The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Filippo De Angelis - One of the best experts on this subject based on the ideXlab platform.
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interface electrostatics of solid state dye sensitized solar cells a joint drift diffusion and density functional theory study
Journal of Physical Chemistry C, 2019Co-Authors: Ajay Singh, Filippo De Angelis, Simona Fantacci, Eros Radicchi, Francesca Nunzi, Alessio GagliardiAbstract:Dye-sensitized solar cells (DSCs) have gained great attention in recent years due to their low-cost fabrication, flexibility and high power conversion efficiency. In a DSC, due to interfaces between the dye and the charge transport materials, the interface electrostatics becomes a key factor determining the overall performance of the cell. Liquid electrolyte based DSCs suffer low stability, electrolyte leakage and in some cases electrode corrosion. Replacing liquid electrolyte with a solid semiconducting material leads to poor interfacial contacts, hence the interface electrostatics becomes one of the limiting factors. In this work, we present a drift-diffusion (DD) and density functional theory (DFT) study of solid-state DSCs to investigate the electrostatics at the TiO2/organic dye/Spiro OMeTAD interface, and its impact to the adsorbed dye energy levels, its absorption spectrum and the related charge Injection. In our 3D drift-diffusion model, we solve a set of drift-diffusion equations coupled to Poisson equation for electrons, holes, doping impurities and the interface traps simultaneously. After that, we use first principles DFT modeling of dye-sensitized interfaces in the presence of the calculated electric fields. We find that interface traps located below the conduction band edge of mesoporous TiO2 influence the accumulation of photogenerated holes and built-in electric field near the interface. The built-in electric field leads to change the energetics at the dye/TiO2 interface leading to poor charge Injection from excited dye into the TiO2. The simulations were carried out for different electronic trap density in TiO2 and different doping levels in the Spiro OMeTAD hole transport layer. This study helps to a better understanding of interface electrostatics and its role in the charge Injection Mechanism of solid-state DSCs.
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interface electrostatics of solid state dye sensitized solar cells a joint drift diffusion and density functional theory study
The Journal of Physical Chemistry, 2019Co-Authors: Ajay Singh, Filippo De Angelis, Simona Fantacci, Eros Radicchi, Francesca Nunzi, Alessio GagliardiAbstract:Dye-sensitized solar cells (DSCs) have gained great attention in recent years due to their low-cost fabrication, flexibility, and high power conversion efficiency. In a DSC, due to interfaces between the dye and the charge-transport materials, the interface electrostatics becomes a key factor determining the overall performance of the cell. Liquid-electrolyte-based DSCs suffer from low stability, electrolyte leakage, and, in some cases, electrode corrosion. Replacing liquid electrolyte with a solid semiconducting material leads to poor interfacial contacts, hence the interface electrostatics becomes one of the limiting factors. In this work, we present a drift-diffusion and density functional theory (DFT) study of solid-state DSCs to investigate the electrostatics at the TiO₂/organic dye/Spiro-OMeTAD interface and its impact on the adsorbed dye energy levels, its absorption spectrum, and the related charge Injection. In our three-dimensional drift-diffusion model, we solve a set of drift-diffusion equations coupled to Poisson equation for electrons, holes, doping impurities, and interface traps simultaneously. After that, we use first-principles DFT modeling of dye-sensitized interfaces in the presence of the calculated electric fields. We find that interface traps located below the conduction band edge of mesoporous TiO₂ influence the accumulation of photogenerated holes and built-in electric field near the interface. The built-in electric field leads to change in the energetics at the dye/TiO₂ interface, leading to poor charge Injection from excited dye into TiO₂. The simulations were carried out for different electronic trap densities in TiO₂ and different doping levels in the Spiro-OMeTAD hole-transport layer. This study helps to a better understanding of the interface electrostatics and its role in the charge Injection Mechanism of solid-state DSCs.
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computational modelling of tio2 surfaces sensitized by organic dyes with different anchoring groups adsorption modes electronic structure and implication for electron Injection recombination
Physical Chemistry Chemical Physics, 2012Co-Authors: Mariachiara Pastore, Filippo De AngelisAbstract:We present a Density Functional Theory investigation aimed to model the possible adsorption modes to the TiO2 surface of two representative TPA-based dyes, termed L0 and rh-L0, having the two mostly employed anchoring groups, namely the cyanoacrylic and rhodanine-3-acetic acids respectively. The bidentate coordination with proton transfer to a nearby surface oxygen is found to be the energetically favored anchoring mode for both dyes. The calculations show that the different dye anchoring groups give rise to a very different electronic coupling between the dye and the manifold of unoccupied semiconductor states, thus implying different electron Injection Mechanisms. The strongly coupled L0 dye possibly shows an adiabatic electron Injection Mechanism, while a non-adiabatic electron Injection can be foreseen for the weakly coupled rh-L0 dye. The different orientation with respect to the TiO2 surface for the two classes of dyes, implying different distances of the donor group from the oxide surface, together with the different electron Injection Mechanisms might account for the faster recombination reaction measured for the rhodanine-based dyes.
