contagion is related to more distant travel networks," Cueto-Felgueroso says. "That's why we see a higher price of anarchy near major arteries, like Interstate 95 in the northeastern United States."

The researchers had previously studied the spread of disease through the air transportation network and found that the interconnectivity and location of an airport in the network, not just the number of travelers moving through it, were key to its ability to spread disease.

Juanes says the next step in this work is to measure the price of anarchy for contagion in the world's 7,000 airports.

"In my view the MIT paper could be a game-changer in the field of epidemic modeling," says Dirk Brockmann, an associate professor of engineering sciences and applied mathematics at Northwestern University who was not involved in the research. "Including decision-making and game-theoretic components into models of disease dynamics is massively overdue and essential, as even the most sophisticated models do not account for this type of feedback. Since mobility is such a sensitive component in terms of shaping disease dynamics, the approach the researchers take is very plausible, and it identifies clearly the intriguing interplay of selfish action versus policy action in the context of epidemiology. This is going to be very important in the future."

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Cracking how life arose on Earth may help clarify where else it might exist

July 30, 2013 — Does life exist elsewhere or is our planet unique, making us truly alone in the universe? Much of the work carried out by NASA, together with other research institutions, is aimed at trying to come to grips with this question.

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A novel and potentially testable theory of how life arose on earth, first advanced more than 25 years ago by Michael Russell, a research scientist in Planetary Chemistry and Astrobiology at the NASA Jet Propulsion Laboratory, was further developed in a recent paper published in Philosophical Transactions of the Royal Society B (PTRSL-B) -- the world's first science journal -- by Russell, Wolfgang Nitschke, a team leader at the National Center for Scientific Research in Marseille, France; and Elbert Branscomb, an affiliate faculty member at the Institute for Genomic Biology (IGB) at the University of Illinois at Urbana-Champaign.

This just-released paper, together with a companion paper by Russell and Nitschke in the same journal issue significantly advance the hypothesis and bring it substantially closer to experimental testing -- an effort already underway by Russell and his collaborators who are developing experimental model systems that can recreate, and test, the essential principals of the theory.

Notably, the Russell theory provides potential explanations for several puzzling aspects of how life works, including, for example, how it taps into and exploits sources of energy.

This strange energy conversion process works by using externally supplied energy to constantly pump a lot more protons onto one side of a biological membrane than the other and then having them flow back "downhill" immediately, but only through a turbine-like molecular engine which creates a chemical fuel called ATP; a fuel that cells "burn" in order to power vital cell processes. This process would be an exact parallel to the hydroelectric generation of electrical energy if some other source of energy was first required to pump water up hill behind a dam to then flow down to drive turbines. The question is why is this strange and seemingly inefficient process used?

Russell's theory suggests an answer: when life began it wasn't necessary to pump protons, the proton gradient was already there for the taking. Russell's theory sees life coming into being as a natural physical consequence of a geochemical process called serpentinization that produced, for free, the system's major components: cell-like compartments surrounded by membranes, the right proton concentration differences between the inside and outside of these mineral membranes, and primitive, "mineral-based" forms of the "turbine" motors needed to make a molecule like ATP.

The process of serpentinization occurs when water gravitates down cracks in hot, newly formed ocean crust, where it reacts chemically with the minerals in the rocks in a reaction that produces an extremely alkaline (pH ~13) effluent, rich in hydrogen and methane and the metal molybdenum, so important as a catalyst in life. This effluent is then driven back to the surface where, in the ocean of early earth, it contacted cooler, acidic (~ pH 5.5), and CO2-rich water to create precipitates that form chimney-like submarine towers. These precipitates are highly structured with a myriad of cell-like compartments surrounded by mineral membranes -- akin to our own. And across these membranes, separating acidic ocean and alkaline effluent, stood essentially the same proton gradient -- in strength and direction -- that the cells of all living things on earth are constantly recreating and then immediately using today.

