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newfuelcelld 031516A powdery mixture of graphene-wrapped magnesium nanocrystals, produced at Berkeley Lab, is stable in air. The mixture’s energy properties show promise for use in hydrogen fuel cells. Credit: Eun Seon Cho/Berkeley Lab

Hydrogen is the lightest and most plentiful element on Earth and in our universe. So it shouldn’t be a big surprise that scientists are pursuing hydrogen as a clean, carbon-free, virtually limitless energy source for cars and for a range of other uses, from portable generators to telecommunications towers—with water as the only byproduct of combustion.

While there remain scientific challenges to making -based energy sources more competitive with current automotive propulsion systems and other energy technologies, researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a new materials recipe for a battery-like cell—which surrounds hydrogen-absorbing magnesium nanocrystals with atomically thin graphene sheets—to push its performance forward in key areas.

The graphene shields the nanocrystals from oxygen and moisture and contaminants, while tiny, natural holes allow the smaller hydrogen molecules to pass through. This filtering process overcomes common problems degrading the performance of metal hydrides for .

These graphene-encapsulated magnesium crystals act as “sponges” for hydrogen, offering a very compact and safe way to take in and store hydrogen. The nanocrystals also permit faster fueling, and reduce the overall “tank” size.

“Among metal hydride-based materials for hydrogen storage for vehicle applications, our materials have good performance in terms of capacity, reversibility, kinetics and stability,” said Eun Seon Cho, a postdoctoral researcher at Berkeley Lab and lead author of a study related to the new fuel cell formula, published recently in Nature Communications.

New fuel cell design powered by graphene-wrapped nanocrystals
Thin sheets of graphene oxide (red sheets) have natural, atomic-scale defects that allow hydrogen gas molecules to pass through while blocking larger molecules such as oxygen (O2) and water (H2O). Berkeley Lab researchers encapsulated …more

In a hydrogen fuel cell-powered vehicle using these materials, known as a “metal hydride” (hydrogen bound with a metal) fuel cell, hydrogen gas pumped into a vehicle would be chemically absorbed by the magnesium nanocrystaline powder and rendered safe at low pressures.

Jeff Urban, a Berkeley Lab staff scientist and co-author, said, “This work suggests the possibility of practical hydrogen storage and use in the future. I believe that these materials represent a generally applicable approach to stabilizing reactive materials while still harnessing their unique activity—concepts that could have wide-ranging applications for batteries, catalysis, and energetic materials.”

The research, conducted at Berkeley Lab’s Molecular Foundry and Advanced Light Source, is part of a National Lab Consortium, dubbed HyMARC (Hydrogen Materials—Advanced Research Consortium) that seeks safer and more cost-effective hydrogen storage, and Urban is Berkeley Lab’s lead scientist for that effort.

The U.S. market share for all electric-drive vehicles in 2015, including full-electric, hybrids and plug-in hybrid vehicles, was 2.87 percent, which amounts to about 500,000 electric-drive vehicles out of total vehicle sales of about 17.4 million, according to statistics reported by the Electric Drive Transportation Association, a trade association promoting electric-drive vehicles.

Hydrogen-fuel-cell vehicles haven’t yet made major in-roads in vehicle sales, though several major auto manufacturers including Toyota, Honda, and General Motors, have invested in developing hydrogen fuel-cell vehicles. Indeed, Toyota released a small-production model called the Mirai, which uses compressed-hydrogen tanks, last year in the U.S.

A potential advantage for hydrogen-fuel-cell vehicles, in addition to their reduced environmental impact over standard-fuel vehicles, is the high specific energy of hydrogen, which means that can potentially take up less weight than other battery systems and fuel sources while yielding more electrical energy.

A measure of the energy storage capacity per weight of hydrogen fuel cells, known as the “gravimetric energy density,” is roughly three times that of gasoline. Urban noted that this important property, if effectively used, could extend the total vehicle range of hydrogen-based transportation, and extend the time between refueling for many other applications, too.

More R&D is needed to realize higher-capacity hydrogen storage for long-range vehicle applications that exceed the performance of existing electric-vehicle batteries, Cho said, and other applications may be better suited for hydrogen fuel cells in the short term, such as stationary power sources, forklifts and airport vehicles, portable power sources like laptop battery chargers, portable lighting, water and sewage pumps and emergency services equipment.

