Nanogenerators Grow Strong Enough to Power Small Conventional ElectronicsNanogenerators Grow Strong Enough to Power Small Conventional Electronics

Blinking numbers on a liquid-crystal display (LCD) often indicate that a device’s clock needs resetting.  But in the laboratory of Zhong Lin Wang at Georgia Tech, the blinking number on a small LCD signals the success of a five-year effort to power conventional electronic devices with nanoscale generators that harvest mechanical energy from the environment using an array of tiny nanowires.

Compressing a nanogenerator between two fingers is enough to drive a liquid-crystal display. (Courtesy: Zhong Lin Wang)

In this case, the mechanical energy comes from compressing a nanogenerator between two fingers, but it could also come from a heartbeat, the pounding of a hiker’s shoe on a trail, the rustling of a shirt, or the vibration of a heavy machine.  While these nanogenerators will never produce large amounts of electricity for conventional purposes, they could be used to power nanoscale and microscale devices – and even to recharge pacemakers or iPods.
Wang’s nanogenerators rely on the piezoelectric effect seen in crystalline materials such as zinc oxide, in which an electric charge potential is created when structures made from the material are flexed or compressed.  By capturing and combining the charges from millions of these nanoscale zinc oxide wires, Wang and his research team can produce as much as three volts – and up to 300 nanoamps.
“By simplifying our design, making it more robust and integrating the contributions from many more nanowires, we have successfully boosted the output of our nanogenerator enough to drive devices such as commercial liquid-crystal displays, light-emitting diodes and laser diodes,” said Wang, a Regents’ professor in Georgia Tech’s School of Materials Science and Engineering.  “If we can sustain this rate of improvement, we will reach some true applications in healthcare devices, personal electronics, or environmental monitoring.”

• VIEW a 2:30 video about nanogenerator research.

Professor Zhong Lin Wang holds an earlier version of the nanogenerators developed using zinc oxide nanowires. (Click image for high-resolution version. Credit: Gary Meek)

Recent improvements in the nanogenerators, including a simpler fabrication technique, were reported online last week in the journal Nano Letters.  Earlier papers in the same journal and in Nature Communications reported other advances for the work, which has been supported by the Defense Advanced Research Projects Agency (DARPA), the U.S. Department of Energy, the U.S. Air Force, and the National Science Foundation.
“We are interested in very small devices that can be used in applications such as health care, environmental monitoring and personal electronics,” said Wang.  “How to power these devices is a critical issue.”
The earliest zinc oxide nanogenerators used arrays of nanowires grown on a rigid substrate and topped with a metal electrode.  Later versions embedded both ends of the nanowires in polymer and produced power by simple flexing.  Regardless of the configuration, the devices required careful growth of the nanowire arrays and painstaking assembly.
In the latest paper, Wang and his group members Youfan Hu, Yan Zhang, Chen Xu, Guang Zhu and Zetang Li reported on much simpler fabrication techniques.  First, they grew arrays of a new type of nanowire that has a conical shape.  These wires were cut from their growth substrate and placed into an alcohol solution.

In a new technique for producing nanogenerators, researchers transfer vertically-aligned nanowires to a flexible substrate. (Courtesy of Zhong Lin Wang)

The solution containing the nanowires was then dripped onto a thin metal electrode and a sheet of flexible polymer film.  After the alcohol was allowed to dry, another layer was created.  Multiple nanowire/polymer layers were built up into a kind of composite, using a process that Wang believes could be scaled up to industrial production.
When flexed, these nanowire sandwiches – which are about two centimeters by 1.5 centimeters – generated enough power to drive a commercial display borrowed from a pocket calculator.
Wang says the nanogenerators are now close to producing enough current for a self-powered system that might monitor the environment for a toxic gas, for instance, then broadcast a warning.  The system would include capacitors able to store up the small charges until enough power was available to send out a burst of data.
While even the current nanogenerator output remains below the level required for such devices as iPods or cardiac pacemakers, Wang believes those levels will be reached within three to five years.  The current nanogenerator, he notes, is nearly 100 times more powerful than what his group had developed just a year ago.
Writing in a separate paper published in October in the journal Nature Communications, group members Sheng Xu, Benjamin J. Hansen and Wang reported on a new technique for fabricating piezoelectric nanowires from lead zirconate titanate – also known as PZT.  The material is already used industrially, but is difficult to grow because it requires temperatures of 650 degrees Celsius.
In the paper, Wang’s team reported the first chemical epitaxial growth of vertically-aligned single-crystal nanowire arrays of PZT on a variety of conductive and non-conductive substrates.  They used a process known as hydrothermal decomposition, which took place at just 230 degrees Celsius.

