Suchergebnisse

The lymphatic system is essential for fluid regulation and for the maintenance of host immunity. However, in vivo lymph flow is difficult to track in real time, because of the lack of an appropriate imaging method. In this study, we combined macro-zoom fluorescence microscopy with quantum-dot (Qdot) optical lymphatic imaging to develop an in vivo real-time optical lymphatic imaging method that allows the tracking of lymph through lymphatic channels and into lymph nodes. After interstitial injection of Qdots in a mouse, rapid visualization of the cervical lymphatics and cervical lymph nodes was achieved. Real-time monitoring of the injected Qdots revealed that the cortex of the node enhanced first followed by a net-like pattern in the central portion of the node. Histology revealed that the rim and net-like enhancing regions corresponded to the subcapsular sinuses and medullary sinuses respectively. Additionally, multiplexed two-color real-time lymphatic tracking was performed with two different Qdots. With this real-time imaging system, we successfully tracked microscopic lymphatic flow in vivo. This method could have a potential impact for lymphatic research in visualizing normal or abnormal functional lymphatic flows. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

Semiconductor quantum dots (QDs) acting as single-photon-emitters are potential building blocks for various applications in future quantum information technology. For such applications, a thorough understanding and precise control of charge states and capture/recombination dynamics of the QDs are vital. In this work, we study the dynamics of QDs spontaneously formed in GaNAsP nanowires, belonging to the dilute nitride material system. By using a random population model modified for these highly mismatched materials, we analyze the results from photoluminescence and photon correlation experiments and show a general trend of disparity in positive and negative trion populations and also a strong dependence of the capture/recombination dynamics and QD charge states on its surroundings. Specifically, we show that the presence of hole-trap defects in the proximity to some QDs facilitates formation of negative trions, which also causes a dramatic reduction of the neutral exciton lifetime. These findings underline the importance of proper understanding of the QD capture and recombination processes and demonstrate the possibility to use highly mismatched materials and defects for charge engineering of QDs. ; Funding Agencies|Swedish Research CouncilSwedish Research CouncilEuropean Commission [2019-04312]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]

Herein we show a solution based synthetic pathway to obtain a resonant optical cavity with embedded colloidal semiconductor quantum dots (CSQDs). The optical cavity pore network, surrounded by two dense Bragg mirrors, was designed ad hoc to selectively host the quantum dots, while uncontrolled infiltration of those in the rest of the layered structure was prevented. Coupling between the optical resonant modes of the host and the natural emission of the embedded nanoparticles gives rise to the fine tuning of the luminescence spectrum extracted from the ensemble. Our approach overcomes, without the need for an encapsulating agent and exclusively by solution processing, the difficulties that arise from the low thermal and chemical stability of the CSQDs. It opens the route to achieving precise control over their location and hence over the spectral properties of light emitted by these widely employed nanomaterials. Furthermore, as the porosity of the cavity is preserved after infiltration, the system remains responsive to environmental changes, which provides an added value to the proposed structure ; European Union 307081, CT-REGPOT-2011-1-285895 ; Ministerio de Economía y Competitividad MAT2014- 54852-R ; Agencia Nacional de Promoción Científica y Tecnológica 2087 ; Consejo Nacional de Investigaciones Científicas y Técnicas 11220100100186

This work was supported by the FWF (P 29603), the Linz Institute of Technology (LIT), the LIT Secure and Correct Systems Lab funded by the state of Upper Austria, the EU project HANAS (No. 601126210), AWS Austria Wirtschaftsservice (PRIZE Programme, Grant No. P1308457), the European Research council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme (SPQRel, Grant Agreement No. 679183), and the German Excellence Initiative via the Cluster of Excellence Nanosystems Initiative Munich (NIM). X. Yuan acknowledges support of the China Scholarship Council (CSC, No. 201306090010). Y. Huo thanks support of NSFC (No. 11774326) and STCSM (Nos. 17ZR1443900 and 17PJ1409900). J.M.-S. acknowledges support through the Clarín Programme from the Government of the Principality of Asturias and a Marie Curie-COFUND European grant (No. PA-18-ACB17-29).

This is the final published version. It first appeared at http://www.sciencedirect.com/science/article/pii/S0927024814003833#. ; The performance of InAs/GaAs quantum dot solar cells was investigated up to an optical concentration of 500-suns. A high temperature spacer layer between successive layers of quantum dots was used to reduce the degradation in the open circuit voltage relative to a control device without quantum dots. This improvement is explained using optical data while structural imaging of quantum dot stacks confirm that the devices are not limited by strain. The evolution of the open circuit voltage as a function of number of suns concentration was observed to be nearly ideal when compared with a high performance single junction GaAs solar cell. Analysis of Suns-Voc measurements reveal diode ideality factors as low as 1.16 which is indicative of a low concentration of defects in the devices. ; The authors acknowledge financial support from the European Union under the Seventh Framework Programme under a contract for an Integrated Infrastructure Initiative. Reference 312483 – ESTEEM2.

Trabajo presentado al 32nd Symposium on Surface Science (3S'19), celebrado en Baqueira Beret, Lleida (España) del 10 al 16 de marzo de 2019. ; Support by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, Grant No. MAT2016-78293-C6-6-R) from the regional Government of Aragón (RASMIA project) and from the European Regional Development Fund (ERDF) under the program Interreg V-A España-Francia-Andorra (Contract No. EFA 194/16 TNSI) is thankfully acknowledged.

