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Water adsorption on palladium(111): ...

Fomin, Evgeny.

Water adsorption on palladium(111): From monomers to a monolayer studied by scanning tunneling microscopy.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Water adsorption on palladium(111): From monomers to a monolayer studied by scanning tunneling microscopy.
作者:	Fomin, Evgeny.
面頁冊數:	99 p.
附註:	Advisers: Yuen-Ron Shen; Miquel Salmeron.
附註:	Source: Dissertation Abstracts International, Volume: 67-08, Section: B, page: 4494.
Contained By:	Dissertation Abstracts International67-08B.
標題:	Physics, Molecular.
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3228326
ISBN:	9780542824197

Water adsorption on palladium(111): From monomers to a monolayer studied by scanning tunneling microscopy.
Fomin, Evgeny.

Water adsorption on palladium(111): From monomers to a monolayer studied by scanning tunneling microscopy. - 99 p.

Advisers: Yuen-Ron Shen; Miquel Salmeron.

Thesis (Ph.D.)--University of California, Berkeley, 2006.

A deep understanding of metal-wetting processes may lead to breakthroughs in many disciplines such as heterogeneous catalysis, corrosion, lubrication and others. In this work I present our results on initial stages of water adsorption on Pd(111) studied by Scanning Tunneling Microscopy. Unlike spectroscopic studies STM is able to provide us with insight on local properties of adsorbents. Local probing is of key importance for understanding of initial growth of water adlayers.

ISBN: 9780542824197Subjects--Topical Terms:

227726
Physics, Molecular.

Water adsorption on palladium(111): From monomers to a monolayer studied by scanning tunneling microscopy.
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245 1 0 $a Water adsorption on palladium(111): From monomers to a monolayer studied by scanning tunneling microscopy.
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500 $a Advisers: Yuen-Ron Shen; Miquel Salmeron.
500 $a Source: Dissertation Abstracts International, Volume: 67-08, Section: B, page: 4494.
502 $a Thesis (Ph.D.)--University of California, Berkeley, 2006.
520 # $a A deep understanding of metal-wetting processes may lead to breakthroughs in many disciplines such as heterogeneous catalysis, corrosion, lubrication and others. In this work I present our results on initial stages of water adsorption on Pd(111) studied by Scanning Tunneling Microscopy. Unlike spectroscopic studies STM is able to provide us with insight on local properties of adsorbents. Local probing is of key importance for understanding of initial growth of water adlayers.
520 # $a After heating up the substrate with preadsorbed water to 80-100 K, hexagonal chain, or lace, structures with the same 10-20 A characteristic width are formed. A simple model is proposed to explain the observed structures. First, water molecules adsorb intact on Pd(111). Second, all hydrogen atoms of water molecules inside the islands participate in a hydrogen network. When these two conditions can no longer be satisfied, the growth of the islands stops. Using these rules we are able to build a model of any structure observed in the STM experiments. DFT/STM simulation calculations confirmed the proposed model as well as predicted the H-down configuration of the edge water molecules, which could not be anticipated otherwise.
520 # $a First, isolated water molecules (coverage less than 1%) were studied at 40K on a clean, well defined singe crystal Pd(111) samples. The adsorption site was experimentally determined to be on-top site, which was later confirmed by DFT calculations. We found that isolated water monomers diffuse via hopping to nearest neighbor sites. Three competitive processes govern diffusion---thermal diffusion, tip proximity and electron-activated diffusion. An Arrhenius plot was acquired and the activation energy was calculated to be 12+/-7 meV for intrinsic thermal diffusion. The diffusion rate is enhanced by several orders of magnitude in the close proximity of the tip and when inelastic electron tunneling excites the vibrational "scissor" modes of the molecules. An isotope effect was observed in the threshold voltage for electron-assisted diffusion of H2O and D2O.
520 # $a Further aggregation of water molecules at 40K leads to a formation of islands with a characteristic size of 10-20 A. The inner structure of these islands was resolved and found to be composed of several hexagons of water molecules forming a honeycomb structure. Water coverage increase leads to a higher concentration of such islands on the surface, but not to a size increase.
520 # $a Upon annealing the system to 130 K larger water islands are formed. They consist of two water layers with a large unit cell in the second layer. The formation of these islands indicates that the structures observed at lower temperature are metastable.
520 # $a Upon collision in the diffusion process, water molecules form dimers, trimers and so on. Unexpectedly, dimers, trimers and tetramers exhibit diffusion rates of several orders of magnitude higher than that of monomers. Aggregations of 5 and more water molecules have a decreased mobility, the hexamer being particularly stable. Isotope dimer diffusion-experiments did not reveal a substantial difference between H2O and D2O dimer diffusion coefficients.
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790 1 0 $a Salmeron, Miquel, $e advisor
790 1 0 $a Shen, Yuen-Ron, $e advisor
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