Understanding Zincblende vs. Wurtzite in ZnS Nanocrystals Raymond E. Schaak, Pennsylvania State Univ University Park, DM

1. Understanding Zincblende vs. Wurtzite in ZnS NanocrystalsRaymond E. Schaak, Pennsylvania State Univ University Park, DMR 0748943 The wide-bandgap semiconductors ZnS and ZnSe have size-dependent optical properties and are used in applications that include light-emitting diodes, photo-detectors, and phosphors. ZnS and ZnSe can cryst-allize in both the zincblende and wurtzite structures, but the properties of the metastable wurtzite forms are often preferred. Nanocrystals of the less-stable wurt-zite polymorphs have been synthesized previously, but the factors that selectively generate the zincblende vs. wurtzite forms have not been well understood. Through careful mechanistic investigations, we dis-covered that nanocrystals of wurtzite-type ZnS and ZnSe form under conditions where wurtzite-type ZnO (the only stable polymorph of ZnO) forms first, and subsequent reaction with molecular sources of sulfur or selenium convert ZnO to ZnS or ZnSe, respectively, via a presumptive anion exchange pathway. This provides mechanistic understanding of polymorph control — a structure templating pathway — in an important nanoscale solid-state semiconductor system. ZnO (wurtzite) ZnS (wurtzite) ZnS ZnO Farah Dawood and Raymond Schaak, J. Am. Chem. Soc.2009, 131, 424-425.

2. “Metallurgy in a Beaker” in the ClassroomRaymond E. Schaak, Pennsylvania State Univ University Park, DMR 0748943 Undergraduate students in Penn State’s Chem 410 (Inorganic Chemistry) class carried out a new laboratory project that incorporated chemistry from the PI’s research proposal. Specifically, the students synthesized AuCu intermetallic compounds using simple beaker-chemistry reactions. This provided a simple mechanism for the students to become introduced to the field of solid-state chemistry and gain hands-on experience with the relevant synthesis and characterization tools. Undergraduate students present a poster describing their laboratory project that involved incorporating chemistry from the PI’s research proposal into the undergraduate classroom