Stanford University: Researchers Make Wires That Are Just Three Atoms Wide

 

Researchers at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have discovered a way to use diamondoids — the smallest possible bits of diamond — to self-assemble atoms, LEGO-style, into the thinnest possible electrical wires, just three atoms wide.

 

Scientists at Stanford University and the US Department of Energy’s SLAC National Accelerator Laboratory have discovered a way to use diamondoids – the smallest possible bits of diamond – to assemble atoms into the thinnest possible electrical wires, just three atoms wide.

By grabbing various types of atoms and putting them together building-block style, the new technique could potentially be used to build tiny wires for a wide range of applications, including fabrics that generate electricity, optoelectronic devices that employ both electricity and light, and superconducting materials that conduct electricity without any loss. The scientists reported their results in Nature Materials.

The animation above shows molecular building blocks joining the tip of a growing nanowire. Each block consists of a diamondoid – the smallest possible bit of diamond – attached to sulfur and copper atoms (yellow and brown spheres). Like LEGO blocks, they only fit together in certain ways that are determined by their size and shape. The copper and sulfur atoms form a conductive wire in the middle, and the diamondoids form an insulating outer shell.

“What we have shown here is that we can make tiny, conductive wires of the smallest possible size that essentially assemble themselves,” said Hao Yan, a Stanford postdoctoral researcher and lead author of the paper. “The process is a simple, one-pot synthesis. You dump the ingredients together and you can get results in half an hour. It’s almost as if the diamondoids know where they want to go.”

Fuzzy white clusters of nanowires on a lab bench, with a penny for scale. Image Source – Hao Yan/SIMES; photo by SLAC National Accelerator Laboratory

In the image above, assembled with the help of diamondoids, the microscopic nanowires can be seen with the naked eye because the strong mutual attraction between their diamondoid shells makes them clump together, in this case by the millions. Also, at top right, is an image made with a scanning electron microscope shows nanowire clusters magnified 10,000 times.

 

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There are other methods to get materials to self-assemble, but this is the first one shown to make a nanowire with a solid, crystalline core that has good electronic properties, said study co-author Nicholas Melosh, an associate professor at SLAC and Stanford and investigator with SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC.

Over the past decade, a SIMES research program led by Melosh and SLAC/Stanford Professor Zhi-Xun Shen has found a number of potential uses for the little diamonds, including improving electron microscope images and making tiny electronic gadgets.

The needle-like wires have a semiconducting core – a combination of copper and sulfur known as a chalcogenide – surrounded by the attached diamondoids, which form an insulating shell.

The wires minuscule size is important, Melosh said, because a material that exists in just one or two dimensions – as atomic-scale dots, wires or sheets – can have very different, extraordinary properties compared to the same material made in bulk. The new method allows researchers to assemble those materials with atom-by-atom precision and control.

“You can imagine weaving those into fabrics to generate energy,” Melosh said. “This method gives us a versatile toolkit where we can tinker with a number of ingredients and experimental conditions to create new materials with finely tuned electronic properties and interesting physics.”

SOURCE  SLAC National Accelerator Laboratory

 

 

 

Theorists predict new state of quantum matter may have big impact on electronics

(Nanowerk News) Constantly losing energy is something we deal with in everything we do. If you stop pedaling a bike, it gradually slows; if you let off the gas, your car also slows. As these vehicles move, they also generate heat from friction. Electronics encounter a similar effect as groups of electrons carry information from one point to another. As electrons move, they dissipate heat, reducing the distance a signal can travel. DARPA-sponsored researchers under the Mesodynamic Architectures (Meso) program, however, may have found a potential way around this fundamental problem.

Meso program researchers at Stanford University recently predicted stanene will support lossless conduction at room temperature. Stanene is the name given by the researchers to 2-D sheets of tin that are only 1-atom thick. In a paper appearing in Physical Review Letters (“Large-Gap Quantum Spin Hall Insulators in Tin Films”) the team predicts stanene would be the first topological insulator to demonstrate zero heat dissipation properties at room temperature, conducting charges around its edges without any loss. Experiments are underway to create the material in laboratory conditions. If successful, the team will use stanene to enhance devices they are building under the Meso program.

