Suchergebnisse

This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 639846). ; AlSb is a less studied member of the III-V semiconductor family, and herein, we report the colloidal synthesis of AlSb quantum dots (QDs) for the first time. Different sizes of colloidal AlSb QDs (5 to 9 nm) were produced by the controlled reaction of AlCl3 and Sb[N(Si(Me)(3))(2)](3) in the presence of superhydride. These colloidal AlSb quantum dots showed excitonic transitions in the UV-A region and a tunable band edge emission (quantum yield of up to 18%) in the blue spectral range. Among all III-V quantum dots, these quantum dots show the brightest core emission in the blue spectral region. ; European Research Council (ERC) 639846

Quantum dots are model systems for quantum thermoelectric behavior because of their ability to control and measure the effects of electron-energy filtering and quantum confinement on thermoelectric properties. Interestingly, nonlinear thermoelectric properties of such small systems can modify the efficiency of thermoelectric power conversion. Using quantum dots embedded in semiconductor nanowires, we measure thermovoltage and thermocurrent that are strongly nonlinear in the applied thermal bias. We show that most of the observed nonlinear effects can be understood in terms of a renormalization of the quantum-dot energy levels as a function of applied thermal bias and provide a theoretical model of the nonlinear thermovoltage taking renormalization into account. Furthermore, we propose a theory that explains a possible source of the observed, pronounced renormalization effect by the melting of Kondo correlations in the mixed-valence regime. The ability to control nonlinear thermoelectric behavior expands the range in which quantum thermoelectric effects may be used for efficient energy conversion. © IOP Publishing and Deutsche Physikalische Gesellschaft. ; Financially supported by ONR, ONR Global, the Swedish Energy Agency (grant number 32920–1), the Swedish Research Council (VR), the Thai government, NSF-IGERT, the Knut and Alice Wallenberg Foundation, the MINECO (grant number FIS2011-23526), the Latvian Council of Science (grant number 146/2012), the National Basic Research Program of the Ministry of Science and Technology of China (grant numbers 2012CB932703 and 2012CB932700), the National Natural Science Foundation of China (grant number 91221202) and the Nanometer Structure Consortium at Lund University (nmC@LU). ; Peer Reviewed

3 pages, 1 figure.-- PACS nrs.: 73.21.La, 73.22.-f, 73.20.At, 71.15.Ap.-- Presented as poster communication to TNT 2008: Trends in NanoTechnology (Oviedo, Spain, Sep 1-5, 2008). ; The interface states of all-metallic carbon nanotube quantum dots are studied based on a tight-binding approach and a Green's function matching technique. We have found that depending on the type of metallic tube, the energy of interface states may show an oscillatory behavior. We identify these as steamming from Friedel oscillations. We comment on the possible implications of this finding on other physical properties, such as stability during the growth of nanotube junctions and magnetic interaction through carbon nanotubes. ; We acknowledge financial support by the ETORTEK (NANOMAT) program of the Basque government, the Intramural Special Project (Ref. No. 2006601242), the Spanish Ministerio de Ciencia y Tecnología (Grants No. Fis 2007-66711-C02-C01 and MAT2006-06242) and the European Network of Excellence NANOQUANTA (NM4-CT-2004-500198). ; Peer reviewed

A recent study by a team of government researchers considered the application of colloidal quantum dots applied as a paint to be used in next-generation optical deformation sensors, with the potential to simplify the non-destructive evaluation process.

