Bio-inspired way to grow graphene for electronic devices

Dr. Gao (left) and research assistant Ms Lim Xiao Fen working on the wafer-scale graphene growth and transfer in the Graphene Research Centre’s clean roomGraphene, a form of two-dimensional carbon, has many desirable properties that make it a promising material in many applications. However, its production especially for high-end electronics such as touch screens faces many challenges. This may soon change with a fresh approach developed by National Univ. of Singapore (NUS) researchers that mimics nature.

Inspired by how beetles and tree frogs keep their feet attached to submerged leaves, the findings published recently in Nature revealed a new method that allows both the growth and transfer steps of graphene on a silicon wafer. This technique enables the graphene to be applied in photonics and electronics, for devices such as optoelectronic modulators, transistors, on-chip biosensors and tunnelling barriers.

Professor Loh Kian Ping, Head of the NUS Department of Chemistry, led a team to come up with the one-step method to grow and transfer high-quality graphene on silicon and other stiff substrates. This promises the use of graphene in high-value areas where no technique currently exists to grow and transfer graphene with minimal defects for use in semiconductors.

Prof Loh, who is also a Principal Investigator with the Graphene Research Centre at NUS Faculty of Science, explained: “Although there are many potential applications for flexible graphene, it must be remembered that to date, most semiconductors operate on “stiff” substrates such as silicon and quartz.”

Thus, a transfer method with the direct growth of graphene film on silicon wafer is needed for enabling multiple optoelectronic applications, he said.

In the process called “face-to-face transfer”, Dr. Gao Libo, the first author who is with the Graphene Research Centre, grew graphene on a copper catalyst layer coating a silicon substrate. After growth, the copper is etched away while the graphene is held in place by bubbles that form capillary bridges, similar to those seen around the feet of beetles and tree frogs attached to submerged leaves. The capillary bridges help to attach the graphene to the silicon surface and prevent its delamination during the etching of the copper catalyst.

The novel technique can potentially be deployed in batch-processed semiconductor production lines, such as the fabrication of large-scale integrated circuits on silicon wafers.

The researchers will be fine-tuning the process to optimise the high throughput production of large diameter graphene on silicon, as well as target specific graphene-enabled applications on silicon. They are also looking at applying the techniques to other two-dimensional films.

Source: National Univ. of Singapore

NANOTECHNOLOGY – Energys Holy Grail Artificial Photosynthesis

 

 

 

What is Nanotechnology?
A basic definition: Nanotechnology is the engineering of functional systems at the molecular scale. This covers both current work and concepts that are more advanced.
In its original sense, ‘nanotechnology’ refers to the projected ability to construct items from the bottom up, using techniques and tools being developed today to make complete, high performance products.

Nanotechnology (sometimes shortened to “nanotech”) is the manipulation of matter on an atomic and molecular scale. The earliest, widespread description of nanotechnology referred to the particular technological goal of precisely manipulating atoms and molecules for fabrication of macroscale products, also now referred to as molecular nanotechnology. A more generalized description of nanotechnology was subsequently established by the National Nanotechnology Initiative, which defines nanotechnology as the manipulation of matter with at least one dimension sized from 1 to 100 nanometers.

This definition reflects the fact that quantum mechanical effects are important at this quantum-realm scale, and so the definition shifted from a particular technological goal to a research category inclusive of all types of research and technologies that deal with the special properties of matter that occur below the given size threshold. It is therefore common to see the plural form “nanotechnologies” as well as “nanoscale technologies” to refer to the broad range of research and applications whose common trait is size. Because of the variety of potential applications (including industrial and military), governments have invested billions of dollars in nanotechnology research. Through its National Nanotechnology Initiative, the USA has invested 3.7 billion dollars. The European Union has invested 1.2 billion and Japan 750 million dollars

Nanotechnology BBC Documentary Nano, the Next Dimension

A BBC documentary on nanotechnology advances in Europe “Nano, The Next Dimension”

 

 

 

 

A very good video to provide “perspective” on how “All Things Nano” have ALREADY impacted our lives and how … the VAST (but tiny!) arena of “Nanotechnologies” (Nano: objects a billionth of a meter in size) will certainly impact ALL of the Sciences, Manufacturing, Communications and Consumer Materials. Impacts such as:

1.  Our abilities to capture and generate abundant renewable sources of energy, (Solar, Hydrogen Fuel Cells)

2. To create abundant sources of CLEAN WATER through vastly improved FILTRATION and WASTE REMEDIATION processes. (Desalination, Oil and Gas Fields)

3. To deliver LIFE SAVING Drug Therapies and provide vastly improved Diagnostics. (Diabetes, Cancer, Alzheimer’s)

4. To create FLEXIBLE SCREENS and PRINTABLE ELECTRONICS that offer vastly improved performance, user experience, with lower energy consumption and with significantly LOWER COSTS. (Flat Panel TV Screens, Smart Phones, Super-Computers, Super-Capacitors, Long-Lived Super Batteries)

5. Completely water, stain proof clothing. Lighter, Stronger Sports Equipment.

6. Coatings and Paints for Buildings, Windows and Highways that capture solar energy. Inks and Sensors that make our everyday life more Secure.

