Surface-Layer Formation

In the anodic polarization of metals, surface layers of adsorbed oxygen are almost always formed by reactions of the type of (10.18) occurring in parallel with anodic dissolution, and sometimes, phase layers (films) of tfie metal s oxides or salts are also formed. Oxygen-containing layers often simply are produced upon contact of the metal with the solution (without anodic polarization) or with air (the air-oxidized surface state). 

The first step of oxide-layer formation is oxygen adsorption (chemisorption). In the case of platinum, the process stops at this stage, and depending on the conditions, an incomplete or complete monolayer of adsorbed oxygen is present on the platinum surface. In the case of other metals, layer formation continues. When its thickness 5 has attained two to three atomic diameters, the layer is converted to an individual surface phase that is crystalline (more seldom, amorphous) and has properties analogous to those of the corresponding bulk oxides. 

The surface-phase layers will difier in character depending on the stractures of metal and oxide. On certain metals (zinc, cadmium, magnesium, etc.), loose, highly porous layers are formed which can attain appreciable thicknesses. On other metals (aluminum, bismuth, titanium, etc.), compact layers with low or zero porosity are formed which are no thicker than 1 pm. In a number of cases (e.g., on iron), compact films are formed wfiicfi fiave a distorted lattice, owing to the influence of substrate metal stracture and of the effect of chemical surface forces. The physicochemical and thermodynamic parameters of such films differ from tfiose of ordinary bulk oxides. Because of the internal stresses in the distorted lattice, such films are stable only when their thickness is insignificant (e.g., up to 3 to 5 nm). 

As a rule, different types of oxide film will form simultaneously on metal electrodes for instance, porous phase layers on top of adsorbed layers. Often, aging processes occur in the oxide layers, which produce time-dependent changes in the properties or even transitions between different forms. 

Sufficiently strong cathodic polarization will reduce the oxide layers on many metals, but in certain cases (on titanium, tantalum, etc.) the oxide film cannot be 

---

Figure 20. Equivalent circuit based on surface layer formation on cathode materials (a. top) and the electrolyte/ cathode interface (b. bottom). (Reconstructed based on ref 295.)...

Irreversible Capacity. Because an SEI and surface film form on both the anode and cathode, a certain amount of electrolyte is permanently consumed. As has been shown in section 6, this irreversible process of SEI or surface layer formation is accompanied by the quantitative loss of lithium ions, which are immobilized in the form of insoluble salts such as Li20 or lithium alkyl carbonate. Since most lithium ion cells are built as cathode-limited in order to avoid the occurrence of lithium metal deposition on a carbonaceous anode at the end of charging, this consumption of the limited lithium ion source during the initial cycles results in permanent capacity loss of the cell. Eventually the cell energy density as well as the corresponding cost is compromised because of the irreversible capacities during the initial cycles. 

Flintoff, J. F. HARKER, A. B. 1985. Detailed processes of surface layer formation in borosilicate waste glass dissolution. In Jantzen, C. M., Stone, J. A. Ewing, R. C. (eds) Scientific Basis for Nuclear Waste Management VIII. Materials Research Society Symposia Proceedings, 44, 147-154. 

The reduction of the external heat flux to the sample due to a surface layer formation, as ratioflux(0 = c/n i is plotted in Figure 19.30 against the pyrolyzed depth, 8pyro, for one of the... 

Lapcik, L., J. Panak, V. Kello and J. Polavka (1976). Kinetics of swollen surface layer formation a in poly(vinyl chloride)-solvent system, 7. Polym. ScL, Polym. Phys. Ed., 14, 981-988. 

In order to establish the prerequisites for interpreting surface layer formation on metals it appears necessary to deal somewhat extensively with transport processes in crystalline substances wdth lattice defects and to explore the relationship between transport of defects and self-diffusion. 

Some Experimental Results Concerning Surface Layer Formation on Metals and Alloys... 

In principle, multi -phase surface layers may be expected on pure metals whenever the metal ion can occur in several valancies, such as in the sulfuridation or oxidation of iron, where the surface layers consist of FeS and FeS2 or FeO, Fe O and Fe20g. The mechanism of surface layer formation can be described quantitatively under the assumption of a preferred parallel stratification of the individual oxides in the surface layer, the lowest oxidation step being located near the metal and the highest being in equilibrium with the gas atmosphere. 

