278 research outputs found
Microprobe Analyses of the Potassium-Calcium Distribution Relationship in Predentine
Apex regions of continuously growing incisors of Wistar rats were quickly dissected, shock-frozen in liquid nitrogen-cooled propane, freeze-dried at -80 °C and infiltrated with Spurr\u27s resin . 400nm thick dry sections were cut with a diamond knife on an ultramicrotome . Relatively flat sections were transferred with an eye lash onto collodium coated aluminum grids. They were flattened with a glass stick and by placing another collodi um coated aluminum grid just on top of the first one, exerting a uniform pressure . After carbon coating the sections were observed using the backscattered and secondary electron signals in a scanning microscope. The predentine was analyzed for calcium and potassium with an energy dispersive x-ray analysis system. The xray spectra revealed in the predentine regions with beginning dentine formation, near the apex, an uneven K-distribution with very low as well as more prominent x-ray peaks. The K peaks were always lower than those of calcium. In areas with advanced dentine formation, prominent K-peaks were always observed. They were normally higher than the Ca-peaks up to a distance of 5- 10 µ.m from the dentine border. Closer to the dentine border the K concentration decreased while the Ca-peak increased. This might indicate that (besides Na) K is used to balance the negative charges of the macromolecules till K is replaced by Ca at the onset of apatite crystal formation
Formation of Organic Color Centers in Air-Suspended Carbon Nanotubes Using Vapor-Phase Reaction
Organic color centers in single-walled carbon nanotubes have demonstrated
exceptional ability to generate single photons at room temperature in the
telecom range. Combining the color centers with pristine air-suspended tubes
would be desirable for improved performance, but all current synthetic methods
occur in solution which makes them incompatible. Here we demonstrate formation
of color centers in air-suspended nanotubes using vapor-phase reaction.
Functionalization is directly verified on the same nanotubes by
photoluminescence spectroscopy, with unambiguous statistics from more than a
few thousand individual nanotubes. The color centers show a strong
diameter-dependent emission intensity, which can be explained with a
theoretical model for chemical reactivity taking into account strain along the
tube curvature. We are also able to estimate the defect density by comparing
the experiments with simulations based on a one-dimensional diffusion equation,
whereas the analysis of diameter dependent peak energies gives insight to the
nature of the dopant states. Time-resolved measurements show a longer lifetime
for color center emission compared to E exciton states. Our results
highlight the influence of the tube structure on vapor-phase reactivity and
emission properties, providing guidelines for development of high-performance
near-infrared quantum light sources.Comment: 8 pages, 6 figure
Room-temperature quantum emission from interface excitons in mixed-dimensional heterostructures
The development of van der Waals heterostructures has introduced
unconventional phenomena that emerge at atomically precise interfaces. For
example, interlayer excitons in two-dimensional transition metal
dichalcogenides show intriguing optical properties at low temperatures. Here we
report on room-temperature observation of interface excitons in
mixed-dimensional heterostructures consisting of two-dimensional tungsten
diselenide and one-dimensional carbon nanotubes. Bright emission peaks
originating from the interface are identified, spanning a broad energy range
within the telecommunication wavelengths. The effect of band alignment is
investigated by systematically varying the nanotube bandgap, and we assign the
new peaks to interface excitons as they only appear in type-II
heterostructures. Room-temperature localization of low-energy interface
excitons is indicated by extended lifetimes as well as small excitation
saturation powers, and photon correlation measurements confirm single-photon
emission. With mixed-dimensional van der Waals heterostructures where band
alignment can be engineered, new opportunities for quantum photonics are
envisioned.Comment: 8 pages, 4 figure
Mn clusterisation in Ga1-xMnxN
Local structure of Mn atoms in Ga1-xMnxN has been investigated by the Mn L3
edge x-ray absorption spectrum (XAS) at total electron yield mode, which
preferentially looks at atoms near the surface. A modeling defects
configuration, the Mn5 micro-clusters complexed with substitutional MnGa and
interstitial MnI is found for the higher Mn doping concentration. This new
configuration is also confirmed by the total energy calculations.Comment: 17 pages, 5 figures, to be published in Solid. State Commu
Large area chemical vapour deposition grown transition metal dichalcogenide monolayers automatically characterized through photoluminescence imaging
Chemical vapour deposition (CVD) growth is capable of producing multiple single-crystal islands of atomically thin transition metal dichalcogenides (TMDs) over large areas. Subsequent merging of perfectly epitaxial domains can lead to single-crystal monolayer sheets, a step towards scalable production of high quality TMDs. For CVD growth to be effectively harnessed for such production it is necessary to be able to rapidly assess the quality of material across entire large area substrates. To date, characterisation has been limited to sub-0.1-mm2 areas, where the properties measured are not necessarily representative of an entire sample. Here, we apply photoluminescence (PL) imaging and computer vision techniques to create an automated analysis for large area samples of monolayer TMDs, measuring the properties of island size, density of islands, relative PL intensity and homogeneity, and orientation of triangular domains. The analysis is applied to ×20 magnification optical microscopy images that completely map samples of WSe2 on hBN, 5.0 mm × 5.0 mm in size, and MoSe2–WS2 on SiO2/Si, 11.2 mm × 5.8 mm in size. Two prevailing orientations of epitaxial growth were observed in WSe2 grown on hBN and four predominant orientations were observed in MoSe2, initially grown on c-plane sapphire. The proposed analysis will greatly reduce the time needed to study freshly synthesised material over large area substrates and provide feedback to optimise growth conditions, advancing techniques to produce high quality TMD monolayer sheets for commercial applications
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