David Kirkpatrick

February 12, 2010

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.

September 10, 2010

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 1, 2010

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 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 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

July 22, 2010

Improving the application of nanocoatings

Nanocoatings do a lot of good, particularly with making solar cells more efficient. The trick is they haven’t been too easy to apply to big areas. Researchers at Stanford have helped change that issue.

From the link:

Nanoscale wires, pores, bumps, and other textures can dramatically improve the performance of solar cells, displays, and even self-cleaning coatings. Now researchers at Stanford University have developed a simpler, cheaper way to add these features to large surfaces.

Nanoscale structures offer particular advantages in devices that interact with light. For example, a thin-film solar cell carpeted with nano pillars is more efficient because the pillars absorb more light and convert more of it into electricity. Other nanoscale textures offer similar advantages in optical devices like display backlights.

The problem is scaling up to large areas, says Yi Cui, a Stanford professor of materials science and engineering who led the new work. “Many methods are really complex and don’t solve the problem,” says Cui. Lithography can be used to carve out nanoscale features with precise dimensions, but it’s expensive and difficult. Simpler techniques, such as spin-coating a surface with nanoparticles or using acids to etch it with tiny holes, don’t allow for much precision.

Nanosphere smear: Using a spinning rod to deposit an ink suspension of silica nanospheres is a simple way to create bumpy, nanotextured coatings like these three.

Credit: ACS/Nano Letters

July 16, 2010

Solar plus nanotech equals lower cost cells

I always love covering news that combines solar and nanotechnology, particularly when the combo leads to lower costs for solar power. I’ve previously blogged about nanopillars leading increased solar efficiency.

From the first link:

A material with a novel nanostructure developed by researchers at the University of California, Berkeley could lead to lower-cost solar cells and light detectors. It absorbs light just as well as commercial thin-film solar cells but uses much less semiconductor material.

The new material consists of an array of nanopillars that are narrow at the top and thicker at the bottom. The narrow tops allow light to penetrate the array without reflecting off. The thicker bottom absorbs light so that it can be converted into electricity. The design absorbs 99 percent of visible light, compared to the 85 percent absorbed by an earlier design in which the nanopillars were the same thickness along their entire length. An ordinary flat film of the material would absorb only 15 percent of the light.

Thick and thin: A scanning electron microscope image shows dual-diameter light-trapping germanium nanopillars.

Credit: Ali Javey, UC Berkeley

May 27, 2010

Nanotech and optics

Very cool findings about light-activated nanoshells.

The release:

Optical Legos: Building nanoshell structures

Self-assembly method yields materials with unique optical properties

IMAGE: Heptamers containing seven nanoshells have unique optical properties.

Click here for more information.

HOUSTON — (May 27, 2010) — Scientists from four U.S. universities have created a way to use Rice University’s light-activated nanoshells as building blocks for 2-D and 3-D structures that could find use in chemical sensors, nanolasers and bizarre light-absorbing metamaterials. Much as a child might use Lego blocks to build 3-D models of complex buildings or vehicles, the scientists are using the new chemical self-assembly method to build complex structures that can trap, store and bend light.

The research appears in this week’s issue of the journal Science.

“We used the method to make a seven-nanoshell structure that creates a particular type of interference pattern called a Fano resonance,” said study co-author Peter Nordlander, professor of physics and astronomy at Rice. “These resonances arise from peculiar light wave interference effects, and they occur only in man-made materials. Because these heptamers are self-assembled, they are relatively easy to make, so this could have significant commercial implications.”

Because of the unique nature of Fano resonances, the new materials can trap light, store energy and bend light in bizarre ways that no natural material can. Nordlander said the new materials are ideally suited for making ultrasensitive biological and chemical sensors. He said they may also be useful in nanolasers and potentially in integrated photonic circuits that run off of light rather than electricity.

The research team was led by Harvard University applied physicist Federico Capasso and also included nanoshell inventor Naomi Halas, Rice’s Stanley C. Moore Professor in Electrical and Computer Engineering and professor of physics, chemistry and biomedical engineering.

Nordlander, the world’s leading theorist on nanoparticle plasmonics, had predicted in 2008 that a heptamer of nanoshells would produce Fano resonances. That paper spurred Capasso’s efforts to fabricate the structure, Nordlander said.

The new self-assembly method developed by Capasso’s team was also used to make magnetic three-nanoshell “trimers.” The optical properties of these are described in the Science paper, which also discusses how the self-assembly method could be used to build even more complex 3-D structures.

Nanoshells, the building blocks that were used in the new study, are about 20 times smaller than red blood cells. In form, they resemble malted milk balls, but they are coated with gold instead of chocolate, and their center is a sphere of glass. By varying the size of the glass center and the thickness of the gold shell, Halas can create nanoshells that interact with specific wavelengths of light.

“Nanoshells were already among the most versatile of all plasmonic nanoparticles, and this new self-assembly method for complex 2-D and 3-D structures simply adds to that,” said Halas, who has helped develop a number of biological applications for nanoshells, including diagnostic applications and a minimally invasive procedure for treating cancer.

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Additional co-authors of the new study include Rice graduate students Kui Bao and Rizia Bardhan; Jonathan Fan and Vinothan Manoharan, both of Harvard; Chihhui Wu and Gennady Shvets, both of the University of Texas at Austin; and Jiming Bao of the University of Houston. The research was supported by the National Science Foundation, the Air Force Office of Scientific Research, the Department of Defense, the Robert A. Welch Foundation, the Department of Energy and Harvard University.

PhysOrg covers this story here.

April 4, 2010

Roadblock to effective transparent, current-carrying nanocoating

Filed under: Science — Tags: , , , , — David Kirkpatrick @ 4:20 pm

This is something of a setback in an exciting area of solar panel improvement.

The release:

NIST scientists address ‘wrinkles’ in transparent film development

IMAGE: This atomic-force microscopy image shows wrinkling in a single-wall carbon nanotube membrane; the inset shows an optical reflection micrograph of the membrane without any strain. The random arrangement of the…

Click here for more information.

A closer look at a promising nanotube coating that might one day improve solar cells has turned up a few unexpected wrinkles, according to new research* conducted at the National Institute of Standards and Technology (NIST) and North Dakota State University (NDSU)—research that also may help scientists iron out a solution.

The scientists have found that coatings made of single-walled carbon nanotubes (SWCNTs) are not quite as deformable as hoped, implying that they are not an easy answer to problems that other materials present. Though films made of nanotubes possess many desirable properties, the team’s findings reveal some issues that might need to be addressed before the full potential of these coatings is realized.

“The irony of these nanotube coatings is that they can change when they bend,” says Erik Hobbie, now the director of the Materials and Nanotechnology program at NDSU. “Under modest strains, these films can develop irreversible changes in nanotube arrangement that reduce their conductivity. Our work is the first to suggest this, and it opens up new approaches to engineering the films in ways that minimize these effects.”

High on the wish list of the solar power industry is a cheap, flexible, transparent coating that can conduct electricity. If this combination of properties can somehow be realized in a single material, solar cells might become far less expensive, and manufacturers might be able to put them in unexpected places—such as articles of clothing. Transparent conductive coatings can be made of indium-tin oxide, but their rigidity and high cost make them less practical for widespread use.

Carbon nanotubes are one possible solution. Nanotubes, which resemble microscopic rolls of chicken wire, are inexpensive, easy to produce, and can be formed en masse into transparent conductive coatings whose weblike inner structure makes them not only strong but deformable, like paper or fabric. However, the team’s research found that some kinds of stretching cause microscopic ‘wrinkles’ in the coating that disrupt the random arrangement of the nanotubes, which is what makes the coating conduct electricity.

“You want the nanotubes to stay randomly arranged,” Hobbie says. “But when a nanotube coating wrinkles, it can lose the connected network that gives it conductivity. Instead, the nanotubes bundle irreversibly into ropelike formations.”

Hobbie says the study suggests a few ways to address the problem, however. The films might be kept thin enough so the wrinkling might be avoided in the first place, or designers could engineer a second interpenetrating polymer network that would support the nanotube network, to keep it from changing too much in response to stress. “These approaches might allow us to make coatings of nanotubes that could withstand large strains while retaining the traits we want,” Hobbie says.

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* E. K. Hobbie, D. O. Simien, J. A. Fagan, J. Y. Huh, J. Y.Chung, S. D. Hudson, J. Obrzut, J. F. Douglas, and C. M. Stafford. Wrinkling and Strain Softening in Single-Wall Carbon Nanotube Membranes. Physical Review Letters, March 26, 2010, 104, 125505.

