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.
Sabtu, 23 Oktober 2010
Decontaminating Dangerous Drywall
Nanomaterial in novel home-air treatment counters hazards from toxic drywall
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.
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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.
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.
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.
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.”
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.
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)
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)
“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)
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)
“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
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."
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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
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.
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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
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
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.
 Credit and Larger Version |
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
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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
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.
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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.
NSF Builds Science and Engineering Capacity in Communities Around the United States
Funding awarded for the creation of five Science Technology Centers
The National Science Foundation (NSF) announced five new Science and Technology Center (STC) awards as a result of a recent, merit-based competition. The STC program supports integrative partnerships that require large-scale, long-term funding to produce research and education of the highest quality. In October of 2008, NSF received 247 preliminary proposals. Following extensive panel review, 45 full proposals were invited and reviewed by both panel and ad hoc experts, 11 sites were visited, and 5 were recommended for awards by a Blue Ribbon panel. Well over 100 program directors from throughout NSF assisted in the review process. "These five new STCs will involve world class teams of researchers and educators, integrate learning and discovery in innovative ways, tackle complex problems that require the long-term support afforded by this program, and lead to the development of new technologies with significant impact well into the future," said NSF Director Arden L. Bement.
Brief descriptions of the new STCs follow:
Center for Dark Energy Biosphere Investigations (C-DEBI)
Katrina J. Edwards from the University of Southern California in partnership with faculty members at the University of Alaska-Fairbanks, University of California (UC)-Santa Cruz, University of Hawaii, Pacific Northwest National Lab, University of Rhode Island, Lawrence Berkeley National Laboratory, Japan Agency for Marine Earth Science & Technology, Harvard University and the University of Bremen will establish a center to facilitate exploration of the Earth's "deep biosphere" beneath the oceans. Although nearly half of the total biomass on Earth resides in sub-surface habitats such as mines, aquifers, soils on the continents and sediments and rocks below the ocean floor, little is known about these sub-surface communities. C-DEBI will explore such fundamental questions as: What type of life exists in the deep biosphere? What are the physical and chemical conditions that promote or limit life? How does this biosphere influence global energy and material cycles such as the carbon cycle? A number of educational and outreach activities such as "science at sea" will inspire students and the public.
BEACON: An NSF Center for the Study of Evolution in Action
Erik D. Goodman from Michigan State University in partnership with colleagues at the University of Texas-Austin, University of Washington, North Carolina A&T State University, and the University of Idaho will establish a center that will promote the transfer of discoveries from biology into computer science and engineering design, and use novel computational methods to address complex biological questions that are difficult or impossible to study using natural organisms. BEACON will bring together scientists who, through research in their own disciplines, hold the interlocking keys to solving complex and fundamental problems in domains as diverse as cyber-security, epidemiology, and environmental sustainability. BEACON education and human resource development plans include K-12 programs, novel curricula development, undergraduate and graduate training, a mentoring program for faculty and post-docs, and outreach programs to educate the general public.
Emergent Behaviors of Integrated Cellular Systems
Roger D. Kamm from the Massachusetts Institute of Technology (MIT) in partnership with researchers at the University of Illinois at Urbana-Champaign (UIUC) and Georgia Institute of Technology will establish a center to develop the science and technology to engineer clusters of living cells or "biological machines" that have desired functionalities and can perform prescribed tasks. This research will help to establish the nascent field of engineering biological systems. The center will develop programs aimed at attracting students to STEM (science, technology, engineering, mathematics) fields, and particularly to the growing area of bioengineering. An integrated inter-institutional graduate program will be developed and courses will be made accessible via OpenCourseWare.
Emerging Frontiers of Science of Information
Wojciech Szpankowski from Purdue University in partnership with colleagues at Bryn Mawr College, Howard University, MIT, Princeton, Stanford, UC Berkeley, UC San Diego, and UIUC will establish a Center for the Science of information that has the potential to launch the next information revolution. These researchers will develop a unifying set of principles to guide the extraction, manipulation, and exchange of information integrating elements of space, time, structure, semantics & context. The center will bring together researchers from diverse fields (physics, life science, chemistry, computer science, economics, etc.) to develop models and methods to apply to these diverse applications. The center will also build an active community of scholars through education and mentoring activities.
