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This research was prompted by the discovery of 35 new or candidate symbiotic stars during a targeted search in the Local Group of Galaxies. A catalogue of a further 200 or so such objects has now been compiled. Many of them could be identified with counterparts in the POINT-AGAPE Catalogue. However, information in the Catalogue is limited to position, brightness and possible period, and light-curves are not available. The poster presented an example of a light-curve of a symbiotic star retrieved from original Point-Agape Catalogue data.
Observations of red giants in the Bulge globular cluster NGC 6273 with the Michigan/Magellan Fiber System (M2FS) mounted on the Nasmuth-East port of the Magellan-Clay 6.5-m telescope at the Las Campanas Observatory reveal a spread in metallicity. Members have been confirmed with radial velocity. NGC 6273 has at least two populations separated by 0.2-0.3 dex in [Fe/H]. The sodium and aluminum abundances are correlated while the magnesium and aluminum abundances are anti-correlated. The cluster also shows a rise in the abundance of the s-process element lanthanum with [Fe/H] similar to other massive clusters. The cluster contains a possible third population depleted in most elements by 0.3 dex.
In the wide-field Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS), we investigate the resolved stellar halos of two nearby galaxies (the elliptical Centaurus A and the spiral Sculptor, D ~ 3.7 Mpc) out to a projected galactocentric radius of 150 kpc with Magellan/Megacam. The survey has led to the discovery of ~20 faint satellites to date, plus prominent streams and substructures in two environments that are substantially different from the Local Group, i.e. the Centaurus A group dominated by an elliptical and the loose Sculptor group of galaxies. These discoveries clearly attest to the importance of past and ongoing accretion processes in shaping the halos of these nearby galaxies, and provide the first census of their satellite systems down to an unprecedented MV < −8. The detailed characterization of the stellar content, shape and gradients in the extended halos of Sculptor, Centaurus A, and their dwarf satellites provides key constraints on theoretical models of galaxy formation and evolution.
Glasses are recognized as the ideal hosts to incorporate plasmonic metal nanoparticles (NPs), semiconductor NPs, and luminescent rare-earth (RE3+) ions. This is due to their unique optical properties, stability, absence of high energy bond vibrations and inertness towards the incorporated NPs. However, conventional methods of metal-glass nanocomposite fabrication involve ion-implantation or sputtering and subsequent heat-treatment under H2, UV-light/X-ray/γ- or laser irradiation. They are (i) multi-step, (ii) require expensive set-up, (iii) bear risk of sample damage and (iv) the formation of NPs occurs only in surface layers. Here we develop two novel glass-systems K2O-B2O3-Sb2O3 and K2O-B2O3-Sb2O3-ZnO. Using the selective reducing property of the main component Sb2O3 in these hosts, here we demonstrate for the first time the strategy for single-step in-situ fabrication of metal (M0) NPs and RE3+ ions co-embedded within bulk glasses. This new series of novel composites co-embedding metal NPs (elliptical Au, elongated Ag NPs and Aucore-AuAgshell NPs) and RE3+ ions exhibit enhanced upconversion for solar panels, advanced displays and other nanophotonic applications. Metal NPs exhibit surface plasmons resonance results in concentration and enhancement of the local electromagnetic field (LFE) around them. The luminescent RE3+ ion in the vicinity experiences the local field effect. We observe that the LFE effect is stronger on electric dipole transitions of the RE3+ than the magnetic dipole ones. LFE induced by nano Au enhance the (i) 4G7/2 → 4I9/2 540 nm green and 4G7/2 → 4I15/2 650 nm red upconversion emissions of Nd3+ by 9 and 11 fold, (ii) electric dipole 4G5/2 → 6H9/2 636 nm red upconversion of Sm3+ by about 7 fold and (ii) 4S3/2 → 4I15/2 536 nm green and 4F9/2 →4I15/2 645 nm red emissions of Er3+ by 2 and 5 fold respectively. LFE induced by nano Ag enhance both the green and red upconversion emission of Er3+ by 8 fold. The Aucore-AuAgshell NPs enhance the red upconversion of Sm3+ only by 2 fold due to smaller LFE effect of bimetallic NPs. All the Au-doped antimony glasses are dichroic. They transmit the blue light and reflect the brown light, which make them very interesting material comparable to the historic Lycurgus Cup.
