Bad virus put to good use: Breakthrough batteries

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(PhysOrg.com) -- Viruses have a bad rep--and rightly so. The ability of a virus to quickly and precisely replicate itself makes it a destructive scourge to animals and plants alike. Now an interdisciplinary team of researchers at the University of Maryland's A. James Clark School of Engineering and College of Agriculture and Natural Resources, brought together by Professor Reza Ghodssi, is turning the tables, harnessing and exploiting the"self-renewing"and"self-assembling"properties of viruses for a higher purpose: to build a new generation of small, powerful and highly efficient batteries and fuel cells.

The rigid, rod-shaped Tobacco mosaicvirus(TMV), which under anelectron microscopelooks like uncooked spaghetti, is a well-known and widespread plant virus that devastates tobacco, tomatoes, peppers, and other vegetation. But in the lab, engineers have discovered that they can harness the characteristics of TMV to build tiny components for the lithium ion batteries of the future. They can modify the TMV rods to bind perpendicularly to the metallic surface of a battery electrode and arrange the rods in intricate and orderly patterns on the electrode. Then, they coat the rods with a conductive thin film that acts as a current collector and finally the battery's active material that participates in the electrochemical reactions.

As a result, the researchers can greatly increase the electrode surface area and its capacity to store energy and enable fast charge/discharge times. TMV becomes inert during the manufacturing process; the resulting batteries do not transmit the virus. The new batteries, however, have up to a 10-fold increase in energy capacity over a standard lithium ion battery.

"The resulting batteries are a leap forward in many ways and will be ideal for use not only in small electronic devices but in novel applications that have been limited so far by the size of the required battery,"said Ghodssi, director of the Institute for Systems Research and Herbert Rabin Professor of Electrical and Computer Engineering at the Clark School."The technology that we have developed can be used to produce energy storage devices for integrated microsystems such as wireless sensors networks. These systems have to be really small in size--millimeter or sub-millimeter--so that they can be deployed in large numbers in remote environments for applications like homeland security, agriculture, environmental monitoring and more; to power these devices, equally small batteries are required, without compromising in performance."

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TMV's nanostructure is the ideal size and shape to use as a template for building battery electrodes. Its self-replicating and self-assembling biological properties produce structures that are both intricate and orderly, which increases the power and storage capacity of the batteries that incorporate them. Because TMV can be programmed to bind directly to metal, the resulting components are lighter, stronger and less expensive than conventional parts.

Three distinct steps are involved in producing a TMV-based battery: modifying, propagating and preparing the TMV; processing the TMV to grow nanorods on a metal plate; and incorporating the nanorod-coated plates into finished batteries. It takes an interdisciplinary team of UM scientists and their students to make each step possible.

James Culver, a member of the Institute for Bioscience and Biotechnology and a professor in the Department of Plant Science and Landscape Architecture, and researcher Adam Brown had already developed genetic modifications to the TMV that enable it to be chemically coated with conductive metals. For this project they extract enough of the customized virus from just a few tobacco plants grown in the lab to synthesize hundreds of battery electrodes. The extracted TMV is then ready for the next step.

Scientists produce a forest of vertically aligned virus rods using a process developed by Culver's former Ph.D. student, Elizabeth Royston. A solution of TMV is applied to a metal electrode plate. The genetic modifications program one end of the rod shaped virus to attach to the plate. Next these viral forests are chemically coated with a conductive metal, mainly nickel. Other than its structure, no trace of the virus is present in the finished product, which cannot transmit a virus to either plants or animals. This process is patent-pending.

Ghodssi, materials science Ph.D. student Konstantinos Gerasopoulos, and former postdoctoral associate Matthew McCarthy (now a faculty member at Drexel University) have used this metal-coating technique to fabricate alkaline batteries with common techniques from the semiconductor industry such as photolithography and thin film deposition.

While the first generation of their devices used the nickel-coated viruses for the electrodes, work published earlier this year investigated the feasibility of structuring electrodes with the active material deposited on top of each nickel-coated nanorod, forming a core/shell nanocomposite where every TMV particle contains a conductive metal core and an active material shell. In collaboration with Chunsheng Wang, a professor in the Department of Chemical and Biomolecular Engineering, and his Ph.D. student Xilin Chen, the researchers have developed several techniques to form nanocomposites of silicon and titanium dioxide on the metalized TMV template. This architecture both stabilizes the fragile, active material coating and provides it with a direct connection to the battery electrode.

In the third and final step, Chen and Gerasopoulos assemble these electrodes into the experimental high-capacity lithium-ion batteries. Their capacity can be several times higher than that of bulk materials and in the case of silicon, higher than that of current commercial batteries.

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SEM image of Ni/TiO2 nanocomposite electrode (top), cross-section TEM image of an individual nanorod showing the core/shell nanostructure Credit: University of Maryland, College Park

"Virus-enabled nanorod structures are tailor-made for increasing the amount of energy batteries can store. They confer an order of magnitude increase in surface area, stabilize the assembled materials and increase conductivity, resulting in up to a10-fold increase in theenergy capacityover a standardlithium ion battery,"Wang said.

A bonus: since the TMV binds metal directly onto the conductive surface as the structures are formed, no other binding or conducting agents are needed as in the traditional ink-casting technologies that are used for electrode fabrication.

"Our method is unique in that it involves direct fabrication of the electrode onto the current collector; this makes the battery's power higher, and its cycle life longer,"said Wang.

The use of the TMV virus in fabricating batteries can be scaled up to meet industrial production needs."The process is simple, inexpensive, and renewable,"Culver adds."On average, one acre of tobacco can produce approximately 2,100 pounds of leaf tissue, yielding approximately one pound of TMV per pound of infected leaves,"he explains.

At the same time, very tiny microbatteries can be produced using this technology."Our electrode synthesis technique, the high surface area of the TMV and the capability to pattern these materials using processes compatible with microfabrication enable the development of such miniaturized batteries,"Gerasopoulos adds.

While the focus of this research team has long been on energy storage, the structural versatility of the TMV template allows its use in a variety of exciting applications."This combination of bottom-up biological self-assembly and top-down manufacturing is not limited to battery development only,"Ghodssi said."One of our lab's ongoing projects is aiming at the development of explosive detection sensors using versions of the TMV that bind TNT selectively, increasing the sensitivity of the sensor. In parallel, we are collaborating with our colleagues at Drexel and MIT to construct surfaces that resemble the structure of plant leaves. These biomimetic structures can be used for basic scientific studies as well as the development of novel water-repellent surfaces and micro/nano scale heat pipes."

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Pure nanotube-type growth edges toward the possible

New research at Rice University could ultimately show scientists the way to make batches of nanotubes of a single type.

A paper in the online journalPhysical Review Lettersunveils an elegant formula by Rice University physicist Boris Yakobson and his colleagues that defines the energy of a piece of graphene cut at any angle.

Yakobson, a professor in mechanical engineering and materials science and of chemistry, said this alone is significant because the way graphene handles energy depends upon the angle -- or chirality -- of its edge, and solving that process for odd angles has been extremely challenging. But, he wrote, the research has"profound implications in the context of nanotube growth, offering rational ways to control their chiral symmetry, a tantalizing yet so far elusive goal."

Graphene is the single-atom-thick form of carbon that has become of tremendous interest for its potential to revolutionize electronics, optics, sensing and mechanical devices. Getting a handle on how this chicken-wire-shaped sheet of carbon atoms transports electricity has been the focus of intense study.

A sheet of graphene with zigzag or armchair edges squares up nicely. Zigzags are metallic, armchairs are semiconductors, and their atoms march in rank, evenly spaced, along the edges. A full 30 degrees of rotation separates one from the other.

