Inter-layer diffusion

Jaberi, F.A., and P. Givi. 1995. Inter-layer diffusion model of scalar mixing in homogeneous turbulence. Combustion Science Technology 104(4-6) 249-72. 

Within the layers of a smectic A mesophase the molecules are aligned parallel to the layer normal and are uncorrelated with respect to center of mass position, except over very short distances. Thus, the layers are individually fluid, with a substantial probability for inter-layer diffusion as well. The layer thickness, determined from x-ray scattering data, is essentially identical to the full molecular length. At thermal equilibrium the smectic A phase is optically uniaxial due to the infinite-fold rotational symmetry about an axis parallel to the layer normal. A schematic representation of smectic A order is shown in Fig. 4(a). 

Inter-layer Diffusion in Dual-Layer Membranes... 

The interconnecting holes are narrow and deep (at times less than 0.25 im wide and up to 2 im or more in depth) and, after a diffusion-barrier layer is applied, it must be filled completely with a high-conductivity metal (usually aluminum or tungsten) to provide the low-resi stance plug for inter-layer connections. Typically, CVD provides better step coverage and conformity than sputtering and other physical-vapor deposition processes. 

Macroscopic experiments allow determination of the capacitances, potentials, and binding constants by fitting titration data to a particular model of the surface complexation reaction [105,106,110-121] however, this approach does not allow direct microscopic determination of the inter-layer spacing or the dielectric constant in the inter-layer region. While discrimination between inner-sphere and outer-sphere sorption complexes may be presumed from macroscopic experiments [122,123], direct determination of the structure and nature of surface complexes and the structure of the diffuse layer is not possible by these methods alone [40,124]. Nor is it clear that ideas from the chemistry of isolated species in solution (e.g., outer-vs. inner-sphere complexes) are directly transferable to the surface layer or if additional short- to mid-range structural ordering is important. Instead, in situ (in the presence of bulk water) molecular-scale probes such as X-ray absorption fine structure spectroscopy (XAFS) and X-ray standing wave (XSW) methods are needed to provide this information (see Section 3.4). To date, however, there have been very few molecular-scale experimental studies of the EDL at the metal oxide-aqueous solution interface (see, e.g., [125,126]). 

A high temperature Pd/Stainless Steel H2 separation membrane manufactured by CRI-Criterion by deposition of Pd on sintered porous metal support with permeable dimensions of 1 inch OD and 6 inches length is shown in Figure 11.7. An SEM cross section of the top layers of the membranes showing the porous stainless support, the inter-metal diffusion barrier, and the selective Pd layer. Note that the picture lack pinholes in Figure 11.8. 

Multiple color displays from one layer can be made from pixelation of colors. The displays have three alternating types of stripes of Ch liquid crystals with three different pitches reflecting blue, green and red light. Partition or some other means of preventing inter-stripe diffusion must be used. Polymer walls, especially field-induced polymer walls, are good candidates. The different pitches can be achieved by two methods. In the first method, three cholesteric liquid crystals with different pitches are filled into empty cells with partitions. The second method is photo color tuning [62,63]. A photosensitive chiral dopant is added to the liquid... 

This inter-layer separation remains slight (which is an essential condition for the battery to woik) because the lithium is inserted without its solvation shell formed by the organic molecules from the electrolyte. This phenomenon of desolvation takes place when lithium ions are diffused in an interfacial passivation layer present between the electrode and the... 

To illustrate these effects, we show in fig. 31 a schematic representation of the diffuse scattering around the (110) point in UAs at 7 -1- 1.2K (Sinha etal. 1981) Along the [001] direction q is parallel to the propagation direction and the moment component in the ordered state, so that this probes X (Q)- We see that the scattering width is wide, so is correspondingly small. Conversely, in the [ < 0] direction we probe Xi(Q)> Ihe inter-layer susceptibility, as discussed earlier, and the widths are quite sharp, leading to a large value of. These values of can be measured as a function of temperature (we shall discuss this below), but their ratio is found to be... 

Figure 8.8 Stages in the ultrasonic welding process. In Phase 1, the horn is placed in contact with the part, pressure is applied, and vibratory motion is started. Heat generation due to friction melts the energy director, and it flows into the joint interface. The weld displacement begins to increase as the distance between the parts decreases. In Phase 2, the melting rate increases, resulting in increased weld displacement, and the part surfaces meet. Steady-state melting occurs in Phase 3, as a constant melt layer thickness is maintained in the weld. In Phase 4, the holding phase, vibrations cease. Maximum di lacement is reached, and inter-molecular diffusion occurs as the weld cools and solidifies. ...

