Establishing a Chemical Toolbox for Programmed Assembly of Metal Chalcogenide Nanoparticles into "Wired" Architectures

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Energy is all around us, but much of it is not very useful. Scientists are interested in ways to take wasted energy, and convert it into useful energy supplies. Dr. Stephanie Brock is investigating how to convert plentiful solar energy into electricity or chemical fuels. She is particularly interested in the challenging problem of how to harvest "light". Quantum dots are very small particles that have dimensions on the order of 1/1000th of a red blood cell and are great at absorbing solar radiation and producing charged particles. Accordingly, Dr. Brock is developing techniques that enable these sub-microscopic quantum dot particles to be assembled into films and 3 dimensional porous structures with millimeter to centimeter dimensions. Dr. Brock is developing methods that enable quantum dots with different chemical potentials to attach to each other, thereby creating a voltage difference that can move an electrical current within the structure. She is also working to understand how the chemical nature of the inter-particle bonding affects the ability to rapidly move the charges, and how these charges can sometimes get "trapped" and resist extraction. This fundamental knowledge helps in the design of efficient solar cells and photochemical water-splitting (hydrogen fuel generation) systems. Dr. Brock's research is attractive to graduate and undergraduate students alike, who are exposed to cutting-edge science through participation in her lab. Dr. Brock is also developing science modules aimed at middle-to-high school students to give them hands-on experiences in the lab. She is implementing these through the Wayne State University's GO-GIRLs outreach program. In this research program, Dr. Stephanie Brock of Wayne State University is supported by the Macromolecular, Supramolecular and Nanochemistry (MSN) Program to develop a chemical toolbox to (1) enable the rate of assembly of different metal chalcogenide nanoparticle components to be varied. This ability may dictate the degree of phase-segregation in multicomponent systems; (2) provide post- and pre-assembly chemical modifications of the interfaces to facilitate electron transport. The kinetic parameters dictating oxidative assembly of nanoparticles (made of MQ where M = cadmium, lead, zinc; Q = sulfur, selenium, tellurium) are studied as a function of the redox properties of Q, the solubility of M, the crystal structure of MQ, the facet energetics and the surface ligand group. In parallel, methods for replacement of oxidized interfaces with metal-ion crosslinks by post-gelation oxidative addition reactions or (pre-gelation) assembly of sulfide or halide-capped nanoparticles via metal cations, are evaluated. The ability to control the rate of solution-phase assembly of metal chalcogenide nanoparticles, thereby enabling programmable assembly of disparate nanoparticle components into 2- and 3-D "wired" architectures with specified degrees of heterogeneity, enable design of multicomponent assemblies for applications that benefit from rapid injection of charges over short distances (e.g., photocatalysts prepared from homogeneous assembly of photosensitizer + catalyst) or require extraction over large distances (e.g., bulk nanoheterojunction solar cells comprising p + n semiconductors). Chemical principles are also employed to tune the nature of the interparticle interfaces, thereby augmenting interparticle transport and the overall stability of the assembly. Dr. Brock involves graduate and undergraduate students in interdisciplinary collaborative research and modern characterization techniques. She introduces Detroit-area adolescent girls, many of whom are minorities, to chemistry through the GO-GIRLs outreach program.