224 research outputs found
Controlled biomineralization of magnetite (Fe<sub>3</sub>O<sub>4</sub>) by <i>Magnetospirillum gryphiswaldense</i>
Results from a study of the chemical composition and micro-structural characteristics of bacterial magnetosomes extracted from the magnetotactic bacterial strain Magnetospirillum gryphiswaldense are presented here. Using high-resolution transmission electron microscopy combined with selected-area electron diffraction and energy dispersive X-ray microanalysis, biogenic magnetite particles isolated from mature cultures were analysed for variations in crystallinity and particle size, as well as chain character and length. The analysed crystals showed a narrow size range (∼14-67 nm) with an average diameter of 46±6.8 nm, cuboctahedral morphologies and typical Gamma type crystal size distributions. The magnetite particles exhibited a high chemical purity (exclusively Fe3O4) and the majority fall within the single-magnetic-domain range
Trion Species-Resolved Quantum Beats in MoSe2
Monolayer photonic materials offer a tremendous potential for on-chip
optoelectronic devices. Their realization requires knowledge of optical
coherence properties of excitons and trions that have so far been limited to
nonlinear optical experiments carried out with strongly inhomogenously
broadened material. Here we employ h-BN encapsulated and electrically gated
MoSe2 to reveal coherence properties of trion-species directly in the linear
optical response. Autocorrelation measurements reveal long dephasing times up
to T2=1.16+-0.05 ps for positively charged excitons. Gate dependent
measurements provide evidence that the positively-charged trion forms via
spatially localized hole states making this trion less prone to dephasing in
the presence of elevated hole carrier concentrations. Quantum beat signatures
demonstrate coherent coupling between excitons and trions that have a dephasing
time up to 0.6 ps, a two-fold increase over those in previous reports. A key
merit of the prolonged exciton/trion coherences is that they were achieved in a
linear optical experiment, and thus are directly relevant to applications in
nanolasers, coherent control, and on-chip quantum information processing
requiring long photon coherence.Comment: 21 pages, 6 figures, 2 SOI figure
Hundredfold Enhancement of Light Emission via Defect Control in Monolayer Transition-Metal Dichalcogenides
Two dimensional (2D) transition-metal dichalcogenide (TMD) based
semiconductors have generated intense recent interest due to their novel
optical and electronic properties, and potential for applications. In this
work, we characterize the atomic and electronic nature of intrinsic point
defects found in single crystals of these materials synthesized by two
different methods - chemical vapor transport and self-flux growth. Using a
combination of scanning tunneling microscopy (STM) and scanning transmission
electron microscopy (STEM), we show that the two major intrinsic defects in
these materials are metal vacancies and chalcogen antisites. We show that by
control of the synthetic conditions, we can reduce the defect concentration
from above to below . Because these point
defects act as centers for non-radiative recombination of excitons, this
improvement in material quality leads to a hundred-fold increase in the
radiative recombination efficiency
Perturbation Mappings in Polynomiography
In the paper, a modification of rendering algorithm of polynomiograph is presented. Polynomiography is a method of visualization of complex polynomial root finding process and it has applications among other things in aesthetic pattern generation. The proposed modification is based on a perturbation mapping, which is added in the iteration process of the root finding method. The use of the perturbation mapping alters the shape of the polynomiograph, obtaining in this way new and diverse patterns. The results from the paper can further enrich the functionality of the existing polynomiography software
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