March 7, 2010

Carbon nanotubes open new area of energy research

Nanotechnology is revolutionizing how we see and deal with electricity, everything from storage to wiring. Now a team at MIT has discovered carbon nanotubes produce electricity in an entirely new way, opening a brand new area in energy research.

From the final link:

A team of scientists at MIT have discovered a previously unknown phenomenon that can cause powerful waves of energy to shoot through minuscule wires known as carbon nanotubes. The discovery could lead to a new way of producing electricity, the researchers say.

The phenomenon, described as thermopower waves, “opens up a new area of energy research, which is rare,” says Michael Strano, MIT’s Charles and Hilda Roddey Associate Professor of Chemical Engineering, who was the senior author of a paper describing the new findings that appeared in  on March 7. The lead author was Wonjoon Choi, a doctoral student in mechanical engineering.

Like a collection of flotsam propelled along the surface by waves traveling across the ocean, it turns out that a thermal wave — a moving pulse of heat — traveling along a microscopic wire can drive electrons along, creating an electrical current.

The key ingredient in the recipe is carbon nanotubes — submicroscopic hollow tubes made of a chicken-wire-like lattice of carbon atoms. These tubes, just a few billionths of a meter () in diameter, are part of a family of novel carbon molecules, including buckyballs and graphene sheets, that have been the subject of intensive worldwide research over the last two decades.

March 5, 2010

Silicon nanowires may improve solar costs

Silicon photovoltaics offer incredible solar cell efficiency and now it looks like nanotechnology may offer a way to add low production cost to that mix. This type of headway and improvement is what will make solar a market-viable power option.

The release:

Trapping Sunlight with Silicon Nanowires

MARCH 03, 2010

Lynn Yarris

This photovoltaic cell is comprised of 36 individual arrays of silicon nanowires featuring radial p-n junctions. The color dispersion demonstrates the excellent periodicity present over the entire substrate. (Photo courtesy of Peidong Yang)

This photovoltaic cell is comprised of 36 individual arrays of silicon nanowires featuring radial p-n junctions. The color dispersion demonstrates the excellent periodicity over the entire substrate. (Photo from Peidong Yang)

Solar cells made from silicon are projected to be a prominent factor in future renewable green energy equations, but so far the promise has far exceeded the reality. While there are now silicon photovoltaics that can convert sunlight into electricity at impressive 20 percent efficiencies, the cost of this solar power is prohibitive for large-scale use. Researchers with the Lawrence Berkeley National Laboratory (Berkeley Lab), however, are developing a new approach that could substantially reduce these costs. The key to their success is a better way of trapping sunlight.

“Through the fabrication of thin films from ordered arrays of vertical silicon nanowires we’ve been able to increase the light-trapping in our solar cells by a factor of 73,” says chemist Peidong Yang, who led this research. “Since the fabrication technique behind this extraordinary light-trapping enhancement is a relatively simple and scalable aqueous chemistry process, we believe our approach represents an economically viable path toward high-efficiency, low-cost thin-film solar cells.”

Yang holds joint appointments with Berkeley Lab’s Materials Sciences Division, and the University of California  Berkeley’s Chemistry Department. He is a leading authority on semiconductor nanowires – one-dimensional strips of materials whose width measures only one-thousandth that of a human hair but whose length may stretch several microns.

“Typical solar cells are made from very expensive ultrapure single crystal silicon wafers that require about 100 micrometers of thickness to absorb most of the solar light, whereas our radial geometry enables us to effectively trap light with nanowire arrays fabricated from silicon films that are only about eight micrometers thick,” he says. “Furthermore, our approach should in principle allow us to use metallurgical grade or “dirty” silicon rather than the ultrapure silicon crystals now required, which should cut costs even further.”

Yang has described this research in a paper published in the journal NANO Letters, which he co-authored with Erik Garnett, a chemist who was then a member of Yang’s research group. The paper is titled “Light Trapping in Silicon Nanowire Solar Cells.”

A radial p-n junction consists of a layer of n-type silicon forming a shell around a p-type silicon nanowire core. This geometry turns each individual nanowire into a photovoltaic cell.

A radial p-n junction consists of a layer of n-type silicon forming a shell around a p-type silicon nanowire core. This geometry turns each individual nanowire into a photovoltaic cell.

Generating Electricity from Sunlight

At the heart of all solar cells are two separate layers of material, one with an abundance of electrons that functions as a negative pole, and one with an abundance of electron holes (positively-charged energy spaces) that functions as a positive pole. When photons from the sun are absorbed, their energy is used to create electron-hole pairs, which are then separated at the interface between the two layers and collected as electricity.

Because of its superior photo-electronic properties, silicon remains the photovoltaic semiconductor of choice but rising demand has inflated the price of the raw material. Furthermore, because of the high-level of crystal purification required, even the fabrication of the simplest silicon-based solar cell is a complex, energy-intensive and costly process.

Yang and his group are able to reduce both the quantity and the quality requirements for silicon by using vertical arrays of nanostructured radial p-n junctions rather than conventional planar p-n junctions. In a radial p-n junction, a layer of n-type silicon forms a shell around a p-type silicon nanowire core. As a result, photo-excited electrons and holes travel much shorter distances to electrodes, eliminating a charge-carrier bottleneck that often arises in a typical silicon solar cell. The radial geometry array also, as photocurrent and optical transmission measurements by Yang and Garrett revealed, greatly improves light trapping.

“Since each individual nanowire in the array has a p-n junction, each acts as an individual solar cell,” Yang says. “By adjusting the length of the nanowires in our arrays, we can increase their light-trapping path length.”

While the conversion efficiency of these solar nanowires was only about five to six percent, Yang says this efficiency was achieved with little effort put into surface passivation, antireflection, and other efficiency-increasing modifications.

“With further improvements, most importantly in surface passivation, we think it is possible to push the efficiency to above 10 percent,” Yang says.

Combining a 10 percent or better conversion efficiency with the greatly reduced quantities of starting silicon material  and the ability to use metallurgical grade silicon, should make the use of silicon nanowires an attractive candidate for large-scale development.

As an added plus Yang says, “Our technique can be used in existing solar panel manufacturing processes.”

This research was funded by the National Science Foundation’s Center of Integrated Nanomechanical Systems.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research for DOE’s Office of Science and is managed by the University of California. Visit our website at http://www.lbl.gov.


Peidong Yang (Photo by Roy Kaltschmidt, Berkeley Lab Public Affairs)

Peidong Yang (Photo by Roy Kaltschmidt, Berkeley Lab Public Affairs)

Additional Information

For more about the research of Peidong Yang and his group, visit the Website at http://www.cchem.berkeley.edu/pdygrp/main.html

For more about the Center of Integrated Nanomechanical Systems (COINS) visit the Website at http://mint.physics.berkeley.edu/coins/

February 17, 2010

Efficient thin-film solar through nanotech

Filed under: Business, Science — Tags: , , , , , — David Kirkpatrick @ 2:54 pm

A nanotechnology design improves the efficiency of thin-film solar cells. An important breakthrough in working to commercially viable solar power because thin-film cells are cheaper than photovoltaics, but efficiency has been an issue. The two key elements  in making solar energy widespread and a credible challenger to petroleum-based energy are lower costs (both in installation and maintenance) and higher efficiencies. Anything that works to combine those two elements is a step in the right direction.

I just love blog posts that combine nanotechnology and solar power.

From the link:

Thin-film solar cells are less expensive than traditional photovoltaics sliced from wafers, but they’re not as efficient at converting the energy in sunlight into electricity. Now a Newton, MA-based startup is developing a nanostructured design that overcomes one of the main constraints on the performance of thin-film solar cells. Solasta fabricates on arrays of nanopillars, rather than flat areas, boosting the efficiency of amorphous silicon solar cells to about 10 percent–still less than crystalline silicon panels, but more than the thin-film amorphous silicon panels on the market today. The company says that the design won’t require new equipment or materials and that it will license its technology to amorphous-silicon manufacturers at the end of this year.

Pillar power: This microscope image shows the layers of a solar cell built on a nanopillar substrate. The core of each pillar is coated first with metal, then amorphous silicon, and then a transparent conductive oxide.

Credit: Solasta

February 12, 2010

Nanogenerators and electric clothes

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

The idea of smart clothes has been around for ages. Looks like this might just be a breakthrough to electric clothing becoming a reality.

That oughta bring a whole new meaning to “social networking.” Thank you, thank you, I’ll be here all weekend. Be sure and come back tomorrow for the complimentary Saturday buffet and half-price happy hour.

The release:

New fiber nanogenerators could lead to electric clothing

By Sarah Yang, Media Relations | 12 February 2010

BERKELEY — In research that gives literal meaning to the term “power suit,” University of California, Berkeley, engineers have created energy-scavenging nanofibers that could one day be woven into clothing and textiles.