Through the month of January, we will be posting videos, articles and research summaries that focus on the coming accelerated “wave” of nano-supported technologies “that will change the way we innovate everything!”

“Great Things from Small Things!”

 

Genesis Nanotechnology: http://genesisnanotech.com/

Twitter: https://twitter.com/GenesisNanoTech   (@Genesisnanotech)

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Quantum Dots Poised to Make IMPACT on LED Back-Lit LCD’s

What technology is in YOUR TV (Display) Screen?!

Ken Marrin, LED Magazine

Quantum dot (QD) technology has promised to enhance LED usage, making LCD TV images more vivid and improving efficacy in warm-CCT, high-CRI solid-state lighting (SSL). Thus far, however, cost, reliability, and lifetime issues have prevented broad commercial deployment. But the technology has progressed to the point that the TV application, with relatively shorter usage hours compared to general lighting, can adopt the technology.

Due to their high resolution, low cost, and thin form-factors, LED-backlit LCDs have become the standard for mobile devices and TVs, although color performance has lagged. (For more details on how LCDs and backlights work, see sidebar at end.) Displays on popular backlit LCD tablets can only express about 20% of the color a human eye can see, while LCD HDTVs can express only about 35%. To achieve more vivid, realistic color, display manufacturers have developed a variety of new technologies such as discrete RGB LED backlights, yttrium aluminum garnet (YAG) enhanced with red phosphor, and organic LEDs (OLEDs). All are beset with cost, scalability, and durability issues that have hampered widespread deployment.

FIG. 1.

One of the most promising new color enhancement technologies for backlit LCDs is QDs, a nanocrystal material that can be tuned to emit an optimized narrow spectrum of light. The unique semiconductor and optical properties of quantum dots make them attractive for a broad range of applications, from SSL, silicon photovoltaic cells, and quantum computing to cellular imaging and organic dye replacement. Due to the high production volumes and ease of integration with existing manufacturing processes, LCD suppliers seem to have taken a particular interest in QDs. By augmenting their backlight units (BLUs) with QDs, LCD manufacturers are able to create vivid displays that can exceed 55% of the spectrum a human eye can detect.

Why quantum dots?

Where vivid color and high efficiency are the objectives, the ideal white light is one that can be tuned to generate lots of visible energy narrowly focused on the primary red, green, and blue wavelengths used by the subpixel filters while producing very little light between. QDs do just that. The tiny nanocrystals, smaller than a virus, emit narrowband light when excited by a photon source.

Unlike conventional phosphor technologies like YAG, which emit with a fixed spectrum, QDs can be fabricated to convert light to nearly any color in the visible spectrum by simply varying the size of the dots. Size and bandgap energy are inversely related, so as the size of the QD decreases, emission frequencies increase, resulting in a color shift from red (low energy) to blue (high energy) in the light emitted. Lifetime fluorescence is also determined by the size of the QD, with larger dots showing a longer lifetime.

By carefully controlling the size of the crystals as they are synthesized, the spectral peak output can be set to within 2 nm of nearly any visible wavelength. Such control enables QDs to be tuned so the backlight spectrum matches the color filters, thereby facilitating displays that are brighter and more efficient, and produce truly vibrant colors.

Integrating QDs with the BLU

Quantum dot approaches are similar to phosphor technologies in the way they attempt to engineer the white light spectrum. As with YAG, a blue GaN LED provides the source light. QDs then downconvert a portion of the blue light into narrowband red and green spectrum, thereby achieving a white light that is rich in red, green, and blue and matched to the subpixel filters. QDs can be tuned (by varying the size) to emit at any wavelength longer than the source wavelength with very high efficiency (over 90% quantum yield under ideal conditions) and with very narrow spectral distribution — just 30–40 nm full width at half maximum (FWHM). This high spectral efficiency in turn reduces display power consumption by 20% compared to other high-gamut color-enhancement techniques — a key factor in meeting Energy Star requirements in TVs or extending battery life in portable devices where displays often consume 40% of the power.

As with YAG, QD backlight technology is easy to integrate with existing LCD manufacturing processes. QD upgrades require no line retooling or process changes. So manufacturers who have invested billions in LCD plants and equipment can quickly deploy QD-enhanced LCD panels that offer the color and efficiency of the best OLEDs at a fraction of the cost.

FIG. 2.

3M, for example, is now using QDs supplied by Nanosys, Inc. to offer a quantum-dot enhancement film (QDEF) a thin, optically-clear sheet with red and green dots that replaces the existing diffuser film in the reflective cavity of an LCD backlight. This packaging, explains 3M marketing development manager Art Lathrop, “not only simplifies integration and protects the dots against flux but boosts efficiency by recycling light emitted in the wrong direction.”

