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News Article | May 9, 2017
Site: www.cemag.us

If they’re quick about it, “hot” electrons excited in a plasmonic metal can tunnel their way across a nanoscale gap to a neighboring metal. Rice University scientists said the cool part is what happens in the gap. A Rice team discovered those electrons can create a photovoltage about a thousand times larger than what is seen if there is no gap. The finding shows it should be possible to create nanoscale photodetectors that convert light into electricity and can be used as sensors or in other sophisticated electronics. Results from the Rice lab of condensed matter physicist Douglas Natelson appear in the American Chemical Society’s Journal of Physical Chemistry Letters. Natelson’s lab studies the electronic, magnetic and optical properties of nanoscale structures, often by testing the properties of systems that can only be viewed under a microscope. Some studies involve whole gold nanowires, and sometimes the lab breaks the wire to form a gap of just a few nanometers (billionths of a meter). One goal is to understand whether and how electrons leap the nanogap under various conditions, like ultracold temperatures. While looking at such structures, the researchers found themselves studying the nanoscale characteristics of what’s known as the Seebeck (thermoelectric) effect, discovered in 1821, in which heat is converted to electricity at the junction of two wires of different metals. Seebeck discovered that a voltage would form across a single conductor when one part is hotter than the other. “If you want to make thermostats for your house or your car climate control, this is how you do it,” Natelson says. “You join together two dissimilar metals to make a thermocouple, and stick that junction where you want to measure the temperature. Knowing the difference between the Seebeck coefficients of the metals and measuring the voltage across the thermocouple, you can work backward from that to get the temperature.” To see how it works in a single metal on the nanoscale, Natelson, lead author and former postdoctoral researcher Pavlo Zolotavin and graduate student Charlotte Evans used a laser to induce a temperature gradient across a bowtie-shaped gold nanowire. That created a small voltage, consistent with the Seebeck effect. But with a nanogap splitting the wire, “the data made clear that a different physical mechanism is at work,” they write. Gold is a plasmonic metal, one of a class of metals that can respond to energy input from a laser or other source by exciting plasmons on their surfaces. Plasmon excitations are the back-and-forth sloshing of electrons in the metal, like water in a basin. This is useful, Natelson explains, because oscillating plasmons can be detected. Depending on the metal and its size and shape, these plasmons may only show up when prompted by light at a particular wavelength. In the bowties, laser light absorbed by the plasmons created hot electrons that eventually transferred their energy to the atoms in the metal, vibrating them as well. That energy is dissipated as heat. In continuous, solid wires, the temperature difference caused by the laser also created small voltages. But when nanogaps were present, the hot electrons passed through the void and created much larger voltages before dispersing. “It’s a neat result,” Natelson says. “The main points are, first, that we can tune the thermoelectric properties of metals by structuring them on small scales, so that we can make thermocouples out of one material. Second, a focused laser can act as a scannable, local heat source, letting us map out those effects. Shining light on the structure produces a small photovoltage. “And third, in structures with truly nanoscale tunneling gaps (1 to 2 nanometers), the photovoltage can be a thousand times larger, because the tunneling process effectively uses some of the high-energy electrons before their energy is lost to heat,” he says. “This has potential for photodetector technologies and shows the potential that can be realized if we can use hot electrons before they have a chance to lose their energy.” Gold seems to be the best metal to show the effect so far, Natelson says, as control experiments with gold-palladium and nickel nanogapped wires did not perform as well. The researchers acknowledge several possible reasons for the dramatic effect, but they strongly suspect tunneling by the photo-generated hot carriers is responsible. “You don’t need plasmons for this effect, because any absorption, at least in a short time, is going to generate these hot carriers,” Zolotavin says. “However, if you’ve got plasmons, they effectively increase the absorption. They interact with light very strongly, and the effect gets bigger because the plasmons make the absorption bigger.” Natelson is a professor of physics and astronomy, of electrical and computer engineering and of materials science and nanoengineering, and chair of the Rice Department of Physics and Astronomy. Zolotavin, a former postdoctoral researcher in Natelson’s lab, is now a scientist with Lam Research. The U.S. Army Research Office, the Robert A. Welch Foundation and the National Science Foundation supported the research.


