Multilayered repeating structures

One of the main features of TP methods is the abUity to pattern on nonplanar or flexible surfaces (such as polymer membranes) and on topographies or previously patterned surfaces. The last feature may be repeated (with some processes, indefinitely), creating multilayered 3D structures and hierarchichal structures. 

Figure 3.9. Scheme of the LB technique (a) deposition of the amphiphiles on the water subphase with the solid substrate submerged (b) by action of the barrier the ML is compressed (c) by pulling out the substrate vertically a ML is transferred to both sides of the substrate (d) a multilayered structure is built up by repeated up and down strokes of the substrate, (e) Distinct arrangements of LB Aims. 

Repeating these transfer cycles, multilayers can be formed on the substrate. The layers are called LB films. To investigate the structure of LB films the same techniques as above are usually applied, namely fluorescence microscopy, Brewster angle microscopy, and X-ray re-flectometry. 

A typical method for fabricating multiple complex layers is illustrated in Figure 2.11,12 First, an Au/mica or Au/ITO plate is immersed in a chloroform solution of tpy-AB-SS-AB-tpy (tpy=2,2 6, 2" -terpyridyl), providing Au-S-AB-tpy SAM on the plate. In the case of connecting the Fe(II) ion, the tpy-terminated plate is immersed in 0.1 M Fe(BF4)2 aq or (NH4)2Fe(S04)2 aq to form a metal complex. Subsequently, the metal-terminated surface is immersed in a chloroform solution of the ligand Lj or L2 to form a bis(tpy)iron structure (Fig. 2b). The latter two processes are repeated for the preparation of multilayered bis(tpy)iron (II) complex films with linear structures. When L3 is used instead of Lj or L2, the resulting molecular wires have a dendritic structure (Fig. 2c). 

The multilayer nanocomposite films containing layers of quasi-spherical Fe nanoparticles (d — 5.8 nm) separated by dielectric layers from boron nitride (BN) are synthesized by the repeated alternating deposition of BN and Fe onto a silicon substrate [54]. In this work the authors managed to realize the correlation in the arrangement of Fe nanoparticles between the layers the thin BN layer deposited on the Fe layer has a wave-like relief, on which the disposition of Fe nanoparticles is imprinted as a result, the next Fe layer deposited onto BN reproduces the structure of the previous Fe layer. Thus, a three-dimensional ordered system of the nanoparticles has been formed on the basis of the initial ordered Fe nanoparticle layer deposited on silicon substrate [54]. The analogous three-dimensional structure composed of the Co nanoparticles layers, which alternate the layers of amorphous A1203, has been obtained by the PVD method [55]. 

Andres and coworkers demonstrated the iCP of densely packed alkanethiolate-functionalized Au nanoparticle arrays in monolayer and multilayer structures.81,82 Dense and hexagonally packed monolayers of nanoparticles were first assembled on a water surface. By using the Langmuir-Schafer technique, the Au nanoparticle monolayer was transferred to a PDMS stamp, and printed onto a substrate. Multilayers were prepared by repeating the printing process in an LbL scheme, in which subsequent particle layers may be made up of the same or different types of particles. Similarly, the assembly of irregular, densely packed monolayers of polystyrene nanoparticles on iCP substrates via carbodiimide coupling was reported.83 The conformal contact of the carbodiimide-functionalized polystyrene particles resulted in the covalent attachment of the nanoparticles at a carboxylate-functionalized surface. 

In the Fangmuir-Blodgett technique, amphiphilic monolayers, formed at a liquid-air interface, are transferred to a solid substrate by horizontal or vertical transfer. The thickness of such monolayers is of the order of a few nanometers, depending on the materials being used. With this method, multilayer structures can also be produced, either by repeated deposition of the same layer or by the deposition of alternate layers. In this manner, multilayers containing several hundred individual components can be obtained. In general, the thermal and mechanical stabilities of such layers are, however, limited. 

A logical explanation of this data can be obtained from the structure of the film. Figure 6 shows a simplified model of the filmed electrode with multilayers present. As one adds small amounts of surfactant one forms an Inverted micelle and obtains the extra catalysis of the Inverted micelle causing a rise In the rate. As more surfactant Is added the normal micelle starts to form on the surface and the rate drops back toward the catalysis of the normal micelle. This process Is repeated through the second and third layers (50). 

The multilayered structure and electroluminescent mechanism of OLEDs is illustrated in Figure 4.45. Depending on whether small organic molecules or long repeating-unit polymers are used (Figure 4.46), the diodes are referred to as OLEDs or PLEDs, respectively. Under positive current, electrons and holes are injected into the emissive layer from opposite directions - from the cathode and anode, respectively. The metal... 

The improved structural homogeneity of the multilayer allowed for stable and repeatable current- and electroluminescence voltage characteristics with low onset voltages of ca. 3 V. Devices operated under ambient conditions and a clear red emission was detected. The typical electroluminescence spectrum matches the PL of initial NCs taken for the assembly (Fig. 2). 

A multilayer structure with one of the repeating layers being a magnetic material is called magnetic... 

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