David Kirkpatrick

May 6, 2011

Graphene paper

Filed under: Science — Tags: , , , , — David Kirkpatrick @ 9:51 am

Pretty cool.

From the link:

A scanning electron microscopy (SEM) image of graphene oxide papers and an analytical model showing the layered structures of graphene sheets, the intralayer and interlayer crosslinks, and an atomic representation of the bridging structure (credit: Yilun Liu et al.)

Scientists at Tsinghua University in Beijing have calculated from first principles what a sheet of graphene might be like.

It’s currently only possible to make graphene in tiny scraps. So they suggest ways to stack these sheets and bond them together to make something larger.

Their model predicts the links between graphene layers will increase the distance between them, thereby reducing the density to about half that of graphite. So graphene paper is not only going to be strong but also very light.

November 4, 2010

Transparent solar panels?

A very real possibility. This sounds like very promising technology.

The release:

Transparent Conductive Material Could Lead to Power-Generating Windows

Combines elements for light harvesting and electric charge transport over large, transparent areas

November 3, 2010

conjugated polymer honeycombClick on the image to download a high-resolution version.Top: Scanning electron microscopy image and zoom of conjugated polymer (PPV) honeycomb. Bottom (left-to-right): Confocal fluorescence lifetime images of conjugated honeycomb, of polymer/fullerene honeycomb double layer and of polymer/fullerene honeycomb blend. Efficient charge transfer within the whole framework is observed in the case of polymer/fullerene honeycomb blend as a dramatic reduction in the fluorescence lifetime.

UPTON, NY — Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Los Alamos National Laboratory have fabricated transparent thin films capable of absorbing light and generating electric charge over a relatively large area. The material, described in the journal Chemistry of Materials, could be used to develop transparent solar panels or even windows that absorb solar energy to generate electricity.

The material consists of a semiconducting polymer doped with carbon-rich fullerenes. Under carefully controlled conditions, the material self-assembles to form a reproducible pattern of micron-size hexagon-shaped cells over a relatively large area (up to several millimeters).

“Though such honeycomb-patterned thin films have previously been made using conventional polymers like polystyrene, this is the first report of such a material that blends semiconductors and fullerenes to absorb light and efficiently generate charge and charge separation,” said lead scientist Mircea Cotlet, a physical chemist at Brookhaven’s Center for Functional Nanomaterials (CFN).

Furthermore, the material remains largely transparent because the polymer chains pack densely only at the edges of the hexagons, while remaining loosely packed and spread very thin across the centers. “The densely packed edges strongly absorb light and may also facilitate conducting electricity,” Cotlet explained, “while the centers do not absorb much light and are relatively transparent.”

Mircea CotletClick on the image to download a high-resolution version.Mircea Cotlet, Ranjith Krishna Pai, and Zhihua Xu (seated at the microscope).

“Combining these traits and achieving large-scale patterning could enable a wide range of practical applications, such as energy-generating solar windows, transparent solar panels, and new kinds of optical displays,” said co-author Zhihua Xu, a materials scientist at the CFN.

“Imagine a house with windows made of this kind of material, which, combined with a solar roof, would cut its electricity costs significantly. This is pretty exciting,” Cotlet said.

The scientists fabricated the honeycomb thin films by creating a flow of micrometer-size water droplets across a thin layer of the polymer/fullerene blend solution. These water droplets self-assembled into large arrays within the polymer solution. As the solvent completely evaporates, the polymer forms a hexagonal honeycomb pattern over a large area.

“This is a cost-effective method, with potential to be scaled up from the laboratory to industrial-scale production,” Xu said.

The scientists verified the uniformity of the honeycomb structure with various scanning probe and electron microscopy techniques, and tested the optical properties and charge generation at various parts of the honeycomb structure (edges, centers, and nodes where individual cells connect) using time-resolved confocal fluorescence microscopy.

The scientists also found that the degree of polymer packing was determined by the rate of solvent evaporation, which in turn determines the rate of charge transport through the material.

“The slower the solvent evaporates, the more tightly packed the polymer, and the better the charge transport,” Cotlet said.

“Our work provides a deeper understanding of the optical properties of the honeycomb structure. The next step will be to use these honeycomb thin films to fabricate transparent and flexible organic solar cells and other devices,” he said.

The research was supported at Los Alamos by the DOE Office of Science. The work was also carried out in part at the CFN and the Center for Integrated Nanotechnologies Gateway to Los Alamos facility. The Brookhaven team included Mircea Cotlet, Zhihua Xu, and Ranjith Krishna Pai. Collaborators from Los Alamos include Hsing-Lin Wang and Hsinhan Tsai, who are both users of the CFN facilities at Brookhaven, Andrew Dattelbaum from the Center for Integrated Nanotechnologies Gateway to Los Alamos facility, and project leader Andrew Shreve of the Materials Physics and Applications Division.

The Center for Functional Nanomaterials at Brookhaven National Laboratory and the Center for Integrated Nanotechnologies Gateway to Los Alamos facility are two of the five DOE Nanoscale Science Research Centers (NSRCs), premier national user facilities for interdisciplinary research at the nanoscale. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The NSRCs are located at DOE’s Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge and Sandia and Los Alamos national laboratories.

 

November 2, 2010

Cool nanotech image — growing nanowires

Cool image and interesting process

nanotechnology image
In the growth of sapphire nanowires using the vapor-liquid-solid method, scientists have observed that a facet at the liquid-solid interface alternately grows and shrinks, which promotes nanowire growth. These images are from the video below. Image credit: Sang Ho Oh, et al.

From the link:

Nanowires can be grown in many ways, but one of the lesser-understood growth processes is vapor-liquid-solid (VLS) growth. In VLS, a vapor adsorbs onto a liquid droplet, and the droplet transports the vapor and deposits it as a crystal at a liquid-solid interface. As the process repeats, a nanowire is built one crystal at a time. One advantage of the VLS process is that it allows scientists to control the nanowire’s growth in terms of size, shape, orientation, and composition, although this requires understanding the growth mechanisms on the atomic scale. In a new study, scientists have investigated the steps involved in VLS growth, and have observed a new oscillatory behavior that could lead to better controlled nanowire growth.

Hit the link for a video of the process.

October 22, 2010

Cool nanotech image — graphene transistors

Filed under: et.al., Science — Tags: , , , , — David Kirkpatrick @ 9:34 am

The article connected to the image is pretty good, too.

Triple transistor: Single graphene transistors like this one can be made to operate in three modes and perform functions that usually require multiple transistors in a circuit.
Credit: Alexander Balandin

Also from the link:

Researchers have already made blisteringly fast graphene transistors. Now they’ve used graphene to make a transistor that can be switched between three different modes of operation, which in conventional circuits must be performed by three separate transistors. These configurable transistors could lead to more compact chips for sending and receiving wireless signals.

Chips that use fewer transistors while maintaining all the same functions could be less expensive, use less energy, and free up room inside portable electronics like smart phones, where space is tight. The new graphene transistor is an analog device, of the type that’s used for wireless communications in Bluetooth headsets and radio-frequency identification (RFID) tags.

 

October 19, 2010

Mass producing graphene

News from the University of Houston:

University of Houston professor taking next step with graphene research

The 2010 Nobel Prize in Physics went to the two scientists who first isolated graphene, one-atom-thick crystals of graphite. Now, a researcher with the University of Houston Cullen College of Engineering is trying to develop a method to mass-produce this revolutionary material.

