Development of novel chip-based integrated optics for miniaturized analytical systems

Most detection schemes for chip-based electrophoresis employ off-chip optics with external sources and detectors that are bulky for microscale analysis. As a step towards a total analysis system, a novel approach for integrating chip-based optics has been developed which uses hollow waveguides. Hollow waveguides simply operate by guiding light in an air core, which is surrounded by a transparent dielectric medium. These waveguides are lossy because they do not work on the principle of total internal reflection. However, we have used theory, experiment, and model simulations to evaluate light losses due to propagation within and insertion into the waveguide. According to our near-field diffraction model, light inserted with a profile of a half-wave cosine significantly enhances reflectivity, thus reducing light losses. A transmission efficiency of 87% over a distance of 10 cm was achieved with a 100 x 100 μm square glass capillary, which was used as a surrogate hollow waveguide. As an application, we have constructed a microchip device that uses square hollow waveguides to integrate measurements of absorption with chip-based electrophoresis. A 50 x 50 μm liquid channel and transverse 50 x 50 μm waveguide are etched as a negative pattern into a silicon master and replicated as a positive in polydimethylsiloxane (PDMS). The integrated waveguide has a 60% transmission efficiency over a distance of 3.2 cm. Separation of fluorescein and the dye BODIPY is demonstrated. A detection limit (S/N = 3) of 200 μM fluorescein is obtained using a 50 μm pathlength and a simple photocell detector. The ultimate goal of miniaturized analytical systems is to perform multiple analyses simultaneously and for high throughput purposes. Novel chip-based beam splitters and bends were integrated on-chip to construct multiplex devices. According to theory we should be able to integrate 26 absorption channels on a 10 cm diameter chip

Halide vapor phase epitaxial growth of β-Ga2O3 and α-Ga2O3 films

Halide vapor phase epitaxy was used to grow homoepitaxial films of β-Ga2O3 on bulk (010) crystals and heteroepitaxial films of α-Ga2O3 on c-plane sapphire substrates. The β-Ga2O3 substrates were prepared prior to growth to remove sub-surface damage and to apply various miscuts to their surfaces. Structural and electrical properties were found to be most impacted by the crystallinity of the β-Ga2O3 substrate itself, while the surface morphology was found to be most impacted by the miscut of the substrate. The appropriate choice of growth conditions and the miscut appear to be critical to realizing smooth, thick (>20 µm) homoepitaxial films of β-Ga2O3. The α-Ga2O3 films were grown on commercially available c-plane sapphire substrates, and the film morphology was found to be strongly impacted by the surface finish of the sapphire substrates. The α-Ga2O3 films were found to be smooth and free of additional phases or crystal twinning when the sapphire was sufficiently polished prior to growth