In an improved technique for fabricating nanogenerators, researchers transfer vertical arrays of nanowires to a flexible substrate. (Credit: Inertia Films)

With a rectifying circuit to convert alternating current to direct current, the researchers used the PZT nanogenerators to power a commercial laser diode, demonstrating an alternative materials system for Wang’s nanogenerator family.  “This allows us the flexibility of choosing the best material and process for the given need, although the performance of PZT is not as good as zinc oxide for power generation,” he explained.
And in another paper published in Nano Letters, Wang and group members Guang Zhu, Rusen Yang and Sihong Wang reported on yet another advance boosting nanogenerator output.  Their approach, called “scalable sweeping printing,” includes a two-step process of (1) transferring vertically-aligned zinc oxide nanowires to a polymer receiving substrate to form horizontal arrays and (2) applying parallel strip electrodes to connect all of the nanowires together.
Using a single layer of this structure, the researchers produced an open-circuit voltage of 2.03 volts and a peak output power density of approximately 11 milliwatts per cubic centimeter.
“From when we got started in 2005 until today, we have dramatically improved the output of our nanogenerators,” Wang noted.  “We are within the range of what’s needed.  If we can drive these small components, I believe we will be able to power small systems in the near future.  In the next five years, I hope to see this move into application.”

Threshold Sea Surface Temperature for Hurricanes and Tropical Thunderstorms Is Rising

Scientists have long known that atmospheric convection in the form of hurricanes and tropical ocean thunderstorms tends to occur when sea surface temperature rises above a threshold. So how do rising ocean temperatures with global warming affect this threshold?  If the threshold does not rise, it could mean more frequent hurricanes. A new study by researchers at the International Pacific Research Center (IPRC) of the University of Hawaiʻi at Mānoa shows this threshold sea surface temperature for convection is rising under global warming at the same rate as that of the tropical oceans. Their paper appears in the Advance Online Publications of Nature Geoscience.

Tropical ocean thunderstorms. Image courtesy NASA

Average observed tropical (black) and estimated SST (blue) rose together in the last 30 years.

 

In order to detect the annual changes in the threshold sea surface temperature (SST) for convection,  Nat Johnson, a postdoctoral fellow at IPRC, and Shang-Ping Xie, a professor of meteorology at IPRC and UH Mānoa, analyzed satellite estimates of tropical ocean rainfall spanning 30 years. They find that changes in the threshold temperature for convection closely follow the changes in average tropical sea surface temperature, which have both been rising approximately 0.1°C per decade.   

“The correspondence between the two time series is rather remarkable,” says lead author Johnson. “The convective threshold and average sea surface temperatures are so closely linked because of their relation with temperatures in the atmosphere extending several miles above the surface.”

The change in tropical upper atmospheric temperatures has been a controversial topic in recent years because of discrepancies between reported temperature trends from instruments and the expected trends under global warming according to global climate models. The measurements from instruments have shown less warming than expected in the upper atmosphere. The findings of Johnson and Xie, however, provide strong support that the tropical atmosphere is warming at a rate that is consistent with climate model simulations.

 

“This study is an exciting example of how applying our knowledge of physical processes in the tropical atmosphere can give us important information when direct measurements may have failed us,” Johnson notes.

The study notes further that global climate models project that the sea surface temperature threshold for convection will continue to rise in tandem with the tropical average sea surface temperature. If true, hurricanes and other forms of tropical convection will require warmer ocean surfaces for initiation over the next century.

Popular Mechanics Breakthrough Awardees Announced

Artificial retina technology, seismic fuses and cell phone microscopes among the winners

A novel, mixed-signal system-on-a-chip was developed as a platform for implantable prosthetics.

