Sandwich structures, effect

This new sandwich structure effectively reduces and even prevents whisker formation, as shown in Table 1.2, because less stress is induced due to the much lower diffusion of both Cu and Sn. This innovative process fulfills the requirements of several currently implemented OEM whisker-reduction specifications. The product was introduced in 2004 with some high volume PCB manufacturers. The PCB manufacturers choosing to apply Ormecon immersion tin technologies can easily change between the standard immersion tin product Ormecon CSN FF and the high-performance, whisker-reducing immersion tin product Ormecon CSN FF-W. The difference between two such products is only the predip step. 

FABMS has been used as a semiquantitative indication of the selectivity of receptors for particular guest metal cations (Johnstone and Rose, 1983). The FABMS competition experiment on [7] with equimolar amounts of the nitrates of sodium, potassium, rubidium and caesium gave gas-phase complex ions of ([7] + K)+ ion (m/z 809) and a minor peak ([7] + Rb)+ ion (m/z 855) exclusively. The relative peak intensities therefore suggested a selectivity order of K+ Rb+ Na+, Cs+, indicative of the bis-crown effect, the ability of bis-crown ether ligands to complex a metal cation of size larger than the cavity of a single crown ether unit, forming a sandwich structure. 

The measurement of properties such as the resistivity or dielectric constant of PS requires some kind of contact with the PS layer. Evaporation of a metal onto the PS film-covered silicon sample produces a metal/PS/Si sandwich, which behaves like an MIS structure with an imperfect insulator. Such sandwich structures usually exhibit a rectifying behavior, which has to be taken into account when determining the resistivity [Si3, Bel4]. This can be circumvented by four-terminal measurements of free-standing PS films, but for such contacts the applied electric field has to be limited to rather small values to avoid undesirable heating effects. An electrolytic contact can also be used to probe PS films, but the interpretation of the results is more complicated, because it is difficult to distinguish between ionic and electronic contributions to the measured conductivity. The electrolyte in the porous matrix may short-circuit the silicon filaments, and wetting of PS in-... 

Henglein, A. Weller, H. Colloidal semiconductors Size quantization, sandwich structures, photo-electron emission, and related chemical effects, Photochemical Energy Conversion, J. R. Norris, Jr. and D. Meisel, eds., Elsevier New York, 1989. 

On the contrary the plateau values for the two copolymers are very different. Since the higher copolymer gives thicker films a surface force component of steric origin may be evoked. However, the thickness hK is an effective parameter which is too crude. As a reasonable compromise between physical relevance and tractability, the three-layer model is adopted. Within the three-layer model the foam film is viewed as a symmetric sandwich structure [159] two adsorption layers symmetrically confine an aqueous core (Fig. 3.34). 

Fig. 1 Side view of slab models of various bimetallic structures often used in computational studies. In each case, the bottom layers of the material are defined using the structure of a specified bulk material. The number of surface and bulk layers varies in different studies, (a) In the sandwich structure the surface is one component, often the same component as the bulk material and the second layer is another component. This structure is often used to determine ligand effects, (b) The pseudomorphic monolayer structure combines strain and ligand effects in one structure by placing a second component on top of a bulk material, (c) The near surface alloy combines strain, ligand and ensemble effects in one structure by considering an alloy film defined by just a few atomic layers on top of an ordered bulk material.

The effects of different interfacial strengths and impact speeds were also investigated. The results show that even small variations in impact speed and bond strength could substantially influence the initiation behavior of de-lamination (location and nucleation time) and lead to substantially different inter-layer crack speed histories and therefore influence the timing sequence and final extent of subsequent intra-layer damage within the sandwich structures. Fig. 11-12, which agrees very well with the observations by Xu and Rosakis [1]. 

The model experiments of Xu and Rosakis on low-speed impact over sandwich structures were simulated applying cohesive models. The simulation captures qualitatively the main experimental observations. The most relevant correspondence is in the development of the first crack at the interface between the layers, the presence of shear stresses along the interface, which renders the crack shear driven and often inter-sonic, and the transition between interlayer crack growth and intra-layer crack branching. The effects of impact speed and bond shear strength are also investigated and highly satisfactory predictions are obtained. 

The all-dry box procedures resulted in another interesting visual effect. By controlling the solvent removal step that is, how long a vacuum was applied to the polymerization vessel, the location of the polyacetylene within the membrane structure could be regulated. For example, sandwich structures could be created by immediately applying a vacuum to a membrane sample wet with catalyst solution. This technique caused the solution to move into the center of the membrane s cross section thus polyacetylene formed only in the center of the cross section as well. The presence of polyacetylene, then, was hidden by the membrane s surface. Consequently, the surface of the membrane appeared almost white when dry (opaque) but instantly turned very dark when wet with solvent (transparent - polyacetylene then could be seen). Upon drying, the membrane again turned white. The phenomenon could be observed countless times with the same sample. 

A bilayer structure usually consists of two different films deposited on a substrate, one overlying the other. A typical system consists of a Pt substrate with an electro-deposited film of poly-[Ru(vbpy)3 ] on which a film of poly-[Os(bpy)2(vbpy)2" ] is elec-trodeposited (25). Another type of sandwich structure involves a pair of closely spaced electrodes such as in an electrode array (26), bridged by a polymer film. Alternatively, a different polymer can be deposited on each electrode of an array pair to form a bilayerlike arrangement having a junction where the films meet. Three-electrode devices of this type can produce a structure functionally equivalent to a field effect transistor (FET) (27). 

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