Center for Energy Efficient Electronics Science (E3S)
Eli Yablonovitch from University of California Berkeley in partnership with faculty members at MIT, Stanford, Contra Costa College, Los Angeles Trade Technical College and the Tuskegee Institute, proposed a center that will take on the challenge of increasing the energy efficiency of electronic information-processing equipment. Recent years have seen a dramatic increase in the share of electricity usage from electronics, and the trend is expected to continue unless fundamental changes are made to the power requirements of the basic logic switch. E3S will research concepts and scientific principles that could enable a few millivolt electronic switch as a successor to the transistor, laying the foundation for a million-fold reduction in power consumption by electronics. The center will also support a number of educational programs and promote energy awareness through outreach activities.
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Brief descriptions of the new STCs follow:
Center for Dark Energy Biosphere Investigations (C-DEBI)
Katrina J. Edwards from the University of Southern California in partnership with faculty members at the University of Alaska-Fairbanks, University of California (UC)-Santa Cruz, University of Hawaii, Pacific Northwest National Lab, University of Rhode Island, Lawrence Berkeley National Laboratory, Japan Agency for Marine Earth Science & Technology, Harvard University and the University of Bremen will establish a center to facilitate exploration of the Earth's "deep biosphere" beneath the oceans. Although nearly half of the total biomass on Earth resides in sub-surface habitats such as mines, aquifers, soils on the continents and sediments and rocks below the ocean floor, little is known about these sub-surface communities. C-DEBI will explore such fundamental questions as: What type of life exists in the deep biosphere? What are the physical and chemical conditions that promote or limit life? How does this biosphere influence global energy and material cycles such as the carbon cycle? A number of educational and outreach activities such as "science at sea" will inspire students and the public.
BEACON: An NSF Center for the Study of Evolution in Action
Erik D. Goodman from Michigan State University in partnership with colleagues at the University of Texas-Austin, University of Washington, North Carolina A&T State University, and the University of Idaho will establish a center that will promote the transfer of discoveries from biology into computer science and engineering design, and use novel computational methods to address complex biological questions that are difficult or impossible to study using natural organisms. BEACON will bring together scientists who, through research in their own disciplines, hold the interlocking keys to solving complex and fundamental problems in domains as diverse as cyber-security, epidemiology, and environmental sustainability. BEACON education and human resource development plans include K-12 programs, novel curricula development, undergraduate and graduate training, a mentoring program for faculty and post-docs, and outreach programs to educate the general public.
Emergent Behaviors of Integrated Cellular Systems
Roger D. Kamm from the Massachusetts Institute of Technology (MIT) in partnership with researchers at the University of Illinois at Urbana-Champaign (UIUC) and Georgia Institute of Technology will establish a center to develop the science and technology to engineer clusters of living cells or "biological machines" that have desired functionalities and can perform prescribed tasks. This research will help to establish the nascent field of engineering biological systems. The center will develop programs aimed at attracting students to STEM (science, technology, engineering, mathematics) fields, and particularly to the growing area of bioengineering. An integrated inter-institutional graduate program will be developed and courses will be made accessible via OpenCourseWare.
Emerging Frontiers of Science of Information
Wojciech Szpankowski from Purdue University in partnership with colleagues at Bryn Mawr College, Howard University, MIT, Princeton, Stanford, UC Berkeley, UC San Diego, and UIUC will establish a Center for the Science of information that has the potential to launch the next information revolution. These researchers will develop a unifying set of principles to guide the extraction, manipulation, and exchange of information integrating elements of space, time, structure, semantics & context. The center will bring together researchers from diverse fields (physics, life science, chemistry, computer science, economics, etc.) to develop models and methods to apply to these diverse applications. The center will also build an active community of scholars through education and mentoring activities.
Center for Energy Efficient Electronics Science (E3S)
Eli Yablonovitch from University of California Berkeley in partnership with faculty members at MIT, Stanford, Contra Costa College, Los Angeles Trade Technical College and the Tuskegee Institute, proposed a center that will take on the challenge of increasing the energy efficiency of electronic information-processing equipment. Recent years have seen a dramatic increase in the share of electricity usage from electronics, and the trend is expected to continue unless fundamental changes are made to the power requirements of the basic logic switch. E3S will research concepts and scientific principles that could enable a few millivolt electronic switch as a successor to the transistor, laying the foundation for a million-fold reduction in power consumption by electronics. The center will also support a number of educational programs and promote energy awareness through outreach activities.
