Smart Economy

Novel exfoliation method developed by NUS chemists paves the way for two-dimensional materials to be used in printable photonics and electronics

 

Versatility of new technique shows promise as new benchmark in exfoliation chemistry of two-dimensional chalcogenides

Singapore, 2 January 2014 - A team of scientists from the National University of Singapore (NUS) has successfully developed a method to chemically exfoliate molybdenum disulfide crystals, a class of chalcogenide compounds, into high quality monolayer flakes, with higher yield and larger flake size than current methods. The exfoliated flakes can be made into a printable solution, which can be applied in printable photonics and electronics.

This breakthrough, led by Professor Loh Kian Ping, who heads the Department of Chemistry at the NUS Faculty of Science, and is also a principal investigator with the Graphene Research Centre at the Faculty, has generic applicability to other two-dimensional chalcogenides, such as tungsten diselenide and titanium disulfide, and results in high yield exfoliation for all of these two-dimensional materials.

The NUS team collaborated with scientists from the Ulsan National Institute of Science and Technology in Korea, and the findings were first published online in prestigious scientific journal Nature Communications on 2 January 2014.

Demand for high efficiency exfoliation method

Transition metal dichalcogenides, formed by a combination of chalcogens, such as sulphur or selenium, and transition metals, such as molybdenum or tungsten, have recently attracted great attention as the next generation of two-dimensional materials due to their unique electronic and optical properties, for applications in optoelectronic devices such as thin film solars, photodetectors flexible logic circuits and sensors.

However, current processes of producing printable single layer chalcogenides take a long time and the yield is poor. The flakes produced are of submicron sizes, which make it challenging to isolate a single sheet for making electronic devices.

As most applications require clean and large-sized flakes, this pinpoints a clear need to explore new ways to make high quality single-layer transition metal dichalcogenides with high yield.

Breakthrough in production

To address the production bottleneck, the NUS team explored the metal adducts of naphthalene. They prepared naphthalenide adducts of lithium, sodium and potassium, and compared the exfoliation efficiency and quality of molybdenum disulfide generated. The processing steps are detailed in the Annex.

Using a two-step expansion and intercalation method, the researchers were able to produce high quality single-layer molybdenum disulfide sheets with unprecedentedly large flake size.

The researchers also demonstrated that the exfoliated molybdenum disulfide flakes can be made into a printable solution, and wafer-size films can be printed, as the good dispersion and high viscosity of the flakes render it highly suitable for inkjet printing.

In a comparative analysis, Dr Zheng Jian, the first author of the paper, who is also a Research Fellow with the Department of Chemistry at NUS Faculty of Science, found that the alkali metal naphthalenide intercalation method applied possesses significant advantages in comparison to the conventional method.

Dr Zheng Jian, the first author of the paper, demonstrating the printing of Molybdenum disulfide flakes from a solution of the exfoliated flakes.

Commenting on the significance of the findings, Prof Loh said, “At present, there is a bottleneck in the development of solution-processed two dimensional chalcogenides. Our team has developed an alternative exfoliating agent using the organic salts of naphthalene and this new method is more efficient than previous solution-based methods. It can also be applied to other classes of two-dimensional chalcogenides.”

“Considering the versatility of this method, it may be adopted as the new benchmark in exfoliation chemistry of two-dimensional chalcogenides,” he added.

Further research into printable devices

The fast growing field of printed photonics, electronics and optoelectronics demands high material quality, precise material deposition, and application-specific optical, electrical, chemical, and mechanical properties.

To further their research and to cater to the industry, Prof Loh and his team will be looking at developing inks based on different types of two-dimensional chalcogenides exfoliated by their novel method so as to produce printable optoelectronic devices. They will also be testing the optical non-linear properties of the flakes they have produced.

 

Annex

Schematic of pre-exfoliation, intercalation and exfoliation processes

 

 

1. Bulk molybdenum disulfide crystal was expanded by decomposition of hydrazine.

2. The expanded molybdenum disulfide reacted with sodium naphthalenide to form an intercalation sample, then exfoliated into single layer sheets by immersing in water.

