New materials Powering the battery Revolution


More phones than people images

There are more mobile phones in the world than there are people. Nearly all of them are powered by rechargeable lithium-ion batteries, which are the single most important component enabling the portable electronics revolution of the past few decades. 

None of those devices would be attractive to users if they didn’t have enough power to last at least several hours, without being particularly heavy.

Lithium-ion batteries are also useful in larger applications, like electric vehicles and smart-grid energy storage systems. And researchers’ innovations in materials science, seeking to improve lithium-ion batteries, are paving the way for even more batteries with even better performance. There is already demand forming for high-capacity batteries that won’t catch fire or explode. And many people have dreamed of smaller, lighter batteries that charge in minutes – or even seconds – yet store enough energy to power a device for days.

New Battery Materialsfile-20181001-195256-1e68x0s

Research is finding better ways to make batteries both big and small. 

Researchers like me, though, are thinking even more adventurously. Cars and grid-storage systems would be even better if they could be discharged and recharged tens of thousands of times over many years, or even decades. Maintenance crews and customers would love batteries that could monitor themselves and send alerts if they were damaged or no longer functioning at peak performance – or even were able to fix themselves. And it can’t be too much to dream of dual-purpose batteries integrated into the structure of an item, helping to shape the form of a smartphone, car or building while also powering its functions.

All that may become possible as my research and others’ help scientists and engineers become ever more adept at controlling and handling matter at the scale of individual atoms.

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3d Illustration of twist sodium ion battery technology

Emerging materials

For the most part, advances in energy storage will rely on the continuing development of materials science, pushing the limits of performance of existing battery materials and developing entirely new battery structures and compositions.

The battery industry is already working to reduce the cost of lithium-ion batteries, including by removing expensive cobalt from their positive electrodes, called cathodes. This would also reduce the human cost of these batteries, because many mines in Congo, the world’s leading source of cobalt, use children to do difficult manual labor.

Workers at a cobalt-copper mine in the Democratic Republic of Congo. Kenny-Katombe Butunka/Reuters

Researchers are finding ways to replace the cobalt-containing materials with cathodes made mostly of nickel. Eventually they may be able to replace the nickel with manganese. Each of those metals is cheaper, more abundant and safer to work with than its predecessor. But they come with a trade-off, because they have chemical properties that shorten their batteries’ lifetimes.

Researchers are also looking at replacing the lithium ions that shuttle between the two electrodes with ions and electrolytes that may be cheaper and potentially safer, like those based on sodium, magnesium, zinc or aluminum.

graphene-supercapacitorMy research group looks at the possibilities of using two-dimensional materials, essentially extremely thin sheets of substances with useful electronic properties. Graphene is perhaps the best-known of these – a sheet of carbon just one atom thick. We want to see whether stacking up layers of various two-dimensional materials and then infiltrating the stack with water or other conductive liquids could be key components of batteries that recharge very quickly.

Looking inside the battery

It’s not just new materials expanding the world of battery innovation: New equipment and methods also let researchers see what’s happening inside batteries much more easily than was once possible.

In the past, researchers ran a battery through a particular charge-discharge process or number of cycles, and then removed the material from the battery and examined it after the fact. Only then could scholars learn what chemical changes had happened during the process and infer how the battery actually worked and what affected its performance.

X-rays generated by a synchotron can illuminate the inner workings of a battery. CLS Research Office/flickrCC BY-SA

But now, researchers can watch battery materials as they undergo the energy storage process, analyzing even their atomic structure and composition in real time. We can use sophisticated spectroscopy techniques, such as X-ray techniques available with a type of particle accelerator called a synchrotron – as well as electron microscopes and scanning probes – to watch ions move and physical structures change as energy is stored in and released from materials in a battery.

Those methods let researchers like me imagine new battery structures and materials, make them and see how well – or not – they work. That way, we’ll be able to keep the battery materials revolution going.