3M has initially focused on mobile displays where the industry has put more emphasis on premium quality and displays sell for a relatively high price per square meter. Larger displays are not only more price sensitive, Lathrop added, but also heavier users of QDs in the film implementation. When an application grows linearly (long strips of displays, for example), the QD film and the number of dots used in the film grows linearly as well, so cost is not a problem. However, when the application grows more by area than length — as in a TV display — then the number of QDs required for the film grows exponentially with display size, and the cost of QDs becomes a significant factor. Lathrop expects this issue to abate as the raw QD materials get cheaper and packaging/manufacturing (inexpensive film vs. glass, for instance) becomes the driver of overall QD cost. Until then, 3M will focus on smaller displays with lower raw material costs such as consumer mobile devices.

Drop-in QD technology

QD Vision also provides a drop-in technology called Color IQ, though instead of packaging the QDs as a film, QD Vision employs a glass tube that mounts on the edge of the display (Fig. 1). Unlike the 3M film, which scales geometrically, the rail solution scales linearly, making it more effective for larger displays. “With an edge solution like Color IQ,” said QD Vision CTO Seth Coe-Sullivan, “we utilize about one-hundredth of the QD materials relative to a film solution of the same screen area. This is why you see 3M launching in the Kindle with a screen area of one-sixtieth of a square meter, while we are in big-screen Sony TVs.”

Nanosys CEO Jason Hartlove concedes that the film solution is a heavier dot user but puts the differential at about 5x. The shorter optical path in the edge solution, he argues, requires a much higher dot density (less opportunity for recycling) and is also susceptible to aggregation and quenching, which reduces the dot’s light output and requires additional LEDs to get the same brightness.

FIG. 3.

Pacific Light Technologies got its start in nanotechnology developing QDs for the solar industry, where the dots are used to convert solar energy into a low-energy format that can be utilized more efficiently by solar panels. From there, the company branched off into SSL, using QDs to create warmer lighting solutions. More recently, the company has attracted interest from display makers. Their key differentiator, according to vice president of marketing Julian Osinski, is the ability to fabricate dots directly onto blue LEDs, eliminating the need for a separate QD subassembly (Fig. 2). “A display requiring coverage over the full surface can be on the order of 10,000x the surface area of the LED chips used to illuminate the display,” said Osinski, “and since the amount of QDs required scales with surface area, that means 10,000 times less QD material is required for on-chip use compared to off-chip.”

Pacific Light uses the same process for adding dots to LEDs that manufacturers use to add phosphor. The QDs are synthesized in a reactor vessel, separated out, mixed into a silicone, and then applied to the chip. “One nice advantage,” noted Osinski, “is that unlike phosphors, there is no settling of QD particles, resulting in more stable color points during manufacturing.” Pacific Light Technologies is currently shipping red dots, with plans for green dots in the future.

Quantum dot reliability

The useful life of the QDs is a complex issue heavily dependent on the application and the operating conditions. Fundamentally, what kills dots the fastest is oxidation. Beyond that, assuming that the dots are very well protected from oxygen, they also deteriorate from being used (like most emitters), and that deterioration accelerates with elevated heat and flux, particularly flux. Temperature at the film is about 40°C vs. 90°C at the edge, and 140°C at the LED, said Hartlove of Nanosys. Flux is 25 MW/cm at the film, 1–10W/cm at the edge, and from tens to hundreds of watts per centimeter at the LED — five orders of magnitude from the film to the LED.

3M’s testing, said Lathrop, shows that in most consumer applications QDEFs last for 20,000 to 30,000 hours of operation before luminance drops by 15%. A larger drop will start to result in a noticeable color shift (blue is not impacted). 3M’s next-generation product is targeting twice that lifetime, not because display makers are looking for 60,000+ hours but because they want to use them in hotter displays (all-in-one PCs or specialty displays, for example).

QD Vision’s edge solution, which encapsulates the dots in a glass tube, provides an excellent barrier to oxygen, as well as other advantages such as lower volume utilization, low-tech barrier materials, and excellent color uniformity (no blue light leakage). “Our edge implementation also presents unique challenges,” explained Coe-Sullivan. Color IQ sits closer to the LED backlight than a film, so the dots must withstand higher heat (100°C) and flux (100x that of a film). Nonetheless, Coe-Sullivan claims to have overcome those challenges and rates the Color IQ lifetime at between 30,000–50,000 hours, essentially the same as present-day LEDs.

FIG. 4.

Pacific Light Technologies’ approach to mounting dots directly on the LED may offer the most significant potential cost and performance advantages of all (Fig. 3) but also the greatest challenges with regard to reliability. In addition to higher temperatures, flux in particular can be 50x that of an edge solution. “In general,” noted Osinski, “white-light LED lifetimes are limited by the silicon-phosphor combination on the chip more than the chip itself, and that remains the same with QDs, where silicone yellowing also contributes to aging blue LEDs.” Reliabilities are still being established because they require very long test times, but Pacific Light claims to have already demonstrated operation over thousands of hours.

