456 research outputs found
Cathodoluminescence and electron microscopy of red quantum dots used for display applications
Cathodoluminescent imaging of the visible light emitted from quantum dots is reported. The shape and uniformity of individual particles is observed in the STEM electron image and the image of the particles created from their visible light collected simultaneously is shown. Visible light images of the 13nm sized particles are reported for clusters of particles. Emission spectra collected from a small clusters of QDs are also reported
Hybrid organic/quantum dot thin film structures and devices
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 157-169).Organic light emitting diodes have undergone rapid advancement over the course of the past decade. Similarly, quantum dot synthesis has progressed to the point that room temperature highly efficient photoluminescence can be realized. It is the purpose of this work to utilize the beneficial properties of these two material sets in a robust light emitting device. New deposition techniques are necessary to the realization of this goal, enabling QD organic hybrids to be created in a quick and reliable manner compatible with known device fabrication methods. With these techniques, quantum dot light emitting devices are fabricated, measured, and analyzed. The devices are of high efficiency and color saturation, and provide us with a test bed for understanding the interactions between inorganic QDs and organic thin films.by Seth Coe-Sullivan.Ph.D
Effect of electric field on the photoluminescence of polymer-inorganic nanoparticles composites
We report on the effect of electric field on the photoluminescence, PL, from
a composite consisting of a conjugated polymer mixed with zinc oxide
nanoparticles. We have found that in the absence of electric field PL emission
from the composite film has two maxima in the blue and green-yellow regions.
Application of a voltage bias to planar gold electrodes suppresses the
green-yellow emission and shifts the only PL emission maximum towards the blue
region. Current-voltage characteristics of the polymer-nanoparticles composite
exhibit the non-linear behavior typical of non-homogeneous polymer-inorganic
structures. Generation of excited states in the composite structure implies the
presence of several radiative recombination mechanisms including formation of
polymer-nanoparticle complexes including exciplex states and charge transfer
between the polymer and nanoparticle that can be controlled by an electric
field.Comment: 5 pages, 5 figures. accepted for publication in Solid State
Communication
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Red quantum dots under the electron microscope
Cathodoluminescent imaging of the visible light emitted from quantum dots is reported. The shape and uniformity of individual particles is observed in the STEM electron image and the image of the particles created from their visible light collected simultaneously is shown. Visible light images of the 12-13nm sized particles are reported for clusters of just 2 particles. Emission spectra collected from small clusters of around 50 nano-particles are also reported.Technology Strategy Board (TSB) (UK) for substantial financial funding in the form of TSB Technology
programs for the CONVERTED, PURPOSE, FAB3D, ACTIVEL and BEDS program
Submicron full- color LED pixels for microdisplays and micro- LED main displays
We demonstrate a bottom- up approach to the construction of micro- LEDs as small as 150 nm in lateral dimension. Molecular beam epitaxy (MBE) is used to fabricate such nanostructured LEDs from InGaN, from the blue to red regions of the spectrum, providing a single material set useful for an entire RGB display.We demonstrate a bottom- up approach to the construction of micro- LEDs as small as 150 nm in lateral dimension. Molecular beam epitaxy (MBE) is used to fabricate such nanostructured LEDs from InGaN, from the blue to red regions of the spectrum, providing a single material set useful for an entire RGB display. We then consider collective effects of arrays of such LEDs.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155468/1/jsid899_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155468/2/jsid899.pd
Gravitationally lensed quasars and supernovae in future wide-field optical imaging surveys
Cadenced optical imaging surveys in the next decade will be capable of
detecting time-varying galaxy-scale strong gravitational lenses in large
numbers, increasing the size of the statistically well-defined samples of
multiply-imaged quasars by two orders of magnitude, and discovering the first
strongly-lensed supernovae. We carry out a detailed calculation of the likely
yields of several planned surveys, using realistic distributions for the lens
and source properties and taking magnification bias and image configuration
detectability into account. We find that upcoming wide-field synoptic surveys
should detect several thousand lensed quasars. In particular, the LSST should
find 8000 lensed quasars, 3000 of which will have well-measured time delays,