Re-Posted from  An Assistant Professor of Materials Science and Engineering, North Carolina State University

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NV-doped Nanodiamonds may “serve as the basic building blocks” for quantum computing – N.Carolina State University


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Researchers at North Carolina State University have developed a new technique for creating NV-doped single-crystal nanodiamonds, only four to eight nanometers wide, which could serve as components in room-temperature quantum computing technologies. These doped nanodiamonds also hold promise for use in single-photon sensors and nontoxic, fluorescent biomarkers.

Currently, computers use binary logic, in which each binary unit – or bit – is in one of two states: 1 or 0. Quantum computing makes use of superposition and entanglement, allowing the creation of quantum bits – or qubits – which can have a vast number of possible states. Quantum computing has the potential to significantly increase computing power and speed.

A number of options have been explored for creating quantum computing systems, including the use of diamonds that have “nitrogen-vacancy” centers. That’s where this research comes in.

Normally, diamond has a very specific , consisting of repeated diamond tetrahedrons, or cubes. Each cube contains five carbon atoms. The NC State research team has developed a new technique for creating diamond tetrahedrons that have two ; one vacancy, where an atom is missing; one carbon-13 atom (a stable carbon isotope that has six protons and seven neutrons); and one nitrogen atom. This is called the NV center. Each NV-doped nanodiamond contains thousands of atoms, but has only one NV center; the remainder of the tetrahedrons in the nanodiamond are made solely of carbon.

It’s an atomically small distinction, but it makes a big difference.nano-diamonds-35-newtechnique

“That little dot, the NV center, turns the nanodiamond into a qubit,” says Jay Narayan, the John C. Fan Distinguished Chair Professor of Materials Science and Engineering at NC State and lead author of a paper describing the work. “Each NV center has two transitions: NV0 and NV-. We can go back and forth between these two states using electric current or laser. These nanodiamonds could serve as the basic building blocks of a quantum computer.”

To create these NV-doped nanodiamonds, the researchers start with a substrate, such as such as sapphire, glass or a plastic polymer. The substrate is then coated with amorphous carbon – elemental carbon that, unlike graphite or diamond, does not have a regular, well-defined crystalline structure. While depositing the film of amorphous carbon, the researchers bombard it with nitrogen ions and carbon-13 ions. The carbon is then hit with a laser pulse that raises the temperature of the carbon to approximately 4,000 Kelvin (or around 3,727 degrees Celsius) and is then rapidly quenched. The operation is completed within a millionth of a second and takes place at one atmosphere – the same pressure as the surrounding air. By using different substrates and changing the duration of the laser pulse, the researchers can control how quickly the carbon cools, which allows them to create the nanodiamond structures.

“Our approach reduces impurities; controls the size of the NV-doped nanodiamond; allows us to place the nanodiamonds with a fair amount of precision; and directly incorporates carbon-13 into the material, which is necessary for creating the entanglement required in quantum computing,” Narayan says. “All of the nanodiamonds are exactly aligned through the paradigm of domain matching epitaxy, which is a significant advance over existing techniques for creating NV-doped nanodiamonds.”

“The not only offers unprecedented control and uniformity in the NV-doped nanodiamonds, it is also less expensive than existing techniques,” Narayan says. “Hopefully, this will enable significant advances in the field of quantum computing.”

The researchers are currently talking with government and private sector groups about how to move forward. One area of interest is to develop a means of creating self-assembling systems that incorporate entangled NV-doped nanodiamonds for .

The paper, “Novel synthesis and properties of pure and NV-doped nanodiamonds and other nanostructures,” is published in the journal Materials Research Letters.