DB Labs has hired Ben Chew to help oversee lab operations, including safety and regulatory compliance for their Las Vegas-based marijuana testing laboratory. Dr. Chew completed his PhD in Physical Chemistry at Cornell University before becoming a postdoctoral fellow at Georgetown University Medical Center. He brings 20 years of industrial chemistry experience working in and managing a variety of analytical chemistry laboratories to the DB Labs team. “We are thrilled that Ben chose to join the qualified team of DB Labs,” Susan Bunce, the DB Lab President stated. “He represents the integrity and leadership that we value as a company. We strive to continually improve the laboratory for the safety of the consumers, which was my primary concern when we interviewed candidates. I feel that Ben is a great addition to our already experienced management staff, including Kelly Zaugg and Glen Marquez.” In his role at DB Labs, Dr. Chew will be responsible for developing employees, adhering to state and county regulations, providing high-quality analytical results to clients, and managing daily operations for the cannabis testing laboratory. When asked why he chose DB Labs, Dr. Chew replied, “In the two years I have been in this industry, I have collaborated with them. They made it clear that they are a lab that takes accuracy and patient safety seriously.” About DB Labs: Located in Las Vegas, Nevada, DB Labs is an independent analytical testing laboratory specializing in organic, inorganic, and microbiological analyses. We take pride knowing our stringent cannabis analyses are of the highest quality. Founded in 2014, DB Labs is committed to meeting industry needs with the highest level of service. To learn more about DB Labs and its safe testing practices, contact DB Labs at Test@DBLabsLV.com.


News Article | May 11, 2017
Site: www.eurekalert.org

Chemists have discovered that tiny particulate matter called aerosols lofted into the atmosphere by sea spray and the bursting of bubbles at the ocean's surface are chemically altered by the presence of biological activity. Their finding, published in this week's issue of the journal Chem, is a critical discovery that should improve the accuracy of future atmospheric and climate models. "Simply put, most atmospheric and climate models assume sea spray aerosol particles are made of pure salt," said Vicki Grassian, a UC San Diego chemistry and biochemistry professor who headed the study, which included scientists at the University of Iowa, University of Wisconsin, UC Davis and Pacific Northwest National Laboratory in Richland, WA. "Our results show that these particles are much more complex in terms of what they are made of, and that this pure salt assumption is a bad one." "Biological activity in the water, which we measured by the amount of chlorophyll and bacteria present," she added, "play a big role in the what sea spray aerosols are, in fact, composed of--that is, mixtures of salts, organic compounds and biological components." The scientists noted in a paper detailing their results that one of the key factors in developing more accurate climate models is a better understanding of the chemical composition and diversity of sea spray aerosol particles. "We wanted to understand their climate properties, including 'hygroscopicity'--the ability to take up water, increase their size as a function of relative humidity and to form clouds," said Grassian, who holds the Distinguished Chair of Physical Chemistry in the Department of Chemistry and Biochemistry and is an associate dean in UC San Diego's Division of Physical Sciences. She is also a Distinguished Professor in the Department of Nanoengineering and at Scripps Institution of Oceanography. By increasing humidity and lofting particles into the atmosphere that can either reflect sunlight during the daylight hours or limit heat loss at night, sea spray aerosols as well as mineral dust are believed to have a major contributing effect on climate. To determine how biological activity impacted sea spray aerosols, scientists at UC San Diego's Center for Aerosol Impacts on Climate and the Environment, including Kimberly Prather, the director of the center and a professor of chemistry and biochemistry, used a unique wave flume facility located at Scripps Institution of Oceanography that allowed them to analyze the molecular composition of individual sea spray aerosol particles during different stages of a phytoplankton bloom. High-resolution mass spectrometry experiments at the Pacific Northwest National Laboratory also enabled the researchers to determine the major classes of organic molecules that make up the sea spray aerosol molecules as the biological conditions changed during the simulated phytoplankton bloom. Other coauthors of the study were (from UC San Diego) Richard Cochran, Jonathan Trueblood, Armando D. Estillore, Camille M. Sultana, Christopher Lee and Kimberly Prather; (from University of Iowa) Olga Laskina, Holly Morris, Thilina Jayarathne, Jacqueline Dowling, Alexi Tivanski, Zhen Qin and Elizabeth Stone; Pacific Northwest National Laboratory scientists Peng Lin, Julia Laskin and Alexander Laskin; UC Davis scientist Christopher Cappa; and Timothy Bertram of the University of Wisconsin-Madison. The study was funded by a grant from the National Science Foundation through the Center for Aerosol Impacts on Climate and the Environment (CHE 1305427).