Cho said that a roadblock to metal hydride storage has been a relatively slow rate in taking in (absorption) and giving out (desorption) hydrogen during the cycling of the units. In fuel cells, separate chemical reactions involving hydrogen and oxygen produce a flow of electrons that are channeled as electric current, creating water as a byproduct.

The tiny size of the graphene-encapsulated nanocrystals created at Berkeley Lab, which measure only about 3-4 nanometers, or billionths of a meter across, is a key in the new fuel cell materials’ fast capture and release of hydrogen, Cho said, as they have more surface area available for reactions than the same material would at larger sizes.

Another key is protecting the magnesium from exposure to air, which would render it unusable for the fuel cell, she added.

Working at The Molecular Foundry, researchers found a simple, scalable and cost-effective “one pan” technique to mix up the graphene sheets and magnesium oxide nanocrystals in the same batch. They later studied the coated nanocrystals’ structure using X-rays at Berkeley Lab’s Advanced Light Source. The X-ray studies showed how pumped into the fuel cell mixture reacted with the magnesium nanocrystals to form a more stable molecule called magnesium hydride while locking out oxygen from reaching the magnesium.

“It is stable in air, which is important,” Cho said.

Next steps in the research will focus on using different types of catalysts—which can improve the speed and efficiency of chemical reactions—to further improve the fuel cell’s conversion of electrical current, and in studying whether different types of material can also improve the fuel cell’s overall capacity, Cho said.

Explore further: Hydrogen released to fuel cell more quickly when stored in metal nanoparticles

More information: Eun Seon Cho et al. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage, Nature Communications (2016). DOI: 10.1038/ncomms10804

Measurements of electrical properties of a plastic tape (yellow), taken using a specially designed microwave cavity (the white cylinder at center) and accompanying electrical circuit, change quickly and consistently in response to changes in the tape’s thickness. The setup is inspired by high-volume roll-to-roll manufacturing devices used to mass-produce nanomaterials. The changes in the tape’s thickness spell NIST in Morse code.
Credit: NIST/Nathan Orloff

Manufacturers may soon have a speedy and nondestructive way to test a wide array of materials under real-world conditions, thanks to an advance that researchers at the National Institute of Standards and Technology (NIST) have made in roll-to-roll measurements. Roll-to-roll measurements are typically optical measurements for roll-to-roll manufacturing, any method that uses conveyor belts for continuous processing of items, from tires to nanotechnology components.

In order for new materials such as carbon nanotubes and graphene to play an increasingly important role in electronic devices, high-tech composites and other applications, manufacturers will need quality-control tests to ensure that products have desired characteristics, and lack flaws. Current test procedures often require cutting, scratching or otherwise touching a product, which slows the manufacturing process and can damage or even destroy the sample being tested.

To add to existing testing non-contact methods, NIST physicists Nathan Orloff, Christian Long and Jan Obrzut measured properties of films by passing them through a specially designed metal box known as a microwave cavity. Electromagnetic waves build up inside the cavity at a specific “resonance” frequency determined by the box’s size and shape, similar to how a guitar string vibrates at a specific pitch depending on its length and tension. When an object is placed inside the cavity, the resonance frequency changes in a way that depends on the object’s size, electrical resistance and dielectric constant, a measure of an object’s ability to store energy in an electric field. The frequency change is reminiscent of how shortening or tightening a guitar string makes it resonate at a higher pitch, says Orloff.

The researchers also built an electrical circuit to measure these changes. They first tested their device by running a strip of plastic tape known as polyimide through the cavity, using a roll-to-roll setup resembling high-volume roll-to-roll manufacturing devices used to mass-produce nanomaterials. As the tape’s thickness increased and decreased–the researchers made the changes in tape thickness spell “NIST” in Morse code–the cavity’s resonant frequency changed in tandem. So did another parameter called the “quality factor,” which is the ratio of the energy stored in the cavity to the energy lost per frequency cycle. Because polyimide’s electrical properties are well known, a manufacturer could use the cavity measurements to monitor whether tape is coming off the production line at a consistent thickness–and even feeding back information from the measurements to control the thickness.