View discussions on the artificial retina, future of the automobile, and development of award winning technologies.
Popular Mechanics has recognized three NSF-funded projects with innovation Breakthrough Awards: an artificial retina returning sight to those who have lost it; a system that uses "controlled rocking" and energy-dissipating fuses to help buildings withstand earthquakes; and an inexpensive medical microscope built for cell-phones that allows doctors in rural villages to identify malaria-infected blood cells.
Those projects, along with 16 others, are featured in the November 2010 issue of Popular Mechanics. The awardees share the issue with the 2010 Leadership Award winner, J. Craig Venter, who is recognized for his breakthroughs in genomics over the last decade.
The artificial retina technology, funded for decades by several NSF biotechnology and transformational research programs, is an experimental system that helps individuals suffering from either macular degeneration or retinitis pigmentosa. Led by University of Southern California engineers Mark Humayun and Wentai Liu, the collaborative team--involving academia, government and industry--has been testing the system with more than 25 individuals, enabling them to progress from total blindness to being able to see shapes and navigate their local surroundings.
The controlled-rocking frame, developed as part of NSF's George E. Brown, Jr. Network for Earthquake Engineering Simulation program, uses replaceable, structural fuses that sacrifice themselves when an earthquake strikes, preserving the buildings they protect. Developed by a team led by Gregory Deierlein of Stanford University and Jerome Hajjar of Northeastern University, the system's self-centering frames and fuses help prevent post-earthquake displacement and are designed for fast and easy repair following a major earthquake, ensuring that an affected building can be reoccupied quickly.
The cellular-phone microscope, also funded by NSF's biotechnology programs, uses no lenses, lowering bulk and cost. The device--developed by NSF CAREER awardee Aydogan Ozcan of the University of California, Los Angeles--focuses LED light onto a slide positioned directly over a cell phone's camera, and after interpretation by software, can differentiate details so clearly that malaria-infected blood cells stand out from healthy ones.
NSF award abstracts contain summaries of Mark Humayun's NSF-funded projects, and the technology is described in a Science Nation video segment. There are also abstracts related to Wentai Liu's NSF-funded projects as well as of NSF NEES projects, and of Aydogan Ozcan's NSF-funded projects.

Exploring Sustainability for Energy and Buildings

The National Science Foundation (NSF) Office of Emerging Frontiers in Research and Innovation (EFRI) has announced 14 grants for fiscal year (FY) 2010, awarding nearly $28 million to 62 investigators at 24 institutions.
Over the next four years, teams of researchers will pursue transformative, fundamental research in two areas of great national need: storing energy from renewable sources; and engineering sustainable buildings.
Energy generated from renewable sources has long promised to satisfy demands for more and cleaner electricity. Because renewable sources, such as sunlight and wind, can produce greatly fluctuating amounts of energy, they are most effectual when excess energy can be stored until it's needed.
EFRI research teams will pursue creative new approaches to making large-scale energy storage efficient and economical. They aim to construct capacitors and regenerative fuel cells with unprecedented capabilities to harness the sun's thermal energy, to produce chemical fuel on demand, and to trap off-shore wind as compressed air.
"These four projects take radically different approaches to storing excess energy from intermittent sources," said Geoffrey Prentice, lead EFRI program officer, "and success in any one of them could guide the development of new processes for large-scale energy storage."
A second set of EFRI research teams will investigate the critical flows and fluxes of buildings--power, heat, light, water, air and occupants--to create new paradigms for the design, construction, and operation of our homes and workplaces.
These researchers aim to improve the ability to predict and control building energy performance and environmental impacts, and to design systems that respond intelligently, in real-time, to changing conditions and to occupant input and needs. The investigations will pursue methods for reducing water consumption; for distributed, integrated approaches to renewable energy production, storage, and use; and for moderating temperature shifts through passive building technologies and systems.
"These awards are significant in the extent to which the research teams are multidisciplinary," said lead EFRI program officer Richard Fragaszy. Engineers, architects, and physical and social scientists are pooling their expertise to conduct the basic research needed to design and construct future homes and offices that will greatly reduce reliance on fossil fuels and demand for potable water, while improving the health and productivity of their occupants."
"These researchers are undertaking bold investigations in order to achieve major leaps in knowledge," said Sohi Rastegar, director of EFRI. "If they are successful, their findings have the potential to significantly impact global warming and promote U.S. energy independence."
The FY 2010 EFRI topics were developed in close collaboration with the NSF Directorates for Computer and Information Science and Engineering (CISE), Mathematical and Physical Sciences (MPS), and Social, Behavioral, and Economic Sciences (SBE), as well as with the U.S. Department of Energy (DOE) and U.S. Environment Protection Agency (EPA). DOE and EPA also contributed financial support to the EFRI SEED projects.
EFRI, established by the NSF Directorate for Engineering in 2007, seeks high-risk interdisciplinary research that has the potential to transform engineering and other fields.  The grants demonstrate the EFRI goal to inspire and enable researchers to expand the limits of our knowledge.

