Tailorable polymer waveguides for miniaturized bio-photonic devices via two-polymer microtransfer molding

Traditional optical fibers have been developed to achieve novel characteristics for both macro- and micro-applications. Inorganic optical waveguides using two-dimensional photonic crystals and silicon-on-insulator technology are examples of recent trends for macro- and micro-scale optical applications, respectively. As bio-photonics devices operate mostly with visible light, visible-transparent materials such as metal oxides and polymers are preferred as the guiding medium. Although polymers have tremendous potential because of their enormous variation in optical, chemical and mechanical properties, their application for optical waveguides is limited by conventional lithography. We present a non-optical lithographic technique, called two-polymer microtransfer molding, to fabricate polymer nano-waveguides, on-chip light sources and couplers. Micro-sources using quantum dots emitting red light (625nm) are successfully embedded in a waveguides array as the on-chip light sources. Fabrication of a grating coupler is also attempted for various external light sources including lasers and white light. We have quantified propagation losses of the waveguides using CCD photometry. The guiding loss is approximately 1.7dB/mm. We also demonstrated that the surface roughness of the fabricated waveguides can be reduced by chemical etching. We demonstrate that low cost, high yield, high fidelity, and tailorable fabrication of bio-photonic devices are achievable by the combination of the presented techniques

Fabrication of submicron metallic grids with interference and phase-mask holography

Complex, submicron Cu metallic mesh nanostructures are made by electrochemical deposition using polymer templates made from photoresist. The polymer templates are fabricated with photoresist using two-beam interference holography and phase mask holography with three diffracted beams. Freestanding metallic mesh structures are made in two separate electrodepositions with perpendicular photoresist grating templates. Cu mesh square nanostructures having large (52.6%) open areas are also made by single electrodeposition with a photoresist template made with a phase mask. These structures have potential as electrodes in photonic devices

Increased Wettability and Surface Free Energy of Polyurethane by Ultraviolet Ozone Treatment

The wettability of polyurethane (PU) was altered using ultraviolet ozone (UVO) treatment. The effect of UVO treatment on PU surface chemistry was investigated with various experiments. The direct measurement of sessile drops was employed to quantify the static contact angle of different wetting liquids on homogeneous PU films with various UV ozone treatment times. The contact angle of DI water droplets was decreased to 17.2º from 70.04º after 5min UVO treatment. The surface free energy of PU films was 51.46mN/m prior to treatment and was increased to 71.5mN/m after being fully treated. X-ray Photoelectron Spectroscopy (XP) analysis shows a significant amount of polar functional species (C-O and C=O bonding) were formed on the PU surface by UVO treatment. Atomic Force Microscopy (AFM) characterization shows the PU surface morphology was different before and after UVO treatment. The effect of water washing on UVO treated surface was also investigated. An aging effect study indicates the UV ozone modification can sustain the improved wettability with limited hydrophobic recovery, where the DI water contact angle remains constant at around 22º after the UVO treatment

Tailorable, 3D microfabrication for photonic applications: Two-polymer microtransfer molding

For photonic devices, extending beyond the planar regime to the third dimension can allow a higher degree of integration and novel functionalities for applications such as photonic crystals and integrated optical circuits. Although conventional photolithography can achieve both high quality and structural control, it is still costly and slow for threedimensional (3D) fabrication. Moreover, as diverse functional polymers emerge, there is potential to develop new techniques for quick and economical fabrication of 3D structures. We present a 3D microfabrication technique based on the soft lithographic technique, called two-polymer microtransfer molding (2P-µTM) to accomplish low cost, high structural fidelity and tailorable 3D microfabrication for polymers. Using 2P-µTM, highly layered polymeric microstructures are achievable by stacking planar structures layer by layer. For increased processing control, the surface chemistry of the polymers is characterized as a function of changing ultraviolet dosage to optimize yield in layer transfer. We discuss the application of the 2P-µTM to build polymer templates for woodpile photonic crystals, and demonstrate methods for converting the polymer templates to dielectric and metallic photonic crystal structures. Finally, we will show that 2P-µTM is promising for fabricating 3D polymeric optical waveguides

Optical photonic crystals fabricated from colloidal systems

Photonic crystals of close-packed arrays of air spheres in a dielectric background of titania have been fabricated with a ceramic technique. Unlike previous methods, ordering of the spheres and the formation of the titania network are performed simultaneously. The photonic crystals exhibit a reflectance peak and a uniform color at the position of the first stop band. The wavelength of the reflectance peak scales very well with the sphere size

Development of Course Modules for Materials Experiments

Recent U.S. government-sponsored studies of the decline of international competitiveness have reported that one of the most severe problems is the lack of education of future engineers in synthesis and processing of advanced engineered materials. In response, the National Science Foundation has made awards 6 universities to develop materials processing course materials for improving processing education. Iowa State University is among those selected

Polarized thermal radiation by layer-by-layer metallic emitters with sub-wavelength grating

Metallic thermal emitters consisting of two layers of differently structured nickel gratings on a homogeneous nickel layer are fabricated by soft lithography and studied for polarized thermal radiation. A thermal emitter in combination with a sub-wavelength grating shows a high extinction ratio, with a maximum value close to 5, in a wide mid-infrared range from 3.2 to 7.8 µm, as well as high emissivity up to 0.65 at a wavelength of 3.7µm. All measurements show good agreement with theoretical predictions. Numerical simulations reveal that a high electric field exists within the localized air space surrounded by the gratings and the intensified electric-field is only observed for the polarizations perpendicular to the top sub-wavelength grating. This result suggests how the emissivity of a metal can be selectively enhanced at a certain range of wavelengths for a given polarization

Photonic crystal: energy-related applications

We review recent work on photonic-crystal fabrication using soft-lithography techniques. We consider applications of the resulting structures in energy-related areas such as lighting and solar-energy harvesting. In general, our aim is to introduce the reader to the concepts of photonic crystals, describe their history, development, and fabrication techniques and discuss a selection of energy-related applications

Fabrication of layer-by-layer photonic crystals using two polymer microtransfer molding

A method of manufacturing photonic band gap structures operable in the optical spectrum has been presented. The method comprises the steps of filling a plurality of grooves of an elastomeric mold with a UV curable first polymer, each groove in parallel with each other and partially curing the first polymer. A second polymer is coated on the first polymer. A substrate or a multi-layer polymer structure is placed on the filled mold and the resulting structure is exposed to UV light (i.e., is UV cured). The mold is peeled away from the first and second polymers such that a layer of polymer rods is formed on the substrate/multi-layer polymer structure. The process is repeated until a desired number of layers have been formed. The multi-layer structure can be used to create ceramic and metallic photonic band gaps by infiltration, electro-deposition, and/or metal coating