3. Scanning electron microscopy image of single layer molybdenum disulfide on silicon dioxide.

4. Atomic force microscopy image of single layer molybdenum disulfide on silicon dioxide.

5. Photograph of bulk single crystal molybdenum disulphide.

6. Photograph of pre-exfoliated molybdenum disulphide.

7. Photograph of sodium-exfoliated single layer molybdenum disulfide dispersion in water.

 

 

 

For more information and scheduling of media interviews, please contact:

Carolyn FONG Manager (Media relations) Office of Corporate Relations National University of Singapore DID: +65 6516 5399 Email:
[email protected]

Synaptic transistor learns while it computes- transistor that mimics the behavior of a synapse

 

First of its kind, brain-inspired device looks toward highly efficient and fast parallel computing

 

Cambridge, Mass. – November 1, 2013 – It doesn't take a Watson to realize that even the world's best supercomputers are staggeringly inefficient and energy-intensive machines.

Our brains have upwards of 86 billion neurons, connected by synapses that not only complete myriad logic circuits; they continuously adapt to stimuli, strengthening some connections while weakening others. We call that process learning, and it enables the kind of rapid, highly efficient computational processes that put Siri and Blue Gene to shame.

Materials scientists at the Harvard School of Engineering and Applied Sciences (SEAS) have now created a new type of transistor that mimics the behavior of a synapse. The novel device simultaneously modulates the flow of information in a circuit and physically adapts to changing signals.

Exploiting unusual properties in modern materials, the synaptic transistor could mark the
beginning of a new kind of artificial intelligence: one embedded not in smart algorithms but in the very architecture of a computer. The findings appear in Nature Communications.

“There’s extraordinary interest in building energy-efficient electronics these days,” says principal investigator Shriram Ramanathan, associate professor of materials science at Harvard SEAS. “Historically, people have been focused on speed, but with speed comes the penalty of power dissipation. With electronics becoming more and more powerful and ubiquitous, you could have a
huge impact by cutting down the amount of energy they consume.”

The human mind, for all its phenomenal computing power, runs on roughly 20 Watts of energy (less
than a household light bulb), so it offers a natural model for engineers.

“The transistor we’ve demonstrated is really an analog to the synapse in our brains,” says co-lead
author Jian Shi, a postdoctoral fellow at SEAS. “Each time a neuron initiates an action and another neuron reacts, the synapse between them increases the strength of its connection. And the faster the neurons spike each time, the stronger the synaptic connection. Essentially, it memorizes the action between the neurons.”

In principle, a system integrating millions of tiny synaptic transistors and neuron terminals could take parallel computing into a new era of ultra-efficient high performance.

Several prototypes of the synaptic transistor are visible on this silicon chip. (Photo by Eliza Grinnell, SEAS Communications.)

While calcium ions and receptors effect a change in a biological synapse, the artificial version
achieves the same plasticity with oxygen ions. When a voltage is applied, these ions slip in and out of the crystal lattice of a very thin (80-nanometer) film of samarium nickelate, which acts as the synapse channel between two platinum "axon" and "dendrite" terminals. The varying concentration
of ions in the nickelate raises or lowers its conductance—that is, its ability to carry information on an electrical current—and, just as in a natural synapse, the strength of the connection depends on the time delay in the electrical signal.

Structurally, the device consists of the nickelate semiconductor sandwiched between two platinum
electrodes and adjacent to a small pocket of ionic liquid. An external circuit multiplexer converts the time delay into a magnitude of voltage which it applies to the ionic liquid, creating an electric field that either drives ions into the nickelate or removes them. The entire device, just a few hundred
microns long, is embedded in a silicon chip.

The synaptic transistor offers several immediate advantages over traditional silicon transistors.
For a start, it is not restricted to the binary system of ones and zeros.

“This system changes its conductance in an analog way, continuously, as the composition of the
material changes,” explains Shi. “It would be rather challenging to use CMOS, the traditional circuit technology, to imitate a synapse, because real biological synapses have a practically unlimited number of possible states—not just ‘on’ or ‘off.’”

The synaptic transistor offers another advantage: non-volatile memory, which means even when
power is interrupted, the device remembers its state.

Additionally, the new transistor is inherently energy efficient. The nickelate belongs to an unusual
class of materials, called correlated electron systems, that can undergo an insulator-metal transition. At a certain temperature—or, in this case, when exposed to an external field—the conductance of the material suddenly changes.

