AmericanChemicalSociety.com

I spent the period August 8, 2009 to August 20, 2010 on sabbatical as a Visiting Scientist at the University of California, Irvine funded by an ACS-PRF UFS grant and my Fullerton College salary. My sabbatical host was Matt Law, Assistant Professor in Chemistry in the Division of Physical Sciences. The goals of the sabbatical were two-fold: 1) To provide funds to conduct fundamental research in the synthesis and characterization of materials for the fabrication of solar cells and 2) To develop expertise and provide time to determine the feasibility of undergraduate research at our community college in nanoscience by collaborating with faculty at four-year institutions.

Since the focus of the sabbatical was to develop expertise I lacked in nanoscience and identify areas in solar cell research that will translate to undergraduate research at the community college level, I limited research to materials, techniques, and equipment useful to undergraduate student research either directly or remotely. I focused on techniques that did not require a glovebox environment because the space and support needs required for use and maintenance of a glovebox is prohibitive for a community college. I conducted my research with the assistance of an undergraduate student at UCI, Meiting Wu, to confirm whether the experimental design used would translate to an undergraduate research experience.

The goal of the research was to synthesize metal oxides and metal sulfides for the use in solar cell devices and further systematically characterize their structural, electronic, and optical properties. Several synthetic routes were considered to tailor the type, size, and composition of nanocrystals with appropriate electronic and optical properties needed for components in photovoltaic devices. Organometallic methods of preparation for nanoparticles of controlled size and shape were studied by varying parameters important to the characterization. The systematic characterization involved studies varying the type of solvent, the concentration of reagents, the nature of the ligand, pH of solutions, rate and time of reactions, temperature of reactions, and composition of materials. A two step method to produce metal oxides and metal sulfides by decomposition and/or reaction with an organometallic precursor and subsequent oxidation of the nanoparticle over a period of time was utilized. Hydrothermal, solvothermal, high temperature non-aqueous reactions with injections, sol-gel, addition of chelating agents, and polymer processing synthetic methods were employed.

With a the high absorptivity near 700 nm and a band gap of about 0.95 eV, Iron Pyrite (FeS₂) was first studied to be used as a material in solar cells.Because of its unique electronic and optical properties, FeS₂ was an ideal candidate to study for use in thin film solar cells. Typically the formation of pyrrhotite (Fe_1-xS) phases along with greigite and orthorhombic marcasite contaminants inhibited the formation of pure FeS₂ nanocrystals. Synthesis of this material using high temperature (325 °C) injection and heating up methods was unsuccessful but provided me an opportunity to identify the important issues in the synthesis of nanoparticles while developing new skills and techniques. I was trained in the use of a variety of instrumental techniques on the UCI campus and they were used regularly during my sabbatical for characterization. XRD was used to determine the phase of the material and the size distribution of the nanocrystals along with SEM and AAS. Because the research direction suggested exploration into air-free techniques using a glove box for the synthesis of pyrite and this was not a reasonable approach for undergraduate research in community college setting, my research turned to the studies of ternary metal oxides and mixed metal oxides for the use as photocathodes in a water-splitting solar cell device.

Calcium ferrite and other p-type mixed metal ferrites are ideal candidates as photocathodes in water splitting solar cells because they share optimal properties with pyrite: high absorptivities and about 2 eV band gaps. The aim of the studies was to synthesize and characterize mixed metal oxide p-type conductors. Using hydrothermal, solvothermal, and non-aqueous heating techniques, I successfully synthesized zinc ferrite (ZnFe₂O₄), magnesium ferrite (MgFe₂O₄), magnetite (Fe₃O₄) and the mixed metal ferrites Ca_xZn_1-xFe₂O₄, Mg_xZn_1-xFe₂O₄. Because these ferrites are synthesized using alkoxide hydrothermal and solvothermal techniques that can be used at a community college laboratory, they were explored in more detail. The phase, structure, and composition were studied using XRD and AA while the morphology was studied using SEM and TEM. Nanocrystals of the mixed metal oxides were on the order of 25- 30 nm while 4 to 10 nm ZnFe₂O₄, MgFe₂O₄, and Fe₃O₄; were synthesized below 225 °C on a Schlenk line. The smaller particles were further characterized using TEM and AFM and found to have 2-3 nm size distribution. Optical properties were studied using near IR UV-Vis and cyclic voltammetry studies were attempted on very thin films of the ZnFe₂O₄. Photoelectrochemical studies were unsuccessful last year, but are currently continuing in the lab.

As an outcome of my research, I have made new connections with faculty at local four year institutions (UCI, CSUF, and UCLA) A REU grant has been submitted by CSUF that will include two positions exclusively for Fullerton College students during the period of the grant. I continue to seek funding for research that can be used in conjunction with other grants at partnering four year institutions. A model previously developed for a research-based undergraduate weekend and summer laboratory course will be proposed as curriculum for approval. Our curriculum process is a two-year process and I expect to have a program in place by 2013.

While I wasn’t involved in the fabrication of solar cell devices, the synthesis and characterization of nanoparticles for use in cells provided me an opportunity to collaborate with local research faculty. The innovation needed to develop authentic undergraduate research at our community college is now clear but obtainable. I am extremely grateful to the host institution, UCI, Matt Law, his group for providing me with such a rich sabbatical experience and the opportunity provided by the ACS-PRF to develop new skills in nanoscience to foster an undergraduate research program at Fullerton College that emphasizes alternative energy resources.