These nano-sized generators have “piezoelectric” properties that allow them to convert into electricity the energy created through mechanical stress, stretches and twists.

“This technology could eventually lead to wearable ‘smart clothes’ that can power hand-held electronics through ordinary body movements,” said Liwei Lin, UC Berkeley professor of mechanical engineering and head of the international research team that developed the fiber nanogenerators.

Because the nanofibers are made from organic polyvinylidene fluoride, or PVDF, they are flexible and relatively easy and cheap to manufacture.

Although they are still working out the exact calculations, the researchers noted that more vigorous movements, such as the kind one would create while dancing the electric boogaloo, should theoretically generate more power. “And because the nanofibers are so small, we could weave them right into clothes with no perceptible change in comfort for the user,” said Lin, who is also co-director of the Berkeley Sensor and Actuator Center at UC Berkeley.

The fiber nanogenerators are described in this month’s issue of Nano Letters, a peer-reviewed journal published by the American Chemical Society.

The goal of harvesting energy from mechanical movements through wearable nanogenerators is not new. Other research teams have previously made nanogenerators out of inorganic semiconducting materials, such as zinc oxide or barium titanate. “Inorganic nanogenerators — in contrast to the organic nanogenerators we created — are more brittle and harder to grow in significant quantities,” Lin said.

The tiny nanogenerators have diameters as small as 500 nanometers, or about 100 times thinner than a human hair and one-tenth the width of common cloth fibers. The researchers repeatedly tugged and tweaked the nanofibers, generating electrical outputs ranging from 5 to 30 millivolts and 0.5 to 3 nanoamps.

Furthermore, the researchers report no noticeable degradation after stretching and releasing the nanofibers for 100 minutes at a frequency of 0.5 hertz (cycles per second).

Lin’s team at UC Berkeley pioneered the near-field electrospinning technique used to create and position the polymeric nanogenerators 50 micrometers apart in a grid pattern. The technology enables greater control of the placement of the nanofibers onto a surface, allowing researchers to properly align the fiber nanogenerators so that positive and negative poles are on opposite ends, similar to the poles on a battery.

Without this control, the researchers explained, the negative and positive poles might cancel each other out and reducing energy efficiency.

The researchers demonstrated energy conversion efficiencies as high as 21.8 percent, with an average of 12.5 percent.

“Surprisingly, the energy efficiency ratings of the nanofibers are much greater than the 0.5 to 4 percent achieved in typical power generators made from experimental piezoelectric PVDF thin films, and the 6.8 percent in nanogenerators made from zinc oxide fine wires,” said the study’s lead author, Chieh Chang, who conducted the experiments while he was a graduate student in mechanical engineering at UC Berkeley.

“We think the efficiency likely could be raised further,” Lin said. “For our preliminary results, we see a trend that the smaller the fiber we have, the better the energy efficiency. We don’t know what the limit is.”

Other co-authors of the study are Yiin-Kuen Fuh, a UC Berkeley graduate student in mechanical engineering; Van H. Tran, a graduate student at the Technische Universität München (Technical University of Munich) in Germany; and Junbo Wang, a researcher at the Institute of Electronics at the Chinese Academy of Sciences in Beijing, China.

The National Science Foundation and the Defense Advanced Research Projects Agency helped support this research.

fiber nanogenerator
Shown is a fiber nanogenerator on a plastic substrate created by UC Berkeley scientists. The nanofibers can convert energy from mechanical stresses and into electricity, and could one day be used to create clothing that can power small electronics. (Chieh Chang, UC Berkeley)

November 18, 2009

Moving nanoscale objects with light

This finding is important toward creating working nanoscale machines.

The release:

Nov. 16, 2009

Small optical force can budge nanoscale objects

By Bill Steele

dual rings
Scanning electron micrograph of two thin, flat rings of silicon nitride, each 190 nanometers thick and mounted a millionth of a meter apart. Light is fed into the ring resonators from the straight waveguide at the right. Under the right conditions optical forces between the two rings are enough to bend the thin spokes and pull the rings toward one another, changing their resonances enough to act as an optical switch.
Image from Cornell Nanophotonics Group

With a bit of leverage, Cornell researchers have used a very tiny beam of light with as little as 1 milliwatt of power to move a silicon structure up to 12 nanometers. That’s enough to completely switch the optical properties of the structure from opaque to transparent, they reported.

The technology could have applications in the design of micro-electromechanical systems (MEMS) — nanoscale devices with moving parts — and micro-optomechanical systems (MOMS) which combine moving parts with photonic circuits, said Michal Lipson, associate professor of electrical and computer engineering.

The research by postdoctoral researcher Gustavo Wiederhecker, Long Chen, Ph.D. ’09, Alexander Gondarenko, Ph.D. ’10, and Lipson appears in the online edition of the journal Nature and will appear in a forthcoming print edition.

Light can be thought of as a stream of particles that can exert a force on whatever they strike. The sun doesn’t knock you off your feet because the force is very small, but at the nanoscale it can be significant. “The challenge is that large optical forces are required to change the geometry of photonic structures,” Lipson explained.

But the researchers were able to reduce the force required by creating two ring resonators — circular waveguides whose circumference is matched to a multiple of the wavelength of the light used — and exploiting the coupling between beams of light traveling through the two rings.

A beam of light consists of oscillating electric and magnetic fields, and these fields can pull in nearby objects, a microscopic equivalent of the way static electricity on clothes attracts lint. This phenomenon is exploited in “optical tweezers” used by physicists to trap tiny objects. The forces tend to pull anything at the edge of the beam toward the center.

When light travels through a waveguide whose cross-section is smaller than its wavelength some of the light spills over, and with it the attractive force. So parallel waveguides close together, each carrying a light beam, are drawn even closer, rather like two streams of rainwater on a windowpane that touch and are pulled together by surface tension.

The researchers created a structure consisting of two thin, flat silicon nitride rings about 30 microns (millionths of a meter) in diameter mounted one above the other and connected to a pedestal by thin spokes. Think of two bicycle wheels on a vertical shaft, but each with only four thin, flexible spokes. The ring waveguides are three microns wide and 190 nanometers (nm — billionths of a meter) thick, and the rings are spaced 1 micron apart.

When light at a resonant frequency of the rings, in this case infrared light at 1533.5 nm, is fed into the rings, the force between the rings is enough to deform the rings by up to 12 nm, which the researchers showed was enough to change other resonances and switch other light beams traveling through the rings on and off. When light in both rings is in phase — the peaks and valleys of the wave match — the two rings are pulled together. When it is out of phase they are repelled. The latter phenomenon might be useful in MEMS, where an ongoing problem is that silicon parts tend to stick together, Lipson said.

An application in photonic circuits might be to create a tunable filter to pass one particular optical wavelength, Wiederhecker suggested.

The work is supported by the National Science Foundation (NSF) and the Cornell Center for Nanoscale Systems. Devices were fabricated at the Cornell Nanoscale Science and Technology Facility, also supported by NSF.

##

November 17, 2009

Incredible nanotech image — graphene

Filed under: et.al., Science, Technology — Tags: , , , , — David Kirkpatrick @ 10:02 pm

I’ve done lots of blogging on the nanomaterial graphene, and here’s an incredible image of the atom-thick sheet of carbon:

A graphene sheet stretched across a gap in a semiconductor chip. Image: Kirill Bolotkin

And here’s a link to the PhysOrg article accompanying the image.

From the link:

Not only is this the thinnest material possible, but it also is 10 times stronger than steel and it conducts electricity better than any other known material at room temperature. These and graphene’s other exotic properties have attracted the interest of physicists, who want to study them, and nanotechnologists, who want to exploit them to make novel electrical and mechanical devices.

“There are two features that make graphene exceptional,” says Kirill Bolotin, who has just joined the Vanderbilt Department of Physics and Astronomy as an assistant professor. “First, its molecular structure is so resistant to defects that researchers have had to hand-make them to study what effects they have. Second, the electrons that carry  travel much faster and generally behave as if they have far less mass than they do in ordinary metals or superconductors.”

September 21, 2009

Getting carbon nanotubes under control

Filed under: Science, Technology — Tags: , , , — David Kirkpatrick @ 3:47 pm

An important aspect of creating nanotubes is controlling their atomic-level structure. Looks like these researchers have found a solution to the issue.

From the link:

Single‐walled carbon nanotubes, made of a cheap and abundant material, have so much potential because their function changes when their atomic‐level structure, referred to as chirality, changes.

But for all their promise, building tubes with the right structure has proven a challenge.

