ABSTRACT
The surface-enhanced Raman spectroscopy (SERS) activity and the optical reflectance of a subwavelength gold nanograting fabricated entirely using top down technologies on silicon wafers are presented. The grating consists of 120 nm gold cladding on top of parallel silica nanowires constituting the grating's lines, with gaps between nanowires <10 nm wide at their narrowest point. The grating produces inordinately intense SERS and shows very strong polarization dependence. Reflectance measurements for the optimized grating indicate that (when p-polarization is used and at least one of the incident electric field components lies across the grating lines) the reflectance drops to <1% at resonance, indicating that essentially all of the radiant energy falling on the surface is coupled into the grating. The SERS intensity and the reflectance at resonance anticorrelate predicatively, suggesting that reflectance measurements can provide a nondestructive, wafer-level test of SERS efficacy. The SERS performance of the gratings is very uniform and reproducible. Extensive measurements on samples cut from both the same wafer and from different wafers, produce a SERS intensity distribution function that is similar to that obtained for ordinary Raman measurements carried out at multiple locations on a polished (100) silicon wafer.
Subject(s)
Crystallization/methods , Gold/chemistry , Nanostructures/chemistry , Nanostructures/ultrastructure , Nanotechnology/instrumentation , Refractometry/instrumentation , Spectrum Analysis, Raman/instrumentation , Equipment Design , Equipment Failure Analysis , Macromolecular Substances/chemistry , Materials Testing , Molecular Conformation , Particle Size , Surface PropertiesABSTRACT
We report achromatic form-birefringence wave plates for optical pickup units. Material dispersion and structure dispersion are balanced in a rigorous multilayer design. A trilayer grating using SiN(x)/SiO(y)N(z)/SiO2 provides easily accessible process control points and relaxed fabrication tolerance. We demonstrate precise patterning by using nanoimprint lithography on UV-curable polymers, alleviating a major fabrication challenge. The achromatic wave plates exhibit 90+/-3 degrees retardance and >95% transmittance as measured by a Mueller matrix method at wavelengths of 640-800 nm.