“We exploit the extreme sensitivity of this material,” says Ramanathan. “A very small excitation allows you to get a large signal, so the input energy required to drive this switching is potentially very small. That could translate into a large boost for energy efficiency.”

The nickelate system is also well positioned for seamless integration into existing silicon-based systems.

“In this paper, we demonstrate high-temperature operation, but the beauty of this type of a device
is that the 'learning' behavior is more or less temperature insensitive, and that’s a big advantage,” says Ramanathan. “We can operate this anywhere from about room temperature up to at least 160 degrees Celsius.”

For now, the limitations relate to the challenges of synthesizing a relatively unexplored material system, and to the size of the device, which affects its speed.

“In our proof-of-concept device, the time constant is really set by our experimental geometry,” says Ramanathan. “In other words, to really make a super-fas device, all you’d have to do is confine the liquid and position the gate electrode closer to it.”

In fact, Ramanathan and his research team are already planning, with microfluidics experts at SEAS,
to investigate the possibilities and limits for this “ultimate fluidic transistor.”

He also has a seed grant from the National Academy of Sciences to explore the integration of
synaptic transistors into bioinspired circuits, with L. Mahadevan, Lola England de Valpine Professor of Applied Mathematics, professor of organismic and evolutionary biology, and professor of physics.

“In the SEAS setting it’s very exciting; we’re able to collaborate easily with people from very
diverse interests,” Ramanathan says.

For the materials scientist, as much curiosity derives from exploring the capabilities of correlated oxides (like the nickelate used in this study) as from the possible applications.

“You have to build new instrumentation to be able to synthesize these new materials, but once
you’re able to do that, you really have a completely new material system whose properties are virtually unexplored,” Ramanathan says. “It’s very exciting to have such materials to work with, where very little is known about them and you have an opportunity to build knowledge from scratch.”

“This kind of proof-of-concept demonstration carries that work into the ‘applied’ world,” he
adds, “where you can really translate these exotic electronic properties into compelling, state-of-the-art devices.”

This research was supported by the National Science Foundation (NSF), the Army Research Office’s
Multidisciplinary University Research Initiative, and the Air Force Office of Scientific Research. The team also benefited from the facilities at the Harvard Center for Nanoscale Systems, a member
of the NSF-supported National Nanotechnology Infrastructure Network. Sieu D. Ha, a postdoctoral fellow at SEAS, was the co-lead author; additional coauthors included graduate student You Zhou and Frank Schoofs, a former postdoctoral fellow.

 

 

 

Smart Desk

Star Trek Classroom: The next generation of school desks

		IMAGE:This shows the SynergyNet classroom. Click here for more information.

Researchers designing and testing the 'classroom of the future' have found that multi-touch, multi-user desks can boost skills in mathematics.

New results from a 3-year project working with over 400 pupils, mostly 8-10 year olds, show that collaborative learning increases both fluency and flexibility in maths. It also shows that using an interactive 'smart' desk can have benefits over doing mathematics on paper.

Using multi-touch desks in the new classroom, the children were able to work together in new ways to solve and answer questions and problems using inventive solutions. Seeing what your friends are doing, and being able to fully participate in group activities, offers new ways of working in class, the researchers say. The 'Star Trek classroom' could also help learning and teaching in other subjects.

The findings published in the journal Learning and Instruction, show that children who use a collaborative maths activity in the SynergyNet classroom improve in both mathematical flexibility and fluency, while children working on traditional paper-based activities only improve in flexibility.

During the project, the team found that 45% of students who used NumberNet increased in the number of unique mathematical expressions they created after using NumberNet, compared to 16% of students in the traditional paper-based activity.

Lead researcher, Professor Liz Burd, School of Education, Durham University, said: "Our aim was to encourage far higher levels of active student engagement, where knowledge is obtained by sharing, problem-solving and creating, rather than by passive listening. This classroom enables both active engagement and equal access.

"We found our tables encouraged students to collaborate more effectively. We were delighted to observe groups of students enhancing others' understanding of mathematical concepts. Such collaboration just did not happen when students used paper-based approaches."

The Durham University team designed software and desks that recognize multiple touches on the desktop using vision systems that see infrared light. The project called SynergyNet set out to integrate a fully collaborative system of desks, building it into the fabric and furniture of the classroom. The new desks with a 'multi-touch' surface are the central component, and these are networked and linked to a main smartboard.