"So, if the Russell theory is correct, it is suddenly obvious why we pump protons and use this silly method," Branscomb said. "We got stuck on this 'free lunch' energy system when life was born, developed a lot of fancy machinery to use it, and have never severed that umbilicus since."

Branscomb, a member of the IGB's Biocomplexity research theme led by Swanlund Professor of Physics Nigel Goldenfeld, was funded in part by a recently awarded, five-year grant totaling $8 million from the NASA Astrobiology Institute. The grant funds the University of Illinois's Institute for Universal Biology, a member of the NASA Astrobiology Institute, which includes many members of the Biocomplexity theme who are studying the origin and evolution of life. Find out more about Illinois's Institute for Universal Biology and the IGB's Biocomplexity theme.

"We have a sample of only one planet known to harbor life," Goldenfeld said. "Thus it is critical that we be creative in extracting the most information from Earthly life as possible, if we are to ever understand the existence, likelihood, and nature of life elsewhere in the Universe. Russell, Nischke, and Branscomb's work lays an intriguing foundation for that endeavor, by cleverly bringing together concepts from thermodynamics, geochemistry and biology to advance a major new hypothesis for life's origins."

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Controlling contagion by restricting mobility: In the face of an epidemic, even moderate government-mandated travel restrictions would slow contagion

Juanes says the next step in this work is to measure the price of anarchy for contagion in the world's 7,000 airports.

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Santa's workshop not flooded -- but lots of melting in the Arctic

July 30, 2013 — Santa's workshop at the North Pole is not under water, despite recent reports. A dramatic image captured by a University of Washington monitoring buoy reportedly shows a lake at the North Pole. But Santa doesn't yet need to buy a snorkel.

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"Every summer when the sun melts the surface the water has to go someplace, so it accumulates in these ponds," said Jamie Morison, a polar scientist at the UW Applied Physics Laboratory and principal investigator since 2000 of the North Pole Environmental Observatory. "This doesn't look particularly extreme."

After media coverage in CBS News, The Atlantic and the U.K.'s Daily Mail, Morison returned from overseas travel late last week to a pile of media inquiries. Over the weekend the team posted an explanatory page on the project website.

One of the issues in interpreting the image, researchers said, is that the camera uses a fisheye lens.

"The picture is slightly distorted," said Axel Schweiger, who heads the Applied Physics Laboratory's Polar Science Center. "In the background you see what looks like mountains, and that's where the scale problem comes in -- those are actually ridges where the ice was pushed together."

Researchers estimate the melt pond in the picture was just over 2 feet deep and a few hundred feet wide, which is not unusual to find on an Arctic ice floe in late July.

In the midst of all the concern, the pool drained late July 27. This is the normal cycle for a meltwater pond that forms from snow and ice -- it eventually drains through cracks or holes in the ice it has pooled on.

The now-infamous buoy was first plunked into floating ice in April, at the beginning of the melt season, about 25 miles from the North Pole. Morison drilled a hole about three football fields away for a second camera, which is pointing in a different direction and shows a more typical scene. Since then the ice floe holding both cameras has drifted about 375 miles south.

North Pole Environmental Observatory
Watch an April interview with Jamie Morison when he was deploying the buoy

The U.S. National Science Foundation has funded an observatory since 2000 that makes yearly observations at fixed locations and installs 10 to 15 drifting buoys.

The buoys record weather, ice, and ocean data, and the webcams transmit images via satellite every 6 hours. Images show the ice, buoys and yardsticks placed in the snow to track the surface conditions throughout the summer melt season. Maybe the instruments will survive the summer without getting crushed by shifting ice to record data for another year. Maybe they will fall in the water and eventually wash ashore. Researchers place the buoys to try to maximize their useful lifetime.

While researchers say the so-called lake at the North Pole is not out of the ordinary, there is a lot of meltwater that could affect the sea ice in coming weeks, in the closely watched lead-up to the September ice minimum.

Last summer the sea-ice hit a record low in extent since measurements began in 1979. This year the melting started a bit later than usual, Schweiger said, but picked up in the last couple of weeks. Late summer is usually the strongest period of shrinking because the ice is already thin.