Decontaminating Dangerous Drywall

Nanomaterial in novel home-air treatment counters hazards from toxic drywall

Artist's interpretation of FAST-ACT absorbing and destroying toxins.

A nanomaterial originally developed to fight toxic waste is now helping reduce debilitating fumes in homes with corrosive drywall.
Developed by Kenneth Klabunde of Kansas State University, and improved over three decades with support from the National Science Foundation, the FAST-ACT material has been a tool of first responders since 2003.
Now, NanoScale Corporation of Manhattan, Kansas--the company Klabunde co-founded to market the technology--has incorporated FAST-ACT into a cartridge that breaks down the corrosive drywall chemicals.
Homeowners have reported that the chemicals--particularly sulfur compounds such as hydrogen sulfide and sulfur dioxide--have caused respiratory illnesses, wiring corrosion and pipe damage in thousands of U.S. homes with sulfur-rich, imported drywall.
"It is devastating to see what has happened to so many homeowners because of the corrosive drywall problem, but I am glad the technology is available to help," said Klabunde. "We've now adapted the technology we developed through years of research for FAST-ACT for new uses by homeowners, contractors and remediators."
The new cartridge, called OdorKlenz®, takes the place of the existing air filter in a home. The technology is similar to one that NanoScale adapted in 2008 for use by a major national disaster restoration service company for odors caused by fire and water damage.
In homes with corrosive drywall, the cartridge is used in combination with related FAST-ACT-based, OdorKlenz® surface treatments (and even laundry additives) to remove the sulfur-bearing compounds causing the corrosion issues.
Developers at NanoScale tested their new air cartridge in affected homes that were awaiting drywall removal, and in every case, odor dropped to nearly imperceptible levels within 10 days or less and  corrosion was reduced.
The FAST-ACT material is a non-toxic mineral powder composed of the common elements magnesium, titanium and oxygen. While metal oxides similar to FAST-ACT have an established history tackling dangerous compounds, none have been as effective.
NanoScale's breakthrough was a new method to manufacture the compound as a nanocrystalline powder with extremely high surface area--only a few tablespoons have as much surface area as a football field.
The surface area allows more interactions between the metal oxides and the toxic molecules, enabling the powder to capture and destroy a large quantity of hazardous chemicals ranging from sulfuric acid to VX gas--and their hazardous byproducts--in minutes.
"The concept of nano-sized adsorbents as both a cost-efficient, useful product for first responders and an effective product for in-home use illustrates the wide spectrum of possibilities for this technology," said NSF program director Rosemarie Wesson, who oversaw NanoScale's NSF Small Business Innovation Resarch grants.  "It is great to see the original work we supported to help reduce the toxic effects of hazardous spills now expand into other applications."
In coming months, the company is proposing its technology for use in Gulf Coast residences affected by the recent oil spill and other hazardous situations where airborne toxins are causing harm.
In addition to extensive support from NSF, the development of FAST ACT and NanoScale's technology has been supported by grants from the U.S. Army, DTRA, Air Force, DARPA, JPEO, MARCORSYSCOM , the CTTSO, USSOCOM, NIOSH, DOE, NIH and EPA.

Transformation Optics Make a U-turn for the Better

Powerful new microscopes able to resolve DNA molecules with visible light, superfast computers that use light rather than electronic signals to process information, and Harry Potteresque invisibility cloaks are just some of the many thrilling promises of transformation optics. In this burgeoning field of science, light waves can be controlled at all lengths of scale through the unique structuring of metamaterials, composites typically made from metals and dielectrics – insulators that become polarized in the presence of an electromagnetic field. The idea is to transform the physical space through which light travels, sometimes referred to as “optical space,” in a manner similar to the way in which outer space is transformed by the presence of a massive object under Einstein’s relativity theory.