Home > Press > 'Hot' electrons don't mind the gap: Rice University scientists find nanogaps in plasmonic gold wires enhance voltage when excited Abstract: If they're quick about it, "hot" electrons excited in a plasmonic metal can tunnel their way across a nanoscale gap to a neighboring metal. Rice University scientists said the cool part is what happens in the gap. A Rice team discovered those electrons can create a photovoltage about a thousand times larger than what is seen if there is no gap. The finding shows it should be possible to create nanoscale photodetectors that convert light into electricity and can be used as sensors or in other sophisticated electronics. Results from the Rice lab of condensed matter physicist Douglas Natelson appear in the American Chemical Society's Journal of Physical Chemistry Letters. Natelson's lab studies the electronic, magnetic and optical properties of nanoscale structures, often by testing the properties of systems that can only be viewed under a microscope. Some studies involve whole gold nanowires, and sometimes the lab breaks the wire to form a gap of just a few nanometers (billionths of a meter). One goal is to understand whether and how electrons leap the nanogap under various conditions, like ultracold temperatures. While looking at such structures, the researchers found themselves studying the nanoscale characteristics of what's known as the Seebeck (thermoelectric) effect, discovered in 1821, in which heat is converted to electricity at the junction of two wires of different metals. Seebeck discovered that a voltage would form across a single conductor when one part is hotter than the other. "If you want to make thermostats for your house or your car climate control, this is how you do it," Natelson said. "You join together two dissimilar metals to make a thermocouple, and stick that junction where you want to measure the temperature. Knowing the difference between the Seebeck coefficients of the metals and measuring the voltage across the thermocouple, you can work backward from that to get the temperature." To see how it works in a single metal on the nanoscale, Natelson, lead author and former postdoctoral researcher Pavlo Zolotavin and graduate student Charlotte Evans used a laser to induce a temperature gradient across a bowtie-shaped gold nanowire. That created a small voltage, consistent with the Seebeck effect. But with a nanogap splitting the wire, "the data made clear that a different physical mechanism is at work," they wrote. Gold is a plasmonic metal, one of a class of metals that can respond to energy input from a laser or other source by exciting plasmons on their surfaces. Plasmon excitations are the back-and-forth sloshing of electrons in the metal, like water in a basin. This is useful, Natelson explained, because oscillating plasmons can be detected. Depending on the metal and its size and shape, these plasmons may only show up when prompted by light at a particular wavelength. In the bowties, laser light absorbed by the plasmons created hot electrons that eventually transferred their energy to the atoms in the metal, vibrating them as well. That energy is dissipated as heat. In continuous, solid wires, the temperature difference caused by the laser also created small voltages. But when nanogaps were present, the hot electrons passed through the void and created much larger voltages before dispersing. "It's a neat result," Natelson said. "The main points are, first, that we can tune the thermoelectric properties of metals by structuring them on small scales, so that we can make thermocouples out of one material. Second, a focused laser can act as a scannable, local heat source, letting us map out those effects. Shining light on the structure produces a small photovoltage. "And third, in structures with truly nanoscale tunneling gaps (1-2 nanometers), the photovoltage can be a thousand times larger, because the tunneling process effectively uses some of the high-energy electrons before their energy is lost to heat," he said. "This has potential for photodetector technologies and shows the potential that can be realized if we can use hot electrons before they have a chance to lose their energy." Gold seems to be the best metal to show the effect so far, Natelson said, as control experiments with gold-palladium and nickel nanogapped wires did not perform as well. The researchers acknowledge several possible reasons for the dramatic effect, but they strongly suspect tunneling by the photo-generated hot carriers is responsible. "You don't need plasmons for this effect, because any absorption, at least in a short time, is going to generate these hot carriers," Zolotavin said. "However, if you've got plasmons, they effectively increase the absorption. They interact with light very strongly, and the effect gets bigger because the plasmons make the absorption bigger." ### Natelson is a professor of physics and astronomy, of electrical and computer engineering and of materials science and nanoengineering, and chair of the Rice Department of Physics and Astronomy. Zolotavin, a former postdoctoral researcher in Natelson's lab, is now a scientist with Lam Research. The U.S. Army Research Office, the Robert A. Welch Foundation and the National Science Foundation supported the research. About Rice University Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,879 undergraduates and 2,861 graduate students, Rice's undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for happiest students and for lots of race/class interaction by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to http://tinyurl.com/RiceUniversityoverview . Follow Rice News and Media Relations via Twitter @RiceUNews 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.


