Acid bath may lead to armchair quantum wires

More nanotech news.

The release:

Nanotubes pass acid test

Rice researchers’ method untangles long tubes, clears hurdle toward armchair quantum wire

HOUSTON – (July 14, 2010) – Rice University scientists have found the “ultimate” solvent for all kinds of carbon nanotubes (CNTs), a breakthrough that brings the creation of a highly conductive quantum nanowire ever closer.

Nanotubes have the frustrating habit of bundling, making them less useful than when they’re separated in a solution. Rice scientists led by Matteo Pasquali, a professor in chemical and biomolecular engineering and in chemistry, have been trying to untangle them for years as they look for scalable methods to make exceptionally strong, ultralight, highly conductive materials that could revolutionize power distribution, such as the armchair quantum wire.

The armchair quantum wire — a macroscopic cable of well-aligned metallic nanotubes — was envisioned by the late Richard Smalley, a Rice chemist who shared the Nobel Prize for his part in discovering the the family of molecules that includes the carbon nanotube. Rice is celebrating the 25th anniversary of that discovery this year.

Pasquali, primary author Nicholas Parra-Vasquez and their colleagues reported this month in the online journal ACS Nano that chlorosulfonic acid can dissolve half-millimeter-long nanotubes in solution, a critical step in spinning fibers from ultralong nanotubes.

Current methods to dissolve carbon nanotubes, which include surrounding the tubes with soap-like surfactants, doping them with alkali metals or attaching small chemical groups to the sidewalls, disperse nanotubes at relatively low concentrations. These techniques are not ideal for fiber spinning because they damage the properties of the nanotubes, either by attaching small molecules to their surfaces or by shortening them.

A few years ago, the Rice researchers discovered that chlorosulfonic acid, a “superacid,” adds positive charges to the surface of the nanotubes without damaging them. This causes the nanotubes to spontaneously separate from each other in their natural bundled form.

This method is ideal for making nanotube solutions for fiber spinning because it produces fluid dopes that closely resemble those used in industrial spinning of high-performance fibers. Until recently, the researchers thought this dissolution method would be effective only for short single-walled nanotubes.

In the new paper, the Rice team reported that the acid dissolution method also works with any type of carbon nanotube, irrespective of length and type, as long as the nanotubes are relatively free of defects.

Parra-Vasquez described the process as “very easy.”

“Just adding the nanotubes to chlorosulfonic acid results in dissolution, without even mixing,” he said.

While earlier research had focused on single-walled carbon nanotubes, the team discovered chlorosulfonic acid is also adept at dissolving multiwalled nanotubes (MWNTs). “There are many processes that make multiwalled nanotubes at a cheaper cost, and there’s a lot of research with them,” said Parra-Vasquez, who earned his Rice doctorate last year. “We hope this will open up new areas of research.”

They also observed for the first time that long SWNTs dispersed by superacid form liquid crystals. “We already knew that with shorter nanotubes, the liquid-crystalline phase is very different from traditional liquid crystals, so liquid crystals formed from ultralong nanotubes should be interesting to study,” he said.

Parra-Vasquez, now a postdoctoral researcher at Centre de Physique Moleculaire Optique et Hertzienne, Universite’ de Bordeaux, Talence, France, came to Rice in 2002 for graduate studies with Pasquali and Smalley.

Study co-author Micah Green, assistant professor of chemical engineering at Texas Tech and a former postdoctoral fellow in Pasquali’s research group, said working with long nanotubes is key to attaining exceptional properties in fibers because both the mechanical and electrical properties depend on the length of the constituent nanotubes. Pasquali said that using long nanotubes in the fibers should improve their properties on the order of one to two magnitudes, and that similar enhanced properties are also expected in thin films of carbon nanotubes being investigated for flexible electronics applications.

An immediate goal for researchers, Parra-Vasquez said, will be to find “large quantities of ultralong single-walled nanotubes with low defects — and then making that fiber we have been dreaming of making since I arrived at Rice, a dream that Rick Smalley had and that we have all shared since.”

