With extremely low material absorption and exceptional surface smoothness, silica-based optical resonators can achieve extremely high cavity quality (Q) factors. However, the intrinsic material limitations of silica (e.g., lack of second order nonlinearity) may limit the potential applications of silica-based high Q resonators. Here we report some results in utilizing layer-by-layer self-assembly to functionalize silica microspheres with nonlinear and plasmonic nanomaterials while maintaining Q factors as high as 10(7). We compare experimentally measured Q factors with theoretical estimates, and find good agreement.
We report the fabrication and characterization of a cylindrically symmetric fiber structure that possesses significant and thermodynamically stable second-order nonlinearity. Such fiber structure is produced through nanoscale self-assembly of nonlinear molecules on a silica fiber taper and possesses full rotational symmetry. Despite its highly symmetric configuration, we observed significant second harmonic generation (SHG) and obtained good agreement between experimental results and theoretical predictions.
We describe a lithographic method for directly patterning the adhesive properties of amine-rich layer-by-layer assembled polymer films, useful for positioning metal and other nanostructures. The adhesive properties of the films are sufficiently robust that the films can be patterned with standard as opposed to soft lithographic methods. We perform the patterning with a lithographically defined evaporated aluminum mask which protects selected regions of the substrate, passivating adhesion in the exposed regions with acetic anhydride. When the aluminum is removed with a HCl etch, the protected regions retain their adhesion, whereas particle adsorption is almost completely eliminated in the passivated areas, making it possible to guide adsorption to the protected areas. The high degree of adhesion comes about because of uncoordinated amine groups that pervade the film. Cycling the pH from high values to low and back causes the amines to be rearranged, rejuvenating the adhesive properties of the surface, which is the likely origin of the robustness of the adhesive properties to processing. pH adjustment also causes reversible swelling and deswelling of the film, so that the vertical position and dielectric environment of the nanostructure can be dynamically adjusted, which can be particularly beneficial for tuning the plasmonic resonances of metallic structures.
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