In terms of current teaching, the new system means that the 'move-to-use' whiteboard is by-passed and the new desks can be both screen and keyboard. The desks act like multi-touch whiteboards and several students can use any one desk at once.

The technology allows all students to take part as opposed to one individual dominating.

Researcher, Emma Mercier, School of Education, Durham University, said: "Cooperative learning works very well in the new classroom because the pupils interact and learn in a different way. The children really enjoy doing maths in this way and are always disappointed when you turn the desks off!

"We can achieve fluency in maths through practice, however, boosting a pupil's ability to find a range of solutions to arithmetic questions is harder to teach. This classroom can help teachers to use collaborative learning to improve their pupils' flexibility in maths."

The teacher plays a key role in the classroom and can send tasks to different tables to individuals and groups. The teacher can also send one group's answers on to the next group to work on and add to, or to the board for a class discussion.  A live feed of the desks goes directly to the teacher who can intervene quickly to help an individual while allowing the group work to continue.

Professor Steve Higgins said: "Technology like this has enormous potential for teaching as it can help the teacher to manage and to orchestrate the learning of individuals and groups of learners to ensure they are both challenged and supported so that they can learn effectively."

Such a classroom may be some way off being a regular feature of schools across the world due to the costs in setting it up, and the level of support needed to make it work, however, in just 3 years the project team have noted major improvements in the technology, and a reduction in costs.

The researchers also recognise that task management in the class environment is an issue requiring thought and planning, but the overall potential of the new classroom for improved numeracy, learning, and on-going assessment is very good.

The project has worked with 12 different schools in the North East.  SynergyNet is one of eight technology enhanced learning research projects funded by the ESRC and EPSRC as part of the £12M Teaching and Learning Research Programme into Technology Enhanced Learning.

The project is an inter-disciplinary collaboration at Durham University between the School of Education, the Department of Psychology and the Department of Computer Science.

Engineers pave the way towards 3D printing of personal electronics

Engineers pave the way towards 3D printing of personal electronics Scientists are developing new materials which could one day allow people to print out custom-designed personal electronics such as games controllers which perfectly fit their hand shape.

The University of Warwick researchers have created a simple and inexpensive conductive plastic composite that can be used to produce electronic devices using the latest generation of low-cost 3D printers designed for use by hobbyists and even in the home.

The material, nicknamed 'carbomorph', enables users to lay down electronic tracks and sensors as part of a 3D printed structure – allowing the printer to create touch-sensitive areas for example, which can then be connected to a simple electronic circuit board.

So far the team has used the material to print objects with embedded flex sensors or with touch-sensitive buttons such as computer game controllers or a mug which can tell how full it is.

The next step is to work on printing much more complex structures and electronic components including the wires and cables required to connect the devices to computers.

The research was led by Dr Simon Leigh in the Department of Engineering at the University of Warwick.

Dr Leigh said: "It's always great seeing the complex and intricate models of devices such as mobile phones or television remote controls that can be produced with 3D printing, but that's it, they are invariably models that don't really function.

"We set about trying to find a way in which we could actually print out a functioning electronic device from a 3D printer.

"In the long term, this technology could revolutionalise the way we produce the world around us, making products such as personal electronics a lot more individualised and unique and in the process reducing electronic waste.

"Designers could also use it to understand better how people tactilely interact with products by monitoring sensors embedded into objects.

"However, in the short term I can see this technology having a major impact in the educational sector for example, allowing the next generation of young engineers to get hands-on experience of using advanced manufacturing technology to design fairly high-tech devices and products right there in the classroom."

The printed sensors can be monitored using existing open-source electronics and freely available programming libraries.

A major advantage of using 3D printing is that sockets for connection to equipment such as interface electronics can be printed out instead of connected using conductive glues or paints.

 

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This research is detailed in the study, A simple, low-cost conductive composite material for 3D printing of electronic sensors, published in the open-access journal PLOS ONE.

The research was funded by the EPSRC project: Novel 3D Printing Technologies for Maximising Industrial Impact (Subproject # 30821) and by the EPSRC UK Research Centre In Nondestructive Evaluation.