But if the hexagons that make up a sheet are offset less than 30 degrees, atoms along a straight edge are unevenly spaced."That makes analysis of the energy very complicated, because it's a large irregular structure. It's like noise,"Yakobson said."We've found a way to calculate the energies in these arbitrary angles,"he said.

Yakobson and his co-authors, Yuanyue Liu, a graduate student in his lab, and Alex Dobrinsky, a former graduate student and now a postdoctoral researcher at Brown University, soon wondered how these findings applied to carbon nanotubes.

"There are as many ways to roll graphene into a nanotube as there are ways to roll a newspaper,"Yakobson said."The text can be aligned circumferentially or run straight along the axis or spiral at an angle."

While rolling a newspaper makes it hard to read, rolling carbon into a nanotube makes it relatively easy to"read"its type -- whether armchair or zigzag or some variation in between. What's impossible is controlling how the tube will roll. The process tends to be willy-nilly, leaving researchers the task of separating the nanotubes they need from the bulk through ultracentrifugation or other expensive procedures.

Yakobson said it would be a real game-changer if they could, for instance, grow batches of pure armchair nanotubes for use in such projects as armchair quantum nanowire (AQW). As imagined by Rice's late Nobel Laureate Richard Smalley, AQW could revolutionize the nation's power grid by carrying 10 times the amount of electricity as copper at only one-sixth the weight.

Yakobson's work may open a path to do so. A nanotube's chirality is determined by the combination of energies at play in its nucleation."When it just emerges from the 'primordial soup' of carbon, the edge of the tube is essentially the same as the edge of graphene,"he said.

"At first, it's just a cap. There's no stem yet. You're frying these caps on a skillet, and they're bubbling,"he said."The probability for different bubbles to emerge is controlled by energy around the edge."

The chirality of the nascent nanotube is set when atoms in the cap self-assemble a sixth pentagon (necessary to mold the hexagons into a dome)."That's where we can, I think for the first time, make some quantitative judgment about how different chiral structures emerge,"Yakobson said.

It may be worth chemists' efforts to look more closely at the energy between the catalyst and carbon structure."This has some promise,"he said."If you can tweak this preference, if you can change energy from the catalyst side, you change the preference of the chirality. And then you can tell these self-assembling carbons, 'Please dance this way; don't dance that way.'"

Yakobson hopes the new work helps solve the long-standing problem of nanotube chirality."For almost two decades, we didn't have a good understanding of this process,"he said."Actually, we didn't have a clue. I'm not saying this is a full solution, but this is the first time we've seen a quantitative approach, an order in the seeming chaos. It just feels satisfying.

"The bottom line is simple. We figured out the graphene edge and bridged it to the holy grail ofnanotubes, which is chirality control."

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Triple-mode transistors show potential: Researchers introduce graphene-based amplifiers

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(PhysOrg.com) -- Rice University research that capitalizes on the wide-ranging capabilities of graphene could lead to circuit applications that are far more compact and versatile than what is now feasible with silicon-based technologies.

Triple-mode, single-transistor amplifiers based ongraphene-- the one-atom-thick form of carbon that recently won its discoverers aNobel Prize-- could become key components in futureelectronic circuits. The discovery by Rice researchers was reported this week in the online journalACS Nano.

Graphene is very strong, nearly transparent and conducts electricity very well. But another key property is ambipolarity, graphene's ability to switch between using positive and negative carriers on the fly depending on the input signal. Traditionalsilicon transistorsusually use one or the other type of carrier, which is determined during fabrication.

A three-terminal single-transistoramplifiermade of graphene can be changed during operation to any of three modes at any time using carriers that are positive, negative or both, providing opportunities that are not possible with traditional single-transistor architectures, said Kartik Mohanram, an assistant professor of electrical and computer engineering at Rice. He collaborated on the research with Alexander Balandin, a professor of electrical engineering at the University of California, Riverside, and their students Xuebei Yang (at Rice) and Guanxiong Liu (at Riverside).

Mohanram likened the new transistor's abilities to that of a water tap."Turn it on and the water flows,"he said."Turn it off and the water stops. That's what a traditional transistor does. It's a unipolar device -- it only opens and closes in one direction."

"But if you close a tap too much, it opens again and water flows. That's what ambipolarity is -- current can flow when you open the transistor in either direction about a point of minimum conduction."

That alone means a graphene transistor can be"n-type"(negative) or"p-type"(positive), depending on whether the carrier originates from the source or drain terminals (which are effectively interchangeable). A third function appears when the input from each carrier is equal: The transistor becomes a frequency multiplier. By combining the three modes, the Rice-Riverside team demonstrated such common signaling schemes as phase and frequency shift keying for wireless and audio applications.

"Our work, and that of others, that focuses on the applications of ambipolarity complements efforts to make a better transistor with graphene,"Mohanram said."It promises more functionality."The research demonstrated that a single graphene transistor could potentially replace many in a typical integrated circuit, he said. Graphene's superior material properties and relative compatibility with silicon-based manufacturing should allow for integration of such circuits in the future, he added.

Technological roadblocks need to be overcome, Mohanram said. Such fabrication steps as dielectric deposition and making contacts"wind up disturbing the lattice, scratching it and introducing defects. That immediately degrades its performance (limiting signal gain), so we have to exercise a lot of care in fabrication.

"But the technology will mature, since so many research groups are working hard to address these challenges,"he said.

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Microbial hair -- it's electric: Specialized bacterial filaments shown to conduct electricity

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(PhysOrg.com) -- Some bacteria grow electrical hair that lets them link up in big biological circuits, according to a University of Southern California biophysicist and his collaborators.

The finding suggests that microbial colonies may survive, communicate and share energy in part through electrically conducting hairs known as bacterial nanowires.

"This is the first measurement of electron transport along biological nanowires produced by bacteria,"said Mohamed El-Naggar, assistant professor of physics and astronomy at the USC College of Letters, Arts and Sciences.

El-Naggar was the lead author of a study appearing online next week inProceedings of the National Academy of Sciences.

Knowing howmicrobial communitiesthrive is the first step in finding ways to destroy harmful colonies, such as biofilms on teeth. Biofilms have proven highly resistant toantibiotics.

The same knowledge could help to promote useful colonies, such as those in bacterial fuel cells under development at USC and other institutions.

"The flow of electrons in various directions is intimately tied to the metabolic status of different parts of thebiofilm,"El-Naggar said."Bacterial nanowires can provide the necessary links… for the survival of a microbial circuit."

A bacterial nanowire looks like a long hair sticking out of a microbe's body. Like human hair, it consists mostly of protein.

To test the conductivity of nanowires, the researchers grew cultures of Shewanella oneidensis MR-1, a microbe previously discovered by co-author Kenneth Nealson, Wrigley Professor of Geobiology at USC College.

Shewanella tend to make nanowires in times of scarcity. By manipulating growing conditions, the researchers produced bacteria with plentiful nanowires.

The bacteria then were deposited on a surface dotted with microscopic electrodes. When a nanowire fell across two electrodes, it closed the circuit, enabling a flow of measurable current. The conductivity was similar to that of a semiconductor– modest but significant.

When the researchers cut the nanowire, the flow of current stopped.

Previous studies showed that electrons could move across a nanowire, which did not prove that nanowires conducted electrons along their length.

El-Naggar's group is the first to carry out this technically difficult but more telling experiment.

Electricity carried on nanowires may be a lifeline. Bacteria respire by losing electrons to an acceptor– for Shewanella, a metal such as iron. (Breathing is a special case: Humans respire by giving up electrons to oxygen, one of the most powerful electron acceptors.)

Nealson said of Shewanella:"If you don't give it an electron acceptor, it dies. It dies pretty rapidly."

