Adatom deposition

In most cases, the adatom deposition is reductive, as sketched in (7.1), because the adatom precursor in the solution is in an oxidized state. However, oxidative adsorption... 

Completely different behavior is observed with S and Se, as shown in Fig. 7.8. With these adatoms, deposition on the terrace starts from the very beginning and no selectivity towards the step is observed. Additionally, deposition of the adatom changes the hydrogen adsorption energy on the (110) step sites, as reflected by the progressive shift of the peak at 0.12 V towards higher potential values. 

The formation of surface dipoles by adatom deposition can also be inferred from work fimction measurements in UHV. In this regard, Bi and Pb deposition causes a marked decrease in the work function of a Pt(lll) surface [Mazinangokoudi and... 

Ensemble or Third-Body Ejfects. These effects concern the selective blockage of a particular adsorption site by adatom deposition. This can be advantageous when the reaction mechanism contains parallel paths that can be affected differently by blocking particular sites. In some cases, the undesired reaction needs more than one free adjacent site (ensemble), and can be inhibited by blocking particular sites without decreasing the reactivity of the surface for the catalyzed reaction. 

Fig. 3.4 (a) Simple metal field ion microscope which uses a Helium Displex Refrigerator for tip cooling. A tip is mounted on a 5 mil Pt wire heating loop with two 1 mil Pt potential leads spot welded onto it. An adatom deposition source, a coil supported by two degassable loops, is also shown. Vacuum is easier to achieve... 

The reasons for this situation are that, although it is easy to follow the small currents associated with changes of coverage of adatoms deposited onto, or desorbed from, a two-dimensional monolayers in the absence of other continuous Faradaic currents, it is very difficult to measure the small partial currents that are involved in changing the coverage by the adsorbed intermediates, for instance, H in the HER, that are kinetically involved in the continuous net reaction since the Faradaic currents for the latter can be 10 ... 

In the presence of steps, in the close vicinity of the step edge, the kink-adatom exchange reaction will keep the adatom concentration at its equilibrium value Co,ads- At a distance from the step greater than the mean displacement yilsd (cf. eq. (2.35)), however, adatoms deposited on the face cannot reach the step edge during their lifetime on the surface, so that the adatom concentration will remain unaffected by the presence of the step and equal to Cads( )-... 

The deposition of Au on Ni(llO) leads to the formation of a one-layer surface alloy [17], in spite of the fact that Au and Ni are immiscible metals. Starting with a single gold adatom deposited on a hollow site on the Ni(l 10) substrate, we consider five possible configurations, shown in Fig. 8. Table 3 displays results for the energy of formation per atom of each cell. These configurations include a Au atom located (a) in the overlayer (Au(0)), (b) in a substituted site in the surface plane (Au(S)), with the substituted Ni atom in the overlayer nearest-neighbor site (Au(S)Ni(0)i), (c) same, with the substituted Ni atom in the overlayer, far from the impurity (Au(S)Ni(0)f), (d) in the first plane below the surface (lb) with the displaced Ni atom somewhere in the overlayer, (Au(lb)+Ni(0)), and (e) two planes below the surface plane (Au(2b)+Ni(0)). The intermediate columns indi-... 

Iwasita T., Schmickler W. and Schultze J. W., (1985) The influence of metal adatoms deposited at underpotential on the kinetics of an outer-sphere redox reaction , J. Electroanal. Chem. 194, 355-359. 

The study of metal adatoms deposited onto the surface of semiconductor electrodes is of interest for electrodeposition of epitaxial [1] and textured [2] films and superlattices of metal chalcogenides [3]. In the past decade, an additional interest in processes of underpotential deposition (upd) has been stimulated by the progress in studying physics and chemistry of nanosize objects [4]. 

Underpotential deposition consists of the formation of metal submonolayers at potentials more positive than the reversible Nernst potential, before bulk deposition can occur [2, 47-51]. This technique is also called adatom deposition [52] or adsorption of metal atoms [53]. 

Experimental methods permitting direct conclusions on transient motion examine the outcome of adatom deposition onto a substrate held at very low temperatures where thermally activated diffusion is frozen. This leads to statistical growth if transient mobility is absent, if present deviations from statistical growth are detected. In FIM experiments the population of adsorption sites is examined, whereas in STM experiments one measures the mean island size or island distance- and size-distributions. 

The behavior of interfacial water molecules on platinmn single-crystal electrodes, under electrochemical conditions, has been characterized for the first time by means of the laser-induced temperature jump method. The fundamentals of this method and the proposed interpretation of the experimental results will be described in Section V.l and V.2. Then, recent results on the three platinum basal planes will be discussed in Section V.3. Afterwards, the application of this technique to Pt(lll) stepped surfaces will be explained in Section V.4. And finally, results on the effect of the chemical modification of the surface composition of Pt(l 11) by adatom deposition will be presented in Section V.5. 

According to the above explanation, the effect of adatom deposition on the potential of water reorientation is dominated by electrostatic effects. Other possible effects, such as chemical interactions between water molecules and the adatoms, seem to play a minor role, in view of the good correlation between the displacement of Apme values and the adatom electronegativity. Accordingly, the main effect of adatom deposition would be to displace the... 

The surface chloride anions also form a highly ordered structure, which can act as a template for Pb adatoms deposition [302]. 

Square lattices with periodic boundary conditions are used to represent the surface. Each lattice node represents an adsorption site for an atom. The adsorbate may adsorb, desorb, or hop between neighboring sites. Also, atoms of the same nature as the substrate may only move on the surface. In this way, the model represents an open system for one of its components (the adsorbate), as in the case of adatom deposition on a foreign surface. 

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