For Nanowires, Nothing Sparkles Quite Like Diamond
Diamond nanowires emit single photons, providing new options for high-speed computing, advanced imaging and secure communication
Diamonds are renowned for their seemingly flawless physical beauty and their interplay with light.Now researchers are taking advantage of the mineral's imperfections to control that light at the atomic scale, generating one photon at a time.
A team of engineers and applied physicists from Harvard University, the Technical University of Munich and Texas A&M has sculpted a novel nanowire from diamond crystal and shown that the wire can act as a source of single photons. The team reported its findings online Feb. 14 in the journal Nature Nanotechnology.
To create their diamond nanowire device, the researchers took advantage of the same physical processes that give some colored diamonds their hues. For example, when a diamond appears blue or yellow, the pure carbon of the diamond crystal has been sullied by scattered impurities that were incorporated into the carbon while the diamond was forming. Atoms of boron result in a blue diamond; atoms of nitrogen yield a yellow diamond.
The interloping atoms are trapped within their solid-state host, causing the perfect diamond latticework to bend to accommodate the imperfections and ultimately changing the electronic states in the atoms. In jewelry, the result is stunning color. In the nanowires, the result is a device that can generate a high flux of individual photons.
"The diamond nanowire device acts as a nanoscale antenna that funnels the emission of single photons from the embedded color center into a microscope lens," said lead researcher Marko Loncar of the School for Engineering and Applied Sciences (SEAS) at Harvard.
For the device, the researchers focused on diamond engineered with Nitrogen-Vacancy (NV) centers, where nitrogen atoms are adjacent to vacancies in the surrounding diamond crystal lattice. Researchers have known about NV centers for some time, and have demonstrated their utility for quantum communications, quantum computing, and nanoscale magnetic-field sensing. But until now, researchers had not engineered the diamond host, yielding a complete device that can be integrated into existing technologies.
"Using a standard manufacturing process, the team has achieved the unique combination of a nanostructure with an embedded defect, all within a commercially available crystal," said Dominique Dagenais, an expert in NSF's Division of Electrical, Communications and Cyber Systems who is familiar with the team's work. "The resulting device may prove easy to couple into a standard optical fiber, Dagenais added. "This novel approach is a key technological step towards achieving fast, secure computing and communication."
The current product is an array with thousands of diamond nanowires--each only a few millionths of a meter tall and 200 billionths of a meter in diameter--sitting on top of the macroscopic diamond crystal from which they came.
Because the NV centers are not uniformly distributed in the original diamond crystal, each wire has its imperfection in a different location, resulting in varied coupling between the NV centers and the diamond nanowire antennas. In the future, a technique called ion implantation could be used to generate the defect centers at predetermined locations, optimizing the devices.
"This exciting result is the first time the tools of nanofabrication have been applied to diamond crystals in order to control the optical properties of a single defect," said Loncar. "We hope that the greater diamond community will be able to leverage the excellent performance of this single photon source."
Loncar's co-authors included graduate student Tom Babinec, research scholar Birgit Hausmann, graduate student Yinan Zhang, and postdoctoral student Mughees Khan, all at SEAS; graduate student Jero Maze in the department of physics at Harvard; and faculty member Phil R. Hemmer at Texas A&M University.
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A team of engineers and applied physicists from Harvard University, the Technical University of Munich and Texas A&M has sculpted a novel nanowire from diamond crystal and shown that the wire can act as a source of single photons. The team reported its findings online Feb. 14 in the journal Nature Nanotechnology.
To create their diamond nanowire device, the researchers took advantage of the same physical processes that give some colored diamonds their hues. For example, when a diamond appears blue or yellow, the pure carbon of the diamond crystal has been sullied by scattered impurities that were incorporated into the carbon while the diamond was forming. Atoms of boron result in a blue diamond; atoms of nitrogen yield a yellow diamond.
The interloping atoms are trapped within their solid-state host, causing the perfect diamond latticework to bend to accommodate the imperfections and ultimately changing the electronic states in the atoms. In jewelry, the result is stunning color. In the nanowires, the result is a device that can generate a high flux of individual photons.
"The diamond nanowire device acts as a nanoscale antenna that funnels the emission of single photons from the embedded color center into a microscope lens," said lead researcher Marko Loncar of the School for Engineering and Applied Sciences (SEAS) at Harvard.