Simon Leigh is available on +44 (0)24 761 51357 or [email protected]

Or you can contact University of Warwick press officer Anna Blackaby on [email protected] or +44(0)2476 575910 or +44 (0)7785 433155

Crucial pieces of equipment used in this research were funded through the Science City Research Alliance (SCRA) Advanced Materials project. SCRA is a strategic research partnership between the University of Warwick and the University of Birmingham with a specific remit to work with businesses across the region. It has benefited from a multi-million pound investment in equipment and research infrastructure across both institutions via Birmingham Science City and the European Regional Development Fund.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Dirty Electricity > Disturbance of the immune system by electromagnetic fields which could lead to disease and impairment

Disturbance of the immune system by electromagnetic fields—A potentially underlying cause for cellular damage and tissue repair reduction which could lead to disease and impairment

Olle Johansson ∗

The Experimental Dermatology Unit,
Department of Neuroscience, Karolinska Institute, Stockholm, Sweden

Received 23
August 2008; accepted 30 January 2009

 

http://www.emrnetwork.org/pdfs/PATPHY_621.pdf

Diabetes and electrification-- Diabetes on Islands and Dirty Electricity (Letter to The Lancet rejected)

Diabetes on Islands and Dirty Electricity (Letter to The Lancet rejected)

http://www.sammilham.com/Islands_Lancet.pdf

 

In the listings of fasting  plasma glucose (FPG)and diabetes prevalence  in 199 countries and territories by Goodarz et al1, islands are over- represented in places with high blood glucose and diabetes prevalence.  Nine of ten of the  places with highest FBG in males are small islands, while none of the ten places with the lowest FPG are. I believe that this is due to exposure to high frequency voltage transients ( dirty electricity) on electric utility wiring coming from generator brush arcing, bad wiring connections  and from cell phone switching power supplies.

Islands without fuel supplies are likely to import  Diesel oil  to fuel generators with arcing brushes.   Dirty electricity DE  is a term coined by the utilities to describe high frequency voltage transients riding along on the 50 and 60 Hz transmission frequencies. DE is generated by arcing, sparking and any device that interrupts current flow, like compact fluorescent lights, computers,  all transmitters, including cell towers, and inverters used in wind mills and photovoltaic solar arrays.

 

These data are also consistent with a dirty electricity etiology in that places without Electricity like sub-Saharan Africa and south east Asia have low FPG and diabetes prevalence. Unfortunately , the epidemic of the so called diseases of civilization, including diabetes, cardiovascular diseases, cancer and suicide began with electrification and Thomas Edison in New York City in the early 1800s.  Historical  US
mortality data and US census electrification data, demonstrate this connection2,3,4.

 

1. Goodarz D,  Finucane MM, Lu Yet al. National, regional, and global trends in fasting plasma glucose and diabetes prevalence since 1980: systematic analysis of health examination surveys and epidemiologic studies with 370 countries and 2.7 million participants. Lancet 2011;378: 31-40.

2. Milham S. Historical evidence that electrification caused the 20th century epidemic of disease of civilization. Medical Hypotheses 74, (2010): 337–345.

3. Milham S. Dirty Electricity, Bloomington Indiana USA, iUniverse. 2010.

4. www.sammilham.com.

 

Samuel Milham MD, MPH

 2318 Gravelly Beach Loop NW

Olympia WA 98502 USA

[email protected]

http://www.sammilham.com/links.shtm

Lifestyle diseases caused by electrification-Historical evidence that electrification caused the 20th century epidemic of ‘‘diseases of civilization”

Historical evidence that electrification caused the 20th century epidemic of ‘‘diseases of civilization”  Medical Hypotheses 74 (2010) 337–345

Samuel Milham;   Washington State Department of Health, Olympia, WA, USA

summary

The slow spread of residential electrification in the US in the first half of the 20th century from urban to rural areas resulted by 1940 in two large populations; urban populations, with nearly complete electrification and rural populations exposed to varying levels of electrification depending on the progress of electrification in their state. It took until 1956 for US farms to reach urban and rural non-farm electrification levels. Both populations were covered by the US vital registration system. US vital statistics tabulations and census records for 1920–1960, and historical US vitalstatistics documents were examined.

