Metal alloys are strengthened by refining their grain size. This is true down to the nanoscale, yet nanostructured alloys have a limited thermal stability. Recovery, recrystallization and grain growth even at mild temperatures lead to weakening. As a consequence, conventional and widespread joining technologies such as welding, brazing and high temperature soldering are inapplicable. This fact severely hinders alloy commercialization and restricts the type and number of applications in which they can be implemented. The obvious solution of using rivets or adhesives is not always possible and has its respective drawbacks. If the preferred joining options are fusion-based, then heat input must be carefully controlled and/or localized.

For the past decade, the focus in this field has been on characterizing the nanostructured materials and improving their production methods, namely the severe plastic deformation processes. Despite the impressive progress, the joining issue has remained open, even though several companies are now making commercial offerings of nanocrystalline metal articles. This is problematic as advanced materials have limited applicability unless they can be joined properly into useful products and assemblies in a way that preserves their unique properties. i.e. their nanoscale characteristics. Luckily, the joining problem has been solved in part here. Only the application performance remains to be assessed.

Source:
Longtin, R., Hack, E., Neuenschwander, J. and Janczak-Rusch, J. (2011), Benign Joining of Ultrafine Grained Aerospace Aluminum Alloys Using Nanotechnology. Advanced Materials.
DOI: 10.1002/adma.201103275 (abstract)

The percentage of the records returned by the search terms for each year dramatically increased from 20 % in 1991 to 80 % in 2010. Also, the term nano* was not sufficient to capture the full activity in these fields and tended to underestimate the literature, especially that of the 1990s. In terms of subject category, the increase in nanoscale studies has been of several-fold for the top 5 Web of Science categories, namely Physics, Materials Science, Chemistry (physical), Chemistry (multidisciplinary) and Nanoscience and Nanotechnology. The latter had the greatest increase from 18 to 70 % from 1997 to 2009.

Clearly, nanotechnology and nanoscience have grown in importance since the 1990s, yet this is not so equally around the world. China, USA, Japan, Germany and South Korea are the top 5 countries by number of records. The percentages of 2010 records returned by the search are stunning for Asian countries in comparison to the so-called G7 countries. Indeed, China, India and Iran have made nanoscale studies a very high research priority with more than 10 % of the total records related to them. On the other hand, England, the Netherlands and Canada are at the bottom of the list with 3.66%, 3.65 % and 3.48 % of their records devoted to nano, respectively. Switzerland with 5.65 % is above the EU-27 average at 5.24 %. The authors conclude by stating that the alarming increase in the proportion taken in the literature by nanoscience and nanotechnology may continue unabated, but that this may depend on how the scientific community delivers concrete application in the ”post-Hype” era.

Although quite informative, this essay does not discuss the reasons behind the discrepancy between the rising Asian countries and the industrialized Western countries. There is also no mention of what is being done in terms of prioritizing nanoscience and nanotechnology in the low ranking countries. Let us quickly consider the case of Canada. Even though it has established a National Institute for Nanotechnology and that some organizations, such as NanoQuébec, exist to support nanotechnology innovation, the country’s output or footprint has remained limited in such a way that it is at the bottom of the list. Why is this so? One could argue that this is the result of differing work ethics and governmental priorities from one country to another.

Others might argue that this depends on which sector of the economy a country is built upon. Economies relying on the primary raw materials sector (mining, forestry and oil) would be less interested, at least immediately, in what nanoscience and nanotechnology has to offer. Conversely, countries based on the secondary manufacturing sector of economy would be far more likely to invest in nano. The push towards continued miniaturization in electronics is a good example of this. In the case of Canada, these questions remain open for discussion.

“Diamond-based devices have the potential to operate at higher speeds and require less power than silicon-based devices,” Research Professor of Electrical Engineering Jimmy Davidson said. “Diamond is the most inert material known, so our devices are largely immune to radiation damage and can operate at much higher temperatures than those made from silicon.” Their design of a logical gate is described in the journal Electronics Letters.

Potential applications include military electronics, circuitry that operates in space, ultra-high speed switches, ultra-low power applications and sensors that operate in high radiation environments, at extremely high temperatures up to 480° Celcius and extremely low temperatures down to -185° Celcius.

Even though their design uses diamond film, it is not exorbitantly expensive. The devices are so small that about one billion of them can be fabricated from one carat of diamond. The films are made from hydrogen and methane using a method called chemical vapor deposition that is widely used in the microelectronics industry for other purposes. This deposited form of diamond is less than one-thousandth the cost of “jewelry” diamond, which has made it inexpensive enough so that companies are putting diamond coatings on tools, cookware and other industrial products. As a result, the cost of producing nanodiamond devices should be competitive with silicon.

