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News Article | September 27, 2016
Site: www.cemag.us

A team of scientists studying solar cells made from cadmium telluride, a promising alternative to silicon, has discovered that microscopic "fault lines" within and between crystals of the material act as conductive pathways that ease the flow of electric current. This research—conducted at the University of Connecticut and the U.S. Department of Energy's Brookhaven National Laboratory, and described in the journal Nature Energy—may help explain how a common processing technique turns cadmium telluride into an excellent material for transforming sunlight into electricity, and suggests a strategy for engineering more efficient solar devices that surpass the performance of silicon. "If you look at semiconductors like silicon, defects in the crystals are usually bad," said co-author Eric Stach, a physicist at Brookhaven Lab's Center for Functional Nanomaterials (CFN). As Stach explained, misplaced atoms or slight shifts in their alignment often act as traps for the particles that carry electric current—negatively charged electrons or the positively charged "holes" left behind when electrons are knocked loose by photons of sunlight, making them more mobile. The idea behind solar cells is to separate the positive and negative charges and run them through a circuit so the current can be used to power houses, satellites, or even cities. Defects interrupt this flow of charges and keep the solar cell from being as efficient as it could be. But in the case of cadmium telluride, the scientists found that boundaries between individual crystals and "planar defects"—fault-like misalignments in the arrangement of atoms—create pathways for conductivity, not traps. Members of Bryan Huey's group at the Institute of Materials Science at the University of Connecticut were the first to notice the surprising connection. In an effort to understand the effects of a chloride solution treatment that greatly enhances cadmium telluride's conductive properties, Justin Luria and Yasemin Kutes studied solar cells before and after treatment. But they did so in a unique way. Several groups around the world had looked at the surfaces of such solar cells before, often with a tool known as a conducting atomic force microscope. The microscope has a fine probe many times sharper than the head of a pin that scans across the material's surface to track the topographic features—the hills and valleys of the surface structure—while simultaneously measuring location-specific conductivity. Scientists use this technique to explore how the surface features relate to solar cell performance at the nanoscale. But no one had devised a way to make measurements beneath the surface, the most important part of the solar cell. This is where the UConn team made an important breakthrough. They used an approach developed and perfected by Kutes and Luria over the last two years to acquire hundreds of sequential images, each time intentionally removing a nanoscale layer of the material, so they could scan through the entire thickness of the sample. They then used these layer-by-layer images to build up a three-dimensional, high-resolution 'tomographic' map of the solar cell—somewhat like a computed tomography (CT) brain scan. "Everyone using these microscopes basically takes pictures of the 'ground,' and interprets what is beneath," Huey said. "It may look like there's a cave, or a rock shelf, or a building foundation down there. But we can only really know once we carefully dig, like archeologists, keeping track of exactly what we find every step of the way—though, of course, at a much, much smaller scale." The resulting CT-AFM maps uniquely revealed current flowing most freely along the crystal boundaries and fault-like defects in the cadmium telluride solar cells. The samples that had been treated with the chloride solution had more defects overall, a higher density of these defects, and what appeared to be a high degree of connectivity among them, while the untreated samples had few defects, no evidence of connectivity, and much lower conductivity. Huey's team suspected that the defects were so-called planar defects, usually caused by shifts in atomic alignments or stacking arrangements within the crystals. But the CTAFM system is not designed to reveal such atomic-scale structural details. To get that information, the UConn team turned to Stach, head of the electron microscopy group at the CFN, a DOE Office of Science User Facility. "Having previously shared ideas with Eric, it was a natural extension of our discovery to work with his group," Huey said. Said Stach, "This is the exact type of problem the CFN is set up to handle, providing expertise and equipment that university researchers may not have to help drive science from hypothesis to discovery." CFN staff physicist Lihua Zhang used a transmission electron microscope (TEM) and UConn's results as a guide to meticulously study how atomic scale features of chloride-treated cadmium telluride related to the conductivity maps. The TEM images revealed the atomic structure of the defects, confirming that they were due to specific changes in the stacking sequence of atoms in the material. The images also showed clearly that these planar defects connected different grains in the crystal, leading to high-conductivity pathways for the movement of electrons and holes. "When we looked at the regions with good conductivity, the planar defects linked from one crystal grain to another, forming continuous pathways of conductance through the entire thickness of the material," said Zhang. "So the regions that had the best conductivity were the ones that had a high degree of connectivity among these defects." The authors say it's possible that the chloride treatment helps to create the connectivity, not just more defects, but that more research is needed to definitively determine the most significant effects of the chloride solution treatment. In any case, Stach says that combining the CTAFM technique and electron microscopy, yields a "clear winner" in the search for more efficient, cost-competitive alternatives to silicon solar cells, which have nearly reached their limit for efficiency. "There is already a billion-dollar-a-year industry making cadmium telluride solar cells, and lots of work exploring other alternatives to silicon. But all of these alternatives, because of their crystal structure, have a higher tendency to form defects," he said. "This work gives us a systematic method we can use to understand if the defects are good or bad in terms of conductivity. It can also be used to explore the effects of different processing methods or chemicals to control how defects form. In the case of cadmium telluride, we may want to find ways to make more of these defects, or look for other materials in which defects improve performance." This research was supported by the DOE Office of Energy Efficiency and Renewable Energy (EERE)—including its SunShot Initiative—and the DOE Office of Science. The cadmium telluride samples were provided by Andrew Moore of Colorado State University.