Martina Havenith has quickly implemented the first research idea, which she wanted to realise with funds from a prestigious grant from the European Research Council. Credit: RUB, Marquard Chemists at Ruhr-Universität Bochum have developed a new method that allows them to map changes in the dynamics and structure of water molecules in the vicinity of solutes. With this technique, called terahertz calorimetry, they investigated the properties of the hydration shell of dissolved alcohol molecules. In the future, they want to also use the method for water mapping around more complex systems such as enzymes, which can be important for drug design. The results were published by Prof Dr Martina Havenith, chair for Physical Chemistry II and spokeswoman for the cluster of excellence Resolv, with Dr Fabian Böhm and Dr Gerhard Schwaab in the journal Angewandte Chemie. Method can now be applied in real time Fundamental biological processes such as enzymatic catalysis or molecular binding occur in aqueous phase. Calorimetry serves as a powerful biophysical tool to study the molecular recognition and stability of biomolecular systems by measuring changes in thermodynamic state variables, e.g. upon protein folding or association, for the purpose of deriving the heat transfer associated with these changes. Calorimetry determines, enthalpy and entropy, which are measures of the heat transfer and disorder in the system. Calorimetry is restricted to timescales of 1 to 100 seconds. In contrast, spectroscopic processes, which are based on short laser pulses, are able to perform measurements on the time scale of a millionth or a billionth of a second. The Bochum-based chemists showed that both approaches are complimentary. "By establishing a terahertz calorimeter in a proof of concept experiment, we have achieved the first aim that we had been working on using the Advanced Grant funds from the European Research Council," explains Martina Havenith. Determining the structure of the watery envelopes A shell of surrounding water molecules, the hydration shell, forms around any dissolved molecule. The solute affects the regular network of hydrogen bridges between the water molecules, causing the water in the hydration shell to behave differently to the free water. The structure of the hydration shell depends on the shape and the chemical composition of the dissolved molecule. Havenith's team investigated the hydration shell of five different alcohol chains and were able to classify differently structured hydration water by terahertz calorimetry. Exposure to terahertz pulses provides fingerprints of the vibrations within the water network. This, in turn, allows the researchers to deduce fundamental quantities such as entropy and enthalpy. "The method allows us for the first time to spectroscopically map entropy and enthalpy around solutes, which are crucial parameters to characterize molecular recognition," summarises Havenith. Explore further: Fingerprint of dissolved glycine in the Terahertz range explained More information: Martina Havenith-Newen et al. Hydration water mapping around alcohol chains by THz-calorimetry reveal local changes in heat capacity and free energy upon solvation, Angewandte Chemie International Edition (2017). DOI: 10.1002/anie.201612162