 

Also Read: Electron ‘spin control’ of levitated nanodiamonds could bring advances in sensors, quantum information processing Read more at: http://phys.org/news/2016-07-electron-levitated-nanodiamonds-advances-sensors.html#jCp

More information: Jagdish Narayan et al, Novel synthesis and properties of pure and NV-doped nanodiamonds and other nanostructures, Materials Research Letters (2016). DOI: 10.1080/21663831.2016.1249805

 

Wearable sensor clears path to long-term EKG, EMG monitoring


January 20, 2015
Source: North Carolina State University
Wearable Sensors 150120102500-largeSummary:
A new, wearable sensor that uses silver nanowires to monitor electrophysiological signals, such as electrocardiographyor electromyography, has been developed by researchers. The new sensor is as accurate as the ‘wet electrode’ sensors used in hospitals, but can be used for long-term monitoring and is more accurate than existing sensors when a patient is moving.
Researchers from North Carolina State University have developed a new, wearable sensor that uses silver nanowires to monitor electrophysiological signals, such as electrocardiography (EKG) or electromyography (EMG). The new sensor is as accurate as the “wet electrode” sensors used in hospitals, but can be used for long-term monitoring and is more accurate than existing sensors when a patient is moving.

Long-term monitoring of electrophysiological signals can be used to track patient health or assist in medical research, and may also be used in the development of new powered prosthetics that respond to a patient’s muscular signals.

The silver nanowire sensors conform to a patient’s skin, creating close contact. Image credit: Yong Zhu. Click to enlarge.

Electrophysiological sensors used in hospitals, such as EKGs, use wet electrodes that rely on an electrolytic gel between the sensor and the patient’s skin to improve the sensor’s ability to pick up the body’s electrical signals. However, this technology poses problems for long-term monitoring, because the gel dries up — irritating the patient’s skin and making the sensor less accurate.

The new nanowire sensor is comparable to the wet sensors in terms of signal quality, but is a “dry” electrode — it doesn’t use a gel layer, so doesn’t pose the same problems that wet sensors do.

“People have developed other dry electrodes in the past few years, and some have demonstrated the potential to rival the wet electrodes, but our new electrode has better signal quality than most — if not all — of the existing dry electrodes. It is more accurate,” says Dr. Yong Zhu, an associate professor of mechanical and aerospace engineering at NC State and senior author of a paper describing the work. “In addition, our electrode is mechanically robust, because the nanowires are inlaid in the polymer.”

The sensors stem from Zhu’s earlier work to create highly conductive and elastic conductors made from silver nanowires, and consist of one layer of nanowires in a stretchable polymer.

The new sensor is also more accurate than existing technologies at monitoring electrophysiological signals when a patient is in motion.

“The silver nanowire sensors conform to a patient’s skin, creating close contact,” Zhu says. “And, because the nanowires are so flexible, the sensor maintains that close contact even when the patient moves. The nanowires are also highly conductive, which is key to the high signal quality.”

The new sensors are also compatible with standard EKG- and EMG-reading devices.

“I think these sensors are essentially ready for use,” Zhu says “The raw materials of the sensor are comparable in cost to existing wet sensors, but we are still exploring ways of improving the manufacturing process to reduce the overall cost.”

An uncorrected proof of the paper, “Wearable Silver Nanowire Dry Electrodes for Electrophysiological Sensing,” was published online Jan. 14 in RSC Advances, immediately after acceptance. Lead author of the paper is Amanda Myers, a Ph.D. student at NC State. The paper was co-authored by Dr. Helen Huang, an associate professor in the joint biomedical engineering program at NC State and the University of North Carolina at Chapel Hill.


Story Source:

The above story is based on materials provided by North Carolina State University. Note: Materials may be edited for content and length.

Direct printing of liquid metal 3D microstructures


By Michael Berger. Copyright © Nanowerk

Nano Particles for Steel 324x182(Nanowerk Spotlight) The ability to pattern materials  into arbitrary three-dimensional (3D) microstructures is important for  electronics, microfluidic networks, tissue engineering scaffolds, photonic band  gap structures, and chemical synthesis.

However, existing commercial processes  to 3D print metals usually require expensive equipment and large temperatures.

In contrast, a novel, relatively simple method developed by researchers at North  Carolina State University can print metal structures at room temperature. This  makes the technique it compatible with many other materials including plastics.  Also, the resulting structures are liquid and are therefore soft and  stretchable.

