Metallic nanorings for broadband, enhanced extraction of light from solid-state emitters

We report on the increased extraction of light emitted by solid-state sources embedded within high refractive index materials. This is achieved by making use of a local lensing effect by sub-micron metallic rings deposited on the sample surface and centered around single emitters. We show enhancements in the intensity of the light emitted by InAs/GaAs single quantum dot lines into free space as high as a factor 20. Such a device is intrinsically broadband and therefore compatible with any kind of solid-state light source. We foresee the fabrication of metallic rings via scalable techniques, like nano-imprint, and their implementation to improve the emission of classical and quantum light from solid-state sources. Furthermore, while increasing the brightness of the devices, the metallic rings can also act as top contacts for the local application of electric fields for carrier injection or wavelength tuning.Comment: 10 pages, 3 figure

Cesium‐vapor‐based delay of single photons emitted by deterministically fabricated quantum dot microlenses

Quantum light sources are key building blocks of photonic quantum technologies. For many applications, it is of interest to control the arrival time of single photons emitted by such quantum devices, or even to store single photons in quantum memories. In situ electron beam lithography is applied to realize InGaAs quantum dot (QD)‐based single‐photon sources, which are interfaced with cesium (Cs) vapor to control the time delay of emitted photons. Via numerical simulations of the light–matter interaction in realistic QD‐Cs‐vapor configurations, the influence of the vapor temperature and spectral QD‐atom detuning is explored to maximize the achievable delay in experimental studies. As a result, this hybrid quantum system allows to trigger the emission of single photons with a linewidth as low as 1.54 GHz even under non‐resonant optical excitation and to delay the emission pulses by up to (15.71 ± 0.01) ns for an effective cell length of 150 mm. This work can pave the way for scalable quantum systems relying on a well‐controlled delay of single photons on a time scale of up to a few tens of nanoseconds.BMBF, 03V0630TIB, Entwicklung einer Halbleiterbasierten Einzelphotonenquelle für die QuanteninformationstechnologieBMBF, 13N14876, Quantenkommunikations-Systeme auf Basis von Einzelphotonenquellen (QuSecure)DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeTU Berlin, Open-Access-Mittel - 201

Metal-free organic chromophores featuring an ethynyl-thienothiophene linker with an n-hexyl chain for translucent dye-sensitized solar cells

We report the simple synthesis of two organic chromophores featuring an ethynyl-thienothiophene linker with an n-hexyl chain (CSD-03 and CSD-04), their optical and electrochemical properties, and their use as photosensitizers in dye-sensitized solar cells (DSSCs). Our theoretical and experimental studies show that adding the second thienothiophene allows for narrowing the bandgap of the molecule and thus ensuring more light harvesting in the visible region. The efficiencies of both CSD-03 (5.46 ± 0.03%) and CSD-04 (5.20 ± 0.03%) are comparable to that of N719 (5.92 ± 0.01%) in translucent DSSCs fabricated with 5 μm-thick TiO2 photoanodes

Metal-free organic chromophores featuring an ethynyl-thienothiophene linker with an n-hexyl chain for translucent dye-sensitized solar cells

We report the simple synthesis of two organic chromophores featuring an ethynyl-thienothiophene linker with an n-hexyl chain (CSD-03 and CSD-04), their optical and electrochemical properties, and their use as photosensitizers in dye-sensitized solar cells (DSSCs). Our theoretical and experimental studies show that adding the second thienothiophene allows for narrowing the bandgap of the molecule and thus ensuring more light harvesting in the visible region. The efficiencies of both CSD-03 (5.46 ± 0.03%) and CSD-04 (5.20 ± 0.03%) are comparable to that of N719 (5.92 ± 0.01%) in translucent DSSCs fabricated with 5 μm-thick TiO2 photoanodes

Discrimination of cultivation ages and cultivars of ginseng leaves using Fourier transform infrared spectroscopy combined with multivariate analysis

AbstractTo determine whether Fourier transform (FT)-IR spectral analysis combined with multivariate analysis of whole-cell extracts from ginseng leaves can be applied as a high-throughput discrimination system of cultivation ages and cultivars, a total of total 480 leaf samples belonging to 12 categories corresponding to four different cultivars (Yunpung, Kumpung, Chunpung, and an open-pollinated variety) and three different cultivation ages (1 yr, 2 yr, and 3 yr) were subjected to FT-IR. The spectral data were analyzed by principal component analysis and partial least squares-discriminant analysis. A dendrogram based on hierarchical clustering analysis of the FT-IR spectral data on ginseng leaves showed that leaf samples were initially segregated into three groups in a cultivation age-dependent manner. Then, within the same cultivation age group, leaf samples were clustered into four subgroups in a cultivar-dependent manner. The overall prediction accuracy for discrimination of cultivars and cultivation ages was 94.8% in a cross-validation test. These results clearly show that the FT-IR spectra combined with multivariate analysis from ginseng leaves can be applied as an alternative tool for discriminating of ginseng cultivars and cultivation ages. Therefore, we suggest that this result could be used as a rapid and reliable F1 hybrid seed-screening tool for accelerating the conventional breeding of ginseng