As a typical example of surface layer formation where significant space charges shall not be present (47), we choose the above-mentioned oxidation of copper at 100°C which can be represented by a cubic rate law. On the basis of the relation derived by Grimley (48) for Cu oxidation one obtains an approximately cubic rate law of the form... 

The principles of electrochemistry are useful in explaining many of the chemical mechanisms of metal CMP. Surface layer formation, metal solubility, and metal dissolution are all explained by electrochemistry.Surface films which are generally oxides or hy-... 

The slurry chemicals quickly re-form the surface layer, however, and a repetitive process of surface layer formation via chemical... 

In this chapter, we shall first propose a model to explain the removal and planarization mechanisms of copper CMP. Next, we discuss surface layer formation during copper CMP, which is important for planarization, followed by copper dissolution during CMP, which is iii5)ortant to maintain high removal rates. Next a comparison of copper CMP to the Preston equation is made, followed by a discussion of the abrasion mode during copper CMP. Lastly, we investigate the dishing and erosion behavior of copper CMP. 

The surface layer formation is a crucial phenomenon as it affects the electrode charge transfer rate. Low-conductivity films determine high electrode overvoltages and lower battery performance. The charge transfer resistance can be monitored by impedance spectroscopy measurements, which represent a useful tool for the in-situ characterization of resistive and capacitive processes occurring in different time scales (1 mHz-100 kHz) [80]. 

M. Matsui, K. Dokko, Y. Akita, H. Munakata, K. Kanamura, J. Power Sources 2012, 210, 60-66. Surface layer formation of LiCoOj thin film electrodes in non-aqueous electrolyte containing lithium bis(oxalate)borate. 

F. Simmen, A. Hintennach, M. Hoiisberger, T. Lippert, P. Novak, C. W. Schneider, A. Wokaun, Aspects of the Surface Layer Formation on Li 1 -I- xMn204 - 5 during Electrochemical Cycling, J. Electrochem. Soc. 2010, 157, A1026-A1029. 

Matsui M., Dokko K., Kanamura K. Surface Layer Formation and Stripping Process on LiMn204 and LiNii/2Mn3/204 Thin Film Electrodes, J. Electrochem. Soc. 2010,157, A121-A129. 

Matsuo Y, Kostecki R., McLamon F. Surface Layer Formation on Thin-Film LiMn204 Electrodes at Elevated Temperatures, J. Electrochem. Soc. 2001, 148, A687-A692. 

C. Masalles, S. Borros, C. Vinas, F. Teixidor, Surface layer formation on polypyrrole films, Advanced Materials 2002, 14, 449. 

Various workers have made suggestions on the possible effects of surface treatment which include removal of a surface layer, formation of a surface group, acid/base interaction,... 

Riickert, J. (1979). Influence of pH value, oxygen content and flow velocity of cold drinking water on corrosion behavior and surface layer formation on galvanized steel tubes. Werkst. Korros., 30, 9-34 (in German). 

Matsuo, Y, Kostecki, R. and McLarnon, F. (2001) Surface layer formation on thin-film LiMu204 electrodes at elevated temperatures. Journal of The EJectrochemical Society, 148, A687-A692. 

Mellott, N. P., Brantley, S. L., Hamilton J. P. Pantano, C. G. (2001) Evaluation of surface preparation methods for glass. Surface and Interface Analysis, 31, 362-68. Mellott, N. P. Pantano, C. G. (2009). Multicomponent almninosilicate glass mechanisms of acid corrosion and surface layer formation. Journal of Non-Crystalline Solids, Submitted Manuscript. 

For all these three Ti02(B) electrode, an apparent irreversible capacity exists during the first cycle. Among them, the Ti02(B) nanotube shows the greatest irreversible capacity. Since it is believed that there is no surface layer formation above 1 V, the... 

A schematic model for SPI surface-layer formation in LiNiggCo jOj based on accumulated experimental evidence is given in Figure 12 the corresponding situation for LiMnj04 was summarised in Figure 8. 

---