In some cases, a nanowire may be a microbe's only means of dumping electrons.

When an electron acceptor is scarce nearby, nanowires may help bacteria to support each other and extend their collective reach to distant sources.

The researchers noted that Shewanella attach to electron acceptors as well as to each other, forming a colony in which every member should be able to respire through a chain of nanowires.

"This would be basically a community response to transfer electrons,"El-Naggar explained."It would be a form of cooperative breathing."

El-Naggar and his team are among the pioneers in a young discipline. The term"bacterial nanowire"was coined in 2006. Fewer than 10 studies on the subject have been published, according to co-author Yuri Gorby of The J. Craig Venter Institute in San Diego, discoverer of nanowires in Shewanella.

Gorby and others became interested in nanowires when they noticed that reduction of metals appeared to be occurring around the filaments. Since reduction requires the transfer of electrons to a metal, the researchers suspected that the filaments were carrying a current.

Nanowires also have been proposed as conductive pathways in several diverse microbes.

"The current hypothesis is that bacterial nanowires are in fact widespread in the microbial world,"El-Naggar said.

Some have suggested that nanowires may help bacteria to communicate as well as to respire.

Bacterial colonies are known to share information through the slow diffusion of signaling molecules. Nealson argued thatelectron transportovernanowireswould be faster and preferable for bacteria.

"You want the telegraph, you don't want smoke signals,"he said.

Bacteria's communal strategy for survival may hold lessons for higher life forms.

In an op-ed published in Wired in 2009, Gorby wrote:"Understanding the strategies for efficient energy distribution and communication in the oldest organisms on the planet may serve as useful analogies of sustainability within our own species."

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Scientists create world's first 'super-twisted' light

(PhysOrg.com) -- The research team at the University of Glasgow twisted the light like a corkscrew by using a polarising filter, before shining it onto a specially shaped piece of gold to create the world's first 'super twisting'.

Super twisted light does not exist in nature and, until now, it had only been theorised by scientists, never produced.

Super twisted light can be used to findproteintraces in incredibly small samples ofbiological materiallike blood, far less than currently used.

The researchers have already used the light to look at many different proteins and have found that it is particularly sensitive to the structures of proteins which cause degenerative diseases such as Alzheimer’s and Parkinson’s Disease.

The findings have been published inNature Nanotechnology.

Dr Malcolm Kadodwala, senior lecturer in the School of Chemistry, said:“We are very excited by this research. Essentially, this twisted light, which does not exist naturally, allows us to detect biological materials at unprecedented low concentrations.

“Due to the nature of the twisted light, it has been shown to be particularly effective at detecting proteins with a structure characteristic of amyloids– insoluble proteins that can stick together to form plaques within different organs in the body.

“It is these plaques which are thought to play a part in neurodegenerative diseases such as Alzheimer’s, Parkinson’s and CJD– though the reasons for this are unclear.

“We’re now looking to see if this same technique can be adapted to detect a wider range of proteins which are indicative of other diseases. The fact this method requires much less material (just one picogram or million millionth of a gram) for analysis than current techniques and uses a form of light previously unrealised is a big step forward.”

The complex science behind the technique takes advantage of the fact light can be twisted like a corkscrew by passing it through a special polarising filter: in much the same way as polarised sunglasses allow only certain alignments of light waves through.

By shining light onto a specially-shaped piece of metal– in this case gold– the light that is emitted from the metal becomes super-twisted.

Polarised or twisted light is already used in some medical techniques to analyse biomolecules, however the multidisciplinary Glasgow team, have been able to achieve a much more powerful system by twisting the light even tighter.

The team included engineer Dr Nikolaj Gadegaard and life scientist, Dr Sharon Kelly, with a team of physicists at the University of Exeter, led by Dr Euan Hendry.

The use of super-twisted light in spectroscopy– the analysis of materials according to way they absorb and emit light– has numerous potential applications in biosensing and could also be used to detect particular types of viruses which have similar structures.

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Physicists use graphene to decode DNA

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Genome sequencing will have a profound effect on our understanding of genetic biology and could usher in a day when doctor and patient are able to review individual genome sequences to fully personalise medical treatment.

As theX PRIZE FOUNDATIONbegins to receive nominations for its $10m prize for the first privately funded company that can accurately sequence 100 genomes in 10 days for less than $10,000 per genome, the science writer Philip Ball looks at the latest advances towards success in DecemberPhysics World's lead feature.

The baton, once firmly in the hands of chemists and biologists, has been grabbed by physicists around the world since the mid-1990s when David Deamer from the University of California, Santa Cruz imagined threading aDNA strandthrough a tiny pore -- reading out the chemical bases strung along the strand as it passes through. His idea was that in a salt solution, the number of dissolved ions passing through the pore would vary depending on which base was sitting in the pore.

Over the past decade, scientists have sought means to use Deamer's technique with far greater control of the pore and the movement of DNA through the pore, while also contemplating how the technique can be turned into a handy device that could be used in doctors' surgeries worldwide.

Initial thoughts were towards the use of a silicon-nitride nanopore but researchers have found the material a little too thick, meaning that more than one nucleotide -- the structural units that make up DNA -- can be in the pore at any one time.

Now, however, graphene -- one-atom thick sheets of carbon that led to this year's Nobel Prize for Physics -- is generating huge excitement as a possible DNA sequencing material following the work of three independent research groups earlier this year.

The teams -- based at the universities of Delft, Pennsylvania and Harvard -- have each drawn DNA through a nanopore drilled into graphene. As the materials is so much thinner thansilicon nitride, the teams are reported to believe that graphene may be a"game changer".

Whether for the physicists it's the lure of a $10m prize, the joy of basic research, or the satisfaction of designing a technique that could revolutionize medicine, it looks like graphene -- already dubbed a"wonder material on account it being ultrathin, ultrastrong and a great electrical conductor -- could be adding one more string to its already powerful bow.

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A forest of nanorods: Amazing nanostructures created by glancing-angle deposition

Just as landscape photographs shot in low-angle light dramatically accentuate subtle swales and mounds, depositing metal vapors at glancing angles turns a rough surface into amazing nanostructures with a vast range of potential properties.

For decades,vapor depositionhas been a standard technique for creating modern microelectronic circuits. But nearly all of industry's efforts have been devoted to making structures as flat and smooth as possible. Rather than placing metal sources in the high-noon position used to make featureless structures, Daniel Gall of Rensselaer Polytechnic Institute is one of several dozen research leaders who place them at very narrow angles akin to sunrise or sunset illumination. Metal atoms then hit primarily any high spots on the target surface. Continued deposition creates a forest of nanorods, rather than flat films, since each growing rod shadows a volume behind it. Starting with a patterned substrate yields a regular array of nanoscale columns, like skyscrapers in downtown Manhattan.

Gall describes his research today at the AVS 57th International Symposium&Exhibition, which takes place this week at the Albuquerque Convention Center in New Mexico.

In his talk, Gall reveals a new theory that predicts how the deposition temperature and diffusion affects the diameters of the nanorods.

"Atomsmoving by surface diffusion typically smooth the surface,"Gall says."Atomic shadowing causes the opposite effects, making thesurfacerough. Glancing-angle deposition extends shadowing effects to higher temperatures, which lead to larger-diameternanorods."

He also illustrates his presentation with images of a variety ofnanostructurescreated in his lab, including curiously shaped half-moons made when he started with a pattern of self-assembled spheres.

Future applications for nanorod structures such as Gall's include nanosensors, optical elements, fuel-cell cathodes and electrical contacts for buffering thermal expansion.

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Scientists create highly ordered artificial spin ice using nanotechnology

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(PhysOrg.com) -- An international team of researchers has succeeded in creating artificial spin ice in a state of thermal equilibrium for the first time, allowing them to examine the precise configuration of this important nanomaterial.

