Vohs, John M
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Publication Interaction of Platinum Films with the (0001#) and (0001) Surfaces of ZnO(1994) Petrie, W. T; Vohs, John MIn this investigation, the growth, structure, and electronic properties of Pt films on the polar surfaces of ZnO were examined using high-resolution electron energy-loss spectroscopy (HREELS) and low-energhy, electron diffraction (LEED). The growth mode of vapor-deposited Pt films on ZnO(0001#) and ZnO(0001) at 300 K was found to be nearly layer-by-layer. The surfaces of Pt films produced in this manner exhibited hexagonal symmetry and were stable up to 600 K. At higher temperatures, the Pt agglomerated into particles which remained oriented with respect to the ZnO substrate. HREELS results indicate that there are only weak interactions at the Pt/ZnO(0001#) interface, while charge transfer and Schottky barrier formation occures at the Pt/ZnO(0001) interface.Publication Inexpensive Ultrahigh Vacuum Heatable/Coolable xyz-Rotary Motion Sample Manipulator(1995) Peterson, Susan L; Schulz, Kirk H; Schulz, Carl A; Vohs, John MA simple design for a heatable, coolable, rotable sample manipulator, suitable for ultrahigh vacuum (UHV) applications, is described. Highlights of the design include using a combination power/thermocouple feedthrough for heating, cooling, and temperature measurement; and the use of primarily "off-the-shelf" components available from most UHV components vendors. The described manipulator is capable of sample cooling to ~100 K, sample heating to above 900 K, while maintaining 360o of rotary motion, ~1 in. of x and y motion, and 2 in. of z motion. The apparatus can be assembled for approximately $5500 (all new parts) and uses about 3 l of liquid N2 per day. © 1995 American Institute of Physics.Publication Ultra-Thin CeO2 Overlayer on YSZ Studied by X-Ray Surface Scattering(1997) Dmowski, Wotjek; Gorte, Raymond J; Putna, S.; Vohs, John M; Egami, T.Transition metal catalysts such as Rh/Pt used in a three-way automotive catalytic converter have to perform reduction and oxidation functions at the same time. This can be accomplished only in a specific range of oxygen pressure and temperature. In order to maintain a constant partial pressure of oxygen in the vicinity of catalysts mixtures of ceria and zirconia are used. Ceria is an essential component due to its capability of storing oxygen under oxidizing and releasing oxygen under reducing conditions. However, this function deteriorates with time and eventually a catalytic converter stops working properly. It is not well understood why this particular mixture of oxides can achieve the role as a oxygen buffer and why its lifetime is limited. In order to address this issue and to understand the structural interplay at the ceria/zirconia interface, we studied the atomic structure of ultra-thin ceria layers deposited on single crystals of (001) oriented Y-stabilized zirconia (YSZ), in situ, during annealing in air using the synchrotron x-ray surface diffraction technique.