Prolonged Power for Mobile Devices: New Technology from U of Texas

Researchers from The University of Texas at Dallas have created technology that could be the first step toward wearable computers with self-contained power sources or, more immediately, a smartphone that doesn’t die after a few hours of heavy use.

This technology, published online in Nature Communications, taps into the power of a single electron to control energy consumption inside transistors, which are at the core of most modern electronic systems.

Researchers from the Erik Jonsson School of Engineering and Computer Science found that by adding a specific atomic thin film layer to a transistor, the layer acted as a filter for the energy that passed through it at room temperature. The signal that resulted from the device was six to seven times steeper than that of traditional devices. Steep devices use less voltage but still have a strong signal.

Dr. Jiyoung Kim (left) and Dr. Kyeongjae “K.J.” Cho examine a wafer used to make transistors. The two created new technology that could reduce energy consumption in mobile devices and computers.

“The whole semiconductor industry is looking for steep devices because they are key to having small, powerful, mobile devices with many functions that operate quickly without spending a lot of battery power,” said Dr. Jiyoung Kim, professor of materials science and engineering in the Jonsson School and an author of the paper. “Our device is one solution to make this happen.”

Tapping into the unique and subtle behavior of a single electron is the most energy-efficient way to transmit signals in electronic devices. Since the signal is so small, it can be easily diluted by thermal noises at room temperature. To see this quantum signal, engineers and scientists who build electronic devices typically use external cooling techniques to compensate for the thermal energy in the electron environment. The filter created by the UT Dallas researchers is one route to effectively filter out the thermal noise.

Dr. Kyeongjae “K.J.” Cho, professor of materials science and engineering and physics and an author of the paper, agreed that transistors made from this filtering technique could revolutionize the semiconductor industry.

“Having to cool the thermal spread in modern transistors limits how small consumer electronics can be made,” said Cho, who used advanced modeling techniques to explain the lab phenomena. “We devised a technique to cool the electrons internally—allowing reduction in operating voltage—so that we can create even smaller, more power efficient devices.”

Continuous Wave and Linear Imagers Academic & Industrial Applications

Each time a device such as a smartphone or a tablet computes it requires electrical power for operation. Reducing operating voltage would mean longer shelf lives for these products and others. Lower power devices could mean computers worn with or on top of clothing that would not require an outside power source, among other things.

To create this technology, researchers added a chromium oxide thin film onto the device. That layer, at room temperature of about 80 degrees Fahrenheit, filtered the cooler, stable electrons and provided stability to the device. Normally, that stability is achieved by cooling the entire electronic semiconductor device to cryogenic temperatures—about minus 321 degrees Fahrenheit.

Another innovation used to create this technology was a vertical layering system, which would be more practical as devices get smaller.

“One way to shrink the size of the device is by making it vertical, so the current flows from top to bottom instead of the traditional left to right,” said Kim, who added the thin layer to the device.

Lab test results showed that the device at room temperature had a signal strength of electrons similar to conventional devices at minus 378 degrees Fahrenheit. The signal maintained all other properties. Researchers will also try this technique on electrons that are manipulated through optoelectronic and spintronic—light and magnetic—means.

The next step is to extend this filtering system to semiconductors manufactured in Complementary Metal-Oxide Semiconductor (CMOS) technology.

“Electronics of the past were based on vacuum tubes,” Cho said. “Those devices were big and required a lot of power. Then the field went to bipolar transistors manufactured in CMOS technology. We are now again facing an energy crisis, and this is one solution to reduce energy as devices get smaller and smaller.”

Explore further: Team uses nanotechnology to help cool electrons with no external sources

Researchers Intoduce an Electric Field to Enhance Solar Cell Performance

 

Researchers at the Kavli Energy Nanosciences Institute, the University of California at Berkeley and the Lawrence Berkeley National Lab, have succeeded in boosting the performance of a new type of solar cell by simply applying an electric field to it. The device (made of low cost zinc phosphide and graphene) is novel in its design in that it lacks a junction between the two p- and n-type semiconductors that make it up – which is a first. The cell might be ideal for use in areas where the intensity of sunlight changes a lot over the course of the year.

The device and experimental results

“Our solar cell does not need to be doped, nor does it require high-quality heterojunctions, which are challenging and expensive to fabricate,” says team member Oscar Vazquez-Mena. “Our work is a novel and promising approach for making photovoltaics with low-cost and abundant materials such as certain phosphides and sulphides that are easy to synthesize and which are environmentally friendly.”

Beside expensive light absorbers like silicon, there are semiconductors like zinc phosphide, copper zinc tin sulphide, cuprous oxide and iron sulphide that are much cheaper. However, for these materials to efficiently convert sunlight into energy, they need to be doped to form homojunctions, or require complementary emitter materials to form high-quality p-n heterojunctions.

