Institute for Physical Chemistry

Göttingen, Germany

Institute for Physical Chemistry

Göttingen, Germany
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Approximately 10 to 20 percent of these white dwarfs exhibit strong magnetic fields. "The strength of the magnetic field in some white dwarfs can reach up to 100,000 Tesla," said Stella Stopkowicz, a theoretical chemistry researcher at the Institute for Physical Chemistry at the University of Mainz in Germany. In comparison, on Earth, the strongest magnetic fields that can be generated using nondestructive magnets are about 100 tesla. Therefore, studying the chemistry in such extreme conditions is only possible using theory and until now has not provided much insight to the spectra accompanying these white dwarfs. Stopkowicz and her colleague, Florian Hampe, describe their work modeling these systems this week in The Journal of Chemical Physics, from AIP Publishing. "At these considerable field strengths, magnetic and Coulombic forces in the atom or molecule become equally important," Stopkowicz said. "The magnetic fields radically alter the electronic structure of atoms and molecules such that their chemistry under these conditions is to this day mostly unknown. This makes the interpretation of observational spectra challenging as they look very different from those obtained in Earth-like conditions. Exploring this problem became an important focus for our research." "The first very accurate theoretical approach for examining the effect of a strong magnetic field on the electronic structure of atoms and molecules was the 'Full Configuration-Interaction' (FCI) method (also known as exact diagonalization). Unfortunately, this methodology is only applicable for systems with very few electrons such as hydrogen, helium, lithium and beryllium," Stopkowicz said. "FCI is computationally too expensive to examine larger atoms such as oxygen and molecules such as small hydrocarbons and their corresponding ions like CH+." Stopkowicz and her colleagues have therefore concentrated on different methodologies that are more widely applicable, while still retaining the desired accuracy to deal with atoms and molecules in the presence of strong magnetic fields. "Building on prior work that we have done in the field, we have adapted the 'Equation of Motion Coupled-Cluster (EOM-CC) method' that can be used to access the electronically excited states of atoms and molecules to deal with strong magnetic fields," Stopkowicz said. We then developed a computer program that incorporated this method to assist us in calculating excitation energies; this was an important step towards the prediction of spectra." "In the next stage, we will implement transition dipole moments which will make it possible to calculate theoretical spectra for atoms in strong fields," Stopkowicz said. "Astrophysicists can compare these theoretical spectra to observational ones and interpret what kinds of atoms and molecules might be present in magnetic white dwarfs." The work is also beneficial to two other fields of research. First, it furthers the understanding of chemical changes in atoms and molecules under extreme conditions where magnetic forces counterbalance Coulombic forces. This is an important area of fundamental chemistry research where, for instance, new phenomena are encountered such as "Perpendicular Paramagnetic Bonding"—a novel type of chemical bond that does not occur on Earth. Second, the accurate data obtained using this methodology may help in the development of better functionals for the calculation of magnetic properties in density functional theory, a widely used method in computational chemistry. "Our biggest challenge is the fact that we are examining something that was previously unexplored. This is also what makes this work so interesting," Stopkowicz said. "The results from the computations are often surprising and not necessarily intuitive. Whenever we obtain something new, we have to make sense of it." Going forward, Stopkowicz and her colleagues will continue their work on the key components necessary to generate theoretical spectra for atoms and molecules in strong fields. "There is still a lot of work to do," Stopkowicz said, "but our vision is to contribute to the larger scientific effort to unveil the composition and chemistry of magnetic white dwarfs." Explore further: Chemists discover new type of molecular bond near white dwarf stars More information: Florian Hampe et al, Equation-of-motion coupled-cluster methods for atoms and molecules in strong magnetic fields, The Journal of Chemical Physics (2017). DOI: 10.1063/1.4979624


