New graphene oxide biosensors may accelerate research of HIV, cancer drugs

 

This is a close-up view to this state-of-art biosensor. Credit: Victor Anaskin Longing to find a cure for cancer, HIV and other yet incurable diseases, researchers have already tried out hundreds of drugs, each requiring preclinical and clinical testing with live subjects. How many chemical agents more to try? Moving at such rate, will we find the cure during our lifetime? One of the easiest ways to speed up the drug development process is to simply perform it outside of the living body (e.g., by watching the substances react with the smallest pieces of live tissue and thus quickly predicting the overall effect it will make to the body when inside). This approach will eventually provide more effective preclinical selection of drug candidates for the subsequent long-term and expensive clinical trial. This could get the humanity closer to finding the cures we've long been seeking for. Researchers from the Laboratory of Nanooptics and Plasmonics, Moscow Institute of Physics and Technology -- MIPT (Russia) have devised a novel type of graphene oxide (GO) based biosensor that could potentially significantly speed up the process of drug development. The outstanding properties of this carbon allotrope help to improve significantly the biosensing sensitivity, which in future may enable the development of new drugs and vaccines against many dangerous diseases including HIV, hepatitis and cancer. The research, led by Yury Stebunov, a scientist at the MIPT, was published in the ACS Applied Materials & Interfaces. The paper is titled "Highly sensitive and selective sensor chips with graphene-oxide linking layer." Valentyn Volkov is the co-lead author, a visiting professor from the University of Southern Denmark. Other co-authors are Olga Aftenieva and Aleksey Arsenin. New GO based biosensor chips exploit the phenomenon of surface plasmon resonance (SPR). Surface plasmons are electromagnetic waves propagating along a metal-dielectric interface (e.g., gold/air) and having the amplitudes exponentially decaying in the neighbor media. Adsorption of molecules from solution onto a sensing surface alters the refractive index of the medium near this surface and, therefore, changes the conditions of SPR. These sensors can detect biomolecule adsorption even at a few trillionth of a gram per millimeter square. Owing to the above-mentioned merits, SPR biosensing is an outstanding platform to boost technological progress in the areas of medicine and biotechnology. Nevertheless, the most distinctive feature of such sensors is an ability to "visualize" molecular interactions in real time. "SPR biosensing is a valuable tool to investigate a wide range of biochemical reactions, estimate their chemical kinetics and other characteristics. All this can be efficiently used for new drug discovery and validation. Widespread introduction of this method into preclinical trials will completely change the pharmaceutical industry. With SPR sensors we just need to estimate the interaction between the drug and targets on the sensing surface," Stebunov said. Most commercial SPR sensor chips comprise a thin glass plate covered by gold layer with thiol or polymer layers on it. The biosensing sensitivity depends on the properties of chip surface. Higher binding capacity for biomolecules increases the signal levels and accuracy of analysis. The last several years, novel carbon materials like graphene have attracted much attention due to their large surface area, low-cost fabrication, and interaction with a wide range of biomolecules. Stebunov and the team from the Laboratory of Nanooptics and Plasmonics at MIPT created and patented a novel type of SPR sensor chips with the linking layer, made of GO, a material with more attractive optical and chemical properties than pristine graphene. The GO "flakes" were deposited on the 35 nm gold layer. Thereafter a layer of streptavidin protein was developed on GO for selective immobilization of biomolecules. Scientists conducted a series of experiments with the GO chip, the commercially available chip with carboxymethylated dextran (CMD) layer and the chip covered by monolayer graphene. Experiments showed that the proposed GO chip has three times higher sensitivity than the CMD chip and 3.7 times than the chip with pristine graphene. These results mean, that the new chip needs much less molecules for detecting a compound and can be used for analysis of chemical reactions with small drug molecules. An important advantage of the new GO based sensor chips is their simplicity and low-cost fabrication compared to sensor chips that are already commercially available. "Our invention will help in drug development against viral and cancer diseases. We are expecting that pharmaceutical industry will express a strong demand for our technology," Stebunov said. "The sensor can also find applications in food quality control, toxin screening, the sensor can significantly shorten a time for a clinical diagnostic," researcher added. However, the developed chip should go through a clinical trial for medical applications. http://www.sciencedaily.com/releases/2015/09/150922115647.htm

Graphene-based film has a thermal conductivity capacity that is four times that of copper.