Molten layer thickness is an important determinant of weld strength. If the thickness of the molten layer is less than the melt stop displacement, melt stops cannot contact holding stops, part dimensions cannot be controlled, and joint quality is poor due to limited inter-molecular diffusion. In addition to contributing to weld strength, adequate displacement in phases I and II compensates for part surface irregularities and ensures that contaminated surface layers flow out before the joining phase. [ 1... 

Lee and Jin (2003) were the first to report the growth of metallic NPs inside a thermotropic LC based on polymeric materials. A polyester matrix polymer consisting of hydrophilic PEG branches attached to a hydrophobic aromatic polyester backbone was used for his purpose (see Table 21.1 and Fig. 21.8a). This structure tended to be organized in smectic-like domains with the PEG branches occupying the inter-layer domains. Gold nanoparticles were obtained in a two-step procedure. First an aqueous solution of HAuCU was allowed to diffuse into the hydrophilic domains. Then, these gold ions were reduced to Au NPs upon addition of a hydrazine solution as shown on TEM micrographs in Fig. 21.8b. The mesomorphous properties of the LC/NP hybrid were not discussed. 

Another problem in the construction of tlrese devices, is that materials which do not play a direct part in the operation of the microchip must be introduced to ensure electrical contact between the elecuonic components, and to reduce the possibility of chemical interactions between the device components. The introduction of such materials usually requires an annealing phase in the construction of die device at a temperature as high as 600 K. As a result it is also most probable, especially in the case of the aluminium-silicon interface, that thin films of oxide exist between the various deposited films. Such a layer will act as a banier to inter-diffusion between the layers, and the transport of atoms from one layer to the next will be less than would be indicated by the chemical potential driving force. At pinholes in the AI2O3 layer, aluminium metal can reduce SiOa at isolated spots, and form the pits into the silicon which were observed in early devices. The introduction of a tlrin layer of platinum silicide between the silicon and aluminium layers reduces the pit formation. However, aluminium has a strong affinity for platinum, and so a layer of clrromium is placed between the silicide and aluminium to reduce the invasive interaction of aluminium. 

The materials problems in the construction of microchips are related to both diffusion and chemical interactions between the component layers, as shown above. There is probably a link between drese two properties, since the formation of inter-metallic compounds of medium or high chemical stability frequently leads to tire formation of a compound ban ier in which tire diffusion coefficients of both components are lower than in the pure metals. 

If the major constituents of a solid alloy in contact with a liquid alloy are highly soluble in the latter without formation of compounds, progressive attack by solution is to be expected. If, on the other hand, a stable inter-metallic compound is formed, having a melting point above the temperature of reaction, a layer of this compound will form at the interface and reduce the rate of attack to a level controlled by diffusion processes in the solid state. By far the most serious attack, however, occurs in the presence of stresses, since in this case the liquid alloy, or a product of its reaction with the solid alloy, may penetrate along the grain boundaries, with resultant embrittlement and serious loss of strength. 

Chen et al. [123] examined the amount-dependent change in morphology for a series of Au/Pt bimetallic nanoparticles. The EXAFS results confirmed the formation of a core/shell structure and inter-diffusion between Au and Pt atoms. The composition of the shell layer was found to be Pt-enriched AuPt alloy. They also characterized bimetallic Ag-core/Au-shell nanoparticles by the EXAFS [124]. 

Room temperature deposition of silver on Pd(lOO) produces a rather sharp Ag/Pd interface [62]. The interaction with a palladium surface induces a shift of Ag 3d core levels to lower binding energies (up to 0.7 eV) while the Pd 3d level BE, is virtually unchanged. In the same time silver deposition alters the palladium valence band already at small silver coverage. Annealing of the Ag/Pd system at 520 K induces inter-diffusion of Ag and Pd atoms at all silver coverage. In the case when silver multilayer was deposited on the palladium surface, the layered silver transforms into a clustered structure slightly enriched with Pd atoms. A hybridization of the localized Pd 4d level and the silver sp-band produces virtual bound state at 2eV below the Fermi level. 

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