12 Sep 2014
It may seem paradoxical that a rare precious metal such as platinum is used in something as simple as smoky truck exhaust systems—nonetheless, this has always been a fundamental technological principle.
When it comes to diesel engine catalysts—i.e. the element responsible for cleansing exhaust fumes particles—platinum has unfortunately proved to be the only viable option, which has resulted in material costs alone accounting for half of the price of a diesel catalyst.
Such dependency on precious metals is both costly and unsustainable, which is why InnovationsFonden invested an impressive DKK 15 million—half of the total budget—in a project to find new catalyst materials based on nanotechnology.
The collaborative project involves Aarhus University, Danish Technological Institute, Dinex A/S tasked with production—and finally DTU, where will bring more than 25 years’ experience in experimental surface physics, nanotechnology and catalysis to bear.
“I have devoted myself exclusively to catalysts and surface physics since 1987. I am therefore excited by the prospect of my research finding a specific technological application,” says Ib Chorkendorff, who usually works with catalysts and nanomaterials at basic research level.
In essence, Aarhus University has developed a new way to manufacture catalysts and is now assessing the further development options that are opening up.
“Our idea is to try and make better catalysts for diesel engines than those currently available, and in particular, to find a viable alternative to platinum, which is, of course, a very expensive raw material,” says Ib Chorkendorff.
“We are focusing on nanoparticles because we want to maximize the surface area, but objects don’t like surfaces—two drops of water merge into one large drop to reduce surface energy, for example. The art is to create small reactive nanoparticles and keep them apart so they don’t merge together. The greater the surface area, the less material you require,” explains Ib Chorkendorff.
Each time you optimize the platinum surface, you save material and thus achieve greater effect at less cost.
Dinex A/S, the company looking to transform the research behind the new technology into new catalysts for the global market, has found it invaluable working with someone of Chorkendorff’s calibre:
“We believe that collaboration between the business sector and the research community is a win-win situation. Such partnerships hold huge untapped potential,” says Lars Christian Larsen, R & D Director, Dinex.
With the assistance of Ib Chorkendorff and the rest of the team, he hopes to achieve a 25% platinum reduction, which will rank Dinex among global leaders in catalyst production.
The project will be launched in the autumn, and in addition to Ib Chorkendorffs 25 years of experience and insight, DTU’s contribution will include a PhD student or a postdoc.
Article from DTUavisen No. 7, September 2014.
Source: Technical University of Denmark
Cadmium telluride nanocrystal colloids could be used as the photovoltaic “ink” in solar cells, according to new experiments by researchers at the National Renewable Energy Laboratory and the University of Chicago. Devices made using CdTe layers as thin as just 330 nm have a sunlight-to-power conversion of efficiency of 10% while those made with 550 nm thick layers have an efficiency of more than 11%. They also boast an impressive blue light response of nearly 80% external quantum efficiency – something that allows for improved photocurrent from these cells.
Thin-film photovoltaic materials could be alternatives to traditional silicon-based solar-cell materials because they absorb sunlight more efficiently – thanks to the fact that they have direct rather than indirect bandgaps. This means that less material, weight for weight, is needed to absorb the same amount of solar radiation. What is more, thin-film photovoltaics, such as cadmium telluride, can be easily and cheaply deposited onto a wide range of flexible and rigid substrates in solution.
There is a problem, however, in that the power-conversion efficiencies of thin-film materials that have been processed from solution are typically lower than those produced by traditional vapour deposition techniques.
Now, a team led by Dmitri Talapin of Chicago and Joseph Luther at NREL has succeeded in synthesizing CdTe inks from solutions of nanocrystals that have controllable shapes, ranging from spheres to tetrapods, and controllable crystallographic phases: wurtzite and zincblende. The researchers found that the best performing solar-cell devices are those containing tetrapodal-shaped nanocrystals in the wurtzite phase. Following a relatively low-temperature short anneal, these crystals undergo a critical phase change from wurtzite to zincblende that coincides with the small grain soluble nanocrystals growing into large grain, photovoltaic quality, CdTe.