Alternatively, a manufacturer could use the new method to monitor the electrical properties of a less well-characterized material of known dimensions. Orloff and Long demonstrated this by passing 12- and 15-centimeter-long films of carbon nanotubes deposited on sheets of plastic through the cavity and measuring the films’ electrical resistance. The entire process took “less than a second,” says Orloff. He added that with industry-standard equipment, the measurements could be taken at speeds beyond 10 meters per second, more than enough for many present-day manufacturing operations.

The new method has several advantages for a thin-film manufacturer, says Orloff. One, “You can measure the entire thing, not just a small sample,” he said. Such real-time measurements could be used to tune the manufacturing process without shutting it down, or to discard a faulty batch of product before it gets out the factory door. “This method could significantly boost prospects of not making a faulty batch in the first place,” Long noted.

And because the method is nondestructive, Orloff added, “If a batch passes the test, manufacturers can sell it.”

Films of carbon nanotubes and graphene are just starting to be manufactured in bulk for potential applications such as composite airplane materials, smartphone screens and wearable electronic devices.

Orloff, Long and Obrzut submitted a patent application for this technique in December 2015.

A producer of such materials has already expressed interest in the new method, said Orloff. “They’re really excited about it.” He added that the method is not specific to nanomanufacturing, and with a properly designed cavity, could also help with quality control of many other kinds of products, including tires, pharmaceuticals and even beer.


Story Source:

The above post is reprinted from materials provided by National Institute of Standards and Technology (NIST). Note: Materials may be edited for content and length.


Journal Reference:

  1. Nathan D. Orloff, Christian J. Long, Jan Obrzut, Laurent Maillaud, Francesca Mirri, Thomas P. Kole, Robert D. McMichael, Matteo Pasquali, Stephan J. Stranick, J. Alexander Liddle. Noncontact conductivity and dielectric measurement for high throughput roll-to-roll nanomanufacturing. Scientific Reports, 2015; 5: 17019 DOI: 10.1038/srep17019

Monash U  031116 1-revolutionar

A new type of graphene-based filter could be the key to managing the global water crisis, a study has revealed. The new graphene filter, which has been developed by Monash University and the University of Kentucky, allows water and other liquids to be filtered nine times faster than the current leading commercial filter.

According to the World Economic Forum’s Global Risks Report, lack of access to safe, clean water is the biggest risk to society over the coming decade. Yet some of these risks could be mitigated by the development of this filter, which is so strong and stable that it can be used for extended periods in the harshest corrosive environments, and with less maintenance than other filters on the market.

The research team was led by Associate Professor Mainak Majumder from Monash University. Associate Professor Majumder said the key to making their filter was developing a viscous form of oxide that could be spread very thinly with a blade.

“This technique creates a uniform arrangement in the graphene, and that evenness gives our filter special properties,” Associate Prof Majumder said.

This technique allows the filters to be produced much faster and in larger sizes, which is critical for developing commercial applications. The graphene-based filter could be used to filter chemicals, viruses, or bacteria from a range of liquids. It could be used to purify water, dairy products or wine, or in the production of pharmaceuticals.

This is the first time that a graphene filter has been able to be produced on an industrial scale – a problem that has plagued the scientific community for years.

Research team member and PhD candidate, Abozar Akbari, said scientists had known for years that graphene filters had impressive qualities, but in the past they had been difficult and expensive to produce.

“It’s been a race to see who could develop this technology first, because until now graphene-based could only be used on a small scale in the lab,” Mr Akbari said.

Graphene is a lattice of carbon atoms so thin it’s considered to be two-dimensional. It has been hailed as a “wonder-material” because of its incredible performance characteristics and range of potential applications.

The team’s new filter can filter out anything bigger than one nanometre, which is about 100,000 times smaller than the width of a human hair.

The research has gathered interest from a number of companies in the United States and the Asia Pacific, the largest and fastest-growing markets for nano-filtration technologies.

The team’s research was supported by industry partner Ionic Industries, as well as a number of Australian Research Council grants.

Ionic Industries’ CEO, Mark Muzzin, said the next step was to get the patented graphene-based filter on the market.

“We are currently developing ways to test how the filter fares against particular contaminants that are of interest to our customers” Mr Muzzin said.