Graphene has shown significant promise—with potential applications in the biomedical, electrical, energy, and environmental spaces—and success has been seen in many small-scale applications. But scaling up the production of graphene-based materials is problematic, and potentially dangerous, because graphene oxide, a flake-like intermediate for making graphene from graphite has been proven to possess a fire hazard. Ryan Tian, associate professor of inorganic chemistry, and his team at the University of Arkansas set out to solve this problem. “We started researching graphene about five years ago and realized that the entire field is talking about graphene’s flammability,” said Tian in an exclusive interview with R&D Magazine. “Graphene oxide once it becomes airborne is extremely explosive. I can tell from my industry experience in production lines that if anything potentially flammable is there, and once it becomes airborne it can be explosive, than the industry always hesitates to do it.” Using metal ions with three or more positive charges, researchers in Tian’s laboratory bonded graphene-oxide flakes into a transparent membrane. This new form of carbon-polymer sheet is flexible, nontoxic and mechanically strong, in addition to being non-flammable. The research was published in The Journal of Physical Chemistry. The Journal of Physical Chemistry describes the process in more detail: “This work reports a simple and facile method to cross-link the GO with Al3+ cations, in one step, into a freestanding flexible membrane. This inorganic membrane resists in-air burning on an open flame, at which non-cross-linked GO was burnt out within ∼5 s. All characterization data suggested that the in situ “epoxy ring-opening” reactions on the GO surface facilitated the cross-linking, which elucidated a new mechanism for the generalized inorganic polymerization. With the much improved thermal and water stabilities, the cross-linked GO film can help to advance high-temperature fuel cells, electronic packaging, etc. as one of the long-sought inorganic polymers known to date.” Using this method, graphene is less likely to cause trouble in the future of graphene-based materials production, its disposal and its environmental impact, said Tian. “This technology and the material we don’t need to worry about anymore, because by converting graphene polymer to graphene-oxide flakes in a liquid phase water solution, we can do the cross linking in the water,” he said. “We can harvest the materials, not as a chunk, but cross-linked into a free-standing membrane, foil type so that the material has much stronger mechanical properties than before when it was non-cross linked. This essentially opens the door widely to all applications. Some of these applications are already in process. At the University of Arkansas’s Sam M. Walton College of Business, several students have already showed interest in using the material for commercialization. Tian’s team, who have a provisional patent on the discovery, are also talking with National Labs about taking on commercialization applications of this product. One potential application is to use graphene, developed using this non-flammable technique, to create an energy-efficient window coating that would bring down heating and cooling costs. “If each pane is covered by graphene, which is very thin and transparent, nearly colorless all kind of properties would be generated and a new building window would be very cool. It can conduct heat and conduct a charge and save energy for cooling and heating,” said Tian. Several academia labs in Arkansas and elsewhere are already in the process of forming a small consortium to better understand the heating and cooling advantage of graphene. There are many more applications, said Tian. “We can expect that future automobile and airplane windows will be much smarter than currently, and there are night vision applications,” said Tian. “After window coating, row to row printing, wearable electronics, optical, electromagnetic, sensor-based devices, and electronic optics have potential; we see all kinds of possibilities.”


News Article | May 18, 2017
Site: www.eurekalert.org

Breast cancer is one of the most common cancers in women in Italy and in the world. Today, however, it seems possible to design more selective and effective drugs through numerical simulations. This is what has been revealed by research carried out by the "Istituto Officina dei Materiali" (IOM) of the Italian National Research Council (CNR) in Trieste and the International School for Advances Studies (SISSA), in collaboration with the Bellinzona Institute for Research in Biomedicine and the University of Italian Switzerland. This study analyzed in detail the mechanisms activating an important pharmacological target involved in female hormone synthesis, exceeding the limits of experimental approaches. This research, funded by AIRC - the Italian Association for Cancer Research, has shown that molecules of different shapes and sizes follow the same pathways within the protein to access the active site i.e. the heart of the protein where female hormones are synthesized and has been published in the Journal of Physical Chemistry Letters. « Cytochromes P450 are enzymes that play a key role in the metabolism of different hormones and drugs. In particular, they are important pharmacological targets for treating breast and prostate cancer» explains Alessandra Magistrato, CNR-IOM / SISSA researcher and first co-author of the work together with Jacopo Sgrignani of the Bellinzona Institute for Research in Biomedicine. «We have known for a long time that these enzymes are characterized by a hidden active site, which can be reached through several of grueling access channels whose real function is not yet known. We chose aromatase as a prototype of the cytochrome P450 family and compared the access paths of two molecules differing in shape, size and hydrophobicity - i.e. the tendency to interact with water». Aromatase is an enzyme responsible for the synthesis of female sex hormones, whose excessive production is among the causes of breast cancer development. In the study, led by Alessandra Magistrato of CNR-IOM/SISSA and Andrea Cavalli of the Bellinzona Institute for Research in Biomedicine and carried out in collaboration with Rolf Krause of the University of Italian Switzerland, the researchers compared a last-generation anti breast cancer drug, an aromatase inhibitor, and a hormone on which the enzyme acts. «Through classical molecular dynamics simulations, which allow us to study the evolution of the processes at an atomistic level, we were able to identify and characterize, from an energetic point of view, the preferential access paths of the two molecules to reach the enzyme catalytic site. Surprisingly we identified the same two channels in both cases, regardless of the different shape, size or hydrophobicity of the two molecules studied. Moreover, the similarity between different cytochromes P450 at the critical points suggests that this feature may be common to the entire enzymatic family». «These are results which cannot be directly observed experimentally, but which are crucial for developing more selective and effective drugs», concludes the researcher. The study is in fact part of a "My First AIRC" project, that was financed to Alessandra Magistrato by AIRC - the Italian Association for Cancer Research for designing, synthesizing and testing new anticancer drugs to fight breast cancer.