“Rather than depositing the whole CdTe layer at once, we use a layer-by-layer approach to build up a very thin layer of the CdTe and control the grain growth,” explains team member Ryan Crisp, graduate student at the Colorado School of Mines. “We then deposit more nanocrystals and repeat the process until we reach the desired layer thickness.”
As the nanocrystals change phase and sinter (or grow) together, they form polycrystalline films, he adds. These films are unique in that they are exceptionally smooth and uniform (compared with films that are produced by traditional sublimation methods). “This means that further layers have a ‘nice’ surface on which we can deposit without fear of encountering short-circuits caused by irregularities and defects,” he tells nanotechweb.org.
“The crystal grains in our material extend from the top to the bottom in a finished device, allowing us to efficiently extract charge carriers (in this case photoexcited electrons) from it. We are able to do this since the electrons do not encounter many grain boundaries – something that minimizes their chance of being ‘lost’ to defect traps as they travel through the structure.”
Higher-efficiency, lower-cost devices
Solar cells made from the CdTe ink boast a sunlight-to-power conversion efficiency of 10–12%. This value might be further improved by placing the ink on the right type of substrate. “By employing this inexpensive solution-processed ink (instead of the more expensive, and slower throughput thin-film photovoltaic materials produced by sublimation), we can make potentially higher-efficiency, lower-cost devices,” says Crisp. “We explored several device structures and found that the ink-based films perform better in a simple ITO/CdTe/ZnO/Al structure rather than the traditional structure with CdS and ZnTe contacts.”
The main limiting factor to improving device efficiency is increasing the open circuit voltage. “We now plan on improving the quality of the ITO/CdTe interface (used in our highest efficiency device) to do this – and in particular by better controlling the energy levels (that is the band alignment) of the materials at this interface,” adds Crisp.
The new photovoltaic ink is described in ACS Nano
12 Sep 2014
The sharp X-ray vision of DESY’s research light source PETRA III paves the way for a new technique to produce cheap, flexible and versatile double solar cells. The method developed by scientists from the Technical University of Denmark (DTU) in Roskilde can reliably produce efficient tandem plastic solar cells of many metres in length, as a team around senior researcher Jens W. Andreasen reports in the journal Advanced Energy Materials (“Enabling Flexible Polymer Tandem Solar Cells by 3D Ptychographic Imaging”).
The scientists used a production process, where the different layers of a polymer (plastic) solar cell are coated from various solutions onto a flexible substrate. This way, the solar cell can be produced fast and cheap in a roll-to-roll process and in almost any desired length – up to several kilometers long single solar cell modules have already been manufactured. However, the energy harvesting efficiency of this type of solar cell is not very high. To increase the efficiency, a DTU team around Frederik C. Krebs stacked two such solar cells onto each other. Each of these absorbs a different part of the solar spectrum, so that the resulting tandem polymer solar cell converts more of the incoming sunlight into electric energy. But the multilayer coating presents several new challenges, as Andreasen explained: “Lab studies have shown that already coated layers may be dissolved by the solvent from the following layer, causing complete failure of the solar cell.”
Ptychographic phase contrast projection of the polymer tandem solar cell stack (two by four microns in size), showing the silver electrode (lower green band) with a polymer layer on top, the upper electrode (upper green band, with red) and the zinc oxide layer (narrow dark blue band) between the two solar cells. The green triangel on top of the sample is the cut-off of a wolfram pin used to manipulate the sample under a scanning electron microscope. (Image: Jens Wenzel Andreasen/DTU)
To prevent redissolution of the first solar cell, the scientists added a carefully composed protective intermediate coating between the two solar cells. The protective coating contains a layer made of zinc oxide (ZnO) that is just 40 nanometres thick – about a thousand times thinner than a human hair. To check shape and function of the protective coating and the other layers of the tandem solar cell, the scientists used the exceptionally sharp X-ray vision of DESY’s research light source PETRA III that can reveal finest details. “The solar cell structure is very delicate, consisting of twelve individual layers altogether.