News Article | April 22, 2016
Site: www.cemag.us

Worldwide growing data volumes make conventional electronic processing reach its limits. Future information technology is therefore expected to use light as a medium for quick data transmission also within computer chips. Researchers under the direction of KIT have demonstrated that carbon nanotubes are suited for use as on-chip light source for tomorrow’s information technology, when nanostructured waveguides are applied to obtain the desired light properties. The scientists have presented their results in Nature Photonics. On the large scale, data transmission by light has long become a matter of routine: Glass fiber cables as light waveguides transmit telephone and internet signals, for instance. For using the advantages of light, i.e. speed and energy efficiency, also on the small scale of computer chips, researchers of KIT have made an important step from fundamental research towards application. By the integration of smallest carbon nanotubes into a nanostructured waveguide, they have developed a compact miniaturized switching element that converts electric signals into clearly defined optical signals. “The nanostructures act like a photonic crystal and allow for customizing the properties of light from the carbon nanotube,” Felix Pyatkov and Valentin Fütterling, the first authors of the study of KIT’s Institute of Nanotechnology, explain. “In this way, we can generate narrow-band light in the desired color on the chip.” Processing of the waveguide precisely defines the wavelength at which the light is transmitted. By engravings using electron beam lithography, the waveguides of several micrometers in length are provided with finest cavities of a few nanometers in size. They determine the waveguide’s optical properties. The resulting photonic crystals reflect the light in certain colors, a phenomenon observed in nature on apparently colorful butterfly wings. As novel light sources, carbon nanotubes of about 1 micrometer in length and 1 nanometer in diameter are positioned on metal contacts in transverse direction to the waveguide. At KIT, a process was developed, by means of which the nanotubes can be integrated specifically into highly complex structures. The researchers applied the method of dielectrophoresis for deposition of carbon nanotubes from the solution and their arrangement vertically to the waveguide. This way of separating particles using inhomogeneous electric fields was originally used in biology and is highly suited to deposit nanoscaled objects on carrier materials. The carbon nanotubes integrated into the waveguide act as a small light source. When electric voltage is applied, they produce photons. The compact electricity/light signal converter presented now meets the requirements of the next generation of computers that combine electronic components with nanophotonic waveguides. The signal converter bundles the light about as strongly as a laser and responds to variable signals with high speed. Already now, the optoelectronic components developed by the researchers can be used to produce light signals in the gigahertz frequency range from electric signals. Among the leading researchers involved in the project were Ralph Krupke, who conducts research at the KIT Institute of Nanotechnology and at the Institute of Materials Science of TU Darmstadt, Wolfram H.P. Pernice, who moved from the KIT to the University of Münster one year ago, and Manfred M. Kappes, Institute of Physical Chemistry and Institute of Nanotechnology of KIT. The project was funded by the Science and Technology of Nanosystems (STN) programme of the Helmholtz Association. It is aimed at studying nanosystems of unique functionality and the potential of materials of a few nanometers in structural size. The Volkswagen Foundation financed a Ph.D. student position for the research project. In addition, the project was supported by the Karlsruhe Nano Micro Facility (KNMF) platform. Source: KIT – The Research University in the Helmholtz Association


