Quantum Dots: Enhancing Light-to-Current Conversion: Better Semiconductors, Solar Cells and Photdetectors


QDs for Solar 042616 quantumdotseSingle nanocrystal spectroscopy identifies the interaction between zero-dimensional CdSe/ZnS nano crystals (quantum dots) and two-dimensional layered tin disulfide as a non-radiative energy transfer, whose strength increases with increasing …more

Harnessing the power of the sun and creating light-harvesting or light-sensing devices requires a material that both absorbs light efficiently and converts the energy to highly mobile electrical current. Finding the ideal mix of properties in a single material is a challenge, so scientists have been experimenting with ways to combine different materials to create “hybrids” with enhanced features.

In two just-published papers, scientists from the U.S. Department of Energy’s Brookhaven National Laboratory, Stony Brook University, and the University of Nebraska describe one such approach that combines the excellent -harvesting properties of quantum dots with the tunable electrical conductivity of a layered tin disulfide semiconductor.

The hybrid material exhibited enhanced light-harvesting properties through the absorption of light by the quantum dots and their energy transfer to tin disulfide, both in laboratory tests and when incorporated into electronic devices. The research paves the way for using these materials in optoelectronic applications such as energy-harvesting photovoltaics, light sensors, and light emitting diodes (LEDs).

According to Mircea Cotlet, the physical chemist who led this work at Brookhaven Lab’s Center for Functional Nanomaterials (CFN), a DOE Office of Science User Facility, “Two-dimensional metal dichalcogenides like tin disulfide have some promising properties for solar energy conversion and photodetector applications, including a high surface-to-volume aspect ratio. But no semiconducting material has it all. These materials are very thin and they are poor light absorbers. So we were trying to mix them with other nanomaterials like light-absorbing quantum dots to improve their performance through energy transfer.”QDs for Solar 042616 quantumdotse

One paper, just published in the journal ACS Nano, describes a fundamental study of the hybrid quantum dot/tin disulfide material by itself. The work analyzes how light excites the quantum dots (made of a cadmium selenide core surrounded by a zinc sulfide shell), which then transfer the absorbed energy to layers of nearby tin disulfide.

“We have come up with an interesting approach to discriminate energy transfer from charge transfer, two common types of interactions promoted by light in such hybrids,” said Prahlad Routh, a graduate student from Stony Brook University working with Cotlet and co-first author of the ACS Nano paper. “We do this using single nanocrystal spectroscopy to look at how individual quantum dots blink when interacting with sheet-like tin disulfide. This straightforward method can assess whether components in such semiconducting hybrids interact either by energy or by charge transfer.”

The researchers found that the rate for non-radiative energy transfer from individual quantum dots to tin disulfide increases with an increasing number of tin disulfide layers. But performance in laboratory tests isn’t enough to prove the merits of potential new materials. So the scientists incorporated the hybrid material into an electronic device, a photo-field-effect-transistor, a type of photon detector commonly used for light sensing applications.

As described in a paper published online March 24 in Applied Physics Letters, the dramatically enhanced the performance of the photo-field-effect transistors-resulting in a photocurrent response (conversion of light to electric current) that was 500 percent better than transistors made with the tin disulfide material alone.

“This kind of energy transfer is a key process that enables photosynthesis in nature,” said Chang-Yong Nam, a materials scientist at Center for Functional Nanomaterials and co-corresponding author of the APL paper. “Researchers have been trying to emulate this principle in light-harvesting electrical devices, but it has been difficult particularly for new material systems such as the disulfide we studied. Our device demonstrates the performance benefits realized by using both processes and new low-dimensional materials.”

Cotlet concludes, “The idea of ‘doping’ two-dimensional layered with to enhance their light absorbing properties shows promise for designing better solar cells and photodetectors.”

