Adsorption electron diffraction

Ross PN Jr. 1982. Studies of adsorption at well-ordered electrode surfaces using low-energy electron diffraction. In Vanselow R, Howe R, editors. Chemistry and Physics of Solid Surfaces IV. Berlin Springer-Verlag, pp. 173-201. 

The characterization of evaporated alloy films can be carried out at widely different levels of sophistication. At the very least, it is necessary to determine the bulk composition, probably after the film has been used for an adsorption or catalytic experiment. Then various techniques can be applied, e.g., X-ray diffraction, electron diffraction, and electron microscopy, to investigate the homogeneity or morphology of the film. The measurement of surface area by chemisorption presents special problems compared with the pure metals. Finally, there is the question of the surface composition (as distinct from the bulk or overall composition), and a brief account is given of techniques such as Auger electron spectroscopy which might be applied to alloy films. 

The good agreement between electrochemical and UHV data, documented in Figure 4, is a very important result, because it proves for the first time that the microscopic information which one obtains with surface science techniques in the simulation studies is indeed very relevant to interfacial electrochemistry. As an example of such microscopic information, Figure 5 shows a structural model of the inner layer for bromide specific adsorption at a halide coverage of 0.25 on Ag 110 which has been deduced from thermal desorption and low energy electron diffraction measurements /12/. Qualitatively similar models have been obtained for H2O / Br / Cu( 110) /18/and also for H2O/CI /Ag 110. ... 

The most conventional investigations on the adsorption of both modifier and substrate looked for the effect of pH on the amount of adsorbed tartrate and MAA [200], The combined use of different techniques such as IR, UV, x-ray photoelectron spectroscopy (XPS), electron microscopy (EM), and electron diffraction allowed an in-depth study of adsorbed tartrate in the case of Ni catalysts [101], Using these techniques, the general consensus was that under optimized conditions a corrosive modification of the nickel surface occurs and that the tartrate molecule is chemically bonded to Ni via the two carbonyl groups. There were two suggestions as to the exact nature of the modified catalyst Sachtler [195] proposed adsorbed nickel tartrate as chiral active site, whereas Japanese [101] and Russian [201] groups preferred a direct adsorption of the tartrate on modified sites of the Ni surface. 

A second form of storage iron is haemosiderin (Weir et al., 1984). This is deposited in humans as a response to the condition of iron overload. Haemosiderin forms as insoluble granules with electron dense cores surrounded by a protein shell. It exists in two forms primary haemosiderin is the result of iron overload due to excessive adsorption of iron in the gut, whereas the secondary form is caused by the numerous blood transfusions which are used to treat thallassaemia (a form of anaemia). Electron diffraction indicated that the iron core in primary haemosiderin is a 3-line ferrihydrite with magnetic hyperfine splitting only below 4 K and, in the secondary form, consists of poorly ordered goethite. As goethite is less soluble in ammonium oxalate buffer solution (pH 3) it has a lower intrinsic toxicity (Mann et al., 1988). 

Wifckowski and coworkers [37] have reported adsorption of bisulfate anions on Au(lll), Pt(lll), and Rh(lll) electrodes in sulfuric acid solution using electrochemical and several nonelectrochemical techniques. It was concluded from the low-energy electron-diffraction data that the structure of bisulfate on gold is different from that on Pt(lll) and Rh(lll). Adsorption of bisulfate on Au(lll) is associated with a charge transfer from the electrode to the adsorbate. However, the formation of this particular bond does... 

Table 5.1. Adsorption properties of metal monolayers on metal substrates. The clean substrate properties are also given for comparison. Substrates are ordered by lattice type (fee, bcc, hep, cubic, diamond and rhombic). The structures, nearest neighbor distances and heats of vaporization refer to the bulk material of the substrate or the adsorbate. VD, ID and S stand for vapor deposition, ion beam deposition and surface segregation, respectively. TD, WF and TED stand for thermal desorption, work function measurements and transmission electron diffraction, respectively...

Adsorption at solid-gas surfaces, derivation of adsorption isotherms, surface area measurement, and structural analysis of surfaces and adsorbed layers using low-energy electron diffraction (Chapter 9)... 

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