This image depicts the flow of electricity along the outside edges of a new topological insulator, stanene. Theorists in DARPA’s Mesodynamic Architectures (Meso) program predict stanene would have perfect energy propagation properties at room temperature. (Image: SLAC National Accelerator Laboratory)

“We recently realized there is another state of electronic matter: a topological insulator. Materials in a topologically insulating state are like paying for the gasoline to accelerate your car to highway speeds, but then cruising as far as you want on that highway without using up any more gas,” said Jeffrey Rogers, DARPA program manager. “Experiments should tell us what penalty electrons would pay for connecting to stanene in a practical application. However, the physics of stanene point to zero dissipation of heat—meaning electrons take an entropy hit once and then travel unimpeded the rest of the distance.”

Researchers at Stanford reported the first topological insulators in 2006 under a previous DARPA effort known as the Focus Center Research Program. The current Meso program developed the theory for stanene as part of research into more efficient ways to move information inside microchips. Other materials’ capabilities have come close, but only at temperatures that require extreme sub-zero temperatures created with bulky methods such as liquid helium.

“Stanene is a bold, yet compelling prediction,” said Rogers. “If the experiments underway confirm the theory, the application of a new lossless conductor becomes a very exciting prospect in the world of electronics. A host of applications—almost any time information is moved electronically from one place to another—could benefit.”

Source: DARPA

Read more: http://www.nanowerk.com/nanotechnology_news/newsid=33742.php#ixzz2nlj7rvXP

Scientists Invent Self-healing Battery Electrode

Menlo Park, Calif. — Researchers have made the first battery electrode that heals itself, opening a new and potentially commercially viable path for making the next generation of lithium ion batteries for electric cars, cell phones and other devices. The secret is a stretchy polymer that coats the electrode, binds it together and spontaneously heals tiny cracks that develop during battery operation, said the team from Stanford University and the Department of Energy’s (DOE) SLAC National Accelerator Laboratory.

They report the advance in the Nov. 19 issue of Nature Chemistry.

This prototype lithium ion battery, made in a Stanford lab, contains a silicon electrode protected with a coating of self-healing polymer. The cables and clips in the background are part of an apparatus for testing the performance of batteries during multiple charge-discharge cycles. (Brad Plummer/SLAC)

“Self-healing is very important for the survival and long lifetimes of animals and plants,” said Chao Wang, a postdoctoral researcher at Stanford and one of two principal authors of the paper. “We want to incorporate this feature into lithium ion batteries so they will have a long lifetime as well.”

Chao developed the self-healing polymer in the lab of Stanford Professor Zhenan Bao, whose group has been working on flexible electronic skin for use in robots, sensors, prosthetic limbs and other applications. For the battery project he added tiny nanoparticles of carbon to the polymer so it would conduct electricity.

”We found that silicon electrodes lasted 10 times longer when coated with the self-healing polymer, which repaired any cracks within just a few hours,” Bao said.

“Their capacity for storing energy is in the practical range now, but we would certainly like to push that,” said Yi Cui, an associate professor at SLAC and Stanford who led the research with Bao. The electrodes worked for about 100 charge-discharge cycles without significantly losing their energy storage capacity. “That’s still quite a way from the goal of about 500 cycles for cell phones and 3,000 cycles for an electric vehicle,” Cui said, “but the promise is there, and from all our data it looks like it’s working.”

Researchers worldwide are racing to find ways to store more energy in the negative electrodes of lithium ion batteries to achieve higher performance while reducing weight. One of the most promising electrode materials is silicon; it has a high capacity for soaking up lithium ions from the battery fluid during charging and then releasing them when the battery is put to work.