Explore further: Small size enhances charge transfer in quantum dots

More information: Yuan Huang et al. Hybrid quantum dot-tin disulfide field-effect transistors with improved photocurrent and spectral responsivity, Applied Physics Letters (2016). DOI: 10.1063/1.4944781

Huidong Zang et al. Nonradiative Energy Transfer from Individual CdSe/ZnS Quantum Dots to Single-Layer and Few-Layer Tin Disulfide, ACS Nano (2016). DOI: 10.1021/acsnano.6b01538

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Nanoco’s Cadmium-Free Quantum Dots and Deep Red CFQD® Quantum Dot Film Honored with Silver Edison Award


Nanoco logo   MANCHESTER, England & CONCORD, Mass.–(BUSINESS WIRE)

Nanoco Group plc (LSE: NANO), a world leader in the development and manufacture of cadmium-free quantum dots and other nanomaterials, today announced it was honored with a Silver Edison Award in the category of Applied Technology: Horticulture for its cadmium-free CFQD® quantum dot technology for LED grow lighting and Deep Red CFQD® Quantum Dot Film for sustainable plant growth. Presented at a recent gala in New York City, the annual Edison Awards — named after Thomas Alva Edison – honors the best in innovation and excellence in the development of new products and services.

“We’re honored to receive this prestigious award for Nanoco’s cadmium-free CFQD ®quantum dot technology and Deep Red CFQD® Quantum Dot Film”

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“We’re honored to receive this prestigious award for Nanoco’s cadmium-free CFQD ®quantum dot technology and Deep Red CFQD® Quantum Dot Film,” said Michael Edelman, chief executive officer of Nanoco. “Receiving this honor from an esteemed program like the Edison Awards is a reflection of the leadership and commitment Nanoco has shown in introducing a non-toxic, cadmium-free quantum dot technology to the market as an innovative and sustainable platform enabler for a broad range of applications including display, lighting, biomedicine and solar. Due to their ability to emit pure colors and be easily tuned to custom wavelengths, quantum dots open up a new world in LED lighting for retail, architecture, agriculture, and other applications where color quality makes all the difference.” Nanoco_6

The Nanoco Deep Red CFQD® Quantum Dot Film is the first of its kind in sustainable plant growth. Free of heavy metals, the film, when combined with blue and/or near-UV LEDs, maximizes chlorophyll absorption to promote healthy and improved growth while minimizing energy consumption. Utilizing the cadmium-free quantum dot film allows custom individual color selection for customers based on the particular plant or product being grown, and provides excellent uniformity of light with greatly reduced heat output compared to traditional sources, allowing the lights to be placed in proximity to the plants for maximum yield and plant quality.

The Edison Awards recognition has become one of the highest accolades a company can receive in the name of innovation and business. Submissions for the Edison Awards were judged by a panel of more than 3,000 leading business executives including past award winners, academics and leaders in the fields of product development, design, engineering, science and medical.

To see the full list of 2016 Edison Award winners: http://www.edisonawards.com/winners2016.php

ABOUT NANOCO

Nanoco (LSE: NANO) is a world leader in the development and production of cadmium-free quantum dots and other nano-materials for use in multiple applications including LCD displays, lighting, solar cells and bio-imaging. In the display market, it has an exclusive manufacturing and marketing licensing agreement with The Dow Chemical Company.

Nanoco was founded in 2001 and is headquartered in Manchester, UK. It has production facilities in Runcorn, UK, and a US subsidiary, Nanoco Inc, based in Concord, MA. Nanoco also has business development executives in Japan, Korea and Taiwan. Its technology is protected worldwide by a large and growing patent estate.

Scientists Discover Nanotechnology Coating That Can Kill 99.9 Percent Of Superbugs


Nano Coating KIlls Super Bugs 042516 mrsa

 

A nanotechnology coating could control the spread of potentially deadly antibiotic-resistant superbugs that are very difficult to kill, a new study found.

This new breakthrough will allow ordinary items like smartphones, door handles and telephones to be protected against antibiotic-resistant bacteria, which are expected to kill about 10 million people around the world by 2050. A team of researchers from Institute of Technology Sligo found a way that could stem the spread of deadly and hard-to-treat superbugs.

