Electrochemical polishing surface roughness

The CPE model has been used152,154,270-274 and it has been found that for electrochemically polished surfaces, the surface roughness is very small compared with mechanically polished surfaces. 

Electrochemically polished and chemically treated Cd(0001), Cd(10T0)t Cd(l 120), Cd(lOTl), and Cd(ll2l) electrodes have been studied by impedance and cychc voltammetry by Lust et al.152 153 249 664 665 a slight variation of capacitance (3 to 6%) has been observed with v. In the case of chemically treated electrodes, a somewhat higher (5 to 10%) dependence of C on v has been explained by the geometric roughness of the electrode surface. 

All investigators have outlined that surface roughness is a prerequisite for such an enhancement in the Raman scattering intensity. This roughness can be created by various types of processes electrochemical chemical reduction mechanical polishing vapour deposition lithography evaporation and photo-... 

Experimental results of electrochem-ically polished, cut, electrochemically etched, and chemically etched Bi, Sb, and Cd electrodes (Fig. 7) demonstrate that R(k) rises with the increase of surface roughness, in agreement with AFM data and conclusions of Refs. [32, 33]. 

The CPE model has been used to study PC Au, Cd, Ag, Bi, Sb and it has been found that for electrochemically polished electrodes the surface roughness is very small compared with mechanically polished surfaces [5,15,16, 22, 35, 36] (see also Chap. 8 in Vol. 3). 

In the case of the mechanically polished surface, the amplitude of roughness was several atomic diameters of Cu (Fig. 2.29c, d), whereas the mechanically and electrochemically polished stuface exhibited smoothness on the atomic level (Fig. 2.29e, f). The increase in the specular reflection of 20-25 % is due to this fact. It is interesting to note (Fig. 2.29g) that the structure of the bright surface was not oriented. This is in accordance with the assumption that the dissolution process under polishing conditions is a random process. 

The line sections analysis of the flat parts of the copper surfaces is shown in Fig. 12. The roughness of the flat parts of the copper surface, polished both mechanically and electrochemically, is very small and less than the atomic diameter of copper. For this reason, it can be said that these flat parts of the surface are smooth on the atomic level. The roughness of the flat parts of the copper surface, only polished mechanically, is less than 2 atomic diameters of copper.12... 

Figure 12. The line sections analysis of the flat parts of surfaces a) the copper surface polished mechanically, b) the copper surface polished both mechanically and electrochemically. The roughnesses of the observed surfaces were a) 0.444 nm, b) 0.111. (Reprinted from Ref.12 with permission from Elsevier.)...

Electrode products can often build up on the surface of a solid or stationary electrode. Species from the solution may adsorb on the surface. Some solid electrode materials may even develop oxide layers on the surface. All of these produce changes in the nature of the electrode and often completely distort the electrochemical response. By regular polishing back to a clean metal or graphite surface, some attempt can be made to achieve a reproducible surface. Better results are usually obtained from a smooth rather than a rough surface. 

Experimental studies confirm that the CPE is often related to the adsorption of impurities. Studies performed on a polycrystalline Au electrode in the double-layer zone [352] in 1 M H2SO4 display almost ideal capacitive behavior with 4> 0.99, while in the same cell on the same electrode in 1 M NaNOs a larger CPE deviation with (j) 0.93 was observed because sodium nitrate is not as pure as sulfuric acid. Moreover, at well-polished and annealed polycrystalline Pt (roughness factor / f = 1.4) the parameter (p is between 0.97 and 0.977 in the double-layer zone in 0.1 M H2SO4 [352]. However, after electrochemical roughening (/ f = 5.1) (p increases to >0.99. This can only be explained by the fact that the surface (ionic) impurities become distributed over a larger surface area and their coverage becomes smaller. 

Figure 3.41 Effect of measurement interval length in the value of the mean roughness of electrochemically or mechanically polished titanium surfaces (after ref. [14]).

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