7 pags., 4 figs. -- Open Access funded by Creative Commons Atribution Licence 4.0 ; The combination of single particle detection and ultrafast laser pulses is an instrumental method to track dynamics at the femtosecond time scale in single molecules, quantum dots and plasmonic nanoparticles. Optimal control of the extremely short-lived coherences of these individual systems has so far remained elusive, yet its successful implementation would enable arbitrary external manipulation of otherwise inaccessible nanoscale dynamics. In ensemble measurements, such control is often achieved by resorting to a closed-loop optimization strategy, where the spectral phase of a broadband laser field is iteratively optimized. This scheme needs long measurement times and strong signals to converge to the optimal solution. This requirement is in conflict with the nature of single emitters whose signals are weak and unstable. Here we demonstrate an effective closed-loop optimization strategy capable of addressing single quantum dots at room temperature, using as feedback observable the two-photon photoluminescence induced by a phase-controlled broadband femtosecond laser. Crucial to the optimization loop is the use of a deterministic and robust-against-noise search algorithm converging to the theoretically predicted solution in a reduced amount of steps, even when operating at the few-photon level. Full optimization of the single dot luminescence is obtained within ∼100 trials, with a typical integration time of 100 ms per trial. These times are faster than the typical photobleaching times in single molecules at room temperature. Our results show the suitability of the novel approach to perform closed-loop optimizations on single molecules, thus extending the available experimental toolbox to the active control of nanoscale coherences. ; This research was funded by the European Commission (ERC Adv. Grant 247330-NanoAntennas and ERC Adv. Grant 670949-LightNet), Spanish Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0522), Plan Nacional Project FIS2012-35527, co-funded by FEDER, the Catalan AGAUR (2014 SGR01540) and Fundació CELLEX (Barcelona). PMdR acknowledges financial support from Spanish Government MINECO-FPI grant and European Science Foundation under the PLASMON-BIONANOSENSE Exchange Grant program. MGS acknowledges financial support from grants MICINN TEC2011-22422 and MINECO TEC2014-52642-C2-1-R. ; Peer Reviewed

The results of a qualitative analysis of a semiclassical model of light generation in low-dimensional solidstate lasers, including quantum-dot microlasers and, on its basis, a numerical modelling of the regular pulsation regime that occurs under conditions of nonlinear shift and broadening of the resonant spectral gain line due to the influence of dipoledipoles interaction and absorption in quasi-resonant transitions on the dielectric susceptibility of the active medium are herein presented. The modelling of lasing was carried out for the parameters of semiconductor quantum-dot structures.

5783 5790 4 10 ; S ; [EN] With energy conversion efficiencies in continuous growth, quantum dot sensitized solar cells (QDSCs) are currently under an increasing interest, but there is an absence of a complete model for these devices. Here, we compile the latest developments in this kind of cells in order to attain high efficiency QDSCs, modeling the performance. CdSe QDs have been grown directly on a TiO(2) surface by successive ionic layer adsorption and reaction to ensure high QD loading. ZnS coating and previous growth of OS were analyzed. Polysulfide electrolyte and Cu(2)S counterelectrodes were used to provide higher photocurrents and fill factors, FF. Incident photon-to-current efficiency peaks as high as 82%, under full 1 sun illumination, were obtained, which practically overcomes the photocurrent limitation commonly observed in QDSCs. High power conversion efficiency of up to 3.84% under full 1 sun illumination (V(oc) = 0.538 V, j(sc) = 13.9 mA/cm(2), FF = 0.51) and the characterization and modeling carried out indicate that recombination has to be overcome for further improvement of QDSC. This work was supported by the Ministerio de Ciencia e Innovacion of Spain under the projects HOPE C5D2007-00007, JES-NANOSOLAR PLE2009-0042, and MAT2007-62982, and by Generalitat Valenciana under the project PROME-TEO/2009/058. The authors want to acknowledge S. Gimenez for the TEM measurements and the calculation of expected currents from IPCE, A. Braga for the preparation of CdS sensitized substrates, and also the SCIC of University Jaume I (Spain) for providing the microscopy facilities. González Pedro, MV.; Xu, X.; Mora-Sero, I.; Bisquert Mascarell, JA. (2010). Modeling High-Efficiency Quantum Dot Sensitized Solar Cells. ACS Nano. 4(10):5783-5790. https://doi.org/10.1021/nn101534y

3 pages, 4 figures. ; We have grown self-organized InSb quantum dots on semi-insulating InP (001) substrates by molecular beam epitaxy. We studied the size dependency of the uncapped InSb quantum dots on the nominal thickness of the deposited InSb by atomic force microscopy. The dot sizes have a pronounced minimum at about 2.2 monolayers of InSb. After a nominal thickness of 3.2 monolayers we observe a drastic change of the dot shape, from quantum dots to quantum dashes. From there on the dots grow in a quasicylindric shape aligned in the (110) direction. ; The authors would like to acknowledge gratefully financial support from the European Union (HCM, Network CT930349). ; Peer reviewed