 

This is graphene-based film on an electronic component with high heat intensity. Credit: Johan Liu / Chalmers University of Technology Researchers at Chalmers University of Technology have developed a method for efficiently cooling electronics using graphene-based film. The film has a thermal conductivity capacity that is four times that of copper. Moreover, the graphene film is attachable to electronic components made of silicon, which favours the film's performance compared to typical graphene characteristics shown in previous, similar experiments. Electronic systems available today accumulate a great deal of heat, mostly due to the ever-increasing demand on functionality. Getting rid of excess heat in efficient ways is imperative to prolonging electronic lifespan, and would also lead to a considerable reduction in energy usage. According to an American study, approximately half the energy required to run computer servers, is used for cooling purposes alone. A couple of years ago, a research team led by Johan Liu, professor at Chalmers University of Technology, were the first to show that graphene can have a cooling effect on silicon-based electronics. That was the starting point for researchers conducting research on the cooling of silicon-based electronics using graphene. "But the methods that have been in place so far have presented the researchers with problems," Johan Liu says. "It has become evident that those methods cannot be used to rid electronic devices off great amounts of heat, because they have consisted only of a few layers of thermal conductive atoms. When you try to add more layers of graphene, another problem arises, a problem with adhesiveness. After having increased the amount of layers, the graphene no longer will adhere to the surface, since the adhesion is held together only by weak van der Waals bonds." "We have now solved this problem by managing to create strong covalent bonds between the graphene film and the surface, which is an electronic component made of silicon," he continues. The stronger bonds result from so-called functionalisation of the graphene, i.e. the addition of a property-altering molecule. Having tested several different additives, the Chalmers researchers concluded that an addition of (3-Aminopropyl) triethoxysilane (APTES) molecules has the most desired effect. When heated and put through hydrolysis, it creates so-called silane bonds between the graphene and the electronic component (see picture). Moreover, functionalisation using silane coupling doubles the thermal conductivity of the graphene. The researchers have shown that the in-plane thermal conductivity of the graphene-based film, with 20 micrometer thickness, can reach a thermal conductivity value of 1600 W/mK, which is four times that of copper. "Increased thermal capacity could lead to several new applications for graphene," says Johan Liu. "One example is the integration of graphene-based film into microelectronic devices and systems, such as highly efficient Light Emitting Diodes (LEDs), lasers and radio frequency components for cooling purposes. Graphene-based film could also pave the way for faster, smaller, more energy efficient, sustainable high power electronics." The research was conducted in collaboration with Shanghai University in China, Ecole Centrale Paris and EM2C -- CNRS in France, and SHT Smart High Tech in Sweden. Story Source: The above post is reprinted from materials provided by Chalmers University of Technology. Note: Materials may be edited for content and length. Journal Reference: Yong Zhang, Haoxue Han, Nan Wang, Pengtu Zhang, Yifeng Fu, Murali Murugesan, Michael Edwards, Kjell Jeppson, Sebastian Volz, Johan Liu. Improved Heat Spreading Performance of Functionalized Graphene in Microelectronic Device Application. Advanced Functional Materials, 2015; DOI: 10.1002/adfm.201500990

Graphene-based sensor is tunable and highly sensitive

 

