Spherical semiconductor nanoplatelets, known as quantum shells (QSs), have captured significant interest for their strong suppression of Auger recombination, which leads to long multiexciton ...lifetimes and wide optical gain bandwidth. Yet, the realization of benefits associated with the multiexciton lasing regime using a suitably designed photonic cavity remains elusive. Here, we demonstrate broadly tunable lasing from close-packed films of CdS/CdSe/CdS QSs deposited over nanopillar arrays on Si substrates. Wide spectral tuning of the stimulated emission in QSs with a fixed bandgap value was achieved by engaging single exciton (λ X ∼ 634 nm), biexciton (λ BX ∼ 627 nm), and multiple exciton (λ MX ∼ 615–565 nm) transitions. The ensemble-averaged gain threshold of ∼ 2.6 electron–hole pairs per QS particle and the low photonic cavity fluence threshold of ∼4 μJ/cm2 were attributed to Auger suppression. The tuning of the lasing emission closely aligns with our model predictions achieved by varying the array period while preserving mode confinement and quality (Q) factors. These results mark a notable step toward the development of colloidal nanocrystal lasers.
The development of a chip-based sensor array composed of individually addressable polystyrene−poly(ethylene glycol) and agarose microspheres has been demonstrated. The microspheres are selectively ...arranged in micromachined cavities localized on silicon wafers. These cavities are created with an anisotropic etch and serve as miniaturized reaction vessels and analysis chambers. A single drop of fluid provides sufficient analysis media to complete ∼100 assays in these microetch pits. The cavities possess pyramidal pit shapes with trans-wafer openings that allows for both fluid flow through the microreactors/analysis chambers and optical access to the chemically sensitive microspheres. Identification and quantitation of analytes occurs via colorimetric and fluorescence changes to receptor and indicator molecules that are covalently attached to termination sites on the polymeric microspheres. Spectral data are extracted from the array efficiently using a charge-coupled device allowing for the near-real-time digital analysis of complex fluids. The power and utility of this new microbead array detection methodology is demonstrated here for the analysis of complex fluids containing a variety of important classes of analytes including acids, bases, metal cations, metabolic cofactors, and antibody reagents.
The concept of utilizing photoluminescent semiconductor nanocrystals for latent fingerprint detection, especially in concert with phase-resolved imaging for background fluorescence suppression, is ...reduced to practice with CdS nanocrystals that are capped with dioctyl sulfosuccinate. The nanocrystals are dissolved in heptane or hexane and are applied in much the same way as staining with fluorescent dye, on articles that have been pre-fumed with cyanoacrylate ester and also on the sticky side of electrical tape without pre-fuming. Since CdS can form a photoluminescent nanocomposite with dendrimers, a feasibility examination of dendrimer tagging of fingerprints has also been conducted.
Polythiophene Nanowires Bjørnholm, T.; Hassenkam, T.; Greve, D. R. ...
Advanced materials (Weinheim),
10/1999, Letnik:
11, Številka:
14
Journal Article
Recenzirano
Nanometer‐size threads of amphiphilic polythiophene are demonstrated to form upon collapsing a monolayer of polythiophene on a Langmuir–Blodgett trough (see also the cover). Bundles of these ...nanowires can be manipulated to fill the gap between gold electrodes, as shown in the Figure, where the wires are depicted in dark gray and the gold electrodes in light gray.
A new method for enhancing the wavelength selectivity and responsivity of hybrid dye/superconductor optical sensors is described. Here, reflective “mirror layers” deposited atop the high-temperature ...superconductor, YBa2Cu3O7 - δ, are used to enhance the optical performance characteristics of such hybrid sensors. Quantification of the wavelength selectivity for such detector structures is detailed for both dye/high-T c superconductor and dye/mirror-layer/high-T c superconductor systems. Optical studies suggest that the inclusion of the mirror layer serves to enhance the wavelength selectivity by reducing the amount of off-resonance signal generated by the detector. On the other hand, the on-resonance signals captured by the dye layer are effectively sensed by the superconductor element. Measurement of the wavelength-dependent optical responsivity of the mirror-layer-modified hybrid detectors shows that energy transfer between the dye and superconducting elements is not diminished by the presence of this reflective layer.
This paper provides the first direct structural evidence describing conjugated polymer self-assembly at the air−water interface. Grazing-incidence X-ray diffraction (GIXD) and X-ray reflectivity ...measurements on a number of derivatives of amphiphilic regioregular polythiophenes (e.g., poly(3‘-dodecyl-3-(2,5,8-trioxanonyl)-2‘,5-bithiophene), polymer 1) show that these conjugated polymers self-assemble as 2-dimensional polycrystalline monolayers at the air/water interface with the amphiphilic polymers preorganized into rigid boards standing edge-on on the water surface. The monolayer consists of highly ordered (∼70% crystalline) domains, with a centered rectangular unit cell having the polymer backbone along the a-axis and the thiophene π-stack along the b axis with a distance of 3.85−3.94 Å depending on the applied surface pressure. These domains are connected by soft, more disordered boundaries. This is evidenced by the macroscopic compressibility of the entire LB film (C macro ≈ 4−7 m/N) being one order of magnitude larger than the microscopic compressibility (C micro ≈ 0.6 m/N) of the polycrystalline domains. The alkyl chains in the 3-position of the thiophene rings are in a crystallographically disordered state due to their cross-sectional mismatch with the packing of the thiophenes. The importance of having the side chains coupled in a regioregular fashion to the 3-position of the thiophene rings is evidenced by a dramatic increase in the coherence length of the crystalline domains for highly regioregular samples (>95% head−tail couplings) as compared to less regioregularly coupled polymers (∼80% head−tail couplings). Transfer to solid support by the Langmuir−Blodgett technique induces an overall orientation of the domains in the film, giving rise to a dichroic ratio of up to 4. Reflection−absorption infrared spectroscopy (RAIRS) shows that the alkyl chains of transferred films are in an all-trans conformation with a locally ordered environment, having only few gauche defects.