Quantum dots are known to confine electrons within their structure. Whenever they periodically aggregate into arrays and cooperative interactions arise, novel quantum properties suitable for technological applications show up. Control over the potential barriers existing between neighboring quantum dots is therefore essential to alter their mutual crosstalk. Here we show that precise engineering of the barrier width can be experimentally achieved on surfaces by a single atom substitution in a haloaromatic compound, which in turn tunes the confinement properties through the degree of quantum dot intercoupling. We achieved this by generating self-assembled molecular nanoporous networks that confine the two-dimensional electron gas present at the surface. Indeed, these extended arrays form up on bulk surface and thin silver films alike, maintaining their overall interdot coupling. These findings pave the way to reach full control over two-dimensional electron gases by means of self-assembled molecular networks. ; This work was supported in part by the Spanish Ministry of Economy (grants MAT2013-46593-C6-4-P, MAT2016-78293-C6-6-R and FIS2013-48286-C2-1-P), by the Spanish Research Council (CSIC- 201560I022), by the Basque Government (grants IT621-13 and IT-756-13), by the Japan Science and Technology Agency (JST), 'Precursory Research for Embryonic Science and Technology' (PRESTO) for a project of 'Molecular technology and creation of new function', by JSPS KAKENHI Grant Number 15K21765, by the Swiss National Science Foundation, by the Swiss Nanoscience Institute, and by COST Action (European Cooperation in Science and Technology) MP1303. Swiss National Supercomputing Center in Lugano (Project s499 and s621) is acknowledged. ; Peer Reviewed

We have performed detailed photoluminescence (PL) and absorption spectroscopy on the same single self-assembled quantum dot in a charge-tunable device. The transition from neutral to charged exciton in the PL occurs at a more negative voltage than the corresponding transition in absorption. We have developed a model of the Coulomb blockade to account for this observation. At large negative bias, the absorption broadens as a result of electron and hole tunneling. We observe resonant features in this regime whenever the quantum dot hole level is resonant with two-dimensional hole states located at the capping layer-blocking barrier interface in our structure. ; We acknowledge fruitful discussions with Atac Imamoglu and financial support from DFG (SFB 631), EPSRC, DAAD and the European Union Network of Excellence SANDiE. ; Peer reviewed

Heisenberg exchange coupling between neighboring electron spins in semiconductor quantum dots provides a powerful tool for quantum information processing and simulation. Although so far unrealized, extended Heisenberg spin chains can enable long-distance quantum information transfer and the generation of nonequilibrium quantum states. In this work, we implement simultaneous, coherent exchange coupling between all nearest-neighbor pairs of spins in a quadruple quantum dot. The main challenge in implementing simultaneous exchange couplings is the nonlinear and nonlocal dependence of the exchange couplings on gate voltages. Through a combination of electrostatic simulation and theoretical modeling, we show that this challenge arises primarily due to lateral shifts of the quantum dots during gate pulses. Building on this insight, we develop two models that can be used to predict the confinement gate voltages for a desired set of exchange couplings. Although the model parameters depend on the number of exchange couplings desired (suggesting that effects in addition to lateral wave-function shifts are important), the models are sufficient to enable simultaneous and independent control of all three exchange couplings in a quadruple quantum dot. We demonstrate two-, three-, and four-spin exchange oscillations, and our data agree with simulations. ; Defense Advanced Research Projects AgencyUnited States Department of DefenseDefense Advanced Research Projects Agency (DARPA) [D18AC00025]; Army Research Office [W911NF16-1-0260, W911NF-19-1-0167]; National Science FoundationNational Science Foundation (NSF) [DMR-1941673] ; This research was sponsored by the Defense Advanced Research Projects Agency under Grant No. D18AC00025, the Army Research Office under Grants No. W911NF16-1-0260 and No. W911NF-19-1-0167, and the National Science Foundation under Grant No. DMR-1941673. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Office or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein.

Graphene quantum dots (GQD) are interesting materials due to the confined sizes which allow to exploit their optoelectronic properties, especially when they interface with organic molecules through physisorption. In particular, when interfaces are formed, charge transfer (CT) processes can occur, in which electrons can flow either from the GQD to the absorbed molecule, or vice versa. These processes are accessible by modeling and computational analysis. Yet, the presence of different environments can strongly affect the outcome of such simulations which, in turn, can lead to wrong results if not taken into account. In this multiscale study, we assess the sensibility of the computational approach and compute the CT, calculated at interfaces composed by GQD and amino-acene derivatives. The hole transfer is strongly affected by dynamic disorder and the nature of the environment, and imposes stringent descriptions of the modeled systems to ensure enhanced accuracy of the transfer of charges. ; Narodowe Centrum Nauki, Grant/Award Number: UMO-2015/19/P/ST4/03636; University of Warsaw, Grant/Award Number: G53-8; Swedish Infrastructure Committee, Grant/Award Numbers: 1-465,, 1-415, 1-87; European Union's Horizon 2020; National Science Centre, Poland, Grant/Award Number: UMO-2015/19/P/ST4/03636