News Article | August 30, 2016
Site: www.spie.org

Plastic foil substrates and chromium oxide interlayers are used in a novel technology that combines high efficiency, low weight, and extreme flexibility in a single platform. In the pursuit to solve the fossil fuel energy crisis, the use and development of photovoltaic technologies is thriving. In this technology, nature's most abundant source of energy—sunlight—is directly tapped. To achieve this, light-absorbing materials that are highly efficient, lightweight, low-cost, and stable during operation are required. Organolead halide perovskites1 are one such class of materials that show promise for photovoltaic applications, and they have recently become a strong focus of solar cell research. Indeed, their cell efficiency has been increased to about 20%2 within only a few years. Organolead halide perovskites are popular because their raw materials are plentiful and cheap, and because they can be fabricated in a simple manner (i.e., optimal prerequisites for cheap solar power). The limited stability of many perovskite absorbers under ambient conditions, however, may ultimately limit the widespread adoption of these materials in solar cells (especially if heavy and costly packaging is to be avoided). The main issue that gives rise to the poor stability of perovskites is water ingress3 and the subsequent liberation of highly corrosive species that rapidly damage metal contacts. In a previous attempt to overcome this problem,4 thick carbon electrodes were used to enable solar cell operation under ambient conditions. Nonetheless, if power output per solar cell weight (a critical metric for all mobile applications)—as well as power conversion efficiency—is to be optimized, alternative strategies are required. In such approaches, it is necessary to maintain the thin and light form factor of a direct band gap absorber material. In our approach,5 we thus demonstrate ultrathin (3μm), highly flexible perovskite solar cells that have stabilized 12% efficiency and a power-per-weight value as high as 23W/g. To realize these devices, we use 1μm-thick plastic foils as substrates and we process (from solution, at low temperature) pinhole-free perovskite films at high yield. We achieve perfect growth of tightly packed perovskite crystallites by treating the transparent polymer electrode with dimethyl sulfoxide. In addition, we introduce a chromium oxide–chromium interlayer, which effectively protects the metal top contacts from reacting with the perovskite, to facilitate air-stable operation. The detailed structure of our solar foils is depicted in Figure 1, together with a photograph of the freestanding ultrathin solar cell. The transparent conducting electrode and the absorber layer are processed from solution, and the electron-selective metal top contacts are thermally evaporated. Figure 1. (a) Schematic illustration of the cell stack. Polyethylene terephthalate (PET) foils (1.4μm thick) serve as the substrate and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is the transparent hole-selective electrode. Using dimethyl sulfoxide as an additive promotes the formation of pinhole-free perovskite layers. A one-step solution precursor deposition method is used to form the methylammonium lead iodide absorber. Perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) or [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) constitute the electron-transport layers. The chromium (Cr) oxide (Cr O ) stabilizes the metal top contact so that the device can be operated in ambient air. Low-resistivity metals, e.g., gold (Au), copper (Cu), and aluminum (Al), complete the device, and a 1μm-thick capping layer of polyurethane is used for mechanical protection. (b) Photograph of freestanding 3μm-thick solar cells (with copper top-metal contacts). (a) Schematic illustration of the cell stack. Polyethylene terephthalate (PET) foils (1.4μm thick) serve as the substrate and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is the transparent hole-selective electrode. Using dimethyl sulfoxide as an additive promotes the formation of pinhole-free perovskite layers. A one-step solution precursor deposition method is used to form the methylammonium lead iodide absorber. Perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) or [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) constitute the electron-transport layers. The chromium (Cr) oxide (Cr) stabilizes the metal top contact so that the device can be operated in ambient air. Low-resistivity metals, e.g., gold (Au), copper (Cu), and aluminum (Al), complete the device, and a 1μm-thick capping layer of polyurethane is used for mechanical protection. (b) Photograph of freestanding 3μm-thick solar cells (with copper top-metal contacts). 