A pair of Case Western Reserve University researchers mixed metals commonly used to grow nanotubes 
and found that the composition of the catalyst can control the chirality.

In a letter to be published Sept. 20 in the online edition of Nature Materials, R. Mohan Sankaran, an assistant professor of chemical engineering at the Case School of Engineering, and Wei‐Hung Chiang, who received his doctorate degree in chemical engineering in May, describe their findings.

“We have established a link between the structure of a catalyst and the chirality of carbon nanotubes,” 
Sankaran said. “Change the catalyst structure by varying its composition, and you can begin to control the chirality of the nanotubes and their electrical and optical properties.”

The chirality of a single‐walled  describes how a lattice of carbon  is rolled into a tube. The rolling can occur at different angles, producing different structures that exhibit very different properties.

Nanotubes are normally grown in bulk mixtures. When using a nickel catalyst, typically one‐third of those grown are metallic and could be used like metal wires to conduct electricity. About two‐thirds are semiconducting nanotubes, which could be used as transistors, Chiang explained. But, separating them according to properties, “is costly and can damage the nanotubes.”

September 17, 2009

Nanosolar’s panels heading to the marketplace

Filed under: Business, Science, Technology — Tags: , , , , — David Kirkpatrick @ 6:36 pm

(Note this is the replacement for this lost post without some of the additional commentary on the feasibility of alternative power.)

Via KurzweilAI.net:

Advanced Solar Panels Coming to Market

Technology Review, Sept. 17, 2009

Nanosolar has opened an automated facility for manufacturing its solar panels, and says power plants made using these panels could produce electricity at five to six cents per kilowatt hour — near the cost of electricity from coal and significantly less than most solar power, which costs about 18 to 22 cents per kilowatt hour.

The panels are made by printing a semiconductor material called CIGS (copper, indium, gallium, and selenium) on aluminum foil.


Nanosolar’s new, fully automated solar-panel manufacturing facility (Nanosolar)

Read Original Article>>

August 5, 2009

Solar cells, nanotech and plastics

This release involves using nanotechnology to help create that efficiently turn light into electricity, improving solar cells in the process.

The release:

Plastics that convert light to electricity could have a big impact

IMAGE: David Ginger, a University of Washington associate professor of chemistry, displays the tiny probe for a conductive atomic force microscope, used to record photocurrents on scales of millionths of an…

Click here for more information. 

Researchers the world over are striving to develop organic solar cells that can be produced easily and inexpensively as thin films that could be widely used to generate electricity.

But a major obstacle is coaxing these carbon-based materials to reliably form the proper structure at the nanoscale (tinier than 2-millionths of an inch) to be highly efficient in converting light to electricity. The goal is to develop cells made from low-cost plastics that will transform at least 10 percent of the sunlight that they absorb into usable electricity and can be easily manufactured.

A research team headed by David Ginger, a University of Washington associate professor of chemistry, has found a way to make images of tiny bubbles and channels, roughly 10,000 times smaller than a human hair, inside plastic solar cells. These bubbles and channels form within the polymers as they are being created in a baking process, called annealing, that is used to improve the materials’ performance.

The researchers are able to measure directly how much current each tiny bubble and channel carries, thus developing an understanding of exactly how a solar cell converts light into electricity. Ginger believes that will lead to a better understanding of which materials created under which conditions are most likely to meet the 10 percent efficiency goal.

As researchers approach that threshold, nanostructured plastic solar cells could be put into use on a broad scale, he said. As a start, they could be incorporated into purses or backpacks to charge cellular phones or mp3 players, but eventually they could make in important contribution to the electrical power supply.

Most researchers make plastic solar cells by blending two materials together in a thin film, then baking them to improve their performance. In the process, bubbles and channels form much as they would in a cake batter. The bubbles and channels affect how well the cell converts light into electricity and how much of the electric current actually gets to the wires leading out of the cell. The number of bubbles and channels and their configuration can be altered by how much heat is applied and for how long.

The exact structure of the bubbles and channels is critical to the solar cell’s performance, but the relationship between baking time, bubble size, channel connectivity and efficiency has been difficult to understand. Some models used to guide development of plastic solar cells even ignore the structure issues and assume that blending the two materials into a film for solar cells will produce a smooth and uniform substance. That assumption can make it difficult to understand just how much efficiency can be engineered into a polymer, Ginger said.

For the current research, the scientists worked with a blend of polythiophene and fullerene, model materials considered basic to organic solar cell research because their response to forces such as heating can be readily extrapolated to other materials. The materials were baked together at different temperatures and for different lengths of time.

Ginger is the lead author of a paper documenting the work, published online last month by the American Chemical Society journal Nano Letters and scheduled for a future print edition. Coauthors are Liam Pingree and Obadiah Reid of the UW. The research was funded by the National Science Foundation and the U.S. Department of Energy.

Ginger noted that the polymer tested is not likely to reach the 10 percent efficiency threshold. But the results, he said, will be a useful guide to show which new combinations of materials and at what baking time and temperature could form bubbles and channels in a way that the resulting polymer might meet the standard.

Such testing can be accomplished using a very small tool called an atomic force microscope, which uses a needle similar to the one that plays records on an old-style phonograph to make a nanoscale image of the solar cell. The microscope, developed in Ginger’s lab to record photocurrent, comes to a point just 10 to 20 nanometers across (a human hair is about 60,000 nanometers wide). The tip is coated with platinum or gold to conduct electrical current, and it traces back and forth across the solar cell to record the properties.

As the microscope traces back and forth over a solar cell, it records the channels and bubbles that were created as the material was formed. Using the microscope in conjunction with the knowledge gained from the current research, Ginger said, can help scientists determine quickly whether polymers they are working with are ever likely to reach the 10 percent efficiency threshold.

Making solar cells more efficient is crucial to making them cost effective, he said. And if costs can be brought low enough, solar cells could offset the need for more coal-generated electricity in years to come.

“The solution to the energy problem is going to be a mix, but in the long term solar power is going to be the biggest part of that mix,” he said.

 

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June 4, 2009

Photon driven nanomotor

Fair warning to all readers, a major press release dump is coming. Mostly nanotechnology news.

First up is research on a molecular nanomotor driven by light.

The release:

New, light-driven nanomotor is simpler, more promising, scientists say

GAINESVILLE, Fla. — Sunflowers track the sun as it moves from east to west. But people usually have to convert sunlight into electricity or heat to put its power to use.

Now, a team of University of Florida chemists is the latest to report a new mechanism to transform light straight into motion – albeit at a very, very, very tiny scale.

In a paper expected to appear soon in the online edition of the journal Nano Letters, the UF team reports building a new type of “molecular nanomotor” driven only by photons, or particles of light. While it is not the first photon-driven nanomotor, the almost infinitesimal device is the first built entirely with a single molecule of DNA — giving it a simplicity that increases its potential for development, manufacture and real-world applications in areas ranging from medicine to manufacturing, the scientists say.

“It is easy to assemble, has fewer parts and theoretically should be more efficient,” said Huaizhi Kang, a doctoral student in chemistry at UF and the first author of the paper.

The scale of the nanomotor is almost vanishingly small.

In its clasped, or closed, form, the nanomotor measures 2 to 5 nanometers — 2 to 5 billionths of a meter. In its unclasped form, it extends as long as 10 to 12 nanometers. Although the scientists say their calculations show it uses considerably more of the energy in light than traditional solar cells, the amount of force it exerts is proportional to its small size.

But that won’t necessarily limit its potential.

In coming years, the nanomotor could become a component of microscopic devices that repair individual cells or fight viruses or bacteria. Although in the conceptual stage, those devices, like much larger ones, will require a power source to function. Because it is made of DNA, the nanomotor is biocompatible. Unlike traditional energy systems, the nanomotor also produces no waste when it converts light energy into motion.

“Preparation of DNA molecules is relatively easy and reproducible, and the material is very safe,” said Yan Chen, a UF chemistry doctoral student and one of the authors of the paper.

Applications in the larger world are more distant. Powering a vehicle, running an assembly line or otherwise replacing traditional electricity or fossil fuels would require untold trillions of nanomotors, all working together in tandem — a difficult challenge by any measure.

“The major difficulty lies ahead,” said Weihong Tan, a UF professor of chemistry and physiology, author of the paper and the leader of the research group reporting the findings. “That is how to collect the molecular level force into a coherent accumulated force that can do real work when the motor absorbs sunlight.”

Tan added that the group has already begun working on the problem.

“Some prototype DNA nanostructures incorporating single photo-switchable motors are in the making which will synchronize molecular motions to accumulate forces,” he said.