Schematic on the left shows the scattering of surface plasmon polaritons (SPPs) on a metal-dielectric interface with a single protrusion. Schematic on right shows how SPP scattering is dramatically suppressed when the optical space around the protrusion is transformed. (Image courtesy of Zhang group)

So far transformation optics have delivered only hints as to what the future might hold, with a major roadblock being how difficult it is to modify the physical properties of metamaterials at the nano or subwavelength scale, mainly because of the metals. Now, a team of researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have shown it might be possible to go around that metal roadblock. Using sophisticated computer simulations, they have demonstrated that with only moderate modifications of the dielectric component of a metamaterial, it should be possible to achieve practical transformation optics results. The key to success is the combination of transformation optics with another promising new field of science known as plasmonics.
A plasmon is an electronic surface wave that rolls through the sea of conduction electrons on a metal. Just as the energy in waves of light is carried in quantized particle-like units called photons, so, too, is plasmonic energy carried in quasi-particles called plasmons. Plasmons will interact strongly with photons at the interface of a metamaterial’s metal and dielectric to form yet another quasi-particle called a surface plasmon polariton(SPP). Manipulation of these SPPs is at the heart of the astonishing optical properties of metamaterials.

Yongmin Liu (left) Xiang Zhang and Thomas Zentgraf used sophisticated compuer modeling to develop a “transformational plasmon optics” technique that may open the door to practical integrated, compact optical data-processing chips. (Photo by Roy Kaltschmidt, Berkeley Lab Public Affairs)

The Berkeley Lab-UC Berkeley team, led by Xiang Zhang, a principal investigator with Berkeley Lab’s Materials Sciences Division and director of UC Berkeley’s Nano-scale Science and Engineering Center (SINAM), modeled what they have dubbed a “transformational plasmon optics” approach that involved manipulation of the dielectric material adjacent to a metal but not the metal itself. This novel approach was shown to make it possible for SPPs to travel across uneven and curved surfaces over a broad range of wavelengths without suffering significant scattering losses. Using this model, Zhang and his team then designed a plasmonic waveguide with a 180 degree bend that won’t alter the energy or properties of a light beam as it makes the U-turn. They also designed a plasmonic version of a Luneburg lens, the ball-shaped lenses that can receive and resolve optical waves from multiple directions at once.
“Since the metal properties in our metamaterials are completely unaltered, our transformational plasmon optics methodology provides a practical way for routing light at very small scales,” Zhang says. “Our findings reveal the power of the transformation optics technique to manipulate near-field optical waves, and we expect that many other intriguing plasmonic devices will be realized based on the methodology we have introduced.”
Zhang is the corresponding author of a paper describing this research that appeared in the journal Nano Letters, titled “Transformational Plasmon Optics.” Co-authoring the paper with Zhang were Yongmin Liu, Thomas Zentgraf and Guy Bartal.

Field distribution after the transformation of a dielectric material shows the nearly perfect transmission of a light beam around a 180 degree bend. (Image courtesy of Zhang group)

Says Liu, who was the lead author of the paper and is a post-doctoral researcher in Zhang’s UC Berkeley group, “In addition to the 180 degree plasmonic bend and the plasmonic Luneburg lens, our approach should also enable the design and production of beam splitters and shifters, and directional light emitters. The technique should also be applicable to the construction of integrated, compact optical data-processing chips.”
Zhang and his research group have been at the forefront of transformation optics research since 2008 when they became the first group to fashion metamaterials that were able to bend light backwards, a property known as “negative refraction,” which is unprecedented in nature. In 2009, he and his group created a “carpet cloak” from nanostructured silicon that concealed the presence of objects placed under it from optical detection.
For this latest work, Zhang and Liu with Zentgraf and Bartal departed from the traditional transformation optics focus on propagation waves and instead focused on the SPPs carried in near-field (subwavelength) region.
“The intensity of SPPs is maximal at the interface between a metal and a dielectric medium and exponentially decays away from the interface,” says Zhang. “Since a significant portion of SPP energy is carried in the evanescent field outside the metal, that is, in the adjacent dielectric medium, we proposed to control SPPs by keeping the metal property fixed and only modifying the dielectric material based on the transformation optics technique.”

In this schematic of a plasmonic Luneburg lens, a dielectric cone is placed on a metal to focus surface plasmon polaritons. (Image courtesy of Zhang group)

Full-wave simulations of different transformed designs proved the proposed methodology by Zhang and his colleagues correct. It was furthermore demonstrated that if a prudent transformational plasmon optics scheme is taken the transformed dielectric materials can be isotropic and nonmagnetic, which further boosts the practicality of this approach. The demonstration of a 180 degree bend plasmonic bend with almost perfect transmission was especially significant.
“Plasmonic waveguides are one of the most important components/elements in integrated plasmonic devices,” says Liu. “However, curvatures often lead to strong radiation loss that reduces the length for transferring an optical signal. Our 180 degree bend plasmonic bend is definitely important and will be useful in the future design of integrated plasmonic devices.”
Compared with silicon-based photonic devices the use of plasmonics could help to further scale- down the total size of photonic devices and increase the interaction of light with certain materials, which should improve performance.
“We envision that the unique design flexibility of the transformational plasmon optics approach may open a new door to nano optics and photonic circuit design,” Zhang says.