The nanodiamond circuits are a hybrid of old fashioned vacuum tubes and modern solid-state microelectronics and combine some of the best qualities of both technologies. Nanodiamond devices consist of a thin film of nanodiamond that is laid down on a layer of silicon dioxide. Much as they do in vacuum tubes, the electrons move through vacuum between the nanodiamond components, instead of flowing through solid material the way they do in normal microelectronic devices. As a result, they require vacuum packaging to operate.

“The reason your laptop gets hot is because the electrons pumping through its transistors bump into the atoms in the semiconductor and heat them up,” Davidson said. “Because our devices use electron transport in vacuum they don’t produce nearly as much heat.” This transmission efficiency is also one reason why the new devices can run on very small amounts of electrical current. Another is that diamond is the best electron emitter in the world so it doesn’t take much energy to produce strong electron beams. “We think we can make devices that use one tenth the power of the most efficient silicon devices,” said Davidson.

The design is also largely immune to radiation damage. Radiation disrupts the operation of transistors by inducing unwanted charge in the silicon, causing an effect like tripping the circuit breaker in your home. In the nanodiamond device, on the other hand, the electrons flow through vacuum so there is nothing for energetic particles to disrupt. If the particles strike the nanodiamond anode or cathode, the impact is limited to a small fluctuation in the electron flow, not complete disruption, as is the case with silicon devices. “When I read about the problems at the Fukushima power plant after the Japanese tsunami, I realized that nanodiamond circuits would be perfect for failsafe circuitry in nuclear reactors,” Davidson said. “It wouldn’t be affected by high radiation levels or the high temperatures created by the explosions.”

Nanodiamond devices can be manufactured by processes that the semiconductor industry currently uses. The one exception is the requirement to operate in vacuum, which would require some modification in the packaging process. Currently, semiconductor chips are sealed in packages filled with an inert gas like argon or simply encapsulated in plastic, protecting them from chemical degradation. Davidson and his colleagues have investigated the packaging process and have found that the metallic seals used in military-grade circuitry are strong enough to hold an adequate vacuum for centuries.

Source: original article

Manufacturer website: http://www.aixtron.com

Materials Today in collaboration with Thermo Scientific are offering a short 45 minute webinar to introduce how Raman spectroscopy can help explore properties of graphene materials.

The presentation will include an overview of several significant applications of Raman spectroscopy:

• measuring thickness
• monitoring chemical properties
• monitoring physical properties

This webinar will be helpful for anyone who is either just starting working with graphene materials or wanting to learn more about Raman spectroscopy.

When: July 28 2011, 16h00 (BST) / 11h00 (EST)
Register here

The 6cm-by-6cm chip holds nine quantum devices, among them four “quantum bits” that do the calculations. The team said further scaling up to 10 qubits should be possible this year. The team’s key innovation was to find a way to completely disconnect – or “decouple” – interactions between the elements of their quantum circuit. The delicate quantum states that they create must be manipulated, moved, and stored without destroying them. “It’s a problem I’ve been thinking about for three or four years now, how to turn off the interactions,” told John Martinis. “Now we’ve solved it, and that’s great – but there’s many other things we have to do.”

Rather than the ones and zeroes of digital computing, quantum computers deal in what are known as superpositions – states of matter that can be thought of as both one and zero at once. In a sense, quantum computing’s one trick is to perform calculations on all superposition states at once. With one quantum bit, or qubit, the difference is not great, but the effect scales rapidly as the number of qubits rises. The figure often touted as the number of qubits that would bring quantum computing into a competitive regime is about 100, so each jump in the race is a significant one.

The RezQu architecture is basically a blueprint for a quantum computer, and several presentations at the American Physical Society conference focused on how to make use of it. RezQu seems to have an edge in one crucial arena – scalability – that makes it a good candidate for the far more complex circuits that would constitute a proper quantum computer. The metric of interest to quantum computing is how long the delicate quantum states can be preserved, and Britton Plourde, a quantum computing researcher from the University of Syracuse, noted that time had increased a thousand fold since the field’s inception.

Source: original article

• Synthesis and selection methods
• Electronic, optical and mechanical properties of carbon nanotubes, graphene and related devices
• Functionnalization, dispersion, processing
• Metrology and standardization
• Composites and materials science
• Other applications and industrial issues

In one promising application, researchers demonstrated the detection of specific odorous molecules with high resolution using a functionalized carbon nanotube based sensor. While the possibilities for CNT-based gas sensors are huge, the problem lies with the fabrication technologies, more specifically with a lack of technology for batch fabrication.

