Electropolishing surface roughness

FIGURE 5 Contour plot of electropolishing surface roughness RMS (A) for n-type P-SiC at 2.0 Vsce [12]. 

The origin of the initial microroughness and the events leading up to its final amplification by mass-transfer limited deposition, have not been clarified definitively (P4a). It has been shown (I9a) that preliminary electropolishing, to assure a smooth surface, does not prevent surface roughness at... 

With copper or brass as base material, the best surface quality is obtained with mechanical precision machining, followed by an electropolishing step. By this means, a surface roughness of down to 30 nm can be reached. Figure 2.7 shows the surface of a single O F copper microchannel after the electropolishing step. For all techniques, details can be found in [1, 4,14—20]. 

In some electrolytes (e.g., phosphoric acid) an effect opposite to amplification of surface roughness is found upon anodic dissolution, i.e., the surface becomes increasingly smooth, until a mirrorlike finish is achieved. This phenomenon has been widely used for practical purposes of electropolishing, since the work of Jacquet in 1936. ... 

A disadvantage is the potential of the coimection working loose dueto vibration. The damage to the electropolished surface was already mentioned. Because of the usually unavoidable rough tubing end siuface, particles are a... 

Electropohshing decreases the surface area available for adsorphon and reduces the contamination retention of the surface. The electropolished surface generally exhibits a lower coefficient of friction than a mechanically polished surface. The various surface treatments can alter the outgassing properties of the stainless steel surface. The chemical composihon of and defect distribution in electropolished surfaces can be specihed for crihcal applicahons. This includes the chromium-to-iron raho with depth in the oxide layer (AES), the metallic and oxide states (XPS), surface roughness (AFM), and surface defects (SEM). 

The R of electropolished Zn single-crystal face electrodes has been obtained from the shape of the adsorption-desorption peak of cyclohex-anol at various Zn and Hg surfaces.154 The roughness factor of Zn electrodes has been found to increase in the order Zn(0001) < Zn(lOlO) < Zn(llZO) with values in the range 1.1 to 1.25. 

The Si wafer industry has achieved very flat Si surfaces by electropolishing a root-mean-square (rms) roughness of 0.3 nm is customary, even for highly-doped degenerate Si. For a 100-nm Au layer deposited atop a 10-nm Ti adhesion layer atop an electropolished Si wafer, an rms roughness of 0.4 nm was measured by AFM [38]. 

In some ways electropolishing and electrochemical pore formation can be understood as the two sides of the same coin. In the first case the rate-limiting species in the chemical reaction is HF, while in the second it is the supply of holes from the electrode. If we assume a rough silicon wafer surface and a reaction that is... 

Figure 1.8 Surface quality obtained in oxygen-free copper by micromachining, followed by an electropolishing step. The mean roughness is about 30 nm.

The observed roughness factors (ratio of true to geometric surface) of the surfaces employed in this study varied from 1.2 to 1.4 (Table IV). This checked with electron microscope pictures of alumina and silica replicas from electropolished single crystal copper surfaces. It is unlikely that the surface areas determined by the Brunauer-Emmett-Teller analysis are too high by 50% or even by 25%, because in several cases this would lead to a roughness factor of less than unity. 

In addition to electrodeposition, ionic liquids and DESs can be used in electropolishing, which aims to remove the roughness from metallic surfaces to increase optical reflectivity for high-tech applications. For example, a eutectic mixture of ethylene glycol and choline chloride has been used in the electropolishing of various stainless steel alloys. This method is preferable to current industrial procedures that use a corrosive mixture of phosphoric and sulfuric adds. 

Fig. 2 Before electropolishing the mechanically polished surface of stainless steel appears rough as viewed under lOOOx magnification on scanning electron microscope.

Mott and Bott illustrated the effect of different materials on the accumulation of Pseudomonas fluor-escens biofilms on the inside of tubes under identical operating conditions (see Fig. 9). The differences between the effects of the materials occur for two reasons roughness and surface electrical properties. The quality of the surface, in terms of roughness, on which microorganisms attach, can affect the biofilm accumulation as discussed earlier. The effect of roughness is illustrated in Fig. 9 by the difference of biofilm accumulation between electropolished and as received 316 stainless steel. The rougher stainless steel is seen to be more hospitable to biofilm growth. 

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