Molecular Robots On the Rise

Researchers announce new breakthrough in developing molecules that behave like robots

As the robot walks on the substrate, it changes each piece by cleaving off a part.

Researchers from Columbia University, Arizona State University, the University of Michigan and the California Institute of Technology (Caltech) have created and programmed robots the size of single molecule that can move independently across a nano-scale track. This development, outlined in the May 13 edition of the journal Nature, marks an important advancement in the nascent fields of molecular computing and robotics, and could someday lead to molecular robots that can fix individual cells or assemble nanotechnology products.
The project was led by Milan N. Stojanovic, a faculty member in the division of experimental therapeutics at Columbia University, who partnered with Erik Winfree, associate professor of computer science at Caltech, Hao Yan, professor of chemistry and biochemistry at Arizona State University and an expert in DNA nanotechnology, and with Nils G. Walter, professor of chemistry and director of the Single Molecule Analysis in Real-Time (SMART) Center at the University of Michigan in Ann Arbor. Their work was supported in part by the National Science Foundation.
The word ‘robot' makes most people think of solid machines that use computer circuitry to perform defined jobs, such as vacuuming a carpet or welding together automobiles. In recent years, scientists have worked to create robots that could also reliably perform useful tasks, but at a molecular level. This is, needless to say, not a simple endeavor, and it involves reprogramming DNA molecules to perform in specific ways. "Can you instruct a biomolecule to move and function in a certain way--researchers at the interface of computer science, chemistry, biology and engineering are attempting to do just that," says Mitra Basu, a program director at NSF responsible for the agency's support to this research.
Recent molecular robotics work has produced so-called DNA walkers, or strings of reprogrammed DNA with 'legs' that enabled them to briefly walk. Now this research team has shown these molecular robotic spiders can in fact move autonomously through a specially-created, two-dimensional landscape. The spiders acted in rudimentary robotic ways, showing they are capable of starting motion, walking for awhile, turning, and stopping.
In addition to be incredibly small--about 4 nanometers in diameter--the walkers are also move slowly, covering 100 nanometers in times ranging 30 minutes to a full hour by taking approximately 100 steps. This is a significant improvement over previous DNA walkers that were capable of only about three steps.
While the field of molecular robotics is still emerging, it is possible that these tiny creations may someday have important medical applications. "This work one day may lead to effective control of chronic diseases such as diabetes or cancer," Basu says.
According to Stojanovich, these practical applications are still many years off, but he and his colleagues hope to continue their work in to the foundations of this young field. Stojanovich believes that their future work will also require extensive collaborations, with each of them bringing a specific expertise to the table, as was the case in the research published today. "If you take anyone of us with our disciplinary expertise out of this," Stojanovic said in an interview "this paper would have collapsed and never be what it is now."

National Science Foundation Launches Green Revolution Video Series

A fresh take on cutting edge research to develop and improve the use of clean energy sources

The Green Revolution video series features cutting edge research on clean energy technologies.

Today the National Science Foundation released online its "Green Revolution" video series. These educational videos, each about five minutes long, feature scientists and engineers who are working to develop and improve the use of clean energy sources, new fuels and other energy-related technologies. Each segment explores the research carried out by men and women at the forefront of discovery and innovation related to clean energy, as well as some of the basic science behind their work.
During a speech at the National Academy of Sciences last year, President Obama spoke of the need to "spark a sense of wonder and excitement" in the nation's young people to pursue careers in science and engineering. As today's researchers develop new ways to convert sunlight to electricity, distribute energy with a smart grid and store clean energy with advanced batteries, they blaze the trail for future explorers and inventors. The Administration's "New Energy for America" plan will provide the opportunity for thousands of American students to pursue careers in science, engineering, and entrepreneurship related to clean energy. These young men and women will invent and help commercialize advanced energy technologies of the future to capture, share and store energy obtained from clean energy sources.
As part of a science and engineering initiative to educate students in fields contributing to energy science and engineering systems, the "Green Revolution" series aims to encourage people to ask questions and look beyond fossil fuels for innovative solutions to our ever-growing energy needs. Each episode is accompanied by supplemental materials for educators, including brief descriptions of the scientific concepts relevant to the technology. Additional videos are scheduled for release this summer.