A team led by Alex Zettl, Harry Atwater, Ali Javey and Michael Crommie has now overcome this problem by making a simple junction with graphene rather than a semiconductor. A voltage applied to a gate over the junction can tune the energy barrier between the graphene and an adjoining layer of zinc phosphide to boost how efficiently solar cells made from these materials convert light into energy.

The devices are relatively simple to fabricate, says Vazquez-Mena. “Jeff Bosco from Harry Atwater’s team at Caltech makes high-quality zinc phosphide films and in our lab at UC Berkeley, we are experts at growing graphene on copper substrates. Basically, we transfer the graphene from the copper onto the zinc phosphide film to form a graphene- zinc phosphide junction. We then add an insulator layer on top of the graphene, prepared by our colleagues in Ali Javey’s team, also at UC Berkeley. Finally we add a thin top gate to the structure.”

Barrier is like a dam

Conventional solar cells normally contain two bulk semiconductors, with their electrons at different energy levels. These semiconductors are brought into contact to form an electric barrier between them that separates the electrons from each side. “This barrier can be likened to the dam in a hydroelectric power plant that separates two reservoirs of water at different heights,” explains Vazquez-Mena. “In a solar cell, the electric charges are the water in the dam and we use energy from the Sun to make the charges jump over the barrier.”

In the new device, the researchers used a layer of graphene in place of one of the semiconductors and added a top gate to it. “Why? Because it is easy to control the energy level of electrons in graphene by doing this,” Vazquez-Mena tells nanotechweb.org. “Such a thing is difficult to do in a bulk semiconductor.”

The top gate can regulate the barrier between graphene and the zinc phosphide, needed for the solar cell to work, he adds. “This is critical for the performance of the device and allows us to optimize the energy extracted from it. Going back to the dam analogy, it is as if we would be controlling the height of the dam.”

The fact that we can manipulate the barrier height in this way means that, in principle, we could make graphene junctions with many other materials, he says.

Modifying the barrier

In bulk semiconductor solar cells, the barrier height depends on the intrinsic properties of the materials making up the barrier. So, once you put the materials together, there is not much you can do to change the barrier, explains Vazquez-Mena.

“Our device is very different in that we can modify this barrier by simply applying an electric field to the top gate and adjusting the strength of the field applied for different materials and light conditions to optimize energy conversion. Our device, which is just a basic graphene-zinc phosphide solar cell, normally has an efficiency of 1% without any applied gate voltage, but we have doubled this to 2% by increasing the gate voltage to 2V. We have thus been able to boost its performance beyond the intrinsic properties of the material it is made up of.”

This type of solar cell might be ideal in climes where the sunlight varies a lot, he says – thanks to the fact that we can adjust the barrier to optimize energy conversion.

The California researchers say that they are looking to improve the efficiency of their devices and improving the quality of the graphene-zinc phosphide junction so that it produces a higher photocurrent. “We also want to apply our technology to other low-cost and readily available materials,” says Vazquez-Mena. “For example, the device we have made can be improved by using graphene itself or a transparent conductor like indium-tin oxide as the top gate.”

The team, reporting its work in Nano Letters, says that it will also test copper zinc tin sulphide, cuprous oxides and copper sulphide. “These materials are less harmful to the environment compared with commonly used solar cell materials like cadmium telluride and are cheaper than pure silicon. We definitely have many ideas to try but we also hope that other research groups will be inspired by our experiments and develop similar strategies to keep improving the efficiencies of alternative photovoltaic materials.”

Dateline Australia: World’s First Technology Breakthrough In Using Graphene For Micro Devices

Next month, Dr. Iacopi will travel to Seattle in the US to address the 4th International Symposium on Graphene Devices.

 

 

 

 

Dr. Francesca Iacopi

Researchers are claiming world-first technology developed at Griffith University will harness the remarkable properties of graphene and could launch the next generation of mass produced, low-cost micro-devices.

Dr. Francesca Iacopi’s novel micro-fabrication process enables production-scale manufacturing of a material companies can use to commercially produce sensor devices which are biocompatible, chemically resistant and highly sensitive.

“We believe this process will change the way we live by providing the ultimate in device miniaturisation,” says Dr Iacopi, from Griffith University’s Queensland Micro- and Nanotechnology Centre.

“It will influence a lot of different sectors because many modern applications relying on micro and nano-devices will be able to advance by incorporating this technology,” says Dr Iacopi, from Griffith University’s Queensland Micro and Nanotechnology Centre.

“For example, medicine is just one area where this technology can be applied. Someone with diabetes could have a nanochip sitting on their skin -– mass produced with the help of our micro-fabrication process — continuously monitoring their blood, and any changes can be relayed directly to a doctor.”

First isolated in the laboratory about a decade ago, graphene is pure carbon and one of the thinnest, lightest and strongest materials known.

A supreme conductor of electricity and heat, much has been written about its mechanical, electrical, thermal and optical properties and the possibilities with the fabrication of new and advanced micro-devices.