In order for CNT-based sensors to be able to compete with state-of-the-art CMOS (Complementary Metal Oxide Semiconductor) technology, researchers need to develop a low cost, reliable and large-scale reproducible CNT deposition process on the wafer level. Given the difficulties that they have encountered so far, scientists believe that a hybrid approach – to grow and integrate CNTs on CMOS wafers and use these CNTs to improve the performance of existing CMOS technology – could be a more realistic approach.

Researchers in the UK have presented a novel concept of wafer level localized growth of ‘spaghetti’-like CNTs on a fully processed CMOS substrate. This is the first successful proof of concept for growing CNTs at the post CMOS wafer stage. Reporting their findings in the online issue of Nanotechnology, a team from the Engineering Department at University of Cambridge and Cambridge CMOS Sensors Ltd used a standard silicon on insulator (SOI) CMOS process to fabricate the basic gas sensor (which incorporated a tungsten micro-heater and interdigitated electrodes) and on-chip circuitry from a commercial foundry.

The CNTs were grown locally and optimized on a wafer already containing CMOS circuits and devices. The researchers point out that “the integration of the two technologies – nanotechnology and conventional SOI CMOS – is of significant interest both from a device and application perspective. This is because CNTs are being used for the detection of different gases and vapours and SOI CMOS has the capability of low leakage current”.

To fabricate their gas sensor, the team used a SOI CMOS process from a commercial foundry. The SOI process handles 6 inch wafers with a 0.25 µm silicon active layer, and a 1.0 µm buried oxide layer. The device contains an embedded micro-heater and exposed interdigitated sensing electrodes. The interconnect metal (tungsten) of the high-temperature SOI process was used to form a resistive micro-heater. The use of tungsten metallization allows the device to operate at the potentially very high temperatures required for on-chip sensing material growth and gas sensor operation. The top layer of the devices is a passivated stable silicon nitride, which was etched away above the electrodes. The interdigitated sensing electrodes were formed from the top metal layer and are used to measure the change in resistance of the CNTs in the presence of a gas.

The dielectric membrane reduces the power consumption, for a given operating temperature (e.g. 500°C), while providing isolation from the electronic circuits present adjacent to the membrane. CNTs were grown onto interdigitated electrodes with tungsten micro-heater local growth at 725°C. This technique was extended to grow CNTs on more than one device to show the concept of wafer level growth by powering several micro-heaters simultaneously.

CNTs grown by this method were found through Raman spectroscopy to be practically identical and reproducible. Long term electrical resistance measurement was also carried out to check the stability of the CNTs, which is particularly useful for resistive chemical sensor applications.

Source: original article

Andre Geim and his colleague (and former postdoctoral assistant) Konstantin Novoselov first produced graphene in 2004 by repeatedly peeling away graphite strips with adhesive tape to isolate a single atomic plane. They analyzed its strength, transparency, and conductive properties in a paper for Science the same year.

It’s a worthy Nobel, for the simple reason that graphene may be one of the most promising and versatile materials ever discovered. It could hold the key to everything from super small computers to high-capacity batteries. Graphene properties are attractive to materials scientists and electrical engineers for a whole host of reasons, not least of which is the fact that it might be possible to build circuits that are smaller and faster than what you can build in silicon.

Imagine “crystals one atom or molecule thick, essentially two-dimensional planes of atoms shaved from conventional crystals,” said Nobel winner Andre Geim. “Graphene is stronger and stiffer than diamond, yet can be stretched by a quarter of its length, like rubber. Its surface area is the largest known for its weight.” Here are some applications of graphene.

Super-Small Transistors

The Manchester team in 2008 created a 1-nanometer graphene transistor, only one atom thick and 10 atoms across. This is not only smaller than the smallest possible silicon transistor; Novoselov claimed that it could very well represent the absolute physical limit of Moore’s Law governing the shrinking size and growing speed of computer processors.

“It’s about the smallest you can get,” Novoselov said. “From the point of view of physics, graphene is a goldmine. You can study it for ages.”

Super-Dense Data Storage

Researchers around the world have already put graphene to work. A Rice University team In 2008 created a new type of graphene-based, flash-like storage memory, more dense and less lossy than any existing storage technology. Two University of South Florida researchers earlier this year reported techniques to enhance and direct its conductivity by creating wire-like defects to send current flowing through graphene strips.

Energy Storage

The energy applications of graphene are also extraordinarily rich. Texas’s Graphene Energy is using the film to create new ultracapacitators to store and transmit electrical power. Companies currently using carbon nanotubes to create wearable electronics are beginning to switch to graphene, which is thinner and potentially less expensive to produce. Much of the emerging research is devoted to devising more ways to produce graphene quickly, cheaply and in high quantities.

