This illustration shows the structure of the molecular motors. (Credit: Saw-Wai Hla)

An international team of scientists has taken the next step in creating nanoscale machines by designing a multi-component molecular motor that can be moved clockwise and counterclockwise.

Although researchers can rotate or switch individual molecules on and off, the new study is the first to create a stand-alone molecular motor that has multiple parts, said Saw-Wai Hla, an Ohio University professor of physics and astronomy who led the study with Christian Joachim of A*Star in Singapore and CEMES/CNRS in France and Gwenael Rapenne of CEMES/CNRS.

It’s an essential step in creating nanoscale devices—quantum machines that operate on different laws of physics than classical machines—that scientists envision could be used for everything from powering quantum computers to sweeping away blood clots in arteries.

In the study, published in Nature Nanotechnology [abstract], the scientists demonstrated that they could control the motion of the motor with energy generated by electrons from a scanning tunneling microscope tip. The motor is about 2 nanometers in length and 1 nanometer high and was constructed on a gold crystal surface. [Watch an animation of the motor at the journal's website here. Credit: F. Ample and C. Joachim. (Scroll down to "Supplementary information" for links to the two animations.)]

At a temperature of minus 315 degrees Fahrenheit, the motor could move independently through thermal excitation. When scientists cooled the sample to minus 450 degrees, the motor stopped rotating. The researchers selectively applied electron energy to different parts of the motor to prompt it to move clockwise and counterclockwise.

“If we want to build an actual device based on this motor, we would install electrodes on the surface to create an energy source,” Hla said.

To construct the molecular motor, the scientific team designed a stationary base of atoms that is connected to an upper moving part by one atom of ruthenium, which serves as the “ball bearing.” The upper piece of the motor features five arms made of iron atoms. The researchers made one arm shorter than the others to be able to track the motion of the machine. The entire device is held upright by using sulfur as an “atomic glue” to secure the motor to the gold surface, Hla explained.

The scientists now plan to use this model to build more complex machines with components that could be automated, Hla said.

One of the three corresponding authors is Christian Joachim, winner of the 2005 Foresight Nanotech Institute Feynman Prize for Theoretical work and one of three winners of the 1997 Foresight Nanotech Institute Feynman Prize for Experimental work.

The molecular motor consists of a single ruthenium atom bearing connecting a tripodal stator to a five-arm rotor. to help detect the motion of the rotor, the five arms are not all equivalent. The centner of the rotor is a cyclopentadiene, one short arms is merely a toluene, while the other four long arms each comprise a phenyl group connected to a ferrocene (two cyclopentadienyl rings sandwiching an iron atom). The ferrocene groups act as reversible electron relays. The four ferrocene end groups enable control of rotation by four nanoelectrodes. The tripodal stator comprises a boron atom connected to three indazolyl groups, each with a thioether foot that binds via a sulfur atom to the gold surface upon which the motor sits.

The motor was imaged using a scanning tunneling microscope (STM) under ultra high vacuum conditions (UHV). For some samples a large bias voltage pulse was used to remove the top (rotor) part of the motor, revealing the tripod stator positioned with each leg along a [211] surface direction of the Au(111) surface. At 80 K the image of the intact motor shows a uniform circle due to the free rotation of the rotor. At 4.6 K rotation has been stopped so that the asymmetric five-lobe structure of the rotor is visible, with four long arms and one short arm.

After positioning the tungsten STM tip above the center of the rotor and then gradually increasing the voltage, rotation was observed at 0.6 V due to inelastic electron tunneling energy transfer. Stepwise rotation was achieved at 4.6 K by placing the STM tip over the molecule at a fixed height for an excitation period of less than one second. The direction of rotation was determined by where the STM tip was placed: predominantly clockwise if electrons were passing through the truncated arm, and mostly counterclockwise if electron excitation was via a ferrocene arm. The authors point out that the tripodal stator lifts the rotor high enough about the gold surface so that the surface does not influence the rotation. They present semi-empirical and density functional theory calculations to explain the detailed rotational mechanisms of the motor. The results show that asymmetries in rotational energy potential lead to the observed rotations by selective excitation of different subunits of the motor. They believe this understanding “will further accelerate the development of complex and automated nanomachinery that can be operated on a material surface.”