OLED

One of the chief competitive technologies to QDs where color quality is of primary importance is OLED, which emits light directly and requires no backlight or LCD filter. In addition to excellent color gamut comparable to QDs, OLED displays feature faster response times and refresh rates, improved brightness, a greater contrast ratio (both dynamic range and static, measured in purely dark conditions), a wider viewing angle than LCD implementations (with or without QD augmentation), and the ability to display true blacks.

Perhaps the biggest technical problem for OLEDs is the limited lifetime of the organic materials, primarily for the blue OLEDs. Blue OLEDs historically have had a lifetime of around 14,000 hours to half original brightness (five years at 8 hours a day) when used for flat-panel displays. Red and green OLEDs offer 2–3x that lifetime. The faster degradation of blue OLEDs relative to red and green creates color balance challenges, requiring either additional control circuitry, or optimization of the red, green, and blue subpixel sizes in order to equalize color balance at full luminance over the lifetime of the display. A blue subpixel, for example, may need to be 100% larger than the green subpixel, whereas the red subpixel may need to be 10% smaller than the green.

High cost has also hampered the widespread use of OLEDs in larger mass-market displays. Eliminating the backlight and LCD filter provides significant cost savings and allows for a thinner display, but the fabrication of the OLED substrate is presently more costly than that of a thin-film transistor LCD. Down the road, the ability to fabricate OLEDs on flexible plastic substrates and the utilization of processes like roll-to-roll vapor-deposition and transfer printing will offer potential cost advantages. For now, though, large-screen applications require low-temperature polysilicon backplanes that cannot currently be used on large-area glass substrates. As a result, large OLED displays are limited to relatively high-end applications, with OLED TVs from LG and Samsung selling in the $10,000 range. On the other hand, Sony uses QD Vision’s technology, branding it Triluminos, in its 4000-pixel Ultra HD LCD TVs that start at about $3500 (Fig. 4). But Sony has also included Triluminos technology in some higher-end standard HDTV sets such as a 55-in. model that sells for around $2000.

Electroluminescent QDs

Even as OLED strives for economies of scale and process improvements that will bring costs down, QD makers like QD Vision are already working on the next generation of technology — electroluminescent QDs that will combine the customizable, saturated, stable color and low-voltage performance of inorganic LEDs with the solution processability of polymers. The new technology, Coe-Sullivan explains, will provide a reliable, energy-efficient, highly tunable color solution for displays and lighting that is less costly to manufacture and that can employ ultrathin, transparent, or flexible substrates.

Quantum-dot light-emitting diodes (QLEDs) are electroluminescent colloidal quantum dots that generate light when excited electrically. Like OLEDs, QLEDs require no backlight or LCD filter. QD Vision claims that its printable thin-film QLEDs match or exceed NSTC color standards for displays without the need for color filters. The excellent color performance of QLEDs ultimately translates into a 30–40% luminance efficiency advantage over OLEDs (at the same color point), which require lossy color filtering to achieve a similar color performance. QLEDs also feature a lower operating voltage, exhibiting turn-on voltages at the bandgap voltage of the material. This gives QLEDs the potential to be more than twice as power efficient as OLEDs at the same color purity.

To reduce cost for QLED-based, full-color, active-matrix displays and lighting devices, QD Vision is developing large-area quantum-dot printing techniques that utilize ultrathin flexible substrates. Today’s LCDs and LED chips are fabricated on glass and crystalline substrates, making them inherently expensive and fragile for mobile and large-area applications. QLEDs, by contrast, are only a couple hundred nanometers thick, making them virtually transparent and flexible, and highly suitable for integration onto plastic or metal foil substrates as well as other surfaces.

QLEDs are still in the early development stages, yielding only 10,000 hours at low brightness, but in theory are a more stable light-emitting material than organic dyes. Meanwhile, the company is already offering high-quality electroluminescent-grade QD materials suitable for certain products that require precise color solutions in an ultraslim form factor. Among these are monochrome visible and infrared displays, and lighting devices for machine and night vision applications.

Nanosys’ Hartlove agreed that the QLEDs are the way of the future. “When emissive pixels will overtake LCDs we cannot say. LCDs get better every day.” Within ten years, however, he expects the manufacturing and production advantages of QLEDs (solution chemistry and roll-printed emitters) to overtake GaN substrates and wafer-based processing — and not just for displays but also general lighting. Right now, the focus is on the ability of QDs to outperform phosphors in the color arena, but eventually the properties of the raw materials will fade in significance, and it will come down to manufacturing, where the ability to print narrowband emissive pixels on thin films in high volume will produce high-quality color inexpensively — without the need for color management.

++++

Backlight enhancement

Liquid-crystal displays (LCDs) combine a light source (the backlight unit, or BLU) with a liquid-crystal module (LCM). The BLU provides a uniform white sheet of light behind the LCM. The LCM contains millions of pixels, each of which is split into red, green, and blue subpixels. By controlling the amount of time each subpixel filter is open (allowing light to pass through it) and making use of the human eye’s persistence of vision, the LCD can display any color that can be rendered from a combination of red, green, and blue at each pixel location. The color filter on each subpixel separates its component color from the white light of the BLU. For example, the red color filter on the red subpixels blocks the green and blue light.

