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.

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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.

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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.

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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.”

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An international team of researchers has made a further step towards this vision and demonstrated a novel analytical sensor which mimics our olfaction system. The difference between this and similar prior e-noses is that the active element of this new device is an individual wedge-like nanowire (nanobelt) made of tin dioxide. The required diversity of the sensing elements is encoded in the nanobelt morphology via longitudinal width variations of the nanobelt realized during its growth and via functionalization of some of the segments with palladium catalyst. “Our approach demonstrates the potential of combining bottom-up nanowire fabrication protocols with state-of-the art microfabrication methods to design prospective simple sensing arrays which, in principle, might be scaled down to the size of few micrometers and thus become the smallest analytical instrument,” tells Andrei Kolmakov, an associate professor in the physics department at Southern Illinois University at Carbondale.

Kolmakov and a team of researchers from Karlsruhe Institute of Technology, Rensselaer Polytechnic Institute, Sincrotrone Trieste, and first author Victor V. Sysoev from Saratov State Technical University, have published their findings in ACS Nano. In what probably is the simplest and yet fully functioning e-nose, the device is made of an individual single-crystal metal oxide quasi-1D nanobelt. The nanobelt was indexed with a number of platinum electrodes in a way that each segment of the nanobelt between two electrodes defines an individual sensing elemental receptor of the array.

“We contacted this individual nanobelt with dozen of electrodes and obtained an array of sensors” explains Kolmakov. “Due to this variation of the resistance along the length on the nanobelt the same gas will produce slightly different responses, which leads to the nanobelt’s recognition ability. In fact, this is similar to our own human olfactory receptors which are not very gas selective individually but slightly differ from each other.” Previous designs of nanowire-based electronic noses were using different nanowires to obtain different responses. That meant that they were more complex, expensive, fragile etc. Compared to this, nothing can be simpler, cheaper, and more robust than just a single individual nanowire.

“Our fabrication advance can be compared with development of integrated electronics versus circuits based on individual electronic components” says Kolmakov. “In our case the main sensor functionality is integrated into one single nanostructure.” The research team based their device on tin oxide. This is a well studied semiconducting oxide which traditionally serves as a testbench material to implement novel sensing principles and platforms in gas sensorics. Using a conventional vapor-solid method they grew tin oxide nanobelts and selectively doped segments of the nanobelt’s surface with palladium nanoparticles in order to enhance the resistivity of these segments.

The real-world applications of e-nose instruments would have to deal with complex odors or aromas, for example, ones widespread in the food industry. To test the performance of their e-nose against such complex environments, the researchers exposed a 10-segment single nanobelt sensor to the vapors from the headspace of four alcoholic beverages (glühwein, sparkling wine, vermouth, brandy). To eliminate the strong influence of the different ethanol content to the sensor signal, all beverages were diluted in distilled water to contain the same amount (10 rel. %) of ethanol. The resistance of all 10 segments of the tested nanobelt were plotted in a radar diagram and the results showed that the results are clearly analyte specific.

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In 2009, the U.S Department of Energy (DOE) proposed on-board hydrogen storage system performance targets that have become widely accepted. So far, researchers haven’t been able to successfully demonstrate a material that is capable of simultaneously meeting all of the requirements and criteria set out by the DOE.

A European research team has now reported on a new concept for hydrogen storage using nanoconfined reversible chemical reactions. They demonstrate that nanoconfined hydride has a significant hydrogen storage potential. Research at the Nano Energy-Materials research group at Interdisciplinary Nanoscience Center (iNANO) at Aarhus University in Denmark, led by Flemming Besenbacher and Torben R. Jensen, focuses on the utilization of nanoporous materials as scaffolds for preparation and confinement of nanosized metal hydrides. This bottom-up approach limits the particle size of the hydride to the average pore size of the scaffold material, which allows for the direct production of smaller particles than obtainable mechanically. Furthermore, particle growth and agglomeration may be hindered by the compartmentalization of the nanoparticles within the scaffold material. Nanoconfinement may also mediate improved re-hydrogenation properties of complex metal hydrides.

“Nanoconfinement of metal hydrides is receiving increasing interest in the field of hydrogen storage and this principle has already been applied to a number of promising hydrogen storage materials,” the researchers explain. In their work published in the online edition of ACS Nano, the team introduces an alternative bottom-up approach where nanoparticles of hydrides are synthesized or melt infiltrated in a nanoporous inert scaffold material, which has several advantages:

1. increased surface area of the reactants
2. nanoscale diffusion distances
3. increased number of grain boundaries, which facilitate release and uptake of hydrogen and enhance reaction kinetics

Lithium borohydride (LiBH4) and magnesium hydride (MgH2) nanoparticles are embedded in a nanoporous carbon aerogel scaffold with a maximum pore size of 21 nm and react during release of hydrogen and form magnesium diboride. The hydrogen desorption kinetics is significantly improved compared to bulk conditions, and the nanoconfined system has a high degree of reversibility and stability and possibly also improved thermodynamic properties. The purpose of this work was to further develop the concept of nanoconfinement by investigating a system of higher complexity. Lithium borohydride and magnesium hydride  have been studied intensively in the past due to their high theoretical hydrogen densities.
“However” explains Nielsen, “the use of lithium borohydride as a solid-state hydrogen storage material is hampered by its unfavorable high thermal stability; that is, release of hydrogen takes place at temperatures above 400°C and, importantly, uptake of hydrogen only occurs under extreme conditions. Similarly, application of the abundant and cheap metal magnesium is also impeded by unfavorable thermodynamic properties.” Jensen adds that, “fortunately, both the kinetic and thermodynamic properties of potential hydrogen storage materials can be significantly improved by combining exothermic and endothermic chemical reactions. A more favorable total enthalpy change may be obtained by the introduction of a new dehydrogenated state which may facilitate hydrogenation. This concept is referred to as reactive hydride composites (RHC), and it helps to preserve a high gravimetric hydrogen storage capacity.”