But this high capacity comes at a price: Silicon electrodes swell to three times normal size and shrink back down again each time the battery charges and discharges, and the brittle material soon cracks and falls apart, degrading battery performance. This is a problem for all electrodes in high-capacity batteries, said Hui Wu, a former Stanford postdoc who is now a faculty member at Tsinghua University in Beijing, the other principal author of the paper.

To make the self-healing coating, scientists deliberately weakened some of the chemical bonds within polymers – long, chain-like molecules with many identical units. The resulting material breaks easily, but the broken ends are chemically drawn to each other and quickly link up again, mimicking the process that allows biological molecules such as DNA to assemble, rearrange and break down.

To show how flexible their self-healing polymer is, researchers coated a balloon with it and then inflated and deflated the balloon repeatedly, mimicking the swelling and shrinking of a silicon electrode during battery operation. The polymer stretches but does not crack. (Brad Plummer/SLAC)

Researchers in Cui’s lab and elsewhere have tested a number of ways to keep silicon electrodes intact and improve their performance. Some are being explored for commercial uses, but many involve exotic materials and fabrication techniques that are challenging to scale up for production.

The self-healing electrode, which is made from silicon microparticles that are widely used in the semiconductor and solar cell industries, is the first solution that seems to offer a practical road forward, Cui said. The researchers said they think this approach could work for other electrode materials as well, and they will continue to refine the technique to improve the silicon electrode’s performance and longevity.

The research team also included Zheng Chen and Matthew T. McDowell of Stanford. Cui and Bao are members of the Stanford Institute for Materials and Energy Sciences, a joint SLAC/Stanford institute. The research was funded by DOE through SLAC’s Laboratory Directed Research and Development program and by the Precourt Institute for Energy at Stanford University.

SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the U.S. Department of Energy Office of Science. To learn more, please visit www.slac.stanford.edu.

The Stanford Institute for Materials and Energy Sciences (SIMES) is a joint institute of SLAC National Accelerator Laboratory and Stanford University. SIMES studies the nature, properties and synthesis of complex and novel materials in the effort to create clean, renewable energy technologies. For more information, please visit simes.slac.stanford.edu.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Citation: C. Wang et al., Nature Chemistry, 17 October 2013 (10.1038/nchem.1802)

Solution coating the easy way

Researchers in the US and China have developed the first solution-coating technique capable of producing high-quality, large-area single-crystalline organic semiconductor thin films suitable for high-performance, low power and inexpensive printed electronic circuits. The technique, dubbed FLUENCE (fluid-enhanced crystal engineering) can be used to make thin film organic semiconductors with record charge carrier mobilities.

Fluid flow around micropillars

Solution coating of organic semiconductors is an excellent method for making large-area and flexible electronic materials. However, it is not at all good for making aligned single-crystalline thin films – the ideal form for organic semiconductors and that have the best electronic properties. Aligned crystals are preferred in these materials because charge carrier transport through these structures depends on the crystal orientation.

A team led by Zhenan Bao at Stanford University and Stefan Mannsfeld of the SLAC National Accelerator Laboratory is now reporting on a new solution-coating method that can produce high-quality, millimetre-wide and centimetre-long highly aligned single-crystalline organic semiconductor thin films. The essence of FLUENCE is that we are able to control the flow of liquid in which the organic semiconductor is dissolved, explains team member Ying Diao. During fast printing, this “ink” often distributes itself unevenly – something that leads to defects and other structural imperfections quickly appearing in the semiconducting crystals.

Single-crystal OFET

FLUENCE tackles this problem from two angles, she says. First, it works using a microstructured printing blade containing tiny pillars that mixes the ink uniformly. Second, specially designed chemical patterns on the substrate prevent the crystals from aligning randomly or “stochastically” in a direction that would be the opposite to that in which printing is taking place. These two methods combined lead to large-area highly aligned single crystalline films that are much more structurally perfect.