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Co-authors of the paper are graduate students Natnael Behabtu, Colin Young, Anubha Goyal and Cary Pint; Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry, and Robert Hauge, a distinguished faculty fellow in chemistry, all at Rice; and Judith Schmidt, Ellina Kesselman, Yachin Cohen and Yeshayahu Talmon of the Department of Chemical Engineering, Technion-Israel Institute of Technology, Haifa, Israel.

The Air Force Office of Scientific Research, the Air Force Research Laboratory, the National Science Foundation Division of Materials Research, the Robert A. Welch Foundation, the United States-Israel Binational Science Foundation and the Evans-Attwell Welch Postdoctoral Fellowship funded the research.

Read the abstract at: http://pubs.acs.org/doi/abs/10.1021/nn100864v

For more about Rice’s 25th anniversary Year of Nano celebrations, visit: http://buckyball.smalley.rice.edu/year_of_nano/

Drug delivery system, electromagnetic fields and nanotech

Medical news about nanotechnology.

The release:

Researchers develop drug delivery system using nanoparticles triggered by electromagnetic field

KINGSTON, R.I. July 8, 2010 – A new system for the controlled delivery of pharmaceutical drugs has been developed by a team of University of Rhode Island chemical engineers using nanoparticles embedded in a liposome that can be triggered by non-invasive electromagnetic fields.

The discovery by URI professors Geoffrey Bothun and Arijit Bose and graduate student Yanjing Chen was published in the June issue of ACS Nano.

According to Bothun, liposomes are tiny nanoscale spherical structures made of lipids that can trap different drug molecules inside them for use in delivering those drugs to targeted locations in the body. The superparamagnetic iron oxide nanoparticles the researchers embed in the shell of the liposome release the drug by making the shell leaky when heat-activated in an alternating current electromagnetic field operating at radio frequencies.

“We’ve shown that we can control the rate and extent of the release of a model drug molecule by varying the nanoparticle loading and the magnetic field strength,” explained Bothun. “We get a quick release of the drug with magnetic field heating in a matter of 30 to 40 minutes, and without heating there is minimal spontaneous leakage of the drug from the liposome.”

Bothun said that the liposomes self-assemble because portions of the lipids are hydrophilic – they have a strong affinity for water – and others are hydrophobic – they avoid water. When he mixes lipids and nanoparticles in a solvent, adds water and evaporates off the solvent, the materials automatically assemble themselves into liposomes. The hydrophobic nanoparticles and lipids join together to form the shell of the liposome, while the water-loving drug molecules are captured inside the spherical shell.

“The concept of loading nanoparticles within the hydrophobic shell to focus the activation is brand new,” Bothun said. “It works because the leakiness of the shell is ultimately what controls the release of the drugs.”

The next step in the research is to design and optimize liposome/nanoparticle assemblies that can target cancer cells or other disease-causing cells. In vitro cancer cell studies are already underway in collaboration with URI pharmacy professor Matthew Stoner.

“We are functionalizing the liposomes by putting in different lipids to help stabilize and target them so they can seek out particular cancer cell types,” he said. “We are building liposomes that will attach to particular cells or tumor regions.”

Bothun said that research on nanomedicine shows great promise, but there are still many challenges to overcome, and the targeting of appropriate cells may be the greatest challenge.

“Any ability to target the drug is better than a drug that goes everywhere in your system and generates off-target effects,” he said, noting that the hair loss and nausea from anti-cancer drugs are the result of the high drug concentrations needed for treatment and the drug’s affect on non-target cells. “If you can get an assembly to a targeted site without losing its contents in the process, that’s the holy grail.”

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Nanotechnology and dentistry

Okay, for many, many years I’ve been reading about all sorts of breakthroughs, innovations and miraculous-sounding dental treatments that never really seem to pan out (remember that cavity removing painless gel anyone?), but I couldn’t resist throwing this bit of nanotech out there.

