The reaction parameters of low-temperature synthesis of colloidal nanocrystals were investigated. It was found the structural and optical properties of CdSe nanocrystal quantum dots synthesized at ...130 degree C are particularly sensitive to alkyl-chain lengths of ligands, the cadmium source, and ligand to precursor ratios. Under optimized synthesis conditions CdSe quantum dots with narrow ensemble size distribution and excellent photoluminescence quantum efficiencies of up to 40 percent were obtained.
Spatiotemporal heterogeneity is one of the hallmarks of the relaxation dynamics associated with the glass transition. A key question in this regard is whether the dynamical heterogeneity has a ...structural origin. We report differential scanning calorimetry (DSC) data that reveal the presence of extreme spatial heterogeneity in the freezing dynamics of water (D2O) and the glass transition dynamics in the supercooled molecular liquid ortho-terphenyl (OTP), when these liquids are confined in nano-architected mesoporous silica with interconnected pores of different geometry. The results demonstrate, for the first time, that despite connectivity between the pores, nanoconfined water and OTP display distinct freezing/melting points and glass transition temperatures characteristic of each pore type. Viewed as a whole, these experimental results point to the coexistence of strong spatial heterogeneities over length scales of a few nanometers in the structure and dynamics of these liquids, suggesting a close mechanistic connection between them.
Highly ordered mesoporous films with a multicompositional nanocrystalline anatase titania/cadmium chalcogenide wall structure (see figure, scale bar is 20 nm) were synthesized by a fast and ...inexpensive one‐pot single‐precursor sol–gel‐chemistry route based on supramolecular templating. These films show enhanced sensitivity to visible light in photocurrent generation experiments.
Control over the morphology of calcium carbonate (CaCO
3) crystals has been achieved through the use of anionic, amphiphilic block copolypeptides during crystallization. Microspheres of CaCO
3 can be ...synthesized by the introduction of preformed organic, amphiphilic block copolypeptide templates, poly(
l-aspartate sodium salt)
100-
block-poly(
l-phenylalanine)
25-
random-(
l-leucine)
25 (
1) and poly(
l-glutamate sodium salt)
100-
block-poly(
l-phenylalanine)
25-
random-(
l-leucine)
25 (
2). When cationic amphiphiles are used in lieu of the anionic amphiphiles, only CaCO
3 rhombohedra are produced. The self-assembling amphiphile controls the precipitation of the microspheres by acting as a template to form giant CaCO
3 microspheres. These microspheres are composed of nanocrystals ranging in size from 10 to 60
nm using
1 and 20 to 100
nm using
2.
We investigated the photonic crystal structure inside iridescent scales of the weevil Lamprocyphus augustus. By combining a high-resolution structure analysis technique based on sequential focused ...ion beam milling and scanning electron microscopy imaging with theoretical modeling and photonic band-structure calculations, we discovered a natural three-dimensional photonic structure with a diamond-based crystal lattice operating at visible wavelengths. Moreover, we found that within individual scales, the diamond-based structure is assembled in the form of differently oriented single-crystalline micrometer-sized pixels with only selected lattice planes facing the scales' top surface. A comparison of results obtained from optical microreflectance measurements with photonic band-structure calculations reveals that it is this sophisticated microassembly of the diamond-based crystal lattice that lends Lamprocyphus augustus its macroscopically near angle-independent green coloration.
A room-temperature synthesis route for the fabrication of a new type of hybrid organic/inorganic mesostructured material based on titania instead of silica as the inorganic component has been ...developed. This approach enables facile processing of the titania/block copolymer surfactant precursor solution into optically activated, transparent, and crack-free fibers and planar waveguides with adjustable thickness. Stabilization of the structures occurs upon solvent evaporation by formation of a solid, glasslike material without heat treatment. These dye-activated, high refractive index, titania-based composites show efficient waveguiding and mirrorless lasing at low thresholds without the need of an ultralow refractive index support layer.
The striking coloration of the weevil Lamprocyphus augustus is the result of exoskeleton photonic structures with a diamond‐based lattice. Michael Bartl and co‐workers report on p. 107 on the ...development of a sol–gel templating method to convert these unique biopolymeric structures into high‐dielectric replicas. Theoretical, structural, and optical studies reveal these bioderived photonic crystals possess a complete bandgap at visible frequencies – the basis for novel optical phenomena based on light localization.
Quantum dot (QD) resonators for microcavity lasing applications were successfully synthesized by a single system diblock copolypeptide mediated process. Using specifically tailored block peptides and ...nanoparticles, we present here the cooperative assembly of cadmium selenide (CdSe) QDs and silica nanoparticles into 3-dimensional microcavities with a high QD volume fraction. These hollow QD microspheres are a perfect combination of both quantum and optical confinement, in which the electronic states of the 3-dimensional confined semiconductor nanocrystals are coupled to the photonic states of the spherical microcavity. We show that the specific interaction between the mode properties of the cavity with the emission of its QD building blocks leads to room-temperature microcavity lasing without the use of additional mirrors, substrate spheres, or gratings.
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