To make the nanomotor, the researchers combined a DNA molecule they created in the lab with azobenzene, a chemical compound that responds to light. A high-energy photon prompts one response; lower energy another.

To demonstrate the movement, the researchers attached a fluorophore, or light-emitter, to one end of the nanomotor and a quencher, which can quench the emitting light, to the other end. Their instruments recorded emitted light intensity that corresponded to the motor movement.

“Radiation does cause things to move from the spinning of radiometer wheels to the turning of sunflowers and other plants toward the sun,” said Richard Zare, distinguished professor and chairman of chemistry at Stanford University. “What Professor Tan and co-workers have done is to create a clever light-actuated nanomotor involving a single DNA molecule. I believe it is the first of its type.”

 

###

 

The National Institutes of Health and the National Science Foundation funded the research. The other coauthors of this paper are Haipeng Liu, Joseph A. Phillips, Zehui Cao, Youngmi Kim, Zunyi Yang and Jianwei Li.

April 24, 2009

Nanotech splitting water cells

An important finding toward developing cost-effective alternative fuel sources.

The release:

Discovery of an unexpected boost for solar water-splitting cells

IMAGE: Scanning electron microscope image of typical titania nanotubes for a photocatalytic cell to produce hydrogen gas from water. Nanotubes average roughly 90-100 nanometers in diameter.

Click here for more information. 

A research team from Northeastern University and the National Institute of Standards and Technology (NIST) has discovered, serendipitously, that a residue of a process used to build arrays of titania nanotubes—a residue that wasn’t even noticed before this—plays an important role in improving the performance of the nanotubes in solar cells that produce hydrogen gas from water. Their recently published results* indicate that by controlling the deposition of potassium on the surface of the nanotubes, engineers can achieve significant energy savings in a promising new alternate energy system.

Titania (or titanium dioxide) is a versatile chemical compound best known as a white pigment. It’s found in everything from paint to toothpastes and sunscreen lotions. Thirty-five years ago Akira Fujishima startled the electrochemical world by demonstrating that it also functioned as a photocatalyst, producing hydrogen gas from water, electricity and sunlight. In recent years, researchers have been exploring different ways to optimize the process and create a commercially viable technology that, essentially, transforms cheap sunlight into hydrogen, a pollution-free fuel that can be stored and shipped.

Increasing the available surface area is one way to boost a catalyst’s performance, so a team at Northeastern has been studying techniques to build tightly packed arrays of titania nanotubes, which have a very high surface to volume ratio. They also were interested in how best to incorporate carbon into the nanotubes, because carbon helps titania absorb light in the visible spectrum. (Pure titania absorbs in the ultraviolet region, and much of the ultraviolet is filtered by the atmosphere.)

This brought them to the NIST X-ray spectroscopy beamline at the National Synchrotron Light Source (NSLS)**. The NIST facility uses X-rays that can be precisely tuned to measure chemical bonds of specific elements, and is at least 10 times more sensitive than commonly available laboratory instruments, allowing researchers to detect elements at extremely low concentrations. While making measurements of the carbon atoms, the team noticed spectroscopic data indicating that the titania nanotubes had small amounts of potassium ions strongly bound to the surface, evidently left by the fabrication process, which used potassium salts. This was the first time the potassium has ever been observed on titania nanotubes; previous measurements were not sensitive enough to detect it.

The result was mildly interesting, but became much more so when the research team compared the performance of the potassium-bearing nanotubes to similar arrays deliberately prepared without potassium. The former required only about one-third the electrical energy to produce the same amount of hydrogen as an equivalent array of potassium-free nanotubes. “The result was so exciting,” recalls Northeastern physicist Latika Menon, “that we got sidetracked from the carbon research.” Because it has such a strong effect at nearly undetectable concentrations, Menon says, potassium probably has played an unrecognized role in many experimental water-splitting cells that use titania nanotubes, because potassium hydroxide is commonly used in the cells. By controlling it, she says, hydrogen solar cell designers could use it to optimize performance.

 

###

 

* C. Richter, C. Jaye, E. Panaitescu, D.A. Fischer, L.H. Lewis, R.J. Willey and L. Menon. Effect of potassium adsorption on the photochemical properties of titania nanotube arrays. J. Mater. Chem., published online as an Advanced Article, March 27, 2009. DOI: 10.1039/b822501j

** The NSLS is part of the Department of Energy’s Brookhaven National Laboratory.

March 31, 2009

DNA as nanoparticle assembly plant

More forward motion in the world of nanotech.


The release:



DNA-based assembly line for precision nano-cluster construction


Method could lead to rapid, reliable assembly of new biosensors and solar cells


UPTON, NY – Building on the idea of using DNA to link up nanoparticles – particles measuring mere billionths of a meter – scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have designed a molecular assembly line for predictable, high-precision nano-construction. Such reliable, reproducible nanofabrication is essential for exploiting the unique properties of nanoparticles in applications such as biological sensors and devices for converting sunlight to electricity. The work will be published online March 29, 2009, by Nature Materials.


The Brookhaven team has previously used DNA, the molecule that carries life’s genetic code, to link up nanoparticles in various arrangements, including 3-D nano-crystals. The idea is that nanoparticles coated with complementary strands of DNA – segments of genetic code sequence that bind only with one another like highly specific Velcro – help the nanoparticles find and stick to one another in highly specific ways. By varying the use of complementary DNA and strands that don’t match, scientists can exert precision control over the attractive and repulsive forces between the nanoparticles to achieve the desired construction. Note that the short DNA linker strands used in these studies were constructed artificially in the laboratory and don’t “code” for any proteins, as genes do.


The latest advance has been to use the DNA linkers to attach some of the DNA-coated nanoparticles to a solid surface to further constrain and control how the nanoparticles can link up. This yields even greater precision, and therefore a more predictable, reproducible high-throughput construction technique for building clusters from nanoparticles.


“When a particle is attached to a support surface, it cannot react with other molecules or particles in the same way as a free-floating particle,” explained Brookhaven physicist Oleg Gang, who led the research at the Lab’s Center for Functional Nanomaterials. This is because the support surface blocks about half of the particle’s reactive surface. Attaching a DNA linker or other particle that specifically interacts with the bound particle then allows for the rational assembly of desired particle clusters.


“By controlling the number of DNA linkers and their length, we can regulate interparticle distances and a cluster’s architecture,” said Gang. “Together with the high specificity of DNA interactions, this surface-anchored technique permits precise assembly of nano-objects into more complex structures.”


Instead of assembling millions and millions of nanoparticles into 3-D nanocrystals, as was done in the previous work, this technique allows the assembly of much smaller structures from individual particles. In the Nature Materials paper, the scientists describe the details for producing symmetrical, two-particle linkages, known as dimers, as well as small, asymmetrical clusters of particles – both with high yields and low levels of other, unwanted assemblies.


“When we arrange a few nanoparticles in a particular structure, new properties can emerge,” Gang emphasized. “Nanoparticles in this case are analogous to atoms, which, when connected in a molecule, often exhibit properties not found in the individual atoms. Our approach allows for rational and efficient assembly of nano-‘molecules.’ The properties of these new materials may be advantageous for many potential applications.”


For example, in the paper, the scientists describe an optical effect that occurs when nanoparticles are linked as dimer clusters. When an electromagnetic field interacts with the metallic particles, it induces a collective oscillation of the material’s conductive electrons. This phenomenon, known as a plasmon resonance, leads to strong absorption of light at a specific wavelength.


“The size and distance between the linked particles affect the plasmonic behavior,” said Gang. By adjusting these parameters, scientists might engineer clusters for absorbing a range of wavelengths in solar-energy conversion devices. Modulations in the plasmonic response could also be useful as a new means for transferring data, or as a signal for a new class of highly specific biosensors.


Asymmetric clusters, which were also assembled by the Brookhaven team, allow an even higher level of control, and therefore open new ways to design and engineer functional nanomaterials.


 


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Because of its reliability and precision control, Brookhaven’s nano-assembly method would be scalable for the kind of high-throughput production that would be essential for commercial applications. Brookhaven Lab has applied for a patent on the assembly method as well as several specific applications of the technology. For information about the patent or licensing this technology, contact Kimberley Elcess at (631) 344-4151, or elcess@bnl.gov.


In addition to Gang, the team included materials scientist Dmytro Nykypanchuk, summer student Marine Cuisinier, and biologist Daniel (Niels) van der Lelie, all from Brookhaven, and former Brookhaven chemist Matthew Maye, now at Syracuse University. Their work was funded by DOE’s Office of Science and through a Goldhaber Distinguished Fellowship sponsored by Brookhaven Science Associates.