The release:

Nano-sized advance toward next big treatment era in dentistry

		IMAGE: Dentists may use a special nano-sized film in the future to bring diseased teeth back to life rather than remove them. Click here for more information.

Scientists are reporting an advance toward the next big treatment revolution in dentistry — the era in which root canal therapy brings diseased teeth back to life, rather than leaving a “non-vital” or dead tooth in the mouth. In a report in the monthly journal ACS Nano, they describe a first-of-its-kind, nano-sized dental film that shows early promise for achieving this long-sought goal.

Nadia Benkirane-Jessel and colleagues note that root canal procedures help prevent tooth loss in millions of people each year. During the procedure, a dentist removes the painful, inflamed pulp, the soft tissue inside the diseased or injured tooth that contains nerves and blood vessels. Regenerative endodontics, the development and delivery of tissues to replace diseased or damaged dental pulp, has the potential to provide a revolutionary alternative to pulp removal.

The scientists are reporting development of a multilayered, nano-sized film — only 1/50,000th the thickness of a human hair — containing a substance that could help regenerate dental pulp. Previous studies show that the substance, called alpha melanocyte stimulating hormone, or alpha-MSH, has anti-inflammatory properties. The scientists showed in laboratory tests alpha-MSH combined with a widely-used polymer produced a material that fights inflammation in dental pulp fibroblasts. Fibroblasts are the main type of cell found in dental pulp. Nano-films containing alpha-MSH also increased the number of these cells. This could help revitalize damaged teeth and reduce the need for a root canal procedure, the scientists suggest.

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ARTICLE FOR IMMEDIATE RELEASE
“Nanostructured Assemblies for Dental Application”

DOWNLOAD FULL TEXT ARTICLE
http://pubs.acs.org/stoken/presspac/presspac/full/10.1021/nn100713m

Graphene as quantum dots

Nanoelectronics is a major — and important — field right now, and graphene and its cousin graphane are very important materials research components. Both of the nanomaterials are getting a lot of  hype, particularly graphene, but there’s far too much smoke for there not to be at least a little fire. It’s exciting to keep watch on the news to see the breakthroughs as they happen, and eventually cover real-world, market-ready uses for graphene and graphane.

The release:

Graphane yields new potential

Rice physicists dig theoretical wells to mine quantum dots

Graphane is the material of choice for physicists on the cutting edge of materials science, and Rice University researchers are right there with the pack – and perhaps a little ahead.

Researchers mentored by Boris Yakobson, a Rice professor of mechanical engineering and materials science and of chemistry, have discovered the strategic extraction of hydrogen atoms from a two-dimensional sheet of graphane naturally opens up spaces of pure graphene that look – and act – like quantum dots.

That opens up a new world of possibilities for an ever-shrinking class of nanoelectronics that depend on the highly controllable semiconducting properties of quantum dots, particularly in the realm of advanced optics.

The theoretical work by Abhishek Singh and Evgeni Penev, both postdoctoral researchers in co-author Yakobson’s group, was published online last week in the journal ACS Nano and will be on the cover of the print version in June. Rice was recently named the world’s No. 1 institution for materials science research by a United Kingdom publication.

Graphene has become the Flat Stanley of materials. The one-atom-thick, honeycomb-like form of carbon may be two-dimensional, but it seems to be everywhere, touted as a solution to stepping beyond the limits of Moore’s Law.

Graphane is simply graphene modified by hydrogen atoms added to both sides of the matrix, which makes it an insulator. While it’s still technically only a single atom thick, graphane offers great possibilities for the manipulation of the material’s semiconducting properties.

Quantum dots are crystalline molecules from a few to many atoms in size that interact with light and magnetic fields in unique ways. The size of a dot determines its band gap – the amount of energy needed to close the circuit – and makes it tunable to a precise degree. The frequencies of light and energy released by activated dots make them particularly useful for chemical sensors, solar cells, medical imaging and nanoscale circuitry.

