Chloride adlayer

FIG. 26. Step faceting associated with formation of a saturated ordered chloride adlayer on Cu(lOO). A saturated (V2 X V2) R45° chloride adlayer covers the surface at —0.25 V (a, k, m, o) while stepping to more negative potential, —0.65 V, leads to partial desorption of the adlayer (d, f, p). The black lines in d, i, and p represent the time at which the potential was stepped between the two potentials. The abscissa and ordinate correspond to the (100) direction. (From Ref. 278.)... 

The role of chloride ions in the anodic dissolution of Au(lll) in perchloric acid solutions has been studied in Ref. 54. The mechanism of anodic dissolution was discussed in relation to the structure of the chloride adlayer on the Au(lll) electrode surface. 

Similar to Pd UPD on Au(lll), Pd deposition on unreconstructed Au(lOO) has also been studied applying CV and in situ STM by Kolb and coworkers [432]. They have investigated both an island-free surface and the surface covered with the islands originating from the lifting of the (hex)-reconstruction. It has been found that approximately one Pd monolayer accompanied with a distorted-hexagon chloride adlayer is formed in the UPD process. First Pd layers on Au(lOO) had different electrochemical behavior than large Pd(lOO) single crystals. 

Herrero and Abruna [25] have also studied the kinetics and mechanism of Hg UPD on Au(lll) electrodes in the presence and absence of bisulfate, chloride, and acetate ions. In the absence of the interacting anions (in perchloric acid), the Hg UPD was significantly controlled by gold-mercury surface interactions. In sulfuric acid solutions, the kinetics of the initial and final stages of mercury deposi-tion/dissolution was altered. The presence of two well-ordered structures at potentials below and above mercury deposition led to the formation of two pairs of sharp spikes in cyclic voltammograms. In the chloride medium, the voltammetric profile exhibited two sharp peaks and thus it was very similar to that obtained in sulfuric acid solution. Neither nucleation, nor growth kinetics mechanism was found to be linked to the process of formation/disruption of the mercury chloride adlayer. The transients obviously deviated from the ideal Langmuir behavior. 

Cut 1001 In comparison to Cu( 111), it is clear from Fig. 1 that the desorption charge prior to the onset of hydrogen evolution amounts to far less than a monolayer equivalent charge. At potentials above - -0.300 V the surface is covered by a (V2 x x/2)R45° chloride adlayer as shown in Fig. 5, while at slightly more negative potentials an order-disorder transition occurs that is accompanied by the desorption of less than 0.006 mC/cm2 (i.e. the first desorption wave in Fig. 7). The (V2 x V2)R45° adlayer leads to step faceting in the <100> direction. This corresponds to the close packed direction of the adlayer which stabilizes the... 

Fig. 11. Potential modulation of the order-disorder transition of the chloride adlayer on Cu( 100) may be used to influence roughness evolution during film growth. Film deposited at -0.1 ML/s from 0.1 M HC104 + 0.001 M Cu(C104)2 + 0.00001 KC1.

The first in situ atomic-scale visualization of this growth mechanism was recently demonstrated for the incorporation of chloride ions at kink positions of the c(2 X 2) chloride adlayer on Cu(lOO) in 0.01 M HCl [144]. 

Fig. 26 A schematic model illustrating the chloride adlayer on an Au(ll 1) surface based on the surface X-ray diffraction measurement. See the text for details [30],...

FIG. 26. Step faceting associated with formation of a saturated ordered chloride adlayer on Cu(100). A saturated (V2 X R45° chloride adlayer covers the surface... 

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