For the device, the researchers focused on diamond engineered with Nitrogen-Vacancy (NV) centers, where nitrogen atoms are adjacent to vacancies in the surrounding diamond crystal lattice. Researchers have known about NV centers for some time, and have demonstrated their utility for quantum communications, quantum computing, and nanoscale magnetic-field sensing. But until now, researchers had not engineered the diamond host, yielding a complete device that can be integrated into existing technologies.
"Using a standard manufacturing process, the team has achieved the unique combination of a nanostructure with an embedded defect, all within a commercially available crystal," said Dominique Dagenais, an expert in NSF's Division of Electrical, Communications and Cyber Systems who is familiar with the team's work. "The resulting device may prove easy to couple into a standard optical fiber, Dagenais added. "This novel approach is a key technological step towards achieving fast, secure computing and communication."
The current product is an array with thousands of diamond nanowires--each only a few millionths of a meter tall and 200 billionths of a meter in diameter--sitting on top of the macroscopic diamond crystal from which they came.
Because the NV centers are not uniformly distributed in the original diamond crystal, each wire has its imperfection in a different location, resulting in varied coupling between the NV centers and the diamond nanowire antennas. In the future, a technique called ion implantation could be used to generate the defect centers at predetermined locations, optimizing the devices.
"This exciting result is the first time the tools of nanofabrication have been applied to diamond crystals in order to control the optical properties of a single defect," said Loncar. "We hope that the greater diamond community will be able to leverage the excellent performance of this single photon source."
Loncar's co-authors included graduate student Tom Babinec, research scholar Birgit Hausmann, graduate student Yinan Zhang, and postdoctoral student Mughees Khan, all at SEAS; graduate student Jero Maze in the department of physics at Harvard; and faculty member Phil R. Hemmer at Texas A&M University.
Watching Crystals Grow May Lead to Faster Electronic Devices
Research could improve manufacture of defect-free, thin films needed to make semiconductors
The quest for faster electronic devices recently got something more than a little bump up in technological knowhow. Scientists at Cornell University, Ithaca, N.Y. discovered that the thin, smooth, crystalline sheets needed to make semiconductors, which are the foundation of modern computers, might be grown into smoother sheets by managing the random darting motions of the atomic particles that affect how the crystals grow.
"The main benefit of smooth crystalline films in electronic devices is that electrons can travel from one place to another in a device with minimal disruption," said Charles Ying, program director in the National Science Foundation's Division of Materials Research. "This in turn leads to faster electronics and lower electricity consumption."
The research is funded in part by the Cornell Center for Materials Research, which is supported by the National Science Foundation. Findings are reported in the Jan. 22 online edition of the journal Science.
Led by assistant professor of physics Itai Cohen at Cornell, researchers recreated conditions of layer-by-layer crystalline growth using particles much bigger than atoms, but still small enough that they behave like atoms. Similar to using beach balls to model the behavior of sand, scientists used a solution of tiny plastic spheres 50 times smaller than a human hair to reproduce the conditions that lead to crystallization on the atomic scale. With this precise modeling, they could watch how crystalline sheets grow.
Using an optical microscope, the scientists could watch exactly what their "atoms"--actually, micron-sized silica particles suspended in fluid--did as they crystallized. What's more, they were able to manipulate single particles one at a time and test conditions that lead to smooth crystal growth.
"These particles are big and slow enough that you can see what's going on in real time," explained graduate student Mark Buckley. Watching them, researchers discovered that the random darting motion of a particle is a key factor that affects how crystals grow.
While some materials grow smooth crystals, others tend to develop bumps and defects--a serious problem for thin-film manufacturing. Researchers are trying to improve the process at the atomic scale, but a major challenge to growing thin films with atoms is that the atoms often randomly form mounds, rather than crystallizing into thin sheets.
This happens because as atoms are deposited onto a substrate, they initially form small crystals, called islands. When more atoms are dumped on top of these crystals, the atoms tend to stay atop the islands, rather than hopping off the edges. This creates the pesky rough spots, "and it's game over" for a perfect thin film, Cohen said.
Conventional theory says that atoms that land on top of islands feel an energetic "pull" from other atoms that keeps them from rolling off. In the system used for the experiment, the researchers eliminated this pull by shortening the bonds between their particles. But they still saw that their particles hesitated at the islands' edges.
