We have obtained visible range polarization spectra of
template-synthesized gold nanoparticles oriented in
polyethylene (PE). The plasmon resonance extinction bands observed
with the incident electric field polarized
parallel, perpendicular, and at intermediate angles to the direction of
friction orientation are consistent with
the long axis of the particles being aligned with the gross orientation
axis. For all particle sizes considered
(radii 16, 38, and 60 nm) the degree of linear dichroism increases with
the amount of gold deposited in the
template synthesis step prior to extraction and orientation. The
experimental spectra agree with the predictions
of the Rayleigh, Maxwell−Garnett, and dynamical Maxwell−Garnett
theories only qualitatively. All of these
treatments fail to predict the dependence of the spectral extinction
intensities on the polarization angle θ.
T-matrix scattering calculations suggest that the contribution
from electric quadrupole modes cannot be ignored
in the 38 and 60 nm radius particles. The calculated
θ-dependence of the extinction intensity does not
resemble
experiment for 16 nm radius particles, but the theory−experiment
comparison is more favorable for the larger
radius systems. Some possible models for these observations are
discussed.
Noncentrosymmetric gold nanoparticle structures were prepared in porous anodic aluminum oxide films via a modified template synthesis procedure. The noncentrosymmetric structures are defined by two gold particles in close proximity (ca. 22 ( 8 nm end to end) within a single host oxide pore, one having average dimensions of a ) 37 ( 6 nm and b ) 26 ( 3, and the other having dimensions of a ) 27 ( 5 nm and b ) 26 ( 3 nm, where a is the axial length and b is the diameter of the quasi-cylindrical structures. Linear UV/vis polarization spectra of the gold particle/porous alumina film composites show plasmon resonance bands whose λ max incidence angle dependence is similar to composites containing centrosymmetric gold structures, where the incidence angle is defined with respect to the surface normal. Second harmonic generation (SHG) studies using an incident wavelength of 780 nm indicate that SHG intensities under s-polarization are low and independent of incidence angle (θ) for composites containing centrosymmetric and noncentrosymmetric gold nanostructures. However, in p-polarization, both composites show an increase in SHG counts with θ, with the noncentrosymmetric structures showing a higher SHG signal than their centrosymmetric counterparts. These results are consistent with local-field enhancements arising from long particle axis dipolar plasmon resonances.
A new type of solid-state variable focal length lens is described. It is based on shape changes in an elastomeric membrane driven by compression of a reservoir of a polymer gel. A novel fabrication process based on individual lens components allows for customization of lens power based on the desired application. The lens shape as a function of applied compressive strain is measured using direct surface profile measurements. The focal length of a solid state lens was reversibly changed by a factor of 1.9. Calculated back focal lengths of the lens were consistent with experimental measurements.
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