However, progress so far has been slow due to the difficulty in synthesising high quality graphene on to Silicon wafers, which would enable cost-effective mass production of such devices.

That problem has now been overcome.

Working with three PhDs, a postdoctorate, national and international collaborators Dr Iacopi has developed:

• a low temperature process to synthesise graphene by using a metal alloy catalyst which produces a continuous, high quality, controllable graphene film;
• a strategy for patterning graphene in such a way that it will grow only on a pre-patterned Silicon Carbide (SiC) layer on Silicon.

“Until now, high quality graphene was restricted to the use of expensive SiC wafers or the use of complicated transfer procedures to Silicon wafers. A cheaper substrate and a simpler methodology was badly needed to ensure the micro-devices would be cost-competitive,” says Dr Iacopi.

“At Griffith, we were the first develop a method for depositing a very high quality thin layer of SiC on to 300mm Si wafers.

“This work is still very early but the prospects are very exciting and broad-ranging.”

Dr Iacopi and her team have already begun seeking industry partners to leverage the technology in an industrial product.

 

Translating Science into Business: The Business of Organic Semiconductors

 

“There are many things which can go wrong when starting a company; but the worst thing that can go wrong is to not do it,” said Prof. Karl Leo, Director of KAUST’s Solar & Photovoltaics Engineering Research Center, when speaking at an Entrepreneurship Center speaker series event this past spring. Wearing the dual hats of scientist and entrepreneur, Prof. Leo is the author of 440 publications, holds more than 50 patents, and has co-created 8 companies which have generated over 300 jobs.

A physicist by training, Prof. Leo highlighted the point that he is primarily a scientist who stumbled onto business by chance. “For me it’s always started with and been about the science,” he says. All his spin-off companies came about as a result of basic research he and his group conducted on organic semiconductors. Speaking specifically to the young KAUST researchers hoping to emulate his success as academics and entrepreneurs, Prof. Leo said: “The message I want to pass along is if you really want to do things, just be curious. Don’t say I want to do research to make a company. Do very basic research and the spin-off ideas will come along.”

The Growing Influence of Organic Semiconductors

Prof. Karl Leo started doing research on organic semiconductors about 20 years ago. He has since been passionate about this field’s developments and future potential. Despite his early skepticism resulting from the ephemeral lifetime of organic semiconductors in the ’90s, the performance levels of LED devices for instance have gone from just a few minutes of useful life then to virtually not aging today. “In the long-term, as in 20 to 30 years from now, almost everything will be organics,” he believes. “Silicon has dominated electronics for a long time but organic is something new.” Organic products have evolved into a variety of applications such as: small OLED displays, OLED televisions, OLED lighting, OPV and organic electronics.

Organics, as opposed to traditional silicon-based semiconductors, are by nature essentially lousy semiconductors. Mobility, or the speed at which electrons move on these materials, is a really important property. However, when looking at the electronic properties of semiconductors, carbon offers interesting developments for the performance of organics. For instance, graphene, which is a carbon-based organic material, has even higher mobility than silicon.

One of the companies Prof. Karl Leo co-founded and began operating out of Dresden, Germany in 2003, Novaled, became a leader in in organic light-emitting diode (OLED) field. OLEDs are made up of multiple thin layers of organic materials, known as OLED stacks. They essentially emit light when electricity is applied to them. Novaled became a pioneer in developing highly efficient and long-lifetime OLED structures; and it currently holds the world record in power efficiency. They key to Novaled’s success, as Prof. Leo explains, is “the simple discovery that you can dope organics.” This was a major breakthrough achieved simply adding a very little amount of another molecule.

This organic conductivity doping technology, used to enhance the performance of OLED devices, was the main factor leading to the company being purchased by Samsung in 2013.

Organic Photovoltaics: Technology of the Future

Following the successful commercial penetration of OLED displays in the consumer electronics market, Prof. Karl Leo has since turned his focus on organic photovoltaics. “I think organic PV is something that can change the world,” said Leo. Among the many advantages of organic photovoltaics are that they are thin organic layers which can be applied on flexible plastic substrates. They consume little energy, can be made transparent, and are compatible with low-cost large-area production technologies. Because they are transparent, they can be made into windows for instance, and also be manufactured in virtually any color. All these characteristics make organic PV ideal for consumer products.

Again based on basic research conducted by his group, Prof. Leo also started a company, Heliatek, which is now a world-leader in the production of organic solar film. Heliatek has developed the current world record in the efficiency of transparent solar cells. The company also holds the record for efficiency of opaque cells at 12 percent. Leo believes that it’s possible to achieve up to 20 percent efficiency in the near future, which will be necessary to compete with silicon and become commercially viable.