The combination of a multicomponent molecular motor and detailed theoretical analysis to elucidate the mechanisms responsible for the action of the motor raises the hope that this work will indeed further accelerate development of complex automated molecular machinery.
—James Lewis, PhD

Darpa's Living Foundries program is looking to transform biology into an engineering practice. Photo: VA

Synthetic biology promises near-term breakthroughs in medicine, materials, and energy, and is also one promising development pathway leading to advanced nanotechnology and a general capability for programmable, atomically-precise manufacturing. Darpa (US Defense Advanced Research Projects Agency) has launched a new program that could greatly accelerate progress in synthetic biology by creating a library of standardized, modular biological units that could be used to build new devices and circuits. A hat tip to KurzweilAI.net for pointing to a recent article in Wired Danger Room “Darpa, Venter launch assembly line for genetic engineering“:

… The program, called “Living Foundries,” was first announced by the agency last year. Now, Darpa’s handed out seven research awards worth $15.5 million to six different companies and institutions. Among them are several Darpa favorites, including the University of Texas at Austin and the California Institute of Technology. Two contracts were also issued to the J. Craig Venter Institute. Dr. Venter is something of a biology superstar: He was among the first scientists to sequence a human genome, and his institute was, in 2010, the first to create a cell with entirely synthetic genome.

“Living Foundries” aspires to turn the slow, messy process of genetic engineering into a streamlined and standardized one. Of course, the field is already a burgeoning one: Scientists have tweaked cells in order to develop renewable petroleum and spider silk that’s tough as steel. And a host of companies are investigating the pharmaceutical and agricultural promise lurking — with some tinkering, of course — inside living cells.

But those breakthroughs, while exciting, have also been time-consuming and expensive. As Darpa notes, even the most cutting-edge synthetic biology projects “often take 7+ years and tens to hundreds of millions of dollars” to complete. Venter’s synthetic cell project, for example, cost an estimated $40 million.

Synthetic biology, as Darpa notes, has the potential to yield “new materials, novel capabilities, fuel and medicines” — everything from fuels to solar cells to vaccines could be produced by engineering different living cells. But the agency isn’t content to wait seven years for each new innovation. In fact, they want the capability for “on-demand production” of whatever bio-product suits the military’s immediate needs.

To do it, Darpa will need to revamp the process of bio-engineering — from the initial design of a new material, to its construction, to its subsequent efficacy evaluation. The starting point, and one that agency-funded researchers will have to create, is a library of “modular genetic parts”: Standardized biological units that can be assembled in different ways — like LEGO — to create different materials.

Once that library is created, the agency wants researchers to come up with a set of “parts, regulators, devices and circuits” that can reliably yield various genetic systems. After that, they’ll also need “test platforms” to quickly evaluate new bio-materials. Think of it as a biological assembly line: Products are designed, pieced together using standardized tools and techniques, and then tested for efficacy. …

The Darpa Living Foundries solicitation will remind long-term Nanodot readers of discussions of the need for an engineering perspective in the development of advanced nanotechnology centered on molecular manufacturing:

The Microsystems Technology Office (MTO) of the Defense Advanced Research Projects Agency (DARPA) is sponsoring an Industry Day for “Living Foundries,” a new DARPA program. The goal of the Living Foundries program is to apply an engineering framework to biology to harness its use as a technology and drive its advance as a manufacturing platform. In turning biological production into an engineering space where the only limit is the creativity of the designer, Living Foundries aims to enable on-demand production of new and high-value materials, devices and capabilities for the Department of Defense and establish a new manufacturing capability for the United States.

Because of the multidisciplinary nature of Living Foundries, DARPA is looking to engage the wider research community from fields both outside and inside the biological sciences to develop new ideas, approaches and tools to overcome current limitations and to create revolutionary capabilities.