Co-author of the research and Director of the Center for Membrane Science, Professor Dibakar Bhattacharyya, from the University of Kentucky, said: “The ability to control the thickness of the filter and attain a sharper cut-off in separation, and the use of only water as the casting solvent, is a commercial breakthrough.”

Explore further: Graphene’s love affair with water

More information: Abozar Akbari et al. Large-area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide, Nature Communications (2016). DOI: 10.1038/ncomms10891

A polybenzimidazole polymer supports the formation of gold nanoparticles with well-defined sizes on graphene.
Credit: International Institute for Carbon-Neutral Energy Research (I²CNER), Kyushu University

Research group develops new method for creating highly efficient gold nanoparticle catalysts for fuel cells

The successful future of fuel cells relies on improving the performance of the catalysts they use. Gold nanoparticles have been cited as an ideal solution, but creating a uniform, useful catalyst has proven elusive. However, a team of researchers at Kyushu University’s International Institute for Carbon-Neutral Energy Research (I2CNER) devised a method for using a new type of catalyst support.

In a potential breakthrough technology for fuel cells, a recently published article in Scientific Reports shows how wrapping a graphene support in a specially prepared polymer provides an ideal foundation for making uniform, highly active gold nanoparticle catalysts.

Fuel cells produce electricity directly from the separate oxidation of the fuel and the reduction of oxygen. The only by-product of the process is water, as fuel cells produce no greenhouse gases and are widely seen as essential for a clean-energy future.

However, the rate at which electricity can be produced in fuel cells is limited, especially by the oxygen reduction reaction (ORR), which must be catalyzed in practical applications. Although current platinum-based catalysts accelerate the reaction, their unhelpful propensity to also catalyze other reactions, and their sensitivity to poisoning by the reactants, limits their overall utility. Despite bulk gold being chemically inert, gold nanoparticles are surprisingly effective at catalyzing the oxygen reduction reaction without the drawbacks associated with their platinum counterparts.

Nevertheless, actually creating uniformly sized gold nanoparticle catalysts has proven problematic. Previous fabrication methods have produced catalysts with nanoparticle sizes that were too large or too widely distributed for practical use. Meanwhile, efforts to regulate the particle size tended to restrict the gold’s activity or make less-stable catalysts.

“Creating small, well-controlled particles meant that we needed to focus on particle nucleation and particle growth,” lead and corresponding author Tsuyohiko Fujigaya says. “By wrapping the support in the polybenzimidazole polymer we successfully developed with platinum, we created a much better support environment for the gold nanoparticles.”

The team also tested the performance of these novel catalyst structures. Their catalysts had the lowest overpotential ever reported for this type of reaction. “The overpotential is a bit like the size of the spark you need to start a fire,” coauthor Naotoshi Nakashima says. “Although we’re obviously pleased with the catalysts’ uniformity, the performance results show this really could be a leap forward for the ORR reaction and maybe fuel cells as well.”

The article “Growth and Deposition of Au Nanoclusters on Polymer-wrapped Graphene and Their Oxygen Reduction Activity” was published in Scientific Reports.


Story Source:

The above post is reprinted from materials provided by Kyushu University, I2CNER. Note: Materials may be edited for content and length.


Journal Reference:

  1. Tsuyohiko Fujigaya, ChaeRin Kim, Yuki Hamasaki, Naotoshi Nakashima. Growth and Deposition of Au Nanoclusters on Polymer-wrapped Graphene and Their Oxygen Reduction Activity. Scientific Reports, 2016; 6: 21314 DOI:10.1038/srep21314

A study conducted by the Solar Energy Industries Association (SEIA) indicates 2016 will be a banner year for U.S. solar installations.

The non-profit based in Washington D.C. predicts an estimated 119 percent increase this year due to tax incentives and price reductions.

First, Congress extended a 30 percent federal Investment Tax Credit for all different types of solar projects through 2019. Plus, the price of panels has dropped by 67 percent since 2010, according to the report.

SEIA’s investigation notes demand will grow in residential and commercial markets, but utility-scale installations will encompass 74 percent of the installations for 2016.

These factors could make solar installations an intriguing option for homeowners and businesses. Whole Foods agreed to a partnership with Solar City in which the alternative energy company will retrofit rooftop solar panels on 100 stores.

Fortune adds that electricity companies have nothing to worry about because solar energy only accounts for 1 percent of the nation’s power output.

