Atomic layer deposition: Applications in plasmonics and catalysis

Understanding the chemistry of heterogeneous catalysts constitutes a research area of enormous importance for the ultimate goal of rational catalyst design. Elucidation of structure-activity relationships requires new methods for the controlled synthesis of nanostructured catalysts as well as in situ characterization techniques capable of probing both catalyst and surface adsorbates. Atomic layer deposition (ALD), with precise size control afforded by the self-limiting nature of the surface reactions, is a versatile method for the synthesis of highly uniform supported metal and metal oxide catalysts. Surface-enhanced Raman spectroscopy (SERS) is ideally suited for probing catalytically relevant interfaces because of its superior surface sensitivity and its compatibility with aqueous environments. In this work, the goals of controlled catalyst synthesis and in situ spectroscopic characterization are realized through the use of ALD.;A flow-type reactor was first constructed and implemented for the ALD of metal oxides such as Al2O3 and TiO2. Deposition of ultrathin Al2O3 layers over SERS-active substrates was shown to greatly enhance the stability of nanoscale structures in solvent, enabling elevated temperature SERS measurements in the liquid phase for the first time.;The surface chemistry and growth of VOx from vanadium oxytriisopropoxide and water was characterized by in situ quartz crystal microbalance studies. VOx/Al2O3 catalysts were then synthesized by ALD and examined by UV Raman spectroscopy. The observed vibrational frequencies for the terminal V=O stretch of VOx indicate primarily monomeric surface species and differences in VOx surface coverage and structure between theta-Al2O3 and ALD Al2O 3 supports.;Finally, ALD of Ag was explored. Traditional AB-type reaction sequences under thermal conditions proved to be quite difficult owing to the lack of effective reducing agents. However, ABC-type ALD was shown to be an effective method for synthesizing Ag nanoparticles of interest for plasmonics and catalysis. Ag growth on TiO2 results in ultrasmall nanoparticles that are uniformly dispersed with a narrow size distribution, while Ag growth on Al 2O3 results in larger plasmonically active nanoparticles.;The work presented here highlights ALD as a promising technique for the controlled synthesis of new catalytic materials as well as the stabilization and functionalization of plasmonic nanostructures for systems of interest in catalysis.