Don’t Believe Business Plans

Prof. Leo explained that the experience he and his team gained from launching a successful company like Novaled helped them to both define the objectives and obtain funding from investors for his solar cell company, Heliatek. “Once you create a successful company, things get much easier,” he said. But Leo also cautioned the budding entrepreneurs in the audience to be willing to adapt as they present and implement their ideas.

“If you have a good idea and you are convinced you have a good idea, never give up,” he said. But being able to adapt to market needs is also crucial. For instance, Leo’s original business plan for Novaled focused on manufacturing displays. But the realities of the market, and the prohibitive cost of manufacturing displays, convinced his team that the smarter way to go was to supply materials. At the end of the day, what really succeeded in getting a venture capital firm’s attention, after haven been told no 49 times, was his team’s ability to demonstrate the value of the technology.

“Business plans are useful but they must not be overestimated,” said Prof. Leo. Business plans are a good indicator of how entrepreneurs are able to structure their thoughts, identify markets and create a roadmap, but “nobody is able to predict the future in a business plan; it’s not possible.”

 

Definition of Organic Semi-Conductors: Background

An organic semiconductor is an organic material with semiconductor properties, that is, with an electrical conductivity between that of insulators and that of metals. Single molecules, oligomers, and organic polymers can be semiconductive. Semiconducting small molecules (aromatic hydrocarbons) include the polycyclic aromatic compounds pentacene, anthracene, and rubrene. Polymeric organic semiconductors include poly(3-hexylthiophene), poly(p-phenylene vinylene), as well as polyacetylene and its derivatives.

There are two major overlapping classes of organic semiconductors. These are organic charge-transfer complexes and various linear-backbone conductive polymers derived from polyacetylene. Linear backbone organic semiconductors include polyacetylene itself and its derivatives polypyrrole, and polyaniline.

At least locally, charge-transfer complexes often exhibit similar conduction mechanisms to inorganic semiconductors. Such mechanisms arise from the presence of hole and electron conduction layers separated by a band gap.

Although such classic mechanisms are important locally, as with inorganic amorphous semiconductors, tunnelling, localized states, mobility gaps, and phonon-assisted hopping also significantly contribute to conduction, particularly in polyacetylenes. Like inorganic semiconductors, organic semiconductors can be doped. Organic semiconductors susceptible to doping such as polyaniline (Ormecon) and PEDOT:PSS are also known as organic metals

 

Further Information

• Novaled AG
• Heliatek GmbH

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SUBCOMMITTE EXAMINES BREAKTHROUGH NANOTECHNOLOGY OPPORTUNITIES FOR AMERICA

Chairman Terry: “Nanotech is a true science race between the nations, and we should be encouraging the transition from research breakthroughs to commercial development.”

WASHINGTON, DC – The Subcommittee on Commerce, Manufacturing, and Trade, chaired by Rep. Lee Terry (R-NE), today held a hearing on:

“Nanotechnology: Understanding How Small Solutions Drive Big Innovation.”

 

 

“Great Things from Small Things!” … We Couldn’t Agree More!

 

Subcommittee Examines Breakthrough Nanotechnology Opportunities for America

SUBCOMMITTE EXAMINES BREAKTHROUGH NANOTECHNOLOGY OPPORTUNITIES FOR AMERICA

July 29, 2014

 

Chairman Terry: “Nanotech is a true science race between the nations, and we should be encouraging the transition from research breakthroughs to commercial development.”

WASHINGTON, DC – The Subcommittee on Commerce, Manufacturing, and Trade, chaired by Rep. Lee Terry (R-NE), today held a hearing on “Nanotechnology: Understanding How Small Solutions Drive Big Innovation.” Nanotechnology is science, engineering, and technology conducted at the nanoscale, which is approximately 1 to 100 nanometers (one nanometer is a billionth of a meter). This technology brings great opportunities to advance a broad range of industries, bolster our U.S. economy, and create new manufacturing jobs. Members heard from several nanotech industry leaders about the current state of nanotechnology and the direction that it is headed.

“Just as electricity, telecommunications, and the combustion engine fundamentally altered American economics in the ‘second industrial revolution,’ nanotechnology is poised to drive the next surge of economic growth across all sectors,” said Chairman Terry.

 

 

Dr. Christian Binek, Associate Professor at the University of Nebraska-Lincoln, explained the potential of nanotechnology to transform a range of industries, stating, “Virtually all of the national and global challenges can at least in part be addressed by advances in nanotechnology. Although the boundary between science and fiction is blurry, it appears reasonable to predict that the transformative power of nanotechnology can rival the industrial revolution. Nanotechnology is expected to make major contributions in fields such as; information technology, medical applications, energy, water supply with strong correlation to the energy problem, smart materials, and manufacturing. It is perhaps one of the major transformative powers of nanotechnology that many of these traditionally separated fields will merge.”