Graphene has several properties that make it different from literally everything else on Earth: it is the first two-dimensional material ever developed; the world’s thinnest and strongest material; the best conductor of heat ever found; a far better conductor of electricity than copper; it is virtually transparent; and is so dense that no gas can pass through it. These properties make graphene a game changer for everything from energy storage devices to flat device displays.

Most importantly, perhaps, is graphene’s potential as a replacement for silicon in computer chips. The properties of graphene would enable the historical growth in computing power to continue for decades to come.

To realize these benefits, though, a way to create plentiful, defect-free graphene must be developed. Qingkai Yu, an assistant research professor with the college’s department of electrical and computer engineering and the university’s Center for Advanced Materials, is developing methods to mass-produce such high-quality graphene.

Yu is using a technology known as chemical vapor deposition. During this process, he heats methane to around 1000 degrees Celsius, breaking the gas down into its building blocks of carbon and hydrogen atoms. The carbon atoms then attach to a metallic surface to form graphene.

“This approach could produce cheap, high-quality graphene on a large scale,” Yu said.

Yu first demonstrated the viability of chemical vapor deposition for graphene creation two years ago in a paper in the journal Applied Physics Letters. He has since continued working to perfect this method.

Yu’s initial research would often result in several layers of graphene stacked together on a nickel surface. He subsequently discovered the effectiveness of copper for graphene creation. Copper has since been adopted by graphene researchers worldwide.

Yu’s work is not finished. The single layers of graphene he is now able to create are formed out of multiple graphene crystals that join together as they grow. The places where these crystals combine, known as the grain boundaries, are defects that limit the usefulness of graphene, particularly as a replacement for silicon-based computer chips.

Yu is attempting to create large layers of graphene that form out of a single crystal.

“You can imagine how important this sort of graphene is,” said Yu. “Semiconductors became a multibillion-dollar industry based on single-crystal silicon and graphene is called the post-silicon-era material. So single-crystal graphene is the Holy Grail for the next age of semiconductors.”

 

###

Yu is conducting his research in collaboration with UH Ph.D. students Wei Wu and Zhihua Su as well as postdoctoral researcher Zhihong Liu. These efforts have been supported by the National Science Foundation, the U.S. Department of Defense, the U.S. Department of Energy, SEMATECH and the UH Center for Advanced Materials.

 

October 16, 2010

Cool nanotech image — graphene

Filed under: et.al., Science, Technology — Tags: , , , , , — David Kirkpatrick @ 9:12 am

Actually the accompanying article is pretty cool, too, so do take the time to check it out.

But now, the image …

This image of a single suspended sheet of graphene taken with the TEAM 0.5, at Berkeley Lab’s National Center for Electron Microscopy shows individual carbon atoms (yellow) on the honeycomb lattice.

Also from the link:

In the current study, the team made graphene nanoribbons using a nanowire mask-based fabrication technique. By measuring the conductance fluctuation, or ‘noise’ of electrons in graphene nanoribbons, the researchers directly probed the effect of quantum confinement in these structures. Their findings map the electronic band structure of these graphene nanoribbons using a robust electrical probing method. This method can be further applied to a wide array of nanoscale materials, including graphene-based electronic devices.

“It amazes us to observe such a clear correlation between the noise and the band structure of these graphene nanomaterials,” says lead author Guangyu Xu, a physicist at University of California, Los Angeles. “This work adds strong support to the quasi-one-dimensional subband formation in graphene nanoribbons, in which our method turns out to be much more robust than conductance measurement.”

One more bit from the link, from the intro actually:

In last week’s announcement of the Nobel Prize in Physics, the Royal Swedish Academy of Sciences lauded graphene’s “exceptional properties that originate from the remarkable world of quantum physics.” If it weren’t hot enough before, this atomically thin sheet of carbon is now officially in the global spotlight.

So expect to hear a lot more about graphene in the coming months. Of course if you’re a regular reader of this blog, you’ve been getting a pretty steady (aside from the last month of light blogging) diet of graphene since almost day one (since February 2008 to be exact).

October 2, 2010

Quantum dots may lead to ultraefficient solar cells

This sounds promising.

From the link (emphasis mine):

Although researchers have steadily increased the amount of electricity that solar cells can produce, they face fundamental limits because of the physics involved in converting photons to electrons in semiconductor materials. Now researchers at the University of Wyoming have demonstrated that by using novel nanomaterials called quantum dots, it might be possible to exceed those limits and produce ultraefficient solar cells.

The theoretical limitation of solar cells has to do with the widely varying amounts of energy from photons in sunlight. The amount varies depending on the color of the light. No matter how energetic the incoming photons are, however, solar cells can only convert one photon into one electron with a given amount of energy. Any extra energy is lost as heat. Scientists have hypothesized that quantum dots, because of their unusual electronic properties, could convert some of this extra energy into electrons. They’ve calculated that this approach could increase the theoretical maximum efficiency of solar cells by about 50 percent.

Solar dots: A micrograph shows lead-sulfide quantum dots, each about five nanometers across, coating an electrode of titanium dioxide.
Credit: Science

September 10, 2010

Graphene could speed up DNA sequencing

I’ve blogged on this topic before (and on this very news bit in the second post from the link), but this just reiterates the versatility of graphene and why the material has so many scientists, researchers and entrepreneurs so excited.

From the second link:

By drilling a tiny pore just a few-nanometers in diameter, called a , in the graphene membrane, they were able to measure exchange of ions through the pore and demonstrated that a long  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 Research Associate in the Department of Physics 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.”

Single ions crossing a nano bridge

Filed under: Science — Tags: , , , , , — David Kirkpatrick @ 11:11 am

Don’t see any current practical applications — aside from desalination — on this right now (but now with a proof-of-concept I bet this’ll be leveraged in new research), but it is impressively cool.

From the link:

In the Sept. 10 issue of Science, MIT researchers report that charged molecules, such as the sodium and  that form when salt is dissolved in water, can not only flow rapidly through carbon nanotubes, but also can, under some conditions, do so one at a time, like people taking turns crossing a bridge. The research was led by associate professor Michael Strano.

The new system allows passage of much smaller molecules, over greater distances (up to half a millimeter), than any existing nanochannel. Currently, the most commonly studied nanochannel is a silicon nanopore, made by drilling a hole through a silicon membrane. However, these channels are much shorter than the new nanotube channels (the nanotubes are about 20,000 times longer), so they only permit passage of large molecules such as DNA or polymers — anything smaller would move too quickly to be detected.

Strano and his co-authors — recent PhD recipient Chang Young Lee, graduate student Wonjoon Choi and postdoctoral associate Jae-Hee Han — built their new nanochannel by growing a nanotube across a one-centimeter-by-one-centimeter plate, connecting two water reservoirs. Each reservoir contains an electrode, one positive and one negative. Because electricity can flow only if protons — positively charged , which make up the electric current — can travel from one electrode to the other, the researchers can easily determine whether  are traveling through the nanotube.

September 9, 2010

Lasing nanoparticles around the room

Filed under: Science — Tags: , , , , , — David Kirkpatrick @ 1:30 pm

Via KurzweilAI.net — This is a pretty astounding feat.