If given the correct geometry, graphene is able to focus the light on a precise spot on its surface and "hear" the vibration of a nanometric molecule that is attached to it. Credit: EPFL / Miguel Spuch / Daniel Rodrigo Many areas of fundamental research are interested in graphene owing to its exceptional characteristics. It is made of one layer of carbon atoms, which makes it light and sturdy, and it is an excellent thermal and electrical conductor. Despite its apparently limitless potential, however, few applications have been demonstrated to date. Scientists at EPFL's Bionanophotonic Systems Laboratory (BIOS) together with researchers from the Institute of Photonic Sciences (ICFO, Spain) have now added another one. They have harnessed graphene's unique optical and electronic properties to develop a reconfigurable highly sensitive molecule sensor. The results are described in an article appearing in the latest edition of the journal Science. Focussing light to improve sensing The researchers used graphene to improve on a well-known molecule-detection method: infrared absorption spectroscopy. In the standard method, light is used to excite the molecules, which vibrate differently depending on their nature. It can be compared to a guitar string, which makes different sounds depending on its length. By virtue of this vibration, the molecules reveal their presence and even their identity. This "signature" can be "read" in the reflected light. This method is not effective, however, in detecting nanometrically-sized molecules. The wavelength of the infrared photon directed at a molecule is around 6 microns (6,000 nanometres -- 0.006 millimeters), while the target measures only a few nanometres (about 0.000001 mm). It is very challenging to detect the vibration of such a small molecule in reflected light. There is where graphene comes in. If given the correct geometry, the graphene is able to focus the light on a precise spot on its surface and "hear" the vibration of a nanometric molecule that is attached to it. "We first pattern nanostructures on the graphene surface by bombarding it with electron beams and etching it with oxygen ions," said Daniel Rodrigo, co-author of the publication. "When the light arrives, the electrons in graphene nanostructures begin to oscillate. This phenomenon, known as 'localized surface plasmon resonance,' serves to concentrate light into tiny spots, which are comparable with the dimensions of the target molecules. It is then possible to detect nanometric structures." Reconfiguring graphene in real time to see the molecule's structure There is more to it. In addition to identifying the presence of nanometric molecules, this process can also reveal the nature of the bonds connecting the atoms that the molecule is composed of. When a molecule vibrates, it does not give off only one type of "sound." It produces a whole range of vibrations, which are generated by the bonds connecting the different atoms. Returning to the example of the guitar: each string vibrates differently and together they form one musical instrument. These nuances provide information on the nature of each bond and on the health of the entire molecule. "These vibrations act as a fingerprint that allow us to identify the molecule; such as proteins, and can even tell their health status" said Odeta Limaj, another co-author of the publication. In order to pick up the sound given off by each of the strings, it has to be possible to identify a whole range of frequencies. And that is something graphene can do. The researchers "tuned" the graphene to different frequencies by applying voltage, which is not possible with current sensors. Making graphene's electrons oscillate in different ways makes it possible to "read" all the vibrations of the molecule on its surface. "We tested this method on proteins that we attached to the graphene. It gave us a full picture of the molecule," said Hatice Altug. A big step closer to using graphene for molecule sensing The new graphene-based process represents a major step forward for the researchers, for several reasons. First, this simple method shows that it is possible to conduct a complex analysis using only one device, while it normally requires many different ones. And all this without stressing or modifying the biological sample. Second, it shows graphene's incredible potential in the area of detection. "There are many possible applications," said Altug. "We focussed on biomolecules, but the method should also work for polymers, and many other substances," she added. Story Source: The above post is reprinted from materials provided by Ecole Polytechnique Fédérale de Lausanne. Note: Materials may be edited for content and length. Journal Reference: Daniel Rodrigo, Odeta Limaj, Davide Janner, Dordaneh Etezadi, F. Javier García De Abajo, Valerio Pruneri, Hatice Altug. Mid-infrared plasmonic biosensing with graphene. Science, 2015 DOI: 10.1126/science.aab2051

Graphene takes on a new dimension

 