Carbon nanotube above a photonic crystal waveguide with electrodes. The structure converts electric signals into light. Credit: WWU Worldwide growing data volumes make conventional electronic processing reach its limits. Future information technology is therefore expected to use light as a medium for quick data transmission also within computer chips. Researchers under the direction of KIT have now demonstrated that carbon nanotubes are suited for use as on-chip light source for tomorrow's information technology, when nanostructured waveguides are applied to obtain the desired light properties. The scientists now present their results in Nature Photonics. On the large scale, data transmission by light has long become a matter of routine: Glass fiber cables as light waveguides transmit telephone and internet signals, for instance. For using the advantages of light, i.e. speed and energy efficiency, also on the small scale of computer chips, researchers of KIT have made an important step from fundamental research towards application. By the integration of smallest carbon nanotubes into a nanostructured waveguide, they have developed a compact miniaturized switching element that converts electric signals into clearly defined optical signals. "The nanostructures act like a photonic crystal and allow for customizing the properties of light from the carbon nanotube," Felix Pyatkov and Valentin Fütterling, the first authors of the study of KIT's Institute of Nanotechnology, explain. "In this way, we can generate narrow-band light in the desired color on the chip." Processing of the waveguide precisely defines the wavelength at which the light is transmitted. By engravings using electron beam lithography, the waveguides of several micrometers in length are provided with finest cavities of a few nanometers in size. They determine the waveguide's optical properties. The resulting photonic crystals reflect the light in certain colors, a phenomenon observed in nature on apparently colorful butterfly wings. As novel light sources, carbon nanotubes of about 1 micrometer in length and 1 nanometer in diameter are positioned on metal contacts in transverse direction to the waveguide. At KIT, a process was developed, by means of which the nanotubes can be integrated specifically into highly complex structures. The researchers applied the method of dielectrophoresis for deposition of carbon nanotubes from the solution and their arrangement vertically to the waveguide. This way of separating particles using inhomogeneous electric fields was originally used in biology and is highly suited to deposit nanoscaled objects on carrier materials. The carbon nanotubes integrated into the waveguide act as a small light source. When electric voltage is applied, they produce photons. The compact electricity/light signal converter presented now meets the requirements of the next generation of computers that combine electronic components with nanophotonic waveguides. The signal converter bundles the light about as strongly as a laser and responds to variable signals with high speed. Already now, the optoelectronic components developed by the researchers can be used to produce light signals in the gigahertz frequency range from electric signals. Among the leading researchers involved in the project were Ralph Krupke, who conducts research at the KIT Institute of Nanotechnology and at the Institute of Materials Science of TU Darmstadt, Wolfram H.P. Pernice, who moved from the KIT to the University of Münster one year ago, and Manfred M. Kappes, Institute of Physical Chemistry and Institute of Nanotechnology of KIT. The project was funded by the Science and Technology of Nanosystems (STN) programme of the Helmholtz Association. It is aimed at studying nanosystems of unique functionality and the potential of materials of a few nanometers in structural size. The Volkswagen Foundation financed a Ph.D. student position for the research project. In addition, the project was supported by the Karlsruhe Nano Micro Facility (KNMF) platform. Explore further: World-record micrometer-sized converter of electrical into optical signals More information: Felix Pyatkov et al. Cavity-enhanced light emission from electrically driven carbon nanotubes, Nature Photonics (2016). DOI: 10.1038/NPHOTON.2016.70


