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104 results on '"FISHER, G. B."'

15. A standard for ultraviolet radiation.

Author

Fisher, G. B, Spicer, W. E, Mckernan, P. C, Pereskok, V. F, and Wanner, S. J

Subjects
Instrumentation And Photography
Abstract

Photoemission diode standards for accurately measuring monochromatic ultraviolet light intensity (3000 A-1100 A) are described that are also blind to visible light. The standard uses an opaque photocathode of Cs2Te and is unique because of its combination of thinness (19 mm), high sensitivity, time stability, and uniformity of response. Design criteria, construction methods, and difficulties overcome in obtaining a stable, uniform, high yield photocathode responses are discussed. Cs2Te is discussed in terms of a model for high yield photoemitters.

Published
1973

27. Suppression of Nitrogen Oxide Dissociation by Gold on Pt(335)

Author

Skelton, D. C., Wang, H., Tobin, R. G., Lambert, D. K., DiMaggio, C. L., and Fisher, G. B.

Abstract

Prototype NOx sensors for use in automotive exhaust can contain Au/Pt electrodes that dissociate O2 for removal by electrochemical pumping, but these electrodes should not dissociate NO. In these sensors, the NO diffuses to a second chamber where it is then detected. To understand the process that occurs at the Au/Pt electrode we have used temperature-programmed desorption to study the dissociation of NO and O2 on Pt(335) and on partially Au covered Pt(335). With a gold coverage of 0.15 ML, the dissociation probability of NO is decreased by a factor of 5 relative to bare Pt. Increasing Au coverage to 0.3 ML decreases NO dissociation to an undetectable level. At 0.3 ML Au, the saturation coverage of atomic O is reduced by only 20%. The variation of NO dissociation with Au coverage occurs in the range where all of the Au atoms are at steps, but Au is more effective at decreasing NO dissociation than can be explained by a simple site-blocking model. The effect of adsorbed O on NO dissociation was also investigated. Both Au and O decrease NO dissociation, but Au is much more effective. Blocking 40% of the step sites with O reduces NO dissociation by 70%&sbd;more than site-blocking, but much less than a comparable coverage of Au. Our observations show how the Au/Pt electrode in a NOx sensor is able to dissociate oxygen ~103 times more efficiently than NO.

Published
2001

28. Suppression of Water Formation over Stepped Pt(335) by Au

Author

Skelton, D. C., Tobin, R. G., Fisher, G. B., Lambert, D. K., and DiMaggio, C. L.

Abstract

A partial monolayer of Au strongly modifies the kinetics of water adsorption and formation on the stepped Pt(335) surface. The effects are more than passivation. With a Au coverage of 0.7 ML as measured by Auger spectroscopy, saturation H and O adsorption are only 15% and 8.5%, respectively, of their values on bare Pt. Adsorption at step sites is nearly eliminated. Water formation is reduced to 5% of its bare Pt value:  one-sixth of what would be expected if each Au atom blocked one site. Water formation on Pt has multiple reaction pathways. The partial Au layer eliminates only the low-temperature pathway. The H recombination temperature is reduced relative to bare Pt, so H recombination competes with water formation and reduces its efficiency. The partial Au layer also changes the desorption spectrum of water. At low water coverage, there is a single desorption peak, intermediate in temperature between those seen on Pt and Au.

Published
2000

29. Oxidation of CO on Gold-Covered Pt(335)

Author

Skelton, D. C., Tobin, R. G., Lambert, D. K., DiMaggio, C. L., and Fisher, G. B.