“The key concept is that the liquid metal forms spontaneously a  thin oxide layer on its surface,” Michael Dickey, an Associate Professor of chemical and  biomolecular engineering at NC State, tells Nanowerk. This oxide layer is solid  and allows the metal to be printed into 3D shapes despite being a liquid.  When  two droplets of water come together, they form a larger droplet.  However, this  does not happen with the liquid metal due to the oxide ‘skin’.”   As the team reports in a recent issue of Advanced  Materials (“3D Printing of Free Standing Liquid Metal  Microstructures”), they have demonstrated that it is possible to direct  write structures composed of a low-viscosity liquid with metallic conductivity  at room temperature. The liquid metal is useful for soft, stretchable, or shape  reconfigurable electronics.

  Direct writing of liquid metal 3D structures

Direct writing of liquid metal 3D structures of varying sizes.  (Image: Dickey Research Group, North Carolina State University) (click image to  enlarge)  

Metals have unique electrical, optical, and thermal properties.  With this novel technique, it is now possible to print metal microstructures  directly to creates various parts including electronics. The resulting parts, if  designed correctly, can be stretchable.    The general approach for printing liquid metal structures  involves applying modest gauge pressure to a syringe needle that then extrudes  the liquid metal – for this work they used the binary eutectic alloy of gallium  and indium but they say that any alloy of gallium will also work – onto a  substrate controlled by a motorized translation stage.   Upon exposure to air, the metal forms a thin (∼1 nanometer)  passivating ‘skin’ composed of gallium oxide. This oxide skin on the surface of  the metal stabilizes the liquid metal wire against gravity and surface tension  of the liquid. Once detached from the syringe, the wires maintain their shape.

3D printing of liquid metals at room temperature.  

“The formation of the wires is remarkable and unexpected” says  Dickey. “The process of forming the wires begins by forming a bead of the metal  on the tip of the syringe.

Although the metal is under pressure the entire time,  it does not flow out of the syringe due to the stabilizing influence of the  oxide skin. Without increasing or decreasing the pressure in the syringe, wires  form when the metal contacts the substrate and the tip of the syringe withdraws  away from the substrate. Because the oxide skin spans from the nozzle of the  syringe to the substrate, increasing the distance between the nozzle and  substrate generates a tensile force along the axis of the wire that yields the  skin and allows the wire to elongate.

The pressure of the liquid metal retards  any destabilizing capillary forces long enough for new skin to form and thereby  mechanically stabilizes the wire.”   Altogether, the researchers describe four different methods to  direct write 3D, free standing, liquid metal microstructures by extruding the  liquid metal through a capillary: “In addition to extruding wires, it is  possible to form free standing liquid metal microstructures using at least three  additional methods,” Dickey explains: “1) Expelling rapidly the metal to form a  stable liquid metal filament; 2) stacking droplets; and 3) injecting the metal  into microchannels and subsequently removing the channels chemically.”

The smallest components that the team fabricated were about 10  µm, but they note that there may be opportunities to create smaller structures  through, for example, the use of smaller nozzles.   Dickey’s team is currently exploring how to further develop  these techniques, as well as how to use them in various electronics applications  and in conjunction with established 3-D printing technologies.

Dickey notes that the work by an undergraduate student, Collin  Ladd, also the paper’s first author, was indispensable to this project. “He  helped develop the concept, and literally created some of this technology out of  spare parts he found himself.”

Read more: http://www.nanowerk.com/spotlight/spotid=32574.php#ixzz2hLXHYA7S

Self-Healing Solar Cells


Large Solar panelsTo understand how solar cells heal themselves, look no further than the nearest tree leaf or the back of your hand.

The “branching” vascular channels that circulate life-sustaining nutrients throughout leaves and hands serve as the inspiration for solar cells that can restore themselves efficiently and inexpensively.

 

 

In a new paper, North Carolina State University researchers Orlin Velev and Hyung-Jun Koo show that creating solar cell devices with channels that mimic organic vascular systems can effectively reinvigorate solar cells whose performance deteriorates due to degradation by the sun’s ultraviolet rays. Solar cells that are based on organic systems hold the potential to be less expensive and more environmentally friendly than silicon-based solar cells, the current industry standard.

