Browsing by Subject "solar-cells"
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Item Precision Synthesis of Silicon Nanowires with Crystalline Core and Amorphous Shell(2013-04) Bogart, Timothy D.; Lu, Xioatang; Korgel, Brian A.; Bogart, Timothy D.; Lu, Xioatang; Korgel, Brian A.A synthetic route to crystalline silicon (Si) nanowires with an amorphous Si shell is reported. Trisilane (Si3H8) and Sn(HMDS)(2) are decomposed in supercritical toluene at 450 degrees C. Sn(HMDS)(2) creates Sn nanoparticles that seed Si nanowire growth by the supercritical fluid-liquid-solid (SFLS) mechanism. The Si : Sn ratio in the reaction determines the growth of amorphous Si shell. No amorphous shell forms at relatively low Si : Sn ratios of 20 : 1, whereas higher Si : Sn ratio of 40 : 1 leads to significant amorphous shell. We propose that hydrogen evolved from trisilane decomposition etches away the Sn seed particles as nanowires grow, which promotes the amorphous Si shell deposition when the higher Si : Sn ratios are used.Item Thermodynamic Synthesis of Solution Processable Ladder Polymers(2015-11) Lee, Jongbok; Rajeeva, Bharath Bangalore; Yuan, Tianyu Y.; Guo, Zi-Hao; Lin, Yen-Hao; Al-Hashimi, Mohammed; Zheng, Yuebing; Fang, Lei; Zheng, Yuebing; Zheng, YuebingThe synthesis of a carbazole-derived, well-defined ladder polymer was achieved under thermodynamic control by employing reversible ring-closing olefin metathesis. This unique approach featured mild conditions and excellent efficiency, affording the ladder polymer backbone with minimum levels of unreacted defects. Rigorous NMR analysis on a C-13 isotope-enriched product revealed that the main-chain contained less than 1% of unreacted precursory vinyl groups. The rigid conformation of the ladder-type backbone was confirmed by photophysical analysis, while the extended rod-like structure was visualized under scanning tunneling microscope. Excellent solubility of this polymer in common organic solvents allowed for feasible processing of thin films using solution-casting techniques. Atomic force microscopy and grazing incident X-ray scattering revealed a uniform and amorphous morphology of these films, in sharp contrast to the polycrystalline thin films of its small molecular counterpart.