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Site: http://phys.org/nanotech-news/

Researchers from CIC nanoGUNE, in collaboration with ICFO and Graphenea, have demonstrated how infrared light can be captured by nanostructures made of graphene. This happens when light couples to charge oscillations in the graphene. The resulting mixture of light and charge oscillations, called plasmon, can be squeezed into record-small volumes millions of times smaller than in conventional dielectric optical cavities. This process has been visualized by the researchers for the first time with the help of a state-of the-art, near-field microscope and explained by theory. The researchers identified two types of plasmons—edge and sheet modes—propagating either along the sheet or along the sheet edges. The edge plasmons are unique for their ability to channel electromagnetic energy in one dimension. The work, reported in Nature Photonics, opens new opportunities for ultra-small and efficient photodetectors, sensors and other photonic and optoelectronic nanodevices. Graphene-based technologies enable extremely small optical nanodevices. The wavelength of light captured by a graphene sheet, a monolayer sheet of carbon atoms, can be shortened by a factor of 100 compared to light propagating in free space. As a consequence, the light propagating along the graphene sheet, which is called graphene plasmon, requires much less space. For that reason, photonic devices can be made much smaller. The plasmonic field concentration can be further enhanced by fabricating graphene nanostructures acting as nanoresonators for the plasmons. The enhanced field has already found application in enhanced infrared and terahertz photodetection and infrared vibrational sensing of molecules, among other things. "The development of efficient devices based on plasmonic graphene nanoresonators will critically depend on precise understanding and control of the plasmonic modes inside them," says Dr. Pablo Alonso-Gonzalez, (now at Oviedo University) who performed the real-space imaging of the graphene nanoresonators with a near-field microscope. "We have been strongly impressed by the diversity of plasmonic contrasts observed in the near-field images," says Dr. Alexey Nikitin, Ikerbasque Research Fellow at nanoGUNE, who developed the theory to identify the individual plasmon modes. The research team has disentangled the individual plasmonic modes and separated them into two different classes. The first class of plasmons—"sheet plasmons"—can exist "inside" graphene nanostructures, extending over the whole area of graphene. Conversely, the second class of plasmons—"edge plasmons"—can exclusively propagate along the edges of graphene nanostructures, leading to whispering gallery modes in disk-shaped nanoresonators or Fabry-Perot resonances in graphene nanorectangles due to reflection at their corners. The edge plasmons are much better confined than the sheet plasmons and, most importantly, transfer the energy in a single dimension. The real-space images reveal dipolar edge modes with a mode volume that is 100 million times smaller than a cube of the free-space wavelength. The researchers also measured the dispersion (energy as a function of momentum) of the edge plasmons based on their near-field images, highlighting the shortened wavelength of edge plasmons compared to sheet plasmons. Thanks to their unique properties, edge plasmons could be a promising platform for coupling quantum dots or single molecules in future quantum opto-electronic devices. "Our results also provide novel insights into the physics of near-field microscopy of graphene plasmons, which could be very useful for interpreting near-field images of other light-matter interactions in two-dimensional materials," says Ikerbasque Research Professor Rainer Hillenbrand who led the project. Explore further: Scientists first to observe plasmons on graphene More information: Real-space mapping of tailored sheet and edge plasmons in graphene nanoresonators Nature Photonics (2016), DOI: 10.1038/nphoton.2016.44


