The Zink Group
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The sol-gel process is a synthesis technique for the preparation of inorganic glasses and ceramics at room temperature. The method is based on the hydrolysis and condensation of molecular precursors (metal alkoxides). The three dimensional mesostructure is due to the ordered arrays of micelles formed by surfactants which serve as templates. The dynamics of the formation from the free surfactant to micelle to the 3D network is followed in real time by spectroscopic probes. Living cells also aggregate into two dimensional packed ordered arrays and template the silica film. [more]
Exotic materials are those with unique physical and chemical properties, examples include conducting polymers, smart materials, macromolecules, and mixed valence compounds. The sol-gel matrix serves as a unique host for harnessing and controlling these properties toward the synthesis of molecular devices. For example, the periodic lamellar (or layered) structure of sodium dodecylsulfate (SDS) templated films is exploited in the synthesis of conducting layers made of conducting polymer or ruthenium mixed-valence compounds, separated by insulating layers of silica. Other applications include synthesis of supramolecular machines using pseudorotaxanes and mesoporous silica, and the controlled, 3D multiphoton deposition of metal nanoparticles in sol-gel monoliths. [more]
Using sol gel methods, porous inorganic glasses can be made into monoliths, and thin films. These glasses provide a transparent matrix for trapping active molecules such as enzymes, antibodies, and organic compounds. Analytes can diffuse through pores to the active molecules resulting in an optical change. The doped sol gel matrices are used as sensors to detect physical properties such as polarity, biomedical analytes such as glucose, and biological or chemical warfare agents. Thin films coated on optical fibers are used for remote sensing. [more]
Our spectroscopic research focuses on understanding the properties of metal-containing molecules in excited electronic states. One important area of investigation is the determination of excited state geometries. Upon excitation, transition metal compounds generally undergo large distortions along many normal modes of vibration. Resonance Raman spectra, in conjunction with electronic emission and absorption spectra, Resonance Enhanced Multi Photon Ionization (REMPI) and the time-dependent theory of spectroscopy, are used to calculate the geometries. Multiple coupled excited states and modes create interesting spectroscopic effects and interpretive challenges; wave packet amplitude transfer between excited states is calculated. The metal compounds are studied in both condensed media, such as single crystals and glasses, and in ultra cold molecular beams. The REMPI experiments use a tunable pulsed laser to probe the vibronic eigenstates of the metal compounds starting from the lowest excited state and continuing upwards in energy to the dissociation continuum. These experiments also allow access to forbidden electronic excited states through multiphoton absorption. [more]
By utilizing luminescence and mass spectroscopic techniques to study the photolytic properties of metal organic molecules (those used in chemical vapor deposition), we have discovered fragmentation pathways and identified the conditions for producing desired materials in the gas phase. We have obtained action spectra and identified the bound or dissociative excited state origins of these species by monitoring the wavelength dependencies of specific photoproducts. Through these studies activation of specific reaction channels to control the photolytic processes are realized. We can use these results to discover deposition conditions which favor the production of the desired material in the gas phase which may have implications on material deposition. [more]
Laser photochemistry of volatile metal-containing molecules is used to deposit films and patterned structures of metals and semiconductors on substrates. An important goal of the research is to understand the mechanisms by which the precursor molecule fragments and forms the desired solid. We are investigating the effects of laser wavelength and fluence, the roles of surface reactions and purely gas phase reactions, and the relative importance of photothermal reactions (caused by laser heating) versus photochemical reactions (from excited electronic states). We are also designing new single-source precursors for metal and semiconductor (II/VI and III/V) deposition, and studying methods of controlling the deposit's purity and dimensions. These studies, together with gas-phase electronic spectroscopy and mass spectroscopy are leading to fundamental knowledge of photodeposition mechanisms. [more]