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Metal monolayer adsorption

Work Function Changes Following Methanol Adsorption on Clean Metals Monolayer Coverages)... [Pg.37]

Beside O P D it is well known that metal deposition can also take place at potentials positive of 0. For this reason called underpotential deposition (UPD) it is characterized by formation of just one or two layer(s) of metal. This happens when the free enthalpy of adsorption of a metal on a foreign substrate is larger than on a surface of the same metal [ 186]. This effect has been observed for a number of metals including Cu and Ag deposited on gold ]187]. Maintaining the formalism of the Nernst equation, deposition in the UPD range means an activity of the deposited metal monolayer smaller than one ]183]. [Pg.219]

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... 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...
In contrast to the minimal activity in infrared reflection studies the technique of inelastic electron tunneling spectroscopy (IETS) recently has contributed a large amount of information on monolayer adsorption of organic molecules on smooth metal oxide surfaces,Q),aluminum oxide layers on evaporated aluminum. These results indicate that a variety of organic molecules with acidic hydrogens, such as carboxylic acids and phenols chemisorb on aluminum Oxide overlayers by proton dissociation - 1 — and that monolayer coverage can be attained quite repro-ducibly by solution doping techniques. - The IETS technique is sensitive to both infrared and Raman modes. — However, almost no examples exist in which Raman il and or infrared spectra have been taken for an adsorbate/substrate system for which IETS spectra have been observed. [Pg.38]

Ten years ago one would have predicted that Raman spectroscopy could never be used to study monolayer adsorption on metals because either (a) the sensitivity of the technique would be too low to permit detection of signals using a single reflection from a smooth metal surface, or (b) oxide supported metal surfaces are black if the metal loading is high and therefore the laser light would be absorbed. Both of the above objections have been shown to be faulty insofar as the technique has now been used to study absorption on silica-supported nickel (51, 52,53) and on single crystal nickel (54). Moreover in the special case of silver,... [Pg.133]

Types of electrode/solution interface studied include oxide films on metals, monolayer deposits obtained by underpotential deposition, adsorption, and spectroelectrochemistry in thin-layer cells. [Pg.262]

The heats of adsorption of nitrogen on evaporated metal films of nickel and iron have been reported to decrease from 10 to 5 kcal./mole as the surface coverage increased from about 0.1 to 1.0 monolayer. Beeck (150) states that nitrogen is unsuitable for the evaluation of surface areas of evaporated iron and nickel films by the Brunauer-Emmett-Teller method because of its high heat of adsorption at 78°K., which would yield a value for monolayer adsorption too high by 50%. The author feels that this objection does not apply to the nitrogen adsorption on reduced electropolished planar copper plates for the following reasons. [Pg.105]

The origin of the temperature-independent solid state broadening, 0.4 eV A <0.6 eV we attributed to spatial variations in the electronic contributions to the intramolecular relaxation energies in the vicinity of the surface (18, 19, 22). Similar widths (to 0.6 eV) have been observed in a variety of other contexts, including condensed thin films of and CO molecules ( ) and the sub-monolayer adsorption of these molecules on metal surfaces (29). Interatomic Auger and electron- hole shakeup processes have been proposed, but found to be too small to account for the observed widths in these cases (28, 48). On... [Pg.135]

The main hypotheses for developing the EHD impedance theory are that the electrode interface is uniformly accessible and the electrode surface has uniform reactivity. However, in many cases, real interfaces deviate from this ideal picture due, for example, either to incomplete monolayer adsorption leading to the concept of partial blocking (2-D adsorption) or to the formation of layers of finite thickness (3-D phenomena). These effects do not involve the interfacial kinetics on bare portions of the metal, which, for simplification, will be assumed to be inherently fast. The changes will affect only the local mass transport toward the reaction sites. Before presenting an application of practical interest, the theoretical EHD impedance for partially blocked electrodes and for electrodes coated by a porous layer will be analyzed. [Pg.296]

For compound semiconductors, one of the simplest approaches involves the monolayer adsorption of metal salts from liquid solutions, and a subsequent conversion of the salt to the desired semiconductor. This second step can be carried out in solution or in the gas phase. [Pg.411]

Considering the adsorption of anions induced by adatoms, it is quite evident that anions can have a profound effect on the metal monolayer formation. In some cases even anions can determine the structure of the metal adsorbate. For instance, the coadsorption structure of upd copper and halides on Pt(lll) and Au(lll) was studied extensively. These studies revealed the bilayer coadsorption structure of copper and halides. An ordered structure of halide ions is formed on an adlayer of copper deposited on the Pt(l 11) surface. [Pg.272]

Specific to the metal, the adsorption isotherm will show an initial rapid increase of uptake with pressure, followed by a linear region of low slope. The monolayer capacity is often reported (when anything at all is said) as the intercept at zero pressure obtained by extrapolation of the linear part. Alternatively, and perhaps better, the results are plotted according to the one of the linearised forms of the Langmuir equation from which the monolayer volume can be obtained. [Pg.60]

Direct Film Growth Protective films may also be formed directly at the metal-solution interface via a 3D growth mechanism. The first step of this process is the monolayer adsorption of the inhibiting species (see Sect. 5.2.2.1.1). [Pg.452]

The reader is referred to Chapter 6 for an in-depth discussion of the DP method. The advantage of this method over SEA is that there is no monolayer adsorption limit with DP it is possible to achieve acceptably high metal dispersions at metal loadings higher than can be achieved with SEA. In many cases this might compensate for the higher complexity of the DP process. [Pg.46]


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See also in sourсe #XX -- [ Pg.133 ]




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