News Article
Site: http://www.nanotech-now.com/

Abstract: Researchers from CIC nanoGUNE, in collaboration with ICFO and Graphenea, have demonstrated how infrared light can be captured by nanostructures made of graphene. This happens when light couples to charge oscillations in the graphene. The resulting mixture of light and charge oscillations - called plasmon - can be squeezed into record-small volumes - millions times smaller than in conventional dielectric optical cavities. This process has been visualized by the researchers now, for the first time, with the help of a state-of the-art near-field microscope and explained by theory. Particularly, the researchers identified two types of plasmons - edge and sheet modes - propagating either along the sheet or along the sheet edges. The edge plasmons are unique for their ability to channel electromagnetic energy in one dimension. The work - funded by the EC Graphene Flagship and reported in Nature Photonics - opens new opportunities for ultra-small and efficient photodetectors, sensors and other photonic and optoelectronic nanodevices. Graphene-based technologies enable extremely small optical nanodevices. The wavelength of light captured by a graphene sheet - a monolayer sheet of carbon atoms can be shortened by a factor of 100 compared to light propagating in free space. As a consequence, this light propagating along the graphene sheet - called graphene plasmon - requires much less space. For that reason, photonic devices can be made much smaller. The plasmonic field concentration can be further enhanced by fabricating graphene nanostructures acting as nanoresonators for the plasmons. The enhanced field have been already applied for enhanced infrared and terahertz photodetection or infrared vibrational sensing of molecules, among others. "The development of efficient devices based on plasmonic graphene nanoresonators will critically depend on precise understanding and control of the plasmonic modes inside them" says Dr. Pablo Alonso-Gonzalez, (now at Oviedo University) who performed the real-space imaging of the graphene nanoresonators (disks and rectangles) with a near-field microscope. "We have been strongly impressed by the diversity of plasmonic contrasts observed in the near-field images" continues Dr. Alexey Nikitin, Ikerbasque Research Fellow at nanoGUNE, who developed the theory to identify the individual plasmon modes. The research team has disentangled the individual plasmonic modes and separated them into two different classes. The first class of plasmons - "sheet plasmons" - can exist "inside" graphene nanostructures, extending over the whole area of graphene. Conversely, the second class of plasmons - "edge plasmons" -can exclusively propagate along the edges of graphene nanostructures, leading to whispering gallery modes in disk-shaped nanoresonators or Fabry-Perot resonances in graphene nanorectangles due to reflection at their corners. The edge plasmons are much better confined than the sheet plasmons and, most importantly, transfer the energy only in one dimension. The real-space images reveal dipolar edge modes with a mode volume that is 100 million times smaller that a cube of the free-space wavelength. The researchers also measured the dispersion (energy as a function of momentum) of the edge plasmons based on their near-field images, highlighting the shortened wavelength of edge plasmons compared to sheet plasmons. Thanks to their unique properties, edge plasmons could be a promising platform for coupling quantum dots or single molecules in future quantum opto-electronic devices. "Our results also provide novel insights into the physics of near-field microscopy of graphene plasmons, which could be very useful for interpreting near-field images of other light-matter interactions in two-dimensional materials", adds Ikerbasque Research Professor Rainer Hillenbrand who led the project. 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
Site: http://cen.acs.org/news/ln.html

A diverse team of global experts has been selected to lead ACS Omega, the American Chemical Society’s newest open access journal publishing peer-reviewed articles. Based in the Americas, Europe, India, and China, the editors not only represent key geographic regions of active R&D, they also bring expertise from four distinct scientific areas of interest. The new editors are Cornelia Bohne, a professor of chemistry at the University of Victoria in Canada; Krishna Ganesh, director of the Indian Institute of Science Education & Research in India; Luis Liz-Marzán, Ikerbasque research professor and scientific director at CIC biomaGUNE in Spain; and Deqing Zhang, director of the Institute of Chemistry, Chinese Academy of Sciences, in China. Bohne’s research focuses on developing the fundamental understanding of the dynamics of supramolecular systems and on the application of this knowledge to functional supramolecular materials. Ganesh is an expert in modified DNA and peptide-nucleic acids as novel cell-penetrating agents. As the first (founding and serving) director of IISER, Ganesh has built a unique, interdisciplinary infrastructure in which teaching and education are wholly integrated into state-of-the-art research. Liz-Marzán’s research focuses on nanoparticle synthesis and assembly, nanoplasmonics, and the development of nanoparticle-based sensing and diagnostic tools. He most recently served as a senior editor of the ACS journal Langmuir. Zhang’s research focuses on organic functional materials involving synthesis of organic functional molecules, spectroscopic studies, characterizations of self-assembly structures and optoelectronic properties, as well as applications for chemo/biosensing and imaging. “The ACS Omega editors have themselves authored in aggregate more than 850 peer-reviewed research articles, book chapters, and patents,” says Penelope Lewis, director of editorial and new product development in ACS Publications. “Their prolific publishing records and academic and professional achievements set the foundation for a team that will define and lead the editorial vision for the journal, drawing on a geographically diverse editorial board they will soon enlist—to be composed of active researchers with wide-ranging expertise and scientific backgrounds across chemistry, chemical engineering, and allied interdisciplinary scientific fields.” ACS Omega will begin accepting research submissions in April 2016 and will publish its first articles online early this summer.