“It’s absolutely wonderful to finally be at this stage. This breakthrough will change the whole fight against superbugs. It can effectively control the spread of bacteria,”said Professor Suresh Pillai from IT Sligo.

The nanotechnology has a 99.9 percent kill rate of potentially fatal bacteria, the researchers found. It contains a potent antimicrobial solution that is robust enough to kill pathogens and even inhibit their growth.

A wide range of items could be used as long as they’re made from metal, ceramic or glass including screens of tablets, smartphones and computers. It could also be used on door handles, television sets, urinals, refrigerators, ATM’s and ceramic tiles or floors.

It will be very useful in hospitals and other medical facilities that face the problem of superbug infections or what is commonly called nosocomial infections. Other common public areas that can use this nanotechnology are public swimming pools, buildings and transportation.

One of the most dominant nosocomial bacteria, those that develop and spread in hospitals, is Methicillin Resistant Staphylococcus aureus (MRSA). This group of bacteria could survive on hospital surfaces for up to five months.

Current methods are not efficient enough in eradicating Staphylococcus aureus. Existing hygiene coatings used today have two drawbacks – it relies on ultraviolet lights to generate electrons and reactive species and a purely photocatalytic hygiene coating is inactive when in the dark.

The nanotechnology, however, will effectively and completely kill superbugs from the surface of items. This is a water-based solution that can be sprayed on while manufacturing glass, metal or ceramic materials.

The transparent coating will be baked into the material, forming a hard surface that is resistant to superbugs including MRSA, some fungi and Escherichia coli. The team is now studying on how the material could be incorporated into paint and plastics to explore a wider use of the discovery.

The study was published in the journal Nature.

Inkjet process to print flexible touchscreens cost-efficiently


Flexible Touch Screen 042516 160415081845_1_540x360

The INM will be presenting flexible touch screens, which are printed on thin plastic foils with recently developed nanoparticle inks, using transparent, conductive oxides (TCOs).

Mobile phones and smart phones still haven‘t been adapted to the carrying habits of their users. That much is clear to anyone who has tried sitting down with a mobile phone in the back pocket: the displays of the innumerable phones and pods are rigid and do not yield to the anatomical forms adopted by the people carrying them. By now it is no longer any secret that the big players in the industry are working on flexible displays. How to produce suitable coatings for those cost-efficiently will be demonstrated by INM – Leibniz-Institute for New Materials at stand B46 in hall 2 at this year’s Hannover Messe as part of the leading trade fair for R & D and Technology Transfer which takes place from 25th to 29th April.

The INM will be presenting flexible touch screens, which are printed on thin plastic foils with recently developed nanoparticle inks, using transparent, conductive oxides (TCOs). These inks are suitable for a one-step printing process. Thus transparent lines and patterns are obtained by inkjet printing or alternatively by direct gravure printing, which are electrically conductive even after bending. Thus, a one-step-printing process for cost-efficient TCO structures is enabled.

Conductive coatings with TCOs are usually applied by means of high vacuum techniques such as sputtering. For patterning of the TCO coatings additional cost-intensive process steps are necessary, for example photolithography and etching.

“We use the TCOs to produce nanoparticles with special properties,” explains Peter William de Oliveira, Head of the Optical Materials Program Division. “The TCO ink is then created by adding a solvent and a special binder to these TCO particles. The binder performs several tasks here: it not only makes the TCO nanoparticles adhere well on the substrate; it also increases the flexibility of the TCO coating: in this way, the conductivity is maintained even when the films are bent”.

The ink can be applied to the film directly by inkjet or gravure printing. After curing under UV light at low temperatures less than 130 degrees centigrade, the coating is completed.
The transparent, electronically conductive inks allow conductor tracks to be produced unproblematically even on a large scale by means of classic reel-to-reel processes. Initial trials at INM have been promising. The researchers all agree that the use of structured rollers will in the future allow large, structured conductive surfaces to be printed with a high throughput at low cost.

