29,068 research outputs found
Disorder in Extra-Large Pore Zeolite ITQ-33 Revealed by Single Crystal XRD
No full textThe single crystal of the extra-large pore zeolite, ITQ-33, was obtained and used to explore its crystal structure details. The ITQ-33 structure was found to be disordered with the columnar periodic building unit, explaining the morphology changes upon the different Si/Ge ratio, and the formation of the hierarchical structure from assembling of ITQ-33 nanofibers.Chemistry, MultidisciplinaryCrystallographyMaterials Science, MultidisciplinarySCI(E)EI0ARTICLE104168-41711
Thin-film photonic crystal LEDs with enhanced directionality
No full textThe use of photonic crystals for light extraction from light-emitting diodes (LEDs)
gives the possibility to shape the farfield emission pattern. This is of particular interest
for étendue-limited LED applications that require a more directional farfield than state-
of-the-art Lambertian emitters. However, the application of a photonic crystal in a LED
results in directional emission only if the photonic crystal and the distribution of guided
modes in the LED are tuned correctly. In this thesis, red- and blue-emitting thin-film
PhC-LEDs in the AlGaInP and InGaN material systems were modelled, designed,
fabricated and characterized. The first experimental results show that light extraction
with photonic crystals from AlGaInP thin-film LEDs several microns thick is neither
directional nor more efficient than state-of-the-art LEDs with a rough surface structure.
Directional light extraction for AlGaInP PhC-LEDs is for the first time demonstrated in
much thinner devices where the photonic crystal light extraction of guided modes is
combined with the resonant-cavity effect. In an attempt to approach the ideal PhC-LED,
strong photonic crystal farfield shaping is demonstrated in InGaN thin-film LEDs of
sub-micron thickness. Analysis of their spectral farfields unexpectedly shows that high
order diffraction contributes significantly to the light extraction efficiency if the mode
absorption is sufficiently low. It is also demonstrated that directional photonic crystal
light extraction is possible in InGaN thin-film LEDs several microns thick. The
directionality stems from the modulation of the spontaneous emission caused by the
proximity of the active region to the bottom mirror. Two new concepts for enhanced
light extraction and high directionality are presented: Photonic crystals with two
dominating lattice constants are found to outperform conventional photonic crystal
LEDs. An alternative approach is the dielectric PhC-LED - FDTD simulations show
that the high extraction efficiency of LEDs with surface roughness is combined with the
higher directionality of photonic crystal light extraction
Photonic crystal interfaces: a design-driven approach
No full textPhotonic Crystal structures have been heralded as a disruptive technology
for the miniaturization of opto-electronic devices, offering as they do the
possibility of guiding and manipulating light in sub-micron scale waveguides.
Applications of photonic crystal guiding - the ability to send light around sharp
bends or compactly split signals into two or more channels have attracted a
great deal of attention. Other effects of this waveguiding mechanism have
become apparent, and attracted much interest - the novel dispersion surfaces
of photonic crystal structures allow the possibility of “slow light” in a dielectric
medium, which as well as the possibility of compact optical delay lines may
allow enhanced light-matter interaction, and hence miniaturisation of active
optical devices. I also consider a third, more traditional type of photonic
crystal, in the form of a grating for surface coupling.
In this thesis, I address many of the aspects of passive photonic crystals,
from the underlying theory through applied device modelling, fabrication
concerns and experimental results and analysis. Further, for the devices
studied, I consider both the relative merits of the photonic crystal approach
and of my work compared to that of others in the field. Thus, the complete
spectrum of photonic crystal devices is covered.
With regard to specific results, the highlights of the work contained in this
thesis are as follows:
Realisation of surface grating couplers in a novel material system
demonstrating some of the highest reported fibre coupling efficiencies.
Development of a short “injecting” taper for coupling into photonic
crystal devices.
Optimisation and experimental validation of photonic crystal routing
elements (Y-splitter and bend).
Exploration of interfaces and coupling for “slow light” photonic crystals
Electrically injected photonic-crystal nanocavities
No full textNano-emitters are the new generation of laser devices. A photonic-crystal cavity, which highly confines light in small volumes, in combination with quantum-dots can enhance the efficiency and lower the threshold of this device. The practical realisation of a reliable, electrically pumped photonic-crystal laser at room-temperature is, however, challenging.
In this project, a design for such a laser was established. Its properties are split up into electrical, optical and thermal tasks that are individually investigated via various device simulations. The resulting device performance showed that with our design the quantum-dots can be pumped in order to provide gain and to overcome the loss of the system. Threshold currents can be as low as 10’s of μA and Q-factors in the range of 1000’s. Gallium arsenide wafers were grown according to our specifications and their diode behaviour confirmed. Photonic-crystal cavities were fabricated through a newly developed process based on a TiOₓ hard-mask. Beside membraned cavities, also cavities on oxidised AlGaAs were fabricated with help to a unique hard-mask removal method. The cavities were measured with a self-made micro-photoluminescence setup with the highest Q-factor of 4000 for the membrane cavity and a remarkable 2200 for the oxide cavity. The fabrication steps, regarding the electrically pumped photonic-crystal laser, were developed and it was shown that this device can be fabricated.