From the link:

Researchers from Australian National University have developed the ability to move particles  over distances of up to 1.5 meters, using a hollow laser beam to trap light-absorbing particles in a “dark core.” The particles are then moved up and down the beam of light, which acts like an optical “pipeline.”

“When the small particles are trapped in this dark core very interesting things start to happen,” said Professor Andrei Rode. “As gravity, air currents, and random motions of air molecules around the particle push it out of the center, one side becomes illuminated by the laser while the other lies in darkness. This creates a tiny thrust, known as a photophoretic force that effectively pushes the particle back into the darkened core. In addition to the trapping effect, a portion of the energy from the beam and the resulting force pushes the particle along the hollow laser pipeline.”

Practical applications for this technology include directing and clustering nanoparticles in air, micro-manipulation of objects, sampling of atmospheric aerosols, and low-contamination/non-touch handling of sampling materials for transport of dangerous substances and microbes in small amounts, he said.

More info: Australian National University news

September 8, 2010

Graphene research may lead to electronics improvement

A fairly radical improvement. Try highly efficient, very-low-heat producing and smaller electronics devices. I enjoy blogging about nanotech research with real promise for market applications.

From the link:

NIST recently constructed the world’s most powerful and stable scanning-probe microscope, with an unprecedented combination of low temperature (as low as 10 millikelvin, or 10 thousandths of a degree above absolute zero), ultra-high vacuum and high . In the first measurements made with this instrument, the team has used its power to resolve the finest differences in the electron energies in graphene, atom-by-atom.

“Going to this resolution allows you to see new physics,” said Young Jae Song, a postdoctoral researcher who helped develop the instrument at NIST and make these first measurements.

And the new physics the team saw raises a few more questions about how the electrons behave in graphene than it answers.

Because of the geometry and electromagnetic properties of graphene’s structure, an electron in any given energy level populates four possible sublevels, called a “quartet.” Theorists have predicted that this quartet of levels would split into different energies when immersed in a magnetic field, but until recently there had not been an instrument sensitive enough to resolve these differences.

“When we increased the magnetic field at extreme low temperatures, we observed unexpectedly complex quantum behavior of the electrons,” said NIST Fellow Joseph Stroscio.

What is happening, according to Stroscio, appears to be a “many-body effect” in which electrons interact strongly with one another in ways that affect their energy levels.

September 7, 2010

Low cost desalination for potable water

Via KurzweilAI.net — A theoretical device from the recently concluded Singularity University. This sounds like a fresh water solution with real promise.

From the first link:

Our approach leverages advances in 3 exponentially growing fields: synthetic biology, nanotechnology, and solar energy.  Synthetic biology is a factor because synthetic molecules are currently being developed that can create ionic bonds with sodium and chloride molecules, enabling fresh water to pass through a nanofilter using only the pressure of the water above the pipe.

Nanotechnology is relevant for reverse osmosis, because using thinner filter further reduces the amount of pressure required to separate fresh water from salt water. A filtration cube measuring 165mm (6.5 inches) per side could produce 100,000 gallons of purified water per day at 1 psi. Finally, as advances in solar energy improve the efficiency of  photovoltaics, the throughput of solar pumps will increase significantly, enabling more efficient movement and storage of fresh water.

Although the individual components described above have not advanced to a point where the solution is possible at present, we were able to speak with leading experts in each of these areas as to the timeline for these capabilities to be realized.

Synthetic molecules capable of bonding with sodium and chloride molecules have already been created, but have not yet been converted to an appropriate form for storage, such as a cartridge. This is expected to occur in the next 2-3 years. Filters are currently in the 10-15nm range, and are expected to reach 1nm over the next 3-5 years. As with the synthetic molecules, 1nm tubes have been built; just not assembled into a filter at this point. Photovoltaics are currently approximately 12% efficient, but it is anticipated that 20% efficiency is achievable in the next 5 years.

A possible implementation of our Naishio solution. The pressure from the water volume is sufficient to propel fresh water across the membrane (A), and photovoltaics (D) generate all the energy needed to pump water from the repository (C) to the water tank and circulator (E). Sensors (B) communicate between the solar pump and membrane to regulate the water level and ensure it doesn’t become contaminated. (Image: Sarah Jane Pell).

September 6, 2010

Self-assembling and reassembling solar cells

Okay, just yesterday I blogged that a lot of the time the mundane “a ha” moment that puts together well-known materials and processes leads to scientific advancement (the case I was referring to in the post was a simple acid bath technique that made creating solar cells much cheaper). And then again sometimes the big sexy breakthrough gets the headline (as usual) and really deserves it.

If this technique for solar cells that self-assembles the light-harvesting element in the cell, and then breaks it down for re-assembly essentially copying what plants do in their chloroplast, is able to reach acceptable levels of efficiency, it will be an absolute game-changer. Instead of a solar cell that’s (hopefully) constantly bombarded with the full effect of the sun and constantly degrading under the solar assault, these cells will essentially be completely renewed by each reassembly. No degradation over time, just a brand new light-harvesting element with a relatively simple chemical process.

From the second link:

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

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

September 3, 2010

Graphene transistors hit 300 GHz

Via KurzweilAI.net — Great news, but as always I’d love to see a market-ready application come out of this research in the near future. Blogging about nanotech breakthroughs is all well and good, but it is excellent when I get the chance to blog about a real-world application of said breakthroughs.

From the link:

High-speed graphene transistors achieve world-record 300 GHz

September 3, 2010 by Editor

UCLA researchers have fabricated the fastest  graphene transistor to date, using a new fabrication process with a  nanowire as a self-aligned gate.

Self-aligned gates are a key element in modern transistors, which are semiconductor devices used to amplify and switch electronic signals.  Gates are used to switch the transistor between various states, and self-aligned gates were developed to deal with problems of misalignment encountered because of the shrinking scale of electronics.

“This new strategy overcomes two limitations previously encountered in graphene transistors,” professor of chemistry and biochemistry Xiangfeng Duan said. “First, it doesn’t produce any appreciable defects in the graphene during fabrication, so the high carrier mobility is retained. Second, by using a self-aligned approach with a nanowire as the gate, the group was able to overcome alignment difficulties previously encountered and fabricate very short-channel devices with unprecedented performance.”

These advances allowed the team to demonstrate the highest speed graphene transistors to date, with a cutoff frequency up to 300 GHz — comparable to the very best transistors from high-electron mobility materials such gallium arsenide or indium phosphide.

Graphene, a one-atom-thick layer of graphitic carbon, has great potential to make electronic devices such as radios, computers and phones faster and smaller. With the highest known carrier mobility — the speed at which electronic information is transmitted by a material — graphene is a good candidate for high-speed radio-frequency electronics. High-speed radio-frequency electronics may also find wide applications in microwave communication, imaging and radar technologies.

Funding for this research came from the National Science Foundation and the National Institutes of Health.

More info: UCLA news

Cool nanotech image — a 2-water molecule thick ice crystal

Researchers used graphene to trap the room-temperature ice on a mica surface.

Atomic force micrograph of ~1 micrometer wide × 1.5 micrometers (millionths of a meter) tall area. The ice crystals (lightest blue) are 0.37 nanometers (billionths of a meter) high, which is the height of a 2-water molecule thick ice crystal. A one-atom thick sheet of graphene is used to conformally coat and trap water that has adsorbed onto a mica surface, permitting it to be imaged and characterized by atomic force microscopy. Detailed analysis of such images reveals that this (first layer) of water is ice, even at room temperature. At high humidity levels, a second layer of water will coat the first layer, also as ice. At very high humidity levels, additional layers of water will coat the surface as droplets. Credit: Heath group/Caltech

Hit the link for the full story on this image.

