Scalable, Green Fabrication of Single-Crystal Noble Metal Films and Nanostructures for Low-Loss Nanotechnology Applications.

The confinement of spatially extended electromagnetic waves to nanometer-scale metal structures can be harnessed for application in information processing, energy harvesting, sensing, and catalysis. Metal nanostructures enable negative refractive index, subwavelength resolution imaging, and patterning through engineered metamaterials and promise technologies that will operate in the quantum plasmonics regime. However, the controlled fabrication of high-definition single-crystal subwavelength metal nanostructures has remained a significant hurdle due to the tendency for polycrystalline metal growth using conventional physical vapor deposition methods and the challenges associated with placing solution-grown nanocrystals in desired orientations and locations on a surface to manufacture functional devices. Here, we introduce a scalable and green wet chemical approach to monocrystalline noble metal thin films and nanostructures. The method enables the fabrication of ultrasmooth, epitaxial, single-crystal films of controllable thickness that are ideal for the subtractive manufacture of nanostructures through ion beam milling and additive crystalline nanostructure via lithographic patterning for large-area, single-crystal metasurfaces and high aspect ratio nanowires. Our single-crystal nanostructures demonstrate improved feature quality, pattern transfer yield, reduced optical and resistive losses, and tailored local fields to yield greater optical response and improved stability compared to those of polycrystalline structures-supporting greater local field enhancements and enabling practical advances at the nanoscale.

Characterization of plasmonic hole arrays as transparent electrical contacts for organic photovoltaics using high-brightness Fourier transform methods.

We present a methodology for probing light-matter interactions in prototype photovoltaic devices consisting of an organic semiconductor active layer with a semitransparent metal electrical contact exhibiting surface plasmon-based enhanced optical transmission. We achieve high-spectral irradiance in a spot size of less than 100 µm using a high-brightness laser-driven light source and appropriate coupling optics. Spatially resolved Fourier transform photocurrent spectroscopy in the visible and near-infrared spectral regions allows us to measure external quantum efficiency with high sensitivity in small-area devices (<1 mm2). This allows for rapid fabrication of variable-pitch sub-wavelength hole arrays in metal films for use as transparent electrical contacts, and evaluation of the evanescent and propagating mode coupling to resonances in the active layer.