We have demonstrated the color conversion of blue micro-LEDs by means of QDs. In this paper, we will present characterizations that highlight this phenomenon. We already obtained conversion with a complete disappearance of the blue incident signal and a strong color saturation from deep blue (x=0,1626; y=0,0144) to deep red (x=0,6743; y=0,3244).
We propose and numerically investigate a tunable metasurface made of an array of graphene ribbons to dynamically control terahertz (THz) wavefront. The metasurface consists of graphene micro ribbons on a silver mirror with a SiO2 gap layer. The graphene ribbons are designed to exhibit localized plasmon resonances depending on their Fermi levels to introduce abrupt phase shifts along the metasurface. With interference of the Fabry-Perot resonances in the SiO2 layer, phase shift through the system is largely accumulated, covering up to 2π range for full control of the THz wavefront. Numerical simulations prove that wide-angle reflected THz beam steering from -53° to +53° with a high reflection efficiency as high as 60% is achieved at 5 THz while the propagation direction of THz beam could be switched within 0.6 ps.
Metamaterial structures composed of ordered arrays of metallic nanoparticles (NPs) and nanocavities are able to support strong plasmon and Fano resonances in the optical frequencies, where the appeared Fano dips can be utilized in bio/chemical sensing and spectroscopic purposes with a significant sensitivity. Herein, we utilize two concentric compositional Aluminum (Al) nanoshells (Al/Al2O3) to design nanomatryushka (NM) structures in periodic arrays, where each one of Al NPs is covered by a certain thickness of the oxide layer. Depositing studied Al NM arrays on metasurfaces, we determined the optical response of the metamaterial. It is shown that the proposed structure is able to support multiple strong Fano resonances in the visible spectrum. Evaluating the plasmon response of the metamaterial configuration for the presence of various semiconductor metasurfaces (Silicon and GaP), the quality of Fano dips is analyzed for different regimes. In this method, we measured the accuracy and sensitivity of the metamaterial structure by plotting the linear figure of merit (FoM) and quantifying this parameter.
In the presented work, we have developed VLSI technology processes for new prototype sensors based on the synthesis of boron doped nanocrystalline diamond (B-NCD) and silicon based commercial detectors. The process is based on commercial passivated implanted planar silicon (PIPS) devices of PD450 and CAM450 types (CANBERRA). A layer of B-NCD of several hundred nanometers thickness and boron concentration up to 1021 atoms/cm3 is grown on the SiOx passivation layer in an ellipsoidal plasma enhanced chemical vapor deposition (PECVD) reactor at temperatures from 520-750°C, in hydrogen atmosphere. . The diamond electrode is dry chemically structured and aluminum electrodes are realized before mounting in a three-fold housing for measurements in aqueous solution. The prototype sensors show an alpha spectroscopy resolution of 100 keV for 241Am electroprecipitated from liquid solution.
3D printing is a versatile fabrication method that offers the potential to realize complex 3D devices with metamaterial characteristics in a single process directly from a computer aided design. However, the range of functional devices that might be realized by 3D printing is limited by the current range of materials that are compatible with a given 3D printing process: fused deposition modelling (FDM), which is a widely used 3D printing method, typically employs only common thermoplastics. Here we describe the development of a magnetic feedstock based on polymer-ferrite composite that is compatible with FDM. The feasibility of the technique is demonstrated by the permittivity and permeability measurement of direct printed blocks and the fabrication of a complex 3D diamond-like lattice structure. The development of printable magnetic composites provides increased design freedom for direct realization of devices with graded electromagnetic properties operating at microwave frequencies.
A sensor which detects mechanical stresses and stores the position and the strength of these loads by color change of embedded quantum dots (QDs) is presented. The top and bottom electrodes of the sensor are inkjet-printed which leads to a fast and accurate deposition of thin (approx. 50 - 300 nm) and conductive layers. The used silver and poly(3,4-ethylenedioxythio-phene) polystyrene sulfonate (PEDOT:PSS) inks are optimized in terms of printability and opportunities of functionality forming without influencing the active layer of the sensor. The active layer of the sensor is spin-coated and consists of the QDs embedded in semi-conducting poly(9-vinylcarba-zole) (PVK). The hole transport characteristic of PVK and the band level alignment of the used materials ensures the preferred injection of only one type of charge carrier into the QDs. As a result the mechanical stress is visualized by a decreasing in photoluminescence (PL) of the QDs.