The Center for Functional Nanomaterials at BNL is one 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 Brookhaven, Argonne, Lawrence Berkeley, Oak Ridge, and Sandia and Los Alamos National Laboratories. For more information about the DOE NSRCs, please visit http://nano.energy.gov.


Related Links


DNA Technique Yields 3-D Crystalline Organization of Nanoparticles, 1/30/2008:
http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=07-127


New DNA-Based Technique For Assembly of Nano- and Micro-sized Particles, 9/12/2007:
http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=07-94


Nanoparticle Assembly Enters the Fast Lane, 10/11/2006:
http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=06-112


One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation of State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.


Visit Brookhaven Lab’s electronic newsroom for links, news archives, graphics, and more: http://www.bnl.gov/newsroom


Update — Here’s this topic from KurzweilAI.net:










DNA-Based Assembly Line for Nano-Construction of New Biosensors, Solar Cells (w/Video)


PhysOrg.com, Mar. 30, 2009

A molecular assembly line using DNA linkers for predictable, high-precision nano-construction has been developed by scientists at the U.S. Department of Energy‘s Brookhaven National Laboratory.





Read Original Article>>



 

March 27, 2009

Nanogenerators

Very cool nanotech. Not sure how close this is to market, but man it’s very cool.

The release:

New nanogenerator may charge iPods and cell phones with a wave of the hand

IMAGE: Pictured is a schematic illustration shows the microfiber-nanowire hybrid nanogenerator, which is the basis of using fabrics for generating electricity.

Click here for more information. 

SALT LAKE CITY, March 26, 2009 — Imagine if all you had to do to charge your iPod or your BlackBerry was to wave your hand, or stretch your arm, or take a walk? You could say goodbye to batteries and never have to plug those devices into a power source again.

In research presented here today at the American Chemical Society’s 237th National Meeting, scientists from Georgia describe technology that converts mechanical energy from body movements or even the flow of blood in the body into electric energy that can be used to power a broad range of electronic devices without using batteries.

“This research will have a major impact on defense technology, environmental monitoring, biomedical sciences and even personal electronics,” says lead researcher Zhong Lin Wang, Regents’ Professor, School of Material Science and Engineering at the Georgia Institute of Technology. The new “nanogenerator” could have countless applications, among them a way to run electronic devices used by the military when troops are far in the field.

The researchers describe harvesting energy from the environment by converting low-frequency vibrations, like simple body movements, the beating of the heart or movement of the wind, into electricity, using zinc oxide (ZnO) nanowires that conduct the electricity. The ZnO nanowires are piezoelectric — they generate an electric current when subjected to mechanical stress. The diameter and length of the wire are 1/5,000th and 1/25th the diameter of a human hair.

In generating energy from movement, Wang says his team concluded that it was most effective to develop a method that worked at low frequencies and was based on flexible materials. The ZnO nanowires met these requirements. At the same time, he says a real advantage of this technology is that the nanowires can be grown easily on a wide variety of surfaces, and the nanogenerators will operate in the air or in liquids once properly packaged. Among the surfaces on which the nanowires can be grown are metals, ceramics, polymers, clothing and even tents.

“Quite simply, this technology can be used to generate energy under any circumstances as long as there is movement,” according to Wang.

To date, he says that there have been limited methods created to produce nanopower despite the growing need by the military and defense agencies for nanoscale sensing devices used to detect bioterror agents. The nanogenerator would be particularly critical to troops in the field, where they are far from energy sources and need to use sensors or communication devices. In addition, having a sensor which doesn’t need batteries could be extremely useful to the military and police sampling air for potential bioterrorism attacks in the United States, Wang says.

While biosensors have been miniaturized and can be implanted under the skin, he points out that these devices still require batteries, and the new nanogenerator would offer much more flexibility.

A major advantage of this new technology is that many nanogenerators can produce electricity continuously and simultaneously. On the other hand, the greatest challenge in developing these nanogenerators is to improve the output voltage and power, he says.

Last year Wang’s group presented a study on nanogenerators driven by ultrasound. Today’s research represents a much broader application of nanogenerators as driven by low-frequency body movement.

 

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The study was funded by the Defense Advanced Research Projects Agency, the Department of Energy, the National Institutes of Health and the National Science Foundation.

The American Chemical Society is a nonprofit organization chartered by the U.S. Congress. With more than 154,000 members, ACS is the world’s largest scientific society and a global leader in providing access to chemistry-related research through its multiple databases, peer-reviewed journals and scientific conferences. Its main offices are in Washington, D.C., and Columbus, Ohio.

 

February 9, 2009

Nanotech and battery efficiency

The latest news on nanotechnology and lithium-ion batteries.

The release from today:

Batteries get a boost at Rice

Researchers create hybrid nanocables to improve lithium battery technology

Need to store electricity more efficiently? Put it behind bars.

That’s essentially the finding of a team of Rice University researchers who have created hybrid carbon nanotube metal oxide arrays as electrode material that may improve the performance of lithium-ion batteries.

With battery technology high on the list of priorities in a world demanding electric cars and gadgets that last longer between charges, such innovations are key to the future. Electrochemical capacitors and fuel cells would also benefit, the researchers said.

The team from Pulickel Ajayan’s research group published a paper this week describing the proof-of-concept research in which nanotubes are grown to look – and act – like the coaxial conducting lines used in cables. The coax tubes consist of a manganese oxide shell and a highly conductive nanotube core.

“It’s a nice bit of nanoscale engineering,” said Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science.

“We’ve put in two materials – the nanotube, which is highly electrically conducting and can also absorb lithium, and the manganese oxide, which has very high capacity but poor electrical conductivity,” said Arava Leela Mohana Reddy, a Rice postdoc researcher. “But when you combine them, you get something interesting.”

That would be the ability to hold a lot of juice and transmit it efficiently. The researchers expect the number of charge/discharge cycles such batteries can handle will be greatly enhanced, even with a larger capacity.

“Although the combination of these materials has been studied as a composite electrode by several research groups, it’s the coaxial cable design of these materials that offers improved performance as electrodes for lithium batteries,” said Ajayan.

“At this point, we’re trying to engineer and modify the structures to get the best performance,” said Manikoth Shaijumon, also a Rice postdoc. The microscopic nanotubes, only a few nanometers across, can be bundled into any number of configurations. Future batteries may be thin and flexible. “And the whole idea can be transferred to a large scale as well. It is very manufacturable,” Shaijumon said.

The hybrid nanocables grown in a Rice-developed process could also eliminate the need for binders, materials used in current batteries that hold the elements together but hinder their conductivity.

 

###

 

The paper was written by Reddy, Shaijumon, doctoral student Sanketh Gowda and Ajayan. It appears in the online version of the American Chemical Society’s Nano Letters.

The project is supported by funding from the Hartley Family Foundation.

The paper can be found online at: http://tinyurl.com/dz7oe8.

December 17, 2008

Clean carbon nanotube clean-up

Studies like this ought to allay some of the nanotech fears out there.

The release:

Pitt Researchers Create Nontoxic Clean-up Method for Common, Potentially Toxic Nano Materials

Horseradish enzyme biodegrades carbon nanotubes increasingly used in products, from electronics to plastics

PITTSBURGH-University of Pittsburgh researchers have developed the first natural, nontoxic method for biodegrading carbon nanotubes, a finding that could help diminish the environmental and health concerns that mar the otherwise bright prospects of the super-strong materials commonly used in products, from electronics to plastics.

A Pitt research team has found that carbon nanotubes deteriorate when exposed to the natural enzyme horseradish peroxidase (HRP), according to a report published recently in “Nano Letters” coauthored by Alexander Star, an assistant professor of chemistry in Pitt’s School of Arts and Sciences, and Valerian Kagan, a professor and vice chair of the Department of Environmental and Occupational Health in Pitt’s Graduate School of Public Health. These results open the door to further development of safe and natural methods-with HRP or other enzymes-of cleaning up carbon nanotube spills in the environment and the industrial or laboratory setting.

Carbon nanotubes are one-atom thick rolls of graphite 100,000 times smaller than a human hair yet stronger than steel and excellent conductors of electricity and heat. They reinforce plastics, ceramics, or concrete; conduct electricity in electronics or energy-conversion devices; and are sensitive chemical sensors, Star said. (Star created an early-detection device for asthma attacks wherein carbon nanotubes detect minute amounts of nitric oxide preceding an attack. See link below.)

“The many applications of nanotubes have resulted in greater production of them, but their toxicity remains controversial,” Star said. “Accidental spills of nanotubes are inevitable during their production, and the massive use of nanotube-based materials could lead to increased environmental pollution. We have demonstrated a nontoxic approach to successfully degrade carbon nanotubes in environmentally relevant conditions.”