Scientists from the University of Leeds, the US Department of Energy's Brookhaven National Laboratory and the UK Science and Technology Facilities Council's Rutherford Appleton Laboratory say the breakthrough will allow them to study in much greater detail a scientific phenomenon known as 'magnetic monopoles', which are thought to exist in such structures. Their findings are published today in the journalNature Physics.

Artificial spin ice is built using nanotechnology and is made up of millions of tiny magnets, each thousands of times smaller than a grain of sand. The magnets exist in a lattice in what is known as a 'frustrated' structure. Like water ice, the geometry of the structure means that all of the interactions between the atoms cannot be satisfied at the same time.

"It's like trying to seat alternating male and female diners around a table with an odd number of seats– however much you re-arrange them you will never succeed,"said Dr Christopher Marrows from the University of Leeds, co-author of the paper.

In spin ice, magnetic dipoles with a north and south pole are arranged in tetrahedron structures. Each dipole has magnetic moments, similar to the protons on H2O molecules inwater ice, which attract and repel each other. Consequently, the dipoles arrange themselves into the lowest possible energy state, which is two poles pointing in and two pointing out.

Dr Marrows said:"Spin ices have created a lot of excitement in recent years as it has been realised that they are a playground for physicists studying magnetic monopole excitations and Dirac string physics in the solid state. However, until now all of the samples of these artificial structures created in the lab have been what we call 'jammed'.

"What we have done is find a way to un-jam spin ice and get it into a well-ordered ground state known as thermal equilibrium. We can then freeze a sample into this state, and use a microscope to see which way all the little magnets are pointing. It's the equivalent of being able take a picture of every atom in a room as it allows us to inspect exactly how the structure is configured."

Jason Morgan, PhD student at the University of Leeds and lead author of the paper, was the first member of the team to observe the sample in equilibrium. He said:"Getting the sample to self-order in such a way has never been achieved experimentally before and for a while had been considered impossible. But when we looked at the sample using magnetic force microscopy and saw this beautiful periodic structure we knew instantly that we had achieved an ordered ground state."

The researchers have also been able to observe individual excitations out of this ground state within their sample, which they say is evidence for monopole dynamics within thelattice.

Magnetic monopoles– magnets with only a single north or south pole¬¬– are former hypothetical particles that are now thought to exist in spin ice. There is hope among scientists that understanding these monopoles in more detail could lead to advances in a novel technology field known as 'magnetricity'– a magnetic equivalent to electricity.

Co-author Sean Langridge, a Science and Technology Facilities Council (STFC) Fellow and visiting Professor at the University of Leeds, added:"In the naturally occurring spin-ice systems this ground state is predicted but has not been experimentally observed.

"Now that is has been observed in an artificial system the next step is to observe dynamically the excitations from this ground state. We can only do this by controlling the interactions with state of the art lithographic techniques. This level of control will provide an even greater level of understanding in this fascinating system."

The team created"artificial"spin ice samples at Brookhaven using a state-of-the-artnanotechnologytool called an electron beam writer. A similar£4 million facility is shortly to be opened at the University of Leeds which will be unique to the UK and will allow continued collaboration with the researchers at Brookhaven.

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Technique allows researchers to examine how materials bond at the atomic level

(PhysOrg.com) -- An approach pioneered by researchers at North Carolina State University gives scientists new insight into the way silicon bonds with other materials at the atomic level. This technique could lead to improved understanding of and control over bond formation at the atomic level, and opportunities for the creation of new devices and more efficient microchips.

Manufacturers build silicon-based devices from layers of different materials. Bonds– the chemical interaction between adjacent atoms– are what give materials their distinctive characteristics.“Essentially, a bond is the glue that holds two atoms together, and it is this glue that determines material properties, like hardness and transparency,” says Dr. Kenan Gundogdu, assistant professor of physics at NC State and co-author of the research.“Bonds are formed as materials come together. We have influenced the assembly process ofsiliconcrystals by applying strain duringbondformation. Manufacturers know that strain makes a difference in how bonds form, but up to now there hasn’t been much understanding of how this works on theatomic level.”

Gundogdu, along with Dr. David Aspnes, Distinguished University Professor of Physics, and doctoral candidate Bilal Gokce, used optical spectroscopy along with a method of analysis pioneered by Aspnes and former graduate student Dr. Eric Adles that allowed them to examine what was happening on the atomic scale when strain was applied to a silicon crystal.

“Strain has been used to affect overall chemistry for a long time,” Aspnes says.“However, no one has previously observed differences in chemical behavior of individual bonds as a result of applying strain in one direction. Now that we can see what is actually happening, we’ll gain a much better understanding of its impact on the atomic scale, and ideally be able to put it to use.”

According to Gundogdu,“Application of even small amount of strain in one direction increases the chemical reactivity of bonds in certain direction, which in turn causes structural changes. Up to now, strain has been applied when devices are made. But by looking at the effect on the individual atomic bonds we now know that we can influence chemical reactions in a particular direction, which in principle allows us to be more selective in the manufacturing process.”

The research appears online in the Sept. 27Proceedings of the National Academy of Sciences.

“While we are able to exert some directional control over reaction rates, there remains much that we still don’t understand,” Aspnes adds.“Continuing research will allow us to identify the relevant hidden variables, and silicon-based devices may become more efficient as a result.”

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The effects of hydrogen on growing carbon nanotubes

Carbon nanotubes -- long, hollow cylinders of carbon billionths of a meter in diameter -- have many potential uses in nanotechnology, optics, electronics, and many other fields. The exact properties of nanotubes depend on their structure, and scientists as yet have little control over that structure, which is determined during the initial formation -- or growth -- of the nanotubes. In fact, says chemical engineer and materials scientist Eray Aydil of the University of Minnesota,"we do not know precisely how the nanotubes grow."

In a paper in the American Institute of Physics'Journal of Applied Physics, Aydil, professor of chemical engineering and materials science and the Ronald L. and Janet A. Christenson Chair in Renewable Energy, and his colleagues shed new light on the process. In particular, the researchers examined the influence of hydrogen gas.

"Carbon nanotubes grow from a metal catalyst particle that is immersed in a gas like methane,"Aydil explains."Sometimeshydrogen gasis also added and it was found that a little bit of hydrogen helps to grow carbon nanotubes with nice straight walls and with few defects. However, too much hydrogen addition gives fibers with thick walls, instead of nanotubes, or no growth at all."

To understand why, Aydil and colleagues usedtransmission electron microscopyand other methods to systematically image and characterize the effects of increasing concentrations of hydrogen."It turns out that the iron metal catalysts turn to iron carbide by reacting with the carbon in methane. Iron carbide is a hard material that is not easily deformed, and carbon nanotubes grown from such catalysts tend to have nice straight walls,"he says.

Adding more hydrogen to the mix causes iron carbide to turn into iron -- which is more malleable and ductile, and"deforms into shapes that give rise to more fiber-like structures rather than hollow carbon nanotubes,"he says. At higher concentrations, hydrogen etches the forming carbon nanotubes,"and growth stops all together. It is the interaction of the hydrogen with the catalysts and its effect on the catalyst's structure that controls thecarbon nanotubestructure."

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Nanogenerators grow strong enough to power small conventional electronics (w/ Video)

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Blinking numbers on a liquid-crystal display (LCD) often indicate that a device's clock needs resetting. But in the laboratory of Zhong Lin Wang at Georgia Tech, the blinking number on a small LCD signals the success of a five-year effort to power conventional electronic devices with nanoscale generators that harvest mechanical energy from the environment using an array of tiny nanowires.