Residential electrification data was available in the US census of population for 1930, 1940 and 1950. Crude urban and rural death rates were calculated, and death rates by state were correlated with electrification rates by state for urban and rural areas for 1940 white resident deaths. Urban death rates were much higher than rural rates for cardiovascular diseases, malignant diseases, diabetes and suicide in 1940. Rural death rates were significantly correlated with level of residential electric service by state for most causes examined. I hypothesize that the 20th century epidemic of the so called diseases of civilization including cardiovascular disease, cancer and diabetes and suicide was caused by electrificatio not by lifestyle. A large proportion of these diseases may therefore be preventable

 

http://www.sammilham.com/historical%20evidence.pdf

energy storage> Enhanced electrical energy storage from a new porus three-dimensional carbon that can be used as a greatly enhanced supercapacitor

Enhanced electrical energy storage may result from professor's research

Researchers at The University of Texas at Austin's Cockrell School of Engineering have created a new porous, three-dimensional carbon that can be used as a greatly enhanced supercapacitor, holding promise for energy storage in everything from energy grids and electric cars to consumer electronics.

The findings of the group, led by materials science and mechanical engineering Professor Rodney S. Ruoff, will be published May 12 by Science magazine in its online publication ScienceXpress.

The significance of the discovery by Ruoff's team, which included postdoctoral fellow Dr. Yanwu Zhu and graduate students Shanthi Murali and Meryl Stoller, is the potential it offers for enabling supercapacitors to deliver significantly more charge, opening the doors to many potential unprecedented uses for this type of electrical energy storage device.

Supercapacitors are known as the "sprinters" among electrical energy storage devices, able to deliver energy much faster and more efficiently than batteries, but usually holding much less electrical charge, while batteries are like marathon runners, delivering energy slowly, but steadily.

"We synthesized a new sponge-like carbon that has a surface area of up to 3,100 square meters per gram (two grams has a surface area roughly equivalent to that of a football field). It also has much higher electrical conductivity and, when further optimized, will be superb for thermal management as well," Ruoff said. "The processes used to make this porous carbon are readily scalable to industrial levels.

"After we realized that we had a new carbon with a highly novel structure that showed superb performance as an electrode, we knew that this direction of research — to create carbon materials that consist of a continuous three-dimensional porous network with single-atom-thick walls — was likely to yield the optimum electrode material for supercapacitors."

The University of Texas at Austin's Office of Technology Commercialization has filed a patent with the U.S. Patent Office on behalf of the inventors.

"Rod and his team define what we mean when we talk about innovation to address grand challenges," said Gregory L. Fenves, dean of the Cockrell School of Engineering. "This team of students, researchers and faculty has discovered a way to improve the efficiency of supercapacitor energy storage."

Ruoff's research team of about 40 people collaborated with faculty and students from The University of Texas at Dallas, scientific staff at Brookhaven National Laboratory in New York and staff members at QuantaChrome Instruments in Florida.

The process used by the university team to synthesize the carbon material involved using microwaves to exfoliate graphite oxide, followed by treatment with potassium hydroxide, which created a carbon full of tiny holes — essentially a sponge that, when combined with an electrolyte, can store a giant electrical charge. The team at Brookhaven then analyzed the atomic structure of the carbon material at the nanoscale using very high resolution electron microscopes. Their observations confirmed Ruoff's hypothesis that the carbon was a new three-dimensional material having highly curved, single-atom-thick walls that form tiny pores.

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Full text of article published in ScienceXpress.

A New Rare Earth Metal - Fulvalene Diruthenium - has the ability to absorb, store sunlight as heat

Researchers at Massachusetts Institute of Technology have discovered a rare earth metal, which is able to absorb sunlight and store it as pure heat until it is needed.

Rare earth metals used to be a collection of seventeen earth metals in the periodic table namely scandium, yttrium, and the fifteen lanthanides. The recently discovered rare earth element is fulvalene diruthenium which has a unique ability to act like a molecular heat battery and harness solar energy and heat from the sun and store it indefinitely by changing its conformation and being stable.

Lead author of the study, Professor Jeffrey Grossman, said that the molecular structure of the metal includes two aromatic carbon rings, attached to a transition metal. When molecule absorbs sunlight it changes state into a semi stable but perfectly safe state and by applying additional heat or some other catalyst, the heat energy that has been contained in the molecule can be released and the molecule will come back to its original state. The huge amount of heat released can be used for various purposes.