Home > Press > Nature Photonics: Light source for quicker computer chips: Waveguide with integrated carbon nanotubes for conversion of electric signals into light / quicker computer chips are feasible / publication in Nature Photonics Abstract: Worldwide growing data volumes make conventional electronic processing reach its limits. Future information technology is therefore expected to use light as a medium for quick data transmission also within computer chips. Researchers under the direction of KIT have now demonstrated that carbon nanotubes are suited for use as on-chip light source for tomorrow's information technology, when nanostructured waveguides are applied to obtain the desired light properties. The scientists now present their results in Nature Photonics. DOI: 10.1038/NPHOTON. 2016.70 On the large scale, data transmission by light has long become a matter of routine: Glass fiber cables as light waveguides transmit telephone and internet signals, for instance. For using the advantages of light, i.e. speed and energy efficiency, also on the small scale of computer chips, researchers of KIT have made an important step from fundamental research towards application. By the integration of smallest carbon nanotubes into a nanostructured waveguide, they have developed a compact miniaturized switching element that converts electric signals into clearly defined optical signals. "The nanostructures act like a photonic crystal and allow for customizing the properties of light from the carbon nanotube," Felix Pyatkov and Valentin Fütterling, the first authors of the study of KIT's Institute of Nanotechnology, explain. "In this way, we can generate narrow-band light in the desired color on the chip." Processing of the waveguide precisely defines the wavelength at which the light is transmitted. By engravings using electron beam lithography, the waveguides of several micrometers in length are provided with finest cavities of a few nanometers in size. They determine the waveguide's optical properties. The resulting photonic crystals reflect the light in certain colors, a phenomenon observed in nature on apparently colorful butterfly wings. As novel light sources, carbon nanotubes of about 1 micrometer in length and 1 nanometer in diameter are positioned on metal contacts in transverse direction to the waveguide. At KIT, a process was developed, by means of which the nanotubes can be integrated specifically into highly complex structures. The researchers applied the method of dielectrophoresis for deposition of carbon nanotubes from the solution and their arrangement vertically to the waveguide. This way of separating particles using inhomogeneous electric fields was originally used in biology and is highly suited to deposit nanoscaled objects on carrier materials. The carbon nanotubes integrated into the waveguide act as a small light source. When electric voltage is applied, they produce photons. The compact electricity/light signal converter presented now meets the requirements of the next generation of computers that combine electronic components with nanophotonic waveguides. The signal converter bundles the light about as strongly as a laser and responds to variable signals with high speed. Already now, the optoelectronic components developed by the researchers can be used to produce light signals in the gigahertz frequency range from electric signals. Among the leading researchers involved in the project were Ralph Krupke, who conducts research at the KIT Institute of Nanotechnology and at the Institute of Materials Science of TU Darmstadt, Wolfram H.P. Pernice, who moved from the KIT to the University of Münster one year ago, and Manfred M. Kappes, Institute of Physical Chemistry and Institute of Nanotechnology of KIT. The project was funded by the Science and Technology of Nanosystems (STN) programme of the Helmholtz Association. It is aimed at studying nanosystems of unique functionality and the potential of materials of a few nanometers in structural size. The Volkswagen Foundation financed a Ph.D. student position for the research project. In addition, the project was supported by the Karlsruhe Nano Micro Facility (KNMF) platform. About Karlsruhe Institute of Technology (KIT) Karlsruhe Institute of Technology (KIT) pools its three core tasks of research, higher education, and innovation in a mission. With about 9,300 employees and 25,000 students, KIT is one of the big institutions of research and higher education in natural sciences and engineering in Europe. KIT - The Research University in the Helmholtz Association Since 2010, the KIT has been certified as a family-friendly university. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