September 2, 2010

Cool nanotech image — the perfect nanocube

Check this out

Caption: These electron microscope images show perfect-edged nanocubes produced in a one-step process created at NIST that allows careful control of the cubes’ size, shape and composition.

Credit: NIST

Usage Restrictions: None

Related news release: The perfect nanocube: Precise control of size, shape and composition

And:

Caption: These electron microscope images show perfect-edged nanocubes produced in a one-step process created at NIST that allows careful control of the cubes’ size, shape and composition.

Credit: NIST

Usage Restrictions: None

Related news release: The perfect nanocube: Precise control of size, shape and composition

Head below the fold for the accompanying release: (more…)

September 1, 2010

More memory news …

… to join this earlier post from today on memristor storage, this one on silicon nanocrystals and 3D storage.

From the second link, the release:

Silicon oxide circuits break barrier

Nanocrystal conductors could lead to massive, robust 3-D storage

Rice University scientists have created the first two-terminal memory chips that use only silicon, one of the most common substances on the planet, in a way that should be easily adaptable to nanoelectronic manufacturing techniques and promises to extend the limits of miniaturization subject to Moore’s Law.

Last year, researchers in the lab of Rice Professor James Tour showed how electrical current could repeatedly break and reconnect 10-nanometer strips of graphite, a form of carbon, to create a robust, reliable memory “bit.” At the time, they didn’t fully understand why it worked so well.

Now, they do. A new collaboration by the Rice labs of professors Tour, Douglas Natelson and Lin Zhong proved the circuit doesn’t need the carbon at all.

Jun Yao, a graduate student in Tour’s lab and primary author of the paper to appear in the online edition of Nano Letters, confirmed his breakthrough idea when he sandwiched a layer of silicon oxide, an insulator, between semiconducting sheets of polycrystalline silicon that served as the top and bottom electrodes.

Applying a charge to the electrodes created a conductive pathway by stripping oxygen atoms from the silicon oxide and forming a chain of nano-sized silicon crystals. Once formed, the chain can be repeatedly broken and reconnected by applying a pulse of varying voltage.

The nanocrystal wires are as small as 5 nanometers (billionths of a meter) wide, far smaller than circuitry in even the most advanced computers and electronic devices.

“The beauty of it is its simplicity,” said Tour, Rice’s T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science. That, he said, will be key to the technology’s scalability. Silicon oxide switches or memory locations require only two terminals, not three (as in flash memory), because the physical process doesn’t require the device to hold a charge.

It also means layers of silicon-oxide memory can be stacked in tiny but capacious three-dimensional arrays. “I’ve been told by industry that if you’re not in the 3-D memory business in four years, you’re not going to be in the memory business. This is perfectly suited for that,” Tour said.

Silicon-oxide memories are compatible with conventional transistor manufacturing technology, said Tour, who recently attended a workshop by the National Science Foundation and IBM on breaking the barriers to Moore’s Law, which states the number of devices on a circuit doubles every 18 to 24 months.

“Manufacturers feel they can get pathways down to 10 nanometers. Flash memory is going to hit a brick wall at about 20 nanometers. But how do we get beyond that? Well, our technique is perfectly suited for sub-10-nanometer circuits,” he said.

Austin tech design company PrivaTran is already bench testing a silicon-oxide chip with 1,000 memory elements built in collaboration with the Tour lab. “We’re real excited about where the data is going here,” said PrivaTran CEO Glenn Mortland, who is using the technology in several projects supported by the Army Research Office, National Science Foundation, Air Force Office of Scientific Research, and the Navy Space and Naval Warfare Systems Command Small Business Innovation Research (SBIR) and Small Business Technology Transfer programs.

“Our original customer funding was geared toward more high-density memories,” Mortland said. “That’s where most of the paying customers see this going. I think, along the way, there will be side applications in various nonvolatile configurations.”

Yao had a hard time convincing his colleagues that silicon oxide alone could make a circuit. “Other group members didn’t believe him,” said Tour, who added that nobody recognized silicon oxide’s potential, even though it’s “the most-studied material in human history.”

“Most people, when they saw this effect, would say, ‘Oh, we had silicon-oxide breakdown,’ and they throw it out,” he said. “It was just sitting there waiting to be exploited.”

In other words, what used to be a bug turned out to be a feature.

Yao went to the mat for his idea. He first substituted a variety of materials for graphite and found none of them changed the circuit’s performance. Then he dropped the carbon and metal entirely and sandwiched silicon oxide between silicon terminals. It worked.

“It was a really difficult time for me, because people didn’t believe it,” Yao said. Finally, as a proof of concept, he cut a carbon nanotube to localize the switching site, sliced out a very thin piece of silicon oxide by focused ion beam and identified a nanoscale silicon pathway under a transmission electron microscope.

“This is research,” Yao said. “If you do something and everyone nods their heads, then it’s probably not that big. But if you do something and everyone shakes their heads, then you prove it, it could be big.

“It doesn’t matter how many people don’t believe it. What matters is whether it’s true or not.”

Silicon-oxide circuits carry all the benefits of the previously reported graphite device. They feature high on-off ratios, excellent endurance and fast switching (below 100 nanoseconds).

They will also be resistant to radiation, which should make them suitable for military and NASA applications. “It’s clear there are lots of radiation-hardened uses for this technology,” Mortland said.

Silicon oxide also works in reprogrammable gate arrays being built by NuPGA, a company formed last year through collaborative patents with Rice University. NuPGA’s devices will assist in the design of computer circuitry based on vertical arrays of silicon oxide embedded in “vias,” the holes in integrated circuits that connect layers of circuitry. Such rewritable gate arrays could drastically cut the cost of designing complex electronic devices.

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Zhengzong Sun, a graduate student in Tour’s lab, was co-author of the paper with Yao; Tour; Natelson, a Rice professor of physics and astronomy; and Zhong, assistant professor of electrical and computer engineering.

The David and Lucille Packard Foundation, the Texas Instruments Leadership University Fund, the National Science Foundation, PrivaTran and the Army Research Office SBIR supported the research.

Read the abstract here: http://pubs.acs.org/journal/nalefd

High-resolution images are available for download here:
https://stage.media.rice.edu/images/media/NewsRels/0830_F2.jpg
https://stage.media.rice.edu/images/media/NewsRels/0830_F2a.jpg
https://stage.media.rice.edu/images/media/NewsRels/0830_F2b.jpg
https://stage.media.rice.edu/images/media/NewsRels/0830_F2c.jpg
https://stage.media.rice.edu/images/media/NewsRels/0830_F2d.jpg

NOTE: The first image (F2) is a key to the other four.

CAPTION: A 1k silicon oxide memory has been assembled by Rice and a commercial partner as a proof-of-concept. Silicon nanowire forms when charge is pumped through the silicon oxide, creating a two-terminal resistive switch. (Images courtesy Jun Yao/Rice University)

(Note: I recommend hitting the link for the first image — 0830_F2.jpg. It’s too big to run in this blog full-size, but it’s a great illustration of the chip.)

Nanotech making water more safe

This development can make a real quality of life difference in developing countries without running water and disaster areas, and it can make “roughing it” just a little bit less rough.