INM conducts research and development to create new materials – for today, tomorrow and beyond. Chemists, physicists, biologists, materials scientists and engineers team up to focus on these essential questions: Which material properties are new, how can they be investigated and how can they be tailored for industrial applications in the future? Four research thrusts determine the current developments at INM: New materials for energy application, new concepts for medical surfaces, new surface materials for tribological applications and nano safety and nano bio. Research at INM is performed in three fields: Nanocomposite Technology, Interface Materials, and Bio Interfaces.
INM – Leibniz Institute for New Materials, situated in Saarbruecken, is an internationally leading centre for materials research. It is an institute of the Leibniz Association and has about 220 employees.


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The above post is reprinted from materials provided by INM – Leibniz-Institut für Neue Materialien gGmbH. Note: Materials may be edited for content and length.

Solar Cell Mystery Solved! Expected to greatly increase efficiency



(Left) The set-up used to grow single crystals of spiro-OMeTAD, based on antisolvent vapor-assisted crystallization. (Right) Single crystal structure of spiro-OMeTAD. Credit: Shi, et al. ©2016 AAAS

 

For the past 17 years, spiro-OMeTAD, has been keeping a secret. Despite intense research efforts, its performance as the most commonly used hole-transporting material in perovskite and dye-sensitized solar cells has remained stagnant, creating a major bottleneck for improving solar cell efficiency. 

Thinking that the material has given all it has to offer, many researchers have begun investigating alternative materials to replace spiro-OMeTAD in future solar cells.

But in a new study published in Science Advances, Dong Shi et al. have taken a closer look at spiro-OMeTAD and found that it still has a great deal of untapped potential. For the first time, they have grown single crystals of the pure material, and in doing so, they have made the surprising discovery that spiro-OMeTAD’s single-crystal structure has a hole mobility that is three orders of magnitude greater than that of its thin-film form (which is currently used in solar cells).

“This paper reports a major breakthrough for the fields of perovskite and solid-state dye-sensitized solar cells by finally clarifying the potential performance of the material and showing that improving the crystallinity of the hole transport layer is the key strategy for further breakthroughs in device engineering of these solar cells,” Osman Bakr, a professor of engineering at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia and leader of the study, told Phys.org.

The findings suggest that, at least in the short term, the time-consuming process of designing and synthesizing radically new organic hole conductors as replacements to spiro-OMeTAD may not be necessary.

In general, perovskite solar cells and dye-sensitized solar cells are made of three critical layers. Two of these layers—the electron-transporting layer and the light-absorbing layer—are well-understood structurally. However, the mesoscale packing structure of the hole-transporting layer, which is usually spiro-OMeTAD, has so far eluded researchers, and consequently its charge transport mechanisms have remained a mystery.

In the new study, the researchers figured out a way to grow pure single crystals of spiro-OMeTAD by dissolving the spiro-OMeTAD in a carefully chosen solvent. They then placed this vial inside a larger vial containing an antisolvent, in which spiro-OMeTAD does not dissolve as well, and allowed the antisolvent vapor to slowly diffuse into the inner vial.

Eventually the solution in the inner vial becomes supersaturated, so that not all of the spiro-OMeTAD can stay dissolved, causing the spiro-OMeTAD to crystallize. The researchers then performed a variety of measurements on the crystals to investigate their charge transport mechanisms and other properties.

The results are much more encouraging than expected, in many ways running contrary to the conventional wisdom based on the material’s large-scale structure, which suggested that the material had reached its limits.

Although the method used here to grow single crystals cannot be performed at a large scale, the researchers predict that similar methods that use an antisolvent to trigger crystallization could be used to enhance the crystallinity of the thin-layer spiro-OMeTAD, improving its hole mobility in order to make more efficient solar cells.

“These astonishing findings open a new direction for the development of perovskite solar cells and dye-sensitized solar cells by showing the still untapped potential of spiro-OMeTAD,” Bakr said. “They unravel a key mystery that has confounded the photovoltaic community for the last 17 years.”