News Article
Site: http://phys.org/chemistry-news/

Visualization of the active site (coloured sticks) that is degraded by oxygen molecules within the core of the Fe-Fe hydrogenase with SOMO orbitals shown in green/pink. Credit: Elhuyar Fundazioa Oxygen inhibits hydrogenases, a group of enzymes that are able to produce and split hydrogen. This degradation is fatal for possible biotechnological applications of these enzymes for the production of clean energy. Understanding the mechanisms of this process is thus essential. An international team lead by researchers from UCL (UK) and CNRS (France), including an Ikerbasque Research Fellow from CIC nanoGUNE, have combined theory and experiment to characterize each chemical reaction step that results in the reduction of oxygen by the enzyme. These results are being published this week in the journal Nature Chemistry. Fossil fuels supply over 80% of the world's energy. Since the energy crises in the 1970's and then in the 90's, when concerns appeared about greenhouse effects, the search for alternative energy sources has been ongoing. Hydrogen has been a particularly popular candidate because its combustion only produces water. Biotechnology is uniquely poised for providing a means for using hydrogen as a source of clean energy. One possibility is using enzymes called hydrogenases that naturally occur in various microorganisms that live in anaerobic ecosystems, such as some bacteria living in soil and in the intestinal tract of animals, or unicellular algae. Hydrogenases catalyze the conversion of protons in hydrogen molecules (H2), whose combustion releases energy that can be utilized for example in fuel cells and therefore be part of biotechnological devices. The active site that catalyzes this reaction contains metallic ions (Iron or both Iron and Nickel). The Iron-only variety of hydrogenases is the most active for the production of hydrogen molecules. Their remarkably complex active site –the so-called H-cluster– is buried within the core of a large protein. A fatal problem for being able to exploit hydrogenases in biotechnological applications is that when brought to the aerobic conditions of a bioreactor (under normal oxygen pressures), molecular oxygen degrades their active site. Understanding the mechanism of the degradation process of the H-cluster is therefore essential to design a hydrogen-based fuel cell, but studies so far had not been conclusive. To solve this conundrum, an international team of researchers has combined experiments, molecular simulations, and theoretical calculations. Using electrochemical methods, they have precisely measured the rates of the different reaction steps involved in the degradation of the enzyme by oxygen. They have studied the dependence of these rates on experimental parameters like the electrode potential, pH, H2O/D2O exchange, and mutation of specific amino acids in the protein. These results confirm predictions from theoretical calculations. On one hand molecular dynamics simulations, conducted by nanoGUNE's Ikerbasque Fellow David de Sancho, show the tunnels that oxygen follows to reach the active site of the protein, a necessary step for the degradation and to identify possible hot-spots for blocking these access tunnels. On the other, density functional theory has been used to elucidate the reaction products and evaluate the rate constants for the individual reaction steps. The study published on August 22nd in Nature Chemistry has allowed to characterize unambiguously the complex reactions that occur in these large biological macromolecules using a highly innovative combination of computational and experimental approaches. "Although important challenges remain ahead for industrial applications, this study opens new avenues to efficiently exploit enzymes from living systems for clean energy production", says De Sancho. More information: Adam Kubas et al. Mechanism of O2 diffusion and reduction in FeFe hydrogenases, Nature Chemistry (2016). DOI: 10.1038/nchem.2592


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