Home > Press > Crystalline Fault Lines Provide Pathway for Solar Cell Current: New tomographic AFM imaging technique reveals that microstructural defects, generally thought to be detrimental, actually improve conductivity in cadmium telluride solar cells Abstract: A team of scientists studying solar cells made from cadmium telluride, a promising alternative to silicon, has discovered that microscopic "fault lines" within and between crystals of the material act as conductive pathways that ease the flow of electric current. This research-conducted at the University of Connecticut and the U.S. Department of Energy's Brookhaven National Laboratory, and described in the journal Nature Energy-may help explain how a common processing technique turns cadmium telluride into an excellent material for transforming sunlight into electricity, and suggests a strategy for engineering more efficient solar devices that surpass the performance of silicon. "If you look at semiconductors like silicon, defects in the crystals are usually bad," said co-author Eric Stach, a physicist at Brookhaven Lab's Center for Functional Nanomaterials (CFN). As Stach explained, misplaced atoms or slight shifts in their alignment often act as traps for the particles that carry electric current-negatively charged electrons or the positively charged "holes" left behind when electrons are knocked loose by photons of sunlight, making them more mobile. The idea behind solar cells is to separate the positive and negative charges and run them through a circuit so the current can be used to power houses, satellites, or even cities. Defects interrupt this flow of charges and keep the solar cell from being as efficient as it could be. But in the case of cadmium telluride, the scientists found that boundaries between individual crystals and "planar defects"-fault-like misalignments in the arrangement of atoms-create pathways for conductivity, not traps. Members of Bryan Huey's group at the Institute of Materials Science at the University of Connecticut were the first to notice the surprising connection. In an effort to understand the effects of a chloride solution treatment that greatly enhances cadmium telluride's conductive properties, Justin Luria and Yasemin Kutes studied solar cells before and after treatment. But they did so in a unique way. Several groups around the world had looked at the surfaces of such solar cells before, often with a tool known as a conducting atomic force microscope. The microscope has a fine probe many times sharper than the head of a pin that scans across the material's surface to track the topographic features-the hills and valleys of the surface structure-while simultaneously measuring location-specific conductivity. Scientists use this technique to explore how the surface features relate to solar cell performance at the nanoscale. But no one had devised a way to make measurements beneath the surface, the most important part of the solar cell. This is where the UConn team made an important breakthrough. They used an approach developed and perfected by Kutes and Luria over the last two years to acquire hundreds of sequential images, each time intentionally removing a nanoscale layer of the material, so they could scan through the entire thickness of the sample. They then used these layer-by-layer images to build up a three-dimensional, high-resolution 'tomographic' map of the solar cell-somewhat like a computed tomography (CT) brain scan. "Everyone using these microscopes basically takes pictures of the 'ground,' and interprets what is beneath," Huey said. "It may look like there's a cave, or a rock shelf, or a building foundation down there. But we can only really know once we carefully dig, like archeologists, keeping track of exactly what we find every step of the way-though, of course, at a much, much smaller scale." The resulting CT-AFM maps uniquely revealed current flowing most freely along the crystal boundaries and fault-like defects in the cadmium telluride solar cells. The samples that had been treated with the chloride solution had more defects overall, a higher density of these defects, and what appeared to be a high degree of connectivity among them, while the untreated samples had few defects, no evidence of connectivity, and much lower conductivity. Huey's team suspected that the defects were so-called planar defects, usually caused by shifts in atomic alignments or stacking arrangements within the crystals. But the CTAFM system is not designed to reveal such atomic-scale structural details. To get that information, the UConn team turned to Stach, head of the electron microscopy group at the CFN, a DOE Office of Science User Facility. "Having previously shared ideas with Eric, it was a natural extension of our discovery to work with his group," Huey said. Said Stach, "This is the exact type of problem the CFN is set up to handle, providing expertise and equipment that university researchers may not have to help drive science from hypothesis to discovery." CFN staff physicist Lihua Zhang used a transmission electron microscope (TEM) and UConn's results as a guide to meticulously study how atomic scale features of chloride-treated cadmium telluride related to the conductivity maps. The TEM images revealed the atomic structure of the defects, confirming that they were due to specific changes in the stacking sequence of atoms in the material. The images also showed clearly that these planar defects connected different grains in the crystal, leading to high-conductivity pathways for the movement of electrons and holes. "When we looked at the regions with good conductivity, the planar defects linked from one crystal grain to another, forming continuous pathways of conductance through the entire thickness of the material," said Zhang. "So the regions that had the best conductivity were the ones that had a high degree of connectivity among these defects." The authors say it's possible that the chloride treatment helps to create the connectivity, not just more defects, but that more research is needed to definitively determine the most significant effects of the chloride solution treatment. In any case, Stach says that combining the CTAFM technique and electron microscopy, yields a "clear winner" in the search for more efficient, cost-competitive alternatives to silicon solar cells, which have nearly reached their limit for efficiency. "There is already a billion-dollar-a-year industry making cadmium telluride solar cells, and lots of work exploring other alternatives to silicon. But all of these alternatives, because of their crystal structure, have a higher tendency to form defects," he said. "This work gives us a systematic method we can use to understand if the defects are good or bad in terms of conductivity. It can also be used to explore the effects of different processing methods or chemicals to control how defects form. In the case of cadmium telluride, we may want to find ways to make more of these defects, or look for other materials in which defects improve performance." This research was supported by the DOE Office of Energy Efficiency and Renewable Energy (EERE)-including its Sunshot Program-and the DOE Office of Science. The cadmium telluride samples were provided by Andrew Moore of Colorado State University. The University of Connecticut's Institute of Materials Science serves as the heart of materials science research at the University of Connecticut, with a mission of supporting materials research and industry throughout Connecticut and the Northeast. It houses the research labs of more than 30 core faculty, with an overall membership of 120 UConn faculty whose work benefits from the available facilities and expertise. About Brookhaven National Laboratory Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov. One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit applied science and technology organization. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