Current, primitive examples of engineering biology rely on an ad hoc, laborious, trial-and-error process, wherein one successful project does not inform subsequent, new designs. This approach combined with the complexity of biological systems restricts current, one-off efforts to modifying only a small set of genes and constructing simple, isolated genetic circuits and metabolic pathways. Consequently, we are limited to producing only a small fraction of the vast number of possible chemicals, materials, and living systems that would be enabled by the ability to truly engineer biology. Through an engineering-driven approach to biology, Living Foundries aims to create a rapid, reliable manufacturing capability where multiple cellular functions can be fabricated, mixed and matched on demand and the whole system controlled by integrated circuitry, opening up the full space of biologically produced materials and systems. Key to success will be the democratization of the biological design and manufacturing process, breaking open the field to those outside the biological sciences.

In order to achieve the vision of Living Foundries, new tools, technologies and methodologies must be developed to transform biology into an engineering practice, decoupling design from fabrication and speeding the biological design, build, test cycle. These include: design tools that span from high-level description to fabrication in cells; modular genetic parts that allow a combination of systems to be designed and reproducibly assembled; methods for developing and fine-tuning new genetic parts and systems; well-understood test platforms, “cell-like” systems and chassis that readily integrate new genetic designs in a predictable fashion; next generation DNA synthesis and assembly techniques; and tools that allow for routine system characterization and debugging, among others. Further, these technological advances and innovations must be integrated to prove-out and push the boundaries of biological design towards the ultimate vision of point-of-use, on-demand, mass-customization biological manufacturing. …

If Darpa’s Living Foundries program achieves its ambitious goals, it should create a methodology, toolbox, and a large group of practitioners ready to pursue a synthetic biology pathway to building complex molecular machine systems, and eventually, atomically precise manufacturing systems.
—James Lewis, PhD

When a sheet of graphene sits atop a sheet of boron nitride at an angle, a secondary hexagonal pattern emerges that determines how electrons flow across the sample. (Illustration by Brian LeRoy)

Despite its superlative properties, graphene has not been used to make electronic devices because electrons travel so well though it that they cannot be easily controlled. Now physicists have discovered that placing graphene sheets on boron nitride at the proper angle creates a superlattice that controls the movement of graphene electrons. A hat tip to ScienceDaily for reprinting this University of Arizona news release written by Daniel Stolte “Microprocessors From Pencil Lead“:

Graphite, more commonly known as pencil lead, could become the next big thing in the quest for smaller and less power-hungry electronics.

Resembling chicken wire on a nano scale, graphene – single sheets of graphite – is only one atom thick, making it the world’s thinnest material. Two million graphene sheets stacked up would not be as thick as a credit card.

The tricky part physicists have yet to figure out how to control the flow of electrons through the material, a necessary prerequisite for putting it to work in any type of electronic circuit. Graphene behaves very different than silicon, the material currently used in semiconductors.

Last year, a research team led by UA physicists cleared the first hurdle by identifying boron nitride, a structurally identical but non-conducting material, as a suitable mounting surface for single-atom sheets of graphene. The team also showed that in addition to providing mechanical support, boron nitride improves the electronic properties of graphene by smoothening out fluctuations in the electronic charges.

Now the team found that boron nitride also influences how the electrons travel through the graphene. Published in Nature Physics [abstract], the results open up new ways of controlling the electron flow through graphene.

“If you want to make a transistor for example, you need to be able to stop the flow of electrons,” said Brian LeRoy, an assistant professor in the University of Arizona’s department of physics. “But in graphene, the electrons just keep going. It’s difficult to stop them.” …

However, as LeRoy’s group has now discovered, mounting graphene on boron nitride prevents some of the electrons from passing to the other side, a first step toward a more controlled electron flow.

The group achieved this feat by placing graphene sheets onto boron nitride at certain angles, resulting in the hexagonal structures in both materials to overlap in such a way that secondary, larger hexagonal patterns are created. The researchers call this structure a superlattice.

If the angle is just right, they found, a point is reached where almost no electrons go through.