Dr. James M. Tour at the Smalley Institute for Nanoscale Science and Technology at Rice University encouraged steps to help the U.S better compete with markets abroad. “The situation has become untenable. Not only are our best and brightest international students returning to their home countries upon graduation, taking our advanced technology expertise with them, but our top professors also are moving abroad in order to keep their programs funded,” said Tour. “This is an issue for Congress to explore further, working with industry, tax experts, and universities to design an effective incentive structure that will increase industry support for research and development – especially as it relates to nanotechnology. This is a win-win for all parties.”

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Professor Milan Mrksich of Northwestern University discussed the economic opportunities of nanotechnology, and obstacles to realizing these benefits. He explained, “Nanotechnology is a broad-based field that, unlike traditional disciplines, engages the entire scientific and engineering enterprise and that promises new technologies across these fields. … Current challenges to realizing the broader economic promise of the nanotechnology industry include the development of strategies to ensure the continued investment in fundamental research, to increase the fraction of these discoveries that are translated to technology companies, to have effective regulations on nanomaterials, to efficiently process and protect intellectual property to ensure that within the global landscape, the United States remains the leader in realizing the economic benefits of the nanotechnology industry.”

James Phillips, Chairman & CEO at NanoMech, Inc., added, “It’s time for America to lead. … We must capitalize immediately on our great University system, our National Labs, and tremendous agencies like the National Science Foundation, to be sure this unique and best in class innovation ecosystem, is organized in a way that promotes nanotechnology, tech transfer and commercialization in dramatic and laser focused ways so that we capture the best ideas into patents quickly, that are easily transferred into our capitalistic economy so that our nation’s best ideas and inventions are never left stranded, but instead accelerated to market at the speed of innovation so that we build good jobs and improve the quality of life and security for our citizens faster and better than any other country on our planet.”

Chairman Terry concluded, “Nanotech is a true science race between the nations, and we should be encouraging the transition from research breakthroughs to commercial development. I believe the U.S. should excel in this area.”

– See more at: http://energycommerce.house.gov/press-release/subcommittee-examines-breakthrough-nanotechnology-opportunities-america#sthash.YnSzFU10.dpuf

Molecular Dynanmics: Visualizing the Invisible

Panagiotis Grammatikopoulos in the OIST Nanoparticles by Design Unit simulates the interactions of particles that are too small to see, and too complicated to visualize. In order to study the particles’ behavior, he uses a technique called molecular dynamics.

This means that every trillionth of a second, he calculates the location of each individual atom in the particle based on where it is and which forces apply. He uses a computer program to make the calculations, and then animates the motion of the atoms using visualization software. The resulting animation illuminates what happens, atom-by-atom, when two nanoparticles collide. Grammatikopoulos calls this a virtual experiment.

He knows what the atoms in his starting nanoparticles look like. He knows their motion follows the laws of Newtonian physics. His colleagues have seen what the resulting particles look like after collision experiments. Once his simulation is complete, Grammatikopoulos compares his end products with his colleagues to check his accuracy. Grammatikopoulos most recently simulated how palladium nanoparticles interact, published in Scientific Reports on July 22, 2014 (“Coalescence-induced crystallisation wave in Pd nanoparticles”).

 

Grammatikopoulos simulated two palladium nanoparticles colliding at different temperatures. The hotter the temperature, the more homogenous the resulting product, and the further the atoms in the particle crystallize. (click on image to enlarge)

Palladium is an expensive but highly efficient catalyst that lowers the energy required to start many chemical reactions. Researchers can make palladium even more efficient by designing palladium nanoparticles, which use the same mass of palladium in tinier pieces, increasing surface area. The more surface area a catalyst has, the more effective it is, because there are more active sites where elements can meet and reactions can occur.

However, shrinking a material to only a few nanometers can change some of the properties of that material. For example, all nanoparticles melt at cooler temperatures than they would normally, which changes what happens when two particles collide. Ordinarily, two particles will collide and release a small amount of heat, but the particles remain more or less the same. But when two nanoparticles collide, sometimes the heat released melts the surface of the two particles, and they fuse together.

Palladium Crystallization at 300K. Grammatikopoulos created this simulation of palladium nanoparticles colliding at 300 Kevin, or about 27 degrees Celsius. The nanoparticles meet, then fuse, then crystallize in orderly planes.

Grammatikopoulos simulated palladium nanoparticles colliding and fusing at different temperatures. He determined that each time the particles fused, their atoms would start to crystallize into orderly rows and planes. At higher temperatures, the particles fuse into one homogeneous structure. At lower temperatures, the products look like classic snowmen, with a few parts that had crystallized with different orientations.

“The simulation gives you an understanding of physical processes,” said Grammatikopoulos. Before his research, Grammatikopoulos could not explain why all the palladium nanoparticles his lab created had a crystalline structure. Furthermore, he noticed that many palladium nanoparticles grew protrusions, giving the particles a lumpy shape. “Since the protrusions stick out, they bond more easily with other molecules,” Grammatikopoulos explained. “I’m not sure yet if it’s beneficial, but it’s definitely affecting the catalytic properties.”