"Whether we're going to see another record or not is still up in the air," Schweiger said.

He flew over the ice last month in a joint project with the U.S. Coast Guard to drop instruments that measure oceanic and atmospheric conditions and ice motion.

Morison was last on the ice in April when he deployed the buoys. His forecast for this summer, based on years of experience, is included on a list of expert predictions compiled by the National Atmospheric and Oceanic Administration's Seattle office.

Morison will not change his June estimate that this summer will come close to, but not pass, the 2012 record, but he is having his doubts. Looking at the photos from the recent flyover shows more melt along the Alaskan coast, and his experience suggests that ice is fragile.

"I think it's going to be pretty close to last year," Morison said. "Up in the Canada Basin the ice looks like Swiss cheese, with lots of holes. Even though the ice extent is pretty good, our thinking is that if there's a big storm event we're going to see a rapid breakup of that ice and it's going to disappear pretty quickly."

The UW team manages another sea-ice tracking tool. The U.S. National Snow and Ice Data Center publishes daily images and calculations of sea-ice extent and area, while the UW group combines those satellite images and other data to tabulate sea-ice volume. For many people, the UW's monthly updates are a go-to source for getting the latest numbers on sea ice.

And while the North Pole lake news stories don't exactly hold water, UW researchers say that it at least shows public interest and concern.

"While the hoopla about Santa's swimming pool was off the mark," Morison said, "it is the long-term observational record from these buoys that provides the perspective needed to understand what really is going on."

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Sequestration and fuel reserves: Storing carbon dioxide to release liquid fuels

While so-called "fracking" as a method for extracting previously untapped fossil fuel reserves has been in the headlines recently, there are alternatives to obtaining the remaining quantities of hydrocarbons from gas/condensate reservoirs, according to Kashy Aminian of West Virginia University in Morgantown, USA, and colleagues there and at Kuwait University in Safat.

Earlier experiments suggests that using carbon dioxide instead of nitrogen or methane to blast out the hydrocarbon stock from depleted reservoirs might be highly effective and have the added benefit of trapping, or sequestering the carbon dioxide underground. Aminian and colleagues have calculated the economic benefits associated with the enhanced liquid recovery and demonstrated that the approach is technically and financially viable.

The team explains that the mixing of carbon dioxide with the condensate reservoir fluid results in a reduction of the saturation pressure, the liquid drop-out, and the compressibility factor, boosting recovery of useful hydrocarbon and allowing the carbon dioxide to be trapped within. The team found that the process works well regardless of the characteristics of the reservoir or even the rate at which the carbon dioxide is injected into the reservoir, the amount that is recovered remains just as high. Moreover, because of the compressibility of the carbon dioxide it is possible to squeeze out 1.5 to 2 times the volume of reservoir gas for the amount of carbon dioxide pumped in, there is also then the possibility of pumping in an additional 15% once as much reservoir liquid as can be retrieved has been extracted.

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Planetary 'runaway greenhouse' more easily triggered, research shows

In the runaway greenhouse stage, a planet absorbs more solar energy than it can give off to retain equilibrium. As a result, the world overheats, boiling its oceans and filling its atmosphere with steam, which leaves the planet glowing-hot and forever uninhabitable, as Venus is now.

One estimate of the inner edge of a star's "habitable zone" is where the runaway greenhouse process begins. The habitable zone is that ring of space around a star that's just right for water to remain in liquid form on an orbiting rocky planet's surface, thus giving life a chance.

Revisiting this classic planetary science scenario with new computer modeling, the astronomers found a lower thermal radiation threshold for the runaway greenhouse process, meaning that stage may be easier to initiate than had been previously thought.

"The habitable zone becomes much narrower, in the sense that you can no longer get as close to the star as we thought before going into a runaway greenhouse," said Tyler Robinson, a UW astronomy postdoctoral researcher and second author on the paper. The lead author is Colin Goldblatt of the University of Victoria.

