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A novel surface emitting distributed feedback quantum cascade laser emitting around λ 4.6 µm is demonstrated by employing an equivalent phase shift (EPS) of quarter-wave (λ/4). The EPS is fabricated through extending one sampling period by 50% in the center of a sampled Bragg grating. Single-lobed far-field radiation pattern with a low divergence angle of about 0.6º x 16.8º is obtained. Selective single-mode lasing with a mean side mode suppression ratio above 20 dB and wavelength coverage range of 72 nm is achieved simultaneously on a single wafer only by changing the sampling period. [ABSTRACT FROM AUTHOR]

An 8‐cell air‐breathing direct methanol fuel cell (DMFC) stack with the active area of 5 cm2 of each cell has been developed. Stainless steel plates of 500 µm thickness with flow channels were fabricated using photochemical etching method as the current collectors. Different conditioning methods for membrane electrode assembly (MEA) activation were discussed. With proper control of water crossover to the cathode, cathode flooding was avoided in the DMFC stack. Methanol crossover at open circuit voltage (OCV) in the air‐breathing DMFC was measured. Further, it was found that flow maldistribution might occur in the parallel flow field of the stack, making carbon dioxide gas management at the anode necessary. Using humidified hydrogen in the anode with a high flow rate, the oxygen transport limiting current density was characterized and found to be sufficient in the air‐breathing cathode. The stack produced a maximum output power of 1.33 W at 2.21 V at room temperature, corresponding to a power density of 33.3 mW cm−2. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A porous InAlAs structure was first obtained by electrochemical etching. Nano-pore arrays were formed when the In0.52Al0.48As membrane was anodized at constant voltages in an HF aqueous solution. These self-assembled structures showed evident blue-shift photoluminescence emissions. While a quantum size effect alone underestimates the blue-shift energy for a sample with a relatively large average pore wall thickness, a novel effect caused by the asymmetric etching is proposed to account for this phenomenon. The results inferred from the x-ray double crystal diffraction are in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

A design of single-mode distributed feedback quantum cascade lasers (DFB-QCLs) with surface metal grating is described. A rigorous modal expansion theory is adopted to analyse the interaction between the waveguide mode and the surface plasmon wave for different grating parameters. A stable single-mode operation can be obtained in a wide range of grating depths and duty cycles. The single-mode operation of surface metal grating DFB-QCLs at room temperature for l = 8.5 um is demonstrated. The device shows a side-mode suppression ratio of above 20 dB. A linear tuning of wavelength with temperature indicates the stable single-mode operation without mode hopping. [ABSTRACT FROM AUTHOR]