Palladium Crystallization at 1000K. Grammatikopoulos created this simulation of palladium nanoparticles colliding at 1000 Kevin, or about 727 degrees Celsius. At this hot temperature, the nanoparticles meet, fuse, and crystallize, forming one large homogenous product.

This study establishes some ground rules and explains certain properties of palladium nanoparticles. Understanding these properties could help design other nanoparticles out of other materials that would rival palladium’s abilities as a catalyst. Palladium plays a role in thousands of important reactions, from making drugs to creating new biofuels. For example, Prof. Mukhles Sowwan’s Nanoparticles by Design Unit and Prof. Igor Goryanin’s Biological Systems Unit at OIST are working with palladium-catalyzed reactions to improve the efficiency of microbial fuel cells. Better palladium nanoparticles will propel this research forward.

“We need to understand the basic science,” explained Sowwan, who is Grammatikopoulos’ advisor. Sowwan says that the field of nanoscience is only starting to move towards applying the research, because there is still so much to learn about the properties of nanoparticles. “If you build something without understanding the basics,” Sowwan said, “you will not be able to explain the results.”

Source: By Poncie Rutsch, Okinawa Institute of Science and Technology

Carbyne: Carbon-Atom Chain Goes from Metal to Semiconductor: Useful in Many Applications

Applying just the right amount of tension to a chain of carbon atoms can turn it from a metallic conductor to an insulator, according to Rice University scientists.

 

Stretching the material known as carbyne — a hard-to-make, one-dimensional chain of carbon atoms — by just 3 percent can begin to change its properties in ways that engineers might find useful for mechanically activated nanoscale electronics and optics.

The finding by Rice theoretical physicist Boris Yakobson and his colleagues appears in the American Chemical Society journal Nano Letters.

Carbyne chains of carbon atoms can be either metallic or semiconducting, according to first-principle calculations by scientists at Rice University. Stretching the chain dimerizes the atoms, opening a band gap between the pairs.

Until recently, carbyne has existed mostly in theory, though experimentalists have made some headway in creating small samples of the finicky material. The carbon chain would theoretically be the strongest material ever, if only someone could make it reliably.

The first-principle calculations by Yakobson and his co-authors, Rice postdoctoral researcher Vasilii Artyukhov and graduate student Mingjie Liu, show that stretching carbon chains activates the transition from conductor to insulator by widening the material’s band gap. Band gaps, which free electrons must overcome to complete a circuit, give materials the semiconducting properties that make modern electronics possible.

In their previous work on carbyne, the researchers believed they saw hints of the transition, but they had to dig deeper to find that stretching would effectively turn the material into a switch.

Each carbon atom has four electrons available to form covalent bonds. In their relaxed state, the atoms in a carbyne chain would be more or less evenly spaced, with two bonds between them. But the atoms are never static, due to natural quantum uncertainty, which Yakobson said keeps them from slipping into a less-stable Peierls distortion.

“Peierls said one-dimensional metals are unstable and must become semiconductors or insulators,” Yakobson said. “But it’s not that simple, because there are two driving factors.”

One, the Peierls distortion, “wants to open the gap that makes it a semiconductor.” The other, called zero-point vibration (ZPV), “wants to maintain uniformity and the metal state.”

Yakobson explained that ZPV is a manifestation of quantum uncertainty, which says atoms are always in motion. “It’s more a blur than a vibration,” he said. “We can say carbyne represents the uncertainty principle in action, because when it’s relaxed, the bonds are constantly confused between 2-2 and 1-3, to the point where they average out and the chain remains metallic.”

But stretching the chain shifts the balance toward alternating long and short (1-3) bonds. That progressively opens a band gap beginning at about 3 percent tension, according to the computations. The Rice team created a phase diagram to illustrate the relationship of the band gap to strain and temperature.

How carbyne is attached to electrodes also matters, Artyukhov said. “Different bond connectivity patterns can affect the metallic/dielectric state balance and shift the transition point, potentially to where it may not be accessible anymore,” he said. “So one has to be extremely careful about making the contacts.”

“Carbyne’s structure is a conundrum,” he said. “Until this paper, everybody was convinced it was single-triple, with a long bond then a short bond, caused by Peierls instability.” He said the realization that quantum vibrations may quench Peierls, together with the team’s earlier finding that tension can increase the band gap and make carbyne more insulating, prompted the new study.

“Other researchers considered the role of ZPV in Peierls-active systems, even carbyne itself, before we did,” Artyukhov said. “However, in all previous studies only two possible answers were being considered: either ‘carbyne is semiconducting’ or ‘carbyne is metallic,’ and the conclusion, whichever one, was viewed as sort of a timeless mathematical truth, a static ‘ultimate verdict.’ What we realized here is that you can use tension to dynamically go from one regime to the other, which makes it useful on a completely different level.”