Though further research is called for, the findings could lead to a recalibration of where the habitable zone begins and ends, with some planets having their candidacy as possible habitable worlds revoked.

"These worlds on the very edge got 'pushed in,' from our perspective -- they are now beyond the runaway greenhouse threshold," Robinson said.

Subsequent research, the astronomers say, is needed in part because their computer modeling was done in a "single-column, clear-sky model," or a one-dimensional measure averaged around a planetary sphere that does not account for the atmospheric effect of clouds.

The findings apply to planet Earth as well. As the sun increases in brightness over time, Earth, too, will move into the runaway greenhouse stage -- but not for a billion and a half years or so. Still, it inspired the astronomers to write, "As the solar constant increases with time, Earth's future is analogous to Venus's past."

Other co-authors are Kevin J. Zahnle of the NASA Ames Research Center in Moffett Field, Calif.; and David Crisp of the Jet Propulsion Laboratory in Pasadena, Calif.

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Plasmonic black metals: Breakthrough in solar energy research?

July 30, 2013 — The use of plasmonic black metals could someday provide a pathway to more efficient photovoltaics (PV) -- the use of solar panels containing photovoltaic solar cells -- to improve solar energy harvesting, according to researchers at Lawrence Livermore National Laboratory (LLNL).

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The LLNL Materials Engineering Division (MED) research team has made breakthroughs experimenting with black metals. These nanostructured metals are designed to have low reflectivity and high absorption of visible and infrared light. The MED research team recently published their black metals research results in a cover-page article in the May issue of Applied Physics Letters.

Authored by MED physicist and research team member Mihail Bora, the article details the work of the nanophotonics and plasmonics research team led by LLNL engineer Tiziana Bond.

It describes the team's concept of black metals, which are not classic metals but can be thought of as an extension of the black silicon concept. When silicon is treated in a certain way, such as being roughened at the nanoscale level, it traps light by multiple reflections, increasing its solar absorption. This gives the silicon a black surface that's able to better trap the full sun's wavelength spectrum.

Similarly, black metals are produced by some sort of random nanostructuring -- either in gold or silver -- without guaranteeing a full, reliable and repeatable full solar absorption. However, Bond's team developed a method to improve and control the absorption efficiency and basically turn the metals as black as they want, allowing them to increase, on demand, the absorption of a higher quantity of solar wavelengths. Her team built nanopillar structures that are trapping and absorbing all the relevant wavelengths of the entire solar spectrum.

"Our article was picked for the cover story of Applied Physics Letters because it represents cutting-edge work in the area of plasmonics, the broadband operation obtained with a clear design and its implication for the photovoltaic yield," Bond said.

This new LLNL technology could one day be used in the energy harvesting industry such as PV. By incorporating metallic nanostructures with strong coupling of incident light, broad spectral and angular coverage, the LLNL team is providing a path for more efficient photovoltaics and thermovoltaics (a form of energy collection) by means of plasmon-exciton conversion, according to Bond and Bora.

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Full body illusion is associated with a drop in skin temperature

Twenty-two volunteers underwent a Full Body Illusion when they were stroked with a robotic device system while they watched an avatar being stroked in the same spot. The study is the first to demonstrate that Full Body Illusions can be accompanied by changes in body temperature.

Participants wore a 3D high-resolution head-mounted display to view the avatar from behind. They were then subjected to 40 seconds of stroking by a robot, on either their left or right back or on their left or right leg. Meanwhile, they were shown a red dot that moved synchronously on the same regions of the avatar (see image).

After the stroking, the participants were prompted to imagine dropping a ball and to signal the moment when they felt that the ball would hit the floor. This allowed the researchers to objectively measure where the participants perceived their body to be.

The volunteers were asked questions about how much they identified with the avatar and where they felt the stroking originated from. Furthermore, to test for physiological changes during the illusion, the participants' skin temperature was measured on four locations on the back and legs across 20 time points.