Optical properties and thermal relaxation dynamics of resonantly excited plasmons are important in applications for optoelectronics, biomedicine, energy, and catalysis. Geometric optics of polydimethylsiloxane (PDMS) thin films containing uniformly or asymmetrically distributed polydisperse reduced AuNPs or uniformly distributed monodisperse solution-synthesized AuNPs were recently evaluated using a compact linear algebraic sum. Algebraic calculation of geometric transmission, reflection, and attenuation for AuNP-PDMS films provides a simple, workable alternative to effective medium approximations, computationally expensive methods, and fitting of experimental data. This approach allows for the summative optical responses of a sequence of 2D elements comprising a 3D assembly to be analyzed. Thin PDMS films containing 3-7 micron layers of reduced AuNPs were fabricated with a novel diffusive-reduction synthesis technique. Rapid diffusive reduction of AuNPs into asymmetric PDMS thin films provided superior photothermal response relative to thicker films with AuNPs reduced throughout, with a photon-to-heat conversion of up to 3000°C/watt which represents 3-230-fold increase over previous AuNP-functionalized systems. Later work showed that introduction of AuNPs into PDMS enhanced thermoplasmonic dissipation coincident with internal reflection of incident resonant irradiation. Measured thermal emission and dynamics of AuNP-PDMS thin films exceeded emission and dynamics attributable by finite element analysis to Mie absorption, Fourier heat conduction, Rayleigh convection, and Stefan-Boltzmann radiation. Refractive-index matching experiments and measured temperature profiles indicated AuNP-containing thin films internally reflected light and dissipated power transverse to the film surface. Enhanced thermoplasmonic dissipation from metal-polymer nanocomposite thin films could affect opto- and bio-electronic implementation of these systems.
The development of efficient large-area organic light emitting diodes (OLED) requires reliable and easily processable charge generation layers (CGL) with low excess voltage drop and high optical transparency. OVPD offers the advantage of a precise control of layer morphology, composition and thickness and is a powerful method for the deposition of advanced OLED designs. In this work, electrical doping of organic semiconductors using OVPD is investigated and applied to stacked OLED utilizing inorganic/organic CGL. The organic p-type dopant NDP-9 of Novaled GmbH is used for doping the hole transport material N,N‘-diphenyl-N,N‘-bis(1-naphthylphenyl)-1,1‘-biphenyl-4,4‘-diamine (α-NPD) in an AIXTRON OVPD tool. A doping concentration of 8 vol.% of NDP-9 in α-NPD is found optimal for hole injection as well as conductivity. This dopant concentration was employed in CGL with the structure: electron transport material/LiF/Al/α-NPD:8 vol.% NDP-9. External quantum efficiencies (EQE) of 15%, 35% and 50% and luminous efficiencies of 37 lm/W, 45 lm/W and 45 lm/W at 1000 cd/m2 are demonstrated for single, double- and triple-unit green phosphorescent OLED, respectively.
Reflection occurs at an air-material interface. The development of antireflection schemes, which aims to cancel such reflection, is important for a wide variety of applications including solar cells and photodetectors. Recently, it has been demonstrated that a periodic array of resonant subwavelength objects placed at an air-material interface can significantly reduce reflection that otherwise would have occurred at such an interface. Here, we introduce the theoretical condition for complete reflection cancellation in this resonant antireflection scheme. Using both general theoretical arguments and analytical temporal coupled-mode theory formalisms, we show that in order to achieve perfect resonant antireflection, the periodicity of the array needs to be smaller than the free-space wavelength of the incident light for normal incidence, and also the resonances in the subwavelength objects need to radiate into air and the dielectric material in a balanced fashion. Our theory is validated using first-principles full-field electromagnetic simulations of structures operating in the infrared wavelength ranges. For solar cell or photodetector applications, resonant antireflection has the potential of providing a low-cost technique for antireflection that does not require nanofabrication into the absorber materials, which may introduce detrimental effects such as additional surface recombination. Our work here provides theoretical guidance for the practical design of such resonant antireflection schemes.