Imaging the complete structure is challenging,” explained co-author Juliane Reinhardt from DESY’s experimental station P06 where the investigations were made. “And the sample was just two by four microns in size.” Still, with the brilliant X-ray beam from PETRA III, the researchers could peer into the layer structure in fine detail, using a technique called 3D ptychography. This method reconstructs the three-dimensional shape and chemistry of a sample from the way it diffracts the incoming X-rays. For a full 3D reconstruction a great number of overlapping X-ray diffraction images have to be recorded from all sides and angles. The advantage of ptychography is that it yields a higher resolution than would be possible with conventional X-ray imaging alone. And in contrast to electron microscopy, X-ray ptychography can also look deep inside the sample.
“With 3D ptychography, we were able to image the complete roll-to-roll coated tandem solar cell, showing, among other things, the integrity of the 40 nanometres thin zinc oxide layer in the protective coating that successfully preserved underlying layers from solution damage,” said DESY scientist Gerald Falkenberg, head of the experimental station P06. “These are the 3D ptychography measurements with the highest spatial resolution we have achieved so far. The results show that with the correct formulation of the intermediate layer, the underlying solar cell is protected from redissolution.”
The investigation paves the way to a possible industrial application of the new technique. “In a complex multilayer device like a polymer tandem solar cell, the device may fail in multiple ways,” Andreasen pointed out.
“What we were able to see with 3D ptychography was that the preparation of the substrate electrode combines the good conductivity of a coarsely structured silver electrode with the good film forming ability of a conducting polymer that infiltrates the silver electrode and forms a smooth surface for the coating of the subsequent layers.” This is what allows the coating of very thin layers, at very high speeds, still forming contiguous layers, without pinholes.
|Looking into the complete structure can also provide valuable information for a possible optimization of the device and the production process. “In principle we make the devices without knowing what the internal structure looks like in detail. But knowing the structure tells us which parameters we can modify, and which factors are important for the device architecture, for example the special type of substrate electrode, and the formulation of the intermediate layer,” Andreasen explained.
“We were now able to verify that we can coat contiguous, homogeneous layers, roll-to-roll from solution, at speeds up to several meters per minute. We have shown that roll-to-roll processing of tandem solar cells is possible, with all of the layers roll-coated from solution, and that it is only possible using a specific formulation of the intermediate layer between the two sub-cells.”
|The resulting polymer tandem solar cell converts 2.67 per cent of the incoming sunlight into electric energy, which is way below the efficiency of conventional solar cells. “The efficiency is low, compared to conventional solar cells, by a factor of 7 to 8, but one should consider that the production cost of this type of solar cell is several orders of magnitude lower than for conventional solar cells. This is the particular advantage of polymer solar cells,” explained Andreasen. “Furthermore, this is the first example of a roll-to-roll coated tandem solar cell where the efficiency of the tandem device actually exceeds that of the individual sub-cell devices by themselves.”|
Genesis Nanotech ‘News and Updates’ – September 9, 2014
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Genesis Nanotechnology – “Great Things from Small Things!”
Why It Matters –
” … I would say the two most interesting areas in the last year or two have been in 3-D printing and nanotechnology. 3-D printing is an additive technology in which one is able to make a three-dimensional product, such as a screw, by adding material rather than using a traditional reduction process, like a CNC (milling) process or a grinding-away process.
The other interesting area has been nanotechnology. Nanotechnology is the science of materials and structures that have a dimension in the nanometer range (1-1,000 nm) – that is, on the atomic or molecular scale. A fascinating aspect of nanomaterials is that they can have vastly different material properties (e.g., chemical, electrical, mechanical properties) than their larger-scale counterparts. As a result, these materials can be used in applications where their larger-scale counterparts have traditionally not been utilized.”
Editor: Deborah, please tell us about the specific practice areas of intellectual property in which you participate.
Vernon: My practice has been directed to helping clients assess, build, maintain and enforce their intellectual property, especially in the technology areas of material science, analytical chemistry and mechanical engineering. Prior to entering the practice of law, I studied mechanical engineering as an undergraduate and I obtained a PhD in material science engineering, where I focused on creating composite materials with improved mechanical properties.