In Situ-Generated Reactive Oxygen Species in Precharged Titania and Tungsten Trioxide Composite Catalyst Membrane Filters: Application to As(III) Oxidation in the Absence of Irradiation

This study demonstrates that in situ-generated reactive oxygen species (ROSs) in prephotocharged TiO₂ and WO₃ (TW) composite particle-embedded inorganic membrane filters oxidize arsenite (As(III)) into arsenate (As(V)) without any auxiliary chemical oxidants under ambient conditions in the dark. TW membrane filters have been charged with UV or simulated sunlight and subsequently transferred to a once-through flow-type system. The charged TW filters can transfer the stored electrons to dissolved O₂, producing ROSs that mediate As(III) oxidation in the dark. Dramatic inhibition of As(V) production with O₂ removal or addition of ROS quenchers indicates an ROS-mediated As(III) oxidation mechanism. Electron paramagnetic spectroscopic analysis has confirmed the formation of the HO₂•/O₂•– pair in the dark. The WO₃ fraction in the TW filter significantly influences the performance of the As(III) oxidation, while As(V) production is enhanced with increasing charging time and solution pH. The As(III) oxidation is terminated when the singly charged TW filter is fully discharged; however, recharging of TW recovers the catalytic activity for As(III) oxidation. The proposed oxidation process using charged TW membrane filters is practical and environmentally benign for the continuous treatment of As(III)-contaminated water during periods of unavailability of sunlight

In Situ-Generated Reactive Oxygen Species in Precharged Titania and Tungsten Trioxide Composite Catalyst Membrane Filters: Application to As(III) Oxidation in the Absence of Irradiation

This study demonstrates that in situ-generated reactive oxygen species (ROSs) in prephotocharged TiO₂ and WO₃ (TW) composite particle-embedded inorganic membrane filters oxidize arsenite (As(III)) into arsenate (As(V)) without any auxiliary chemical oxidants under ambient conditions in the dark. TW membrane filters have been charged with UV or simulated sunlight and subsequently transferred to a once-through flow-type system. The charged TW filters can transfer the stored electrons to dissolved O₂, producing ROSs that mediate As(III) oxidation in the dark. Dramatic inhibition of As(V) production with O₂ removal or addition of ROS quenchers indicates an ROS-mediated As(III) oxidation mechanism. Electron paramagnetic spectroscopic analysis has confirmed the formation of the HO₂•/O₂•– pair in the dark. The WO₃ fraction in the TW filter significantly influences the performance of the As(III) oxidation, while As(V) production is enhanced with increasing charging time and solution pH. The As(III) oxidation is terminated when the singly charged TW filter is fully discharged; however, recharging of TW recovers the catalytic activity for As(III) oxidation. The proposed oxidation process using charged TW membrane filters is practical and environmentally benign for the continuous treatment of As(III)-contaminated water during periods of unavailability of sunlight

GaAs droplet quantum dots with nanometer-thin capping layer for plasmonic applications

We report on the growth and optical characterisation of droplet GaAs quantum dots with extremely-thin (11 nm) capping layers. To achieve such result, an internal thermal heating step is introduced during the growth and its role in the morphological properties of the quantum dots obtained is investigated via scanning electron and atomic force microscopy. Photoluminescence measurements at cryogenic temperatures show optically stable, sharp and bright emission from single quantum dots, at near-infrared wavelengths. Given the quality of their optical properties and the proximity to the surface, such emitters are ideal candidates for the investigation of near field effects, like the coupling to plasmonic modes, in order to strongly control the directionality of the emission and/or the spontaneous emission rate, crucial parameters for quantum photonic applications.Comment: 1 pages, 3 figure

Electrocatalytic arsenite oxidation in bicarbonate solutions combined with CO₂ reduction to formate

Sunlight-driven water-energy nexus technologies are receiving increasing attention. This study presents a hybrid electrochemical system that catalyzes the oxidation of As(III) to As(V) with a nanoparticulate TiO₂ electrocatalyst (Ti/Ir_(1-x)Ta_xO_y/TiO₂; denoted as an n-TEC) while simultaneously converting CO₂ to formate on a Bi electrode in aqueous bicarbonate solutions at circum-neutral pH. Linear sweep voltammograms of n-TEC exhibit a specific As(III) oxidation peak (E_(p,As)), at which the Faradaic efficiency (FE) of As(V) production is ∼100%. However, the application of a potential higher than the peak (E > E_(p,As)) leads to a significant decrease in the FE due to water oxidation. Upon the addition of chloride, the oxidation of water and chloride occur competitively, producing reactive chlorine species responsible for mediating the oxidation of As(III). The Bi electrodes synthesized via the electrodeposition of Bi³⁺ typically show high FEs of >80% for formate production in bicarbonate solution purged with CO₂. The addition of chloride significantly enhances the current while maintaining the FE. The n-TEC catalyst and Bi electrodes are paired in a single device equipped with a membrane, and significant effort is made to achieve the same FEs in both the anodic and cathodic reactions as in their half-reactions. Finally, the optimized n-TEC/Bi pair is coupled with a low-cost, commercially available photovoltaic (PV). Various technical factors that drive the overall reactions with the PV are considered, and maximum FEs of ∼95% are achieved for the production of both As(V) and formate