News Article | October 8, 2016
Site: www.nanotech-now.com

Home > Press > When Push Comes to Shove: Size Matters for Particles in Bloodstream Abstract: Researchers at the University of Connecticut have uncovered new information about how particles behave in our bloodstream, an important advancement that could help pharmaceutical scientists develop more effective cancer drugs. Making sure cancer medications reach the leaky blood vessels surrounding most tumor sites is one of the critical aspects of treatment and drug delivery. While surface chemistry, molecular interactions, and other factors come into play once drug-carrying particles arrive at a tumor, therapeutic medication doesn't do very much good if it never reaches its intended target. Anson Ma, an assistant professor of chemical and biomolecular engineering at UConn, used a microfluidic channel device to observe, track, and measure how individual particles behaved in a simulated blood vessel. The research team's goal: to learn more about the physics influencing a particle's behavior as it travels in our blood and to determine which particle size might be the most effective for delivering drugs to their targets. The team's experimental findings mark the first time such quantitative data has been gathered. The study was published Oct. 4 in the Biophysical Journal. "Even before particles reach a target site, you have to worry about what is going to happen with them after they get injected into the bloodstream," Ma says. "Are they going to clump together? How are they going to move around? Are they going to get swept away and flushed out of our bodies?" Using a high-powered fluorescence microscope in UConn's Complex Fluids Lab, Ma was able to observe particles being carried along in the simulated blood vessel in what could be described as a vascular Running of the Bulls. Red blood cells race through the middle of the channel as the particles - highlighted under the fluorescent light - get carried along in the rush, bumping and bouncing off the blood cells until they are pushed to open spaces - called the cell-free layer - along the vessel's walls. What Ma found was that larger particles - the optimum size appeared to be about 2 microns - were most likely to get pushed to the cell-free layer where their chances of carrying medication into a tumor site are greatest. The research team also determined that 2 microns was the largest size that should be used if particles are going to have any chance of going through the leaky blood vessel walls into the tumor site. "When it comes to using particles for the delivery of cancer drugs, size matters," Ma says. "When you have a bigger particle, the chance of it bumping into blood cells is much higher, there are a lot more collisions, and they tend to get pushed to the blood vessel walls." The results were somewhat surprising. In preparing their hypothesis, the research team estimated that smaller particles were probably the most effective since they would move the most in collisions with blood cells, much like what happens when a small ball bounces off a larger one. But just the opposite proved true. The smaller particles appeared to skirt through the mass of moving blood cells and were less likely to experience the "trampoline" effect and get bounced to the cell-free layer, says Ma. The research was funded by the National Science Foundation's Early-concept Grants for Exploratory Research or EAGER program, which supports exploratory work in its early stages on untested, but potentially transformative, research ideas or approaches. Knowing how particles behave in our circulatory system should help improve targeted drug delivery, Ma says, which in turn will further reduce the toxic side effects caused by potent cancer drugs missing their target and impacting the body's healthy tissue. Measuring how different sized particles move in the bloodstream may also be beneficial in bioimaging, where scientists and doctors want to keep particles circulating in the bloodstream long enough for imaging to occur. In that case, smaller particles would be better, says Ma. Moving forward, Ma would like to explore other aspects of particle flow in our circulatory system such as how particles behave when they pass through a constricted area, such as from a blood vessel to a capillary. Capillaries are only about 7 microns in diameter. The average human hair is 100 microns. Ma says he would like to know how that constricted space might impact particle flow or the ability of particles to accumulate near the vessel walls. "We have all of this complex geometry in our bodies," says Ma. "Most people just assume there is no impact when a particle moves from a bigger channel to a smaller channel because they haven't quantified it. Our plan is to do some experiments to look at this more carefully, building on the work that we just published." ### Joining Ma on the study were Ph.D. candidate Erik Carboni; Dr. Brice Bognet from UConn's polymer program in the Institute of Materials Science; Chemical and Biomolecular Engineering Associate Professor Leslie Shor; Ph.D. students Grant Bouchillon and Andrea Kadilak; and undergraduate student Michael Ward. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