Singh and Penev calculated that removing islands of hydrogen from both sides of a graphane matrix leaves a well with all the properties of quantum dots, which may also be useful in creating arrays of dots for many applications.

“We arrived at these ideas from an entirely different study of energy storage in a form of hydrogen adsorption on graphene,” Yakobson said. “Abhishek and Evgeni realized that this phase transformation (from graphene to graphane), accompanied by the change from metal to insulator, offers a novel palette for nanoengineering.”

Their work revealed several interesting characteristics. They found that when chunks of the hydrogen sublattice are removed, the area left behind is always hexagonal, with a sharp interface between the graphene and graphane. This is important, they said, because it means each dot is highly contained; calculations show very little leakage of charge into the graphane host material. (How, precisely, to remove hydrogen atoms from the lattice remains a question for materials scientists, who are working on it, they said.)

“You have an atom-like spectra embedded within a media, and then you can play with the band gap by changing the size of the dot,” Singh said. “You can essentially tune the optical properties.”

Along with optical applications, the dots may be useful in single-molecule sensing and could lead to very tiny transistors or semiconductor lasers, he said.

Challenges remain in figuring out how to make arrays of quantum dots in a sheet of graphane, but neither Singh nor Penev sees the obstacles as insurmountable.

“We think the major conclusions in the paper are enough to excite experimentalists,” said Singh, who will soon leave Rice to become an assistant professor at the Indian Institute of Science in Bangalore. “Some are already working in the directions we explored.”

“Their work is actually supporting what we’re suggesting, that you can do this patterning in a controlled way,” Penev said.

When might their calculations bear commercial fruit? “That’s a tough question,” Singh said. “It won’t be that far, probably — but there are challenges. I don’t know that we can give it a time frame, but it could happen soon.”

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Funding from the Office of Naval Research supported the work. Computations were performed at the Department of Defense Supercomputing Resource Center at the Air Force Research Laboratory.

US government puts $145M into anti-cancer nanotech research

I’ve done a ton of blogging on cancer fighting nanotechnology, so I’m particularly pleased to read about this government initiative. Nanotech may well be the “magic bullet” researchers have been searching for in the battle against cancer.

From the second link, the release:

New advances in science of the ultra-small promise big benefits for cancer patients

		IMAGE: Gold nanoparticles, the bright structures attached to the cultured human cell in this electron microscope image, are among the ultra-small technologies that may help improve the diagnosis and treatment of… Click here for more information.

A $145-million Federal Government effort to harness the power of nanotechnology to improve the diagnosis, treatment, and prevention of cancer is producing innovations that will radically improve care for the disease. That’s the conclusion of an update on the status of the program, called the National Cancer Institute Alliance for Nanotechnology in Cancer. It appears in ACS Nano, a monthly journal published by the American Chemical Society.

Piotr Grodzinski and colleagues note in the article that the alliance, launched in 2004, funds and coordinates research specifically intended to move knowledge about the small science out of laboratories and into hospitals and doctors offices in a big way. It builds on more than 50 years of advances in cancer care that although substantial, still leave cancer as the No. 1 cause of death in the United States and globally.

The article describes a range of advances, including some showing significant promise in clinical trials that are poised to make a big impact on cancer. They promise earlier disease diagnosis, highly targeted treatments that kill cancer cells but leave normal cells alone, fewer side effects, and improved survival, the article

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ARTICLE FOR IMMEDIATE RELEASE “Recent Advances from the National Cancer Institute Alliance for Nanotechnology in Cancer”

DOWNLOAD FULL TEXT ARTICLE http://pubs.acs.org/stoken/presspac/presspac/full/10.1021/nn100073g

Nanoparticles, optics and electricity

(Number one of two posts on nanotechnology and electricity. Hit this link for part two)

This sounds like a tech with a range of applications.