 

The design of NC State's regenerative solar cell mimics nature by use of microfluidic channels.

The nature-mimicking devices are a type of dye-sensitized solar cells (DSSCs), composed of a water-based gel core, electrodes, and inexpensive, light-sensitive, organic dye molecules that capture light and generate electric current. However, the dye molecules that get “excited” by the sun’s rays to produce electricity eventually degrade and lose efficiency, Velev says, and thus need to be replenished to reboot the device’s effectiveness in harnessing the power of the sun.

Organic material in DSSCs tends to degrade, so we looked to nature to solve the problem,” Velev said. “We considered how the branched network in a leaf maintains water and nutrient levels throughout the leaf. Our microchannel solar cell design works in a similar way. Photovoltaic cells rendered ineffective by high intensities of ultraviolet rays were regenerated by pumping fresh dye into the channels while cycling the exhausted dye out of the cell. This process restores the device’s effectiveness in producing electricity over multiple cycles.”

Velev, Invista Professor of Chemical and Biomolecular Engineering at NC State and the lead author of a paper in Scientific Reports describing the research, adds that the new gel-microfluidic cell design was tested against other designs, and that branched channel networks similar to the ones found in nature worked most effectively.

Study co-author Dr. Hyung-Jun Koo is a former NC State Ph.D. student who is now a postdoctoral researcher at the University of Illinois. The study was funded by the National Science Foundation and the U.S. Department of Energy.

Koo and Velev reported earlier a new type of biomimetic hydrogel solar cell.

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Note to editors: The abstract of the paper follows.

“Regenerable Photovoltaic Devices with a Hydrogel-Embedded Microvascular Network”

Authors: Hyung-Jun Koo and Orlin D. Velev, NC State University

Published: Aug. 5, 2013, in Scientific Reports

DOI: 10.1038/srep02357

Abstract: Light-driven degradation of photoactive molecules could be one of the major obstacles to stable long term operation of organic dye-based solar light harvesting devices. One solution to this problem may be mimicking the regeneration functionality of a plant leaf. We report an organic dye photovoltaic system that has been endowed with such microfluidic regeneration functionality. A hydrogel medium with embedded channels allows rapid and uniform supply of photoactive reagents by a convection-diffusion mechanism. A washing-activation cycle enables reliable replacement of the organic component in a dye-sensitized photovoltaic system.

 

Release Date: 08.07.13 Filed under Releases

 

 

Interface Properties of Graphene Paves Way for New Applications


201306047919620Researchers from North Carolina State University and the University of Texas have revealed more about graphene’s mechanical properties and demonstrated a technique to improve the stretchability of graphene – developments that should help engineers and designers come up with new technologies that make use of the material.

Graphene is a promising material that is used in technologies such as transparent, flexible electrodes and nanocomposites. And while engineers think graphene holds promise for additional applications, they must first have a better understanding of its mechanical properties, including how it works with other materials.

“This research tells us how strong the interface is between graphene and a stretchable substrate,” says Dr. Yong Zhu, an associate professor of mechanical and aerospace engineering at NC State and co-author of a paper on the work. “Industry can use that to design new flexible or stretchable electronics and nanocomposites. For example, it tells us how much we can deform the material before the interface between graphene and other materials fails. Our research has also demonstrated a useful approach for making graphene-based, stretchable devices by ‘buckling’ the graphene.”

The researchers looked at how a graphene monolayer – a layer of graphene only one atom thick – interfaces with an elastic substrate. Specifically, they wanted to know how strong the bond is between the two materials because that tells engineers how much strain can be transferred from the substrate to the graphene, which determines how far the graphene can be stretched.

The researchers applied a monolayer of graphene to a polymer substrate, and then stretched the substrate. They used a spectroscopy technique to monitor the strain at various points in the graphene. Strain is a measure of how far a material has stretched.

