The design, characterization, and optical modeling of aluminum nano-hole arrays are discussed for potential applications in surface plasmon resonance (SPR) sensing, surface-enhanced Raman scattering (SERS), and surface-enhanced fluorescence spectroscopy (SEFS). In addition, recently-commercialized work on narrow-band, cloaked wire grid polarizers composed of nano-stacked metal and dielectric layers patterned over 200 mm diameter wafers for projection display applications is reviewed. The stacked sub-wavelength nanowire grid results in a narrow-band reduction in reflectance by 1-2 orders of magnitude, which can be tuned throughout the visible spectrum for stray light control.
Broad and narrow-band wire grid polarizer (WGP) products suitable for MWIR and LWIR applications requiring high contrast were developed on antireflection (AR) coated silicon using Moxtek nanowire patterning capabilities. Accurate metrology was gathered in both transmission and reflection from the SWIR to LWIR using a combination of FTIR and dispersive spectrometers, as well as laser-based light sources. The WGP structures were analyzed using SEM, FIB, and STEM techniques and optical data was derived from IR VASE, transmission, and reflectance measurements. Modeling of device performance was achieved using rigorous coupled wave analysis. Laser damage thresholds were determined and various damage mechanisms identified.
Moxtek has developed a high contrast IR polarizer on silicon suitable for long wavelength thermal IR applications using our aluminum nanowire, large area patterning capabilities. Between 7 and 15 microns, our 144 nm pitch polarizers transmit better than 70% of the passing polarization state and have a contrast ratio better than 40 dB. Transmission and reflectance measurements were made using a Fourier Transform Infrared (FTIR) spectrometer with instrument accuracy verified using silicon and germanium reference standards. Results were compared to RCWA modeling of the wire grid polarizer (WGP) performance on antireflection-coated wafers. The FTIR instrument noise floor limited the maximum contrast measurement to about 40 dB, but high polarizer contrast was verified at 10.6 μm using a CO2 laser and pyroelectric detector. A continuous wave Gaussian beam from a CO2 laser was used for Laser Damage Threshold (LDT) testing and showed LDT values of 110 kW/cm2 and 10 kW/cm2 in the blocking and passing states respectively. Analysis of laser damage threshold test samples shows the damage propagating from defects in the anti-reflection (AR) coating. Removing these AR coating defects should improve LDT performance and transmission in the thermal IR.
We have been studying fluorescence enhancement from labeled oligonucleotides immobilized inside metallic
nanoapertures. Fluorescence enhancement is a direct result of the localized field intensity enhancement within
these nanoapertures from plasmonic excitation. We have also been developing specific surface chemistries
for metallic films to localize capture oligos only inside these nanoapertures. Some of our recent results are
overviewed.
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