Editor: Please describe some of the new areas of biological and chemical research into which your practice takes you, such as nanotechnology, three-dimensional printing technology, and other areas.
Vernon: I would say the two most interesting areas in the last year or two have been in 3-D printing and nanotechnology. 3-D printing is an additive technology in which one is able to make a three-dimensional product, such as a screw, by adding material rather than using a traditional reduction process, like a CNC (milling) process or a grinding-away process. The other interesting area has been nanotechnology. Nanotechnology is the science of materials and structures that have a dimension in the nanometer range (1-1,000 nm) – that is, on the atomic or molecular scale.
A fascinating aspect of nanomaterials is that they can have vastly different material properties (e.g., chemical, electrical, mechanical properties) than their larger-scale counterparts. As a result, these materials can be used in applications where their larger-scale counterparts have traditionally not been utilized.
I was fortunate to work in the nanotech field in graduate school. During this time, I investigated and developed methods for forming ceramic composites, which maintain a nanoscale grain size even after sintering. Sintering is the process used to form fully dense ceramic materials. The problem with sintering is that it adds energy to a system, resulting in grain growth of the ceramic materials. In order to maintain the advantageous properties of the nanosized grains, I worked on methods that pinned the ceramic grain boundaries to reduce growth during sintering.
The methods I developed not only involved handling of nanosized ceramic particles, but also the deposition of nanofilms into a porous ceramic material to create nanocomposites. I have been able to apply this experience in my IP practice to assist clients in obtaining and assessing IP in the areas of nanolaminates and coatings, nanosized particles and nanostructures, such as carbon nanotubes, nano fluidic devices, which are very small devices which transport fluids, and 3D structures formed from nanomaterials, such as woven nanofibers.
Editor: I understand that some of the components of the new Boeing 787 are examples of nanotechnology.
Vernon: The design objective behind the 787 is that lighter, better-performing materials will reduce the weight of the aircraft, resulting in longer possible flight times and decreased operating costs. Boeing reports that approximately 50 percent of the materials in the 787 are composite materials, and that nanotechnology will play an important role in achieving and exceeding the design objective. (See, http://www.nasc.com/nanometa/Plenary%20Talk%20Chong.pdf).
While it is believed that nanocomposite materials are used in the fuselage of the 787, Boeing is investigating applying nanotechnology to reduce costs and increase performance not only in fuselage and aircraft structures, but also within energy, sensor and system controls of the aircraft.
Editor: What products have incorporated nanotechnology? What products are anticipated to incorporate its processes in the future?
Vernon: The products that people are the most familiar with are cosmetic products, such as hair products for thinning hair that deliver nutrients deep into the scalp, and sunscreen, which includes nanosized titanium dioxide and zinc oxide to eliminate the white, pasty look of sunscreens. Sports products, such as fishing rods and tennis rackets, have incorporated a composite of carbon fiber and silica nanoparticles to add strength. Nano products are used in paints and coatings to prevent algae and corrosion on the hulls of boats and to help reduce mold and kill bacteria. We’re seeing nanotechnology used in filters to separate chemicals and in water filtration.
The textile industry has also started to use nano coatings to repel water and make fabrics flame resistant. The medical imaging industry is starting to use nanoparticles to tag certain areas of the body, allowing for enhanced MRI imaging. Developing areas include drug delivery, disease detection and therapeutics for oncology. Obviously, those are definitely in the future, but it is the direction of scientific thinking.
Editor: What liabilities can product manufacturers incur who are incorporating nanotechnology into their products? What kinds of health and safety risks are incurred in their manufacture or consumption?
Vernon: There are three different areas that we should think about: the manufacturing process, consumer use and environmental issues. In manufacturing there are potential safety issues with respect to the incorporation or delivery of nanomaterials. For example, inhalation of nanoparticles can cause serious respiratory issues, and contact of some nanoparticles with the skin or eyes may result in irritation. In terms of consumer use, nanomaterials may have different material properties from their larger counterparts.