A new process for creating 3D objects out of graphene opens up the possibility of fashioning a whole new range of innovative electronic devices (Credit: Shutterstock) Graphene is the modern go-to material for scientists and engineers looking to create all manner of new electronic devices. From ultra-frugal light bulbs (both big and small), to super-efficient solar cells, flexible displays and much more, graphene is a multi-tasking marvel. However, in all of these instances, graphene in its original form of atom-thin, flat sheets has had to be used with peripheral supports and structures because it lacks a solid shape and form of its own. Now researchers from the University of Illinois at Urbana-Champaign (UIUC)have come up with a way of creating 3D objects out of graphene that opens up the possibility of fashioning a whole new range of innovative electronic devices. To create 3D shapes in graphene, the researchers first had to ensure that their approach was sufficient to maintain the structural integrity of the material when it was subjected to deformation. As such, the team used an underlying substrate former over which they laid a film of graphene that had been soaked in solvent to make it swell and become malleable. Once overlaid on the former, the solvent then evaporated over time, leaving behind a layer of graphene that had taken on the shape of the underlying structure. In this way the team was able to produce a range of relatively intricate shapes. "To the best of our knowledge, this study is the first to demonstrate graphene integration to a variety of different microstructured geometries, including pyramids, pillars, domes, inverted pyramids, and the 3D integration of gold nanoparticles (AuNPs)/graphene hybrid structures," said SungWoo Nam, assistant professor of mechanical science and engineering at UIUC. "Our swelling, shrinking, and adaptation steps are optimized to minimize the degree of graphene suspension around the 3D microstructures and facilitate successful 3D integration. We control the amount of substrate swelling by adjusting the time of immersion in organic solvent and the mixing ratios of monomer and curing agent of the polydimethylsiloxane (PDMS) substrate." Varying in size from just 3.5 to 50 μm, the dimensions of the graphene microstructures developed by UIUC put them right in the middle of a range of electronic devices, including various types of photodetectors, nano antennas, and other sub-miniature components that were once only the domain of silicon-based products. According to the team, these factors, along with graphene's high carrier mobility, chemical inertness, and biocompatibility, mean that three-dimensional graphene could be adapted over even wider areas. "We also expect that our new 3D integration approach will facilitate advanced classes of hybrid devices between microelectromechanical systems (MEMS) and 2D materials for sensing and actuation," said SungWoo Nam. Due to the fragility of atom-thin graphene, previous methods to bend or mold it into complex shapes resulted in uneven, ill-formed objects at best, and a ruptured mess at worst. In investigating the new technique, the researchers at UIUC were diligent in their testing of the formed graphene via electron microscopy, atomic force microscopy, Raman spectroscopy, and electrical resistance measurement to confirm that it maintained its shape and consistency after forming. "Our results demonstrate a simple, versatile, and scalable method to integrate graphene with 3D geometries with various morphologies and dimensions," said Jonghyun Choi, a graduate student in Nam’s research group. "Not only are these 3D features larger than those reported in previous works, but we also demonstrate the uniformity and damage-free nature of integrated graphene around the 3D features." The results of this research were recently published in the journal Nano Letters. Source: University of Illinois at Urbana-Champaign

Scientists give graphene one more quality – magnetism

 

A diagram of the magnetized graphene (Image: Shi Lab, UC Riverside) Graphene is extremely strong for its weight, it's electrically and thermally conductive, and it's chemically stable ... but it isn't magnetic. Now, however, a team from the University of California, Riverside has succeeded in making it so. The resulting magnetized graphene could have a wide range of applications, including use in "spintronic" computer chips. While other groups have previously magnetized graphene, they've done so by doping it with foreign substances, and the presence of these impurities has negatively affected its electronic properties. In this case, though, the graphene was able to remain pure. Led by professor of physics and astronomy Jing Shi, the UC Riverside team laid a sheet of regular graphene down on an atomically smooth layer of magnetic yttrium iron garnet. That material then simply magnetized the graphene as it lay against it. Yttrium iron garnet was used due to the fact that certain other magnetic materials could disrupt the graphene’s electrical transport properties. When the sheet of graphene was removed and subsequently exposed to a magnetic field, it was shown to indeed possess magnetic qualities of its own. "This is the first time that graphene has been made magnetic this way," said Shi. "The magnetic graphene acquires new electronic properties so that new quantum phenomena can arise. These properties can lead to new electronic devices that are more robust and multi-functional." Those devices could include improved spintronic chips, that use the spin of electrons – which can be magnetically manipulated – to store data. A paper on the research was recently published in the journal Physical Review Letters. Source: University of California, Riverside

'Mind the gap' between atomically thin materials

 

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Colorized TEM image of tungsten disulfide triangles (black) growing on graphene substrate (green).