Results showed that stroking the same body part simultaneously on the real body and the avatar induced a Full Body Illusion. The volunteers were confused as to where their body was and they partly identified with the avatar. More than 70% of participants felt that the touch they had felt on their body was derived from the stroking seen on the avatar.

Data revealed a continuous widespread decrease in skin temperature that was not specific to the site of measurement and showed similar effects in all locations. The changes in body temperature "were highly significant, but very small," write the authors in the study, adding that the decrease was in the range of 0.006-0.014 degrees Celsius.

The recorded temperature change was smaller than an earlier study found (0.24 degrees Celsius) that looked at fluctuations during rubber hand illusion, probably because the latter used a hand-held thermometer over longer periods and different regions of the body, the authors explain.

"When the brain is confronted with a multisensory conflict, such as that produced by the Full Body Illusion, the way we perceive our real body changes. This causes a decrease in our body temperature, " says Dr. Roy Salomon, a postdoctoral fellow at the EPFL and the lead author of the study.

The scientists also say that the field of cognitive neuroprosthetics carries great promise for new prosthetics that are based on a neuroscientific understanding of the link between body and mind.

"This study helps us to understand the brain mechanisms that underlie the bodily aspects of consciousness and idea of 'self'. It may contribute to the design of novel prosthetic devices and treatment of pain, for example, after stroke, amputation, or tetraplegia," says Prof. Olaf Blanke, director of the newly founded Center for Neuroprosthetics.

"This type of research may also help to understand and treat psychiatric disorders, such as schizophrenia and depression. We hope that by identifying the mechanisms involved in these processes and how they are altered in psychosis we can help these patients," adds Dr. Salomon.

Dr. Salomon and colleagues are currently investigating how to help treat psychiatric disorders through understanding the cognitive and neural mechanisms involved in these disorders as part of the National Center of Competence in Research (NCCR)'s project titled The Synaptic Bases of Mental Diseases (SYNAPSY), financed by the Swiss National Science Foundation.

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Novel technology for producing 'electronic ink' may lead to inexpensive, durable electronics and solar cells

Researchers in the University of Minnesota's College of Science and Engineering and the National Renewable Energy Laboratory in Golden, Colo., have overcome technical hurdles in the quest for inexpensive, durable electronics and solar cells made with non-toxic chemicals. The research was published in the most recent issue of Nature Communications, an international online research journal.

"Imagine a world where every child in a developing country could learn reading and math from a touch pad that costs less than $10 or home solar cells that finally cost less than fossil fuels," said Uwe Kortshagen, a University of Minnesota mechanical engineering professor and one of the co-authors of the paper.

The research team discovered a novel technology to produce a specialized type of ink from non-toxic nanometer-sized crystals of silicon, often called "electronic ink." This "electronic ink" could produce inexpensive electronic devices with techniques that essentially print it onto inexpensive sheets of plastic.

"This process for producing electronics is almost like screen printing a number on a softball jersey," said Lance Wheeler, a University of Minnesota mechanical engineering Ph.D. student and lead author of the research.

But it's not quite that easy. Wheeler, Kortshagen and the rest of the research team developed a method to solve fundamental problems of silicon electronic inks.

First, there is the ubiquitous need of organic "soap-like" molecules, called ligands, that are needed to produce inks with a good shelf life, but these molecules cause detrimental residues in the films after printing. This leads to films with electrical properties too poor for electronic devices. Second, nanoparticles are often deliberately implanted with impurities, a process called "doping," to enhance their electrical properties.

In this new paper, researchers explain a new method to use an ionized gas, called nonthermal plasma, to not only produce silicon nanocrystals, but also to cover their surfaces with a layer of chlorine atoms. This surface layer of chlorine induces an interaction with many widely used solvents that allows production of stable silicon inks with excellent shelf life without the need for organic ligand molecules. In addition, the researchers discovered that these solvents lead to doping of films printed from their silicon inks, which gave them an electrical conductivity 1,000 times larger than un-doped silicon nanoparticle films. The researchers have a provisional patent on their findings.