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time dependent density functional theory investigations on the excited states of ru ii dye sensitized tio2 nanoparticles the role of sensitizer protonation
Journal of the American Chemical Society, 2007Co-Authors: Filippo De Angelis, Simona Fantacci, Annabella Selloni, Mohammad Khaja Nazeeruddin, Michael GratzelAbstract:We performed fully first principles quantum mechanical calculations of the ground- and excited-state properties of the [cis-(NCS)2-Ru(II)-bis(2,2‘-bipyridine-4,4‘-dicarboxylate)] dye, N719, adsorbed onto a model TiO2 nanoparticle. Our study confirms an indirect electron Injection Mechanism for Ru(II) dyes on TiO2 and indicates a remarkable effect of dye protonation on the electronic properties of N719-sensitized TiO2 nanoparticles. We find that two different electron Injection Mechanisms (adiabatic and nonadiabatic) may be present in DSSCs employing dyes carrying a different number of protons. Despite such differences, the absorption spectra corresponding to strongly and weakly coupled dye/TiO2 excited states are remarkably similar, so that a discrimination of the two electron Injection regimes does not appear to be feasible based on inspection of the absorption spectra.
Stefan Raunser - One of the best experts on this subject based on the ideXlab platform.
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tc toxin activation requires unfolding and refolding of a beta propeller
Nature, 2018Co-Authors: Christos Gatsogiannis, Felipe Merino, Daniel Roderer, David Balchin, Evelyn Schubert, Anne Kuhlee, Manajit Hayerhartl, Stefan RaunserAbstract:Tc toxins secrete toxic enzymes into host cells using a unique syringe-like Injection Mechanism. They are composed of three subunits, TcA, TcB and TcC. TcA forms the translocation channel and the TcB-TcC heterodimer functions as a cocoon that shields the toxic enzyme. Binding of the cocoon to the channel triggers opening of the cocoon and translocation of the toxic enzyme into the channel. Here we show in atomic detail how the assembly of the three components activates the toxin. We find that part of the cocoon completely unfolds and refolds into an alternative conformation upon binding. The presence of the toxic enzyme inside the cocoon is essential for its subnanomolar binding affinity for the TcA subunit. The enzyme passes through a narrow negatively charged constriction site inside the cocoon, probably acting as an extruder that releases the unfolded protein with its C terminus first into the translocation channel.
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a syringe like Injection Mechanism in photorhabdus luminescens toxins
Nature, 2013Co-Authors: Christos Gatsogiannis, Roland Benz, D Meusch, Vanda Pfaumann, Oliver Hofnagel, Stefan RaunserAbstract:The TcA component of Photorhabdus luminescens ABC-type toxin complexes forms a transmembrane pore and injects TcC, the functional component of the toxin, into the target cell by means of a syringe-like Mechanism.
