Publications

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We report on the fabrication and characterization of large-area 2-D square arrays of subwavelength holes in Ag and Al films. Fabrication is based on thermal nanoimprint lithography and metal evaporation, without the need for etching, and is compatible with low-cost, large-scale production. Reflectance spectra for these arrays display an intensity minimum whose amplitude, center wavelength, and line width depend on the geometry of the array and the reflectivity of the metal film. By placing various fluids in contact with the subwavelength aperture arrays, we observe that the center wavelength of the reflectance minimum varies linearly with the refractive index of the fluid with a sensitivity of over 500 nm per refractive index unit. The surface plasmon theory is used to predict sensitivities to refractive index change with accuracies better than 0.5%. © 2008 IEEE.

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We present the design, fabrication, and testing of a microelectromechanical systems (MEMS) light modulator based on pixels patterned with periodic nanohole arrays. Flexure-suspended silicon pixels are patterned with a two dimensional array of 150 nm diameter nanoholes using nanoimprint lithography. A top glass plate assembled above the pixel array is used to provide a counter electrode for electrostatic actuation. The nanohole pattern is designed so that normally-incident light is coupled into an in-plane grating resonance, resulting in an optical stop-band at a desired wavelength. When the pixel is switched into contact with the top plate, the pixel becomes highly reflective. A 3:1 contrast ratio at the resonant wavelength is demonstrated for gratings patterned on bulk Si substrates. The switching time is 0.08 ms and the switching voltage is less than 15V. © 2008 Optical Society of America.

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Optical filters based on resonant gratings have spectral characteristics that are lithographically defined. Nanoimprint lithography is a relatively new method for producing large area gratings with sub-micron features. Computational modeling using rigorous coupled-wave analysis allows gratings to be designed to yield sharp reflectance maxima and minima. Combining these gratings with microfluidic channels and micromechanical actuators produced using micro electromechanical systems (MEMS) technology forms the basis for producing tunable filters and other wavelength selective elements. These devices achieve tunable optical characteristics by varying the index of refraction on the surface of the grating. Coating the grating surface with water creates a 33% change in the resonant wavelength whereas bringing a grating into contact with a quartz surface shifts the resonant wavelength from 558 nm to 879 nm, a fractional change of 58%. The reflectivity at a single wavelength can be varied by approximately a factor of three. Future applications of these devices may include tunable filters or optical modulators. © 2008 Society of Photo-Optical Instrumentation Engineers.

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LDRD Project 102662 provided support to pursue experiments aimed at measuring the basic electrodynamic response and possible applications of carbon nanotubes and silicon nanowires at radiofrequency to microwave frequencies, approximately 0.01 to 50 GHz. Under this project, a method was developed to integrate these nanomaterials onto high-frequency compatible co-planar waveguides. The complex reflection and transmission coefficients of the nanomaterials was studied as a function of frequency. From these data, the high-frequency loss characteristics of the nanomaterials were deduced. These data are useful to predict frequency dependence and power dissipation characteristics in new rf/microwave devices incorporating new nanomaterials.

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