Joseph R. Brewer

Defect Engineering in Cubic Cerium Oxide Nanostructures for Catalytic Oxidation

Traditional nanostructured design of cerium oxide catalysts typically focuses on their shape, size, and elemental composition. We report a different approach to enhance the catalytic activity of cerium oxide nanostructures through engineering high density of oxygen vacancy defects in these catalysts without dopants. The defect engineering was accomplished by a low pressure thermal activation process that exploits the nanosize effect of decreased oxygen storage capacity in nanostructured cerium oxides.

Thermal stability of nanostructurally stabilized zirconium oxide

Nanostructurally stabilized zirconium oxide (NSZ) hard transparent films were produced without chemical stabilizers by the ion beam assisted deposition technique (IBAD). A transmission electron microscopy study of the samples produced below 150 °C revealed that these films are composed of zirconium oxide (ZrO2) nanocrystallites of diameters 7.5 ± 2.3 nm. X-ray and selected-area electron diffraction studies suggested that the as-deposited films are consistent with cubic phase ZrO2. Rutherford backscattering spectroscopy (RBS) indicated the formation of stoichiometric ZrO2. The phase identity of these optically transparent NSZ films was in agreement with cubic ZrO2, as indicated by the matching elastic modulus values from the calculated results for pure cubic zirconium oxide and results of nanoindentation measurements. Upon annealing in air for 1 h, these NSZ films were found to retain most of their room temperature deposited cubic phase x-ray diffraction signature up to 850 °C. Size effect and vacancy stabilization mechanisms and the IBAD technique are discussed to explain the present results.

Conformal filling of silicon micropillar platform with b10oron

A recently proposed micropillar semiconductor platform filled with a high volume of isotopic b10oron (B10) has great potential to yield efficient thermal neutron detectors because B10 has a high thermal neutron cross section. Here, the authors report the development of conformal filling of high aspect ratio silicon micropillar platforms with B10 by low pressure chemical vapor deposition (LPCVD) using B10-enriched decaborane (B10H14). The relationships between the pillar structure and the key process parameters including reaction temperature, process pressure, and buffer gas flow rates were investigated to optimize the conformal filling on these structures. Reaction temperature of 420–530 °C, process pressure of 50–450 mTorr, 0.3 SCCM (SCCM denotes cubic centimeter per minute at STP) B10H14 flow rate, and argon buffer gas flow rate of 0–200 SCCM were used to deposit B10 materials into the micropillar structures with aspect ratios of 3:1, 6:1, and 10:1. All three mentioned pillar structures were found to be...

Resonant Photoemission Observations and DFT Study of s–d Hybridization in Catalytically Active Gold Clusters on Ceria Nanorods

Gold clusters have garnered intense interest because of their unusual catalytic activities towards chemical reactions of industrial importance. Electronic structures of oxide supported gold clusters can provide critical clues to the mechanisms for their catalytic activity. Gold atoms possess an electronic configuration of [Xe] 4f145d106s1. However, both relativistic effects and 5d band upshift of gold clusters result in a theoretically expected hybridization of the 5d and 6s orbitals. These s-d hybridized orbitals are expected to, essentially, increase the number of free d states (or d holes) available for bonding with incoming reactant molecules, thus lowering the transition state energy and promoting the reactions.