Metal Clusters, Metal Nanostructures, Semiconductor Nanocrystals, Single-Ion Magnets

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My research program seeks to understand and optimize the catalytic properties of metal clusters, the optoelectronic properties of the metal nanostructures and semiconductor nanocrystals, and the operational properties of doped gold cluster single-ion magnets. i) How can we optimize the catalytic properties of metal clusters for ethanol oxidation? Ethanol is renewable, biodegradable, hydrogen rich and can be oxidized to synthesize a wide range of valuable chemicals. We examined the ability of unsupported coinage metal clusters to catalyze the first step of ethanol oxidation at zero Kelvin. We found that copper clusters were better catalysts than silver or gold catalysts and that anionic clusters are better than neutral clusters, and that single M atoms are better catalysts than M2, M3, and M4. These results will guide our future studies of supported metal clusters at finite temperature. ii) How can we optimize the optoelectronic properties of metal nanostructures and semiconductor nanocrystals? For metal nanostructures we will focus on gold since it is relatively unreactive and can adopt many (locally) stable geometries. Our focus is on gold rod structures because they could be used as electrical connectors in nanostructured devices. Semiconductor nanocrystals are used in photovoltaic devices. Upon absorption of a photon, an electron-hole pair is formed and an electrical current can be generated. They are also used in display devices in which the reverse process takes place. Due to quantum confinement, a smaller nanocrystal has a larger band gap, which makes better use of higher energy photons. Under experimental conditions these species are typically cadmium rich (and positively charged) and must be passivated using negatively charged X-type ligands e.g. Cd16Se10Cl12 and Cd59Se50(CH3COO)18. Motivated by experimental studies, we will examine the effect on charge mobility of doping small CdSe nanocrystals with silver atoms. Also, we will examine the magnetic properties of CdSe nanocrystals doped with a high-spin atom such as Mn, Fe, or Co. iii) How can we optimize the magnetic properties of novel single-ion magnets? Single molecule magnets (SMMs) have potential for use as quantum bits (qubits) in quantum information processing devices. SMMs typically have six to twelve high-spin atoms connected to one another via oxygen or nitrogen bridging atoms. Our primary objective is to gain insight into a subset of SMMs called single ion magnets (SIMs) which are usually comprised of a ligand-protected high-spin atom that is trapped in a crystal lattice with fixed SIM-SIM distances. If a gold cluster is doped with a high-spin atom such as Mn, Fe, Co then, due to the greater electronegativity of Au, the high-spin atom will have a positive charge. These species are therefore a novel type of "free standing" SIM that could be arrayed on a surface with optimum SIM-SIM distances. This could result in a qubit with unique functionality.