The news release points out that the researchers cannot yet control the angle at which the graphene and boron nitride are oriented so that only 10-20% of the samples they make show the desired effect. This process must be automated before graphene electronics become practical.
—James Lewis, PhD

Credit: Lab of Jene Golovchenko, Harvard University

One of the greatest promises of near-term nanotechnoloogy is cheaper DNA sequencing to speed the development of personalized medicine. There are not only genetic differences between different patients, but also genetic differences between, for example, different cancers of the same organ diagnosed in different patients, or even from different locations in the same patient, that can greatly affect the success of a therapy. Nanopore sensors are among the promising new third-generation DNA sequencing technologies being developed to make inexpensive whole genome sequencing a reality. A review of the potential of this emerging nanotechnology was published recently in Nature Nanotechnology [abstract]. The full text of the review “Nanopore sensors for nucleic acid analysis” has been made available by the authors for down-loading. Nanopores and other third generation sequencing technologies sequence single molecules of DNA in real time. Single molecules of DNA are pulled through a nanopore of some type and changes in the ionic current, dependent on whether an A, G, C, or T nucleotide is passing through the pore, are recorded. The review discusses the different types of nanopore that have been tried, both biological and solid-state, and the challenges encountered, such as reducing the speed at which the DNA molecule transits the nanopore, and improving sensitivity.

Research done by scientists at Harvard and MIT and published in Nature [abstract, free authors' manuscript deposited in PubMedCentral] showed that a graphene sheet one or two atomic layers thick could form an electrode separating two liquid reservoirs so that current from ions passing through a nanopore in the graphene sheet could be measured, and the current blockade seen when DNA molecules passed through the pore indicated it should be possible to resolve individual nucleotides with an insulating membrane this thin. From a Harvard Gazette article by Michael Rutter “Graphene may help speed up DNA sequencing“:

… By drilling a tiny pore just a few nanometers in diameter, called a nanopore, in the graphene membrane, the researchers were able to measure exchange of ions through the pore and demonstrate that a long DNA molecule can be pulled through the graphene nanopore just as a thread is pulled through the eye of a needle.

“By measuring the flow of ions passing through a nanopore drilled in graphene we have demonstrated that the thickness of graphene immersed in liquid is less then 1 nm thick, or many times thinner than the very thin membrane which separates a single animal or human cell from its surrounding environment,” says lead author Slaven Garaj, a physics research associate at Harvard. “This makes graphene the thinnest membrane able to separate two liquid compartments from each other. The thickness of the membrane was determined by its interaction with water molecules and ions.” …

“Although the membrane prevents ions and water from flowing through it, the graphene membrane can attract different ions and other chemicals to its two atomically close surfaces. This affects graphene’s electrical conductivity and could be used for chemical sensing,” says co-author Jene Golovchenko, the Rumford Professor of Physics and Gordon McKay Professor of Applied Physics at Harvard, whose pioneering work started the field of artificial nanopores in solid-state membranes. “I believe the atomic thickness of the graphene makes it a novel electrical device that will offer new insights into the physics of surface processes and lead to a wide range of practical application, including chemical sensing and detection of single molecules.” …

When the researchers added long DNA chains in the liquid, they were electrically pulled one by one through the graphene nanopore. As the DNA molecule threaded the nanopore, it blocked the flow of ions, resulting in a characteristic electrical signal that reflects the size and conformation of the DNA molecule. …

As a DNA chain passes through the nanopore, the nucleobases, which are the letters of the genetic code, can be identified. But a nanopore in graphene is the first nanopore short enough to distinguish between two closely neighboring nucleobases.…

More recently another group at Harvard has integrated nanowire field-effect transistors with a solid-state nanopore to achieve rapid, sensitive detection of the very small currents created as DNA molecules zip through the nanopore. From a Harvard Gazette story by Peter Reuell “Reading life’s building blocks“:

Scientists are one step closer to a revolution in DNA sequencing, following the development in a Harvard lab of a tiny device designed to read the minute electrical changes produced when DNA strands are passed through tiny holes — called nanopores — in an electrically charged membrane.

As described in Nature Nanotechnology [abstract, free full text provided by authors] on Dec. 11, a research team led by Charles Lieber, the Mark Hyman Jr. Professor of Chemistry [and also winner of the 2001 Feynman Prize in Nanotechnology-Experimental], have succeeded for the first time in creating an integrated nanopore detector, a development that opens the door to the creation of devices that could use arrays of millions of the microscopic holes to sequence DNA quickly and cheaply.

First described more than 15 years ago, nanopore sequencing measures subtle electrical current changes produced as the four base molecules that make up DNA pass through the pore. By reading those changes, researchers can effectively sequence DNA.