5 Solar cells that have aluminum or gold in direct contact with the perovskite degrade immediately upon exposure to ambient atmosphere. The ingress of water into the absorber layer causes this degradation of the perovskite crystal structure, i.e., by the formation of intermediate hydrated phases. The degradation culminates in the reforming of lead iodide, after enough water has permeated the film. In contrast, chromium oxide is resistant to aggressive oxidizing conditions (even nitric acid and aqua regia). It is for this reason (i.e., the excellent stability) that chromium plating is used to form corrosion-resistant coatings on various metals, and why we use a chromium oxide interlayer to provide an excellent buffer to shield the top-contact metal from chemical etching. We packaged our air-stable, thin, light solar cells (with a micrometer-thick spray-on polyurethane coating) so that they could be operated in field tests, where we used the solar panels to power various unmanned aerial vehicles. A snapshot of our model airplane, on a solar-powered flight, is shown in Figure 2. The same airplane is shown with our solar-powered blimp and a ‘solar leaf’ in a short video clip available online.6 For these tests, we powered the airplane and blimp with a 3μm-thick, 5.2g/cm2, light solar panel (with 64 individual cells). The high power-per-weight performance of our devices (i.e., up to 23W/g) is vital for such applications. Several other solar technologies for decentralized power generation and distribution (e.g., blimps, weather balloons, robotic insects, smart buildings, and aerospace applications), environmental and industrial monitoring, rescue and emergency response, as well as tactical security applications, all have a similar requirement. With our new technology we combine high power conversion efficiency, minimal weight, flexibility, mechanical resilience, operational stability, and low cost in a single platform and thus make the realization of these future concepts possible. Figure 2. Snapshot of the model airplane powered by the perovskite solar cell. This image was captured while the airplane was flying on a sunny winter afternoon (on the campus of the Johannes Kepler University). The airplane has a total weight of about 4.8g and is powered by air-stable, 3μm-thick solar arrays (with a power-per-weight value of 23W/g). The wingspan is 58cm. Through our tests we have also clearly demonstrated the high yield at which we fabricated the solar cells (even on thin, rough plastic foils). Our solar foils are extremely flexible and can endure severe mechanical deformation. In addition, they become stretchable (as shown in the video6) when they are laminated on a pre-stretched rubber band and they conform to arbitrary surfaces. Our foils are therefore ideal power sources for applications where conformability, stretchability, and light weight are required (e.g., portables, wearables, and robotics). In summary, we have presented a novel approach for achieving ultrathin, highly flexible perovskite solar cells. Our devices exhibit stable operation in air, 12% efficiency, and a power-per-weight value of up to 23W/g. The concepts we introduce (i.e., plastic foil substrates and chromium oxide interlayers) are readily applicable to the growing family of perovskite absorbers and could be used to increase the power-per-weight of such materials even further. By merging high efficiency, low weight, and extreme flexibility in our single photovoltaic platform, there seem to be few obstacles to keeping perovskite solar cells grounded. Indeed, our aeronautic models are still fully functional more than six months after their initial flights. In our future research we plan to focus on realizing perovskites with improved efficiency and moisture resistance (by exploring electrode transport materials, alternative metals, and superhydrophobic coatings). We will also investigate further ways to unify the high efficiency of perovskite cells with the low weight and flexibility of our technology. This work was supported by a European Research Council Advanced Investigators Grant (‘Soft-Map’) to Siegfied Bauer and the Austrian Science Fund's Wittgenstein Award (Solare Energie Umwandlung Z222-N19) to Niyazi Serdar Sariciftci. Department of Soft Matter Physics Johannes Kepler University Martin Kaltenbrunner received his PhD from the Johannes Kepler University Linz and then joined the Someya-Sekitani Laboratory for Organic Electronics at the University of Tokyo, Japan. He is now an assistant professor. His research interests include soft transducers, photovoltaics, as well as thin-film, flexible, and stretchable electronics. Siegfried Bauer received his PhD from the University of Karlsruhe, Germany. After stays at the Heinrich Hertz Institute in Berlin and the University of Potsdam (both Germany), he became a professor at the Johannes Kepler University Linz. He has has been head of the department since 2002. His research is devoted to functional soft matter. Institute for Physical Chemistry Johannes Kepler University Niyazi Serdar Sariciftci received his PhD from the University of Vienna, Austria. Following time at the University of Stuttgart, Germany, and the University of California at Santa Barbara, he became a professor at the Johannes Kepler University Linz in 1996. He has been a fellow of SPIE since 2009. His research is focused on organic photovoltaics and energy conversion. 3. A. M. A. Leguy, Y. Hu, M. Campoy-Quiles, M. I. Alonso, O. J. Weber, P. Azarhoosh, M. van Schilfgaarde, et al., Reversible hydration of CH NH PbI in films, single crystals, and solar cells, Chem. Mater. 27, p. 3397-3407, 2015. 5. M. Kaltenbrunner, G. Adam, E. D. Glowacki, M. Drack, R. Schwödiauer, L. Leonat, D. H. Apaydin, et al., Flexible high power-per-weight perovskite solar cells with chromium oxide–metal contacts for improved stability in air, Nat. Mater. 14, p. 1032-1039, 2015. 6. http://spie.org/documents/newsroom/videos/6223/Kaltenbrunner-solar_plane.mp4 a ‘solar leaf’ operated outdoors on sunny winter afternoons, with about 40 kilolux solar irradiation.


