Silicon anodes, electrochemical oxidation

The cyclic voltammetry of polysilanes adsorbed on the electrode surface has also been investigated [65]. The oxidation potentials depend upon the nature of the organic groups on silicon. The electrochemical oxidation is irreversible to give soluble products which are liberated from the surface of the anode. 

Electrochemical etching is one way of controlling the etch rate and determine a clear etch stop layer when bulk micromachining Silicon. In this case, the wafer is used as anode in an HF-Electrolyte. Sufficiently high currents lead to oxidation of the silicon. The resulting oxide which is dissolved by the HF-solution. Since lowly doped silicon material is not exhibiting a notable etch rate, it can be used as an etch stop. 

G. Mende, Detection of mobile ion during the anodic oxidation of silicon, J. Electrochem. Soc. 127, 2085, 1980. 

Another interesting phenomenon is producing luminescence from electrochemical reactions. This can be achieved by doping crystalline metal oxides and related materials or anodic metal oxide layers (Meulenkamo et al., 1993) or depositing organic molecules onto nanostructured porous materials such silicon (Martin et al., 2006). 

In this paper we examine the conditions of 4-15 nm thick oxide layers synthesis against the physicochemical properties of the electrochemical system (solvents, current-conducting additives of the electrolyte, silicon anode) and their roles in chemisorption processes. 

Anodic porous alumina is conventionally grown on aluminum foils, as indicated in Fig. 2. Similar self-assembled growth is achieved on Si by depositing an A1 thin film on the front side of a silicon wafer and forming an ohmic contact on the back side that is used as anode. The electrochemical solutions currently used are oxalic or sulfuric acid aqueous solutions. Details for the fabrication of thin alumina templates on Si with adjustable pore size and density are given elsewhere [8]. Electrochemical oxidation of A1 starts from the A1 surface and continues down to the Al/Si interface, following an anodization current density/time curve as shown in Fig. 3. 

Electrochemical oxidation of (Hg,Cd)Te has several shortcomings. Various reports have indicated a lack of thermal stability of the oxide (2)(10-13). Also, the oxide-semiconductor interface and oxide near the interface has relatively poor interface quality as compared to thermally oxidized silicon (14-18). Anodic oxidation at an elevated temperature has been used in one instance (9), and was reported to have increased stabiiity over room temperature anodic oxides. This idea has not been further explored. 

When the surface is completely covered by an oxide film, dissolution becomes independent of the geometric factors such as surface curvature and orientation, which are responsible for the formation and directional growth of pores. Fundamentally, unlike silicon, which does not have an atomic structure identical in different directions, anodic silicon oxides are amorphous in nature and thus have intrinsically identical structure in all orientations. Also, on the oxide covered surface the rate determining step is no longer electrochemical but the chemical dissolution of the oxide.1... 

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