In this case, themechanical energycomes from compressing a nanogenerator between two fingers, but it could also come from a heartbeat, the pounding of a hiker's shoe on a trail, the rustling of a shirt, or thevibrationof a heavy machine. While these nanogenerators will never produce large amounts ofelectricityfor conventional purposes, they could be used to power nanoscale and microscale devices– and even to recharge pacemakers or iPods.

Wang's nanogenerators rely on the piezoelectric effect seen in crystalline materials such aszinc oxide, in which an electric charge potential is created when structures made from the material are flexed or compressed. By capturing and combining the charges from millions of these nanoscale zinc oxide wires, Wang and his research team can produce as much as three volts– and up to 300 nanoamps.

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In the laboratory of Zhong Lin Wang at Georgia Tech, a blinking LCD signals the success of a five-year effort to power conventional electronic devices using nanoscale generators that harvest mechanical energy from the environment. Credit: Georgia Tech

"By simplifying our design, making it more robust and integrating the contributions from many morenanowires, we have successfully boosted the output of our nanogenerator enough to drive devices such as commercial liquid-crystal displays, light-emitting diodes and laser diodes,"said Wang, a Regents' professor in Georgia Tech's School of Materials Science and Engineering."If we can sustain this rate of improvement, we will reach some true applications in healthcare devices, personal electronics, or environmental monitoring."

Recent improvements in the nanogenerators, including a simpler fabrication technique, were reported online last week in the journalNano Letters. Earlier papers in the same journal and in Nature Communications reported other advances for the work, which has been supported by the Defense Advanced Research Projects Agency (DARPA), the U.S. Department of Energy, the U.S. Air Force, and the National Science Foundation.

"We are interested in very small devices that can be used in applications such as health care, environmental monitoring and personal electronics,"said Wang."How to power these devices is a critical issue."

The earliest zinc oxide nanogenerators used arrays of nanowires grown on a rigid substrate and topped with a metal electrode. Later versions embedded both ends of the nanowires in polymer and produced power by simple flexing. Regardless of the configuration, the devices required careful growth of the nanowire arrays and painstaking assembly.

In the latest paper, Wang and his group members Youfan Hu, Yan Zhang, Chen Xu, Guang Zhu and Zetang Li reported on much simpler fabrication techniques. First, they grew arrays of a new type of nanowire that has a conical shape. These wires were cut from their growth substrate and placed into an alcohol solution.

The solution containing the nanowires was then dripped onto a thin metal electrode and a sheet of flexible polymer film. After the alcohol was allowed to dry, another layer was created. Multiple nanowire/polymer layers were built up into a kind of composite, using a process that Wang believes could be scaled up to industrial production.

When flexed, these nanowire sandwiches– which are about two centimeters by 1.5 centimeters– generated enough power to drive a commercial display borrowed from a pocket calculator.

Wang says the nanogenerators are now close to producing enough current for a self-powered system that might monitor the environment for a toxic gas, for instance, then broadcast a warning. The system would include capacitors able to store up the small charges until enough power was available to send out a burst of data.

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Compressing a nanogenerator between two fingers is enough to drive a liquid-crystal display. Credit: Courtesy Zhong Lin Wang

While even the current nanogenerator output remains below the level required for such devices as iPods or cardiac pacemakers, Wang believes those levels will be reached within three to five years. The current nanogenerator, he notes, is nearly 100 times more powerful than what his group had developed just a year ago.

Writing in a separate paper published in October in the journal Nature Communications, group members Sheng Xu, Benjamin J. Hansen and Wang reported on a new technique for fabricating piezoelectric nanowires from lead zirconate titanate– also known as PZT. The material is already used industrially, but is difficult to grow because it requires temperatures of 650 degrees Celsius.

In the paper, Wang's team reported the first chemical epitaxial growth of vertically-aligned single-crystal nanowire arrays of PZT on a variety of conductive and non-conductive substrates. They used a process known as hydrothermal decomposition, which took place at just 230 degrees Celsius.

With a rectifying circuit to convert alternating current to direct current, the researchers used the PZT nanogenerators to power a commercial laser diode, demonstrating an alternative materials system for Wang's nanogenerator family."This allows us the flexibility of choosing the best material and process for the given need, although the performance of PZT is not as good as zinc oxide for power generation,"he explained.

And in another paper published inNano Letters, Wang and group members Guang Zhu, Rusen Yang and Sihong Wang reported on yet another advance boosting nanogenerator output. Their approach, called"scalable sweeping printing,"includes a two-step process of (1) transferring vertically-aligned zinc oxide nanowires to a polymer receiving substrate to form horizontal arrays and (2) applying parallel strip electrodes to connect all of the nanowires together.

Using a single layer of this structure, the researchers produced an open-circuit voltage of 2.03 volts and a peak output power density of approximately 11 milliwatts per cubic centimeter.

"From when we got started in 2005 until today, we have dramatically improved the output of our nanogenerators,"Wang noted."We are within the range of what's needed. If we can drive these small components, I believe we will be able to power small systems in the near future. In the next five years, I hope to see this move into application."

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Ultrathin alternative to silicon for future electronics

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There's good news in the search for the next generation of semiconductors. Researchers with the U.S. Department of Energy's Lawrence Berkeley National Laboratory and the University of California Berkeley, have successfully integrated ultra-thin layers of the semiconductor indium arsenide onto a silicon substrate to create a nanoscale transistor with excellent electronic properties. A member of the III–V family of semiconductors, indium arsenide offers several advantages as an alternative to silicon including superior electron mobility and velocity, which makes it an oustanding candidate for future low-power, high-speed electronic devices.

"We've shown a simple route for the heterogeneous integration of indium arsenide layers down to a thickness of 10 nanometers onsiliconsubstrates,"says Ali Javey, a faculty scientist in Berkeley Lab's Materials Sciences Division and a professor of electrical engineering and computer science at UC Berkeley, who led this research.

"The devices we subsequently fabricated were shown to operate near the projected performance limits of III-V devices with minimal leakage current. Our devices also exhibited superior performance in terms of current density and transconductance as compared to silicon transistors of similar dimensions."

For all its wondrouselectronic properties, silicon has limitations that have prompted an intense search for alternative semiconductors to be used in future devices. Javey and his research group have focused on compound III–V semiconductors, which feature superb electron transport properties. The challenge has been to find a way of plugging these compound semiconductors into the well- established, low-cost processing technology used to produce today's silicon-based devices. Given the large lattice mismatch between silicon and III-V compound semiconductors, direct hetero-epitaxial growth of III-V on silicon substrates is challenging and complex, and often results in a high volume of defects.

"We've demonstrated what we are calling an 'XOI,' or compound semiconductor-on-insulator technology platform, that is parallel to today's 'SOI,' or silicon-on-insulator platform,"says Javey."Using an epitaxial transfer method, we transferred ultrathin layers of single-crystal indium- arsenide on silicon/silica substrates, then fabricated devices using conventional processing techniques in order to characterize the XOI material and device properties."

The results of this research have been published in the journalNature,in a paper titled,"Ultrathin compound semiconductor on insulator layers for high-performance nanoscale transistors."Co-authoring the report with Javey were Hyunhyub Ko, Kuniharu Takei, Rehan Kapadia, Steven Chuang, Hui Fang, Paul Leu, Kartik Ganapathi, Elena Plis, Ha Sul Kim, Szu-Ying Chen, Morten Madsen, Alexandra Ford, Yu-Lun Chueh, Sanjay Krishna and Sayeef Salahuddin.

To make their XOI platforms, Javey and his collaborators grew single-crystal indium arsenide thin films (10 to 100 nanometers thick) on a preliminary source substrate then lithographically patterned the films into ordered arrays of nanoribbons. After being removed from the source substrate through a selective wet-etching of an underlying sacrificial layer, the nanoribbon arrays were transferred to the silicon/silicasubstratevia a stamping process.