The fidelity of each color is a function of the quality of light in the BLU and the color filters. The narrower the filters, the narrower the backlight color spectrum (for the desired peak red, blue, and green colors), and the closer the color spectrum is matched to the filters, the higher the color quality. Because making perfect color filters is impractical from a cost and brightness perspective (narrow filters attenuate out-of-band photons and reduce brightness), display makers have instead focused their efforts on improving the BLU.

The problem with standard BLUs is that the LEDs used to create the backlight produce a broad spectrum of light that cannot be used efficiently by the LCD. Most white LEDs are created by coating blue LEDs made of indium gallium nitride (InGaN) with an yttrium aluminum garnet (YAG) phosphor. These two-color YAG white LEDs produce a spectrum rich in blue wavelengths with a broad yellow component, but the greens vary from cyan through lime, and the reds vary from orange to deep red. Because the filters can’t stop these in-between colors, the result is poor color saturation.

Red-emitting phosphor can be added to boost color performance, but red phosphors suffer from poor conversion efficiency, wasting much of their power-generating spectrum like infrared that is not visible to the human eye. Like the yellow phosphors, red phosphors have a relatively wide full width at half maximum (FWHM) — a characterization of the width of the spectrum at which emitted radiometric power has dropped by half — so they cannot be precisely tuned to match either existing color filters or the manufacturers’ peak color specifications. So the resulting white light, while offering a richer spectrum, still incurs substantial light and efficiency losses

Atoms in a nanocrystal cooperate, much like in biomolecules

Nanocrystals of cadmium selenide, known for their brilliant luminescence, display intriguing chemical behavior resulting from positive cooperation between atoms, a behavior akin to that found in biomolecules. Credit: Prashant Jain        

(Phys.org) —Researchers have long thought that biological molecules and synthetic nanocrystals were similar only in size. Now, University of Illinois at Urbana-Champaign chemists have found that they can add reactivity to the list of shared traits. Atoms in a nanocrystal can cooperate with each other to facilitate binding or switching, a phenomenon widely found in biological molecules.

The finding could catalyze manufacturing of nanocrystals for smart sensors, solar cells, tiny transistors for optical computers, and medical imaging. Led by chemistry professor Prashant Jain, the team published its findings in the journal Nature Communications.

“In geological, industrial and domestic environments, the nanoscale grains of any material undergo chemical transitions when they are put under reactive conditions,” Jain said. “Iron rusting over time and diamond forming from carbon are examples of two commonly occurring transitions. Understanding how these transitions occur on the scale of the tiniest grains of the material is a major motivation of our work.”

Scientists can exploit such transitions to make nanocrystals that conform to a particular structure. They can make a nanocrystal of one material and transform it into another material, essentially using the original nanocrystal framework as a template for creating a nanocrystal of the new material with the same size and shape. This lets researchers create nanocrystals of new materials in shapes and structures they may not be able to otherwise.

In the new study, the researchers transformed tiny crystals of the material cadmium selenide to crystals of copper selenide. Copper selenide nanocrystals have a number of interesting properties that can be used for solar energy harvesting, optical computing and laser surgery. Transformation from cadmium selenide creates nanocrystals with a purity difficult to attain from other methods.

The researchers, including graduate student Sarah White, used advanced microscopy and spectroscopy techniques to determine the dynamics of the atoms within the crystals during the transformation and found that the transformation occurs not as a slow diffusion process, but as a rapid switching thanks to co-operativity.

The researchers saw that once the cadmium-selenide nanocrystal has taken up a few initial copper “seed” impurities, atoms in the rest of the lattice can cooperate to rapidly swap out the rest of the cadmium for copper. Jain compares the crystals to hemoglobin, the molecule in red blood cells that carries oxygen. Once one oxygen molecule has bound to hemoglobin, other binding sites within hemoglobin slightly change conformation to more easily pick up more oxygen. He posits that similarly, copper impurities might cause a structural change in the nanocrystal, making it easier for more copper ions to infiltrate the nanocrystal in a rapid cascade.

The researchers reproduced the experiment with silver, in addition to copper, and saw similar, though slightly less speedy, cooperative behavior.

Now, Jain’s team is using its advanced imaging to watch transitions happen in single nanocrystals, in real time.

“We have a sophisticated optical microscope in our lab, which has now allowed us to catch a single nanocrystal in the act of making a transition,” Jain said. “This is allowing us to learn hidden details about how the transition actually proceeds. We are also learning how one nanocrystal behaves differently from another.”

Next, the researchers plan to explore biomolecule-like cooperative phenomena in other solid-state materials and processes. For example, co-operativity in catalytic processes could have major implications for solar energy or manufacturing of expensive specialty chemicals.

“In the long term, we are interested in exploiting the co-operative behavior to design artificial smart materials that respond in a switch-like manner like hemoglobin in our body does,” Jain said.