Yakobson noted the findings should encourage more research into the formation of stable carbyne chains and may apply equally to other one-dimensional chains subject to Peierls distortions, including conducting polymers and charge/spin density-wave materials.

The Robert Welch Foundation, the U.S. Air Force Office of Scientific Research and the Office of Naval Research Multidisciplinary University Research Initiative supported the research. The researchers utilized the Data Analysis and Visualization Cyberinfrastructure (DAVinCI) supercomputer supported by the NSF and administered by Rice’s Ken Kennedy Institute for Information Technology.

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Story Source:

The above story is based on materials provided by Rice University. The original article was written by Mike Williams. Note: Materials may be edited for content and length.

Flexible Glass for the Display Industry? Not So Fast!

** From NanoMarkets LC July 21st, 2014

 

Flexible glass seemed like a natural fit for the display industry, combining the impermeability of glass with the flexibility of plastic. In 2012 it appeared as though flexible and ultrathin glass companies were going to benefit from the explosion of touch screens in displays of all sizes. Unfortunately, the market took a different turn. Now suppliers of ultrathin and flexible glass are looking for applications beyond displays to bring in revenue in the next few years, and one of the places they are looking is in semiconductor packaging.

For those who approach flexible glass from the point of view of a display, an application where the glass is hidden between layers of silicon and other materials may not seem to make a lot of sense. As far as NanoMarkets can tell, no one really thought about semiconductor packaging as a use for flexible glass until the display market failed to emerge as an opportunity.

Nonetheless, using ultrathin glass in semiconductor packaging may actually be a very good idea, even though its optical properties and flexibility are irrelevant in this application.

The Role of Glass in Interposers

For many years the semiconductor packaging industry has been developing packages that are smaller, thinner, and lighter than what has come before. Ultrathin glass, 30 to 100 μm, may be able to further progress toward this goal.

The target application is 2.5D or 3D multi-chip or chip scale packages (CSP), where semiconductor chips are placed in close proximity or stacked on top of each other to provide a space-saving configuration. Such packages traditionally use a layer of thinned silicon as an interposer to connect chips to each other and to the underlying organic substrate. Silicon has the advantage of being a familiar material with a well-established infrastructure in the semiconductor packaging industry, but it does have some drawbacks, the major one being cost.

Glass may be preferable to silicon as an interposer because it is a less expensive material, it can be provided in thin sheets (silicon has to be ground and polished to the proper thickness) and it is thermally insulating. Silicon is a semiconductor, not an electrical insulator, which can cause problems with crosstalk between chips.

Silicon conducts heat better than glass, making the semiconductor industry a bit suspicious of the ability of glass to conduct heat sufficiently to avoid hot spots in sensitive ICs. The answer is in the through-glass vias (TGV), channels drilled through the interposer that are filled with metal (usually copper) and form electrical connections between the chip and the organic substrate. Solid filled vias act like heat pipes to provide a path for heat conduction.

The potential cost advantages of glass can best be achieved using large sheets of glass, thus allowing facilities to process more units in parallel than is possible with silicon wafers. The largest possible cost savings of using flexible glass is realized if it can be integrated into a roll-to-roll production process. Several suppliers are producing flexible glass on rolls, but the semiconductor industry is not necessarily prepared to process it.

Re-evaluating the Supply Chain

While glass may be a compelling interposer material from the point of view of glass makers, lack of infrastructure in this application is a real problem. In order for glass to be useful as an interposer, someone needs to drill vias through the glass and metallize them, and it is not yet clear who that would be. Several industries could participate in the supply chain, but there are barriers in all cases:

Semiconductor packaging houses: This industry is not used to working with glass and is not inclined to do so. It is very resistant to change and may be especially averse to implementing R2R processing. Convincing semiconductor packaging facilities to process glass will clearly be an uphill battle.

Flat-panel display manufacturers: These companies have experience with glass but have not historically had anything to do with semiconductor packaging. It may be possible to build awareness in this sector, but the flat panel display industry prefers to sell large pieces of glass.

Printed circuit board manufacturers: The PCB industry currently makes organic interposers, geared toward applications where fine pitch is not required. Glass suppliers might be able to work with the PCB industry, which is used to large panels, if they want to supply sheets of glass. It still may be difficult, however, to implement very thin glass using this approach. It also will probably be difficult to integrate TGV production into a PCB-like process flow.

Organizations that are promoting ultrathin glass interposers are attempting to address the infrastructure challenge:

Georgia Tech: The Packaging Resource Center (PRC) at Georgia Tech has been working with industry partners on glass interposers since 2010 and has moved from initial trials with 180-μm thick glass down to the thinnest products that today’s glass suppliers are producing. The PRC is working with major glass suppliers such as Corning and Schott, who are interested in flexible glass interposers.

