Structural surface inhomogeneities

Structural surface inhomogeneity influences the anodic dissolution process in the case of metals with appreciable activation polarization. As a rule, segments with perturbed structure dissolve more rapidly than ordered segments. In a number of cases this causes crystallites to break away from the electrode surface and form metal sludge. 

Another problem, which can be treated by using cluster models, is the study of the influence produced by various structural surface inhomogeneities (fractures, steps, protruding faces, etc.) upon the energy spectrum of the crystal. This is of special importance in the description of the phenomena that involve highly dispersed particles. 

Atomic processes that constitute the electrodeposition process, Eq. (6.93), can be seen by presenting the structure of the initial, M"+(solution), and the final state, Mn+(lattice). Since metal ions in the aqueous solution are hydrated the structure of the initial state in Eq. (6.93) is represented by [M(H20)J"+. The structure of the final state is the M adion (adatom) at the kink site (Fig. 6.13), since it is generally assumed that atoms (ions) are attached to the crystal via a kink site (3). Thus, the final step of the overall reaction, Eq. (6.93), is the incorporation of M"+ adion into the kink site. Because of surface inhomogeneity the transition from the initial state [M(H20)J"+(solution) to the final state Mn+(kink)... 

TTie surface structure as well as the nature, density, and distribution of surface inhomogeneities determine the thermodynamic and dynamic properties of a crystalline substrate/electrol5de interface. Surface structure and surface inhomogeneities are mainly affected by the 3D crystal structure and crystal imperfections as well as by temperature, electrode potential, and electrolyte composition. 

We believe that a consistent interpretation of the results presented can be obtained based on the assumption that the microscopic structure of the adsorbent surfaces studied may be associated with two types or scales of surface porosity (i) inhomogeneities with a characteristic size substantially smaller than that of the adsorbate molecule (surface inhomogeneity due to the atomic structure of the adsorbent), and (ii) inhomogeneities possessing a characteristic size comparable to that of the adsorbed molecule (surface microporosity arising from removal of fragments of the modifier layer during thermooxidation). 

Rapid advances in semiconductor techrwlogy, including thin film formation by deposition, interface preparation or microstructuring, demand characterization techniques that provide understanding of the fundamental processes involved, including information on structural order—disorder and spatial inhomogeneity. Raman spectroscopy is used both in process control and quality assessment [34]. Typical examples of semiconductor applications are composition determination, analysis of crystal structure, surface and interface analysis, phase determination, doping, point defects, temperature influence and mechanical stress. 

Structural and dynamic properties of pure water in contact with uncharged realistic metal surfaces are obtained by molecular dynamics simulations. The influences of adsorption energy, surface corrugation, electronic polarizability and surface inhomogeneity are investigated. The adsorption energy of water on the metal surface is found to be the most important parameter. 

A systematic study of physical effects that influence the water structure at the water/metal interface has been made. Water structure, as characterized by the atom density proflles, depends most strongly on the adsorption energy and on the curvature of the water-metal interaction potential. Structural differences between liquid/liquid and liquid/solid interfaces, investigated in the water/mercury two-phase system, are small if the the surface inhomogeneity is taken into account. The properties of a polarizable water model near the interface are almost identical to those of unpolarizable models, at least for uncharged metals. The water structure also does not depend much on the surface corrugation. 

Of course, the above discussion apphes only to systems exhibiting domain wall structure, i.e., to weakly inhomogeneous phases formed on surfaces with low corrugation of the gas-solid potential and characterized by the presence of more then one type of equivalent sublattices. When this is not the case, i.e., when the dense incommensurate phase can be considered to be... 

Recently, many experiments have been performed on the structure and dynamics of liquids in porous glasses [175-190]. These studies are difficult to interpret because of the inhomogeneity of the sample. Simulations of water in a cylindrical cavity inside a block of hydrophilic Vycor glass have recently been performed [24,191,192] to facilitate the analysis of experimental results. Water molecules interact with Vycor atoms, using an empirical potential model which consists of (12-6) Lennard-Jones and Coulomb interactions. All atoms in the Vycor block are immobile. For details see Ref. 191. We have simulated samples at room temperature, which are filled with water to between 19 and 96 percent of the maximum possible amount. Because of the hydrophilicity of the glass, water molecules cover the surface already in nearly empty pores no molecules are found in the pore center in this case, although the density distribution is rather wide. When the amount of water increases, the center of the pore fills. Only in the case of 96 percent filling, a continuous aqueous phase without a cavity in the center of the pore is observed. 

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