Explore further:     Researchers extend galvanic replacement reactions to metal oxide nanocrystals

More information: “Co-operativity in a nanocrystalline solid-state transition.” Sarah L. White, Jeremy G. Smith, Mayank Behl, Prashant K. Jain. Nature Communications 4, Article number: 2933 DOI: 10.1038/ncomms3933

Read more at: http://phys.org/news/2013-12-atoms-nanocrystal-cooperate-biomolecules.html#jCp

Read more at: http://phys.org/news/2013-12-atoms-nanocrystal-cooperate-biomolecules.html#jCp

Roots of the Lithium Battery Problem: Berkeley Lab Researchers Find Dendrites Start Below the Surface

The lithium-ion batteries that power our laptops, smartphones and electric vehicles could have significantly higher energy density if their graphite anodes were to be replaced by lithium metal anodes. Hampering this change, however, has been the so-called dendrite problem. Over the course of several battery charge/discharge cycles, particularly when the battery is cycled at a fast rate, microscopic fibers of lithium, called “dendrites,” sprout from the surface of the lithium electrode and spread like kudzu across the electrolyte until they reach the other electrode. An electrical current passing through these dendrites can short-circuit the battery, causing it to rapidly overheat and in some instances catch fire. Efforts to solve the problem by curtailing dendrite growth have met with limited success, perhaps because they’ve just been scratching the surface of the problem.

These 3D reconstructions show how dendritic structures that can short-circuit a battery form deep within a lithium electrode, break through the surface and spread across the electrolyte.

Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have discovered that during the early stages of development, the bulk of dendrite material lies below the surface of the lithium electrode, underneath the electrode/electrolyte interface. Using X-ray microtomography at Berkeley Lab’s Advanced Light Source (ALS), a team led by Nitash Balsara, a faculty scientist with Berkeley Lab’s Materials Sciences Division, observed the seeds of dendrites forming in lithium anodes and growing out into a polymer electrolyte during cycling. It was not until the advanced stages of development that the bulk of dendrite material was in the electrolyte. Balsara and his colleagues suspect that non-conductive contaminants in the lithium anode trigger dendrite nucleation.

Nitash Balsara and Katherine Harry at ALS beamline 8.3.2 where they shed important new light on the dendrite problem in lithium batteries. (Photo by Roy Kaltschmidt)

“Contrary to conventional wisdom, it seems that preventing dendrite formation in polymer electrolytes depends on inhibiting the formation of subsurface dendritic structures in the lithium electrode,” Balsara says. “In showing that dendrites are not simple protrusions emanating from the lithium electrode surface and that subsurface non-conductive contaminants might be the source of dendritic structures, our results provide a clear prescription for the path forward to enabling the widespread use of lithium anodes.”

Balsara, who is a professor of chemical engineering at the University of California (UC) Berkeley, is the corresponding author of a paper describing this research in Nature Materials titled “Detection of subsurface structures underneath dendrites formed on cycled lithium metal electrodes.” Co-authors are Katherine Harry, Daniel Hallinan, Dilworth Parkinson and, Alastair MacDowell.

The tremendous capacity of lithium and the metal’s remarkable ability to move lithium ions and electrodes in and out of an electrode as it cycles through charge/discharge make it an ideal anode material. Until now, researchers have studied the dendrite problem using various forms of electron microscopy. This is the first study to employ microtomography using monochromatic beams of high energy or “hard” X-rays, ranging from 22 to 25 keV, at  ALS beamline 8.3.2. This technique allows non-destructive three-dimensional imaging of solid objects at a resolution of approximately one micron.

“We observed crystalline contaminants in the lithium anode that appeared at the base of every dendrite as a bright speck,” says Katherine Harry, a member of Balsara’s research group and the lead author of the Nature Materials paper. “The lithium foils we used in this study contained a number of elements other than lithium with the most abundant being nitrogen. We can’t say definitively that these contaminants are responsible for dendrite nucleation but we plan to address this issue by conducting in situ X-ray microtomography.”

Balsara and his group also plan further study of the role played by the electrolyte in dendrite growth, and they have begun to investigate ways to eliminate non-conductive impurities from lithium anodes.

This research was funded by the DOE Office of Science.

Theorists predict new state of quantum matter may have big impact on electronics

(Nanowerk News) Constantly losing energy is something we deal with in everything we do. If you stop pedaling a bike, it gradually slows; if you let off the gas, your car also slows. As these vehicles move, they also generate heat from friction. Electronics encounter a similar effect as groups of electrons carry information from one point to another. As electrons move, they dissipate heat, reducing the distance a signal can travel. DARPA-sponsored researchers under the Mesodynamic Architectures (Meso) program, however, may have found a potential way around this fundamental problem.

