David Kirkpatrick

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.

March 18, 2010

Graphene may be key to storing hydrogen

Needless to say this will have a major impact on using hydrogen as a power source in fuel cells or other applications.

The release:

Layered graphene sheets could solve hydrogen storage issues

IMAGE: A graphene-oxide framework (GOF) is formed of layers of graphene connected by boron-carboxylic “pillars.” GOFs such as this one are just beginning to be explored as a potential storage medium…

Click here for more information.

Graphene—carbon formed into sheets a single atom thick—now appears to be a promising base material for capturing hydrogen, according to recent research* at the National Institute of Standards and Technology (NIST) and the University of Pennsylvania. The findings suggest stacks of graphene layers could potentially store hydrogen safely for use in fuel cells and other applications.

Graphene has become something of a celebrity material in recent years due to its conductive, thermal and optical properties, which could make it useful in a range of sensors and semiconductor devices. The material does not store hydrogen well in its original form, according to a team of scientists studying it at the NIST Center for Neutron Research. But if oxidized graphene sheets are stacked atop one another like the decks of a multilevel parking lot, connected by molecules that both link the layers to one another and maintain space between them, the resulting graphene-oxide framework (GOF) can accumulate hydrogen in greater quantities.

Inspired to create GOFs by the metal-organic frameworks that are also under scrutiny for hydrogen storage, the team is just beginning to uncover the new structures’ properties. “No one else has ever made GOFs, to the best of our knowledge,” says NIST theorist Taner Yildirim. “What we have found so far, though, indicates GOFs can hold at least a hundred times more hydrogen molecules than ordinary graphene oxide does. The easy synthesis, low cost and non-toxicity of graphene make this material a promising candidate for gas storage applications.”

The GOFs can retain 1 percent of their weight in hydrogen at a temperature of 77 degrees Kelvin and ordinary atmospheric pressure—roughly comparable to the 1.2 percent that some well-studied metal-organic frameworks can hold, Yildirim says.

Another of the team’s potentially useful discoveries is the unusual relationship that GOFs exhibit between temperature and hydrogen absorption. In most storage materials, the lower the temperature, the more hydrogen uptake normally occurs. However, the team discovered that GOFs behave quite differently. Although a GOF can absorb hydrogen, it does not take in significant amounts at below 50 Kelvin (-223 degrees Celsius). Moreover, it does not release any hydrogen below this “blocking temperature”—suggesting that, with further research, GOFs might be used both to store hydrogen and to release it when it is needed, a fundamental requirement in fuel cell applications.

Some of the GOFs’ capabilities are due to the linking molecules themselves. The molecules the team used are all benzene-boronic acids that interact strongly with hydrogen in their own right. But by keeping several angstroms of space between the graphene layers—akin to the way pillars hold up a ceiling—they also increase the available surface area of each layer, giving it more spots for the hydrogen to latch on.

According to the team, GOFs will likely perform even better once the team explores their parameters in more detail. “We are going to try to optimize the performance of the GOFs and explore other linking molecules as well,” says Jacob Burress, also of NIST. “We want to explore the unusual temperature dependence of absorption kinetics, as well as whether they might be useful for capturing greenhouse gases such as carbon dioxide and toxins like ammonia.”

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The research is funded in part by the Department of Energy.

* J. Burress, J. Simmons, J. Ford and T.Yildirim. “Gas adsorption properties of graphene-oxide-frameworks and nanoporous benzene-boronic acid polymers.” To be presented at the March meeting of the American Physical Society (APS) in Portland, Ore., March 18, 2010. An abstract is available at http://meetings.aps.org/Meeting/MAR10/Event/122133

August 20, 2008

Optical computing coming soon?

Filed under: Science, Technology — Tags: , , , , — David Kirkpatrick @ 5:59 pm

From KurzweilAI.net — optical computing is an exciting development and looks like it’s coming down the pike.

Scientists Move Optical Computing Closer to Reality
PhysOrg.com, Aug. 19, 2008

University of Pennsylvania scientists have theorized a way to increase the speed of pulses of light traveling in nanoparticle chains (acting as miniature waveguides) to 2.5 times the speed of light by altering the particle shape.

As the velocity of the light pulse increases, so too does the operating bandwidth of a waveguide, thus increasing the number of information channels and allowing more information to flow simultaneously through a waveguide.

They found that shaping the particles as prolate, cigar-shaped or oblate, saucer-shaped spheroids boosted the velocities of surface plasmon pulses reflecting off the surface to 2.5 times the speed of light in a vacuum, while decreasing power loss.

Application of this theory would use nanosized metal chains as building blocks for novel optoelectronic and optical devices, which would operate at higher frequencies than conventional electronic circuits. Such devices could eventually find applications in the developing area of high-speed optical computing, in which protons and light replace electrons and transistors for greater performance.

 
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July 27, 2008

One-step nanoassembly announced

Filed under: Science, Technology — Tags: , , — David Kirkpatrick @ 8:43 am

Researchers at the University of Pennsylvania have announced a customizable, one-step method for creating nanoscale objects.

Here’s the complete release:

University of Pennsylvania Researchers Demonstrate a Flexible, One-Step Assembly of Nanoscale Structures
July 25, 2008

PHILADELPHIA –- Scientists at the University of Pennsylvania have created a one-step, repeatable method for the production of functional nanoscale patterns or motifs with adjustable features, size and shape using a single master “plate.”

Researchers took advantage of the elastic instability of a widely used, flexible polymer membrane, polydimethylsiloxane, or PDMS. When exposed to a solvent, circular pores in the membrane elliptically deform, and elastic interactions between them generate long-range orientational order of their axes into a “diamond plate” pattern. By lacing the solvent with iron nanoparticles, the team found that evaporation of the solvent drives the assembly of the nanoparticles onto the membrane surface along these distorted pores.