As a result, we are not quite sure how these materials will affect the human body insofar as they might have a higher toxicity level than in their larger counterparts. With respect to an environmental impact, waste or recycled products may lead to the release of nanoparticles into bodies of water or impact wildlife. The National Institute for Occupational Safety and Health has established the Nanotechnology Research Center to develop a strategic direction with respect to occupational safety and nanotechnology. Guidance and publications can be found at http://www.cdc.gov/niosh/topics/nanotech.
Editor: The European Union requires the labeling of foods containing nanomaterials. What has been the position of the Food & Drug Administration and the EPA in the United States about food labeling?
Vernon: So far the FDA has taken the position that just because nanomaterials are smaller, they are not materially different from their larger counterparts, and therefore there have been no labeling requirements on food products. The FDA believes that their current standards for safety assessment are robust and flexible enough to handle a variety of different materials. That being said, the FDA has issued some guidelines for the food and cosmetic industries, but there has not been any requirement for food labeling as of now. The EPA has a nanotechnology division, which is also studying nanomaterials and their impact, but I haven’t seen anything that specifically requires a special registration process for nanomaterials.
Editor: What new regulations regarding nanotech products are expected? Should governmental regulations be adopted to prevent nanoparticles in foods and cosmetics from causing toxicity?
Vernon: The FDA has not telegraphed that any new regulations will be put into place. The agency is currently in the data collection stage to make sure that these materials are being safely delivered to people using current FDA standards – that materials are safe for human consumption or contact with humans. We won’t really understand whether or not regulations will be coming into place until we see data coming out that indicates that there are issues that are directly associated with nanomaterials. Rather than expecting regulations, I would suggest that we examine the data regarding nano products to optimize safe handling and use procedures.
Editor: Have there ever been any cases involving toxicity resulting from nano products?
Vernon: There are current investigations about the toxicity of carbon nano tubes, but the research is in its infancy. There is no evidence to show any potential harm from this technology. Unlike asbestos or silica exposure, the science is not there yet to demonstrate any toxicity link. The general understanding is that it may take decades for any potential harm to manifest. I believe my colleague, Patrick J. Comerford, head of McCarter’s product liability team in Boston, summarizes the situation well by noting that “if any supportable science was available, plaintiff’s bar would have already made this a high-profile target.”
Editor: While some biotech cases have failed the test of patentability before the courts, such as the case of Mayo v. Prometheus, what standard has been set forth for a biotech process to pass the test for patentability?
Vernon: There is no specified bright-line test for determining if a biotech process is patentable. But what the U.S. Patent and Trademark Office has done is to issue some new examination guidelines with respect to the Mayo decision that help examiners figure out whether a biotech process is patent eligible. Specifically, the guidelines look to see if the biotech process (i.e., a process incorporating a law of nature) also includes at least one additional element or step. That additional element needs to be significant and not just a mental or correlation step. If a biotech process patent claim includes this significant additional step, there still needs to be a determination if the process is novel and non-obvious over the prior art. So while this might not be a bright-line test to help us figure out whether a biotech process is patentable, it at least gives us some direction about what the examiners are looking for in the patent claims.
Editor: What effect do you think the new America Invents Act will have in encouraging biotech companies to file early in the first stages of product development? Might that not run the risk that the courts could deny patentability as in the Ariad case where functional results of a process were described rather than the specific invention?
Vernon: The AIA goes into effect next month. What companies, especially biotech companies, need to do is file early. Companies need to submit applications supported by their research to include both a written description and enablement of the invention. Companies will need to be more focused on making sure that they are not only inventing in a timely manner but are also involving their patent counsel in planned and well-thought-out experiments to make sure that the supporting information is available in a timely fashion for patenting.
Editor: Have there been any recent cases relating to biotechnology or nanotechnology that our readers should be informed about?
Vernon: The Supreme Court will hear oral arguments in April in the Myriad case. This case involves the BRCA gene, the breast cancer gene – and the issue is whether isolating a portion of a gene is patentable. While I am not a biotechnologist, I think this case will also impact nanotechnology as a whole. Applying for a patent on a portion of a gene is not too far distant from applying for a patent on a nanoparticle of a material that already exists but which has different properties from the original, larger-counterpart material. Would this nanosize material be patentable? This will be an important case to see what guidance the Supreme Court delivers this coming term.
