Substrate topography

The second category was concerned with adhesion to porous or microfibrous surfaces on metals. Aluminium may be anodised to form an oxide surface comprising pores of diameter of tens of nanometers. Electroforming and chemical oxidation can be used to produce microfibrous or needle-like coatings on metals, including copper, steel and titanium. The substrate topography was demonstrated to play an vital part in adhesion to these surfaces [45-48]. 

Properties of deposits Deposits can be produced that are adherent, coherent and finely crystalline. Addition agents, e.g. organic sulphonamides can improve the deposit structure so that thick coatings can be produced free of nodules and blisters. The production of very smooth thick deposits of copper has been reported Thin deposits tend to reproduce the substrate topography, but some cases of levelling have been reported. The brightness tends to fall with increasing thickness. 

Fig. 3 shows a topographic image of a Pt/y-A s catalyst. Contrast from particles is clearly separated from the substrate topography. On the other hand pores on the substrate are well defined. If the aperture includes some portion of the dark field spot then the resolution for small particles is improved. Fig. 4 shows an image of a 100% dispersed catalyst (as measur ed by chemisorption methods) in which particles of about 5 A can be seen. 

Figure 5.1 Illustration of (a) molecular architecture of a SAM-forming molecule, (b) an idealized SAM and (c) a more realistic description with molecular defects (1), domain boundaries (2) and substrate topography such as steps (3).

Epitaxial crystallization of helical polymers may involve three different features of the polymer chain or lattice. These are (a) the interchain distance (as for stretched out polymers), (b) the chain axis repeat distance, and (c) the interstrand distance - the distance between the exterior paths of two successive turns of the helix. The two former periodicities are normal and parallel to the chain axis direction, and are therefore not usually sensitive to the chirality of the helix (unless the substrate topography is asymmetric and favors a given helical hand). However, the interstrand distance is oblique to the helix axis (it is normal to the orientation of the outer chain path) and therefore has different, symmetric orientations relative to the helix axis for left-handed and right-handed helices (Fig. 2). In other words, epitaxies that involve the interstrand distances are discriminative with respect to helix chirality. This discrimination becomes visible if the crystal structure is based on whole layers of isochiral helices. Such a situation does indeed exist for isotactic poly(l-butene), Form I, that will be considered soon. 

Electron diffraction used in combination with AFM probes the thickness of the layer (and therefore the true bulk crystallization). Its results are consistent with those of AFM about the organization of helical hands. Both techniques indicate that for iPBul and sPP, selection processes are at play for helical hand, that involve the immediate neighborhood of the depositing stem substrate topography on which the helix is deposited and/or the neighboring helix in the growth front. 

Multi-level systems(l) allow the planarization of substrate topography formation of high aspect ratio patterns, and better resolution than single level resists. There is a drawback to such systems, however, and that is additional process complexity. To reduce this complexity, two-level resist systems have been reported(2). The top imaging layer in two-level resist systems must exibit Op-RIE resistance as well as desirable lithographic characteristics. 

The importance of substrate surface chemistry has been extensively studied and will not be described in detail here. The cellular environment emphasizes the importance of neighboring cells. Living cells constantly communicate with other cells in their surroundings and this cell-cell interaction partially explains the success of in vitro cell co-cultures in better maintaining the viability and normal functions of primary hepatocytes, which was discussed in Section 25.4. In this section we focus only on the microfluidic control of extracellular environment, and the influence of substrate topography on cell functions. 

S0rensen, PA, Kiil, S, Dam-Johansen, K, Weinell, CE. 2008. Influence of Substrate Topography on Cathodic Delamination of Anticorrosive Coatings. Prog. Org. Coat. doi 10.1016/j.porgcoat.08.027. 

Teixeira, A.I., McKie, G.A., Foley, J.D., Bertics, P.J., Nealey, P.F., Murphy, C.J., 2006. The effect of environmental factors on the response of human comeal epithelial cells to nanoscale substrate topography. Biomaterials 27 (21), 3945—3954. 

Cells within tissues receive inputs from a range of signaling cues, ranging from proximal signals, such as molecules produced by the neighboring cells and substrate topography, to... 

SECM has been applied to the investigation of various technologically important materials and interfaces, for example, metallic corrosion [91-96], fuel cell electrocatalysts [97], semiconductor photocatalysts [12, 60-63, 98], conducting polymers [49, 50, 85, 86, 99-103], liquid-liquid and liquid-gas interfaces [29, 30, 68]. The SECM may be used to image the substrate topography and/or reactivity, or with the tip at a fixed location, to study the local kinetics of the interfacial reactions of interest. 

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