By 2020, SEIA predicts solar power will grow to 3.5 percent.

Henkel Electronic Materials LLC is a division of global material supplier, Henkel Corporation. Headquartered in Irvine, California with sales, service, manufacturing and advanced R&D centers around the globe.

Henkel is focused on developing next-generation materials for a variety of applications in semiconductor packaging, industrial, consumer, displays and emerging electronics market sectors. With a broad portfolio of silver, carbon, dielectric and clear conductive inks, Henkel is making today’s medical solutions, in-home conveniences, handheld connectivity, RFID and automotive advances reliable and effective. Watch an interview taken at the IDTechEx Printed Electronics event at this link: www.IDTechEx.com/peusa

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Drone for Trees 12970826404_59ff05e8a8_oDrones are used for various applications such as aero picturing, disaster recovery, and delivering. Despite attracting attention as a new growth area, the biggest problem of drones is its small battery capacity and limited flight time of less than an hour. A fuel cell developed by Prof. Gyeong Man Choi (Dept. of Materials Science and Engineering) and his research team at POSTECH can solve this problem.

 

Prof. Choi and his Ph.D. student Kun Joong Kim have developed a miniaturized solid oxide fuel cell (SOFC) to replace lithium-ion batteries in smartphones, laptops, drones, and other small electronic devices. Their results were published in the March edition of Scientific Reports, the sister journal of Nature.

Their achievement has been highly evaluated because it can be utilized, not only for a small fuel cell, but also for a large-capacity fuel cell that can be used for a vehicle.

The SOFC, referred to as a third-generation fuel cell, has been intensively studied since it has a simple structure and no problems with corrosion or loss of the electrolyte. This fuel cell converts hydrogen into electricity by oxygen-ion migration to fuel electrode through an oxide electrolyte. Typically, silicon has been used after lithography and etching as a supporting component of small oxide fuel cells. This design, however, has shown rapid degradation or poor durability due to thermal-expansion mismatch with the electrolyte, and thus, it cannot be used in actual devices that require fast On/Off.

The research team developed, for the first time in the world, a new technology that combines porous stainless steel, which is thermally and mechanically strong and highly stable to oxidation/reduction reactions, with thin-film electrolyte and electrodes of minimal heat capacity. Performance and durability were increased simultaneously. In addition, the fuel cells are made by a combination of tape casting-lamination-cofiring (TLC) techniques that are commercially viable for large scale SOFC.

The fuel cells exhibited a high power density of ~ 560 mW cm-2 at 550 oC. The research team expects this fuel cell may be suitable for portable electronic devices such as smartphones, laptops, and drones that require high power-density and quick on/off. They also expect to develop large and inexpensive fuel cells for a power source of next-generation automotive.

With this fuel cell, drones can fly more than one hour, and the team expects to have smartphones that charge only once a week.

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This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology.

Iowa Cloak Skin 110528_webIMAGE: This flexible, stretchable and tunable “meta-skin ” can trap radar waves and cloak objects from detection. view more  Credit: Liang Dong/Iowa State University

Iowa State University engineers have developed a new flexible, stretchable and tunable “meta-skin” that uses rows of small, liquid-metal devices to cloak an object from the sharp eyes of radar.

The meta-skin takes its name from metamaterials, which are composites that have properties not found in nature and that can manipulate electromagnetic waves. By stretching and flexing the polymer meta-skin, it can be tuned to reduce the reflection of a wide range of radar frequencies.

The journal Scientific Reports recently reported the discovery online. Lead authors from Iowa State’s department of electrical and computer engineering are Liang Dong, associate professor; and Jiming Song, professor. Co-authors are Iowa State graduate students Siming Yang, Peng Liu and Qiugu Wang; and former Iowa State undergraduate Mingda Yang. The National Science Foundation and the China Scholarship Council have partially supported the project.

“It is believed that the present meta-skin technology will find many applications in electromagnetic frequency tuning, shielding and scattering suppression,” the engineers wrote in their paper.

Dong has a background in fabricating micro and nanoscale devices and working with liquids and polymers; Song has expertise in looking for new applications of electromagnetic waves.

Working together, they were hoping to prove an idea: that electromagnetic waves – perhaps even the shorter wavelengths of visible light – can be suppressed with flexible, tunable liquid-metal technologies.

