Best oven for young atoms
Naked eye can’t see
CEA Grenoble - INAC
Title: GaN/Al(Ga)N heterostructures for infrared optoelectronics: polar vs nonpolar orientations
GaN/Al(Ga)N nanostructures have emerged as promising materials for intersubband (ISB) optoelectronics devices, with the potential to cover the whole infrared spectrum. The large conduction band offset and sub-ps ISB recovery times make III-nitrides particularly appealing for ultrafast devices in the short-wavelength infrared (1-3 µm) and mid-wavelength infrared (3-5 µm) regions. A variety of GaN-based ISB optoelectronic devices have already been demonstrated, including photodetectors, switches and electro-optical modulators. In addition to these applications, the large energy of GaN longitudinal-optical phonon (92 meV, 13 µm) opens prospect for room-temperature THz quantum cascade lasers and ISB devices covering the 5-10 THz band, inaccessible to GaAs.
The presence of internal electric fields in polar materials imposes an additional confinement which increases the energetic distance between the ISB electronic levels, and constitutes one of the main challenges to extend the GaN-ISB technology towards the far-infrared (FIR). Furthermore, the high piezoelectric constants and lattice mismatch in the GaN/AlN system results in piezoelectric polarization along the  axis, which renders the ISB transition energies sensitive to the strain state, and hampers precise device design. This has motivated research on alternative crystallographic orientations with reduced or zero polarization fields.
Plasma-assisted molecular-beam epitaxy is the growth technique that has provided better results for the study of ISB transitions in III-nitride materials. The low growth temperature prevents interdiffusion and allows interface control at the atomic layer scale. In this presentation, we summarize recent progress in ISB studies of GaN/AlGaN heterostructures.
As a first approach, growing along the polar axis, we analyze multi-layer complex QW designs that create a pseudo-square potential profile.
As an alternative, we use nonpolar orientations, which allows to suppress the internal electric field and enhance the ISB oscillator strength, at the price of increasing the lattice mismatch.
Accept or reject
Concept clearer with hands on
Title: Effect of an interactive component on students conceptual understanding of hypothesis testing
First year statistics course especially inferential statistics, has many college students baffled. I created some hands on place based interactive components into the curriculum for the dissertation, only the hypothesis testing unit was used. The control group had hsyal lecture and home assignments while the experimental group participated in a collaborative interactive lab. Using Ancova, there was a statistical significant difference between the two groups based on the University of minnesota's Comprehemsive Assessmentment of Outcomes in Statistics
Growth versus breakdown
climate change threatens balance
reefs of the future
University of Hawaii at Manoa
Title: Environmental drivers of the coral reef accretion-erosion balance in present and future ocean conditions.
Worldwide, declines in coral cover and shifts in coral reef community composition have raised concerns about whether reef accretion (reef growth by coral and other calcifiers) will continue to exceed reef erosion (reef breakdown by borers and grazers). Reef persistence is influenced by global and local anthropogenic factors, such as ocean warming, acidification, eutrophication, and overfishing, as well as natural environmental variability. Predicting reef response to environmental stress requires an understanding of both natural and anthropogenic environmental drivers of reef accretion and erosion, and how these drivers interact at different spatiotemporal scales. For my dissertation, I measured variation in accretion and erosion along a natural gradient to determine the dominant environmental drivers of accretion-erosion rates at fine (tens of meters) and broad (1000s of kilometers) spatial scales. I also used a controlled mesocosm experiment to directly examine the effects of global anthropogenic stressors (i.e., temperature and ocean acidification) on the coral reef accretion-erosion balance. My results highlight the importance of spatial scale in interpreting accretion-erosion data on coral reefs and also indicate that increases in reef erosion, combined with expected decreases in calcification, could accelerate the shift of coral reefs to an erosion-dominated system in a high CO2 world.
Snow is coming soon
the mercury trapped reacts
goes around the world
University of Ottawa
Title: Mercury redox transformations in snow and surface waters from temperate and high Arctic regions
Mercury is a global pollutant distributed throughout the world travelling via the atmosphere. It is deposited onto aquatic and terrestrial environments where it can become a potent neurotoxin. Light and microbes can send mercury back to the atmosphere before the toxin forms. I studied photochemical and microbial processes leading to Hg evasion.
(PhD thesis completed at the Université de Montréal in 2007)
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