44 research outputs found
Ultrastrong Light-Matter Coupling in 2D Metal-Chalcogenates
Hybridization of excitons with photons to form hybrid quasiparticles,
exciton-polaritons (EPs), has been widely investigated in a range of
semiconductor material systems coupled to photonic cavities. Self-hybridization
occurs when the semiconductor itself can serve as the photonic cavity medium
resulting in strongly-coupled EPs with Rabi splitting energies > 200 meV at
room temperatures which recently were observed in layered two-dimensional (2D)
excitonic materials. Here, we report an extreme version of this phenomenon, an
ultrastrong EP coupling, in a nascent, 2D excitonic system, the metal organic
chalcogenate (MOCHA) compound named mithrene. The resulting self-hybridized EPs
in mithrene crystals placed on Au substrates show Rabi Splitting in the
ultrastrong coupling range (> 600 meV) due to the strong oscillator strength of
the excitons concurrent with the large refractive indices of mithrene. We
further show bright EP emission at room temperature as well as EP dispersions
at low-temperatures. Importantly, we find lower EP emission linewidth narrowing
to ~1 nm when mithrene crystals are placed in closed Fabry-Perot cavities. Our
results suggest that MOCHA materials are ideal for polaritonics in the deep
green-blue part of the spectrum where strong excitonic materials with large
optical constants are notably scarce
Exchange Reactions between Alkanethiolates and Alkaneselenols on Au{111}
When alkanethiolate self-assembled monolayers on Au{111} are exchanged with alkaneselenols from solution, replacement of thiolates by selenols is rapid and complete, and is well described by perimeter-dependent island growth kinetics. The monolayer structures change as selenolate coverage increases, from being epitaxial and consistent with the initial thiolate structure to being characteristic of selenolate monolayer structures. At room temperature and at positive sample bias in scanning tunneling microscopy, the selenolate-gold attachment is labile, and molecules exchange positions with neighboring thiolates. The scanning tunneling microscope probe can be used to induce these place-exchange reactions
Sub-30-nm patterning on quartz for imprint lithography templates
A parallel and economical method for obtaining nanoscale features on large-area quartz substrates has been developed for use in nanoimprint lithography template fabrication. Self-assembled multilayer films (molecular rulers) are used in conjunction with photolithographically defined metallic features to generate precise nanogaps with sub-30-nm resolution on quartz substrates. These nanopatterns are then transferred to the quartz substrates using the metallic thin films as etch masks
Nanostructures using self-assembled multilayers as molecular rulers and etch resists
Self-assembled multilayers, composed of alternating layers of α,Ï-mercaptoalkanoic acids and Cu2+ ions (âmolecular rulersâ), are used as organic sidewall spacers and etch resists for the fabrication of registered microstructures with precisely tailored nanometer-scale spacings. The method outlined here eases the stringency of the lithographic processing for patterning second-generation features. Additionally, a new method to lift off the self-assembled multilayered films for the generation of the tailored nanogaps is demonstrated. The advantages of these techniques are discussed
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Effective Remediation of Groundwater Fluoride with Inexpensively Processed Indian Bauxite
India
represents one-third of the worldâs fluorosis burden
and is the fifth global producer of bauxite ore, which has previously
been identified as a potential resource for remediating fluoride-contaminated
groundwater in impoverished communities. Here, we use thermal activation
and/or groundwater acidification to enhance fluoride adsorption by
Indian bauxite obtained from Visakhapatnam, an area proximate to endemic
fluorosis regions. We compare combinatorial water treatment and bauxite-processing
scenarios through batch adsorption experiments, material characterization,
and detailed cost analyses. Heating Indian bauxite above 300 °C
increases available surface area by > 15Ă (to âŒ170
m<sup>2</sup>/g) through gibbsite dehydroxylation and reduces the
bauxite
dose for remediating 10 ppm F<sup>â</sup> to 1.5 ppm F<sup>â</sup> by âŒ93% (to 21 g/L). Additionally, lowering
groundwater pH to 6.0 with HCl or CO<sub>2</sub> further reduces the
average required bauxite doses by 43â73% for ores heated at
300 °C (âŒ12 g/L) and 100 °C (âŒ77 g/L). Product
water in most examined treatment scenarios complies with EPA standards
for drinking water (e.g., As, Cd, Pb, etc.) but potential leaching
of Al, Mn, and Cr is of concern in some scenarios. Among the defluoridation
options explored here, bauxite heated at 300 °C in acidified
groundwater has the lowest direct costs ($6.86 per person per year)
and material-intensity
On the Conversion of Bauxite Ores to Highly Activated Alumina Media for Water Remediation
Good quality drinking water is necessary to maintain a high quality of life. Millions lack access to clean and safe drinking water, and current trends suggest that billions will face acute water shortages in the coming decades. Development of new materials has led to technological impacts on water purification, from desalination membranes to atmospheric water scavenging. However, the most challenging aspect of technological solutions is cost: if the community being serviced cannot afford the solution, it is not likely to be sustainable. Repurposing Earth-abundant materials to replace highly engineered solutions is an atractive solution. Herein, minimal processing of bauxite rocks produces a high-porosity and reactive activated alumina in situ, without purification directly from the ore. This acid-treated, thermally activated bauxite (ATAB) exhibits a high surface area of 401 ± 6 m2 gâ1, a 40-fold increase relative to its parent ore, and a 2Ă increase relative to the state-of-the-art fluoride adsorbent, activated alumina. The composition, preparation, and mechanism of adsorption are studied by X-ray diffraction, X-ray photoelectron spectroscopy, and multiple-quantum magic-angle spinning 27Al nuclear magnetic resonance (NMR). The maximum adsorption density of ATAB is comparable with that of activated alumina, but ATAB requires fewer processing steps, thus warranting future consideration as a primary adsorbent of choice for fluoride removal from water
Combining Conventional Lithography with Molecular SelfâAssembly for Chemical Patterning
An innovative method to obtain chemical patterns with tailored functionality and directed alignment is described (see figure). The patterns are generated by employing lithographic processing, which is compatible with molecular selfâassembly and capable of withstanding photoâoxidation. The robust lithographic resist protects against crossâ contamination, permitting several selfâassembled monolayers terminated with different functional groups to be patterned