The release:

High-speed filter uses electrified nanostructures to purify water at low cost

IMAGE: This scanning electron microscope image shows the silver nanowires in which the cotton is dipped during the process of constructing a filter. The large fibers are cotton.

Click here for more information.

By dipping plain cotton cloth in a high-tech broth full of silver nanowires and carbon nanotubes, Stanford researchers have developed a new high-speed, low-cost filter that could easily be implemented to purify water in the developing world.

Instead of physically trapping bacteria as most existing filters do, the new filter lets them flow on through with the water. But by the time the pathogens have passed through, they have also passed on, because the device kills them with an electrical field that runs through the highly conductive “nano-coated” cotton.

In lab tests, over 98 percent of Escherichia coli bacteria that were exposed to 20 volts of electricity in the filter for several seconds were killed. Multiple layers of fabric were used to make the filter 2.5 inches thick.

“This really provides a new water treatment method to kill pathogens,” said Yi Cui, an associate professor of materials science and engineering. “It can easily be used in remote areas where people don’t have access to chemical treatments such as chlorine.”

Cholera, typhoid and hepatitis are among the waterborne diseases that are a continuing problem in the developing world. Cui said the new filter could be used in water purification systems from cities to small villages.

Faster filtering by letting bacteria through

Filters that physically trap bacteria must have pore spaces small enough to keep the pathogens from slipping through, but that restricts the filters’ flow rate.

IMAGE: This is professor of materials science and engineering Yi Cui.

Click here for more information.

Since the new filter doesn’t trap bacteria, it can have much larger pores, allowing water to speed through at a more rapid rate.

“Our filter is about 80,000 times faster than filters that trap bacteria,” Cui said. He is the senior author of a paper describing the research that will be published in an upcoming issue of Nano Letters. The paper is available online now.

The larger pore spaces in Cui’s filter also keep it from getting clogged, which is a problem with filters that physically pull bacteria out of the water.

Cui’s research group teamed with that of Sarah Heilshorn, an assistant professor of materials science and engineering, whose group brought its bioengineering expertise to bear on designing the filters.

Silver has long been known to have chemical properties that kill bacteria. “In the days before pasteurization and refrigeration, people would sometimes drop silver dollars into milk bottles to combat bacteria, or even swallow it,” Heilshorn said.

Cui’s group knew from previous projects that carbon nanotubes were good electrical conductors, so the researchers reasoned the two materials in concert would be effective against bacteria. “This approach really takes silver out of the folk remedy realm and into a high-tech setting, where it is much more effective,” Heilshorn said.

Using the commonplace keeps costs down

But the scientists also wanted to design the filters to be as inexpensive as possible. The amount of silver used for the nanowires was so small the cost was negligible, Cui said. Still, they needed a foundation material that was “cheap, widely available and chemically and mechanically robust.” So they went with ordinary woven cotton fabric.

“We got it at Wal-mart,” Cui said.

To turn their discount store cotton into a filter, they dipped it into a solution of carbon nanotubes, let it dry, then dipped it into the silver nanowire solution. They also tried mixing both nanomaterials together and doing a single dunk, which also worked. They let the cotton soak for at least a few minutes, sometimes up to 20, but that was all it took.

The big advantage of the nanomaterials is that their small size makes it easier for them to stick to the cotton, Cui said. The nanowires range from 40 to 100 billionths of a meter in diameter and up to 10 millionths of a meter in length. The nanotubes were only a few millionths of a meter long and as narrow as a single billionth of a meter. Because the nanomaterials stick so well, the nanotubes create a smooth, continuous surface on the cotton fibers. The longer nanowires generally have one end attached with the nanotubes and the other end branching off, poking into the void space between cotton fibers.

“With a continuous structure along the length, you can move the electrons very efficiently and really make the filter very conducting,” he said. “That means the filter requires less voltage.”

Minimal electricity required

The electrical current that helps do the killing is only a few milliamperes strong – barely enough to cause a tingling sensation in a person and easily supplied by a small solar panel or a couple 12-volt car batteries. The electrical current can also be generated from a stationary bicycle or by a hand-cranked device.

The low electricity requirement of the new filter is another advantage over those that physically filter bacteria, which use electric pumps to force water through their tiny pores. Those pumps take a lot of electricity to operate, Cui said.

In some of the lab tests of the nano-filter, the electricity needed to run current through the filter was only a fifth of what a filtration pump would have needed to filter a comparable amount of water.

The pores in the nano-filter are large enough that no pumping is needed – the force of gravity is enough to send the water speeding through.

Although the new filter is designed to let bacteria pass through, an added advantage of using the silver nanowire is that if any bacteria were to linger, the silver would likely kill it. This avoids biofouling, in which bacteria form a film on a filter. Biofouling is a common problem in filters that use small pores to filter out bacteria.

Cui said the electricity passing through the conducting filter may also be altering the pH of the water near the filter surface, which could add to its lethality toward the bacteria.

Cui said the next steps in the research are to try the filter on different types of bacteria and to run tests using several successive filters.

“With one filter, we can kill 98 percent of the bacteria,” Cui said. “For drinking water, you don’t want any live bacteria in the water, so we will have to use multiple filter stages.”

Cui’s research group has gained attention recently for using nanomaterials to build batteries from paper and cloth.

###

David Schoen and Alia Schoen were both graduate students in Materials Science and Engineering when the water-filter research was conducted and are co–lead authors of the paper in Nano Letters. David Schoen is now a postdoctoral researcher at Stanford.

Liangbing Hu, a postdoctoral researcher in Materials Science and Engineering, and Han Sun Kim, a graduate student in Materials Science and Engineering at the time the research was conducted, also contributed to the research and are co-authors of the paper.

August 26, 2010

Cool nanotech image — microneedles

Cool to look, even more cool when put into practice. Microneedles can deliver quantum dots into skin and should lead to new diagnosis and treatment of medical conditions such as skin cancer.

And now, the image:

Hollow microneedles open the door to new techniques for diagnosing and treating a variety of medical conditions, including skin cancer. Image reproduced by permission of the Royal Society of Chemistry.

For more on microneedles, here’s the full release.

August 25, 2010

Making nano-brushes even smaller

Filed under: Science — Tags: , , , , , , — David Kirkpatrick @ 11:52 am

Now this is a nanotech development that can lead to real-world applications.

From the link:

In their latest series of experiments, Duke University engineers have developed a novel approach to synthesize these nano-brushes, which could improve their versatility in the future. These polymer brushes are currently being used in biologic sensors and microscopic devices, such as microcantilevers, and they will play an important role in the future drive to miniaturization, the researchers said.

Nano-brushes are typically made of  grown on flat surfaces with strands of the molecules growing up and out from a surface, much like hairs on a brush. Polymers are large man-made molecules ubiquitous in the manufacture of everyday products.

An atomic force microscopy topographic image of the nano-brushes. The relative heights of the brushes can be tailored by changing the substrate and initiators. Credit: Stefan Zauscher, Pratt School of Engineering

August 23, 2010

Making graphene electronics friendly

Electronics is a very attractive application for both carbon nanotubes and graphene, but graphene is proving fairly stubborn to working out in real world deployment. This news out of the Oak Ridge National Laboratory sounds very promising.

