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Synthesis and Property Characterization of Novel Ternary Semiconductor Nanomaterials

Mao, Baodong

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2012, Doctor of Philosophy, Case Western Reserve University, Chemistry.
Alloying and doping have been widely used for band gap engineering and property tuning of semiconductor nanocrystals, providing novel composition and structure dependent properties. Ternary I–III–VI semiconductors represent one of the best heavy-metal-free optoelectronic materials. Here, efforts are devoted to improving the optical and electrical properties of the semiconductor nanocrystals and photophysical studies of related mechanisms. AgInS2 nanocrystals with tunable sizes and optical properties were synthesized in toluene at low temperature. The role of surface and intrinsic defects were studied using time-resolved photoluminecence and femtosecond transient absorption spectroscopies. Extremely long-lived excitons were observed in the AgInS2 nanocrystals, which can benefit potential phototovoltaic applications by increasing charge separation. Series of AgInS2-ZnS nanocrystals were synthesized by heating a Ag/In/Zn/S solution showing tunable PL which initially exhibits a red shift but ultimately finishes with blue shifted emission with increasing temperature. The incorporation of Zn and the increased cation exchange of silver by zinc at higher temperatures strongly influences the PL behavior. Systematic investigation by time-resolved spectroscopy showed distinguishable PL behaviors between developing and fully grown AgInS2-ZnS nanocrystals. We also synthesized near-infrared emitting AgInS2/ZnS nanocrystals with a thin layer of ZnS by carefully controlling the growing condition. The unexpected PL red shift and band gap reduction was ascribed to the local structural ordering in the thin gradient alloyed surface layer. Zinc concentration and growth temperatures played important roles in the formation of the near-infrared emitting nanocrystals, which are promising for bioimaging applications. For the self-doped Cu2-xS nanocrystals, several methods were explored to tune the free carrier plasmon absorption properties, which showed dramatic change with the amount of hole doping resulted from copper deficiency. X-ray photoelectron spectroscopy was used to identify the copper oxidation stayes and the origin of the valence band vacancies. Detailed analysis suggested an interesting partially oxidized layer on the nanocrystal surface. The last section is devoted to improving the thermoelectric performance of nanostructured ternary Bi0.5Sb1.5Te3. Sintering was found to increase ZT as a function of sintering temperature by increasing the charge carrier mobility more than the lattice thermal conductivity, resulting in an overall increase of thermoelectric performance.
John Stuehr, PhD (Committee Chair)
Alfred Anderson, PhD (Committee Member)
Thomas Gray, PhD (Committee Member)
Jeffery Dyck, PhD (Committee Member)
Clemens Burda, PhD (Advisor)
169 p.

Recommended Citations

Citations

  • Mao, B. (2012). Synthesis and Property Characterization of Novel Ternary Semiconductor Nanomaterials [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1334065821

    APA Style (7th edition)

  • Mao, Baodong. Synthesis and Property Characterization of Novel Ternary Semiconductor Nanomaterials. 2012. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1334065821.

    MLA Style (8th edition)

  • Mao, Baodong. "Synthesis and Property Characterization of Novel Ternary Semiconductor Nanomaterials." Doctoral dissertation, Case Western Reserve University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1334065821

    Chicago Manual of Style (17th edition)