-Successive Ionic Layer Deposition-
Thomas Gilbert and Johannes Schwank
Figure 1. X-ray Photoelectron Spectroscopy (XPS)
identifies nanolayers of cerium oxide and zirconium
oxide successively deposited on a silicon wafer by SILD
Recent advances in nanoscale characterization have led to an increased understanding of heterogeneous catalysis. Modeling studies have helped guide research with the design of improved catalyst systems. However the bulk-scale synthesis of a model catalyst system is not a simple process. Once synthesized the true heterogeneity and complexity of supported catalyst systems makes it difficult to isolate the effects of localized catalyst-support interactions. Successive Ionic Layer Deposition (SILD) is a layer-by-layer synthesis method which enables the controlled deposition of catalyst materials on a support.
SILD is an aqueous method which exploits the electric double layer effect to sequentially adsorb multiple layers of aqueous metal catalyst complexes on a support material. By requiring only simple hardware and ambient synthesis conditions, SILD is well suitable for bulk-scale catalyst synthesis. SILD offers the flexibility to systematically choose the material loading, composition and morphology by varying the SILD synthesis conditions and aqueous metal salt precursors. In principle, this method allows for increased catalyst loading while maintaining a desirably high level of catalyst dispersion.
Recent work from our group suggests that a dispersed phase of barium oxide supported on γ-alumina is a better catalyst for NOx storage in lean burn engine emissions than a bulk-like phase of supported barium oxide. Through SILD we have been able to create a disperse film of barium oxide nanoislands supported on a thin film of aluminum oxide nanoislands. We are currently extending the SILD method to develop other catalytic systems. We feel that SILD is a useful method to exclusively prepare a dispersed phase of supported catalyst to better characterize the effects of dispersion on overall catalytic performance.
Figure 2. Atomic Force Microscopy (AFM) images of (a) blank silicon wafer (b) Al2O3
nanoislands synthesized on a blank silicon wafer by SILD (c) smaller BaO nanoislands
synthesized on the larger Al2O3 nanoislands by SILD.