But reading those subtle changes in current is far from easy. A series of challenges — from how to record the tiny changes in current to how to scale up the sequencing process — meant the process has never been possible on a large scale. Lieber and his team, however, believe they have found a unified solution to most of those problems.

“Until we developed our detector, there was no way to locally measure the changes in current,” Lieber said. “Our method is ideal because it is extremely localized. We can use all the existing work that has been done on nanopores, but with a local detector we’re one step closer to completely revolutionizing sequencing.”

The detector developed by Lieber and his team grew out of earlier work on nanowires. Using the ultra-thin wires as a nanoscale transistor, they are able to measure the changes in current more locally and accurately than ever before.

“The nanowire transistor measures the electrical potential change at the pore and effectively amplifies the signal,” Lieber said. “In addition to a larger signal, that allows us to read things much more quickly. That’s important because DNA is so large [that] the throughput for any sequencing method needs to be high. In principle, this detector can work at gigahertz frequencies.”

The highly localized measurement also opens the door to parallel sequencing, which uses arrays of millions of pores to speed the sequencing process dramatically.

In addition to the potential for greatly improving the speed of sequencing, the new detector holds the promise of dramatically reducing the cost of DNA sequencing, said Ping Xie, an associate of the Department of Chemistry and Chemical Biology and co-author of the paper describing the research. …

“Right now, we are limited in our ability to perform DNA sequencing,” Xie said. “Current sequencing technology is where computers were in the ’50s and ’60s. It requires a lot of equipment and is very expensive. But just 50 years later, computers are everywhere, even in greeting cards. Our detector opens the door to doing a blood draw and immediately knowing what a patient is infected with, and very quickly making treatment decisions.”

Rapid, inexpensive DNA sequencing and other nanotechnology-based innovations in drug-delivery and tissue regeneration may transform health care in the coming decade.
—James Lewis

Australian and American physicists have built a working transistor from a single phosphorus atom embedded in a silicon crystal.

The group of physicists, based at the University of New South Wales and Purdue University, said they had laid the groundwork for a futuristic quantum computer that might one day function in a nanoscale world and would be orders of magnitude smaller and quicker than today’s silicon-based machines. …

“Their approach is extremely powerful,” said Andreas Heinrich, an I.B.M. physicist. “This is at least a 10-year effort to make very tiny electrical wires and combine them with the placement of a phosphorous atom exactly where they want them.”

He said the research was a significant step toward making a functioning quantum computing system. However, whether quantum computing will ever be harnessed for useful tasks remains uncertain, and the researchers also noted that their work demonstrated the fundamental limits that today’s computers would be able to shrink to.

“It shows that Moore’s Law can be scaled toward atomic scales in silicon,” said Gerhard Klimeck, professor of electrical and computer engineering at Purdue, referring to the rate at which computing gets faster and cheaper. “The technologies for classical computing can survive to the atomic scale.”

The results were published in Nature Nanotechnology [abstract]. At least for the moment (February 19, 2012), the full text is available without charge. Also available in the same issue is a commentary by Gabriel P. Lansbergen “Nanoelectronics: Transistors arrive at the atomic limit“, which gives additional background and details on this accomplishment.

… Single-atom transistors represent the ultimate limit in solid-state device miniaturization, but they are also interesting for another reason. Deterministically positioned single-dopant atoms in silicon, electrically addressable by metallic leads, are at the heart of a number of promising proposals for quantum-information-processing devices3. The long coherence and relaxation times associated with single dopants make them very attractive candidates for quantum-device architectures.

The atom-by-atom fabrication technique developed by Simmons and co-workers therefore fulfills a long-standing need for a method that is capable of atomic-scale device fabrication in silicon. And although the technique is not directly applicable on an industrial scale, it does bring the development of truly atomistic electronics — and the possibilities they offer — into the experimental realm.

This latest accomplishment from Prof. Simmons and her collaborators follows swiftly on their recent demonstration published just last month in Science [abstract], that Ohms law holds for nanowire only four phosphorous atoms wide. From the Purdue University news service “Down to the wire for silicon: Researchers create a wire 4 atoms wide, 1 atom tall“:

The smallest wires ever developed in silicon – just one atom tall and four atoms wide – have been shown by a team of researchers from the University of New South Wales, Melbourne University and Purdue University to have the same current-carrying capability as copper wires.