In subway stations around London, the warning to "Mind the Gap" helps commuters keep from stepping into empty space as they leave the train. When it comes to engineering single-layer atomic structures, minding the gap will help researchers create artificial electronic materials one atomic layer at a time.

The gap is a miniscule vacuum that can only be seen under a high-power transmission electron microscope. The gap, researchers in Penn State's Center for 2-Dimensional and Layered Materials (2DLM) believe, is an energy barrier that keeps electrons from easily crossing from one layer of material to the next.

"It's a natural insulating layer Mother Nature built into these artificially created materials," said Joshua Robinson, assistant professor of materials science and engineering and associate director of the 2DLM Center. "We're still trying to understand how electrons move vertically through these layered materials, and we thought it should take a lot less energy. Thanks to a combination of theory and experiment, we now know we have to account for this gap when we design new materials."

For the first time, the Penn State researchers grew a single atomic layer of tungsten diselenide on a one- atom-thick substrate of graphene with pristine interfaces between the two layers. When they tried to put a voltage from the top tungsten diselenide (WSe2) layer down to the graphene layer, they encountered a surprising amount of resistance. About half of the resistance was caused by the gap, which introduced a large barrier, about 1 electron volt (1eV), to the electrons trying to move between layers. This energy barrier could prove useful in designing next generation electronic devices, such as vertical tunneling field effect transistors, Robinson said.

The interest in these van der Waals materials arose with the discovery of methods to make single layer graphite by using Scotch tape to mechanically cleave a one-atom-thick layer of carbon called graphene from bulk graphite. The van der Waals force that binds layers of graphite together is weak enough to allow stripping of the single atomic layer. The Penn State researchers use a different, more scalable method, called chemical vapor deposition, to deposit a single layer of crystalline WSe2 on top of a few layers of epitaxial graphene that is grown from silicon carbide. Although graphene research exploded in the last decade, there are many van der Waal solids that can be combined to create entirely new artificial materials with unimaginable properties.

In a paper published online this month in Nano Letters, the Penn State team and colleagues from UT Dallas, the Naval Research Laboratory, Sandia National Lab, and labs in Taiwan and Saudi Arabia, discovered that the tungsten diselenide layer grew in perfectly aligned triangular islands 1-3 microns in size that slowly coalesced into a single crystal up to 1 centimeter square. Robinson believes it will be possible to grow these crystals to industrially useful wafer-scale sizes, although will require a larger furnace than he currently has in his lab.

"One of the really interesting things about this gap," Robinson said, "is that it allows us to grow aligned layers despite the fact that the atoms in the graphene are not lined up with the atoms in the tungsten diselenide. In fact there is a 23 percent lattice mismatch, which is huge. Mother Nature really relaxed the rules when it comes to these big differences in atom spacing."

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Story Source:

The above story is based on materials provided by Penn State Materials Research Institute. Note: Materials may be edited for content and length.

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Journal Reference:

1. Yu-Chuan Lin, Chih-Yuan S. Chang, Ram Krishna Ghosh, Jie Li, Hui Zhu, Rafik Addou, Bogdan Diaconescu, Taisuke Ohta, Xin Peng, Ning Lu, Moon J. Kim, Jeremy T. Robinson, Robert M Wallace, Theresa S. Mayer, Suman Datta, Lain-Jong Li, Joshua A. Robinson. Atomically Thin Heterostructures Based on Single-Layer Tungsten Diselenide and Graphene. Nano Letters, 2014; 141117143307009 DOI: 10.1021/nl503144a

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New species of electrons can lead to better computing

 

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In a research paper published this week in Science, the collaboration led by MIT's theory professor Leonid Levitov and Manchester's Nobel laureate Sir Andre Geim report a material in which electrons move at a controllable angle to applied fields, similar to sailboats driven diagonally to the wind.

The material is graphene -- one atom-thick chicken wire made from carbon -- but with a difference. It is transformed to a new so-called superlattice state by placing it on top of boron nitride, also known as `white graphite', and then aligning the crystal lattices of the two materials. In contrast to metallic graphene, a graphene superlattice behaves as a semiconductor.

