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Triple-layer omnidirectional reflectors (ODRs) consisting of a semiconductor, a quarter-wavelength transparent dielectric layer, and a metal have high reflectivities for all angles of incidence. Internal ODRs (ambient material's refractive index n >> 1.0) are demonstrated that incorporate nanoporous SiO2, a low-refractive-index material (n = 1.23), as well as dense SiO2 (n = 1.46). GaP and Ag serve as the semiconductor and the metal layer, respectively. Reflectivity measurements, including angular dependence, are presented. Calculated angle-integrated TE and TM reflectivities for ODRs employing nanoporous SiO2 are R(int)/TE = 99.9% and R(int)/TM = 98.9%, respectively, indicating the high potential of the ODRs for low-loss waveguide structures.

An internal high-reflectivity omni-directional reflector ͑ODR͒ for the visible spectrum is realized by the combination of total internal reflection using a low-refractive-index ͑low-n͒ material and reflection from a one-dimensional photonic crystal ͑1D PC͒. The low-n layer limits the range of angles in the 1D PC to values below the Brewster angle, thereby enabling high reflectivity and omni-directionality. This ODR is demonstrated using GaP as ambient, nanoporous SiO 2 with a very low refractive index ͑n = 1.10͒, and a four-pair TiO 2 /SiO 2 multilayer stack. The results indicate a two orders of magnitude lower angle-integrated transverse-electric-transverse-magnetic polarization averaged mirror loss of the ODR compared with conventional distributed Bragg reflectors and metal reflectors. This indicates the high potential of the internal ODRs for optoelectronic semiconductor devices, e.g., light-emitting diodes.

The transport processes that occur at small length scales are greatly influenced by interfacial and intermolecular forces. Surface roughness at the nanoscale generates additional intermolecular interactions that arise due to the increased surface area. In this work, we have experimentally studied how the magnitude as well as the shape of surface roughness influences the microscale transport processes that occur in the contact line region of a liquid corner meniscus. The surface roughness contribution to the interaction potential was calculated and a direct relationship between the wetting properties of the liquid and the underlying surface properties was obtained. Since the underlying roughness alters the surface potential, the shape of the meniscus and in turn, the resulting capillary and disjoining pressure forces also changed. Atomic force microscopy was utilized to obtain a detailed characterization of the shape of the prepared surfaces. Surface morphology features were obtained from a height-height correlation function. These features were related to the wetting and transport properties of the meniscus at the contact line. Finally, the modified capillary and disjoining pressure forces on the structured surfaces were observed to influence the evaporative heat transfer from the corner meniscus.

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Polymerization occurring during fluorocarbon plasma treatment as a potential method for pore sealing was investigated. CHF 3 was used as a reactant gas to expedite the rate of polymerization due to the presence of hydrogen and the low C/F ratio. The reactor pressure was varied from 30mTorr to 90mTorr to change the number of neutrals that act as the polymerizing species. The films were exposed to the plasma for times of 1min, 3min, and 5 min to observe the penetration depth of neutrals and the thickness of modified layer as a function of time. Dielectric constants were measured before and after plasma treatment. The film morphology was investigated by scanning electron microscopy before and after plasma treatment and a featureless surface morphology was observed at 90mTorr on a 56% porosity film. After plasma treatment, the average pore neck size decreases which may help reduce metal precursor penetration during metallization.

The polymerization and pore sealing that occurs during fluorocarbon plasma treatment of nanoporous silica xerogel was investigated experimentally by Rutherford backscattering spectroscopy and successfully modeled using a diffusion-reaction analysis. CHF 3 was used as a reactant gas to expedite the rate of polymerization due to the presence of hydrogen in its structure and its low C/F ratio. Knudsen diffusion was assumed to be the dominant mechanism for the motion of polymer precursor species through the nanoporous material over the range of pressures used in the plasma experiments. The amount of fluorine atoms deposited on the sidewalls of the pores was measured as a function of depth in the dielectric film and that amount was assumed to correspond with the mass of the polymer layer formed inside the pores. By applying a Thiele-type analysis to this system, we successfully matched model calculations with measured fluorine amounts, predicted the time required to reach a steady-state concentration of the polymer precursor in a pore ͑ϳ10 −7 s͒ and predicted the time required to seal off pore necks at the surface of the dielectric ͑ϳ70 s͒. Both the model and experimental results show a greater depth of penetration and an enhanced deposition of polymer at higher porosities, confirming the need for pore sealing during back-end-of-the-line processing of nanoporous materials.