News Article | September 27, 2016
Site: www.rdmag.com

Whether for use in safe data encryption, ultrafast calculation of huge data volumes or so-called quantum simulation of highly complex systems: Optical quantum computers are a source of hope for tomorrow's computer technology. For the first time, scientists now have succeeded in placing a complete quantum optical structure on a chip, as outlined Nature Photonics. This fulfills one condition for the use of photonic circuits in optical quantum computers. "Experiments investigating the applicability of optical quantum technology so far have often claimed whole laboratory spaces," explains Professor Ralph Krupke of the KIT. "However, if this technology is to be employed meaningfully, it must be accommodated on a minimum of space." Participants in the study were scientists from Germany, Poland, and Russia under the leadership of Professors Wolfram Pernice of the Westphalian Wilhelm University of Münster (WWU) and Ralph Krupke, Manfred Kappes, and Carsten Rockstuhl of the Karlsruhe Institute of Technology (KIT). The light source for the quantum photonic circuit used by the scientists for the first time were special nanotubes made of carbon. They have a diameter 100,000 times smaller than a human hair, and they emit single light particles when excited by laser light. Light particles (photons) are also referred to as light quanta. Hence the term "quantum photonics." That carbon tubes emit single photons makes them attractive as ultracompact light sources for optical quantum computers. "However, it is not easily possible to accommodate the laser technology on a scalable chip," admits physicist Wolfram Pernice. The scalability of a system, i.e. the possibility to miniaturize components so as to be able to increase their number, is a precondition for this technology to be used in powerful computers up to an optical quantum computer. As all elements on the chip now developed are triggered electrically, no additional laser systems are required any more, which is a marked simplification over the optical excitation normally used. "The development of a scalable chip on which a single-photon source, detector, and waveguide are combined, is an important step for research," emphasizes Ralph Krupke, who conducts research at the KIT Institute for Nanotechnology and the Institute of Materials Science of the Darmstadt Technical University. "As we were able to show that single photons can be emitted also by electric excitation of the carbon nanotubes, we have overcome a limiting factor so far preventing potential applicability." About the methodology: The scientists studied whether the flow of electricity through carbon nanotubes caused single light quanta to be emitted. For this purpose, they used carbon nanotubes as single-photon sources, superconducting nanowires as detectors, and nanophotonic waveguides. One single-photon source and two detectors each were connected with one waveguide. The structure was cooled with liquid helium to allow single light quanta to be counted. The chips were produced in an electron beam scribing device. The scientists' work is fundamental research. It is not yet clear whether and when it will lead to practical applications. Wolfram Pernice and the first author, Svetlana Khasminskaya, were supported by the Deutsche Forschungsgemeinschaft and the Helmholtz-Gemeinschaft, Ralph Krupke was funded by the Volkswagen Foundation.