Experiments and atom-by-atom supercomputer models of the wires have found that the wires maintain a low capacity for resistance despite being more than 20 times thinner than conventional copper wires in microprocessors.

The discovery, which was published in this week’s journal Science, has several implications, including:

• For engineers it could provide a roadmap to future nanoscale computational devices where atomic sizes are at the end of Moore’s law. The theory shows that a single dense row of phosphorus atoms embedded in silicon will be the ultimate limit of downscaling.
• For computer scientists, it places donor-atom based silicon quantum computing closer to realization.
• And for physicists, the results show that Ohm’s Law, which demonstrates the relationship between electrical current, resistance and voltage, continues to apply all the way down to an atomic-scale wire.

…

Although the path from this laboratory demonstration to a practical technology is not yet clear, as emphasized above by the researchers themselves and commentators, the progress at Zyvex Labs (and elsewhere) that we cited in Oct. 2010 in this basic technology of using an STM for atomically precise lithography holds hope that a convergence of manufacturing technology and demonstrated prototypes will not be too distant.
—James Lewis

Tunnelling transistor

Credit: University of Manchester. L. Britnell et al. Science DOI: 10.1126/science.1218461

Combining atomically thin graphene with layers of atomically thin insulators appears to open the door to using graphene in computer chips. A hat tip to KurzweilAI.net for reprinting this University of Manchester news release “Graphene electronics moves into a third dimension“:

Wonder material graphene has been touted as the next silicon, with one major problem—it is too conductive to be used in computer chips. Now scientists from The University of Manchester have given its prospects a new lifeline.

In a paper published this week in Science [abstract], a Manchester team lead by Nobel laureates Professor Andre Geim and Professor Konstantin Novoselov has literally opened a third dimension in graphene research. Their research shows a transistor that may prove the missing link for graphene to become the next silicon.

Graphene—one atomic plane of carbon—is a remarkable material with endless unique properties, from electronic to chemical and from optical to mechanical.

One of many potential applications of graphene is its use as the basic material for computer chips instead of silicon. This potential has alerted the attention of major chip manufactures, including IBM, Samsung, Texas Instruments and Intel. Individual transistors with very high frequencies (up to 300 GHz) have already been demonstrated by several groups worldwide.

Unfortunately, those transistors cannot be packed densely in a computer chip because they leak too much current, even in the most insulating state of graphene. This electric current would cause chips to melt within a fraction of a second. …

The University of Manchester scientists now suggest using graphene not laterally (in plane)—as all the previous studies did—but in the vertical direction. They used graphene as an electrode from which electrons tunnelled through a dielectric into another metal. This is called a tunnelling diode.

Then they exploited a truly unique feature of graphene—that an external voltage can strongly change the energy of tunnelling electrons. As a result they got a new type of a device—vertical field-effect tunnelling transistor in which graphene is a critical ingredient.

Dr Leonid Ponomarenko, who spearheaded the experimental effort, said: “We have proved a conceptually new approach to graphene electronics. Our transistors already work pretty well. I believe they can be improved much further, scaled down to nanometre sizes and work at sub-THz frequencies.” …

The Manchester team made the transistors by combining graphene together with atomic planes of boron nitride and molybdenum disulfide. The transistors were assembled layer by layer in a desired sequence, like a layer cake but on an atomic scale.

Such layer-cake superstructures do not exist in nature. It is an entirely new concept introduced in the report by the Manchester researchers. The atomic-scale assembly offers many new degrees of functionality, without some of which the tunnelling transistor would be impossible.

“The demonstrated transistor is important but the concept of atomic layer assembly is probably even more important,” explains Professor Geim.

Professor Novoselov added: “Tunnelling transistor is just one example of the inexhaustible collection of layered structures and novel devices which can now be created by such assembly.

“It really offers endless opportunities both for fundamental physics and for applications. Other possible examples include light emission diodes, photovoltaic devices, and so on.”

Graphene is one area of nanotechnology that is generating both increased scientific rewards and increased application potential as work continues. It provides an example of the opportunities that can be opened by an apparently serendipitous discovery. It is also an indication of the rich rewards that are to be found from approaching atomic precision in the control of the structure of matter.
—James Lewis

SAN JOSE, Calif. — Researchers at I.B.M. have stored and retrieved digital 1s and 0s from an array of just 12 atoms, pushing the boundaries of the magnetic storage of information to the edge of what is possible.