Initially, the graphene stretched with substrate. However, while the substrate continued to stretch, the graphene eventually began to stretch more slowly and slide on the surface instead. Typically, the edges of the monolayer began to slide first, with the center of the monolayer stretching further than the edges.

“This tells us a lot about the interface properties of the graphene and substrate,” Zhu says. “For the substrate used in this study, polyethylene terephthalate, the edges of the graphene monolayer began sliding after being stretched 0.3 percent of its initial length. But the center continued stretching until the monolayer had been stretched by 1.2 to 1.6 percent.”

The researchers also found that the graphene monolayer buckled when the elastic substrate was returned to its original length. This created ridges in the graphene that made it more stretchable because the material could stretch out and back, like the bellows of an accordion. The technique for creating the buckled material is similar to one developed by Zhu’s lab for creating elastic conductors out of carbon nanotubes.

The paper, “Interfacial Sliding and Buckling of Monolayer Graphene on a Stretchable Substrate,” was published online Aug. 1 in Advanced Functional Materials. Lead author of the paper is Dr. Tao Jiang, a postdoctoral researcher at NC State. The paper was co-authored by Dr. Rui Huang of the University of Texas. The research was funded by the National Science Foundation (NSF) and the NSF’s ASSIST Engineering Research Center at NC State.

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Note to Editors: The study abstract follows.

“Interfacial Sliding and Buckling of Monolayer Graphene on a Stretchable Substrate”

Authors: Tao Jiang and Yong Zhu, North Carolina State University; Rui Huang, University of Texas at Austin

Published: Aug. 1 2013, Advanced Functional Materials

Elastic conductors for new sensing applications


201306047919620Researchers from North Carolina State University have developed elastic conductors made from silver nanowires, as the basis of stretchable electronic devices.

The silver nanowires can be printed to fabricate patterned stretchable conductorsStretchable circuitry could be used, for example, to create tactile, strain and motion sensors in wearable or conformable applications.

Dr Yong Zhu, an assistant professor of mechanical and aerospace engineering at NC State, and Feng Xu, a PhD student in Zhu’s lab have developed elastic conductors using silver nanowires. Silver has very high electric conductivity. The technique developed at NC State embeds silver nanowires in a polymer that can withstand significant stretching without adversely affecting the material’s conductivity. This makes it attractive as a component for use in stretchable electronic devices.

Simple fabrication

Silver nanowires are placed on a silicon plate and a liquid polymer is poured over the silicon substrate, which flows around the silver nanowires. High heat turns the polymer from a liquid into an elastic solid, trapping the nanowires in the polymer. The polymer is peeled off the silicon plate.

Zhu says the elastic conductor technology could be commercially viable within five years. Fabrication is simple and is compatible with printing and patterning techniques, including screen and inkjet. Zhu’s team has made some prototypes, filed for patents and discussions about next steps towards commercialisation are taking place. When the polymer is stretched and relaxed, the surface containing nanowires buckles, creating a composite that is wavy on the side that contains silver nanowires and flat on the other.

After the nanowire-embedded surface has buckled, the material can be stretched up to 50% of its elongation, or tensile strain, without affecting the conductivity of the silver nanowires, because the buckled shape of the material allows the nanowires to stay in a fixed position in relation to each other, as the polymer is being stretched.

The research was supported by the National Science Foundation.

Nano-particles Release Insulin into Diabetics’ Bloodstream


QDOTS imagesCAKXSY1K 8Diabetics could cut their need for injections to less than once a week thanks  to new insulin-releasing “smart” particles.

Researchers in the US have developed a type of nanoparticle that  automatically releases insulin into the blood when glucose levels get too high,  and have demonstrated that its effects last for 10 days in mice.

Regular injections of the particles could mean type 1 diabetics  wouldn’t have to check their blood sugar levels several times a day, or inject  the exact right amount of insulin when needed, which can result in too high or  low doses being administered, with further health problems following.