More information: Dong Shi, et al. “Spiro-OMeTAD single crystals: Remarkably enhanced charge-carrier transport via mesoscale ordering.” Science Advances. DOI: 10.1126/sciadv.1501491

Abstract 

We report the crystal structure and hole-transport mechanism in spiro-OMeTAD [2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene], the dominant hole-transporting material in perovskite and solid-state dye-sensitized solar cells.

Despite spiro-OMeTAD’s paramount role in such devices, its crystal structure was unknown because of highly disordered solution-processed films; the hole-transport pathways remained ill-defined and the charge carrier mobilities were low, posing a major bottleneck for advancing cell efficiencies.

We devised an antisolvent crystallization strategy to grow single crystals of spiro-OMeTAD, which allowed us to experimentally elucidate its molecular packing and transport properties. Electronic structure calculations enabled us to map spiro-OMeTAD’s intermolecular charge-hopping pathways.

Promisingly, single-crystal mobilities were found to exceed their thin-film counterparts by three orders of magnitude. Our findings underscore mesoscale ordering as a key strategy to achieving breakthroughs in hole-transport material engineering of solar cells.



 

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MIT: Filtering Drinking Water with Nanofibers: Video


Published on Apr 21, 2016

Liquidity, an Alameda, California-based startup, has developed a low-cost water filter made from nanofibers that it hopes will reduce water-borne diseases in poor countries. A version designed for the developed world, Naked Filter, attaches to a plastic water bottle. Its membrane of electrospun nanofibers allows water to pass through it quickly.

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MIT.Nano Rising


MIT-nano-steel-1_0 042216

MIT’s future home for cutting-edge nanoscience and nanotechnology research gets fitted with 23 tons of steel per day.

A spectacular show has been going on outside the windows of central-campus buildings all spring. An enormous steel structure has been growing — piece by piece, and bolt by bolt — out of a giant hole in the ground formerly occupied by Building 12.

At a March 24 “tool talk” information session for the MIT community on the construction of MIT.nano, representatives from MIT Facilities and the contractors who are building the new 200,000 square foot nanoscale characterization and fabrication facility gave an overview not only of where things stand with the project, but how they got stood up.

“In our structural-steel erection progress log, we’ve been averaging around 23 tons per day,” said Peter Johnson of Turner Construction. “We’re putting up 2,101 tons total, and we’re 22 percent complete.”

On day 469 of the 1,000 days of construction for the project, about 75 percent of the first level was complete, and a quarter of the level 3 cleanroom was installed down to the floor decking. The framing for the entire structure, which will reach a final height of 90 feet above grade, is scheduled to be complete by late May. To get there, Johnson and others have spent years organizing and refining a minutely detailed project plan that links engineering design and fabrication, and the installation process. They have had to map out construction logistics on an hour-to-hour, and foot-by-foot basis. It all must be calibrated to unfold within specific timelines and within the tight confines of MIT.nano’s central campus location. “There’s not a lot of space when it comes to material handling and the movement of workers,” Johnson noted.

Decisions about cranes, Johnson said, were particularly critical. “While we could have used a single crane to reach the entire footprint, it was too slow. We have a several thousand line item project schedule with hundreds of steel-related tasks,” Johnson explained. “So having two cranes for a shorter period of time made the job more efficient.”

The first crane was erected during the excavation phase, so workers could use it to lower concrete and rebar into the excavated hole for elements of the foundation. The next crane arrived just prior to steel installation. Positioned strategically in locations that do not block truck routes, the cranes hoist pre-fabricated, specially packaged bundles of steel into the specific locations where they will be needed for construction.

Within these packages, each piece has a number that corresponds to its function and placement, and each one has been specifically manufactured for its location, with features like pre-drilled holes to accommodate plumbing and electrical connections. (“So someone knows where the number goes, and that side A connects to side B?” asked Vladimir Bulovic, the faculty lead on the design and construction of MIT.nano. “Just like my Ikea furniture, but bigger.” The construction experts did not dismiss the comparison.)