The findings, being reported Thursday in the journal Science, could help lead to a new class of nanomaterials for a generation of memory chips and disk drives that will not only have greater capabilities than the current silicon-based computers but will consume significantly less power. And they may offer a new direction for research in quantum computing. …

The group at I.B.M.’s Almaden Research Center here, led by Andreas Heinrich, has now created the smallest possible unit of magnetic storage by painstakingly arranging two rows of six iron atoms on a surface of copper nitride. …

Although the research took place at a temperature near absolute zero, the scientists wrote that the same experiment could be done at room temperature with as few as 150 atoms. …

The remainder of the article quotes Dr. Heinrich as saying that these tiny devices built with scanning tunneling microscopes are primarily of interest as a way to explore the quantum mechanical properties of the antiferromagnetic effect in the hope of developing novel nanomaterials that might lead to quantum computers. He also noted that many research groups are exploring self-assembly methods that could lead to practical manufacturing technologies to replace current microelectronic technologies.

For a long time miniaturization has been the magic word in electronics. Dr. Willi Auwaerter and Professor Johannes Barth, together with their team of physicists at the Technische Universitaet Muenchen (TUM), have now presented a novel molecular switch in the journal “Nature Nanotechnology.” Decisive for the functionality of the switch is the position of a single proton in a porphyrin ring with an inside diameter of less than half a nanometer. The physicists can set four distinct states on demand.

Porphyrins are ring-shaped molecules that can flexibly change their structure, making them useful for a wide array of applications. Tetraphenylporphyrin is no exception: It likes to take on a saddle shape and is not limited in its functionality when it is anchored to a metal surface. The molecule holds has a pair of hydrogen atoms that can change their positions between two configurations each. At room temperature this process takes place continuously at an extremely rapid rate.

In their experiment, the scientists suppressed this spontaneous movement by cooling the sample. This allowed them to induce and observe the entire process in a single molecule using a scanning tunneling microscope. This kind of microscope is particularly well suited for the task since – in contrast to other methods – it can be used not only to determine the initial and final states, but also allows the physicists to control the hydrogen atoms directly. In a further step they removed one of the two protons from the inside of the porphyrin ring. The remaining proton could now take on any one of four positions. A tiny current that flows through the fine tip of the microscope stimulates the proton transfer, setting a specific configuration in the process.

Although the respective positions of the hydrogen atoms influence neither the basic structure of the molecule nor its bond to the metallic surface, the states are not identical. This small but significant difference, taken together with the fact that the process can be arbitrarily repeated, forms the basis of a switch whose state can be changed up to 500 times per second. A single tunneled electron initiates the proton transfer. …

Perhaps the next step is to see if a number of such molecular switches could be linked and integrated in a nanoscale environment to build a circuit or other functional assemblage. The abstract of the research paper is here.

This weekend – full of plenary talks, panels, and breakout sessions – is a unique opportunity to be stimulated, enlightened and inspired by direct interaction with ground-breaking movers and shakers in nanotechnology, including:

Keynotes:

- JIM VON EHR – President of Zyvex Labs LLC

Founder of Altsys, the Texas Nanotech Initiative, & the world’s first successful molecular nanotech company

- BARNEY PELL – CoFounder/CTO of Moon Express

Silicon Valley VC best known for AI work on NASA’s Clarissa & Remote Agent, now competing for Google’s Lunar X PRIZE

SingularityU trustee SONIA ARRISON will also emcee panels on:

• The Scientific Challenges of Truly Transformative Nanotech

• From Research to Application: Turning innovation into success

• Funding, Development & the Valley of Death: Transcending entrepreneurial challenges

• Jumpstarting a Career in Nanotech: How to make your move

With speakers and panelists including: Halcyon Molecular CEO WILLIAM ANDREGG, CalTech’s WILLIAM GODDARD, NanoInk CTO MIKE NELSON, Paypal’s LUKE NOSEK, Stanford forecaster PAUL SAFFO, motor-molecule creator SIR FRASER STODDART, Intel’s MIKE GARNER, IBM’s THOMAS THEIS, and more at:

http://www.foresight.org/reunion/schedule.html

Don’t miss our reception Friday night, and Saturday’s 25th Anniversary Banquet.