Researchers Demonstrate New Understanding of Nanotube Growth

Scientists take first step toward controlling the growth of nanomaterials without catalysts

A schematic illustration showing the formation of nanotubes driven by screw dislocations. Credit and Larger Version

April 22, 2010

Researchers at the University of Wisconsin-Madison recently made a significant first step toward understanding how to control the growth of the nanotubes, nanowires and nanorods needed for renewable energy and other technology applications.
These nanocrystalline materials, or nanomaterials, possess unique chemical and physical properties that can be used in solar energy panels, high energy density batteries, or better electronics. But, writing in the April 23 edition of the journal Science, a UW-Madison research team notes that the formation of these materials is often not well understood.
In particular, the question of how one-dimensional (1D) crystals grow sometimes without catalysts has been troublesome for scientists and engineers who need to produce large amounts of nanomaterials for specific applications. Working with zinc oxide, a common semiconductor widely used as a nanomaterial, assistant professor of chemistry Song Jin and his students demonstrated a new understanding of the subject by showing that nanotubes can be formed solely due to the strain energy and screw dislocations that drive their growth.
Screw dislocations are frequently observed defects in crystalline materials that can be thought of as a screw or a helical staircase that can drive fast 1D crystal growth. But these defects produce strain and stress during nanotube formation.
"The strain energy within dislocation-driven nanomaterials dictates if the material will be hollow or solid," explained Jin. "Tubes are formed when strain energy gets large enough and the center of the nanostructure hollows out to relieve the stress and strain."
Jin and his students investigated the possibility of dislocation-driven growth by carefully regulating the amount of available nanotube building blocks in a solution. Essentially, the team controllably oversaturated or supersaturated a vat of water with zinc salts to favor dislocation-driven growth and observe the formation of solid nanowires and hollow nanotubes.
This mechanism differs from previous growth strategies in that it doesn't require a catalyst or a template to produce nanotubes, but relies solely on a dislocation and the strain energy associated with it. A catalyst is usually another metal nanoparticle such as gold added to the growth process, which in turn drives 1D growth.
"Once we understand that the growth of these 1D nanomaterials can be driven by screw dislocations, we can see nanotubes and nanowires are related." said Jin. "Furthermore, we've shown that growth of nanotubes or nanowires without the use of a catalyst in solutions can be rationally designed by following a fundamental understanding of crystal growth theories and the concept of dislocation-driven nanomaterial growth.
"For more practical purposes, we think that this work provides a general theoretical framework for controlling solution nanowire/nanotube growth that can be applicable to many other materials," Jin said.
Growing large amounts of nanotubes or nanowires from water-based solutions without a catalyst would be much more cost-effective. "This could open up the exploitation of large scale/low cost solution growth for rational catalyst-free synthesis of 1D nanomaterials," said Jin.
Scientists take first step toward controlling the growth of nanomaterials without catalysts

A schematic illustration showing the formation of nanotubes driven by screw dislocations.