Working with Ontario-based steel fabricator, Canatal, Johnson and his colleagues at Turner developed a four-dimensional plan for steel engineering, delivery, and installation. “We went through a painstaking process to maximize efficiency of this sequence,” says Johnson. “This allows us to avoid times when a crane is down because it’s waiting” for a delivery of steel.

As the structure grows, engineers continuously monitor the basement walls and foundation of the structure with inclinometers, a seismograph, and a three-dimensional laser scanner to gauge how they are responding to the additional weight of the steel. The corner braces in the building’s 50-foot-deep excavation that counteract pressure coming from outside the walls will be removed after the steel is finished and concrete is poured on the building’s first floor. “The building is performing the way we expected it to,” said Richard Amster, director of campus construction.

“Just Add Salt” Drexel U Researchers Discover Method for Improvong Energy Storage Materials: May also offer attractive properties for Desalination Membranes and Photocatalysis


energy_storage_2013 042216 _11-13-1The secret to making the best energy storage materials is growing them with as much surface area as possible. Like baking, it requires just the right mixture of ingredients prepared in a specific amount and order at just the right temperature to produce a thin sheet of material with the perfect chemical consistency to be useful for storing energy.

A team of researchers from Drexel University, Huazhong University of Science and Technology (HUST) and Tsinghua University recently discovered a way to improve the recipe and make the resulting materials bigger and better and soaking up energy—the secret? Just add salt.

The team’s findings, which were recently published in the journal Nature Communications, show that using salt crystals as a template to grow thin sheets of conductive metal oxides make the materials turn out larger and more chemically pure—which makes them better suited for gathering ions and storing energy.

“The challenge of producing a metal oxide that reaches theoretical performance values is that the methods for making it inherently limit its size and often foul its chemical purity, which makes it fall short of predicted performance,” said Jun Zhou, a professor at HUST’s Wuhan National Laboratory for Optoelectronics and an author of the research. Our research reveals a way to grow stable with less fouling that are on the order of several hundreds of times larger than the ones that are currently being fabricated.”

In an energy storage device—a battery or a capacitor, for example—energy is contained in the chemical transfer of ions from an electrolyte solution to thin layers of conductive materials. As these devices evolve they’re becoming smaller and capable of holding an electric charge for longer periods of time without needing a recharge. The reason for their improvement is that researchers are fabricating materials that are better equipped, structurally and chemically, for collecting and disbursing ions.

In theory, the best materials for the job should be thin sheets of metal oxides, because their chemical structure and high makes it easy for ions to attach—which is how energy storage occurs. But the metal oxide sheets that have been fabricated in labs thus far have fallen well short of their theoretical capabilities.

According to Zhou, Tang and the team from HUST, the problem lies in the process of making the nanosheets—which involves either a deposition from gas or a chemical etching—often leaves trace chemical residues that contaminate the material and prevent ions from bonding to it. In addition, the materials made in this way are often just a few square micrometers in size.

Using salt crystals as a substrate for growing the crystals lets them spread out and form a larger sheet of oxide material. Think of it like making a waffle by dripping batter into a pan versus pouring it into a big waffle iron; the key to getting a big, sturdy product is getting the solution—be it batter, or chemical compound—to spread evenly over the template and stabilize in a uniform way.

“This method of synthesis, called ‘templating’—where we use a sacrificial material as a substrate for growing a crystal—is used to create a certain shape or structure,” said Yury Gogotsi, PhD, University and Trustee Chair professor in Drexel’s College of Engineering and head of the A.J. Drexel Nanomaterials Institute, who was an author of the paper. “The trick in this work is that the crystal structure of salt must match the crystal structure of the oxide, otherwise it will form an amorphous film of oxide rather than a thing, strong and stable nanocrystal. This is the key finding of our research—it means that different salts must be used to produce different oxides.”