From the link:

Structural loops that sometimes form during a graphene cleaning process can render the material unsuitable for electronic applications. Overcoming these types of problems is of great interest to the electronics industry.

“Graphene is a rising star in the materials world, given its potential for use in precise electronic components like transistors or other semiconductors,” said Bobby Sumpter, a staff scientist at ORNL.

The team used quantum  to simulate an experimental graphene cleaning process, as discussed in a paper published in . Calculations performed on ORNL supercomputers pointed the researchers to an overlooked intermediate step during processing.

Imaging with a transmission electron microscope, or TEM, subjected the graphene to electron irradiation, which ultimately prevented loop formation. The ORNL simulations showed that by injecting  to collect an image, the electrons were simultaneously changing the material’s structure.

Scientists help explain graphene mystery

ORNL simulations demonstrate how loops (seen above in blue) between graphene layers can be minimized using electron irradiation (bottom).

August 20, 2010

Is the US in danger of losing its nanotech hegemony?

Via KurzweilAI.net — Not just yet, but there are a number of countries putting money and other resources into nanotechnology. One place the United States could stand to see a lot of improvement is commercializing the nanotech developments going on right now.

From the link:

U.S. Risks Losing Global Leadership in Nanotech

August 20, 2010 by Editor

The U.S. dominated the rest of the world in nanotech funding and new patents last year, as U.S. government funding, corporate spending, and VC investment in nanotech collectively reached $6.4 billion in 2009. But according to a new report from Lux Research, countries such as China and Russia launched new challenges to U.S. dominance in 2009, while smaller players such as Japan, Germany and South Korea surpassed the United States in terms of commercializing nanotechnology and products.

The report, titled “Ranking the Nations on Nanotech: Hidden Havens and False Threats,” compares nanotech innovation and technology development in 19 countries in order to provide government policymakers, corporate leaders and investors a detailed map of the nanotech’s international development landscape. Overall, the report found global investment in nanotech held steady through the recent financial crisis, drawing $17.6 billion from governments, corporations and investors in 2009, a 1% increase over 2008’s $17.5 billion. Only venture capitalists dialed back their support, cutting investments by 43% relative to 2008.

“Part of what motivated our research was the emerging possibility that ambitious new government funding in Russia and China represented a threat to U.S. dominance in nanotech innovation,” said David Hwang, an Analyst at Lux Research, and the report’s lead author. “But while the field certainly gained momentum in both countries as a result of the increased funding, both countries have economic and intellectual property protection issues that prevent them from being real threats just yet.”

To uncover the most fertile environments for technology developers, buyers, and investors, Lux Research mapped the nanotech ecosystems of select nations, building on earlier reports published from 2005 through 2008. In addition to tracking fundamentals, such as the number of nanotech publications and patents issued, the report also inventoried direct and indirect spending on nanotech from government, corporate and venture sources. Among its key observations:

  • The U.S. continues to dominate in nanotech development… for now. Last year saw the U.S. lead all other countries in terms of government funding, corporate spending, VC investment, and patent issuances. But its capacity to commercialize those technologies and leverage them to grow the economy is comparatively mediocre. U.S. competitiveness in long-term innovation is also at risk, as the relative number of science and engineering graduates in its population is significantly lower than it is in other countries.
  • Other countries stand to get more bang for their nanotech buck. Japan, Germany, and South Korea continued their impressive trajectories from 2008, earning top spots in publications, patents, government funding, and corporate spending. Compared to the U.S., all three also remain more focused on nanotech and appear more adept at commercializing new technology. The relative magnitude of the technology manufacturing sectors in these three countries are the world’s highest, meaning their economies stand to benefit the most from nanotech commercialization.
  • Russian and Chinese investment in nanotech yields slow progress. While both governments launched generous nanotech investment programs last year, the technology hasn’t gained momentum in either country’s private sector, both of which have a history of skimping on R&D. The relative lack of momentum was further underscored by the abysmal number of new nanotech patents for either country last year.

“Ranking the Nations on Nanotech: Hidden Havens and False Threats,” is part of the Lux Nanomaterials Intelligence service. Clients subscribing to this service receive ongoing research on market and technology trends, continuous technology scouting reports and proprietary data points in the weekly Lux Research Nanomaterials Journal, and on-demand inquiry with Lux Research analysts.

More info: Lux Research

August 19, 2010

Graphene and DNA sequencing

News on potential applications of graphene is always interesting, but I’ll have to admit I’d like see more actual market-ready solutions. This news is both intriguing and promising, but the nut graf contains those dreaded words, “could help (insert the gist of any story here).” It’ll be a pretty exciting day when I blog about something that will help, instead of could help with graphene as the key helping element.

From the second link:

Layers of graphene that are only as thick as an atom could help make human DNA sequencing faster and cheaper. Harvard University and MIT researchers have shown that sheets of graphene could be a big improvement over membranes that are currently used for nanopore sequencing–a technique that promises to speed up and simplify the sequencing of long strands of DNA.

And:

The researchers create their membrane by placing a graphene flake over a 200-nanometer-wide opening in the middle of a silicon-nitride surface. Then they drill a few pores, just nanometers wide, in the graphene with an electron beam. The membrane is finally immersed in a salt solution that’s in contact with silver electrodes. The researchers observed dips in the current when a DNA strand passed through the pore, showing that the method could eventually be used to identify DNA bases.

August 18, 2010

The world’s darkest material

I’ve previously blogged on a world’s darkest material in the past (couldn’t find the post in the archives, however) and it was nanotech-based as well so it’s possible this is the same stuff. Pretty cool either way.

From the link:

Harnessing darkness for practical use, researchers at the National Institute of Standards and Technology have developed a laser power detector coated with the world’s darkest material — a forest of carbon nanotubes that reflects almost no light across the visible and part of the infrared spectrum.

NIST will use the new ultra-dark detector, described in a new paper in ,* to make precision laser power measurements for advanced technologies such as optical communications, laser-based manufacturing, solar energy conversion, and industrial and satellite-borne sensors.

Inspired by a 2008 paper by Rensselaer Polytechnic Institute (RPI) on “the darkest man-made material ever,”** the NIST team used a sparse array of fine nanotubes as a coating for a thermal detector, a device used to measure . A co-author at Stony Brook University in New York grew the nanotube coating. The coating absorbs  and converts it to heat, which is registered in pyroelectric material (lithium tantalate in this case). The rise in temperature generates a current, which is measured to determine the power of the laser. The blacker the coating, the more efficiently it absorbs light instead of reflecting it, and the more accurate the measurements.

This is a colorized micrograph of the world’s darkest material — a sparse “forest” of fine carbon nanotubes — coating a NIST laser power detector. Image shows a region approximately 25 micrometers across. Credit: Aric Sanders, NIST

August 17, 2010

Nanotech and solar efficiency

Nanotechnology and solar energy get a lot of virtual ink around here, and I always enjoy getting the chance to blog about both topics in the same post. This study finds that incorporating quantum dots in photovoltaic solar cells through nanoscience should both increase the efficiency of the cells and reduce their cost. A win-win all the way around.

From the link:

As the fastest growing energy technology in the world, solar energy continues to account for more and more of the world’s energy supply. Currently, most commercial photovoltaic power comes from bulk semiconductor materials. But in the past few years, scientists have been investigating how semiconductor nanostructures can increase the efficiency of solar cells and the newer field of solar fuels.

