Submonolayer deposition

Fig. 13.11 (a) The molecular absorbance MNF sensor (inset PTCDA molecule) (b) Evolution of spectrum of submonolayer deposition at 1,2, 4, and 8 s after beginning of molecule exposure (c) Subsequent evolution of the spectral absorption at constant molecule number at 13, 53, 413, and 2,393 s after beginning of molecule exposure. Reprinted from Ref. 19 with permis sion. 2008 Optical Society of America... 

In heterogeneous catalysis, the first tests on UPD were performed on bulk catalysts which allows, for the preparation of the bimetallic catalyst, easy control of the electrochemical potential by an external device (potentiostat). In the same way all electrochemical techniques, particularly the control of catalyst potential required for submonolayer deposition, can be extrapolated to metallic catalysts supported on conductive materials such as carbon or carbides [8]. 

Conclusions. Submonolayer deposits of titania grow on the surface of Rh in the form of two-dimensional islands until a coverage of nearly a monolayer is achieved, at which point some three-dimensional growth of the islands is observed. The titania islands exclude CO chemisorption on Rh sites covered by the titania. The Ti + ions in the overlayer are readily reduced to TP+. This process begins at the perimeter of the islands and extends inwards as reduction proceeds. Titania promotion of Rh enhances the rate of CO hydrogenation by up to a factor of three and increases the selectivity to C2+ hydrocarbons. By contrast, the activity of Rh for the hydrogenolysis of ethane decreases monotonically with increasing titania promotion. 

Figure 19. CO stripping voltammograms of Ru/Au(lll) (solid line) and the baselines obtained on CO free surfaces (dotted line) obtained in 0.1 M FI2 SO4 for (a) a multilayer deposit (b) a saturated monolayer (0.85 ML coverage) (c) a submonolayer deposit (0.15 ML coverage). Reprinted from Ref.12 with permission from Elsevier.

The nucleation and growth of islands during submonolayer deposition is, of course, a problem that has been studied for decades [121,122]. Analyses based on mean-field rate equations have led to an understanding of the dependence of mean island density, Nav, on deposition conditions. More recently, kinetic Monte Carlo simulation studies have been used to test... 

Prussian Blue and related inorganic redox films have proved very popular for spectroelectrochemical studies and elec-trochromic applications. Early investigations used rapid scan techniques to collect spectra as a function of potential [51], Prussian Blue grows by a three-dimensional nucleation and growth mechanism, which includes surface diffusion of Prussian Blue particles to kinks at growing nuclei [250]. DCVA traces were better defined than the CVs [251], and allowed determination of the molar absorptivity and the amount of film on the electrode. A recent study used a waveguide to study the formation of Prussian Blue [30]. It showed that the technique could detect submonolayer deposition of Prussian Blue film. The technique is typically 10 times more sensitive than rival techniques. 

Gokcen D, Bae SE, Brankovic SR (2010) Stoichiran-etry of Pt submonolayer deposition via galvanic displacement of underpotentially deposited Cu mraio-layer. J Electrochem Soc 157 D582... 

Differential eleetroehemieal mass speetrometry was used by Vidal-Iglesias et al. to study the HCOOH oxidation on Pd submonolayers deposited on Pt(lOO) and Pt(lll) [170], It was found that the adsorption of S04 inhibits HCOOH oxidation. Competitive adsorption between hydrogen and sulfate was responsible for the voltammetric peak at 0.26 V vs. RHE on Pd, while at 0.3 V vs. RHE, Had was eompletely displaced by the adsorbed sulfate. At E > 0.3 V the S04 adsorption was stronger, further diminishing the HCOOH oxidation current on the Pd modified electrodes [170]. The deposition mechanism and surface analysis of Pd on Pt(l 11) was published by Ball et al. [171]. 

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