This results in two-dimensional patterns with sub-100 nanometer features. The traditional fabrication process can take as long as a month and cost $50,000 per print. In this new process, a master can be made for a fraction of the cost and can be reused many times. The Penn team’s technique does not require delicate surface preparation or the complex chemistry of standard lithographic processes. Instead, the new process relies on patterns that form spontaneously in equilibrium. The resulting, “diamond-plate” pattern persists over the entire sample, as large as a square centimeter, with no imperfections.

The features of the resultant nanoparticle patterns are up to 10 times sharper than the original membrane. The resulting symmetry of the film can be transferred onto a substrate, both flat or curved, where it can be used to generate similar anisotropic magnetic, photonic, phononic and plasmonic properties.

“These functional nano-motifs could in turn benefit novel technologies that are sensitive to local environment change such as smart clothing, biomarkers and eco-friendly buildings,” Shu Yang, assistant professor in the Department of Materials Science and Engineering of the School of Engineering and Applied Scienceat Penn, said. “Using similar pattern transformation principles, our technique could be extended to pattern a variety of material systems such as polymers and composites, creating a new design mechanism for nanoscale manufacturing.”

The team modeled the elastic instability of the membrane in terms of elastically interacting “dislocation dipoles” and found complete agreement between the theoretical ground state and the observed pattern. This model allows for the manipulation of the structural details of the membrane to tailor the elastic distortions and generate a variety of nanostructures.

“It is both surprising and serendipitous that the simple theory is corroborated by experiment and by complex numerical simulations by other groups,” Randall Kamien, professor in the Department of Physics and Astronomy in the School of Arts and Sciences at Penn, said.

The natural world provides many examples of the type of intrinsic, bottom-up effects that engineers see here, from the arrangement of growing leaves on a plant to the pattern of animal stripes to fingerprints. In these systems, instabilities, packing constraints and simple geometries drive the formation of delicate, detailed and beautiful patterns. Mechanical instabilities in soft polymers, precipitated by dewetting, swelling and buckling during the production stage, are often viewed as failure mechanisms that can interfere with the performance of devices. However, these instabilities are now being exploited to assemble complex patterns, to fabricate novel devices such as stretchable electronics and flexible microlenses and to provide a metrology for measuring elastic moduli and the thickness of ultrathin films.

PDMS membranes have been widely used in soft lithography for low-cost fabrication of microdevices. The Penn team replica-molded a PDMS membrane with circular pores from an array of 1 μm diameter silicon pillars spaced 2 μm apart on a square lattice. When exposed to the organic solvent toluene, PDMS gels swell by as much as 130 percent. As the osmotic pressure builds, the circular pores in the PDMS deform and eventually snap shut to relieve the stress, much as the joints in railways and bridges expand and contract to maintain structural integrity in response to changes in moisture and temperature.

Because the elastic deformation of the PDMS membrane is induced by solvent swelling, the diamond plate pattern in PDMS is stable in the wet state and snaps back to the original square lattice once the solvent evaporates. To capture the diamond plate before evaporation and, more important, to utilize this deformation for assembly of complex functional structures, the team suspended superparamagnetic Fe3O4 nanoparticles in toluene and applied the solution to the PDMS membrane. As the PDMS swells, the convective assembly of the nanoparticles follows, faithfully replicating the deformed PDMS membrane. Once dry, the elastic membrane returns to its original state and can be reused.

The study was published in the journal Nano Letters and was conducted by members of the Laboratory for Research on the Structure of Matter at Penn: Ying Zhang, Anna Peter, Pei-Chun Lin and Yang of the Department of Materials Science and Engineering and Elisabetta A. Matsumoto and Kamien of the Department of Physics and Astronomy.

Funding was provided by the National Science Foundation MRSEC Program and an NSF Career Award bestowed upon Yang.

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July 3, 2008

Solar moratorium news, nanowire memory and tiny, tiny computer chips

From KurzweilAI.net — the US government comes to its senses on the solar moratorium, breakthroughs in nanowire memory, and computer chips heading toward smaller than 10 nanometers.

U.S. Lifts Moratorium on New Solar Projects
New York Times, July 3, 2008

Under increasing public pressure over its decision to temporarily halt all new solar development on public land, the Bureau of Land Management said Wednesday that it was lifting the freeze, barely a month after it was put into effect.

See also: Citing Need for Assessments, U.S. Freezes Solar Energy Projects

 
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New Nanowire-Based Memory Could Beef Up Information Storage
PhysOrg.com, July 2, 2008

University of Pennsylvania researchers have created a type of nanowire-based information storage device that is capable of storing three bit values rather than the usual two.

This ability could lead to a new generation of high-capacity information storage for electronic devices.

The phase changes are achieved by subjecting the nanowires to pulsed electric fields. This process heats the nanowires, altering the core and shell structure from crystalline (ordered) to amorphous (disordered). These two states correspond to two different electrical resistances.

The third value corresponds to the case where the core is amorphous while the shell is crystalline (or visa versa), resulting in an intermediate resistance.

Creating information storage from nanowires can be done via “bottom-up” approaches, using the natural tendency of tiny structures to self-assemble into larger structures, so they may be able to break free of the limitations faced by traditional “top-down” methods, such as patterning a circuit onto a silicon wafer by depositing a nanowire thin film.

 
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Intel’s Gelsinger Sees Clear Path To 10nm Chips
ChannelWeb, June 30, 2008

Intel sees a “clear way” to manufacturing chips under 10 nanometers, according to Pat Gelsinger, VP of Intel’s Digital Enterprise Group.

The next die shrink milestone will be the 32nm process, set to kick off next year, followed by 14nm a few years after that and then sub-10nm, he said.

 
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