What they came up with are rows of split ring resonators embedded inside layers of silicone sheets. The electric resonators are filled with galinstan, a metal alloy that’s liquid at room temperature and less toxic than other liquid metals such as mercury.

Those resonators are small rings with an outer radius of 2.5 millimeters and a thickness of half a millimeter. They have a 1 millimeter gap, essentially creating a small, curved segment of liquid wire.

The rings create electric inductors and the gaps create electric capacitors. Together they create a resonator that can trap and suppress radar waves at a certain frequency. Stretching the meta-skin changes the size of the liquid metal rings inside and changes the frequency the devices suppress.

Tests showed radar suppression was about 75 percent in the frequency range of 8 to 10 gigahertz, according to the paper. When objects are wrapped in the meta-skin, the radar waves are suppressed in all incident directions and observation angles.

“Therefore, this meta-skin technology is different from traditional stealth technologies that often only reduce the backscattering, i.e., the power reflected back to a probing radar,” the engineers wrote in their paper.

As he discussed the technology, Song took a tablet computer and called up a picture of the B-2 stealth bomber. One day, he said, the meta-skin could coat the surface of the next generation of stealth aircraft.

But the researchers are hoping for even more – a cloak of invisibility.

“The long-term goal is to shrink the size of these devices,” Dong said. “Then hopefully we can do this with higher-frequency electromagnetic waves such as visible or infrared light. While that would require advanced nanomanufacturing technologies and appropriate structural modifications, we think this study proves the concept of frequency tuning and broadening, and multidirectional wave suppression with skin-type metamaterials.”

Intl Womens Day 1 large_CWf4dIfmFR5LkqgN_CELM1k_QlPhl5L4m3wTSpxa3oA

*** From the World Economic Forum (WEF)

Five videos to watch on International Women’s Day

As we celebrate International Women’s Day on 8 March, here are five videos that highlight the struggle for gender parity.

I. The Global Gender Gap Report

The Global Gender Gap Index ranks over 140 economies according to how well they are leveraging their female talent pool, based on economic, educational, health-based and political indicators. With a decade of data, the 2015 edition of the Global Gender Gap Report– first published in 2006 – reveals patterns of change around the world.

II. Davos 2016 – Progress Towards Parity

At the Annual Meeting 2016 in Davos, an all-star panel gathered to discuss the challenges facing the journey towards gender parity. What are the opportunities to achieve progress towards parity as the demand on workforces and societies rapidly shift?

Panelists:
· Melinda Gates, Co-Chair, Bill & Melinda Gates Foundation, USA.
· Jonas Prising, Chairman and Chief Executive Officer, ManpowerGroup, USA.
· Sheryl Sandberg, Chief Operating Officer and Member of the Board, Facebook, USA.
· Justin Trudeau, Prime Minister of Canada.
· Zhang Xin, Chief Executive Officer and Co-Founder, SOHO China, People’s Republic of China.

III. China 2015 – Parity Equals Performance

Moderated by Joe Palca, Science Correspondent at NPR, this session held at the Annual Meeting of the New Champions 2015 in Dalian, People’s Republic of China, addresses the gender gap in science and technology. Are companies missing out on female-led innovation in the digital economy?

Panelists include:
– Masako Egawa, Professor, Hitotsubashi University, Japan; Global Agenda Council on Japan
– Maria Pinelli, Global Vice-Chair, Strategic Growth Markets, EY, United Kingdom
– Jun Qin, Chairman, Tsinghua Holding Technological Innovation Co., People’s Republic of China; Young Global Leader
– Nina Tandon, President and Chief Executive Officer, EpiBone, USA

IV. Emma Watson

UN Women Goodwill Ambassador, Emma Watson, delivered a stirring speech encouraging world and corporate leaders to take action for gender equality during the kickoff of a HeForShe programme launch during the World Economic Forum Annual Meeting in Davos on January 23rd, 2015.

V. Davos 2016: The Gender Impact on the Fourth Industrial Revolution

This issue briefing examined the degree and breadth of gender gaps across key industries and possible remedies to consider for each.
Speakers: – Mara Swan, Executive Vice-President, Global Strategy and Talent, ManpowerGroup, USA. – Theresa Whitmarsh, Executive Director, Washington State Investment Board, USA. – Saadia Zahidi, Head of Employment and Gender Initiatives, Member of the Executive Committee, World Economic Forum.