and also ~130 lensed supernovae, which is compared with ~15 lensed supernovae
predicted to be found by the JDEM. We predict the quad fraction to be ~15% for
the lensed quasars and ~30% for the lensed supernovae. Generating a mock
catalogue of around 1500 well-observed double-image lenses, we compute the
available precision on the Hubble constant and the dark energy equation
parameters for the time delay distance experiment (assuming priors from
Planck): the predicted marginalised 68% confidence intervals are
\sigma(w_0)=0.15, \sigma(w_a)=0.41, and \sigma(h)=0.017. While this is
encouraging in the sense that these uncertainties are only 50% larger than
those predicted for a space-based type-Ia supernova sample, we show how the
dark energy figure of merit degrades with decreasing knowledge of the the lens
mass distribution. (Abridged)Comment: 17 pages, 10 figures, 3 tables, accepted for publication in MNRAS;
mock LSST lens catalogue may be available at
http://kipac-prod.stanford.edu/collab/research/lensing/mocklen
Aerosol emissions from prescribed fires in the United States: A synthesis of laboratory and aircraft measurements
Aerosol emissions from prescribed fires can affect air quality on regional scales. Accurate representation of these emissions in models requires information regarding the amount and composition of the emitted species. We measured a suite of submicron particulate matter species in young plumes emitted from prescribed fires (chaparral and montane ecosystems in California; coastal plain ecosystem in South Carolina) and from open burning of over 15 individual plant species in the laboratory. We report emission ratios and emission factors for refractory black carbon (rBC) and submicron nonrefractory aerosol and compare field and laboratory measurements to assess the representativeness of our laboratory-measured emissions. Laboratory measurements of organic aerosol (OA) emission factors for some fires were an order of magnitude higher than those derived from any of our aircraft observations; these are likely due to higher-fuel moisture contents, lower modified combustion efficiencies, and less dilution compared to field studies. Nonrefractory inorganic aerosol emissions depended more strongly on fuel type and fuel composition than on combustion conditions. Laboratory and field measurements for rBC were in good agreement when differences in modified combustion efficiency were considered; however, rBC emission factors measured both from aircraft and in the laboratory during the present study using the Single Particle Soot Photometer were generally higher than values previously reported in the literature, which have been based largely on filter measurements. Although natural variability may account for some of these differences, an increase in the BC emission factors incorporated within emission inventories may be required, pending additional field measurements for a wider variety of fires
Influence of regional development policies and clean technology adoption on future air pollution exposure
Cluster Lenses
Clusters of galaxies are the most recently assembled, massive, bound
structures in the Universe. As predicted by General Relativity, given their
masses, clusters strongly deform space-time in their vicinity. Clusters act as
some of the most powerful gravitational lenses in the Universe. Light rays
traversing through clusters from distant sources are hence deflected, and the
resulting images of these distant objects therefore appear distorted and
magnified. Lensing by clusters occurs in two regimes, each with unique
observational signatures. The strong lensing regime is characterized by effects
readily seen by eye, namely, the production of giant arcs, multiple-images, and
arclets. The weak lensing regime is characterized by small deformations in the
shapes of background galaxies only detectable statistically. Cluster lenses
have been exploited successfully to address several important current questions
in cosmology: (i) the study of the lens(es) - understanding cluster mass
distributions and issues pertaining to cluster formation and evolution, as well
as constraining the nature of dark matter; (ii) the study of the lensed objects
- probing the properties of the background lensed galaxy population - which is
statistically at higher redshifts and of lower intrinsic luminosity thus
enabling the probing of galaxy formation at the earliest times right up to the
Dark Ages; and (iii) the study of the geometry of the Universe - as the
strength of lensing depends on the ratios of angular diameter distances between
the lens, source and observer, lens deflections are sensitive to the value of
cosmological parameters and offer a powerful geometric tool to probe Dark
Energy. In this review, we present the basics of cluster lensing and provide a
current status report of the field.Comment: About 120 pages - Published in Open Access at:
http://www.springerlink.com/content/j183018170485723/ . arXiv admin note:
text overlap with arXiv:astro-ph/0504478 and arXiv:1003.3674 by other author
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