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a syringe like Injection Mechanism in photorhabdus luminescens toxins
Nature, 2013Co-Authors: Christos Gatsogiannis, Roland Benz, D Meusch, Vanda Pfaumann, Oliver Hofnagel, Stefan RaunserAbstract:The TcA component of Photorhabdus luminescens ABC-type toxin complexes forms a transmembrane pore and injects TcC, the functional component of the toxin, into the target cell by means of a syringe-like Mechanism. The bacterium Photorhabdus luminescens lives in symbiosis with nematodes that invade and — by releasing bacterial virulence factors — kill insect larvae. Among the toxins produced by P. luminescens are large tripartite ABC-type toxin complexes (Tcs). Here Stefan Raunser and colleagues show that the TcA (TcdA1) component of the Tcs forms a transmembrane pore and report its structure in the pre-pore and pore state determined by cryoelectron microscopy. Their analysis reveals a syringe-like Mechanism of protein translocation and demonstrates how ABC-type toxin complexes bridge a membrane to inject directly into the cytoplasm of the host cell. Photorhabdus luminescens is an insect pathogenic bacterium that is symbiotic with entomopathogenic nematodes1. On invasion of insect larvae, P. luminescens is released from the nematodes and kills the insect through the action of a variety of virulence factors including large tripartite ABC-type toxin complexes2 (Tcs). Tcs are typically composed of TcA, TcB and TcC proteins and are biologically active only when complete3,4,5. Functioning as ADP-ribosyltransferases, TcC proteins were identified as the actual functional components that induce actin-clustering, defects in phagocytosis and cell death5,6,7. However, little is known about the translocation of TcC into the cell by the TcA and TcB components. Here we show that TcA in P. luminescens (TcdA1) forms a transmembrane pore and report its structure in the prepore and pore state determined by cryoelectron microscopy. We find that the TcdA1 prepore assembles as a pentamer forming an α-helical, vuvuzela-shaped channel less than 1.5 nanometres in diameter surrounded by a large outer shell. Membrane insertion is triggered not only at low pH as expected, but also at high pH, explaining Tc action directly through the midgut of insects8. Comparisons with structures of the TcdA1 pore inserted into a membrane and in complex with TcdB2 and TccC3 reveal large conformational changes during membrane insertion, suggesting a novel syringe-like Mechanism of protein translocation. Our results demonstrate how ABC-type toxin complexes bridge a membrane to insert their lethal components into the cytoplasm of the host cell. We believe that the proposed Mechanism is characteristic of the whole ABC-type toxin family. This explanation of toxin translocation is a step towards understanding the host–pathogen interaction and the complex life cycle of P. luminescens and other pathogens, including human pathogenic bacteria, and serves as a strong foundation for the development of biopesticides.
Christos Gatsogiannis - One of the best experts on this subject based on the ideXlab platform.
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tc toxin activation requires unfolding and refolding of a beta propeller
Nature, 2018Co-Authors: Christos Gatsogiannis, Felipe Merino, Daniel Roderer, David Balchin, Evelyn Schubert, Anne Kuhlee, Manajit Hayerhartl, Stefan RaunserAbstract:Tc toxins secrete toxic enzymes into host cells using a unique syringe-like Injection Mechanism. They are composed of three subunits, TcA, TcB and TcC. TcA forms the translocation channel and the TcB-TcC heterodimer functions as a cocoon that shields the toxic enzyme. Binding of the cocoon to the channel triggers opening of the cocoon and translocation of the toxic enzyme into the channel. Here we show in atomic detail how the assembly of the three components activates the toxin. We find that part of the cocoon completely unfolds and refolds into an alternative conformation upon binding. The presence of the toxic enzyme inside the cocoon is essential for its subnanomolar binding affinity for the TcA subunit. The enzyme passes through a narrow negatively charged constriction site inside the cocoon, probably acting as an extruder that releases the unfolded protein with its C terminus first into the translocation channel.
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a syringe like Injection Mechanism in photorhabdus luminescens toxins
Nature, 2013Co-Authors: Christos Gatsogiannis, Roland Benz, D Meusch, Vanda Pfaumann, Oliver Hofnagel, Stefan RaunserAbstract:The TcA component of Photorhabdus luminescens ABC-type toxin complexes forms a transmembrane pore and injects TcC, the functional component of the toxin, into the target cell by means of a syringe-like Mechanism.
