International Collaborations in Chemistry: Characterization of organically capped Si and group 14 alloy nanoparticle heterojunctions

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This award is made by the Macromolecular, Supramolecular and Nanochemistry program of the Chemistry Division within the International Collaboration in Chemistry between US investigators and their counterparts in Germany and is co-funded by the Office of International Science and Engineering. The recipient is Professor Susan Kauzlarich of the University of the California-Davis. Applications such as solar energy conversion are faced with fundamental challenges in device architecture that limit efficiencies. Semiconductor nanoparticles (NP) are currently an active area of research in solar energy conversion with the benefits of a tunable band gap to potential carrier multiplication. Silicon is one of the semiconductor NPs of interest; however, there is still a great deal of debate concerning the nature of the electronic structure. In particular, the surface oxidation and interface termination play an important role in determining the optical gap and electronic properties. Synthesis of Si(1-x)Gex NPs allows for systematic tuning of the bandgap without changing size of the NP. In addition, the fundamental question concerning whether reversible charge transport between inorganic semiconductors typically exhibiting a band-like electronic structure and organic semiconductors featuring localized electronic states can take place freely is unanswered. The goal of this project is to study charge transport between inorganic nanoparticles of Si or Si(1-x)Gex alloys and hole-conducting organic molecules. The organic molecules are covalently bonded to the nanoparticle surface via Si-C bonds. Gaining insight on the electron transport process in this p-type system is relevant to photovoltaics. The synthesis focus of the project resides on the surface functionalization of the nanoparticles. This component of the project is the theme of the US partner's project. Pure Si and Si-Ge alloyed nanoparticles are very reactive and their synthesis and surface chemistry are opened fields of study. The German component of the project focuses on optoelectronic measurements of the synthesized organo-capped nanoparticles. The project ensures mentoring women and minority students and participation of the research team in campus-wide and nation-wide activities such as "Memberships for Undergraduate Researchers in Agriculture, Letters, and Science" (MURALS), "Alliance for Graduate Education and the Professoriate" (AGEP), STEM, collaboration with National Laboratories for joint training of students, teaching, and outreach activities. At UC Davis, underrepresented undergraduates (MURPPS program) and high school students (ACS SEED) are recruited to participate in this research. International exchange activities include two graduate students and three undergraduates having the opportunity to interact with peers at the University of Cologne.