The team’s work focused on nanotubes in their raw form as a fine, graphite-like powder, Kagan explained. In this form, nanotubes have caused severe lung inflammation in lab tests. Although small, nanotubes contain thousands of atoms on their surface that could react with the human body in unknown ways, Kagan said. Both he and Star are associated with a three-year-old Pitt initiative to investigate nanotoxicology.

“Nanomaterials aren’t completely understood. Industries use nanotubes because they’re unique-they are strong, they can be used as semiconductors. But do these features present unknown health risks? The field of nanotoxicology is developing to find out,” Kagan said. “Studies have shown that they can be dangerous. We wanted to develop a method for safely neutralizing these very small materials should they contaminate the natural or working environment.”

To break down the nanotubes, the team exposed them to a solution of HRP and a low concentration of hydrogen peroxide at 4 degrees Celcius (39 degrees Fahrenheit) for 12 weeks. Once fully developed, this method could be administered as easily as chemical clean-ups in today’s labs, Kagan and Star said.

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12/16/08/tmw

December 15, 2008

Nanotech and smart textiles

A promising use of carbon nanotubes.

The release:

Nature, nanotechnology fuse in electric yarn that detects blood

ANN ARBOR, Mich.— A carbon nanotube-coated “smart yarn” that conducts electricity could be woven into soft fabrics that detect blood and monitor health, engineers at the University of Michigan have demonstrated.

“Currently, smart textiles are made primarily of metallic or optical fibers. They’re fragile. They’re not comfortable. Metal fibers also corrode. There are problems with washing such electronic textiles. We have found a much simpler way—an elegant way—by combining two fibers, one natural and one created by nanotechnology,” said Nicholas Kotov, a professor in the departments of Chemical Engineering, Materials Science and Engineering and Biomedical Engineering.

Kotov and Bongsup Shim, a doctoral student in the Department of Chemical Engineering, are among the co-authors of a paper on this material currently published online in Nano Letters.

To make these “e-textiles,” the researchers dipped 1.5-millimeter thick cotton yarn into a solution of carbon nanotubes in water and then into a solution of a special sticky polymer in ethanol. After being dipped just a few times into both solutions and dried, the yarn was able to conduct enough power from a battery to illuminate a light-emitting diode device.

“This turns out to be very easy to do,” Kotov said. “After just a few repetitions of the process, this normal cotton becomes a conductive material because carbon nanotubes are conductive.”

The only perceptible change to the yarn is that it turned black, due to the carbon. It remained pliable and soft.

In order to put this conductivity to use, the researchers added the antibody anti-albumin to the carbon nanotube solution. Anti-albumin reacts with albumin, a protein found in blood. When the researchers exposed their anti-albumin-infused smart yarn to albumin, they found that the conductivity significantly increased. Their new material is more sensitive and selective as well as more simple and durable than other electronic textiles, Kotov said.

Clothing that can detect blood could be useful in high-risk professions, the researchers say. An unconscious firefighter, ambushed soldier, or police officer in an accident, for example, couldn’t send a distress signal to a central command post. But the smart clothing would have this capability.

Kotov says a communication device such as a mobile phone could conceivably transmit information from the clothing to a central command post.

“The concept of electrically sensitive clothing made of carbon-nanotube-coated cotton is flexible in implementations and can be adapted for a variety of health monitoring tasks as well as high performance garments,” Kotov said.

It is conceivable that clothes made out of this material could be designed to harvest energy or store it, providing power for small electronic devices, but such developments are many years away and pose difficult challenges, the engineers say.

 

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The paper published online in Nano Letters is titled, “Smart Electronic Yarns and Wearable Fabrics for Human Biomonitoring Made by Carbon Nanotube Coating with Polyelectrolytes.” Other contributors are with Jiangnan University in China.

This research was funded by the National Science Foundation, the Office of Naval Research, the Air Force Office of Scientific Research and the National Natural Science Foundation of China.

For more information: Nicholas Kotov: http://www.engin.umich.edu/dept/cheme/people/kotov.html

Michigan Engineering

The University of Michigan College of Engineering is ranked among the top engineering schools in the country. At more than $130 million annually, its engineering research budget is one of largest of any public university. Michigan Engineering is home to 11 academic departments and a National Science Foundation Engineering Research Center. The college plays a leading role in the Michigan Memorial Phoenix Energy Institute and hosts the world class Lurie Nanofabrication Facility. For more information, visit: http://www.engin.umich.edu/.

November 18, 2008

NASA to launch nano satellite to study TGFs

Sounds like a wicked cool project.

The release:

NSF / NASA ‘Firefly’ CubeSat Mission to Study Link Between Lightning and Terrestrial Gamma Ray Flashes

Massive energy releases occur every day in the upper reaches of Earth’s atmosphere. Lightning may give rise to these bursts of radiation. However, unlike the well-known flashes of light and peals of thunder familiar to Earth-dwellers, these energy releases are channeled upward and can be detected only from space. Our atmosphere protects us from the effects of this radiation, but the mechanisms at work can impact Earth’s upper atmosphere and its space environment.

A new nano satellite mission, called ‘Firefly,’ sponsored by the National Science Foundation (NSF) and led by NASA’s Goddard Space Flight Center in Greenbelt, Md. will explore the relationship between lightning and these sudden bursts, called Terrestrial Gamma Ray Flashes (TGFs).

NASA’s Compton Gamma Ray Observatory (CGRO) first discovered TGFs in the 1990s. Designed to look outward at cosmic sources of gamma rays, CGRO also caught rare but tantalizing glimpses of gamma rays coming from Earth.

TGFs are likely produced by beams of very energetic electrons, which are accelerated in the intense electric fields generated by large thunderstorm systems. Before CGRO, many scientists thought these very energetic types of radiation could be generated only near the Sun, or in black holes, large galaxies, or neutron stars.

“These electron beams are more powerful than any produced in near-Earth space, and understanding their acceleration mechanisms will shed light on a physical process that may occur on other planets, or in astrophysical environments, as well as in the sun’s corona,” said Doug Rowland, principal investigator for the Firefly mission at NASA Goddard’s Space Weather Laboratory.

Firefly will explore which types of lightning produce these electron beams and associated TGFs. In addition, Firefly will explore the occurrence rate of TGFs that are weaker than any previously been studied. The result with be a better understanding of the effect that the millions of lightning flashes that occur worldwide each day have on the Earth’s upper atmosphere and near-Earth space environment.

“This mission could provide the first direct evidence for the relationship between lightning and TGFs, and addresses an important research question in atmospheric electricity,” said Anne-Marie Schmoltner, head of NSF’s Atmospheric Sciences Division’s Lower Atmosphere Research Section. “Identifying the source of terrestrial gamma ray flashes would be a great step toward fully understanding the physics behind lightning and its effect on the Earth’s atmosphere.”

The NSF CubeSat program represents a new “low cost access to space” approach to performing high-quality, targeted science on a smaller budget than is typical of larger satellite projects, which have price tags starting at $100 million. In contrast, the CubeSat Firefly will carry out its science mission in a much smaller package and at a considerably lower cost. The nano satellite is about the size of a football (4 by 4 by 12 inches). The cost to develop, launch, and operate Firefly for three years during its science mission is expected to be less than $1 million.

The Firefly mission also emphasizes student involvement as part of the ongoing effort to train the next generation of scientists and engineers. Students at Siena College, in Loudonville, N.Y., and the University of Maryland Eastern Shore, in Princess Anne, Md., will be involved in all phases of the Firefly mission.

“Integrating innovative and creative educational efforts with front-line research is what NSF is all about,” said NSF Deputy Director Kathie L. Olsen. “The new CubeSat program uses the transformational technology of CubeSats to do just that. The Firefly mission is a terrific example of a program that will pursue scientific discovery, while providing unique and inspiring educational opportunities.”

Firefly is funded and managed by the National Science Foundation, and will be developed as a collaborative effort by NASA Goddard Space Flight Center, Universities Space Research Association (USRA), Columbia, Md.; Siena College; University of Maryland Eastern Shore, Princess Anne, Md.; and the Hawk Institute for Space Sciences, in Pocomoke City, Md.

NASA Goddard, USRA, and Siena College will provide the instrument payload, while the Hawk Institute will build the CubeSat. NASA’s Wallops Flight Facility on Wallops Island, Va., will provide technical oversight for the integration of Firefly to the launch vehicle.

Firefly’s launch date is likely to be in 2010 or 2011. The micro satellite will fly as a secondary payload inside a Poly-Picosatellite Orbital Deployer (P-POD) provided by California Polytechnic State University, San Luis Obispo, Calif. Firefly will utilize the excess room and lift capacity not required by the primary mission payload.