Mattner C.,Institute for Physical Chemistry | Roling B.,University of Marburg | Heuer A.,Institute for Physical Chemistry
Solid State Ionics | Year: 2014

For a single-particle hopping model of arbitrary dimension we determine analytically the linear and nonlinear parts of the response to a periodic external field. Despite its simplicity the model contains the effects of localized double-well potential dynamics as well as long-range transport, i.e. reflecting key elements of the dynamics in truly disordered systems. The model parameters reflect typical symmetries between adjacent sites as well as the degree of barrier disorder. It is shown that in the 1D case the dc-limit of the nonlinear conductivity behaves differently than that in higher dimensions. Only for low dimensions the nonlinear conductivity displays a minimum. The scaling of this minimum with system parameters is derived. It is shown that for a broad range of frequencies the nonlinear conductivity can be expressed as a superposition of one contribution related to the linear conductivity, and another one related to the nonlinearity in a double-well potential. The present results are also discussed in the context of recent measurements of the non-linear conductivity for inorganic ion conductors as well as ionic liquids. © 2014 Elsevier B.V.


News Article | March 9, 2016
Site: phys.org

What exactly are the processes when x-ray photons damage biomolecules with a metal centre? This question has been investigated by a team of scientists at the Institute for Physical Chemistry of Heidelberg University. Using the methods of quantum chemistry, they examined the underlying electronic processes caused by x-ray absorption. It turned out that the metal centre plays a key role in destroying a biomolecule. The research results of Vasili Stumpf, Dr. Kirill Gokhberg and Prof. Dr. Lorenz S. Cederbaum have appeared in Nature Chemistry. Radiation damage, arising from the interaction of high-energy x-rays with biological material, is a phenomenon widely known in science. It occurs, for example, when substrates – such as proteins – are analysed using x-ray light in order to determine their electronic structure or the spatial order of atoms. According to Prof. Cederbaum, this damage is most visible in the direct neighbourhood of metal centres, which are essential for the stability and biological function of biomolecules. The Heidelberg researchers investigated the related processes of electronic decay using computer-aided methods from quantum chemistry. They focused on processes occurring when radiation is absorbed through the metal centre of a biomolecule. As a model system they used a microcluster. That is a chemical system in which water molecules are arranged around a metal centre, in this case the positive doubly charged magnesium ion. Prof. Cederbaum explains that the metal centre initially loses several electrons through absorbing the radiation. That produces a highly charged, high-energy metal ion, which then returns to its original state through a cascade of electronic decay steps. In some of them the energy is transferred from the metal centre to the neighbouring molecules – a process known as interatomic Coulombic decay (ICD). In others, electrons from the neighbouring molecules are transferred to the metal ion in the so called electron transfer mediated decay (ETMD). According to Prof. Cederbaum, the two processes are ultrafast and take place on a scale of femtoseconds – the thousand millionth part of a micro-second. So they leave very little time for determination of the accurate molecular structure. In the course of the decay cascade, several neighbouring molecules emit slow electrons, both through the ICD and the ETMD processes. The molecules therefore charge positively, which leads to an explosion of the microcluster. In a bigger system, e.g. a protein with a metal centre, the positively charged neighbouring molecules and the slow electrons would react with the biomolecule and do more secondary damage, Prof. Cederbaum adds. The metal centre works like a lens that focuses the energy of the x-ray light onto its immediate environment. The result is a massive alteration of the surrounding chemical structure on a fast time scale. "We assume that the mechanism we have identified plays an important role when it comes to radiation damage in biological building-blocks with metal atoms – notably proteins and DNA," says Prof. Cederbaum. He hopes that these findings will contribute to decoding the complicated processes caused by radiation in living organisms. Explore further: How do free electrons originate? More information: V. Stumpf et al. The role of metal ions in X-ray-induced photochemistry, Nature Chemistry (2016). DOI: 10.1038/nchem.2429


