For nearly a century, oxygen has been widely accepted as the key element that triggers photoresponse in polycrystalline PbSe photoconductive detectors. Our photoluminescence and responsivity studies on PbSe samples, however, suggest that oxygen only serves as an effective sensitization improver and it is iodine rather than oxygen that plays the key role in triggering the photo-response. These studies shed light on the sensitization process for detector applications and ways to passivate defects in IV-VI semiconductors. As a result, high peak detectivity of 2.8 Â 10 10 cm Á Hz 1/2 Á W À1 was achieved at room temperature. V

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A series of Cu−Ni/CeO 2 -nanotube catalysts is prepared by an impregnation method for CO 2 hydrogenation to CH 3 OH. Regular CeO 2 nanotubes are perfectly formed with a tube diameter of about 30−50 nm and Cu−Ni alloy is well dispersed on CeO 2 nanotube without nanotube morphology change. There is a synergistic effect between Ni and Cu, promoting the bimetallic Cu−Ni dispersion, reducibility, CO adsorption and hydrogenation. Additionally, a strong interaction is observed between Cu−Ni alloy and CeO 2 , and it contributes to partial reduction of Ce 4+ to Ce 3+ and formation of oxygen vacancies which adsorb and activate CO 2 . It is shown that both CO 2 conversion and CH 3 OH space-time yield increase at first, reach their maximum values at a Ni/ (Cu+Ni) ratio of 2/3, and then decrease with increasing the Ni/(Cu+Ni) ratio. The CeO 2 -nanotube supported CuNi 2 catalyst gives CO 2 conversion of 17.8% and CH 3 OH space-time yield of 18.1 mmol/(g cat •h) after preliminary optimization. Furthermore, it exhibits an excellent catalytic performance within a wide range of space velocity.

n-CdS/p-PbSe heterojunction is investigated. A thin CdS film is deposited by chemical bath deposition on top of epitaxial PbSe film by molecular beam epitaxy on Silicon. Current-voltage measurements demonstrate very good junction characteristics with rectifying ratio of $178 and ideality factor of 1.79 at 300 K. Detectors made with such structure exhibit mid-infrared spectral photoresponse at room temperature. The peak responsivity R k and specific detectivity D * are 0.055 A/W and 5.482 Â 10 8 cmÁHz 1/2 /W at k ¼ 4.7 lm under zero-bias photovoltaic mode. Temperature-dependent photoresponse measurements show abnormal intensity variation below $200 K. Possible reasons for this phenomenon are also discussed. V

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