The release:

Penn material scientists turn light into electrical current using a golden nanoscale system

		IMAGE: Material scientists at the Nano/Bio Interface Center of the University of Pennsylvania have demonstrated the transduction of optical radiation to electrical current in a molecular circuit. Click here for more information.

PHILADELPHIA –- Material scientists at the Nano/Bio Interface Center of the University of Pennsylvania have demonstrated the transduction of optical radiation to electrical current in a molecular circuit. The system, an array of nano-sized molecules of gold, respond to electromagnetic waves by creating surface plasmons that induce and project electrical current across molecules, similar to that of photovoltaic solar cells.

The results may provide a technological approach for higher efficiency energy harvesting with a nano-sized circuit that can power itself, potentially through sunlight. Recently, surface plasmons have been engineered into a variety of light-activated devices such as biosensors.

It is also possible that the system could be used for computer data storage. While the traditional computer processor represents data in binary form, either on or off, a computer that used such photovoltaic circuits could store data corresponding to wavelengths of light.

Because molecular compounds exhibit a wide range of optical and electrical properties, the strategies for fabrication, testing and analysis elucidated in this study can form the basis of a new set of devices in which plasmon-controlled electrical properties of single molecules could be designed with wide implications to plasmonic circuits and optoelectronic and energy-harvesting devices.

Dawn Bonnell, a professor of materials science and the director of the Nano/Bio Interface Center at Penn, and colleagues fabricated an array of light sensitive, gold nanoparticles, linking them on a glass substrate. Minimizing the space between the nanoparticles to an optimal distance, researchers used optical radiation to excite conductive electrons, called plasmons, to ride the surface of the gold nanoparticles and focus light to the junction where the molecules are connected. The plasmon effect increases the efficiency of current production in the molecule by a factor of 400 to 2000 percent, which can then be transported through the network to the outside world.

In the case where the optical radiation excites a surface plasmon and the nanoparticles are optimally coupled, a large electromagnetic field is established between the particles and captured by gold nanoparticles. The particles then couple to one another, forming a percolative path across opposing electrodes. The size, shape and separation can be tailored to engineer the region of focused light. When the size, shape and separation of the particles are optimized to produce a “resonant” optical antennae, enhancement factors of thousands might result.

Furthermore, the team demonstrated that the magnitude of the photoconductivity of the plasmon-coupled nanoparticles can be tuned independently of the optical characteristics of the molecule, a result that has significant implications for future nanoscale optoelectronic devices.

“If the efficiency of the system could be scaled up without any additional, unforeseen limitations, we could conceivably manufacture a one-amp, one-volt sample the diameter of a human hair and an inch long,” Bonnell said.

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The study, published in the current issue of the journal ACS Nano, was conducted by Bonnell, David Conklin and Sanjini Nanayakkara of the Department of Materials Science and Engineering in the School of Engineering and Applied Science at Penn; Tae-Hong Park of the Department of Chemistry in the School of Arts and Sceicnes at Penn; Parag Banerjee of the Department of Materials Science and Engineering at the University of Maryland; and Michael J. Therien of the Department of Chemistry at Duke University.

This work was supported by the Nano/Bio Interface Center, National Science Foundation, the John and Maureen Hendricks Energy Fellowship and the U.S. Department of Energy.

Moving molecules

A nanotech breakthrough.

The release:

Step forward for nanotechnology: Controlled movement of molecules

		IMAGE: In a step forward for nanotechnology, scientists are reporting an advance that allows the controlled movement of individual molecules without help from outside forces. Shown is a model of the… Click here for more information.

Scientists in the United Kingdom are reporting an advance toward overcoming one of the key challenges in nanotechnology: Getting molecules to move quickly in a desired direction without help from outside forces. Their achievement has broad implications, the scientists say, raising the possibility of coaxing cells to move and grow in specific directions to treat diseases. It also could speed development of some long-awaited nanotech innovations. They include self-healing structures that naturally repair tears in their surface and devices that deliver medication to diseased while sparing healthy tissue. The study is scheduled for the October issue of ACS Nano, a monthly journal.