Perovskite quantum dots (QDs) are of interest for solution-processed lasers; however, their short Auger lifetime has limited lasing operation principally to the femtosecond temporal regime the photoexcitation levels to achieve optical gain threshold are up to two orders of magnitude higher in the nanosecond regime than in the femtosecond. Here the authors report QD superlattices in which the gain medium facilitates excitonic delocalization to decrease Auger recombination and in which the macroscopic dimensions of the structures provide the optical feedback required for lasing. The authors develope a self-assembly strategy that relies on sodiumd—an assembly director that passivates the surface of the QDs and induces self-assembly to form ordered three-dimensional cubic structures. A density functional theory model that accounts for the attraction forces between QDs allows to explain self-assembly and superlattice formation. Compared to conventional organic-ligand-passivated QDs, sodium enables higher attractive forces, ultimately leading to the formation of micron-length scale structures and the optical faceting required for feedback. Simultaneously, the decreased inter-dot distance enabled by the new ligand enhances exciton delocalization among QDs, as demonstrated by the dynamically red-shifted photoluminescence. These structures function as the lasing cavity and the gain medium, enabling nanosecond-sustained lasing with a threshold of 25 μJ cm–2. ; C.Z., J.M.P., and T.Z. contributed equally to this work. L.Z. and H.D. acknowledge the National Natural Science Foundation of China (Grant Nos. 61875256, 61675219, and 91950201). This work was partially funded by the Natural Sciences and Engineering Research Council of Canada (NSERC). M.I.S. acknowledges the support of Banting Postdoctoral Fellowship Program, administered by the Government of Canada. WAXS and SAXS measurements were performed in the Canadian Light Source CLS, a national research facility of the University of Saskatchewan, which is supported by the Canada Foundation for Innovation (CFI), NSERC, the National Research Council (NRC), the Canadian Institutes ofHealth Research (CIHR), the Government of Saskatchewan, and the University of Saskatchewan. The authors acknowledge the technical assistance and scientific guidance of C.-Y. Kim and A. Leontowich at the CLS. The authors also acknowledge the help and useful discussions of A. Johnston, S. Teale, and J. Fan regarding the WAXS and SAXS data. They also acknowledge the useful discussions with R. Sabatini regarding transient PL data. H.D. acknowledges the Youth Top-notch Talent Support Program in Shanghai. The authors again acknowledge the University of Chinese Academy of Sciences (UCAS) Joint Ph.D. Training Program.

10 pags., 4 fiigs. ; Topological quantum dots (TQDs) are 3D topological insulator (TI) nanoparticles, displaying symmetry-protected surface states with discretized energies. We present a theoretical proposal to harness these energy levels in a closed lasing scheme operating in the terahertz (THz) frequency range. In this scheme, a single TQD lases from its topological surface states in the THz regime when pumped with low intensity, incoherent THz frequency light. The time scales associated with the system are unusually slow, and we find that lasing occurs with a very low threshold. THz lasers are often bulky or require intricately engineered nanostructures. Topological quantum dots present a new, compact and simple platform for THz lasing. The lasing threshold is so low, we predict that the room-temperature blackbody radiation can substantially contribute to population inversion, providing a route to room-temperature THz lasing pumped via blackbody radiation. ; M. S. R. would like to acknowledge the financial support of the Centre for Doctoral Training on Theory and Simulation of Materials at Imperial College London funded by EPSRC Grant No. EP/L015579/1. V. G. acknowledges the Spanish Ministerio de Economia y Competitividad for financial support through the grant NANOTOPO (FIS2017-91413-EXP), and also the Ministerio de Ciencia, Innovación y Universidades through the grant MELODIA (PGC2018-095777-B-C21). V. G. thanks the "ENSEMBLE3 - Centre of Excellence for nanophotonics, advanced materials and novel crystal growth-based technologies" project (GA No. MAB/2020/14) carried out within the International Research Agendas programme of the Foundation for Polish Science co-financed by the European Union under the European Regional Development Fund and the European Union's Horizon 2020 research and innovation programme Teaming for Excellence (GA. No. 857543) for support of this work.