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‘We’ve created a ‘smart’ system that is injected into the body and  responds to changes in blood sugar by releasing insulin, effectively controlling  blood-sugar levels,’ said Dr Zhen Gu, an assistant professor in the joint  biomedical engineering program at North Carolina State University and the  University of North Carolina.

‘This technology effectively creates a ‘closed-loop’ system that mimics  the activity of the pancreas in a healthy person, releasing insulin in response  to glucose level changes. This has the potential to improve the health and  quality of life of diabetes patients.’

The nanoparticles have a solid core of insulin surrounded by a layer of  a modified glucose-based material known as dextran and another of glucose  oxidase enzymes.

When the enzymes are exposed to high glucose levels they effectively  convert the sugar into gluconic acid, which breaks down the modified dextran and  releases the insulin.

The insulin then brings the glucose levels under control. The gluconic  acid and dextran are biocompatible and dissolve in the body.

The nanoparticle cores are given a biocompatible coating that makes  them positively or negatively charged, causing them to form a network that  prevents them from dispersing throughout the body.

The positively charged coatings are made of chitosan (a material  normally found in shrimp shells), abnd the negatively charged coatings are made  of alginate (a material normally found in seaweed).

When the solution of coated nanoparticles is mixed together, the  positively and negatively charged coatings are attracted to each other to form a “nano-network.”

Once injected into the subcutaneous layer of the skin, the nano-network  holds the nanoparticles together. Both the nano-network and the coatings are  porous, allowing blood – and blood sugar – to reach the nanoparticle cores.

Gu’s research team is now in discussions to move the technology into  clinical trials for use in humans.

A paper on the research has been published in the scientific journal  ACS Nano.

Read more:  http://www.theengineer.co.uk/medical-and-healthcare/news/smart-particles-release-insulin-into-diabetics-bloodstream/1016213.article#ixzz2ScNHSXmx

Major Breakthroughs in Solar Technology for 2013


QDOTS imagesCAKXSY1K 8Despite a tough market leading to widespread cost reductions and negative returns for many operators in the photovoltaic sector in 2012, solar technology nonetheless took major strides and achieved a number of landmark breakthroughs in key research areas.

 

In materials research, the North Carolina State University (NCSU) in Raleigh, North Carolina used cutting-edge nanotechnology to develop slimmer and more affordable solar cells.

The cells are comprised of sandwiched nanostructures which not only cut down on material usage and expenditures but also improve solar absorption and raise conversion efficiency.

As an added bonus, the manufacturing processes for the new technology are compatible with techniques currently employed throughout the industry for the production of thin-film solar cells.

In terms of government-funded initiatives, the National Renewable Energy Laboratory (NREL), a research arm of the US Department of Energy, teamed up with Natcore Technology to create the most absorbent solar cell ever devised, capable of capturing some 99.7 per cent of available sunlight.

 The new technology resulting from this collaborative effort between the government and private sectors could reduce the cost of solar cells by around two to three per cent while lifting energy output by up to 10 per cent. The black silicon used for the cells is also far cheaper than standard anti-reflection technologies.
nanotechnology-solar-cells-1A key area of research for 2012 was improved storage techniques for renewable energies, with scientists from Houston’s Rice University in Texas developing a remarkable “paintable” battery which can be applied to any tractable surface. The rechargeable battery opens a new vista of possibilities for the convenient storage of solar energy.

In the field of flexible thin-film cells, a joint undertaking between scientists from Canada and Saudi Arabia smashed the world record for solar efficiency, surpassing the ousted place holder by a staggering 37 per cent. The colloidal quantum dot (CQD) thin-film solar cell, developed by scientists from Canada’s University of Toronto and the King Abdullah University of Science & Technology in Saudi Arabia, achieved a world-record efficiency level of seven per cent via the application of a “hybrid passivation scheme.”

The new technology could potentially be applied to the cheap, mass manufacture of thin-film solar cells by using flexible substrates to “print” the devices in a process akin to that traditionally employed for the production of newspapers.paintable-battery-rice-university

 

 

Researchers Create ‘Nanoflowers’ for Energy Storage, Solar Cells


Release Date: 10.11.2012

Researchers from North Carolina State University have created flower-like structures out of germanium sulfide (GeS) – a semiconductor material – that have extremely thin petals with an enormous surface area. The GeS flower holds promise for next-generation energy storage devices and solar cells.