Mark Geoghegan and colleagues note long-standing efforts to produce directed, controlled movement of individual molecules in the nano world, where objects are about 1/50,000ththe width of a human hair. The main solutions so far have involved use of expensive, complex machines to move the molecules and they have been only partially successful, the scientists say.

The scientists used a special surface with hydrophobic (water repelling) and hydrophilic (water-attracting) sections. The region between the two sections produced a so-called “energy gradient” which can move tiny objects much like a conveyor belt. In lab studies, the scientists showed that plastic nanoparticles (polymer molecules) moved quickly and in a specific direction on this surface. “This could have implications in many technologies such as coaxing cells to move and grow in given directions, which could have major implications for the treatment of paralysis,” the scientists said.

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RTICLE #1 FOR IMMEDIATE RELEASE
“Directed Single Molecule Diffusion Triggered by Surface Energy Gradients”

DOWNLOAD FULL TEXT ARTICLE http://pubs.acs.org/stoken/presspac/presspac/full/10.1021/nn900991r

Graphite, data storage and semiconductors

Interesting release from Rice involving graphite and nanotechnology, but not the usual carbon nanotubes, graphene or graphane.

The release:

Graphitic memory techniques advance at Rice

Researchers simplify fabrication of nano storage, chip-design tools

Advances by the Rice University lab of James Tour have brought graphite’s potential as a mass data storage medium a step closer to reality and created the potential for reprogrammable gate arrays that could bring about a revolution in integrated circuit logic design.

In a paper published in the online journal ACS Nano, Tour and postdoctoral associate Alexander Sinitskii show how they’ve used industry-standard lithographic techniques to deposit 10-nanometer stripes of amorphous graphite, the carbon-based, semiconducting material commonly found in pencils, onto silicon. This facilitates the creation of potentially very dense, very stable nonvolatile memory for all kinds of digital devices.

With backing from a major manufacturer of memory chips, Tour and his team have pushed the technology forward in several ways since a paper that appeared last November first described two-terminal graphitic memory. While noting advances in other molecular computing techniques that involve nanotubes or quantum dots, he said none of those have yet proved practical in terms of fabrication.

Not so with this simple-to-deposit graphite. “We’re using chemical vapor deposition and lithography — techniques the industry understands,” said Tour, Rice’s Chao Professor of Chemistry and a professor of mechanical engineering and materials science and of computer science. “That makes this a good alternative to our previous carbon-coated nanocable devices, which perform well but are very difficult to manufacture.”

Graphite makes a good, reliable memory “bit” for reasons that aren’t yet fully understood. The lab found that running a current through a 10-atom-thick layer of graphite creates a complete break in the circuit — literally, a gap in the strip a couple of nanometers wide. Another jolt repairs the break. The process appears to be indefinitely repeatable, which provides addressable ones and zeroes, just like today’s flash memory devices but at a much denser scale.

Graphite’s other advantages were detailed in Tour’s earlier work: the ability to operate with as little as three volts, an astoundingly high on/off ratio (the amount of juice a circuit holds when it’s on, as opposed to off) and the need for only two terminals instead of three, which eliminates a lot of circuitry. It’s also impervious to a wide temperature range and radiation; this makes it suitable for deployment in space and for military uses where exposure to temperature extremes and radiation is a concern.

Tour’s graphite-forming technique is well-suited for other applications in the semiconductor industry. One result of the previous paper is a partnership between the Tour group and NuPGA (for “new programmable gate arrays”), a California company formed around the research to create a new breed of reprogrammable gate arrays that could make the design of all kinds of computer chips easier and cheaper.