Javey attributed the excellent electronic performance of the XOI transistors to the small dimensions of the active"X"layer and the critical role played by quantum confinement, which served to tune the material's band structure and transport properties. Although he and his group only used indium arsenide as their compound semiconductor, the technology should readily accommodate other compound III/V semiconductors as well.

"Future research on the scalability of our process for 8-inch and 12-inch wafer processing is needed,"Javey said.

"Moving forward we believe that the XOI substrates can be obtained through a wafer bonding process, but our technique should make it possible to fabricate both p- and n- type transistors on the same chip for complementary electronics based on optimal III–V semiconductors.

"Furthermore, this concept can be used to directly integrate high performance photodiodes, lasers, and light emitting diodes on conventional silicon substrates. Uniquely, this technique could enable us to study the basic material properties of inorganicsemiconductorswhen the thickness is scaled down to only a few atomic layers."

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Scientists crack materials mystery in vanadium dioxide

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(PhysOrg.com) -- A systematic study of phase changes in vanadium dioxide has solved a mystery that has puzzled scientists for decades, according to researchers at the Department of Energy's Oak Ridge National Laboratory.

Scientists have known that vanadium dioxide exhibits several competing phases when it acts as an insulator at lower temperatures. However, the exact nature of the phase behavior has not been understood since research began on vanadium dioxide in the early 1960s.

Alexander Tselev, a research associate from the University of Tennessee-Knoxville working with ORNL's Center for Nanophase Materials Sciences, in collaboration with Igor Luk'yanchuk from the University of Picardy in France used acondensed matter physicstheory to explain the observed phase behaviors of vanadium dioxide, a material of significant technological interest for optics and electronics.

"We discovered that the competition between several phases is purely driven by the lattice symmetry,"Tselev said."We figured out that the metallic phase lattice of vanadium oxide can 'fold' in different ways while cooling, so what people observed was different types of its folding."

Vanadium dioxide is best known in the materials world for its speedy and abrupt phase transition that essentially transforms the material from a metal to an insulator. The phase change takes place at about 68 degrees Celsius.

"These features ofelectrical conductivitymake vanadium dioxide an excellent candidate for numerous applications in optical, electronic and optoelectronic devices,"Tselev said.

Devices that might take advantage of the unusual properties of VO2 include lasers, motion detectors and pressure detectors, which could benefit from the increased sensitivity provided by the property changes of vanadium dioxide. The material is already used in technologies such asinfrared sensors.

Researchers said their theoretical work could help guide future experimental research in vanadium dioxide and ultimately aid the development of new technologies based on VO₂.

"In physics, you always want to understand how the material ticks,"said Sergei Kalinin, a senior scientist at the CNMS."The thermodynamic theory will allow you to predict how the material will behave in different external conditions."

The results were published in the American Chemical Society'sNano Letters. The research team also included Ilia Ivanov, John Budai and Jonathan Tischler at ORNL and Evgheni Strelcov and Andrei Kolmakov at Southern Illinois University.

The team's theoretical research expands upon previous experimental ORNL studies with microwave imaging that demonstrated how strain and changes of crystal lattice symmetry can produce thin conductive wires in nanoscale vanadium dioxide samples.

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Mechanical engineering at the molecular level: Self-assembly of nano-rotors (w/ Video)

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German scientists from the Technische Universitaet Muenchen have managed to direct the self-assembly of rod-shaped molecules into rotors only few nanometers in size. The tiny systems serve the study of forces that act on molecules on surfaces and in cage-like structures. Their findings are published in the current online issue of the<i>Proceedings of the National Academy of Sciences</i>.

In the nanoworld many things are different. Scientists only recently started unveiling and harnessing the underlying laws and principles. A team associated with Professor Johannes Barth from the Physics Department of the TU Muenchen have now succeeded in capturing rod-shaped molecules in a two-dimensional network in such a way that they autonomously form small rotors that turn in their honeycomb-like cages.

Nature itself provides the role model for such self-organizing systems. This is how proteins bring reactants so close together that reactions can take place– reactions that are possible only in very close proximity. These effects are put to use in catalysts: surface reactants find their way to each other on the surface of these facilitators. However, the coveted dream of using self-organization effects in such a way that nano machines assemble themselves is still a thing of the future.

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Driven by thermal energy, the nano-rotors start rotating. Credit: Video: Florian Klappenberger, TUM

The rotors developed in Garching are an important step in this direction. First, the physicists built up an extensive nano lattice by allowing cobalt atoms and rod-shaped molecules of sexiphenyl-dicarbonitrile to react with each other on a silver surface. This results in a honeycomb-like lattice of extreme regularity with astonishing stability. Just like graphene, for which its discoverers were awarded the Nobel Prize only a few weeks ago, this lattice is exactly one atom thick.

When the researchers added further molecular building blocks, the rods spontaneously gathered, typically in groups of three, in a honeycomb cell while neighboring cells remained empty. The chummy molecules must have had a reason for organizing themselves in threesomes. Under a scanning tunneling microscope the scientists were able to recognize why. The three molecules oriented themselves in such a way that the nitrogen ends each faced a phenyl-ring hydrogen atom. This triple-bladed rotor arrangement is so energetically advantageous that the molecules maintain this structure even when thermal energy drives it to rotation.

Because the honeycomb-cell is not round, but hexagonal, there are two different positions for the rotors that can be distinguished as a result of the interactions between the outer nitrogen atoms and the hydrogen atoms of the cell wall. Furthermore, the three molecules arrange in a clockwise and a counter-clockwise manner. In experiments at various carefully controlled temperatures the physicists were able to"freeze"all four states and examine them closely. They could thus determine the energy of these thresholds from the temperature at which the rotation resumed.

"We hope that in future we will be able to extend these simple mechanical models to optical or electronic switching,"says Professor Johannes Barth."We can set a specific cell size, we can specifically bring in furthermoleculesand study their interaction with the surface and the cell wall. These self-organizing structures hold enormous potential."

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World-first to provide building blocks for new nano devices

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(PhysOrg.com) -- Scientists at The University of Nottingham have made a major breakthrough that could help shape the future of nanotechnology, by demonstrating for the first time that 3-D molecular structures can be built on a surface.

The discovery could prove a significant step forward towards the development of new nano devices such as cutting-edge optical and electronic technologies and even molecular computers.

In a paper published in the prestigious journalNature Chemistry, the team of chemists and physicists at Nottingham have shown that by introducing a 'guest' molecule they can buildmoleculesupwards from a surface rather than just 2-D formations previously achieved.

A naturalbiological processknown as 'self-assembly' meant that once the scientists introduced other molecules on to a surface their host then spontaneously arranged them into a rational 3-D structure.

Professor Neil Champness said:"It is the molecular equivalent of throwing a pile of bricks up into the air and then as they come down again they spontaneously build a house.

"Until now this has only been achievable in 2-D, so to continue the analogy the molecular 'bricks' would only form a path or a patio but our breakthrough now means that we can start to build in the third dimension. It's a significant step forward tonanotechnology."

Previously, scientists have employed a technique found in nature of usinghydrogen bondsto hold DNA together to build two-dimensional molecular structure.

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The new process involved introducing a guest molecule— in this case a 'buckyball' or C₆₀— on to a surface patterned by an array of tetracarboxylic acid molecules. The spherical shape of the buckyballs means they sit above the surface of the molecule and encourage other molecules to form around them. It offers scientists a completely new and controlled way of building up additional layers on the surface of the molecule.

The work is the culmination of four years' of research led by Professors Champness and Beton from the School of Chemistry and the School of Physics and Astronomy.