Abstract

We have studied the adsorption and reaction of oxygen and CO on a stepped Pt surface with varying amounts of Au, using temperature-programmed desorption and reaction (TPD and TPR), low-energy electron diffraction (LEED), high-resolution electron energy loss spectroscopy, and steady-state reaction measurements. When the surface is fully covered with Au it is inert to oxygen adsorption and to CO oxidation, and supports only a single weakly bound CO adsorption state. The surface covered with 0.7 ML Au, however, exhibits properties different from either bare Pt or bare Au. Our TPD and LEED results suggest the coexistence of completely Au-covered regions and regions with Au on the step edges but not on the terraces. Dissociative oxygen adsorption is reduced by 90%, and the remaining oxygen is confined to Pt sites near the Au/Pt boundaries. The Au-covered regions support weakly bound CO adsorption states with desorption temperatures of 120, 190, and 240 K. CO in these states can diffuse rapidly and react efficiently with adsorbed atomic oxygen at temperatures as low as 150 K. In low-temperature TPR experiments the reaction is limited by the availability of adsorbed oxygen under almost all conditions. Under steady-state conditions, however, it is limited by the availability of CO even at low temperatures and CO partial pressures up to 10-6 Torr. Adding CO partial pressure does not inhibit the reaction. Consequently, adsorbed CO does not completely block all the sites at which oxygen dissociates on this surface, unlike on bare platinum.

Published
1999

31. X-ray absorption fine structure of diamond films grown by chemical vapor deposition.

Author

Capehart, T. W., Perry, T. A., Beetz, C. B., Belton, D. N., Fisher, G. B., Beall, C. E., Yates, B. N., and Taylor, J. W.

Subjects
DIAMOND thin films, CHEMICAL vapor deposition
Abstract

We report the x-ray absorption spectra for two hard carbon films grown by filament-assisted chemical vapor deposition in gas mixtures of 1% and 0.18% methane in hydrogen. Although the Raman spectra of these two films suggest significant differences in structure, the x-ray absorption near-edge structure and extended x-ray absorption fine structure (EXAFS) are very similar. Analyzing the EXAFS from these films with a diamond crystal as a reference gives carboncarbon bond lengths of 1.53±0.03 Å. This result is consistent with diamond and incompatible with graphite. We conclude that the carbon films have the same local structure as diamond. [ABSTRACT FROM AUTHOR]

Published
1989
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32. Catalytic Reaction Mechanisms. The Role of Surface Structure and Composition. Proceedings of a Symposium at the Annual Meeting of the Materials Research Society Held at Boston, Massachusetts on 14-16 November 1983

Author

MATERIALS RESEARCH SOCIETY UNIVERSITY PARK PA, Fisher,G. B., Stair,P. C., MATERIALS RESEARCH SOCIETY UNIVERSITY PARK PA, Fisher,G. B., and Stair,P. C.

Abstract

This volume contains a large majority of the invited and contributed papers presented at the three day symposium. Catalytic Reaction Mechanisms: The Role of Surface Structure and Composition, which took place at the annual Materials Research Society Meeting in Boston, Massachusetts, November 14-16, 1983. This conference was organized in response to the recent growth in basic research on the catalytic reactivity of chemically and structurally modified surfaces. The eight invited and their eight contributed talks were given on experimental and theoretical research which included comment on the following issues in surface science and heterogeneous catalysis: the effect of additives on surface reactions, short-range versus long-range effects on reactions by promoters or poisons, ensemble size of active sites, strong and weak metal-support interactions identification of surface reaction intermediates, particle size effects, and the reconstruction of metal and alloy surfaces. In general, characterizing the composition or structure of a particular surface or catalyst was not sufficient for a successful presentation at this conference; it was necessary to go further and demonstrate the effect of a surface compositional or structural variable on a surface reaction. By the end of the symposium several observations were inescapable concerning research discussed at the meeting. The technological importance of metal-oxide catalysts was made clear and was contrasted with the relative dearth of surface science studies in this area.

Published
1984

33. Structure and Kinetics of Surface Species.

Author

NATIONAL BUREAU OF STANDARDS WASHINGTON DC SURFACE SCIENCE DIV, Madey,T E, Goodman,D W, Fisher,G B, Yates,J T , Jr, NATIONAL BUREAU OF STANDARDS WASHINGTON DC SURFACE SCIENCE DIV, Madey,T E, Goodman,D W, Fisher,G B, and Yates,J T , Jr

Abstract

The ONR-supported research in the Surface Science Division at the National Bureau of Standards has been concentrated in two areas: the characterization of the structure of adsorbed species using the Electron Stimulated Desorption Ion Angular Distribution (ESDIAD) method, and kinetic and spectroscopic studies of surface species, with particular emphasis on molecular species of catalytic interest. Recent examples from each of these efforts are summarized herein. (Author)

Published
1979

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