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Weak Exciton-Phonon Coupling in CdSe Nanoplatelets from Quantitative Resonance Raman Intensity Analysis
Resonance
Raman spectra, cross sections, and depolarization ratios have been
measured for 4.5 monolayer thick CdSe nanoplatelets dispersed in chloroform.
Five excitation wavelengths between 514.5 and 476.5 nm were employed.
The resonance Raman spectra are dominated by the longitudinal optical
(LO) phonon near 201 cmâ1 and its overtone, as in
CdSe quantum dots. The absolute scattering intensity is much higher
for excitation on resonance with the sharp, lowest-energy heavy-hole
to conduction band transition than with higher energy transitions,
decreasing by about a factor of 30 between 514.5 and 496.5 nm excitation.
The LO phonon overtone is weak directly on resonance with the heavy-hole
transition but much stronger at higher excitation energies, a result
that is reproduced by simulations of the spectra using standard resonance
Raman intensity theory. The absolute Raman cross sections imply a
HuangâRhys parameter for the LO phonon of about 0.08 on resonance
with the lowest heavy-hole transition. This is a factor of 2â3
lower than found previously for CdSe quantum dots. The depolarization
ratios on resonance with the lowest heavy-hole excitonic transition
are slightly higher than expected for a degenerate, plane-polarized
transition even when the local field factors are taken into account
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Photophysics of Two-dimensional Semiconductor Nanoparticle/Liquid Interfaces
These studies have investigated the optical properties of two very different types of two-dimensional semiconductor nanoclusters and superlattices of these nanoclusters
Planning Activity Report for NDE of Adhesive Bonded Structures
Following a workshop held at the Rockwell International Science Center, Thousand Oaks, California in January, 1979, an ad hoc planning activity was undertaken to set forth a program plan to address the needs in NDE for adhesive bonded structures. The objectives of the planning activity were to develop a program rationale and strategy, determine the existence of reasonable approaches, and to propose a detailed plan of action for review at the annual DARPA/AF meeting in September, 1979. The plan encompasses the basic elements of an accept/reject methodology based on fracture mechanics, expected developments of valid flaw growth models, stress analysis, and non-destructive measurement techniques. A central issue is the prospect for determining a valid non-destructive measure of strength for the bonded joint as might be reflected in the tendency for preexistent flaws to propagate under environmental loads
A Spitzer Study of Comets 2P/Encke, 67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT)
We present infrared images and spectra of comets 2P/Encke,
67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT) as part of a larger
program to observe comets inside of 5 AU from the sun with the Spitzer Space
Telescope. The nucleus of comet 2P/Encke was observed at two vastly different
phase angles (20 degrees and 63 degrees). Model fits to the spectral energy
distributions of the nucleus suggest comet Encke's infrared beaming parameter
derived from the near-Earth asteroid thermal model may have a phase angle
dependence. The observed emission from comet Encke's dust coma is best-modeled
using predominately amorphous carbon grains with a grain size distribution that
peaks near 0.4 microns, and the silicate contribution by mass to the sub-micron
dust coma is constrained to 31%. Comet 67P/Churyumov-Gerasimenko was observed
with distinct coma emission in excess of a model nucleus at a heliocentric
distance of 5.0 AU. The coma detection suggests that sublimation processes are
still active or grains from recent activity remain near the nucleus. Comet
C/2001 HT50 (LINEAR-NEAT) showed evidence for crystalline silicates in the
spectrum obtained at 3.2 AU and we derive a silicate-to-carbon dust ratio of
0.6. The ratio is an order of magnitude lower than that derived for comets
9P/Tempel 1 during the Deep Impact encounter and C/1995 O1 (Hale-Bopp).Comment: Accepted for publication in the Astrophysical Journal 48 pages, 15
figures, 10 table
Hydrothermal Chimney Distribution on the Endeavour Segment, Juan de Fuca Ridge
The Endeavour Segment of the Juan de Fuca Ridge is well known for its abundance of hydrothermal vents and chimneys. Oneâmeter scale multibeam mapping data collected by an autonomous undersea vehicle revealed 572 chimneys along the central 14 km of the segment, although only 47 are named and known to be active. Hydrothermal deposits are restricted to the axial graben and the nearârims of the graben above a seismically mapped axial magma lens. The sparse eruptive activity on the segment during the last 4,300 years has not buried inactive chimneys, as occurs at more magmatically robust midâocean ridges
Advancing the speed, sensitivity and accuracy of biomolecular detection using multi-length-scale engineering
Rapid progress in identifying disease biomarkers has increased the importance of creating high-performance detection technologies. Over the last decade, the design of many detection platforms has focused on either the nano or micro length scale. Here, we review recent strategies that combine nano- and microscale materials and devices to produce large improvements in detection sensitivity, speed and accuracy, allowing previously undetectable biomarkers to be identified in clinical samples. Microsensors that incorporate nanoscale features can now rapidly detect disease-related nucleic acids expressed in patient samples. New microdevices that separate large clinical samples into nanocompartments allow precise quantitation of analytes, and microfluidic systems that utilize nanoscale binding events can detect rare cancer cells in the bloodstream more accurately than before. These advances will lead to faster and more reliable clinical diagnostic devices
Hydrothermal Chimney Distribution on the Endeavour Segment, Juan de Fuca Ridge
The Endeavour Segment of the Juan de Fuca Ridge is well known for its abundance of hydrothermal vents and chimneys. One-meter scale multibeam mapping data collected by an autonomous undersea vehicle revealed 572 chimneys along the central 14 km of the segment, although only 47 are named and known to be active. Hydrothermal deposits are restricted to the axial graben and the near-rims of the graben above a seismically mapped axial magma lens. The sparse eruptive activity on the segment during the last 4,300 years has not buried inactive chimneys, as occurs at more magmatically robust mid-ocean ridges
Explorations, Vol. 2, No. 2
Cover: The painting reproduced on the cover is an oil on canvas entitled âKonrad Oberhuberâs Visit to Compass Harbor, Maine, â by Michael Lewis, 1985. Lewis is Professor of Art at the University of Maine at Orono. ©Michael Lewis, 1985
Articles include: The Gulf of Maine: A Sea Beside a Sea, by Kathleen Lignell
The Gulf of Maine Littoral world of promise, by Carole J. Bombard for David Sanger
Marine Worms Worth Fifteen Dollars Each? by David Dean
Free Trade, Not Trade War, by James A. Wilson
Inner SpaceâThe Gulf of Maine: its history and future for research, by Robert S. Steneck
The Shape of Mud and Its Importance to Marine Animals, by Les Watling
The Humble Herring gold-plated sardine, by David K. Stevenson
Seismic Profiling: The Search for the Submerged Geological Record in the Gulf of Maine, by Daniel F. Belknap and Joseph T. Kelley
Our Cover Artist: Michael Lewis
In the Classroom, by Michael Brody
Nobody Told the Bumblebee He Couldn\u27t Fly, by Herbert Hidu
The Tie That Binds: technology and research, by Robert S. Steneck
Diet Developments for the Maine Lobster, by Robert Bayer
A Wet Desert: secrets of the salt marsh, by Gary M. King
Maine Marshes, by George L. Jacobson
Mya Arenaria: return of the clam, by Devon Phillips
CES: commitment and action, by Devon Phillips
EPSCoR benthic research, by Lawrence M. Mayer
In the Field of Researc
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