Meso program researchers at Stanford University recently predicted stanene will support lossless conduction at room temperature. Stanene is the name given by the researchers to 2-D sheets of tin that are only 1-atom thick. In a paper appearing in Physical Review Letters (“Large-Gap Quantum Spin Hall Insulators in Tin Films”) the team predicts stanene would be the first topological insulator to demonstrate zero heat dissipation properties at room temperature, conducting charges around its edges without any loss. Experiments are underway to create the material in laboratory conditions. If successful, the team will use stanene to enhance devices they are building under the Meso program.

This image depicts the flow of electricity along the outside edges of a new topological insulator, stanene. Theorists in DARPA’s Mesodynamic Architectures (Meso) program predict stanene would have perfect energy propagation properties at room temperature. (Image: SLAC National Accelerator Laboratory)

“We recently realized there is another state of electronic matter: a topological insulator. Materials in a topologically insulating state are like paying for the gasoline to accelerate your car to highway speeds, but then cruising as far as you want on that highway without using up any more gas,” said Jeffrey Rogers, DARPA program manager. “Experiments should tell us what penalty electrons would pay for connecting to stanene in a practical application. However, the physics of stanene point to zero dissipation of heat—meaning electrons take an entropy hit once and then travel unimpeded the rest of the distance.”

Researchers at Stanford reported the first topological insulators in 2006 under a previous DARPA effort known as the Focus Center Research Program. The current Meso program developed the theory for stanene as part of research into more efficient ways to move information inside microchips. Other materials’ capabilities have come close, but only at temperatures that require extreme sub-zero temperatures created with bulky methods such as liquid helium.

“Stanene is a bold, yet compelling prediction,” said Rogers. “If the experiments underway confirm the theory, the application of a new lossless conductor becomes a very exciting prospect in the world of electronics. A host of applications—almost any time information is moved electronically from one place to another—could benefit.”

Source: DARPA

Read more: http://www.nanowerk.com/nanotechnology_news/newsid=33742.php#ixzz2nlj7rvXP

Nanomanufacturing: path to implementing nanotechnology

(Nanowerk News) If the promise of nanotechnology is to be fulfilled, then research programs must leapfrog to new nanomanufacturing processes. That’s the conclusion of a review of the current state of nanoscience and nanotechnology to be published in the International Journal of Nanomanufacturing (“Nanomanufacturing: path to implementing nanotechnology”).

Khershed Cooper of the Materials Science and Technology Division, at the Naval Research Laboratory, in Washington, DC and Ralph Wachter of the Division of Computer and Network Systems, at the National Science Foundation, in Arlington, Virginia, USA, explain how research in nanoscience and the emerging applications in nanotechnology have led to new understanding of the properties of matter as well producing many novel materials, structures and devices.

Indeed, the list of possible applications of nanotechnology continues to grow: water filtration and purification, engineered composite materials with modified mechanical properties controlled electrical behaviour and corrosion resistance. There are nano-based materials being used as sealants, anti-fogging and abrasion resistant coatings for glass and other materials, conductive resins, paints and electromagnetic shielding as well as sensors, self-healing materials, super-hydrophobic surfaces, solar cells and ultracapacitors for energy storage as well as materials for armour and protection against bullets and bombs.

The team’s own research has focused on developing tools and techniques to make scalable processes for nanomanufacturing. They are investigating massively parallel techniques, masks and maskless processes for making 3D structures with nanoscopic features. However, they also suggest that several obstacles must be surmounted for nanotechnology to thrive as a future industrial endeavour. In particular, the team believes that research and development should be directed in the following areas:

– Multi-scale design, modelling and simulation of nanosystems. – Component integration within large-scale systems. – Integration across physical scales. – Qualification, certification, verification and validation. – Cyber-enabled manufacturing systems.

“Looking ahead, nanotechnology is slated to move into complex, multi-functional, multi-component nanosystems, e.g., nano-machines and nano-robots,” the team concludes. “These nanosystems will be adaptive, responsive to external stimuli, biomimetic, intelligent, smart and autonomous. Nanomanufacturing R&D will be needed to develop the knowledge base for the reliable production of these complex nanosystems.”

Source: Inderscience

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New unique nanostructure to target drug-delivery treatment of cancer cells

A unique nanostructure developed by a team of international researchers, including those at the University of Cincinnati, promises improved all-in-one detection, diagnoses and drug-delivery treatment of cancer cells.

 

The first-of-its-kind nanostructure is unusual because it can carry a variety of cancer-fighting materials on its double-sided (Janus) surface and within its porous interior. Because of its unique structure, the nano carrier can do all of the following:

• Transport cancer-specific detection nanoparticles and biomarkers to a site within the body, e.g., the breast or the prostate. This promises earlier diagnosis than is possible with today’s tools.
• Attach fluorescent marker materials to illuminate specific cancer cells, so that they are easier to locate and find for treatment, whether drug delivery or surgery.
• Deliver anti-cancer drugs for pinpoint targeted treatment of cancer cells, which should result in few drug side effects. Currently, a cancer treatment like chemotherapy affects not only cancer cells but healthy cells as well, leading to serious and often debilitating side effects.