During this project, a novel type of gentle confinement cavity was developed, based on the adaption of the dispersion curve (DA cavity) of a photonic-crystal waveguide. Q-factors of as high as 600.000 were measured for these cavities made in Silicon
Feltham, S. Model of Winifrid Lee, Glovertown
No full textModel of the Winifred Lee built by Sam Feltham, Glovertown. The Winfrid Lee was a coastal boat that provided passenger and freight service along the Northern Labrador Coast during the 1950s
Hanging the harp on the willow tree: music and national identity in postcolonial Ireland
No full textAn inquiry into how music served as a nation building tool in the early decades of the Irish Free State.M.A.Includes bibliographical referencesby Crystal N. Galyea
Planar Photonic Crystal Nanocavities with Active Quantum Nanostructures
No full textExtreme photon localization is applicable to constructing building blocks in photonic systems and quantum information systems. A finding fact that photon localization in small space modifies the radiation process was reported in 1944 by Purcell, and advances in fabrication technology enable such structures to be constructed at optical frequencies. Many demands of building compact photonic systems and quantum information systems have enhanced activities in this field. The photonic crystal cavity has potential in providing a cavity that supports only the fundamental mode of (lambda/2n)^3 together with good confinement of light within a resonator. This thesis addresses experimental and theoretical aspects of building such photon localization blocks embedding active quantum nanostructures in a planar photonic crystal platform. Examples given in this thesis are (1) quantum dot photonic crystal nanolasers, (2) high-speed photonic crystal nanolasers, and (3) light-matter coupling in a single quantum dot photonic crystal cavity system.
(1) A combination of quantum dots and photonic crystal nanocavities provides chirpless high-speed nanolasers. Room temperature low-threshold lasing action was demonstrated from a coupled cavity design (0.7 - 1.2(lambda/n)^3) embedding InAs/GaAs self-assembled quantum dots. The nanolasers showed small (absorbed) pumping power threshold as sub-20 microW and high spontaneous coupling factors of 0.1. Single quantum dot lasing is likely to occur both by proper alignment of the single quantum dot relative to geometries of photonic crystals and by a narrow QD emission line in the high-Q localized mode.
(2) Enhancement of radiation process in a small cavity was used to demonstrate high frequency relaxation oscillation up to 130 GHz. Built-in quantum well saturable absorbers enable us to probe the relaxation oscillation of such small lasers.
(3) Onset of intermediate light-matter coupling was demonstrated in a single quantum dot photonic crystal cavity system. A tripling in Q/V (quality factor divided by mode volume) is found to enable photons to start a strong interaction with a single quantum dot.</p
Growth, optical, and luminescence characterization of LiCsMoO4 crystal
No full text© 2021 Elsevier B.V.A crack-free LiCsMoO4 crystal was grown with the conventional Czochralski technique. The optical properties of the crystal show it transparent well in the visible region. The luminescence properties of the crystal were studied from 300 to 14 K under the excitation with a 280 nm light-emitting diode (LED). At room temperature, the luminescence light yield is low; however, it increases significantly at low temperatures. The decay time of the crystal is measured under the excitation of the crystal with the 280 nm LED source. The decay times at all the temperatures are fitted with three exponential functions. The average decay time from 300 to 14 K varies from 6.7 to 8.6 μs. A thermoluminescence (TL) study of the crystal was carried out from 9 to 300 K. Three TL peaks are found between 165 and 250 K. This study shows that the developed crystal has a potential application in search of neutrinoless double-beta decay of 100Mo at cryogenic temperatures.11Nsciescopu
Liquid crystal nanoparticle formulation as an oral drug delivery system for liver-specific distribution
No full textDong Ryeol Lee,1,2 Ji Su Park,1 Il Hak Bae,1 Yan Lee,1 B Moon Kim1 1Department of Chemistry, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea; 2Technology Development Center, BASF Company Ltd., Hwaseong, Gyeonggi-do, Republic of Korea Abstract: Liquid crystal nanoparticles have been utilized as an efficient tool for drug delivery with enhanced bioavailability, drug stability, and targeted drug delivery. However, the high energy requirements and the high cost of the liquid crystal preparation have been obstacles to their widespread use in the pharmaceutical industry. In this study, we prepared liquid crystal nanoparticles using a phase-inversion temperature method, which is a uniquely low energy process. Particles prepared with the above method were estimated to be ~100 nm in size and exhibited a lamellar liquid crystal structure with orthorhombic lateral packing. Pharmacokinetic and tissue distribution studies of a hydrophobic peptide-based drug candidate formulated with the liquid crystal nanoparticles showed a five-fold enhancement of bioavailability, sustained release, and liver-specific drug delivery compared to a host–guest complex formulation. Keywords: LCNP, PIT, sustained release, bioavailabilit
The Na2W2O7 crystal: a crystal scintillator for dark matter search experiment
No full textA single crystal of Na 2W 2O 7?(NWO) was grown by a low-thermal-gradient Czochralski technique (LTG-CZ). The scintillation properties of the crystal were evaluated for the first time as a potential material for dark matter search experiments. The luminescence and scintillation characteristics of the crystal were studied at room temperature and low temperatures by using a light-emitting diode (LED) and a 90Sr beta source. The luminescence and scintillation light yield at 10?K were significantly higher than those at room temperature. The crystal showed higher light yield at 10?K than a CaMoO4?(CMO) crystal. The decay time of the crystal was investigated at temperatures between 10 and 300?K. The sensitivity to spin-independent weakly interacting massive particle-nucleon interactions based on 10?kg (2?months) and 50?kg (12?months) data for the NWO crystal detectors was estimated by a simulated experiment using the standard halo model. The luminescence, scintillation, and sensitivity results revealed that the NWO crystal is a promising candidate for a dark matter search experiment in the near future. (c) 2018, The Author(s)11Nsciescopu
- …