Researchers have used a variety of chemicals, compounds, polymers and objects as growth templates for nanomaterials. But this discovery shows the importance of matching a template to the structure of the material being grown. Salt crystals turn out to be the perfect substrate for growing oxide sheets of magnesium, molybdenum and tungsten.

The precursor solution coats the sides of the salt crystals as the oxides begin to form. After they’ve solidified, the salt is dissolved in a wash, leaving nanometer-thin two-dimensional sheets that formed on the sides of the salt crystal—and little trace of any contaminants that might hinder their energy storage performance. By making oxide nanosheets in this way, the only factors that limit their growth is the size of the salt crystal and the amount of precursor solution used.

“Lateral growth of the 2D oxides was guided by salt crystal geometry and promoted by lattice matching and the thickness was restrained by the raw material supply. The dimensions of the are tens of micrometers and guide the growth of the 2D oxide to a similar size,” the researchers write in the paper. “On the basis of the naturally non-layered crystal structures of these oxides, the suitability of salt-assisted templating as a general method for synthesis of 2D oxides has been convincingly demonstrated.”

As predicted, the larger size of the oxide sheets also equated to a greater ability to collect and disburse ions from an electrolyte solution—the ultimate test for its potential to be used in energy storage devices. Results reported in the paper suggest that use of these materials may help in creating an aluminum-ion battery that could store more charge than the best lithium-ion batteries found in laptops and mobile devices today.

Gogotsi, along with his students in the Department of Materials Science and Engineering, has been collaborating with Huazhong University of Science and Technology since 2012 to explore a wide variety of materials for energy storage application. The lead author of the Nature Communications article, Xu Xiao, and co-author Tiangi Li, both Zhou’s doctoral students, came to Drexel as exchange students to learn about the University’s supercapacitor research. Those visits started a collaboration, which was supported by Gogotsi’s annual trips to HUST. While the partnership has already yielded five joint publications, Gogotsi speculates that this work is only beginning.

“The most significant result of this work thus far is that we’ve demonstrated the ability to generate high-quality 2D oxides with various compositions,” Gogotsi said. “I can certainly see expanding this approach to other oxides that may offer attractive properties for , water desalination membranes, photocatalysis and other applications.”

Explore further: New nanosheet growth technique has potential to revolutionize nanotechnology industry

More information: Nature Communications, DOI: 10.1038/NCOMMS11296

 

U of California Irvine: Researchers Create “Nano-Wire” Based Battery that Would Never Require Replacement


UC Battery 042216 id43192University of California, Irvine researchers have invented nanowire-based battery material that can be recharged hundreds of thousands of times, moving us closer to a battery that would never require replacement. The breakthrough work could lead to commercial batteries with greatly lengthened lifespans for computers, smartphones, appliances, cars and spacecraft.
Scientists have long sought to use nanowires in batteries. Thousands of times thinner than a human hair, they’re highly conductive and feature a large surface area for the storage and transfer of electrons. However, these filaments are extremely fragile and don’t hold up well to repeated discharging and recharging, or cycling. In a typical lithium-ion battery, they expand and grow brittle, which leads to cracking.
UCI researchers have solved this problem by coating a gold nanowire in a manganese dioxide shell and encasing the assembly in an electrolyte made of a Plexiglas-like gel. The combination is reliable and resistant to failure.
text
UCI chemist Reginald Penner (shown) and doctoral candidate Mya Le Thai have developed a nanowire-based technology that allows lithium-ion batteries to be recharged hundreds of thousands of times.
The study leader, UCI doctoral candidate Mya Le Thai, cycled the testing electrode up to 200,000 times over three months without detecting any loss of capacity or power and without fracturing any nanowires. The findings were published today in the American Chemical Society’s Energy Letters (“100k Cycles and Beyond: Extraordinary Cycle Stability for MnO2Nanowires Imparted by a Gel Electrolyte”).
Hard work combined with serendipity paid off in this case, according to senior author Reginald Penner.
“Mya was playing around, and she coated this whole thing with a very thin gel layer and started to cycle it,” said Penner, chair of UCI’s chemistry department. “She discovered that just by using this gel, she could cycle it hundreds of thousands of times without losing any capacity.”
“That was crazy,” he added, “because these things typically die in dramatic fashion after 5,000 or 6,000 or 7,000 cycles at most.”
The researchers think the goo plasticizes the metal oxide in the battery and gives it flexibility, preventing cracking.
“The coated electrode holds its shape much better, making it a more reliable option,” Thai said. “This research proves that a nanowire-based battery electrode can have a long lifetime and that we can make these kinds of batteries a reality.”
The study was conducted in coordination with the Nanostructures for Electrical Energy Storage Energy Frontier Research Center at the University of Maryland, with funding from the Basic Energy Sciences division of the U.S. Department of Energy.
Source: University of California, Irvine