Register now! Space is limited.

$50 off with code: NANODOT

See you soon!

Desiree D. Dudley
Director of Development and Outreach
desiree@foresight.org

MIT researchers use genetically modified virus to produce structures that improve solar-cell efficiency by nearly one-third.

Researchers at MIT have found a way to make significant improvements to the power-conversion efficiency of solar cells by enlisting the services of tiny viruses to perform detailed assembly work at the microscopic level.

In a solar cell, sunlight hits a light-harvesting material, causing it to release electrons that can be harnessed to produce an electric current. The new MIT research, published online this week in the journal Nature Nanotechnology [abstract], is based on findings that carbon nanotubes — microscopic, hollow cylinders of pure carbon — can enhance the efficiency of electron collection from a solar cell’s surface.

Previous attempts to use the nanotubes, however, had been thwarted by two problems. First, the making of carbon nanotubes generally produces a mix of two types, some of which act as semiconductors (sometimes allowing an electric current to flow, sometimes not) or metals (which act like wires, allowing current to flow easily). The new research, for the first time, showed that the effects of these two types tend to be different, because the semiconducting nanotubes can enhance the performance of solar cells, but the metallic ones have the opposite effect. Second, nanotubes tend to clump together, which reduces their effectiveness.

And that’s where viruses come to the rescue. Graduate students Xiangnan Dang and Hyunjung Yi — working with Angela Belcher, the W. M. Keck Professor of Energy, and several other researchers — found that a genetically engineered version of a virus called M13, which normally infects bacteria, can be used to control the arrangement of the nanotubes on a surface, keeping the tubes separate so they can’t short out the circuits, and keeping the tubes apart so they don’t clump.

The system the researchers tested used a type of solar cell known as dye-sensitized solar cells, a lightweight and inexpensive type where the active layer is composed of titanium dioxide, rather than the silicon used in conventional solar cells. But the same technique could be applied to other types as well, including quantum-dot and organic solar cells, the researchers say. In their tests, adding the virus-built structures enhanced the power conversion efficiency to 10.6 percent from 8 percent — almost a one-third improvement.

This dramatic improvement takes place even though the viruses and the nanotubes make up only 0.1 percent by weight of the finished cell. “A little biology goes a long way,” Belcher says. With further work, the researchers think they can ramp up the efficiency even further.

The viruses are used to help improve one particular step in the process of converting sunlight to electricity. In a solar cell, the first step is for the energy of the light to knock electrons loose from the solar-cell material (usually silicon); then, those electrons need to be funneled toward a collector, from which they can form a current that flows to charge a battery or power a device. After that, they return to the original material, where the cycle can start again. The new system is intended to enhance the efficiency of the second step, helping the electrons find their way: Adding the carbon nanotubes to the cell “provides a more direct path to the current collector,” Belcher says.

The viruses actually perform two different functions in this process. First, they possess short proteins called peptides that can bind tightly to the carbon nanotubes, holding them in place and keeping them separated from each other. Each virus can hold five to 10 nanotubes, each of which is held firmly in place by about 300 of the virus’s peptide molecules. In addition, the virus was engineered to produce a coating of titanium dioxide (TiO2), a key ingredient for dye-sensitized solar cells, over each of the nanotubes, putting the titanium dioxide in close proximity to the wire-like nanotubes that carry the electrons.

The two functions are carried out in succession by the same virus, whose activity is “switched” from one function to the next by changing the acidity of its environment. This switching feature is an important new capability that has been demonstrated for the first time in this research, Belcher says.

In addition, the viruses make the nanotubes soluble in water, which makes it possible to incorporate the nanotubes into the solar cell using a water-based process that works at room temperature. …

Using a virus particle as the biomolecular framework does not enable individually addressing specific sites on the framework, as could be done with scaffolded DNA origami, so it doesn’t seem likely that this approach could be used to assemble systems complex enough for atomically precise manufacturing. On the other hand, this is a very neat demonstration of the MMCN principle for something simpler that might be very near to practical application.