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a syringe like Injection Mechanism in photorhabdus luminescens toxins
Nature, 2013Co-Authors: Christos Gatsogiannis, Roland Benz, D Meusch, Vanda Pfaumann, Oliver Hofnagel, Stefan RaunserAbstract:The TcA component of Photorhabdus luminescens ABC-type toxin complexes forms a transmembrane pore and injects TcC, the functional component of the toxin, into the target cell by means of a syringe-like Mechanism. The bacterium Photorhabdus luminescens lives in symbiosis with nematodes that invade and — by releasing bacterial virulence factors — kill insect larvae. Among the toxins produced by P. luminescens are large tripartite ABC-type toxin complexes (Tcs). Here Stefan Raunser and colleagues show that the TcA (TcdA1) component of the Tcs forms a transmembrane pore and report its structure in the pre-pore and pore state determined by cryoelectron microscopy. Their analysis reveals a syringe-like Mechanism of protein translocation and demonstrates how ABC-type toxin complexes bridge a membrane to inject directly into the cytoplasm of the host cell. Photorhabdus luminescens is an insect pathogenic bacterium that is symbiotic with entomopathogenic nematodes1. On invasion of insect larvae, P. luminescens is released from the nematodes and kills the insect through the action of a variety of virulence factors including large tripartite ABC-type toxin complexes2 (Tcs). Tcs are typically composed of TcA, TcB and TcC proteins and are biologically active only when complete3,4,5. Functioning as ADP-ribosyltransferases, TcC proteins were identified as the actual functional components that induce actin-clustering, defects in phagocytosis and cell death5,6,7. However, little is known about the translocation of TcC into the cell by the TcA and TcB components. Here we show that TcA in P. luminescens (TcdA1) forms a transmembrane pore and report its structure in the prepore and pore state determined by cryoelectron microscopy. We find that the TcdA1 prepore assembles as a pentamer forming an α-helical, vuvuzela-shaped channel less than 1.5 nanometres in diameter surrounded by a large outer shell. Membrane insertion is triggered not only at low pH as expected, but also at high pH, explaining Tc action directly through the midgut of insects8. Comparisons with structures of the TcdA1 pore inserted into a membrane and in complex with TcdB2 and TccC3 reveal large conformational changes during membrane insertion, suggesting a novel syringe-like Mechanism of protein translocation. Our results demonstrate how ABC-type toxin complexes bridge a membrane to insert their lethal components into the cytoplasm of the host cell. We believe that the proposed Mechanism is characteristic of the whole ABC-type toxin family. This explanation of toxin translocation is a step towards understanding the host–pathogen interaction and the complex life cycle of P. luminescens and other pathogens, including human pathogenic bacteria, and serves as a strong foundation for the development of biopesticides.
Sergej O. Demokritov - One of the best experts on this subject based on the ideXlab platform.
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route toward high speed nano magnonics provided by pure spin currents
Applied Physics Letters, 2016Co-Authors: B Divinskiy, Sergej O. Demokritov, V E Demidov, A B Rinkevich, Sergei UrazhdinAbstract:We study experimentally the possibility to utilize pulses of pure spin current, produced via the nonlocal spin Injection Mechanism, to generate short packets of spin waves propagating in nanoscale magnetic waveguides. Spatially and time-resolved micro-focus Brillouin light scattering spectroscopy measurements demonstrate that the excitation by spin current results in extremely fast transient response, enabling efficient generation of short spin-wave packets with duration down to a few nanoseconds. The proposed method opens a route for the implementation of high-speed magnonic systems for transmission and processing of information on the nanoscale.
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excitation of coherent propagating spin waves by pure spin currents
Nature Communications, 2016Co-Authors: Vladislav E. Demidov, Sergei Urazhdin, Sergej O. Demokritov, R H Liu, B Divinskiy, A V TeleginAbstract:Utilization of pure spin currents not accompanied by the flow of electrical charge provides unprecedented opportunities for the emerging technologies based on the electron's spin degree of freedom, such as spintronics and magnonics. It was recently shown that pure spin currents can be used to excite coherent magnetization dynamics in magnetic nanostructures. However, because of the intrinsic nonlinear self-localization effects, magnetic auto-oscillations in the demonstrated devices were spatially confined, preventing their applications as sources of propagating spin waves in magnonic circuits using these waves as signal carriers. Here, we experimentally demonstrate efficient excitation and directional propagation of coherent spin waves generated by pure spin current. We show that this can be achieved by using the nonlocal spin Injection Mechanism, which enables flexible design of magnetic nanosystems and allows one to efficiently control their dynamic characteristics.
Kaustav Banerjee - One of the best experts on this subject based on the ideXlab platform.
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proposal for tunnel field effect transistor as ultra sensitive and label free biosensors
Applied Physics Letters, 2012Co-Authors: Deblina Sarkar, Kaustav BanerjeeAbstract:Tunnel field-effect-transistor (TFET) based biosensor is proposed, and it is shown that they can surpass by several orders, the performance of those based on conventional FET (CFET) and hence, can potentially revolutionize the biosensing applications. Analytical formula is derived for the sensitivity and response time to provide physical insights in terms of material bandgap and operation regime of the TFET biosensor for achieving optimal results. At the same time, rigorous numerical simulations have been performed in order to obtain accurate values of sensitivity for both biomolecule and pH sensing operations. The time dependent response of the biosensors has also been discussed through analytical and numerical solutions. It is shown that while the CFET biosensors suffer from fundamental limitations on the maximum sensitivity and minimum detection time achievable, TFET biosensors, with their fundamentally different current Injection Mechanism in the form of band-to-band tunneling, can overcome such limitations and lead to over four orders of magnitude higher sensitivity and over an order of magnitude lower response time.