Although there has been some controversy about just how much nanoscience can improve solar cells, a recent overview of this research by Arthur Nozik, a researcher at the National Renewable Energy Laboratory (NREL) and professor at the University of Colorado, shows that semiconductor nanostructures have significant potential for converting solar energy into electricity


August 11, 2010

Better understanding graphene

Yes, graphene is something of a miracle material (hit this link for my extensive graphene blogging), and yes it’s proving to be very vexing material as well. There’s a whole lot of promise, but not so much practice because graphene is proving to be a very fickle material. Research like this from the Georgia Institute of Technology is particularly important because unlocking the secret life of graphene will allow for increasing practical applications. Better understanding will lead to better utilization.

The release:

Study of electron orbits in multilayer graphene finds unexpected energy gaps

Electron transport

IMAGE: Stacking of graphene sheets creates regions where the moiré alignment is of type AA (all atoms have neighbors in the layer below), AB (only A atoms have neighbors) or BA…

Click here for more information.

Researchers have taken one more step toward understanding the unique and often unexpected properties of graphene, a two-dimensional carbon material that has attracted interest because of its potential applications in future generations of electronic devices.

In the Aug. 8 advance online edition of the journal Nature Physics, researchers from the Georgia Institute of Technology and the National Institute of Standards and Technology (NIST) describe for the first time how the orbits of electrons are distributed spatially by magnetic fields applied to layers of epitaxial graphene.

The research team also found that these electron orbits can interact with the substrate on which the graphene is grown, creating energy gaps that affect how electron waves move through the multilayer material. These energy gaps could have implications for the designers of certain graphene-based electronic devices.

“The regular pattern of energy gaps in the graphene surface creates regions where electron transport is not allowed,” said Phillip N. First, a professor in the Georgia Tech School of Physics and one of the paper’s co-authors. “Electron waves would have to go around these regions, requiring new patterns of electron wave interference. Understanding such interference will be important for bi-layer graphene devices that have been proposed, and may be important for other lattice-matched substrates used to support graphene and graphene devices.”

In a magnetic field, an electron moves in a circular trajectory – known as a cyclotron orbit – whose radius depends on the size of the magnetic field and the energy of electron. For a constant magnetic field, that’s a little like rolling a marble around in a large bowl, First said.

“At high energy, the marble orbits high in the bowl, while for lower energies, the orbit size is smaller and lower in the bowl,” he explained. “The cyclotron orbits in graphene also depend on the electron energy and the local electron potential – corresponding to the bowl – but until now, the orbits hadn’t been imaged directly.”

Placed in a magnetic field, these orbits normally drift along lines of nearly constant electric potential. But when a graphene sample has small fluctuations in the potential, these “drift states” can become trapped at a hill or valley in the material that has closed constant potential contours. Such trapping of charge carriers is important for the quantum Hall effect, in which precisely quantized resistance results from charge conduction solely through the orbits that skip along the edges of the material.

IMAGE: This graphic shows electrons that move along an equipotential, while those that follow closed equipotentials (as in a potential-energy valley) become localized (right). The arrows denote the magnetic field,…

Click here for more information.

The study focused on one particular electron orbit: a zero-energy orbit that is unique to graphene. Because electrons are matter waves, interference within a material affects how their energy relates to the velocity of the wave – and reflected waves added to an incoming wave can combine to produce a slower composite wave. Electrons moving through the unique “chicken-wire” arrangement of carbon-carbon bonds in the graphene interfere in a way that leaves the wave velocity the same for all energy levels.

In addition to finding that energy states follow contours of constant electric potential, the researchers discovered specific areas on the graphene surface where the orbital energy of the electrons changes from one atom to the next. That creates an energy gap within isolated patches on the surface.

“By examining their distribution over the surface for different magnetic fields, we determined that the energy gap is due to a subtle interaction with the substrate, which consists of multilayer graphene grown on a silicon carbide wafer,” First explained.

In multilayer epitaxial graphene, each layer’s symmetrical sublattice is rotated slightly with respect to the next. In prior studies, researchers found that the rotations served to decouple the electronic properties of each graphene layer.

“Our findings hold the first indications of a small position-dependent interaction between the layers,” said David L. Miller, the paper’s first author and a graduate student in First’s laboratory. “This interaction occurs only when the size of a cyclotron orbit – which shrinks as the magnetic field is increased – becomes smaller than the size of the observed patches.”

The origin of the position dependent interaction is believed to be the “moiré pattern” of atomic alignments between two adjacent layers of graphene. In some regions, atoms of one layer lie atop atoms of the layer below, while in other regions, none of the atoms align with the atoms in the layer below. In still other regions, half of the atoms have neighbors in the underlayer, an instance in which the symmetry of the carbon atoms is broken and the Landau level – discrete energy level of the electrons – splits into two different energies.

Experimentally, the researchers examined a sample of epitaxial graphene grown at Georgia Tech in the laboratory of Professor Walt de Heer, using techniques developed by his research team over the past several years.

They used the tip of a custom-built scanning-tunneling microscope (STM) to probe the atomic-scale electronic structure of the graphene in a technique known as scanning tunneling spectroscopy. The tip was moved across the surface of a 100-square nanometer section of graphene, and spectroscopic data was acquired every 0.4 nanometers.

The measurements were done at 4.3 degrees Kelvin to take advantage of the fact that energy resolution is proportional to the temperature. The scanning-tunneling microscope, designed and built by Joseph Stroscio at NIST’s Center for Nanoscale Science and Technology, used a superconducting magnet to provide the magnetic fields needed to study the orbits.

According to First, the study raises a number of questions for future research, including how the energy gaps will affect electron transport properties, how the observed effects may impact proposed bi-layer graphene coherent devices – and whether the new phenomenon can be controlled.

“This study is really a stepping stone in long path to understanding the subtleties of graphene’s interesting properties,” he said. “This material is different from anything we have worked with before in electronics.”

###

In addition to those already mentioned, the study also included Walt de Heer, Kevin D. Kubista, Ming Ruan, and Markus Kinderman from Georgia Tech and Gregory M. Rutter from NIST. The research was supported by the National Science Foundation, the Semiconductor Research Corporation and the W.M. Keck Foundation. Additional assistance was provided by Georgia Tech’s Materials Research Science and Engineering Center (MRSEC)

August 5, 2010

Separating and sizing nanoparticles

Filed under: Science — Tags: , , , — David Kirkpatrick @ 2:12 pm

A useful nanotech development.

The release:

NIST nanofluidic ‘multi-tool’ separates and sizes nanoparticles

IMAGE: A 3-D nanofluidic “staircase ” channel with many depths was used to separate and measure a mixture of different-sized fluorescent nanoparticles. Larger (brighter) and smaller (dimmer) particles were forced toward the…

Click here for more information.

A wrench or a screwdriver of a single size is useful for some jobs, but for a more complicated project, you need a set of tools of different sizes. Following this guiding principle, researchers at the National Institute of Standards and Technology (NIST) have engineered a nanoscale fluidic device that functions as a miniature “multi-tool” for working with nanoparticles—objects whose dimensions are measured in nanometers, or billionths of a meter.

First introduced in March 2009 (see “NIST-Cornell Team Builds World’s First Nanofluidic Device with Complex 3-D Surfaces”, the device consists of a chamber with a cascading “staircase” of 30 nanofluidic channels ranging in depth from about 80 nanometers at the top to about 620 nanometers (slightly smaller than an average bacterium) at the bottom. Each of the many “steps” of the staircase provides another “tool” of a different size to manipulate nanoparticles in a method that is similar to how a coin sorter separates nickels, dimes and quarters.