Editor: Is there anything else you’d like to add?
Vernon: I think the next couple of years for nanotech will be very interesting. As I mentioned, I did my PhD thesis in the nanotechnology area a few years ago. My studies, like those of many other students, were funded in part with government grants. There is a great deal of government money being poured into nanotechnology. In the next ten years we will start seeing more and more of this research being commercialized and adopted into our lives. To keep current of developments, readers can visit www.nano.gov.
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” … Understanding the SCL (space charge limit) effect is important to manipulate transport, recombination, and extraction of photocarriers, which will significantly affect the power conversion efficiency (PCE) of OSCs. (Organic Solar Cells)”
As a fundamental electrostatic limit, space charge limit (SCL) for photocurrent is a universal phenomenon and of paramount importance for organic semiconductors with unbalanced photocarriers mobility and high exciton generation. Here we proposed a new plasmonic-electrical concept to manipulate electrical properties of organic devices including photocarriers recombination, transport and collection.
As a proof-of-concept, organic solar cells (OSCs) comprising metallic planar and grating electrodes are systematically investigated with normal and inverted device structures. Interestingly, although strong plasmonic resonances induce abnormally dense photocarriers around a grating anode, the grating-inverted OSC is exempt from space charge accumulation (limit) and degradation of electrical properties in contrast to the planar-inverted and planar-normal ones.
The particular reason is that plasmonically induced photocarriers redistribution shortens the transport path of low-mobility holes, which are collected by the grating anode. The work demonstrated and explained the SCL breaking with the plasmonic-electrical effect. Most importantly, the plasmonic-electrical concept will open up a new way to manipulate both optical and electrical properties of semiconductor devices simultaneously.
This work is supported by the General Research Fund (grants: HKU711813 and HKU711612E), the National Natural Science Foundation of China (NSFC)/Research Grants Council (RGC) grant (N_HKU709/12) and Ministry of Education (MOE)/Research Grants Council (RGC) (M-HKU703/12) from RGC of Hong Kong Special Administrative Region, China. This project is also supported in part by Collaborated Research Fund (CUHK1/CRF/12G) of RGC, NSFC grant (No. 61201122), and UGC of Hong Kong (No. AoE/P-04/08).
Abstract ** The complete referenced article is available here online at:
The space charge limit (SCL) effect is a universal phenomenon in semiconductor devices involving light emitting diodes, solar cells, and photodetectors1, 2, 3, 4, 5, 6, 7, 8, 9. It also sets a fundamental electrostatic limit in electrical properties of organic semiconductor devices with unbalanced photocarriers (electrons and holes) mobility and high exciton generation efficiency10, 11, 12, 13, 14. With the interesting features of low cost, low-temperature fabrication, semi-transparency, and mechanical flexibility, organic solar cell (OSC) is currently one of emerging optoelectronic devices and shows a bright outlook for green energy industry12, 13, 15, 16, 17, 18. Understanding the SCL effect is important to manipulate transport, recombination, and extraction of photocarriers, which will significantly affect the power conversion efficiency (PCE) of OSCs.
Typically, the occurrence of SCL4 satisfies the following conditions: (1) unbalanced hole and electron mobility; (2) thick active layer; (3) high light intensity or dense photocarriers (electrons and holes) generation; and (4) moderate reverse bias. Compared to electron mobility, a low mobility of holes typically occurs in organic semiconductor devices depending on fabrication procedures19, 20, 21, 22 e.g. thermal annealing, solvent annealing, etc; and even occurs in the OSCs with robust active materials such as the polymer blend of poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM). To investigate SCL characteristics, the inverted OSC with a planar multilayered structure is taken as a representative example. In the planar-inverted OSCs, photocarriers will be generated at the region close to the transparent cathode, such as indium tin oxide (ITO), where incident light will first penetrate. The photogenerated holes with a low mobility will have to transport through the whole active layer, and finally reach the anode (see Figure 1(a)). SCL will occur if the length of active layer is longer than the mean drift length of holes, which is very short because of the low mobility. Meanwhile, holes pile up inside the device to a greater degree than electrons. In other words, positive space charges are accumulated due to the unbalanced photocarriers mobility and a long transport path of holes. As a result, the short-circuit current and fill factor of OSCs will drop significantly due to both the bulk recombination and space charge formation4, 7, 9, 23, 24. In this work, we will demonstrate the SCL breaking in the OSCs incorporating metallic (Ag or Au) nanostructures, which offers a novel route to eliminate the SCL effect in semiconductor devices.
