We introduce an imaging technique based on second-harmonic generation with cylindrical vector beams that is extremely sensitive to three-dimensional orientation and nanoscale morphology of metal nano-objects. Our experiments and second-harmonic field calculations based on frequency-domain boundary element method are in very good agreement. The technique provides contrast for structural features that cannot be resolved by linear techniques or conventional states of polarization and shows great potential for simple and cost-effective far-field optical imaging in plasmonics.
Dense arrays of zinc oxide nanorods with high specific
surface
areas were grown by hydrothermal method and functionalized by self-assembled
monolayer (SAM) of porphyrins. The growth process was optimized to
obtain dense arrays of nanorods with diameter of 60–80 nm and
length up to 1.5 μm. The increase in the effective surface area
was monitored by comparing the absorbances of SAM deposited both on
the flat and nanorod surfaces of ZnO. To alter further semiconductor-organic
SAM interactions, a 2 or 5 nm thick layer of either Al2O3 or TiO2 was deposited on the ZnO nanorods.
The present results show that both carboxylic acid and triethoxysilane
anchors can be used to form porphyrin SAMs on the studied metal oxide
substrates, and the electronic interactions between the metal oxide
and porphyrin SAM are strongly modified by a thin layer of Al2O3 or TiO2. These hybrid semiconductor-organic
SAM constructions present promising model systems for advanced spectroscopy
studies of semiconductor-organic interfaces with high degree of control
over electronic interactions and system morphology.
We show that nanoimprint lithography combined with electron-beam evaporation provides a cost-efficient, rapid, and reproducible method to fabricate conical nanostructures with very sharp tips on flat surfaces in high volumes. We demonstrate the method by preparing a wafer-scale array of gold nanocones with an average tip radius of 5 nm. Strong local fields at the tips enhance the second-harmonic generation by over 2 orders of magnitude compared with a nonsharp reference.
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