Further analysis using optical tweezers that manipulated individual particles allowed the researchers to measure just how long it took for particles to move off the crystal islands. Because the particles were suspended in a fluid that knocks them about, they exhibited Brownian motion--a random walk of sorts. As the particles move and diffuse from one area to another, the researchers noted that the distance a particle had to travel to "fall" off an island's edge was three times farther than moving laterally from one site on the island to another. Because the particles have to traverse this distance in a Brownian fashion, it can take particles nine times longer to complete the "fall." This difference explained why the researchers still saw a barrier at the island edge.
Atoms on an atomic crystalline film move in a manner similar to the Brownian particles, since the vibrations of the underlying crystal, called phonons, tend to jostle them about. The researchers surmised that in addition to the bonding between the atoms, this random motion may also contribute to the barrier at the crystal's edge, and hence, the roughness of the crystal film.
"If the principles we have uncovered can be applied to the atomic scale, scientists will be able to better control the growth of thin films used to manufacture electronic components for our computers and cell phones," Cohen said.
The paper's authors are former postdoctoral associate Rajesh Ganapathy, now a faculty member Jawaharlal Nehru Centre for Advanced Scientific Research in Bangalore, India, as well as Sharon Gerbode and Mark Buckley, graduate students in the Cohen lab at Cornell.
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"The main benefit of smooth crystalline films in electronic devices is that electrons can travel from one place to another in a device with minimal disruption," said Charles Ying, program director in the National Science Foundation's Division of Materials Research. "This in turn leads to faster electronics and lower electricity consumption."
The research is funded in part by the Cornell Center for Materials Research, which is supported by the National Science Foundation. Findings are reported in the Jan. 22 online edition of the journal Science.
Led by assistant professor of physics Itai Cohen at Cornell, researchers recreated conditions of layer-by-layer crystalline growth using particles much bigger than atoms, but still small enough that they behave like atoms. Similar to using beach balls to model the behavior of sand, scientists used a solution of tiny plastic spheres 50 times smaller than a human hair to reproduce the conditions that lead to crystallization on the atomic scale. With this precise modeling, they could watch how crystalline sheets grow.
Using an optical microscope, the scientists could watch exactly what their "atoms"--actually, micron-sized silica particles suspended in fluid--did as they crystallized. What's more, they were able to manipulate single particles one at a time and test conditions that lead to smooth crystal growth.
"These particles are big and slow enough that you can see what's going on in real time," explained graduate student Mark Buckley. Watching them, researchers discovered that the random darting motion of a particle is a key factor that affects how crystals grow.
While some materials grow smooth crystals, others tend to develop bumps and defects--a serious problem for thin-film manufacturing. Researchers are trying to improve the process at the atomic scale, but a major challenge to growing thin films with atoms is that the atoms often randomly form mounds, rather than crystallizing into thin sheets.
This happens because as atoms are deposited onto a substrate, they initially form small crystals, called islands. When more atoms are dumped on top of these crystals, the atoms tend to stay atop the islands, rather than hopping off the edges. This creates the pesky rough spots, "and it's game over" for a perfect thin film, Cohen said.
Conventional theory says that atoms that land on top of islands feel an energetic "pull" from other atoms that keeps them from rolling off. In the system used for the experiment, the researchers eliminated this pull by shortening the bonds between their particles. But they still saw that their particles hesitated at the islands' edges.
Further analysis using optical tweezers that manipulated individual particles allowed the researchers to measure just how long it took for particles to move off the crystal islands. Because the particles were suspended in a fluid that knocks them about, they exhibited Brownian motion--a random walk of sorts. As the particles move and diffuse from one area to another, the researchers noted that the distance a particle had to travel to "fall" off an island's edge was three times farther than moving laterally from one site on the island to another. Because the particles have to traverse this distance in a Brownian fashion, it can take particles nine times longer to complete the "fall." This difference explained why the researchers still saw a barrier at the island edge.
Atoms on an atomic crystalline film move in a manner similar to the Brownian particles, since the vibrations of the underlying crystal, called phonons, tend to jostle them about. The researchers surmised that in addition to the bonding between the atoms, this random motion may also contribute to the barrier at the crystal's edge, and hence, the roughness of the crystal film.
"If the principles we have uncovered can be applied to the atomic scale, scientists will be able to better control the growth of thin films used to manufacture electronic components for our computers and cell phones," Cohen said.
The paper's authors are former postdoctoral associate Rajesh Ganapathy, now a faculty member Jawaharlal Nehru Centre for Advanced Scientific Research in Bangalore, India, as well as Sharon Gerbode and Mark Buckley, graduate students in the Cohen lab at Cornell.
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