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- Eriksson, Mats, 1963-, et al.
(författare)
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The water-forming reaction on thin, SiO2 supported, palladium films
- 1990
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Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 41:1-3, s. 137-138
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Tidskriftsartikel (refereegranskat)abstract
- The water-forming reaction has been studied on thin Pd films, evaporated on planar SiO2 substrates. The nominal film thickness varied between 5 and 100 Å. The studies were performed in uhv by means of mass spectrometry, UPS and work function measurements in the temperature range 323–523 K. The film structure was also studied with TEM. The results are compared with previous measurements on 1000 Å, thick, homogeneous Pd films. The structure of the thin Pd films changed dramatically during cyclic H2 and O2 exposures, from that of a continuous film with cracks to that of drop-like metal particles. These structural changes are not observed on the thick (1000 Å) Pd films. Even though there are large structural changes, the water-forming reaction looks qualitatively the same as on a thick Pd film. The total water production however, decreases with decreasing film thickness. We believe that some minor qualitative differences in the water-forming reaction for different nominal Pd film thicknesses, are due to the increasing PdSiO2 boundary as the thickness is reduced.
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| 3. |
- Fogelberg, J., et al.
(författare)
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A hydrogen sensitive palladium metal-oxide-semiconductor device as sensor for dissociating NO in H2-atmospheres
- 1990
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Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 41, s. 705-
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Tidskriftsartikel (refereegranskat)abstract
- A Pd-MOS structure can be used as a sensitive analytical tool in the study of dissociating oxygen containing molecules. Nitric oxide has been studied as a test case. Initially NO adsorbs very effectively and dissociatively on polycrystalline Pd at temperatures above 473 K. At this temperature H2O, N2O and N2 desorbs during an NO exposure in a hydrogen background. After such exposure the surface is probably left with only residual nitrogen atoms adsorbed on the surface. Below 390 K the dissociation probability is insignificant.
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| 5. |
- Rubel, M., et al.
(författare)
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Deuterium interaction with silicon-graphite materials exposed to the tokamak plasma
- 1994
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Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 45:4, s. 429-434
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Tidskriftsartikel (refereegranskat)abstract
- Silicon-containing composites are considered as plasma facing materials in controlled fusion devices. Comparative studies of deuterium interaction with carbon based substrates were performed for graphite-silicon mixtures (5-50 wt% of Si), carbon fibres and isotropic graphite. Both virgin and deuterium treated surfaces were characterized by means of several surface sensitive techniques. The substrates were exposed to the deuterium plasma in the TEXTOR tokamak, in a magnetron or in a hollow cathode. The uptake, retention and release of deuterium were investigated. Migration of deuterium from the plasma deposited layer to the bulk of the substrates was found for the graphite-silicon mixtures. The structure of the deuterium-containing deposits was studied using atomic force microscopy. The initial stage of bubble formation was observed on the surfaces exposed to the tokamak plasma
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| 6. |
- Shao, Yidong, et al.
(författare)
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Water adsorption on Ge(100) : a computational study
- 1991
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Ingår i: Vacuum. - 0042-207X .- 1879-2715. ; 42:4, s. 313-319
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Tidskriftsartikel (refereegranskat)abstract
- Cluster calculations simulating water dissociation on Ge(100) are presented. We evaluate the electronic structure of molecular water and dissociation products (OH, O, H) in a LCAO-X scheme. Ge 3d core level shifts were approximated by the ionization potentials (IPs) of nonbonding a2 orbitals. Finally, we discuss the nomenclature of hydroxyl groups ligated to different adsorbents. The germanium-adsorbate atomic distance and not simply the perpendicular position above the first Ge(100) layer was found to be the most important chemisorption parameter. This illustrates the importance of directional bonding and contrasts adsorption on metals. Adsorption at open bridge sites will give significantly less perturbation than adsorption at terminal sites. Major perturbations at the former site require movement of substrate atoms to accommodate the necessary short GeO distances. Our calculations suggest that (i) some water dissociation occurs already at 100 K, (ii) two different hydroxyl species are present at the surface, and (iii) one of the hydroxyl ligands is akin to adsorbed oxygen.
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