News Article | May 15, 2017
Site: phys.org

Everything we see with the unaided eye in a painting – from the Australian outback images of Albert Namatjira or Russell Drysdale, to the vibrant works of Pro Hart – is thanks to the mix of colours that form part of the visible spectrum. But if we look at the painting in a different way, at a part of the spectrum that is invisible to our eyes, then we can see something very different. As our recently published research shows, it could even help us detect art fraud. The electromagnetic spectrum ranges from very high-frequency gamma rays down to the extremely low-frequency radiation of just a few hertz. Hertz is the unit of measurement for frequency. The frequency of colours in the visible spectrum range from blue, at about 800 terahertz (THz), through to red at about 400THz (1 THz = 1012 or 1,000,000,000,000 hertz). If we drop to frequencies below the visible spectrum we find the near-infrared at about 300THz and then the mid-infrared at about 30THz. Then comes the far-infrared and at last we meet the frequencies around 1THz. Continuing even further brings us to microwaves and radio waves where frequencies range from the gigahertz down to kilohertz. Thus the terahertz part of the electromagnetic spectrum lies between the radio and the visible parts – in other words, between electronics and photonics. Things can look very different when viewed with "eyes" that can see in the terahertz range. Some things that are transparent to visible light, such as water, are opaque to terahertz light. Conversely, some things that visible light won't penetrate, such as black plastic, readily transmit terahertz radiation. Intriguingly, two objects that have the same colour when viewed by the unassisted eye may transmit terahertz radiation differently. So their terahertz signal can be used to tell them apart. This points to the potential use of terahertz radiation in differentiating paints and pigments. Terahertz spectroscopy can distinguish different pigments with similar colours. We recently used terahertz spectroscopy to distinguish between three related pigments. All come from a family of chemical compounds called quinacridones. These are used widely in producing stable, reproducible pigments that range in colour from red to violet. Measurements at the University of Wollongong provided the experimental data in the range of 1THz to 10THz. Numerical modelling at Syracuse University (New York) reproduced the experimental data, and gave physical insight into the origin of the features observed. The combined experimental and theoretical work, published last month in the Journal of Physical Chemistry, unequivocally demonstrates that terahertz spectroscopy is able to distinguish three different quinacridones. This brings us to the subject of art authentication – or more importantly, detecting cases of art fraud. Museums, galleries and collectors are typically very protective of their art collections, but terahertz spectroscopy is well suited to examining their works. While terahertz spectrometers are often located in laboratories, there are also portable models. Unlike an analysis that requires removing and consuming some material (by reacting it with chemicals, or burning it), there is no contact made with the material, and thus no harm done to the artwork. The terahertz radiation simply shines on the painting, and the transmitted radiation is measured. The low energy and low density of terahertz radiation means that the painting is not damaged in any way. This all makes it suitable for examining art in a way that does not damage it and can be performed where it is located – in a gallery, or home, or almost anywhere. So how can terahertz spectroscopy assist in detecting art fraud in practice? Here's an example. Let's say terahertz spectroscopy picks up a quinacridone pigment in a painting. Quinacridone is an artificial material that was first synthesised in 1935, so the painting must date from 1935 or later. Any claim that the painting is a work by Leonardo da Vinci (who died in 1519), Vincent van Gogh (died 1890) or Claude Monet (died 1926) could therefore be dismissed. Any claim the the work was by an artist who worked after 1935 could not be so easily disproved on this basis. Of course, other physical methods than terahertz spectroscopy may be applied to analyse paintings. One direct way to analyse art work is by sophisticated, quantitative measurements of the visible spectrum. Artworks may also be interrogated by other species of light that lie above the blue end visible spectrum. Here the ultraviolet (uv) photons are higher in energy than visible photons. That means they can put energy into a material that is re-radiated as visible photons. This is the phenomenon of fluorescence, and uv-fluorescence is an established tool in art conservation. Moving further above the ultraviolet, X-rays may be used to examine works of art. For example, X-ray fluorescence at the Australian Synchrotron has been used to find hidden layers in works by Degas and Streeton. There are many aspects to authenticating an artwork, the physical examination being but one of them. Nonetheless, technical analysis of the materials used – the paints, the canvas, the frames – plays a fundamental role, and that is where terahertz spectroscopy contributes. But other approaches also play a role. For example, documentation such as records of sales may provide key evidence, as may the more subtle appraisal of style by art historians. The perceptions of people who assess and buy art is itself an important factor. The word of the artist might be thought to be definitive, but even this has been overruled by expert opinion, as in the case of Lucian Freud. Finally, the legal dimension is critical, as has been reported recently in the quashing of the art fraud convictions of Peter Gant and Mohamed Siddique. These related to the paintings Blue Lavender Bay, Orange Lavender Bay, and Through the Window. At issue was whether the paintings were the work of Brett Whiteley. Of course, art fraud is just one application of terahertz spectroscopy. There are many more. Able to penetrate paper and cardboard, terahertz radiation can be used to look inside envelopes for contraband, or inside packaged food for contamination. Terahertz methods have been used to assess burns and to monitor the hydration of plants. As better terahertz sources, detectors and components are developed, the range of applications will further expand. Explore further: Researchers nearly double the continuous output power of a type of terahertz laser