The research paper is the second significant breakthrough to be reported by the team in recent weeks. In September, a paper inNature Communicationsrevealed they had demonstrated for the first time the way in which an irregularly shaped molecule is adsorbed on asurface. It represents a step towards being able to harness the potential of these molecules, which have extremely useful properties, by organising them to form structures. They could offer a way of building new data storage devices that are orders of magnitude smaller than their existing silicon-based counterparts.

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Damaging graphene to create a band gap

(PhysOrg.com) --"Graphene offers a lot of interesting potential applications for nanoelectronics,"Florian Banhart tells<i>PhysOrg.com</i>,"but there is no band gap. This is a well-known problem. Without the band gap, switching as needed in electronic devices is difficult."

Banhart, a scientist at the University of Strasbourg in Strasbourg, France, believes that there is a solution to this problem.“Everyone tries to solve this problem, trying to create different properties in order to create aband gap. Our solution is doping with metal atoms attached to reconstructeddefectsin thegraphene.”

Working with Ovidiu Cretu and Julio Rodríguez-Manzo at the University of Stasbourg, and with Arkady Krasheninnikov at the University of Helsinki, Risto Nieminen at Aalto University in Finland and Litao Sun at Southeast University in Nanjing, China, Banhart developed a method to modify the properties of graphene. The group’s work is published inPhysical Review Letters:“Migration and Localization of Metal Atoms on Strained Graphene.”

“The idea is to be able to attach something to the surface of the graphene, changing some of the properties to get a band gap,” Banhart explains. By creating reconstructed defects, we can enhance the activity of the graphene and attach metal atoms firmly, possibly producing a band gap.”

Banhart and his colleagues created graphene layers that were then damaged.“We used an electron beam to damage the graphene,” Banhart says.“For this paper, we used tungsten atoms to bond to the graphene. The defects we created made it possible for the tungsten atoms to be trapped by the defects, creating stable bonds.”

Reconstructed defects increase the activity seen in graphene, making bonding to other atoms possible.“The graphene surface is normally rather inert,” Banhart explains,“but defects such as pentagonal or heptagonal rings enhance its activity. We saw enhanced chemical activity with the graphene.”

Even though Banhart and his colleagues hope that this work will lead to the eventual creation of nanoelectronic devices made with graphene, he points out that they were unable to show definitive evidence of band gap creation.“There is no evidence that we did create a band gap,” he admits.“But perhaps tungsten is not ideal. We used it because it is large, and easy to see with the electron microscope when trapped by the graphene.”

Banhart says that the tungsten has served its purpose, showing that it is possible to attachmetal atomsto graphene with the help of defects on the graphene’s surface. He also points out that their recent work shows that it is possible to use this technique to modify graphene’s properties locally.“We have shown that our method might be used in the future to control graphene’s electronic properties better.”

The next step is to try to trap other atoms using defects in graphene. Banhart would also like to do more tests on the electronic properties of graphene doped in this manner.“It would be good to do more tests of graphene,” he says.“With more experiments, we should be able to begin to model the electronic structure of graphene more accurately. Once we better understand the properties of graphene, we should be able to better manipulate them so that we can get a band gap, and so that we can use them in nanoelectronic devices.”

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AFM tips from the microwave

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Scientists from the Friedrich-Schiller-University Jena (Germany) have succeeded in improving a fabrication process for Atomic Force Microscopy (AFM) probe tips.

Atomic Force Microscopy is able to scan surfaces so that even tiniestnano structuresbecome visible. Knowledge about these structures is for instance important for the development of new materials and carrier systems for active substances. The size of the probe is highly important for the image quality as it limits the dimensions that can be visualized– the smaller the probe, the smaller the structures that are revealed.

Carbon nanotubes are supposed to be a superior material for the improvement of such scanning probes. However, it is difficult to attach them on scanning probes, which limits their practical use.

Chemists of the Friedrich-Schiller-University Jena found a way to overcome these problems. The research team of Prof. Dr. Ulrich S. Schubert succeeded in developing a new type of process that allows the growth of carbon nanotubes on the actual scanning probe. These innovative discoveries are published in theNano Lettersand areavailable online.

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Dr. Stephanie Hoeppener from Jena University holds a glass cylinder with carbon nanotubes for atomic force microscopy. Credit: Jan-Peter Kasper/University Jena

For this process the Jena scientists are usingmicrowaveradiation for a gentle but very fast growth of the nanotubes. The growth starts at small cobalt particles, that are being taken up with the help of the AFM tip."The metal particles strongly heat up in the microwave and reach a temperature that is sufficient to convert alcohol vapor into carbon. The heating process works similar like a forgotten spoon in the kitchen microwave which also absorbs the microwave radiation very effectively,"explains Tamara Druzhinina from Schubert's research team."Carbon nanotubes can be grown very quickly due to the special conditions inside of the microwave which can generate a pressure up to 20 bar"adds her colleague Dr. Stephanie Hoeppener.

The Jena chemist Prof. Schubert points out the practical benefits of the process:"The method we developed can potentially result in a very cost-efficient production technology of for instance high resolution probes for Scanning Force Microscopy. These are already available on the market but they are very expensive at 350 Euro each. With the process we can reach a price level, that would justify the use of such tips also just for routine measurements."

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Scientists build world's smallest 'water bottle'

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Scientists have designed and built a container that holds just a single water molecule. The container consists of a fullerene cage and a phosphate moiety that acts as the“cap” to keep the water inside.

The researchers, Qianyan Zhang, et al., from institutes in Beijing and Germany, have published their study on the tinyfullerenecage in a recent issue ofAngewandte Chemie. While previous research has shown that fullerene cages can be used to surround molecules, here the chemists also designed a way to close (and re-open) the cage to let a water molecule in and out.

One of the keys was making the cap the exact size to allow a single water molecule to pass through, and modifying the classic carbon-60 form of fullerene accordingly. Due to its chemical properties, thephosphatemoiety used for the cap can be easily removed and re-attached to the edge of an orifice in the fullerene cage, and can sufficiently lock a single water molecule inside.

The tiny container could have applications in transporting small molecules or radioactive atoms for medical purposes and other uses.

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New microscope reveals ultrastructure of cells

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German researchers at Helmholtz-Zentrum Berlin have developed a new X-ray nanotomography microscope. Using their new system, they can reveal the structures on the smallest components of mammalian cells in three dimensions.

For the first time, there is no need to chemically fix, stain or cut cells in order to study them. Instead, whole living cells are fast-frozen and studied in their natural environment. The new method delivers an immediate 3-D image, thereby closing a gap between conventional microscopic techniques.

The new microscope delivers a high-resolution 3-D image of the entire cell in one step. This is an advantage overelectron microscopy, in which a 3-D image is assembled out of many thin sections. This can take up to weeks for just one cell. Also, the cell need not be labelled with dyes, unlike influorescence microscopy, where only the labelled structures become visible. The new X-ray microscope instead exploits the natural contrast between organic material and water to form an image of all cell structures. Dr. Gerd Schneider and his microscopy team at the Institute forSoft MatterandFunctional Materialshave published their development inNature Methods.

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This is a conventional TEM image of a stained thin section. Credit: HZB

With the high resolution achieved by their microscope, the researchers, in cooperation with colleagues of the National Cancer Institute in the USA, have reconstructed mouse adenocarcinoma cells in three dimensions. The smallest of details were visible: the double membrane of thecell nucleus, nuclear pores in the nuclear envelope, membrane channels in the nucleus, numerous inva­ginations of the inner mitochondrial membrane and inclusions in cell organelles such as lysosomes. Such insights will be crucial for shedding light on inner-cellular processes: such as how viruses or nanoparticles penetrate into cells or into the nucleus, for example.