(For the complete article see this link)
“Genesis Nanotechnology – Great Things from Small Things”
Researchers at the National Institute of Standards and Technology (NIST), working in collaboration with the Naval Research Laboratory, have found that a particular species of quantum dots that weren’t commonly thought to blink, do.
So what? Well, although the blinks are short—on the order of nanoseconds to milliseconds—even brief fluctuations can result in efficiency losses that could cause trouble for using quantum dots to generate photons that move information around inside a quantum computer or between nodes of a future high-security internet based on quantum telecommunications.
Beyond demonstrating that the dots are blinking, the team also suggests a possible culprit.
Scientists have regarded indium arsenide and gallium arsenide (InAs/GaAs) quantum dots to be promising as single photon sources foruse in different future computing and communication systems based on quantum technologies. Compared to other systems, researchers have preferred these quantum dots because they appeared to not blink and because they can be fabricated directly into the types of semiconductor optoelectronics that have been developing over the past few decades.
The NIST research team also thought these quantum dots were emitting steady light perfectly, until they came upon one that was obviously blinking (or was “fluorescently intermittent,” in technical terms). They decided to see if they could find others that were blinking in a less obvious way.
While most previous experiments surveyed the dots in bulk, the team tested these dots as they would be used in an actual device. Using an extremely sensitive photon autocorrelation technique to uncover subtle signatures of blinking, they found that the dots blink over timescales rangingfrom tens of nanoseconds to hundreds of milliseconds. Their results suggest that building photonic structures around the quantum dots—something you’d have to do to make many applications viable—may make them significantly less stable as a light source.
“Most of the previous experimental studies of blinking inInAs/GaAs quantum dots looked at their behavior after the dots have been grown but before the surrounding devices have been fabricated,” says Kartik Srinivasan, one of the authors of the study. “However, there is no guarantee that a quantum dot will remain non-blinking after the nanofabrication of a surrounding structure, which introduces surfaces and potential defects within 100 nanometers of the quantum dot. We estimate the radiative efficiency of the quantum dots to be between about 50 and 80 percent after the photonic structures are fabricated, significantly less than the 100 percent efficiency that future applications will require.”
According to Marcelo Davanço, another author of the study, future work will focus on measuring dots both before and after device fabrication to better assess whether the fabrication is indeed a source of the defects thought to cause the blinking. Ultimately, the authors hope to understand what types of device geometries will avoid blinking while still efficiently funneling the emitted photons into a useful transmission channel, such as an optical fiber.
The NIST Center for Nanoscale Science and Technology (CNST) is a national nanotechnology user facility that enables innovation by providing rapid access to the tools needed to make and measure nanostructures. Researchers interested in accessing the techniques described here or in collaborating on their future development should contact Kartik Srinivasan.
More information: M. Davanço, C. Stephen Hellberg, S. Ates, A. Badolato and K. Srinivasan. “Multiple time scale blinking in InAs quantum dot single-photon sources.” Phys. Rev. B 89, 161303(R) – Published 16 April 2014.
Researchers in the University of Toronto’s Edward S. Rogers Sr. Department of Electrical & Computer Engineering have designed and tested a new class of solar-sensitive nanoparticle that outshines the current state of the art employing this new class of technology.
This new form of solid, stable light-sensitive nanoparticles, called colloidal quantum dots, could lead to cheaper and more flexible solar cells, as well as better gas sensors, infrared lasers, infrared light emitting diodes and more. The work, led by post-doctoral researcher Zhijun Ning and Professor Ted Sargent, was published this week in Nature Materials.