News Article | October 27, 2015
Site: phys.org

Professor Challa V. Kumar, who holds appointments in the departments of Chemistry, Molecular and Cell Biology, and the Institute of Materials Science, and his team have created a gel that enhances the ability of solar cells to absorb energy from sunlight. Sunlight strikes Earth every day with more energy than is used globally in a year. But finding an efficient way to capture and store solar energy to replace fossil fuels as the world's go-to energy source remains a challenge. "Most of the light from the sun is emitted over a very broad window of wavelengths," says Kumar, who recently presented his work at the 250th National Meeting & Exposition of the American Chemical Society in Boston. "If you want to use solar energy to produce electric current, you want to harvest as much of that spectrum as possible." Silicon photovoltaic solar cells, the most common type currently used on rooftop panels to convert photons – tiny particles of light – into electricity, can't take advantage of the blue part of the light spectrum. Only photons with the right amount of energy get absorbed by the photovoltaic cell. The antenna built by Kumar and his team, collects unused blue photons in the light spectrum and, via a process of "artificial photosynthesis," converts them to lower energy photons that the silicon can then turn into current, Kumar explains. Taking inspiration from plants, the team used a mixture of biodegradable materials to collect sunlight, much like plant chlorophyll. The concoction includes cow blood protein (a waste product in the meat industry), fatty acid from coconuts, and different organic dyes. Together these substances form a gel that, when placed in a Gratzel cell, a particular type of solar cell, increases their absorption of unused photons and the power output of the cell. "This process is great for coating solar cells' light-emitting diodes, which mostly emit in the blue region," Kumar says. "Our vision is to integrate this technology into the manufacturing process of solar panels, which cost homeowners thousands of dollars, to make them more affordable and efficient. Kumar says that many groups around the world are working to make this kind of antenna, but claims his is the first of its kind. He says the gel is easy to make and relatively inexpensive, but the mixture needs to be stable and tough enough to last multiple years to be incorporated into existing manufacturing techniques. The University has filed a provisional patent application, and Kumar is working with a Connecticut company to figure out how to apply the gel to silicon solar cells. Explore further: New kind of solar cell could capture significantly more energy than current cells


Pradhan S.K.,Institute of Materials Science
Journal of Materials Science: Materials in Electronics | Year: 2013

Monophasic rhombohedral structure of BiFeO3 electroceramic is successfully synthesized by conventional solid state reaction route followed by slow step sintering schedule. Effect of sintering temperature is found to greatly influence its structural, dielectric, ferroelectric, capacitance and leakage behavior of bulk ceramic. From XRD analysis it is seen that at lower sintering temperature (750 C) bulk BiFeO3 sample showed rhombohedral structure (R3c) along with few impurity phases, which become suppressed at higher sintering temperature and facilitates the compactness of grains and formation of dense microstructure. The leakage current and capacitive characteristic of the sample was improved significantly with increase in sintering temperature of BiFeO3 (850 C). At higher sintering temperature, ferroelectric behavior of the sample is found to change its shape from semi elliptical lossy P-E features to a typical ferroelectric loop with improvement of its remnant as well as saturation polarization value. Raman spectra over the frequency range of 100-700 cm-1 have been systematically investigated. Besides the changes of the peak position and the line width of all modes, the prominent frequency shift, the line broadening and variation of the intensity were observed with increase in sintering temperature. © 2013 Springer Science+Business Media New York.


Pradhan S.K.,Institute of Materials Science
Journal of Materials Science: Materials in Electronics | Year: 2013

The effect of iron deficiency for the improvement of multiferroic properties of Ho doped BiFeO3 ceramics (BiHoXFe 1-XO3 for x = 0, 0.05, 0.1 and 0.15) prepared by conventional solid state reaction route were investigated carefully. As pure BiFeO3 exhibited antifer-romagnetism, lossy ferroelectric (P-E) hysteresis loop and low dielectric constant value so, device integration is significantly hindered due to the presence of impurity phases associated with it. However, suitable variation of metal ion concentration in Ho doped BiFeO3 significantly enhanced both ferroelectric and ferromagnetic properties of the samples. Therefore, increase of Ho concentration certainly favors for suppression of impurity phases in rhombohedral (R3c) structure of BiFeO3 along with no structural transformation. On the other hand, increase of iron deficiency may suppress transformation of Fe from Fe 3+ to Fe2+ as a result, the dielectric constant value of the sample increases along with large reduction of leakage current behavior. © Springer Science+Business Media New York 2012.

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