Hydrogen sensing with Pd-coated long-range surface plasmon membrane waveguides.

A low power, reusable optical hydrogen sensor using long-range surface plasmon polariton (LRSPP) cladded membrane waveguides is demonstrated. The sensor incorporates a 5 µm wide, 20 nm thick gold stripe embedded in a 160 nm thick free-standing Cytop membrane with a 5 nm thick Pd over-layer. Input and output coupling is achieved with directly integrated broadside grating couplers. The sensor is tested with hydrogen concentrations up to 3% and demonstrates a strong response with an estimated detection limit of 290 ppm, and a response time of 7 s to a 0.6% H2 step - this level of performance is among the best reported for optical H2 sensors. Cycling of the hydrogen exposure shows a significant hysteresis response, however no film deformation or delamination was observed over many cycles. The high stress that is induced in clamped films during hydrogenation is relaxed in due to the film being deposited on the flexible and elastic Cytop membrane. This could result in improved lifetimes for this sensor and increased uptake ability.

Modeling wall effects in capillary electrochromatography.

A volume averaging technique for modeling electroosmotic and pressure driven flow in microchannels is applied to a packed capillary electrochromatography column. This model can be applied to fluid flow in both porous and open channels and can account for porosity variation in the column due to packing and zeta potential mismatches between the wall and the packing material. Numerical results are presented and compared with experimental results from the literature. Several different porosity models are shown to produce similar concentration profiles and allow the model to reproduce wall effects observed in experimental columns.

Optical selection, manipulation, trapping, and activation of a microgear structure for applications in micro-optical-electromechanical systems.

The optical processes involved in laser trapping and optical manipulation are explored theoretically and experimentally as a means of activating a micrometer-size gear structure. We modeled the structure by using an enhanced ray-optics technique, and results indicate that the torque present on the gear can induce the gear to rotate about the gear-arm plane center with light as the driving energy source. We confirmed these findings experimentally by using gears manufactured with conventional semiconductor techniques and from a layer of polyimide. It is expected that such a simple gear design activated by use of light could lead to an entire new class of micro-optical-electromechanical systems.