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Inorganic QD id42790_1

Posted: Mar 07, 2016

Luminescent quantum dots (LQDs), which possess high photoluminescence quantum yields, flexible emission color controlling, and solution processibility, are promising for applications in lighting systems (warm white light without UV and infrared irradiation) and high quality displays.

However, the commercialization of LQDs has been held back by the prohibitively high cost of their production. Currently, LQDs are prepared by the HI method, requiring at high temperature and tedious surface treating in order to improve both optical properties and stability.

In a breakthrough approach, researchers have now succeeded in preparing highly emissive inorganic perovskite quantum dots (IPQDs) at room temperature.

“Our synthesis technique is designed according to supersaturated recrystallization, which is operated at room temperature, within few seconds, free from inert gas and injection operation,” Professor Haibo Zeng, Director of the Institute of Optoelectronics & Nanomaterials at Nanjing University of Science and Technology, tells Nanowerk. “Although formed at room temperature, our IPQDs’ photoluminescence have quantum yields of 80%, 95%, 70%, and very small line-widths of 35, 20, and 18 nm for red, green, and blue emissions.”

text

Schematic of RT formation of IPQDs (CsPbX3 (X = Cl, Br, I)). a) The SR can be finished within 10 s through transferring the Cs+, Pb2+, and X- ions from the soluble to insoluble solvents at RT without any protecting atmosphere and heating. C: ion concentration in different solvents. C0: saturated solubilities in DMF, toluene, or mixed solvents (DMF+toluene). b) Clear toluene under a UV light. Snapshots of four typical samples after the addition of precursor ion solutions for 3 s, blue (c, Cl:Br = 1), green (d, pure Br), yellow (e, I:Br = 1), and red (f, I:Br = 1.5), respectively. (Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)

Zeng and his team have reported their findings in the February 29, 2016 online edition of Advanced Functional Materials (“CsPbX3 Quantum Dots for Lighting and Displays: Room-Temperature Synthesis, Photoluminescence Superiorities, Underlying Origins and White Light-Emitting Diodes”).

The room temperature procedures developed by the researchers make scaled production possible so that gram-scale of quantum dots can be synthesized easily with very low cost and in short time.

Already applied in the production of some organic nanoparticles, under the assist of surfactants, a supersaturated recrystallization (SR) process can be applied to fabricate QDs with well size and composition controls in solutions, especially when considering the ionic crystal features of halide perovskites.

Zeng explains the process: “In supersaturated recrystallization, that is, when the constrainedly sustentative nonequilibrium state of a soluble system is activated by an accident, for example, stirring or impurity, the supersaturated ions will precipitate in the form of crystal, which is frequently observed in natural minerals, alloys, and ion solutions. Such spontaneous precipitation and crystallization reactions will not stop until the system reaches an equilibrium state again.”

He points out that the operation of his team’s SR synthesis is very simple, and can be summarized as transferring various inorganic ions from their very good into very poor solvents.

“So, when considering supersaturation-induced recrystallization and no usage of heating, it seems to be similar to solarizing seawater to obtain edible salt, which has been used for a long time in human history,” Zeng notes. “But the key point of SR process, the obtaining of supersaturated state, is achieved by using transfer from good into poor solvents in our work, but not the evaporation of solvent, which could be the reason why our IPQDs can be formed completely at room temperature and only need trace amount of energy.”

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Controllable photoluminescence. a) Optical images of solution and film samples with different bandgaps under a 365 nm UV lamp. b) Optical absorption and c) photoluminescence spectra of IPQDs with different composition. (Reprinted with permission by Wiley-VCH Verlag)

Although developed only recently, inorganic halide perovskite quantum dot systems have exhibited comparable and even better performances than traditional QDs in many fields. With this novel room-temperature preparation technique, IPQDs’ superior optical merits could lead to promising applications in lighting and displays.

“Though more investigations are needed to reveal the correlations between structural – especially the surface states – and physical properties, our findings will provide good references and enhance researchers’ understanding of this quantum dot system, pushing it to a new research paradigm in the field of optoelectronic devices, as well as sensors and memristors,” concludes Zeng.

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