In original graphene, charge carriers behave like massless neutrinos moving at the speed of light and having the electron charge. Although an excellent conductor, graphene does not allow for easy switching on and off of current, which is at the heart of what a transistor does.

Electrons in graphene superlattices are different and behave as neutrinos that acquired a notable mass. This results in a new, relativistic behaviour so that electrons can now skew at large angles to applied fields. The effect is huge, as found in the Manchester-MIT experiments.

The reported relativistic effect has no known analogue in particle physics and extends our understanding of how the universe works.

Beyond the discovery, the observed phenomenon may also help enhance the performance of graphene electronics, making it a worthy companion to silicon.

The research suggests that transistors made from graphene superlattices should consume less energy than conventional semiconductor transistors because charge carriers drift perpendicular to the electric field, which results in little energy dissipation.

The Manchester-MIT researchers demonstrate the first such transistor, which opens a venue for less power hungry computers.

Professor Geim comments 'It is quite a fascinating effect, and it hits a very soft spot in our understanding of complex, so-called topological materials. It is extremely rare to come across with a phenomenon that bridges materials science, particle physics, relativity and topology.'

Professor Levitov adds 'It is widely believed than unconventional approaches to information processing are key for the future of IT hardware. This belief has been the driving force behind a number of important recent developments, in particular the development of spintronics. The demonstrated transistor highlights the promise of graphene-based systems for alternative ways of information processing. '

 

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Story Source:

The above story is based on materials provided by University of Manchester. Note: Materials may be edited for content and length.

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Journal Reference:

1. R. V. Gorbachev, J. C. W. Song, G. L. Yu, A. V. Kretinin, F. Withers, Y. Cao, A. Mishchenko, I. V. Grigorieva, K. S. Novoselov, L. S. Levitov, and A. K. Geim. Detecting topological currents in graphene superlattices. Science, 11 September 2014 DOI: 10.1126/science.1254966

Graphene's multi-colored butterflies

 

June 1, 2014

University of Manchester

Combining black and white graphene can change the electronic properties of the one-atom thick materials, researchers have found. One of the major challenges for using graphene in electronics applications is the absence of a band gap, which basically means that graphene's electrical conductivity cannot be switched off completely. Whatever researchers tried to do with the material so far, it remained highly electrically conductive.

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Writing in Nature Physics, a large international team led by Dr Artem Mishchenko and Sir Andre Geim from The University of Manchester shows that the electronic properties of graphene change dramatically if graphene is placed on top of boron nitride, also known as 'white graphite'.

One of the major challenges for using graphene in electronics applications is the absence of a band gap, which basically means that graphene's electrical conductivity cannot be switched off completely. Whatever researchers tried to do with the material so far, it remained highly electrically conductive.

A new direction that has recently emerged in graphene research is to try to modify graphene's electronic properties by combining it with other similar materials in multilayered stacks. This creates an additional landscape for electrons moving through graphene and, therefore, its electronic properties can change strongly.

The University of Manchester scientists have used capacitance measurements to probe these changes. They found that in combination with a magnetic field this creates numerous replicas of the original graphene spectrum. This phenomenon is known as the Hofstadter butterfly but it is the first time that well developed replica spectra have been observed.

The researchers found a wealth of unexpected physics in this new system. For example, the Hofstadter butterflies turned out to be strongly contorted, very different from the theoretical predictions. This happens because electrons feel not only the landscape but also each other, which modifies the butterfly.

Another phenomenon that the Manchester paper reports is that graphene starts behaving at very low temperatures like a tiny ferromagnet. Usually, the higher the magnetic field, the more magnetic graphene become. The Hofstadter butterfly in Manchester's capacitors leads to an unexpected oscillating behaviour of the ferromagnetism. As new replica spectra emerge and disappear, so does the ferromagnetism.

Dr Mishchenko said: "It is really a new nice electronic system both similar to and different from graphene. We expect many more surprises. Let us first understand what it is and then we start talking about possible applications."