 

 

 

 

 

Matt Shipman |

Dr. Linyou Cao |

The GeS “nanoflowers” have petals only 20-30 nanometers thick, and provide a large surface area in a small amount of space. (Click to enlarge image.)

“Creating these GeS nanoflowers is exciting because it gives us a huge surface area in a small amount of space,” says Dr. Linyou Cao, an assistant professor of materials science and engineering at NC State and co-author of a paper on the research. “This could significantly increase the capacity of lithium-ion batteries, for instance, since the thinner structure with larger surface area can hold more lithium ions. By the same token, this GeS flower structure could lead to increased capacity for supercapacitors, which are also used for energy storage.”

To create the flower structures, researchers first heat GeS powder in a furnace until it begins to vaporize. The vapor is then blown into a cooler region of the furnace, where the GeS settles out of the air into a layered sheet that is only 20 to 30 nanometers thick, and up to 100 micrometers long. As additional layers are added, the sheets branch out from one another, creating a floral pattern similar to a marigold or carnation.

“To get this structure, it is very important to control the flow of the GeS vapor,” Cao says, “so that it has time to spread out in layers, rather than aggregating into clumps.”

GeS is similar to materials such as graphite, which settle into neat layers or sheets. However, GeS is very different from graphite in that its atomic structure makes it very good at absorbing solar energy and converting it into useable power. This makes it attractive for use in solar cells, particularly since GeS is relatively inexpensive and non-toxic. Many of the materials currently used in solar cells are both expensive and extremely toxic.

The paper, “Role of Boundary Layer Diffusion in Vapor Deposition Growth of Chalcogenide Nanosheets: The Case of GeS,” is published online in the journal ACS Nano. The paper was co-authored by Cao; Dr. Chun Li, a former postdoctoral researcher at NC State, now a professor at the University of Electronic Science and Technology of China; Liang Huang, a former visiting Ph.D. student at NC State; Gayatri Pongur Snigdha, a former undergraduate student at NC State; and Yifei Yu, a Ph.D. student at NC State. The work was supported by the U.S. Army Research Office.

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Note to Editors: The study abstract follows.

“Role of Boundary Layer Diffusion in Vapor Deposition Growth of Chalcogenide Nanosheets: The Case of GeS”

Authors: Chun Li, Liang Huang, Gayatri Pongur Snigdha and Linyou Cao, North Carolina State University

Published: Online, ACS Nano

Abstract: We report a synthesis of single crystalline two-dimensional (2D) GeS nanosheets using vapor deposition processes, and show that the growth behavior of the nanosheet is substantially different from those of other nanomaterials and thin films grown by vapor depositions. The nanosheet growth is subject to strong influences of the diffusion of source materials through the boundary layer of gas flows. This boundary layer diffusion is found to be the rate-determining step of the growth under typical experimental conditions, evidenced by a substantial dependence of the nanosheet’s size on diffusion fluxes. We also find that high quality GeS nanosheets can only grow in the diffusion-limited regime, as the crystalline quality substantially deteriorates when the rate-determining step is changed away from the boundary layer diffusion. We establish a simple model to analyze the diffusion dynamics in experiments. Our analysis uncovers an intuitive correlation of diffusion flux with the partial pressure of source materials, the flow rate of carrier gas, and the total pressure in synthetic setup. The observed significant role of boundary layer diffusions in the growth is unique for nanosheets. It may be correlated to the high growth rate of GeS nanosheets, ~3-5 [micrometer]/min, which is one order of magnitude higher than other nanomaterials (such as nanowires) and thin films. This fundamental understanding on the effect of boundary layer diffusions may generally apply to other chalcogenide nanosheets that can grow rapidly. It can provide useful guidance for the development of general paradigms to control the synthesis of nanosheets.