Walter G. Klemperer
Emeritus Professor of Chemistry
Professor Klemperer received his B.A. from Harvard College in 1968 and his Ph.D. from Massachusetts Institute of Technology in 1973. He was a Professor of Chemistry at Columbia University before joining the University of Illinois faculty in 1981.
Research
We study inorganic chemistry at the interface between solution and the solid state: the design and synthesis of heterogeneous catalysts from preassembled molecular building blocks, solution chemical processing of ceramic materials with unusual electrical properties, and the fabrication of nanostructured materials on semiconductor surfaces for microelectronic applications.
One current interest is solid superacids and their catalytic activity in alkane isomerization. It has been known for some time that extremely active solid superacid catalysts may be prepared by precipitating amorphous, hydrated titanium or zirconium dioxide from aqueous solution and treating these reactive materials with with sulfuric acid. However, difficulties associated with catalyst lifetime and thermal stability have not been overcome, in part because the nature of the sulfuric acid—metal oxide interaction in these amorphous solids is ill-defined. We have developed an alternative approach that reverses the order of synthesis: structurally well-defined, sulfated molecular oxides are prepared and subsequently converted into a solid superacid, thus tailoring a well-defined sulfate—oxide interaction on the molecular scale. For example, titanium tetraethoxide reacts with aqueous sulfuric acid in ethanol solution, yielding a diprotontated, octanuclear complex containg two sulfate and six titanate subunits. This molecular complex is a very strong acid whose properties can be studied in detail, since its conjugate base has the same oxide core structure. Moreover, it can be polymerized into a solid acid using sol-gel processing techniques.
Another area of interest is the chemical assembly of ultrathin (< 30 Å) oxide films. This research has yielded a solution chemical process for fabricating uniform, conformal, robust and pinhole-free zirconia thin films. These materials, when deposited on silicon surfaces, have suitable electrical properties and the proper dimensions for application as gate oxide materials in the next generation of semiconductor devices. When deposited on oxide superconductor surfaces, they provide passivating electron barriers whose electron tunneling spectra show features that cannot be observed using traditional approaches.
We also study the assembly of inorganic structures on silicon surfaces, where the silicon surface atoms serve as ligands that bind to metal complexes in solution. For example, cobalt carbonyl in heptane reacts with Si-H groups on hydrogen-passivated Si(111) surfaces, yielding cobalt tetracarbonyl groups attached to the Si(111) surface by silicon-carbon bonds. These groups are stable in an inert atmosphere but have the reaction profile anticipated for cobalt carbonyl derivatives.
Publications
"Methyltriskaidecazirconates, Molecular Forms of Zirconia," V. W. Day, W. G. Klemperer, and M. M. Pafford, Inorg. Chem., 44, 5397-5404 (2005).
"Solution Deposition of Ultrathin Zirconia Films on YBa2Cu3O7-δ by Molecular Layering of Tetra-n-Propyl Zirconate," L. H. Greene, P. J. Hentges, W. G. Klemperer, J. G. Wen, and G. Westwood, J. Mat. Chem., 14, 3158-3166 (2004).
"Solution Growth of Ultra-Thin, Insulating Layers of Zirconia for Passivation and Tunnel Junction Fabrication on YBCO Thin Films," P. J. Hentges, G. Westwood, H. Aubin, W. G. Klemperer, L. H. Greene, IEEE Transactions on Applied Superconductivity, 13, 801 (2003).
"Complex Oxides as Molecular Materials: Structure and Bonding in High-Valent Early Transition Metal Compounds," J. C. Goloboy, W. G. Klemperer, T. A. Marquart, G. C. Westwood, O. Y.Yaghi, in Polyoxometalate Molecular Science, Borrás-Almenar, J. J.; Coronado, E.; Müller, A.; Pope, M. T., Eds., Kluver Academic Publishers, Dordrecht, p 79, (2003).
"Isolation and Characterization of Tetra-n-propyl Zirconate in Hydrocarbon Solution and the Solid State," V .W. Day, W. G. Klemperer, and M. M. Pafford, Inorganic Chemistry,40, 5738 (2001).
"Heteropolyanions: Molecular Building Blocks for Ultrathin Oxide Films," J. D. Powell, A. A. Gewirth, and W. G. Klemperer, in Polyoxometalates: From Topology to Industrial Applications, M. T. Pope and A. Müller, eds. Kluwer Academic Publishers, Dordrecht, p. 329 (2001).
"Silver Nanoparticle Formation: Predictions and Verification of the Aggregative Growth Model," D. L. Van Hyning, W. G. Klemperer, and C. F. Zukoski, Langmuir, 17, 3128 (2001).