News Article | November 15, 2016
Site: phys.org

The formation of exciton-polaritons through strong light-matter coupling is a promising strategy for producing electrically pumped carbon-based lasers. Scientists from Heidelberg University and the University of St Andrews (Scotland) have now, for the first time, demonstrated this strong light-matter coupling in semiconducting carbon nanotubes. Credit: Arko Graf (Heidelberg University) With their research on nanomaterials for optoelectronics, scientists from Heidelberg University and the University of St Andrews (Scotland) have succeeded for the first time to demonstrate a strong interaction of light and matter in semiconducting carbon nanotubes. Such strong light-matter coupling is an important step towards realising new light sources, such as electrically pumped lasers based on organic semiconductors. They would be, amongst other things, important for applications in telecommunications. These results are the outcome of a cooperation between Prof. Dr Jana Zaumseil (Heidelberg) and Prof. Dr Malte Gather (St Andrews), and have been published in Nature Communications. Organic semiconductors based on carbon are a cost and energy-efficient alternative to conventional inorganic semiconductors such as silicon. Light-emitting diodes consisting of these materials are already ubiquitously found in smartphone displays. Further components for application in lighting technology, data transmission and photovoltaics are currently at the prototype stage. So far, however, it has not been possible to produce one important component of optoelectronics with organic materials – the electrically pumped laser. The main reason is that organic semiconductors have only limited capacity for charge transport. Prof. Zaumseil explains that research over the past few years has increasingly focused on laser-like light emission of organic semiconductors based on light-matter coupling. If photons (light) and excitons (matter) are brought to interact sufficiently, they couple so strongly that they produce so called exciton-polaritons. These are quasi-particles that also emit light. Under certain conditions, such emissions can take on the properties of laser light. Combined with sufficiently fast charge transport, exciton-polaritons could bring the production of an electrically pumped carbon-based laser within reach, according to Jana Zaumseil who is the head of the Nanomaterials for Optoelectronics research group at the Heidelberg University's Institute for Physical Chemistry. Thanks to the cooperation between Prof. Zaumseil and Prof. Gather, it was possible for the first time to demonstrate the formation of exciton-polaritons in semiconducting carbon nanotubes. Unlike other organic semiconductors, these microscopically small, tube-shaped carbon structures transport positive and negative charges extremely well. PhD student Arko Graf, the first author of the study, explains that exciton-polaritons also display extraordinary optical properties. The scientists in Heidelberg and St Andrews see their research results as an important step towards realising electrically pumped lasers on the basis of organic semiconductors. Prof. Zaumseil emphasises: "Besides the potential generation of laser light, exciton-polaritons already allow us to vary the wavelength of the light emitted by the carbon nanotubes over a wide range in the near-infrared." Explore further: Novel light sources made of 2-D materials More information: Arko Graf et al. Near-infrared exciton-polaritons in strongly coupled single-walled carbon nanotube microcavities, Nature Communications (2016). DOI: 10.1038/ncomms13078