By studying the effect of nanoconfinement on the hydrogen storage properties of a lithium-borohydride/magnesium-hydride system, the team (which included scientists from the Institute of Material Research in Germany and Lund University in Sweden) found that it possesses a high degree of reversible stability and improved hydrogen desorption kinetics as compared to the bulk. Furthermore, the concept of nanoconfined chemical reactions may develop to become an important tool within the emerging area of nanotechnology for the improvement of the properties and reaction yield of a wide range of chemical reactions. This new scheme of nanoconfined chemistry may have a wide range of interesting applications in the future, for example, within the merging area of chemical storage of renewable energy.

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The technique works with multiple forms of graphene and is poised to become an important finding for the development of graphene electronics. The research is published in the Science journal. Scientists who work with nanocircuits are enthusiastic about graphene because electrons meet with less resistance when they travel along graphene compared to silicon and because today’s silicon transistors are nearly as small as allowed by the laws of physics. Graphene also has the edge due to its thickness – it’s a carbon sheet that is a single atom thick. While graphene nanoelectronics could be faster and consume less power than silicon, no one knew how to produce graphene nanostructures on such a reproducible or scalable method. That is until now.

“We’ve shown that by locally heating insulating graphene oxide, both the flakes and epitaxial varieties, with an atomic force microscope tip, we can write nanowires with dimensions down to 12 nanometers. And we can tune their electronic properties to be up to four orders of magnitude more conductive. We’ve seen no sign of tip wear or sample tearing,” said Elisa Riedo, associate professor in the School of Physics at the Georgia Institute of Technology.

On the macroscopic scale, the conductivity of graphene oxide can be changed from an insulating material to a more conductive graphene-like material using large furnaces. Now, the research team used TCNL to increase the temperature of reduced graphene oxide at the nanoscale, so they can draw graphene-like nanocircuits. They found that when it reached 130 degrees Celsius, the reduced graphene oxide began to become more conductive.

“So the beauty of this is that we’ve devised a simple, robust and reproducible technique that enables us to change an insulating sample into a conducting nanowire. These properties are the hallmark of a productive technology,” said Paul Sheehan, head of the Surface Nanoscience and Sensor Technology Section at the Naval Research Laboratory in Washington, D.C.

The research team tested two types of graphene oxide – one made from silicon carbide, the other with graphite powder. “I think there are three things about this study that make it stand out,” said William P. King, associate professor in the Mechanical Science and Engineering department at the University of Illinois at Urbana-Champaign. “First, is that the entire process happens in one step. You go from insulating graphene oxide to a functional electronic material by simply applying a nano-heater.  Second, we think that any type of graphene will behave this way. Third, the writing is an extremely fast technique. These nanostructures can be synthesized at such a high rate that the approach could be very useful for engineers who want to make nanocircuits.”

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A surface plasmon is a collective excitation involving all conducting electrons in a metallic layer moving relatively to the static positive ions of the metal as shown in the diagram. Research on plasmonics, a relatively new branch of optics, has received an increasing level of international attention over the last decade. This interest is mainly driven by the fact that surface plasmons, travelling along the interface between a metal and a dielectric, allow confining optical energy to volumes that are significantly smaller than those accessible with conventional dielectric waveguiding structures such as optical fibers.

Apart from being of fundamental interest on its own, tightly focused optical energy can be used as a ‘nano-probe’ which provides valuable measurements in fields like solid-state physics, chemistry and the life sciences. In addition, the tight confinement of the optical field is an interesting feature as it promises optical devices with reduced dimensions. This is of particular relevance for the field of optical communications, optical computing and hybrid microelectronic/optical circuits. However, under normal circumstances, optical energy travels over very short distances in plasmonic waveguides, before it is absorbed due to Ohmic loss in the metal.

Although clever design can somewhat increase the useful length of plasmonic waveguides, it is widely accepted that the only way to completely overcome this problem is to add a mechanism that continuously amplifies the light as it travels along the plasmonic waveguide.

However, integrating such plasmonic amplification has turned out to be a challenging task. The researchers team developed a structure that provides sufficient amplification to overcome the intrinsic absorption of a plasmonic waveguide. In fact, the optical amplification is sufficient to provide a net gain of the plasmon-bound light as it travels along the waveguide. The researchers used a structure consisting of an ultra-thin gold film that was embedded in a highly fluorescent polymer, optically pumped by an ultrafast laser source. The structure was designed to channel the light generated by the fluorescent polymer to the plasmonic waveguide. As the plasmonic wave travels along the waveguide, its intensity is increased by stimulated emission of the optical energy stored in the fluorescent polymer.

“For many years the propagation loss issue in plasmonic waveguides has been a major hurdle for the development of devices that make use of surface plasmon effects,” says Klaus Meerholz. “The key to the success of our work was that we found a way to embed the plasmonic waveguides into an amplifying fluorescent polymer without affecting the properties of the waveguide too much,” explains Malte Gather.

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