This is the first time the so-called ultrastructure of cells has been imaged with X-rays to such precision, down to 30 nanometres. Ten nanometres are about one ten-thousandth of the width of a human hair. Ultrastructure is the detailed structure of a biological specimen that is too small to be seen with an optical microscope.

Researchers achieved this high 3-D resolution by illuminating the minute structures of the frozen-hydrated object with partially coherent light. This light is generated by BESSY II, the synchrotron source at HZB. Partial coherence is the property of two waves whose relative phase undergoes random fluctuations which are not, however, sufficient to make the wave completely incoherent. Illumination with partial coherent light generates significantly higher contrast for small object details compared to incoherent illumination. Combining this approach with a high-resolution lens, the researchers were able to visualize the ultrastructures ofcellsat hitherto unattained contrast.

The new X-ray microscope also allows for more space around the sample, which leads to a better spatial view. This space has always been greatly limited by the setup for the sample illumination. The required monochromatic X-ray light was created using a radial grid and then, from this light, a diaphragm would select the desired range of wavelengths. The diaphragm had to be placed so close to the sample that there was almost no space to turn the sample around. The researchers modified this setup: Monochromatic light is collected by a new type of condenser which directly illuminates the object, and the diaphragm is no longer needed. This allows the sample to be turned by up to 158 degrees and observed in three dimensions. These developments provide a new tool in structural biology for the better understanding of the cell structure.

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Nanoscale probe reveals interactions between surfaces and single molecules

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(PhysOrg.com) -- As electronics become smaller and smaller the need to understand nanoscale phenomena becomes greater and greater. Because materials exhibit different properties at the nanoscale than they do at larger scales, new techniques are required to understand and to exploit these new phenomena. A team of researchers led by Paul Weiss, UCLA's Fred Kavli Chair in NanoSystems Sciences, has developed a tool to study nanoscale interactions. Their device is a dual scanning tunneling and microwave-frequency probe that is capable of measuring the interactions between single molecules and the surfaces to which the molecules are attached.

"Our probe can generate data on the physical, chemical, and electronic interactions between singlemoleculesand substrates, the contacts to which they are attached. Just as insemiconductor devices, contacts are critical here,"remarked Weiss, who directs UCLA's CaliforniaNanoSystemsInstitute and is also a distinguished professor of chemistry and biochemistry&materials science and engineering.

The team, which also includes theoretical chemist Mark Ratner from Northwestern University and synthetic chemist James Tour from Rice University, published their findings in the peer-reviewed journalACS Nano.

For the past 50 years, the electronics industry has endeavored to keep up with Moore's Law, the prediction made by Gordon E. Moore in 1965 that the size of transistors in integrated circuits would halve approximately every two years. The pattern of consistent decrease in the size of electronics is approaching the point where transistors will have to be constructed at the nanoscale to keep pace. However, researchers have encountered obstacles in creating devices at the nanoscale because of the difficulty of observing phenomena at such minute sizes.

The connections between components are a vital element of nanoscale electronics. In the case of molecular devices, polarizability measures the extent to which electrons of the contact interact with those of the single molecule. Two key aspects of polarizability measurements are the ability to do the measurement on a surface with subnanometer resolution, and the ability to understand and to control molecular switches in both the on and off states.

To measure the polarizability of single molecules the research team developed a probe capable of simultaneous scanning tunneling microscopy (STM) measurements and microwave difference frequency (MDF) measurements. With the MDF capabilities of the probe, the team was able to locate single molecule switches on substrates, even when the switches were in the off state, a key capability lacking in previous techniques. Once the team located the switches, they could use the STM to change the state to on or off and to measure the interactions in each state between the single molecule switches and the substrate.

The new information provided by the team's probe focuses on what the limits of electronics will be, rather than targeting devices for production. Also, because the probe is capable of a wide variety of measurements— including physical, chemical and electronic— it could enable researchers to identify submolecular structures in complex biomolecules and assemblies.

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Securing the nation with fingerprinting materials

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Lawrence Livermore National Laboratory researchers may have found a way to improve Raman spectroscopy as a tool for identifying substances in extremely low concentrations. Potential applications for Raman spectroscopy include medical diagnosis, drug/chemical development, forensics and highly portable detection systems for national security.

The ability to identify molecules at low concentrations with great specificity and provide non-invasive, nondestructive measurements has led to the increasing use of Raman spectroscopy as an accepted analytical technique. But a shortcoming of this technique has been its lack of sensitivity and reliability at extremely low concentrations.

Raman spectroscopy consists of observing the scattering of light, usually from a laser, by molecules of a transparent substance. The difference in the wavelength ofscattered lightand incident light can provide detailed information about the nature of the substance.

"Raman scattering provides a nice fingerprint of materials of interest for national security,"said Tiziana Bond of LLNL's Center for Micro and Nano Technology.

Bond and her group develop surface-enhanced Raman spectroscopy (SERS), a method that increases sensitivity orders of magnitude by improving signals. While showing great potential, the substrates used for SERS, typically roughened metal surfaces, have yielded variable signals considered, as yet, unreliable. The roughened surface enhances the interaction of the molecule with the metal. The challenge has been to find a way to create a substrate with uniform topographic features that yield consistent signal enhancements.

Some of this work is described in a paper published in the September 2010 edition ofNanotechnologyentitled"Rigorous Surface Enhanced Raman Spectral Characterization of Large-Area, High-Uniformity, Silver-Coated Tapered Silica Nanopillar Arrays,"which was published by Bond and her group in collaboration with researchers from the University of Illinois at Urbana-Champaign.

Improved nano-engineering techniques and semiconductor manufacture methods have enabled the production of SERS substrates -- the base layer or texture on 4- to 6-inch wafers -- that are more reliable. The key is substrates with"reproducibility"sufficient for reliable analysis. LLNL researchers have worked on several techniques to achieve a more robust and uniform substrate that maintains high sensitivity and reproducibility.

Electromagnetic and chemical enhancements are two factors that affect SERS total enhancement (with respect to Raman). The first is stronger and accounts for 106-108 magnitude improvements, while the second is typically responsible for 10-100 factors. To exploit the electromagnetic effects, the metallic nanostructures need to be properly designed.

In an article entitled"Plasmon Resonant Cavities in Vertical Nanowire Arrays"published inNano Lettersearlier this year, Bond's group, investigate an innovative design using a vertical a gold-coated nanowire array substrate that would provide strong and controllable enhancement. The LLNL team's innovation is the fabrication of"tunable"plasmon resonant cavities in the vertical wire arrays -- cavities are the space between the vertical wires. Mihail Bora, a postdoc that joined Bond's group a year ago, is heavily involved in this part of the project and explains that surface plasmons are electromagnetic waves similar to light, except they are confined on metallic surfaces. Tuning of plasmon resonance is achieved by controlling the geometrical dimensions of the cavity.

They introduce the smallest optical resonant cavity that is thousands of times smaller than wavelength of light and showed that it is possible to go beyond this diffraction limit by using surface plasmons. Resonant cavities are currently used for surface enhancedRaman spectroscopyto detect chemical analytes (concentration)."By confining the light in such tight spaces we are able to create intense fields that are useful in increasing the spectroscopy signal,"Bond said.

These design features offer a number of advantages. For example, it allows the sensitivity of the substrates to be tuned, or adapted, to different wavelengths offering researchers greater versatility.

Among possible application extensions of the plasmonic substrate beyond the enhancement of SERS are enabling the demonstration of sub-wavelength plasmonic lasers, and broadband nanoantenna arrays for photovoltaics by playing with geometry factors.

The group's work has been funded by Defense Advanced Research Projects Agency (DARPA) and LLNL's Laboratory Directed Research and Development (LDRD) program.

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