News Article | May 19, 2017
Site: www.materialstoday.com

An international team of scientists has developed a new way to produce single-layer graphene from a simple precursor: ethene – also known as ethylene – the smallest alkene molecule, which contains just two atoms of carbon. By heating the ethene in stages to a temperature of slightly more than 700°C – hotter than had been attempted before – the researchers produced pure layers of graphene on a rhodium catalyst substrate. The stepwise heating and higher temperatures overcame problems that hampered earlier efforts to produce graphene directly from hydrocarbon precursors. Because of its lower cost and simplicity, the technique could open new potential applications for graphene, which has attractive physical and electronic properties. This work also provides a novel mechanism for the self-evolution of carbon cluster precursors, whose diffusional coalescence results in the formation of the graphene layers. The research, reported in a paper in the Journal of Physical Chemistry C, was conducted by scientists at the Georgia Institute of Technology, the Technische Universität München in Germany and the University of St. Andrews in the UK. In the US, the research was supported by the US Air Force Office of Scientific Research and the US Department of Energy's Office of Basic Energy Sciences. "Since graphene is made from carbon, we decided to start with the simplest type of carbon molecules and see if we could assemble them into graphene," explained Uzi Landman, a professor in the Georgia Tech School of Physics who headed the theoretical component of the research. "From small molecules containing carbon, you end up with macroscopic pieces of graphene." Graphene is currently produced using a variety of different methods including chemical vapor deposition, evaporation of silicon from silicon carbide and simple exfoliation of graphene sheets from graphite. A number of earlier efforts aimed at producing graphene from simple hydrocarbon precursors had proven largely unsuccessful, creating disordered soot rather than structured graphene. Guided by a theoretical approach, the researchers reasoned that the path from ethene to graphene would involve formation of a series of structures as hydrogen atoms leave the ethene molecules and the remaining carbon atoms self-assemble into the honeycomb pattern that characterizes graphene. To explore the nature of the thermally-induced rhodium surface-catalyzed transformations from ethene to graphene, experimental groups in Germany and the UK raised the temperature of the material in steps under an ultra-high vacuum. They then used scanning-tunneling microscopy (STM), thermal programed desorption (TPD) and high-resolution electron energy loss (vibrational) spectroscopy (HREELS) to observe and characterize the structures that form at each step of the process. They found that, upon heating, ethene adsorbed on the rhodium catalyst evolves via coupling reactions to form segmented one-dimensional polyaromatic hydrocarbons (1D-PAH). Further heating leads to dimensionality crossover – transforming from one dimensional to two dimensional structures – and dynamical restructuring processes at the PAH chain ends. Next comes the activated detachment of size-selective carbon clusters, following a mechanism revealed through first-principles quantum mechanical simulations. Finally, rate-limiting diffusional coalescence of these dynamically self-evolved cluster-precursors leads to their condensation into graphene with high purity. At the final stage before the formation of graphene, the researchers observed nearly round, disk-like clusters containing 24 carbon atoms, which spread out to form the graphene lattice. "The temperature must be raised within windows of temperature ranges to allow the requisite structures to form before the next stage of heating," Landman explained. "If you stop at certain temperatures, you are likely to end up with coking." An important component is the dehydrogenation process that frees the carbon atoms to form intermediate shapes. However, some of the hydrogen atoms reside temporarily on, or near, the metal catalyst surface and assist in the subsequent bond-breaking process that detaches the 24-carbon cluster-precursors. "All along the way, there is a loss of hydrogen from the clusters," said Landman. "Bringing up the temperature essentially 'boils' the hydrogen out of the evolving metal-supported carbon structure, culminating in graphene." The resulting graphene structure is adsorbed onto the catalyst. Although this may be useful for some applications, a way to remove the graphene will have to be developed. "This is a new route to graphene, and the possible technological application is yet to be explored," said Landman. This story is adapted from material from the Georgia Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