News Article | November 15, 2016
Site: www.cemag.us

With their research on nanomaterials for optoelectronics, scientists from Heidelberg University and the University of St Andrews have succeeded for the first time to demonstrate a strong interaction of light and matter in semiconducting carbon nanotubes. Such strong light-matter coupling is an important step towards realising new light sources, such as electrically pumped lasers based on organic semiconductors. They would be, amongst other things, important for applications in telecommunications. These results are the outcome of a cooperation between Professor Dr. Jana Zaumseil (Heidelberg) and Professor Dr. Malte Gather (St Andrews), and have been published in Nature Communications. Organic semiconductors based on carbon are a cost and energy-efficient alternative to conventional inorganic semiconductors such as silicon. Light-emitting diodes consisting of these materials are already ubiquitously found in smartphone displays. Further components for application in lighting technology, data transmission and photovoltaics are currently at the prototype stage. So far, however, it has not been possible to produce one important component of optoelectronics with organic materials – the electrically pumped laser. The main reason is that organic semiconductors have only limited capacity for charge transport. Zaumseil explains that research over the past few years has increasingly focused on laser-like light emission of organic semiconductors based on light-matter coupling. If photons (light) and excitons (matter) are brought to interact sufficiently, they couple so strongly that they produce so called exciton-polaritons. These are quasi-particles that also emit light. Under certain conditions, such emissions can take on the properties of laser light. Combined with sufficiently fast charge transport, exciton-polaritons could bring the production of an electrically pumped carbon-based laser within reach, according to Zaumseil who is the head of the Nanomaterials for Optoelectronics research group at the Heidelberg University's Institute for Physical Chemistry. Thanks to the cooperation between Zaumseil and Gather, it was possible for the first time to demonstrate the formation of exciton-polaritons in semiconducting carbon nanotubes. Unlike other organic semiconductors, these microscopically small, tube-shaped carbon structures transport positive and negative charges extremely well. PhD student Arko Graf, the first author of the study, explains that exciton-polaritons also display extraordinary optical properties. The scientists in Heidelberg and St Andrews see their research results as an important step towards realizing electrically pumped lasers on the basis of organic semiconductors. Zaumseil emphasises: “Besides the potential generation of laser light, exciton-polaritons already allow us to vary the wavelength of the light emitted by the carbon nanotubes over a wide range in the near-infrared.”


News Article | November 19, 2016
Site: www.sciencedaily.com

With their research on nanomaterials for optoelectronics, scientists from Heidelberg University and the University of St Andrews (Scotland) have succeeded for the first time to demonstrate a strong interaction of light and matter in semiconducting carbon nanotubes. Such strong light-matter coupling is an important step towards realising new light sources, such as electrically pumped lasers based on organic semiconductors. They would be, amongst other things, important for applications in telecommunications. These results are the outcome of a cooperation between Prof. Dr Jana Zaumseil (Heidelberg) and Prof. Dr Malte Gather (St Andrews), and have been published in Nature Communications. Organic semiconductors based on carbon are a cost and energy-efficient alternative to conventional inorganic semiconductors such as silicon. Light-emitting diodes consisting of these materials are already ubiquitously found in smartphone displays. Further components for application in lighting technology, data transmission and photovoltaics are currently at the prototype stage. So far, however, it has not been possible to produce one important component of optoelectronics with organic materials -- the electrically pumped laser. The main reason is that organic semiconductors have only limited capacity for charge transport. Prof. Zaumseil explains that research over the past few years has increasingly focused on laser-like light emission of organic semiconductors based on light-matter coupling. If photons (light) and excitons (matter) are brought to interact sufficiently, they couple so strongly that they produce so called exciton-polaritons. These are quasi-particles that also emit light. Under certain conditions, such emissions can take on the properties of laser light. Combined with sufficiently fast charge transport, exciton-polaritons could bring the production of an electrically pumped carbon-based laser within reach, according to Jana Zaumseil who is the head of the Nanomaterials for Optoelectronics research group at the Heidelberg University's Institute for Physical Chemistry. Thanks to the cooperation between Prof. Zaumseil and Prof. Gather, it was possible for the first time to demonstrate the formation of exciton-polaritons in semiconducting carbon nanotubes. Unlike other organic semiconductors, these microscopically small, tube-shaped carbon structures transport positive and negative charges extremely well. PhD student Arko Graf, the first author of the study, explains that exciton-polaritons also display extraordinary optical properties. The scientists in Heidelberg and St Andrews see their research results as an important step towards realising electrically pumped lasers on the basis of organic semiconductors. Prof. Zaumseil emphasises: "Besides the potential generation of laser light, exciton-polaritons already allow us to vary the wavelength of the light emitted by the carbon nanotubes over a wide range in the near-infrared."