Read more: Chemists create battery technology with off-the-charts charging capacity

‘On-Demand ‘ Nanotube Forests’ for Electronics Fabrication


Nanotube Forrests 042116 id43200A system that uses a laser and electrical current to precisely position and align carbon nanotubes represents a potential new tool for creating electronic devices out of the tiny fibers.
 

Because carbon nanotubes have unique thermal and electrical properties, they may have future applications in electronic cooling and as devices in microchips, sensors and circuits. Being able to orient the carbon nanotubes in the same direction and precisely position them could allow these nanostructures to be used in such applications.

However, it is difficult to manipulate something so small that thousands of them would fit within the diameter of a single strand of hair, said Steven T. Wereley, a professor of mechanical engineering at Purdue University.
“One of the things we can do with this technique is assemble carbon nanotubes, put them where we want and make them into complicated structures,” he said.

 

This graphic illustrates a system that uses a laser and electrical field to precisely position and align carbon nanotube
This graphic illustrates a system that uses a laser and electrical field to precisely position and align carbon nanotubes, representing a potential new tool for assembling sensors and devices out of the tiny nanotubes and nanowires. The two microscope images at the bottom show the nanotubes aligned (left) and returning to their random orientation after the electric field and laser were turned off. (Image: Avanish Mishra and Steven Wereley)
New findings from research led by Purdue doctoral student Avanish Mishra are detailed in a paper that has appeared online March 24 in the journal Microsystems and Nanoengineering (“Dynamic optoelectric trapping and deposition of multiwalled carbon nanotubes”).
The technique, called rapid electrokinetic patterning (REP), uses two parallel electrodes made of indium tin oxide, a transparent and electrically conductive material. The nanotubes are arranged randomly while suspended in deionized water. Applying an electric field causes them to orient vertically. Then an infrared laser heats the fluid, producing a doughnut-shaped vortex of circulating liquid between the two electrodes. This vortex enables the researchers to move the nanotubes and reposition them.
“When we apply the electric field, they are immediately oriented vertically, and then when we apply the laser, it starts a vortex, that sweeps them into little nanotube forests,” Wereley said.
The research paper was authored by Mishra; Purdue graduate student Katherine Clayton; University of Louisville student Vanessa Velasco; Stuart J. Williams, an assistant professor of mechanical engineering at the University of Louisville and director of the Integrated Microfluidic Systems Laboratory; and Wereley. Williams is a former doctoral student at Purdue.
The technique overcomes limitations of other methods for manipulating particles measured on the scale of nanometers, or billionths of a meter. In this study, the procedure was used for multiwalled carbon nanotubes, which are rolled-up ultrathin sheets of carbon called graphene. However, according to the researchers, using this technique other nanoparticles such as nanowires and nanorods can be similarly positioned and fixed in vertical orientation.
The researchers have received a U.S. patent on the system.
The experimental work was performed at the Birck Nanotechnology Center in Purdue’s Discovery Park. Future research will explore using the technique to create devices.
Source: By Emil Venere, Purdue University