The Tour lab and NuPGA, led by industry veteran Zvi Or-Bach (founder of eASIC and Chip Express), have applied for a patent based on vertical arrays of graphite embedded in “vias,” the holes in integrated circuits connecting the different layers of circuitry. When current is applied to a graphite-filled via, the graphite alternately splits and repairs itself (a process also described in the latest paper), just like it does in strip form. Essentially, it becomes an “antifuse,” the basic element of one type of field programmable gate array (FPGA), best described as a blank computer chip that uses software to rewire the hardware.

Currently, antifuse FPGAs can be programmed once. But this graphite approach could allow for the creation of FPGAs that can be reprogrammed at will. Or-Bach said graphite-based FPGAs would start out as blanks, with the graphite elements split. Programmers could “heal” the antifuses at will by applying a voltage, and split them with an even higher voltage.

Such a device would be mighty handy to computer-chip designers, who now spend many millions to create the photolithography mask sets used in chip fabrication. If the design fails, it’s back to square one.

“As a result of that, people are only hesitantly investing in new chip designs,” said Tour. “They stick with the old chip designs and make modifications. FPGAs are chips that have no specific ability, but you use software to program them by interconnecting the circuitry in different ways.”  That way, he said, fabricators don’t need expensive mask sets to try new designs.

“The No. 1 problem in the industry, and one that gives an opportunity for a company like ours, is that the cost of masks keeps moving up as people push semiconductors into future generators,” said Or-Bach. “Over the last 10 years, the cost of a mask set has multiplied almost 10 times.

“If we can really make something that will be an order of magnitude better, the markets will be happy to make use of it. That’s our challenge, and I believe the technology makes it possible for us to do that.”

The ACS Nano paper appears here: http://pubs.acs.org/doi/pdf/10.1021/nn9006225

Read more about Tour’s research of graphitic memory here: 
http://www.media.rice.edu/media/NewsBot.asp?MODE=VIEW&ID=11817

To download images, go here: http://www.rice.edu/nationalmedia/images/graphitestripes.jpg
http://www.rice.edu/nationalmedia/images/graphitestripes2.jpg
http://www.rice.edu/nationalmedia/images/vias.jpg

Nanotube integrated circuits

Built on introduced flaws in the nanotubes themselves. This research was published in ACS Nano (abstract).

From the Nanodot link:

Computational nanotech studies have shown that deliberate introduction of structural defects at specific sites in carbon nanotubes can guide electrons along specific paths, providing a way to fabricate complex electronic circuits from nanotubes. Although this research was theoretical, the researchers are quoted as saying focused electron beams could be used to create the defects where they would be needed to make complicated networks. An item on KurzweilAI.net led to this article on New Scientist Tech, written by Colin Barras. From “Flawed nanotubes could be perfect silicon replacement“:

The paradox of perfection — that flaws make things perfect — could be the key to designing nanoelectronic circuits from carbon nanotubes, according to US scientists.

They have discovered that a circuit of nanotubes can only guide a current if some of the tubes carry structural defects.

Individual carbon nanotubes are exceptionally good conductors because they are essentially a single carbon molecule. They can even outdo silicon at transmitting charge, which means nanotube circuits could boost computing speeds while reducing chip size…

More nanotech transistor news

Just blogged on a Technology Review story a few minutes ago, and here’s a press release on another nanotech transistor breakthrough. Bonus because this one even involves LEDs.

The release:

USC researchers print dense lattice of transparent nanotube transistors on flexible base

Low-temperature process produces both n-type and p-type transistors; allows embedding of LEDs

		IMAGE: See-through circuit makers: Hsaioh-Kang Chang, left, and Fumiaki Ishikawa, with their transparent, flexible transistor array. Click here for more information.

It’s a clear, colorless disk about 5 inches in diameter that bends and twists like a playing card, with a lattice of more than 20,000 nanotube transistors capable of high-performance electronics printed upon it using a potentially inexpensive low-temperature process.