News Article | May 22, 2017
Site: www.eurekalert.org

Chemists at Ruhr-Universität Bochum have developed a new method that allows them to map changes in the dynamics and structure of water molecules in the vicinity of solutes. With this technique, called terahertz calorimetry, they investigated the properties of the hydration shell of dissolved alcohol molecules. In the future, they want to also use the method for water mapping around more complex systems such as enzymes, which can be important for drug design. The results were published by Prof Dr Martina Havenith, chair for Physical Chemistry II and spokeswoman for the cluster of excellence Resolv, with Dr Fabian Böhm and Dr Gerhard Schwaab in the journal Angewandte Chemie. Method can now be applied in real time Fundamental biological processes such as enzymatic catalysis or molecular binding occur in aqueous phase. Calorimetry serves as a powerful biophysical tool to study the molecular recognition and stability of biomolecular systems by measuring changes in thermodynamic state variables, e.g. upon protein folding or association, for the purpose of deriving the heat transfer associated with these changes. Calorimetry determines, enthalpy and entropy, which are measures of the heat transfer and disorder in the system. Calorimetry is restricted to timescales of 1 to 100 seconds. In contrast, spectroscopic processes, which are based on short laser pulses, are able to perform measurements on the time scale of a millionth or a billionth of a second. The Bochum-based chemists showed that both approaches are complimentary. "By establishing a terahertz calorimeter in a proof of concept experiment, we have achieved the first aim that we had been working on using the Advanced Grant funds from the European Research Council," explains Martina Havenith. In 2016, she was awarded the grant endowed with 2.5 million euros. Determining the structure of the watery envelopes A shell of surrounding water molecules, the hydration shell, forms around any dissolved molecule. The solute affects the regular network of hydrogen bridges between the water molecules, causing the water in the hydration shell to behave differently to the free water. The structure of the hydration shell depends on the shape and the chemical composition of the dissolved molecule. Havenith's team investigated the hydration shell of five different alcohol chains and were able to classify differently structured hydration water by terahertz calorimetry. Exposure to terahertz pulses provides fingerprints of the vibrations within the water network. This, in turn, allows the researchers to deduce fundamental quantities such as entropy and enthalpy. "The method allows us for the first time to spectroscopically map entropy and enthalpy around solutes, which are crucial parameters to characterize molecular recognition," summarises Havenith.

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