COLL 402 |
| Frontier orbital energies of organic materials and semiconductor nanoparticles often control rates of electron transfer in technologies as diverse as condensed phase photovoltaic devices and photoelectrochemical production of chemical fuels. The offsets in these energies at interfaces with metals, metal oxides, and other organic phases can often be difficult to determine, and one cannot generally assume a constant vacuum level between the two materials, i.e. significant interface dipoles can exist which are critical in determining rates of electron transport across the interface. UV-photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) have proven useful for systematic investigations of normal and semi-fluorinated alkanethiol monolayers on gold, and more recently on indium-tin oxide (ITO) electrodes. We will review these recent results, with special attention paid to characterization of the sign and size of the interface dipole introduced by these modifiers. We will then review even more recent studies where CdSe and TiO2 nanoparticles have been tethered to bi-functional modifiers on Au surfaces, permitting a close examination of their HOMO energies, the role of interface dipoles in these measurements, and prospects for characterization of the energetic effect of adding ligands to the nanoparticle surface. |
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Interfacial Electron Transfer and Solar Energy Conversion: From Molecules to Nanomaterials
2:00 PM-5:40 PM, Wednesday, April 9, 2008 Morial Convention Center -- Rm. 226, Oral
Division of Colloid & Surface Chemistry |