For more information about NASA’s Compton Gamma Ray Observatory, visit:

http://heasarc.gsfc.nasa.gov/docs/cgro/index.html

 
 

Laura Layton
NASA’s Goddard Space Flight Center

The ‘Firefly’ CubeSat satellite will investigate Terrestrial Gamma Ray Flashes (TGFs) when it launches in 2010.
The ‘Firefly’ CubeSat satellite will investigate Terrestrial Gamma Ray Flashes (TGFs) when it launches in 2010.

September 10, 2008

Nanonets improve solar, too

Filed under: Science, Technology — Tags: , , , , , — David Kirkpatrick @ 8:20 am

I’ve blogged on nanonets and how they improve electronics and energy applications. Here’s a Technology Review story with more detail on how nanonets improve solar energy.

And as a bonus, with picutures!

From the second link:

One problem with solar cells is that they only produce electricity during the day. A promising way to use the sun’s energy more efficiently is to enlist it to split water into hydrogen gas that can be stored and then employed at any time, day or night. A cheap new nanostructured material could prove an efficient catalyst for performing this reaction. Called a nanonet because of its two-dimensional branching structure, the material is made up of a compound that has been demonstrated to enable the water-splitting reaction. Because of its high surface area, the nanonet enhances this reaction.

Researchers led by Dunwei Wang, a chemist at Boston College, grew the nanonets, creating structures made up of branching wires of titanium and silicon. Last year, researchers at the Max Planck Institute, in Germany, showed that titanium disilicide, which absorbs a broad spectrum of visible light, splits water into hydrogen and oxygen–and can store the hydrogen, which it absorbs or releases depending on the temperature. Other semiconducting materials have been tested as water-splitting catalysts but have proved unstable.

Nanonets, structures made up of branching titanium and silicon wires, are flat yet have a high surface area, making them more efficient at using solar energy to split water into oxygen and hydrogen fuel. The top image shows a nanonet magnified 50,000 times. At bottom, a flexible nanonet rolls up when poked by the tip of a scanning tunneling microscope. Both images were taken with a tunneling electron microscope.

Net reaction: Nanonets, structures made up of branching titanium and silicon wires, are flat yet have a high surface area, making them more efficient at using solar energy to split water into oxygen and hydrogen fuel. The top image shows a nanonet magnified 50,000 times. At bottom, a flexible nanonet rolls up when poked by the tip of a scanning tunneling microscope. Both images were taken with a tunneling electron microscope.

September 3, 2008

Using nanotech to improve electronics and energy

Filed under: Science, Technology — Tags: , , , — David Kirkpatrick @ 10:05 pm

From KurzweilAI.net — Nanonets made of silicon and titanium wires crank up the surface area and improve electronics and energy usage and apps.

Scientists Grow ‘Nanonets’ Able To Snare Added Energy Transfer
ScienceDaily, Sep. 3, 2008

Boston College chemists have produced nanonets, a flexible webbing of self-assembling nanoscale titanium and silicon wires that multiplies surface area, critical to improving the performance of the wires in electronics and energy applications.

Test shows improved performance in the material’s ability to conduct electricity and ability to absorb light across a wide range of the solar spectrum.

 
Read Original Article>>

July 15, 2008

Nanotech improves hydrogen generation

Filed under: Science, Technology — Tags: , , , , , — David Kirkpatrick @ 10:28 pm

A more green method of creating hydrogen is outlined in this press release from Penn State:

Researchers generate hydrogen without the carbon footprint

A greener, less expensive method to produce hydrogen for fuel may eventually be possible with the help of water, solar energy and nanotube diodes that use the entire spectrum of the sun’s energy, according to Penn State researchers.

“Other researchers have developed ways to produce hydrogen with mind-boggling efficiency, but their approaches are very high cost,” says Craig A. Grimes, professor of electrical engineering. “We are working toward something that is cost effective.”

Currently, the steam reforming of natural gas produces most of our hydrogen. As a fuel source, this produces two problems. The process uses natural gas and so does not reduce reliance on fossil fuels; and, because one byproduct is carbon dioxide, the process contributes to the carbon dioxide in the atmosphere, the carbon footprint.

Grimes’ process splits water into its two components, hydrogen and oxygen, and collects the products separately using commonly available titanium and copper. Splitting water for hydrogen production is an old and proven method, but in its conventional form, it requires previously generated electricity. Photolysis of water solar splitting of water has also been explored, but is not a commercial method yet.

Grimes and his team produce hydrogen from solar energy, using two different groups of nanotubes in a photoelectrochemical diode. They report in the July issue of Nano Lettersthat using incident sunlight, “such photocorrosion-stable diodes generate a photocurrent of approximately 0.25 milliampere per centimeter square, at a photoconversion efficiency of 0.30 percent.”

“It seems that nanotube geometry is the best geometry for production of hydrogen from photolysis of water,” says Grimes

In Grimes’ photoelectrochemical diode, one side is a nanotube array of electron donor material – n-type material – titanium dioxide, and the other is a nanotube array that has holes that accept electrons – p-type material – cuprous oxide titanium dioxide mixture. P and n-type materials are common in the semiconductor industry. Grimes has been making n-type nanotube arrays from titanium by sputtering titanium onto a surface, anodizing the titanium with electricity to form titanium dioxide and then annealing the material to form the nanotubes used in other solar applications. He makes the cuprous oxide titanium dioxide nanotube array in the same way and can alter the proportions of each metal.

While titanium dioxide is very absorbing in the ultraviolet portion of the sun’s spectrum, many p-type materials are unstable in sunlight and damaged by ultraviolet light, they photo-corrode. To solve this problem, the researchers made the titanium dioxide side of the diode transparent to visible light by adding iron and exposed this side of the diode to natural sunlight. The titanium dioxide nanotubes soak up the ultraviolet between 300 and 400 nanometers. The light then passes to the copper titanium side of the diode where visible light from 400 to 885 nanometers is used, covering the light spectrum.

The photoelectrochemical diodes function the same way that green leaves do, only not quite as well. They convert the energy from the sun into electrical energy that then breaks up water molecules. The titanium dioxide side of the diode produces oxygen and the copper titanium side produces hydrogen.

Although 0.30 percent efficiency is low, Grimes notes that this is just a first go and that the device can be readily optimized.

“These devices are inexpensive and because they are photo-stable could last for years,” says Grimes. “I believe that efficiencies of 5 to 10 percent are reasonable.”

Grimes is now working with an electroplating method of manufacturing the nanotubes, which will be faster and easier.

 

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Working with Grimes are Gopal K. Mor, Oomman K. Varghese and Karthik Shankar, research associates; Rudeger H. T. Wilke and Sanjeev Sharma, Ph.D. candidates; Thomas J. Latempa, graduate student, all at Penn State; and Kyoung-Shin Choi, associate professor of chemistry, Purdue University.

The U.S. Department of Energy supported this research.

May 7, 2008

Display nanowires, ultramicroelectrodes, more affordable solar news

From KurzweilAI.net — Upright copper nanowires may be key to better flat panel displays, single-walled carbon nanotubes form ultramicroelectrodes, more news on solar electricity that rivals fossil fuels in cost.

Nanowires for Displays
Technology Review, May 6, 2008

Researchers at the University of Illinois in Urbana Champaign have developed a simple process to grow upright copper nanowires on different surfaces.

The nanowire arrays could find use in field-emission displays, a new type of display technology that promises to provide brighter, more vivid pictures than existing flat-panel displays.

 
Read Original Article>>

Nanotube production leaps from sooty mess in test tube to ready formed chemical microsensors
PhysOrg.com, May 6, 2008

University of Warwick chemists have produced single-walled carbon nanotubes that instantly form ultramicroelecrodes that could be used to create biocompatible, ultrasensitive sensors with high signal-to-noise ratios and fast response times.

The research team is exploring how these ultramicroelecrodes could be used to measure levels of neurotransmitters and catalysis in fuel cells.

 
Read Original Article>>

Focusing on Solar’s Cost
Technology Review, May 7, 2008

Solar startup Sunrgi says that it will soon be able to produce electricity from the sun at costs that are competitive with fossil-fuel generation.

The company has created a concentrated photovoltaic system that uses a lens to focus sunlight up to 2,000 times sun concentration onto tiny solar cells that can convert 37.5 percent of the sun’s energy into electricity. Stronger concentrations of sunlight allow engineers to use much smaller solar cells, making it more economical to use higher-efficiency–but higher-cost–cells.

 
Read Original Article>>

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