To prove that their technique works, the researchers fabricated an organic semiconductor made from TIPS-pentacene, a routinely used and much studied organic semiconductor material, and found a charge carrier mobility of as high as 11 cm² V⁻¹ s⁻¹. This is the first time a mobility of greater than 10 cm² V⁻¹ s⁻¹ has been reported for TIPS-pentacene.

Micropillar-patterned blade

“The concepts we have developed in FLUENCE could easily be scaled up and applied to commercial printing methods,” said Diao. “The significant improvement in structural quality and electrical performance of the thin films printed with our method could allow to make higher performance, lower power, small and inexpensive organic circuitry,” she told nanotechweb.org. “We hope that our work will help advance such a morphology-by-design approach to make organic semiconductors for high-performance, large-area printed electronics.”

The team, which includes researchers from Nanjing University in China, says that it will now look at pattering aligned crystals at length scales suitable for making sub-micron devices.

The present work is reported in Nature Materials.

About the author

Belle Dumé is contributing editor at nanotechweb.org.

World record for battery storage set with nanoparticles

30 January 2013 (created 30 January 2013)

SLAC and Stanford scientists have set a world record for energy storage, using a clever “yolk-shell” design to store five times more energy in the sulfur cathode of a rechargeable lithium-ion battery than is possible with today’s commercial technology. The cathode also maintained a high level of performance after 1,000 charge/discharge cycles, paving the way for new generations of lighter, longer-lasting batteries for use in portable electronics and electric vehicles.

The research was led by Yi Cui, a Stanford associate professor of materials science and engineering and a member of the Stanford Institute for Materials and Energy Sciences, a SLAC/Stanford joint institute.
Lithium-ion batteries work by moving lithium ions back and forth between two electrodes, the cathode and anode. Charging the battery forces the ions and electrons into the anode, creating an electrical potential that can power a wide range of devices. Discharging the battery – using it to do work – moves the ions and electrons to the cathode. Today’s lithium-ion batteries typically retain about 80 percent of their initial capacity after 500 charge/discharge cycles.

For some 20 years, researchers have known that sulfur could theoretically store more lithium ions, and thus much more energy, than today’s cathode materials. But two critical disadvantages prevented its commercial use: When lithium ions enter a sulfur cathode during discharging, they bond with sulfur atoms to create an intermediate compound that’s important for the cathode’s performance; but this compound kept dissolving, limiting the cathode’s energy-storage capacity. At the same time, the influx of ions caused the cathode to expand by about 80 percent. When scientists applied protective coatings to keep the intermediate compound from dissolving, the cathode would expand and crack the coating, rendering it useless.

Cui’s innovation is a cathode made of nanoparticles, each a tiny sulfur nugget surrounded by a hard shell of porous titanium dioxide, like an egg yolk in an eggshell. Between the yolk and shell, where the egg white would be, is an empty space into which the sulfur can expand. During discharging, lithium ions pass through the shell and bind to the sulfur, which expands to fill the void but not so much as to break the shell. The shell, meanwhile, protects the sulfur-lithium intermediate compound from electrolyte solvent that would dissolve it.

Over the past seven years, Cui’s group has demonstrated a succession of increasingly capable anodes that use silicon rather than carbon because it can store up to 10 times more charge per weight. Their most recent anode also has a yolk-shell design that retains its energy-storage capacity over 1,000 charge/discharge cycles.

The group’s next step is to combine the yolk-shell sulfur cathode with a yolk-shell silicon anode to see if together they produce a high-energy, long-lasting battery. Source: From Egg-cellent World-record Battery Performance by Mike Ross. This work is detailed in the paper “Sulphur–TiO2 yolk–shell nanoarchitecture with internal void space for long-cycle lithium–sulphur batteries” by  Zhi Wei Seh, Weiyang Li, Judy J. Cha, Guangyuan Zheng, Yuan Yang, Matthew T. McDowell, Po-Chun Hsu & Yi Cui.