This research, titled “Dual Surface Functionalized Janus Nanocomposites of Polystyrene//Fe304@Si02 for Simultaneous Tumor Cell Targeting and pH-Triggered Drug Release,” will be presented as an invited talk on Oct. 30, 2013, at the annual Materials Science & Technology Conference in Montreal, Canada. Researchers are Feng Wang, a former UC doctoral student and now a postdoc at the University of Houston; Donglu Shi, professor of materials science and engineering at UC’s College of Engineering and Applied Science (CEAS); Yilong Wang of Tongji University, Shanghai, China; Giovanni Pauletti, UC associate professor of pharmacy; Juntao Wang of Tongji University, China; Jiaming Zhang of Stanford University; and Rodney Ewing of Stanford University.

This recently developed Janus nanostructure is unusual in that, normally, these super-small structures (that are much smaller than a single cell) have limited surface. This makes is difficult to carry multiple components, e.g., both cancer detection and drug-delivery materials. The Janus nanocomponent, on the other hand, has functionally and chemically distinct surfaces to allow it to carry multiple components in a single assembly and function in an intelligent manner.

“In this effort, we’re using existing basic nano systems, such as carbon nanotubes, graphene, iron oxides, silica, quantum dots and polymeric nano materials in order to create an all-in-one, multidimensional and stable nano carrier that will provide imaging, cell targeting, drug storage and intelligent, controlled drug release,” said UC’s Shi, adding that the nano carrier’s promise is currently greatest for cancers that are close to the body’s surface, such as breast and prostate cancer.

If such nano technology can someday become the norm for cancer detection, it promises earlier, faster and more accurate diagnosis at lower cost than today’s technology. (Currently, the most common methods used in cancer diagnosis are magnetic resonance imaging or MRI; Positron Emission Tomography or PET; and Computed Tomography or CT imaging, however, they are costly and time consuming to use.)

In addition, when it comes to drug delivery, nano technology like this Janus structure, would better control the drug dose, since that dose would be targeted to cancer cells. In this way, anticancer drugs could be used much more efficiently, which would, in turn, lower the total amount of drug administered.

Source: University of Cincinnati

MIT researchers discover platform that manipulates organic molecules’ emission

Enhancing and manipulating the light emission of organic molecules is at heart of many important technological and scientific advances, including in the fields of organic light emitting devices, bio-imaging, bio-molecular detection. Researchers at MIT have now discovered a new platform that enables dramatic manipulation of the emission of organic molecules when simply suspended on top of a carefully designed planar slab with a periodic array of holes: so-called photonic crystal surface.

 

Influenced by the fast and directional emission channels (called ‘resonances’) provided by the photonic crystal surface, molecules in the solution that are suspended on top of the surface no longer behave in their usual fashion: instead of sending light isotropically into all directions, they rather send light into specific directions.

The researchers say that this platform could also be applied to enhance other type of interactions of light with matter, such as Raman scattering. Furthermore, this process applies to any other nano-emitters as well, such as quantum dots.

Physics Professors Marin Soljacic and John Joannopoulos, Associate Professor of Applied Mathematics Steven Johnson, Research scientist Dr. Ofer Shapira, Postdocs Dr. Alejandro Rodriguez, Dr. Xiangdong Liang, and graduate students Bo Zhen, Song-Liang Chua, Jeongwon Lee report this discovery as featured in Proceedings of the National Academy of Sciences.

“Most fluorescing molecules are like faint light bulbs uniformly emitting light into all directions,” says Soljacic. Researchers have often sought to enhance this emission by incorporating organic emitters into sub-wavelength structured cavities that are usually made out of inorganic materials. However, the challenge lies in an inherent incompatibility in the fabrication of cavities for such hybrid systems.

Zhen et al present a simple and direct methodology to incorporate the organic emitters into their structures. By introducing a microfluidic channel on top of the photonic crystal surface, organic molecules in solution are delivered to the active region where interaction with light is enhanced. Each molecule then absorbs and emits significantly more energy with an emission pattern that can be designed to be highly directional. “Now we can turn molecules from being simple light bulbs to powerful flashlights that are thousands of times stronger and can all be aligned towards the same direction,” says Shapira, the senior author of the paper.

This discovery lends itself to a number of practical applications. “During normal blood tests, for example,” adds Shapira, “cells and proteins are labeled with antibodies and fluorescing molecules that allow their recognition and detection. Their detection limit could be significantly improved using such a system due to the enhanced directional emission from the molecules.”

The researchers also demonstrated that the directional emission can be turned into organic lasers with low input powers. “This lasing demonstration truly highlights the novelty of this system,” says the first author Zhen. For almost any lasing system to work there is a barrier on the input power level, named the lasing threshold, below which lasing will not happen. Naturally, the lower the threshold, the less power it takes to turn on this laser. Exploring the enhancement mechanisms present in the current platform, lasing was observed with a substantially lower barrier than before: the measured threshold in this new system is at least an order of magnitude lower than any previously reported results using the same molecules.

Source: Massachusetts Institute of Technology, Institute for Soldier Nanotechnologies