Sensitivity to Lattice Structure

FIGURE 9.3. Schematic illustration of the conditions of surface lattice structure (a) amorphous-like surface with no identity of orientation, (b) surface with kinds, steps and terraces characteristic of certain crystalline orientation, and (c) surface with no identity of the lattice structure of the crystal due to the coverage of an amorphous oxide film (a) and (b) after Jeong and Williams. 

An important mechanistic aspect is the relative nature of the dimensions and events in space and in time. The electrochemical reaction processes can vary in quality and quantity in temporal and spatial scales of many orders of magnitude, which is responsible for the diverse phenomena observed on silicon electrodes. The understanding of the relative nature of dimensions and events are essential in mechanistic descriptions of this complex system. The following are the relative dimensions and events that are important in determining the electrode phenomena of silicon. 

The amount of reaction with fluoride based species relative to that with water based species determines the relative surface coverage by hydride, hydroxide, and oxide, the reactivity of the surface and the crystallographic character of the surface. 

The amount of chemical reactions relative to electrochemical reactions determines the amount of anodic hydrogen evolution and the value of effective dissolution valence. 

The rate of oxide formation relative to dissolution of the oxide determines the surface coverage, thickness, and properties of oxide, occurrence of passivation and current oscillation as well as uniformity of anodic dissolution. 

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Radiation Damage. It has been known for many years that bombardment of a crystal with eneigetic (keV to MeV) heavy ions produces regions of lattice disorder. An implanted ion entering a solid with an initial kinetic energy of 100 keV comes to rest in the time scale of about 10 13 due to both electronic and nuclear collisions. As an ion slows down and comes to rest in a crystal, it makes a number of collisions with the lattice atoms. In these collisions, sufficient eneigy may be transferred from the ion to displace an atom from its lattice site. Lattice atoms which are displaced by an incident ion are called primary knock-on atoms (PKA). A PKA can in turn displace other atoms, secondary knock-ons, etc. This process creates a cascade of atomic collisions and is collectively referred to as the collision, or displacement, cascade. The disorder can be directly observed by techniques sensitive to lattice structure, such as electron-transmission microscopy, MeV-partide channeling, and electron diffraction. 

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