News Article | November 24, 2016
Site: www.materialstoday.com

As part of their research on nanomaterials for optoelectronics, scientists from Heidelberg University in Germany and the University of St Andrews in the UK have succeeded for the first time in demonstrating a strong interaction between light and matter in semiconducting carbon nanotubes. Such strong light-matter coupling is an important step towards realizing new light sources such as electrically-pumped lasers based on organic semiconductors, which could find several important applications, including in telecommunications. These results came out of a cooperation between Jana Zaumseil at Heidelberg and Malte Gather at St Andrews, and are reported in a paper in Nature Communications. Organic semiconductors based on carbon are an inexpensive and energy-efficient alternative to conventional inorganic semiconductors such as silicon. Light-emitting diodes (LEDs) made from these organic materials are already found in smartphone displays, while other organic semiconductor components for use in lighting technology, data transmission and photovoltaics are currently at the prototype stage. So far, however, it has not been possible to produce one important component of optoelectronics with organic materials – the electrically-pumped laser. The main reason being that organic semiconductors have only a limited capacity for charge transport. Research over the past few years has increasingly focused on laser-like light emission by organic semiconductors based on light-matter coupling, says Zaumseil, who is head of the Nanomaterials for Optoelectronics research group at Heidelberg University's Institute for Physical Chemistry. If photons (light) and excitons (matter) are brought together to interact, they can couple strongly enough to produce so-called exciton-polaritons, which are quasi-particles that also emit light. Under certain conditions, such emissions can take on the properties of laser light. Combined with a sufficiently fast charge transport, exciton-polaritons could bring the production of an electrically-pumped carbon-based laser within reach. Now, for the first time, the team led by Zaumseil and Gather has been able to demonstrate the formation of exciton-polaritons in semiconducting carbon nanotubes. Unlike other organic semiconductors, these microscopically small, tube-shaped carbon structures transport positive and negative charges extremely well. According to PhD student Arko Graf, the first author of the paper, exciton-polaritons also display extraordinary optical properties. The scientists see their research results as an important step towards realizing electrically-pumped lasers made from organic semiconductors. “Besides the potential generation of laser light, exciton-polaritons already allow us to vary the wavelength of the light emitted by the carbon nanotubes over a wide range in the near-infrared,” says Zaumseil. This story is adapted from material from Heidelberg University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


Pandey S.K.,CSIR - National Chemical Laboratory | Jogdand G.F.,CSIR - National Chemical Laboratory | Oliveira J.C.A.,Institute for Physical Chemistry | Mata R.A.,Institute for Physical Chemistry | And 2 more authors.
Chemistry - A European Journal | Year: 2011

The synthesis of homochiral homo-oligomers of cis- and trans-3- aminotetrahydrofuran-2-carboxylic acids (parent cis- and trans-furanoid-β- amino acids, referred to as "cis-/trans-FAA") has been carried out to understand their secondary structures and their dependence on the ring heteroatom. The oligomers of two diastereomers have been shown to have a distinct left-handed helicity. The cis-FAA homo-oligomers show a 14-helix structure, in contrast to the homo-oligomers of cis-ACPC, which adopt a sheet like structure. The trans-FAA homo-oligomers were found to adopt a 12-helix structure, the same trend found in trans-ACPC homo-oligomers. With the help of ab initio calculations, the structural features of cis-ACPC and cis-FAA hexamers were compared. We believe that the more compact packing of the cis-FAA hexapeptide should be due to a more favorable interaction between the ring and the backbone amide hydrogen. It's the heteroatom that counts: trans-Furanoid-β-amino acid (FAA) homo-oligomers adopt a 12-helix structure similar to that of trans-ACPC (2-aminocyclopentane carboxylic acid) oligomers. However, cis-FAA oligomers seem to adopt 14-helix solution structures, which is in contrast to cis-ACPC oligomers, for which a sheetlike structure has been observed. Calculations reveal that this preference in cis-FAAs is due to a more favorable contact between the backbone and the ring (see scheme). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


News Article | November 25, 2015
Site: www.forbes.com

Starfire Energy is picking up where the Kaiser Wilhelm Institute for Physical Chemistry left off.

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