Its University of Southern California creators believe the prototype points the way to such long sought after applications as affordable “head-up” car windshield displays. The lattices could also be used to create cheap, ultra thin, low-power “e-paper” displays.

They might even be incorporated into fabric that would change color or pattern as desired for clothing or even wall covering, into nametags, signage and other applications.

A team at the USC Viterbi School of Engineering created the new device, described and illustrated in a just-published paper on “Transparent Electronics Based on Printed Aligned Nanotubes on Rigid and Flexible Structures” in the journal ACS Nano.

Graduate students Fumiaki Ishikawa and Hsiaoh-Kang Chang worked under Professor Chongwu Zhou of the School’s Ming Hsieh Department of Electrical Engineering on the project, solving the problems of attaching dense matrices of carbon nanotubes not just to heat-resistant glass but also to flexible but highly heat-vulnerable transparent plastic substrates.

The researchers not only created printed circuit lattices of nanotube-based transistors to the transparent plastic but also additionally connected them to commercial gallium nitrate (GaN) light-emitting diodes, which change their luminosity by a factor of 1,000 as they are energized.

“Our results suggest that aligned nanotubes have great potential to work as building blocks for future transparent electronics,” say the researchers.

The thin transparent thin-film transistor technology developed employs carbon nanotubes – tubes with walls one carbon atom thick – as the active channels for the circuits, controlled by iridium-tin oxide electrodes which function as sources, gates and drains.

Earlier attempts at transparent devices used other semiconductor materials with disappointing electronic results, enabling one kind of transistor (n-type); but not p-types; both types are needed for most applications.

The critical improvement in performance, according to the research, came from the ability to produce extremely dense, highly patterned lattices of nanotubes, rather than random tangles and clumps of the material. The Zhou lab has pioneered this technique over the past three years.

The paper contains a description of how the new devices are made.

“These nanotubes were first grown on quartz substrates and then transferred to glass or PET substrates with pre-patterned indium-tin oxide (ITO) gate electrodes, followed by patterning of transparent source and drain electrodes. In contrast to random networked nanotubes, the use of massively aligned nanotubes enabled the devices to exhibit high performance, including high mobility, good transparency, and mechanical flexibility.

“In addition, these aligned nanotube transistors are easy to fabricate and integrate, as compared to individual nanotube devices. The transfer printing process allowed the devices to be fabricated through low temperature process, which is particularly important for realizing transparent electronics on flexible substrates. … While large manufacturability must be addressed before practical applications are considered, our work has paved the way for using aligned nanotubes for high-performance transparent electronics ”

 

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Ishikawa and Chang are the principal authors of the paper. Viterbi School graduate students Koungmin Ryu, Pochiang Chen, Alexander Badmaev, Lewis Gomez De Arco, and Guozhen Shen also participated in the project. Zhou, an associate professor, holds the Viterbi School’s Jack Munushian Early Career Chair.

The Focus Center Research Program (FCRP FENA) and the National Science Foundation supported the research. The original article can be read at: http://pubs.acs.org/doi/abs/10.1021/nn800434d

 

Chemical “signals” power nanomachines

Link goes to abstract:

Using simulation and theory, we demonstrate how nanoparticles can be harnessed to regulate the interaction between two initially stationary microcapsules on a surface and promote the self-propelled motion of these capsules along the substrate. The first microcapsule, the “signaling” capsule, encases nanoparticles, which diffuse from the interior of this carrier and into the surrounding solution; the second capsule is the “target” capsule, which is initially devoid of particles. Nanoparticles released from the signaling capsule modify the underlying substrate and thereby initiate the motion of the target capsule. The latter motion activates hydrodynamic interactions, which trigger the signaling capsule to follow the target. The continued release of the nanoparticles sustains the motion of both capsules. In effect, the system constitutes a synthetic analogue of biological cell signaling and our findings can shed light on fundamental physical forces that control interactions between cells. Our findings can also yield guidelines for manipulating the interactions of synthetic microcapsules in microfluidic devices.