This project addresses two types of nanostructured systems based on metal sulfides (CdS, PbS, Cu2S, and Ag2S): 1)Arrays of ultra-long (> 500 um) metal sulfide nanowires and 2)Wired metal sulfide nanoparticles linked by metal nanowire connecting segments. The approach to the synthesis of these systems relies on Electrochemical Step Edge Decoration, a technique developed by the PI over the past two years. The synthesis and characterization (both structural and chemical) of these structures will be carried out as Phase 1 of the project. In Phase 2 electrical conduction, photoconductivity, and electroluminescence of these materials will be investigated by transferring the nanowires from HOPG (Highly Ordered Pyrolytic Graphite) surfaces onto glass substrates and evaporating metal contacts onto the ends of the transferred wire arrays. Recent work has demonstrated feasibility of the approach. Fundamental understanding is sought of how the bulk electronic structure of metal sulfide semiconductors is manifested in the optical and electrical properties of polycrystalline 1-D wires. The ultra-long wires to be synthesized in this study will make possible direct electrical measurements of conduction in wire arrays with the possibility of electrical excitation of luminescence in these systems. Broader understanding and fundamental insights into the properties of polycrystalline 1-D semiconductor nanowires are anticipated outcomes from these studies. %%% The project addresses basic research issues in a topical area of electronic materials with high technological relevance. An important feature of the project is the strong emphasis on education, with emphasis on integration of research and education involving university and high school students. The PI has established outreach activities to students at University High School near the UCI campus. An educational objective of this proposal is to broaden this outreach program to include an additional 1-2 high-school students a year from high schools with a high concentration of economically disadvantaged students within the Newport Mesa and Santa Ana Unified School Districts. It is planned to identify prospective candidates for research by interfacing with the NSF-funded Faculty Outreach Collaborations Uniting Scientists, Students and Schools, or FOCUS! Program at UCI. Each student works as an apprentice with a senior graduate student during the summer until they cultivate the research skills necessary to embark on an independent research project. This project will take place during the balance of the summer, and possibly extend into the school year on weekends and after school. Research projects will be tailored to the abilities and interests of the students. A sample project may involve the synthesis of one type of semiconductor nanowire, and the characterization of these wires using scanning electron microscopy and EDX (Energy Dispersive X-ray Analysis) elemental analysis. ***
