99 research outputs found
Wetting and Strain Engineering of 2D Materials on Nanopatterned Substrates
The fascinating realm of strain engineering and wetting transitions in
two-dimensional (2D) materials takes place when placed on a two-dimensional
array of nanopillars or one-dimensional rectangular grated substrates. Our
investigation encompasses a diverse set of atomically thin 2D materials,
including transition metal dichalcogenides, hexagonal boron nitride, and
graphene, with a keen focus on the impact of van der Waals adhesion energies to
the substrate on the wetting/dewetting behavior on nanopatterned substrates. We
find a critical aspect ratio of the nanopillar or grating heights to the period
of the pattern when the wetting/dewetting transition occurs. Furthermore,
energy hysteresis analysis reveals dynamic detachment and re-engagement events
during height adjustments, shedding light on energy barriers of 2D monolayer
transferred on patterned substrates. Our findings offer avenues for strain
engineering in 2D materials, leading to promising prospects for future
technological applications
Surface depletion mediated control of inter-sub-band absorption in GaAs/AlAs semiconductor quantum well systems
The modification of quantum well inter-sub-band absorption properties due to surface depletion induced band bending is reported. Fourier transform infrared spectroscopy measurements of a GaAs/AlAs multiple quantum well system reveal a reduction in the characteristic absorption resonance in correlation with wet chemical etching. High resolution transmission electron microscopy confirms the presence of the quantum wells after etching, suggesting the quantum wells are positioned within the surface depletion region of the structure. This method of inter-sub-band absorption modification could be used for the formation of quantum dots from a quantum well system with the precise, deterministic control of their location
Wavelength and power dependence on multilevel behavior of phase change materials
We experimentally probe the multilevel response of GeTe, Ge2Sb2Te5 (GST), and 4% tungsten-doped GST (W-GST) phase change materials (PCMs) using two wavelengths of light: 1550 nm, which is useful for telecom-applications, and near-infrared 780 nm, which is a standard wavelength for many experiments in atomic and molecular physics. We find that the materials behave differently with the excitation at the different wavelengths and identify useful applications for each material and wavelength. We discuss thickness variation in the thin films used as well and comment on the interaction of the interface between the material and the substrate with regard to the multilevel behavior. Due to the differences in penetration depths, absorption, and index contrast, different PCMs could be more suitably used depending on the application and wavelength of operation
7700-Year Persistence of an Isolated, Free-Living Coral Assemblage in the Galapagos Islands: A Model for Coral Refugia?
In an eastern-Pacific coral assemblage at Devil’s Crown, Galápagos Islands, Ecuador, two coral species, Psammocora stellata and Cycloseris (Diaseris) distorta, form dense populations of unattached colonies on sand and rubble substrata. In the Galápagos, living C. (D.) distorta is found only at this single site, whereas populations of P. stellata are found throughout the Archipelago. Six cores dating to ~ 7700 yBP showed P. stellata to be dominant throughout the history of this isolated community, but C. (D.) distorta increased in abundance from ~ 2200 yBP and reached peak abundance between 1471 yBP and the present. The relative frequency of the two coral species may be linked to millennial-scale climatic variability, and this site may represent a refuge for C. (D.) distorta from unfavorable climatic fluctuations on millennial timescales. Our results demonstrate that some corals can persist in isolated populations for millennia
Discovery of novel reductive elimination pathway for 10-hydroxywarfarin
Coumadin (R/S-warfarin) anticoagulant therapy is highly efficacious in preventing the formation of blood clots; however, significant inter-individual variations in response risks over or under dosing resulting in adverse bleeding events or ineffective therapy, respectively. Levels of pharmacologically active forms of the drug and metabolites depend on a diversity of metabolic pathways. Cytochromes P450 play a major role in oxidizing R- and S-warfarin to 6-, 7-, 8-, 10-, and 4\u27-hydroxywarfarin, and warfarin alcohols form through a minor metabolic pathway involving reduction at the C11 position. We hypothesized that due to structural similarities with warfarin, hydroxywarfarins undergo reduction, possibly impacting their pharmacological activity and elimination. We modeled reduction reactions and carried out experimental steady-state reactions with human liver cytosol for conversion o
Broadband Thermal Imaging using Meta-Optics
Subwavelength diffractive optics known as meta-optics have demonstrated the
potential to significantly miniaturize imaging systems. However, despite
impressive demonstrations, most meta-optical imaging systems suffer from strong
chromatic aberrations, limiting their utilities. Here, we employ inverse-design
to create broadband meta-optics operating in the long-wave infrared (LWIR)
regime (8 - 12 m). Via a deep-learning assisted multi-scale differentiable
framework that links meta-atoms to the phase, we maximize the
wavelength-averaged volume under the modulation transfer function (MTF) of the
meta-optics. Our design framework merges local phase-engineering via meta-atoms
and global engineering of the scatterer within a single pipeline. We
corroborate our design by fabricating and experimentally characterizing
all-silicon LWIR meta-optics. Our engineered meta-optic is complemented by a
simple computational backend that dramatically improves the quality of the
captured image. We experimentally demonstrate a six-fold improvement of the
wavelength-averaged Strehl ratio over the traditional hyperboloid metalens for
broadband imaging.Comment: 28 pages, 12 figure
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