Photonics: Solar Cells and Flexible Touchscreens

A Cambridge University team argues in a paper of Nature Photonics that the true potential of graphene lies in its ability to conduct light as well as electricity. Strong, flexible, light-sensitive graphene could improve the efficiency of solar cells and LEDs, as well as aiding in the production of next-generation devices like flexible touch screens, photodetectors and ultrafast lasers. In particular, graphene could replace rare and expensive metals like platinum and indium, performing the same tasks with greater efficiency at a fraction of the cost.

High-Energy Particle Physics

In pure science, according to Geim, graphene “makes possible experiments with high-speed quantum particles that researchers at CERN near Geneva, Switzerland, can only dream of.” Because graphene is effectively only two-dimensional, electrons can move through its lattice structure with virtually no resistance. In fact, they behave like Heisenberg’s relative particles, with an effective resting mass of zero.

It’s slightly more complicated than this, but here’s a quick and dirty explanation. To have mass in the traditional sense, objects need to have volume; electrons squeezed through two-dimensional graphene have neither. In other words, the same properties that makes graphene such an efficient medium for storing and transmitting energy also demonstrate something fundamental about the nature of the subatomic universe.

Source: original article

Two theoretical physicists from Rice University are reporting initial success in that area in a paper published in the Proceedings of the National Academy of Science. Their new conceptual model, which was created to learn more about the quantum quirks of high-temperature superconductors and other high-tech materials, has also proven useful in describing the origins of ferromagnetism — the everyday “magnetism” of compass needles and refrigerator magnets.

“As a theorist, you strive to have exact solutions, and even though our new model is purely theoretical, it does produce results that match what’s observed in the real world,” said Rice physicist Qimiao Si, the lead author of the paper. “In that sense, it is reassuring to have designed a model system in which ferromagnetism is allowed.”

Ferromagnets are what most people think of as magnets. They’re the permanently magnetic materials that keep notes stuck to refrigerators the world over. Scientists have long understood the large-scale workings of ferromagnets, which can be described theoretically from a coarse-grained perspective. But at a deeper, fine-grained level — down at the scale of atoms and electrons — the origins of ferromagnetism remain fuzzy.

“When we started on this project, we were aware of the surprising lack of theoretical progress that had been made on metallic ferromagnetism,” Si said. “Even a seemingly simple question, like why an everyday refrigerator magnet forms out of electrons that interact with each other, has no rigorous answer.”

Si and graduate student Seiji Yamamoto’s interest in the foundations of ferromagnetism stemmed from the study of materials that were far from ordinary. Si’s specialty is an area of condensed matter physics that grew out of the discovery more than 20 years ago of high-temperature superconductivity. In 2001, Si offered a new theory to explain the behaviour of the class of materials that includes high-temperature superconductors. This class of materials — known as “quantum correlated matter” — also includes more than ten known types of ferromagnetic composites.

Si’s 2001 theory and his subsequent work have aimed to explain the experimentally observed behaviour of quantum-correlated materials based upon the strangely correlated interplay between electrons that goes on inside them. In particular, he focuses on the correlated electron effect that occur as the materials approach a “quantum critical point,” a tipping point that’s the quantum equivalent of the abrupt solid-to-liquid change that occurs when ice melts.

The quantum critical point that plays a key role in high-temperature superconductivity is the tipping point that marks a shift to antiferromagnetism, a magnetic state that has markedly different subatomic characteristics from ferromagnetism. Because of the key role in high-temperature superconductivity, most studies in the field have focused on antiferromagnetism. In contrast, ferromagnetism — the more familiar, everyday form of magnetism — has received much less attention theoretically in quantum-correlated materials.

“So our initial theoretical question was, ‘What would happen, in terms of correlated electron effects, when a ferromagnetic material moves through one of these quantum tipping points?” said Yamamoto, who is now a postdoctoral researcher at the National High Magnetic Field Laboratory in Tallahassee, Fla.

To carry out this thought experiment, Si and Yamamoto created a model system that idealizes what exists in nature. Their jumping off point was a well-studied phenomenon known as the Kondo effect — which also has its roots in quantum magnetic effects. Based on what they knew of this effect, they created a model of a “Kondo lattice,” a fine-grained mesh of electrons that behaved like those that had been observed in Kondo studies of real-world materials.

Si and Yamamoto were able to use the model to provide a rigorous answer about the fine-grained origins of metallic ferromagnetism. Furthermore, the ferromagnetic state that was predicted by the model turned out to have quantum properties that closely resemble those observed experimentally in heavy fermion ferromagnets.

“The model is useful because it allows us to predict how real-world materials might behave under a specific set of circumstances,” Yamamoto said. “And, in fact, we have been able to use it to explain experimental observations on heavy fermion metals, including both the antiferromagnets as well as the less well understood ferromagnetic materials.”

Source: original article