Local oxygen transport resistances around the surface of Pt particles were examined by analyzing varying equivalent weight (EW) of ionomer in cathode catalyst layers (CCLs) of polymer electrolyte fuel cells. Traditional limiting current method was performed to estimate total oxygen transport resistances in CCLs. The local oxygen transport resistances were determined analytically from the total oxygen transport resistances in CCLs with different Pt loadings. Analysis applying a macro homogeneous model in CCLs revealed that lowering ionomer EW in CCLs caused significant increase in not only the oxygen transport resistance in thickness direction of a CCL (rO2,macro), but also the local oxygen transport resistance (RO2,local). Additionally, the obtained oxygen transport resistances were reexamined by simple dissolution/diffusion models considering the results of measurement of water sorption isotherm. Results revealed rO2,macro were within the expected range. However, experimental RO2,local values were much higher than values calculated by use of both the oxygen transport property of Nafion membrane and bulk PTFE/water approximated model. This indicates that unconsidered parameters related to interfacial phenomena of ionomer such as the coverage of absorbed water on the surface, oxygen dissolution rate in ionomer or blockage of Pt surface by sulfonic acid group should be employed.

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This paper studies the effects of gate voltage on heat generation and transport in a metal–semiconductor field effect transistor made of gallium arsenide (GaAs) with a gate length of 0.2 μm. Based on the interactions between electrons, optical phonons, and acoustic phonons in GaAs, a self-consistent model consisting of hydrodynamic equations for electrons and phonons is developed. Concurrent study of the electrical and thermal behavior of the device shows that under a source-to-drain bias at 3 V and zero gate bias, the maximum electron temperature rise in this device is higher than 1000 K whereas the lattice temperature rise is of the order of 10 K, thereby exhibiting nonequilibrium characteristics. As the gate voltage is decreased from 0 to −2 V the maximum electron temperature increases due to generation of higher electric fields whereas the maximum lattice temperature reduces due to lower power dissipation. The nonequilibrium hot-electron effect can reduce the drain current by 15% and must be included in the analysis. More importantly, it is found that the electron temperature rise is nearly independent of the thermal package conductance whereas the lattice temperature rise depends strongly on it. In addition, an increase of lattice temperature by 100 K can reduce the drain current by 25%.

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A reduction of the adhesion between polysilicon surface-micromachined structures and its silicon substrate using ultrashort pulse laser irradiation has been demonstrated. Polysilicon cantilevers, which adhered to the silicon substrate after final rinse and dry, were freed after irradiation by a 800 nm wavelength laser with pulse duration of 150 fs (full width at half-maximum) and fluences up to 40 mJ/cm2. Increasing the pulse widths to 2.7 ps resulted in significantly fewer freed cantilevers indicating that the process depends heavily on the presence of high-temperature carriers in the silicon. Adhesion reduction has been observed from exposure to a single pulse which results in minimal lattice temperature increase.