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Story Source:

The above story is based on materials provided by University of Manchester. Note: Materials may be edited for content and length.

Graphene Helps Copper Wires Keep Their Cool

 

An exotic form of carbon could help relieve a growing problem with the copper used in computer processors.

• By Katherine Bourzac on March 21, 2014

 

Why It Matters

As computers become more powerful, we’ll need new ways of cooling their components.

Cooling off: A close-up shows copper before graphene has been added (top), and after (below).

When people in the chip industry talk about the thermal problems in computer processors, they get dramatic. In 2001, Pat Gelsinger, then vice president of Intel, noted that if the temperatures produced by the latest chips kept rising on their current path, they would exceed the heat of a nuclear reactor by 2005, and the surface of the sun by 2015. Fortunately, such thermal disaster was averted by slowing down the switching speeds in microprocessors, and by adopting multicore chip designs in which several processors run in parallel.

Now the semiconductor industry has another thermal problem to sort out. As chip components shrink, the copper wiring that connects them must shrink, too. And as these wires get thinner, they heat up tremendously.

A potential solution to this interconnect fever has been found in the form of graphene, an exotic material made from single-atom-thick sheets of carbon that is a superlative conductor of both electrons and heat.

Materials scientists already use copper as a catalyst to grow graphene for other uses. So Alexander Balandin of the University of California, Riverside, and Kostya Novoselov, a physicist at University of Manchester, U.K., who won the 2010 Nobel Prize in Physics for his foundational work with graphene (see “Graphene Wins Nobel Prize”), decided to leave the graphene on the copper to see how it affected the metal’s thermal properties. In a paper published in the journal Nano Letters, they report that a sandwich made of graphene on both sides of a sheet of copper improves the copper’s ability to dissipate heat by 25 percent—a significant figure for chip designers.

Balandin says that the graphene itself doesn’t seem to conduct the heat away. Rather, it alters the structure of the copper, improving the metal’s conductive properties. Heat moving through copper is usually slowed by the crystalline structure of the metal. Graphene changes this structure, causing those walls to move farther apart, and allowing heat to flow more readily, says Balandin.

Studies were done with relatively thick sheets of copper—much larger than the copper wires found in computer chips—but Balandin expects that the heat-conducting effect will be seen in thinner copper wires, too. He’s now working on copper-graphene wires as small as those used in commercial computer chips.

The problem is an urgent one. This year, Intel is expected to announce products containing 14-nanometer transistors, with copper interconnects about on this scale or even smaller. Copper wires will not work below 10 nanometers, and it’s not clear what will. “We haven’t yet found an interconnect material that can work beyond 10 nanometers,” partly due to overheating, says Saroj Nayak, a physicist at the Center for Integrated Electronics at the Rensselaer Polytechnic Institute in Troy, New York.

Majeed Foad, an electrical engineer at Applied Materials, a semiconductor-equipment maker headquartered in Santa Clara, California, who helps the company track research on new materials, says graphene’s properties are exciting, but adds that as chip components are miniaturized, they become more sensitive to high temperatures. It takes a lot of heat to make good quality graphene—Balandin and Novoselov heated their wires to over 1,000 °C. Foad says such temperatures would degrade transistors and other chip components. Balandin, however, points to lab experiments that demonstrate that graphene can be grown at lower temperatures, at least in the research setting.

Regardless, Foad says, chip makers won’t be in any rush to embrace graphene. “Changing materials is very painful, so we will squeeze every last drop of performance out of what we have,” he says.

It’s clear that simply cramming more transistors into processors and putting more processors in chips is not going to be tenable much longer. High-end chips already contain about 50 to 60 kilometers of copper wiring and multiple cores.

Jonathan Candelaria, director of interconnect research at the Semiconductor Research Corporation, an industry consortium in Durham, North Carolina, says that adding more transistors doesn’t improve performance the way it used to. The solution may again turn out to be adopting fundamentally different architectures. New ways of designing and packaging chips could help solve the heat problem, says Candelaria, and this will give the industry time to work out problems with new materials, perhaps including the new graphene-copper hybrids.