To watch a research video of how silicon nanocrystals are synthesized in a plasma reactor, visit http://www.youtube.com/watch?v=5Un_HnOl6lQ&feature=youtu.be.

"What this research means is that we are one step closer to producing more pure and more stable electronic ink with non-toxic chemicals," Kortshagen said. "The bigger goal here is to find a way that this research can benefit everyone and make a real difference."

In addition to Kortshagen and Wheeler, members of the research team include Nathan R. Neale, a staff scientist at the National Renewable Energy Laboratory, and Ting Chen, a University of Minnesota chemical engineering and materials science Ph.D. student. The research was funded primarily by the Department of Energy Frontier Research Center for Advanced Solar Photophysics.

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Water clears path for nanoribbon development

July 30, 2013 — New research at Rice University shows how water makes it practical to form long graphene nanoribbons less than 10 nanometers wide.

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And it's unlikely that many of the other labs currently trying to harness the potential of graphene, a single-atom sheet of carbon, for microelectronics would have come up with the technique the Rice researchers found while they were looking for something else.

The discovery by lead author Vera Abramova and co-author Alexander Slesarev, both graduate students in the lab of Rice chemist James Tour, appears online this month in the American Chemical Society journal ACS Nano.

A bit of water adsorbed from the atmosphere was found to act as a mask in a process that begins with the creation of patterns via lithography and ends with very long, very thin graphene nanoribbons. The ribbons form wherever water gathers at the wedge between the raised pattern and the graphene surface.

The water formation is called a meniscus; it is created when the surface tension of a liquid causes it to curve. In the Rice process, the meniscus mask protects a tiny ribbon of graphene from being etched away when the pattern is removed.

Tour said any method to form long wires only a few nanometers wide should catch the interest of microelectronics manufacturers as they approach the limits of their ability to miniaturize circuitry. "They can never take advantage of the smallest nanoscale devices if they can't address them with a nanoscale wire," he said. "Right now, manufacturers can make small features, or make big features and put them where they want them. But to have both has been difficult. To be able to pattern a line this thin right where you want it is a big deal because it permits you to take advantage of the smallness in size of nanoscale devices."

Tour said water's tendency to adhere to surfaces is often annoying, but in this case it's essential to the process. "There are big machines that are used in electronics research that are often heated to hundreds of degrees under ultrahigh vacuum to drive off all the water that adheres to the inside surfaces," he said. "Otherwise there's always going to be a layer of water. In our experiments, water accumulates at the edge of the structure and protects the graphene from the reactive ion etching (RIE). So in our case, that residual water is the key to success.

"Nobody's ever thought of this before, and it's nothing we thought of," Tour said. "This was fortuitous."

Abramova and Slesarev had set out to fabricate nanoribbons by inverting a method developed by another Rice lab to make narrow gaps in materials. The original method utilized the ability of some metals to form a native oxide layer that expands and shields material just on the edge of the metal mask. The new method worked, but not as expected.

"We first suspected there was some kind of shadowing," Abramova said. But other metals that didn't expand as much, if at all, showed no difference, nor did varying the depth of the pattern. "I was basically looking for anything that would change something."

It took two years to develop and test the meniscus theory, during which the researchers also confirmed its potential to create sub-10-nanometer wires from other kinds of materials, including platinum. They also constructed field-effect transistors to check the electronic properties of graphene nanoribbons.

To be sure that water does indeed account for the ribbons, they tried eliminating its effect by first drying the patterns by heating them under vacuum, and then by displacing the water with acetone to eliminate the meniscus. In both cases, no graphene nanoribbons were created.

The researchers are working to better control the nanoribbons' width, and they hope to refine the nanoribbons' edges, which help dictate their electronic properties.

"With this study, we figured out you don't need expensive tools to get these narrow features," Tour said. "You can use the standard tools a fab line already has to make features that are smaller than 10 nanometers."

The Air Force Office of Scientific Research and the Office of Naval Research Multidisciplinary University Research Initiative Graphene Program supported the research.

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