Most solar power devices in recent use can convert solar energy into electrical energy but do not act as a storage material for heat energy. When the heat is released from this rare metal either by introducing some heat or by using a catalyst a temperature of 200oC can be achieved.

 Professor Grossman said that a reversible and stable form of stored solar heat is very advantageous as it does not need any insulation and can be used where and when on demand. The major obstacle in using this advanced technology is that fulvalene diruthenium is extremely rare, making it very expensive to use. The element comes from ruthenium, which is a rare, costly hard white metal of the platinum group and only 12 tons of ruthenium are mined each year. The plus point that emerges from this very important research is that scientists are able to determine the exact mechanism and are sure that they will be able to find cheaper materials to perform the function in future.

The results of the study are published in Angewandte Chemie, a scientific journal that covers all aspects of chemistry.

More info see here http://onlinelibrary.wiley.com/doi/10.1002/ange.201002994/full and here  http://pubs.acs.org/doi/abs/10.1021/ja9707062

Walter Derzko

Smart Self-assembling photovoltaic technology can keep repairing itself

 

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This proof-of-concept version of the photoelectrochemical cell, which was used for laboratory tests, contains a photoactive solution made up of a mix of self-assembling molecules (in a glass cylinder held in place by metal clamp) with two electrodes protruding from the top, one made of platinum (the bare wire) and the other of silver (in a glass tube). (Patrick Gillooly)

MIT scientists have created a novel set of self-assembling molecules that can turn sunlight into electricity; the molecules can be repeatedly broken down and then reassembled quickly, just by adding or removing an additional solution.

In an attempt to imitate the  process of photosynthesis, Michael Strano, the Charles and Hilda Roddey Associate Professor of Chemical Engineering, and his team, supported by grants from the MIT Energy Initiative, the Eni Solar Frontiers Center at MIT and the Department of Energy, produced synthetic molecules called phospholipids that form disks; these disks provide structural support for other molecules that actually respond to light, in structures called reaction centers, which release electrons when struck by particles of light.

The disks, carrying the reaction centers, are in a solution where they attach themselves spontaneously to carbon nanotubes — wire-like hollow tubes of carbon atoms that are a few billionths of a meter thick yet stronger than steel and capable of conducting electricity a thousand times better than copper. The nanotubes hold the phospholipid disks in a uniform alignment so that the reaction centers can all be exposed to sunlight at once, and they also act as wires to collect and channel the flow of electrons knocked loose by the reactive molecules.

The system Strano’s team produced is made up of seven different compounds, including the carbon nanotubes, the phospholipids, and the proteins that make up the reaction centers, which under the right conditions spontaneously assemble themselves into a light-harvesting structure that produces an electric current. Strano says he believes this sets a record for the complexity of a self-assembling system. When a surfactant — similar in principle to the chemicals that BP has sprayed into the Gulf of Mexico to break apart oil — is added to the mix, the seven components all come apart and form a soupy solution. Then, when the researchers removed the surfactant by pushing the solution through a membrane, the compounds spontaneously assembled once again into a perfectly formed, rejuvenated photocell.

“We’re basically imitating tricks that nature has discovered over millions of years” — in particular, “reversibility, the ability to break apart and reassemble,” Strano says. The team, which included postdoctoral researcher Moon-Ho Ham and graduate student Ardemis Boghossian, came up with the system based on a theoretical analysis, but then decided to build a prototype cell to test it out. They ran the cell through repeated cycles of assembly and disassembly over a 14-hour period, with no loss of efficiency.

Strano says that in devising novel systems for generating electricity from light, researchers don’t often study how the systems change over time. For conventional silicon-based photovoltaic cells, there is little degradation, but with many new systems being developed — either for lower cost, higher efficiency, flexibility or other improved characteristics — the degradation can be very significant. “Often people see, over 60 hours, the efficiency falling to 10 percent of what you initially saw,” he says.

The individual reactions of these new molecular structures in converting sunlight are about 40 percent efficient, or about double the efficiency of today’s best solar cells. Theoretically, the efficiency of the structures could be close to 100 percent, he says. But in the initial work, the concentration of the structures in the solution was low, so the overall efficiency of the device — the amount of electricity produced for a given surface area — was very low. They are working now to find ways to greatly increase the concentration.

More info: MIT news