Diagram of quantum dot. Credit: University of Toronto
Collecting sunlight using these tiny colloidal quantum dots depends on two types of semiconductors: n-type, which are rich in electrons; and p-type, which are poor in electrons. The problem? When exposed to the air, n-type materials bind to oxygen atoms, give up their electrons, and turn into p-type. Ning and colleagues modelled and demonstrated a new colloidal quantum dot n-type material that does not bind oxygen when exposed to air.
Maintaining stable n- and p-type layers simultaneously not only boosts the efficiency of light absorption, it opens up a world of new optoelectronic devices that capitalize on the best properties of both light and electricity. For the average person, this means more sophisticated weather satellites, remote controllers, satellite communication, or pollution detectors.
“This is a material innovation, that’s the first part, and with this new material we can build new device structures,” said Ning. “Iodide is almost a perfect ligand for these quantum solar cells with both high efficiency and air stability—no one has shown that before.”
Ning’s new hybrid n- and p-type material achieved solar power conversion efficiency up to eight per cent—among the best results reported to date.
But improved performance is just a start for this new quantum-dot-based solar cell architecture. The powerful little dots could be mixed into inks and painted or printed onto thin, flexible surfaces, such as roofing shingles, dramatically lowering the cost and accessibility of solar power for millions of people.
“The field of colloidal quantum dot photovoltaics requires continued improvement in absolute performance, or power conversion efficiency,” said Sargent. “The field has moved fast, and keeps moving fast, but we need to work toward bringing performance to commercially compelling levels.”
Published on Jul 2, 2014 The Zero Line with Dr. Kent Moors
How Graphene could Increase Water Supplies for The Poorest Countries
More than 780 million people in the world need clean water. The desalination process has been a huge roadblock to solving this global water crisis — until now. Graphene Desalination is going to change the world for good.
Given most of earth is water & just 2.5% of that is fresh, this miracle material could have just unlocked our most abundant water source. That’s right. Up to now, the earths oceans have served very little in terms of drinking water. Now, graphene could make water scarcity a thing of the past. For the poorest countries & the most well-off, graphene could completely change the way we live.
What is Graphene Desalination & How could it Increase Water Supplies?
Graphene Desalination to Increase Water Supplies
Graphene is a single layer of carbon atoms that are bonded in a repeating pattern of hexagons like the image above. Graphene is approximately 1,000,000 times thinner than paper; so thin that it is actually considered two dimensional.
Graphene’s flat honeycomb pattern grants it many unusual characteristics, including the status of strongest material in the world.
Graphene’s mesh is so fine, it can be used to filter out the smallest particles. In this case, graphene would be used as a desalination filter. Because it’s so strong & resiliant tearing, it would serve as the worlds strongest, finest desalination filter with the durability to withstand massive ammounts of water pressure.
See (Video) how a defense company made a major breakthrough in water filtration using the miracle material of grapheme … “Genesis Nanotechnology … Great Things from Small Things!”
A new combination of materials can efficiently guide electricity and light along the same tiny wire, a finding that could be a step towards building computer chips capable of transporting digital information at the speed of light.
The continually increasing demands for higher-speed and lower-operating-power devices have resulted in the continued impetus to shrink photonic components. We demonstrate a primitive nanophotonic integrated circuit element composed of a single silver nanowire and single-layer molybdenum disulfide (MoS2 ) flake.
Using scanning confocal fluorescence microscopy and spectroscopy, we find that nanowire plasmons can excite MoS2 photoluminescence and that MoS2 excitons can decay into nanowire plasmons. Finally, we show that the nanowire may serve the dual purpose of both exciting MoS2 photoluminescence via plasmons and recollecting the decaying exciton as nanowire plasmons. The potential for subwavelength light guiding and strong nanoscale light–matter interaction afforded by our device may facilitate compact and efficient on-chip optical processing.
© 2014 Optical Society of America
Funding By: Directorate for Mathematical and Physical Sciences (MPS)10.13039/100000086 (DMR-1309734); Office of Science, U.S. Department of Energy10.13039/100006132 (DE-FG02-05ER46207); NSF IGERT (DGE-0966089); Institute of Optics.
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