In a new article in the journal Lab on a Chip*, the NIST research team demonstrates that the device can successfully perform the first of a planned suite of nanoscale tasks—separating and measuring a mixture of spherical nanoparticles of different sizes (ranging from about 80 to 250 nanometers in diameter) dispersed in a solution. The researchers used electrophoresis—the method of moving charged particles through a solution by forcing them forward with an applied electric field—to drive the nanoparticles from the deep end of the chamber across the device into the progressively shallower channels. The nanoparticles were labeled with fluorescent dye so that their movements could be tracked with a microscope.

As expected, the larger particles stopped when they reached the steps of the staircase with depths that matched their diameters of around 220 nanometers. The smaller particles moved on until they, too, were restricted from moving into shallower channels at depths of around 110 nanometers. Because the particles were visible as fluorescent points of light, the position in the chamber where each individual particle was stopped could be mapped to the corresponding channel depth. This allowed the researchers to measure the distribution of nanoparticle sizes and validate the usefulness of the device as both a separation tool and reference material. Integrated into a microchip, the device could enable the sorting of complex nanoparticle mixtures, without observation, for subsequent application. This approach could prove to be faster and more economical than conventional methods of nanoparticle sample preparation and characterization.

The NIST team plans to engineer nanofluidic devices optimized for different nanoparticle sorting applications. These devices could be fabricated with tailored resolution (by increasing or decreasing the step size of the channels), over a particular range of particle sizes (by increasing or decreasing the maximum and minimum channel depths), and for select materials (by conforming the surface chemistry of the channels to optimize interaction with a specific substance). The researchers are also interested in determining if their technique could be used to separate mixtures of nanoparticles with similar sizes but different shapes—for example, mixtures of tubes and spheres.

###

* S.M. Stavis, J. Geist and M. Gaitan. Separation and metrology of nanoparticles by nanofluidic size exclusion. Lab on a Chip, forthcoming, August 2010

August 3, 2010

Platinum nanoparticles may radically improve fuel cells

This nanotech-based catalyst would put electric cars — among other ideas and products — on a much faster track.

From the link:

In the quest for efficient, cost-effective and commercially viable fuel cells, scientists at Cornell University’s Energy Materials Center have discovered a catalyst and catalyst-support combination that could make fuel cells more stable, conk-out free, inexpensive and more resistant to carbon monoxide poisoning.

The research, “Highly Stable and CO-Tolerant Pt/Ti0.7W0.3O2 Electrocatalyst for Proton-Exchange Membrane Fuel Cells,” (, July 12, 2010) led by Hector D. Abruna, Cornell professor of Chemistry and Chemical Biology and director of the Energy Materials Center at Cornell (emc2); Francis J. DiSalvo, Cornell professor Chemistry and Chemical Biology; Deli Wang, post doctoral researcher; Chinmayee V. Subban, graduate student; Hongsen Wang, research associate; and Eric Rus, graduate student.

offer an appealing alternative to gasoline-burning cars: They have the potential to power vehicles for long distances using hydrogen as fuel, mitigate carbon dioxide production and emit only water vapor.

However, fuel cells generally require very pure hydrogen to work. That means that conventional fuels must be stripped of  – a process that is too expensive to make fuel cells commercially viable.

Fuel cells work by electrochemically decomposing fuel instead of burning it, converting energy directly into electricity

August 2, 2010

Making nanofabrication better

This sounds very promising. Lower costs mean more freedom to tinker and more practical utilization. Totally different field here, but on-site 3D printing  is within reach of the small- to mid-sized business now with some of Objet‘s smaller models.

From the first link:

A Northwestern University research team has done just that — drawing 15,000 identical skylines with tiny beams of  using an innovative nanofabrication technology called beam-pen lithography (BPL).

Details of the new method, which could do for nanofabrication what the desktop printer has done for printing and information transfer, will be published Aug. 1 by the journal Nature Nanotechnology.

The Northwestern technology offers a means to rapidly and inexpensively make and prototype circuits, optoelectronics and medical diagnostics and promises many other applications in the electronics, photonics and life sciences industries.

“It’s all about miniaturization,” said Chad A. Mirkin, George B. Rathmann Professor of Chemistry in the Weinberg College of Arts and Sciences and director of Northwestern’s International Institute for Nanotechnology. “Rapid and large-scale transfer of information drives the world. But conventional micro- and nanofabrication tools for making structures are very expensive. We are trying to change that with this new approach to photolithography and nanopatterning.”

And:

Beam-pen lithography could lead to the development of a desktop printer of sorts for , giving individual researchers a great deal of control of their work.

“Such an instrument would allow researchers at universities and in the electronics industry around the world to rapidly prototype — and possibly produce — high-resolution electronic devices and systems right in the lab,” Mirkin said. “They want to test their patterns immediately, not have to wait for a third-party to produce prototypes, which is what happens now.”

July 30, 2010

High tech contact lenses and NASA

News from NASA hot from today’s inbox. And a bit of a departure from the expected space news out of NASA.

The release:

NASA Talk is High Tech Prescription for Contact Lenses

HAMPTON, Va., July 30 /PRNewswire-USNewswire/ — Imagine your contact lenses being able to improve your vision and tell your temperature.

(Logo: http://www.newscom.com/cgi-bin/prnh/20081007/38461LOGO)
(Logo: http://photos.prnewswire.com/prnh/20081007/38461LOGO)

On Tuesday, Aug. 3, at NASA’s Langley Research Center in Hampton, Professor Babak Parviz, from the University of Washington presents, “What If Your Contact Lens Could Show You Images” at 2 p.m. in the Reid Conference Center. Parviz will provide an overview of the process it took to build contact lenses to display and monitor information about a person’s health.

On Tuesday evening, Parviz will present a similar talk for the general public at 7:30 p.m. at the Virginia Air & Space Center in downtown Hampton. The evening presentation is free and no reservations are required.

Through advancements in nanotechnology, Parviz will explain the how contact lenses have been converted into systems that can complete extraordinary tasks.

Researchers at the University of Washington are working on integrating small optical, electronic and biosensing devices into contact lenses. The lenses are designed to display information to the user and to continuously monitor the person’s health through the biochemistry of the eye surface.

Parviz’ research at the University of Washington includes nanotechnology, bionanotechnolgy and microsystems. His work was chosen by Time magazine as one of the top inventions of the year in 2008 and is on display at the London Museum of Science.

Parviz attended the University of Michigan, earning graduate degrees in physics and electrical engineering and studied chemistry and chemical biology at Harvard University. The Massachusetts Institute of Technology Review selected Parviz as one of the top innovators under the age of 35 in 2007. He is also the recipient of the National Science Foundation Faculty Early Career Development Award for his exceptional integration of education and research.

For more information about NASA Langley’s Colloquium and Sigma Series Lectures:

http://shemesh.larc.nasa.gov/Lectures/

Photo:  http://www.newscom.com/cgi-bin/prnh/20081007/38461LOGO
http://photos.prnewswire.com/prnh/20081007/38461LOGO
PRN Photo Desk photodesk@prnewswire.com
Source: NASA

Web Site:  http://www.nasa.gov/

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