RESUMEN
The optimum geometry for waveguide propagation was determined by comparing bowtie and semicircle antenna cuts to a standard plain waveguide with a 635 nm laser. The results of both experimental data and COMSOL simulations proved that the bowtie antenna increased waveguide output in comparison to the plain waveguide with the semicircle pattern showing no enhancement. It was also determined that the propagation was highest when the polarization direction of the laser was perpendicular to the direction of the waveguide for all patterns, while polarization along the propagation direction led to little or no output in all antenna and plain waveguide cases. The waveguide output of the bowtie antenna and plain structures was then measured using a tunable laser for wavelengths from 570 nm to 958 nm under both parallel and perpendicular polarization conditions. The results indicated that the bowtie antenna performed better over the entire range with an average increase factor of 2.12±0.40 over the plain waveguide pattern when perpendicularly polarized to the waveguide direction, and 1.10±0.48 when parallel. The measured values indicate that the structure could have applications in broadband devices.
RESUMEN
A method has been developed for the wet solution synthesis of core shell heterogeneous nanowires. An ultrathin silica layer was first grown around plain silver nanowires to act as a suitable insulator. An outer nanoparticle layer was then attached through heteroaggregation by dispersing the un-functionalized nanowires in toluene solutions containing nanoparticles of CdSe or Au. Total coverage of nanoparticles on nanowires was found to increase with the nanoparticle size, which is attributed to the increase in the van der Waals interaction between the nanoparticles and the nanowire with the increasing size of nanoparticles. Using this method, we achieved over 79.5% coverage of CdSe nanoparticles (24 nm × 11 nm) on the nanowire surface. Although following the same trend, Au nanoparticles show an overall lower coverage than CdSe, with only 24.2% coverage at their largest particle size of 19 nm in diameter. This result is attributed to the increase in steric repulsion during attachment due to the increasing length of capping ligands. Investigation of the core-shell nanowire's optical properties yielded CdSe Raman peak enhancement by a factor of 2-3 due to the excitation of surface plasmon propagation. Our method can be applied to the attachment of a wide range of nanoparticles to nanowire materials in non-polar solution and the core-shell nanowires show great potential for incorporation into various microscopic and drug delivery applications.
RESUMEN
Although confocal infrared (IR) absorption micro-spectroscopy is well established for far-field chemical imaging, its scope remains restricted since diffraction limits the spatial resolution to values a little above half the radiation wavelength. Yet, the successful implementations of below-the-diffraction limit far-field fluorescence microscopies using saturated irradiation patterns for example for stimulated-emission depletion and saturated structured-illumination suggest the possibility of using a similar optical patterning strategy for infrared absorption mapping at high resolution. Simulations are used to show that the simple mapping of the difference in transmitted/reflected IR energy between a saturated vortex-shaped beam and a Gaussian reference with a confocal microscope affords the generation of high-resolution vibrational absorption images. On the basis of experimentally relevant parameters, the simulations of the differential absorption scheme reveal a spatial resolution better than a tenth of the wavelength for incident energies about a decade above the saturation threshold. The saturated structured illumination concepts are thus expected to be compatible with the establishment of point-like point-spread functions for measuring the absorbance of samples with a scanning confocal microscope recording the differential transmission/reflection.