The PRC has been working on transferring the technology from prototype to low volume, and perhaps eventually high volume, commercial production. It has made some real progress in developing the technology and moving prototyping from labs into industry, but admits that the greatest challenge in moving forward is lack of infrastructure to support the transition.

Triton: Triton Micro Technologies, a subsidiary of nMode solutions that is partially funded by Asahi Glass Company, is providing some missing segments in the supply chain. Triton has developed a production process to create through glass vias (TGVs) that is sufficient for today’s 2.5D applications and it is making interposers for MEMS, RF, and optics at its manufacturing facility in Carlsbad, CA. According to Triton, the major advantage it provides over silicon is the ability to produce solid filled, hermetic TGVs.

Existing commercial products use glass interposers from Triton, but this is much thicker glass, typically 0.3 mm or greater. The glass is cut into wafers, matching the form factor of silicon but not requiring backgrinding. This provides the convenience of a process that fits easily into existing manufacturing lines but doesn’t take advantage of glass’ potential to provide thinner interposers at much lower cost than silicon. Triton can make large panels of 0.1-mm glass with TGVs, but customers do not know how to handle it and may not be inclined to learn.

NanoMarkets understands the potential advantage thin glass would have as an interposer, but is not especially optimistic about its future, especially in the near term. It seems very unlikely that flexible glass will be able to generate large revenues in this space, even if penetration rates get large. Each product uses a very small amount of glass compared to what would be needed for even a smart phone display.

The semiconductor packaging industry may be an even more difficult environment for introducing new processes than the display industry, and we know flexible glass has had challenges there. Still, we feel this sector is worth keeping an eye on to see if glass has an opportunity to succeed where silicon has not.

See More: http://nanomarkets.net/market_reports/report/flexible-glass-markets-2014-and-beyond

Haydale and InVentures Announce Collaborative Agreement Team Up to Accelerate Commercialisation of Graphene

Haydale, the company focused on enabling technology for the commercialisation of graphene and other nano materials, has announced a major consulting agreement with The InVentures Group to accelerate the commercial application of its patent applied for plasma functionalisation technology in graphene, carbon nanotubes and other high performance nanomaterial systems.

The agreement will significantly increase Haydale’s market presence in North America, allowing the North American R&D market access to graphene nanomaterials with customised functionalisation for specific applications in markets such as inks and coatings, composites and energy harvesting.

The agreement will see The InVentures Group, a major player in bringing new technologies to the North American market and instrumental in the formation of the Graphene Stakeholders Association (GSA) in 2012, promote Haydale’s plasma functionalisation technology to potential R&D customers and commercial partners in the inks and coatings, composites and energy harvesting markets. As part of the agreement, The InVentures Group will identify and prioritise areas of application for Haydale’s technology and engage high profile organisations as potential strategic partners, customers and/or licensees.

Ray Gibbs, CEO at Haydale, commented: “Haydale’s goal is to be the premier solutions provider in enabling commercialisation of certain nano materials such as graphenes. Our novel functionalisation process enables the nano particles to be uniformly dispersed in a target material.

In our view, dispersion is the key to commercialising materials like graphenes and recent third party results demonstrate that our technology works well. This agreement will enable Haydale to significantly increase its market presence in North America and Canada. We expect this agreement to allow a greater number of potential R&D customers to test and analyse our plasma functionalised materials for integration into their specific products and applications.”

He continued: “We are excited to be working with the outstanding team at InVentures, most of whom have spent their careers developing, scaling, and commercialising advanced materials and understand the challenges and opportunities. Their reputation, relationships, and network of partners and customers, combined with their experience in overcoming the hurdles that face companies introducing new materials into established markets, are expected to serve Haydale well as we look to expand the impact of our technology onto the global market.”

Keith Blakely, Chairman and CEO of The InVentures Group, commented: “Graphene is unquestionably one of the most exciting material discoveries so far this century and has astounding intrinsic properties including incredible strength, the highest thermal and electrical conductivity known, and other characteristics that have the potential to impact nearly every industry. We are very excited to be working with Haydale to accelerate the process of identifying, specifically in the North American and Canadian markets, the most promising applications of their technology and materials in commercial applications.”

Following the discovery by Andre Geim and Konstantin Novoselov in 2004, graphene has been heralded to revolutionise the 21st Century through its exceptional physical and mechanical properties in applications ranging from transparent electronics to supercapacitors and advanced batteries, high efficiency solar panels and ultra-strong composites. However, questions still remain over the commercial reality in delivering graphene and the relevance it has to real products and applications.

In order to effectively utilise graphene and achieve its full potential, it must be functionalised, dispersed and easily incorporated into other materials and structures. Haydale’s plasma functionalisation technology overcomes the key barrier to the material’s commercialisation which industry is currently trying to overcome, offering the tailored surface modification of graphene nanomaterials whilst maintaining structural integrity.

To find out more about Haydale’s proprietary plasma process, visit http://www.haydale.com