Researchers at the University of Wisconsin-Madison recently made a significant first step toward understanding how to control the growth of the nanotubes, nanowires and nanorods needed for renewable energy and other technology applications.
These nanocrystalline materials, or nanomaterials, possess unique chemical and physical properties that can be used in solar energy panels, high energy density batteries, or better electronics. But, writing in the April 23 edition of the journal Science, a UW-Madison research team notes that the formation of these materials is often not well understood.
In particular, the question of how one-dimensional (1D) crystals grow sometimes without catalysts has been troublesome for scientists and engineers who need to produce large amounts of nanomaterials for specific applications. Working with zinc oxide, a common semiconductor widely used as a nanomaterial, assistant professor of chemistry Song Jin and his students demonstrated a new understanding of the subject by showing that nanotubes can be formed solely due to the strain energy and screw dislocations that drive their growth.
Screw dislocations are frequently observed defects in crystalline materials that can be thought of as a screw or a helical staircase that can drive fast 1D crystal growth. But these defects produce strain and stress during nanotube formation.
"The strain energy within dislocation-driven nanomaterials dictates if the material will be hollow or solid," explained Jin. "Tubes are formed when strain energy gets large enough and the center of the nanostructure hollows out to relieve the stress and strain."
Jin and his students investigated the possibility of dislocation-driven growth by carefully regulating the amount of available nanotube building blocks in a solution. Essentially, the team controllably oversaturated or supersaturated a vat of water with zinc salts to favor dislocation-driven growth and observe the formation of solid nanowires and hollow nanotubes.
This mechanism differs from previous growth strategies in that it doesn't require a catalyst or a template to produce nanotubes, but relies solely on a dislocation and the strain energy associated with it. A catalyst is usually another metal nanoparticle such as gold added to the growth process, which in turn drives 1D growth.
"Once we understand that the growth of these 1D nanomaterials can be driven by screw dislocations, we can see nanotubes and nanowires are related." said Jin. "Furthermore, we've shown that growth of nanotubes or nanowires without the use of a catalyst in solutions can be rationally designed by following a fundamental understanding of crystal growth theories and the concept of dislocation-driven nanomaterial growth.
"For more practical purposes, we think that this work provides a general theoretical framework for controlling solution nanowire/nanotube growth that can be applicable to many other materials," Jin said.
Growing large amounts of nanotubes or nanowires from water-based solutions without a catalyst would be much more cost-effective. "This could open up the exploitation of large scale/low cost solution growth for rational catalyst-free synthesis of 1D nanomaterials," said Jin.

A Tiny Defect That May Create Smaller, Faster Electronics

Researchers at the University of South Florida have developed a technique to turn defects in graphene into tiny metallic wires

An artist's conception of a row of intentional molecular defects in a sheet of graphene.

When most of us hear the word 'defect', we think of a problem that has to be solved. But a team of researchers at the University of South Florida (USF) created a new defect that just might be a solution to a growing challenge in the development of future electronic devices.
The team lead by USF Professors Matthias Batzill and Ivan Oleynik, whose discovery was published yesterday in the journal Nature Nanotechnology, have developed a new method for adding an extended defect to graphene, a one-atom-thick planar sheet of carbon atoms that many believe could replace silicon as the material for building virtually all electronics.
It is not simple to work with graphene, however. To be useful in electronic applications like integrated circuits, small defects must be introduced to the material. Previous attempts at making the necessary defects have either proved inconsistent or produced samples in which only the edges of thin strips of graphene or graphene nanoribbons possessed a useful defect structure. However, atomically-sharp edges are difficult to create due to natural roughness and the uncontrolled chemistry of dangling bonds at the edge of the samples.
The USF team has now found a way to create a well-defined, extended defect several atoms across, containing octagonal and pentagonal carbon rings embedded in a perfect graphene sheet. This defect acts as a quasi-one-dimensional metallic wire that easily conducts electric current. Such defects could be used as metallic interconnects or elements of device structures of all-carbon, atomic-scale electronics.
So how did the team do it? The experimental group, guided by theory, used the self-organizing properties of a single-crystal nickel substrate, and used a metallic surface as a scaffold to synthesize two graphene half-sheets translated relative to each other with atomic precision. When the two halves merged at the boundary, they naturally formed an extended line defect. Both scanning tunneling microscopy and electronic structure calculations were used to confirm that this novel one-dimensional carbon defect possessed a well-defined, periodic atomic structure, as well as metallic properties within the narrow strip along the defect.
This tiny wire could have a big impact on the future of computer chips and the myriad of devices that use them. In the late 20th century, computer engineers described a phenomenon called Moore's Law, which holds that the number of transistors that can be affordably built into a computer processor doubles roughly every two years. This law has proven correct, and society has been reaping the benefits as computers become faster, smaller, and cheaper. In recent years, however, some physicists and engineers have come to believe that without new breakthroughs in new materials, we may soon reach the end of Moore's Law. As silicon-based transistors are brought down to their smallest possible scale, finding ways to pack more on a single processor becomes increasingly difficult.
Metallic wires in graphene may help to sustain the rate of microprocessor technology predicted by Moore's Law well into the future. The discovery by the USF team, with support from the National Science Foundation, may open the door to creation of the next generation of electronic devices using novel materials. Will this new discovery be available immediately in new nano-devices? Perhaps not right away, but it may provide a crucial step in the development of smaller, yet more powerful, electronic devices in the not-too-distant future.