Preparation of multilayer films

Preparation of Multilayer Films of Polyamic Acid Alkylamine Salts ... 

This chapter provides a brief introduction to the preparation of multilayer films however, the main focus is on their potential applications in the field of electronics, especially in those areas that capitalize on the nonlinear properties of LB layers. 

Polycations used for the preparation of multilayer films in DDSs include natural polymers such as chitosan " or protamine/ and synthetic polymers, e.g. poly(4-vinylpyridine) (P4VP), polyaromatic... 

An alternative approach concerns the preparation of multilayer films in which each layer has different refractive indexes. Li et al. [107] fabricated multilayers with an increasing refractive index from the top to the bottom of the film. They prepared blends of BCP/homopolymers (PS-b-PMMA/PMMA). They used an octadecyltri-chlorosilane-modified glass substrate, and a mixture of solvents made the PMMA domains form a gradient distribution in the vertical direction of the entire micro-phase-separated film. This unique behavior allows, upon removal of PMMA, to obtain porous PS-based structures with variable porosity in the vertical direction (Fig. 6.17). Later, the authors investigated further the parameters [total degree of polymerization (AO, the volume fraction of the PMMA block (/pmma). the weight percentage of the homopolymer, and the solution concentration] that direct the structure formation and related them with the broadband antireflection properties [108]. 

Zhao G, Ishizaka T, Kasai H, Oikawa H, Nakanishi H (2007) Preparation of Multilayered Film of Polyimide Nanoparticles for Low-k Applications. Mol. Cryst. Liq. 

Silver Thick Films. About half of the silver consumed in the United States for its electrical properties is used by the electronics industry. Of this amount some 40% is used for the preparation of thick-film pastes in circuit paths and capacitors. These are silk-screened onto ceramic or plastic circuit boards for multilayer circuit sandwich components. 

Transfer experiments of the Langmuir films onto solid substrates and the preparation of LB films were investigated for 43. The deposition of films of 43 occurred regularly on quartz sHdes or silicon wafers with a transfer ratio of 1 0.05. The diblock structure of dendrimer 43 also appeared crucial for efficient transfers of the Langmuir films in order to obtain well-ordered multilayered LB films. Effectively, the transfer of the Langmuir films of the dendrimer 42 with the small polar head group was found to be difficult with a transfer ratio of about... 

Unlike the approach in which LB multilayers are formed from polymerizable fluoromonomers followed by UV-polymerization,69 we started to use functional fluoropolymers for the preparation of LB films. These films seem to be better, because in the case of monomeric LB film the polymerization process causes contraction and hence possible defects in the final cured film. Two different kinds of functional amphiphilic fluoropolymers were used for LB-film preparation. One type (referred to in Section 7.4.2), which has large fluoroalkyl groups as side... 

Prepare the multilayer-film dsDNA electrochemical biosensor by evaporation on the HOPG surface of three consecutive drops, each containing 5pL of 50pg/mL dsDNA in pH 4.5 0.1M acetate buffer electrolyte solution and leave the electrode in sterile atmosphere to dry [2],... 

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). 

Finally, we will consider briefly the formation of multilayer thin films by layer-by-layer deposition of hydrogen-bonded polymer pairs [51,52]. In this way a multilayer structure is obtained from potentially miscible polymer pairs. The stability of these films very much depends on the presence of hydrogen bonds, and pH may be used as an external trigger to erase the layered structure [53,54] and selectively dissolve one of the components [25-27]. This procedure allows for the preparation of microporous films not unlike the nanoporous films obtained by dissolution of the hydrogen-bonded side groups from self-assembled block copolymer-based comb-shaped supramo-lecules [15,17,18]. 

A very versatile approach to the formation of multilayer films has been developed by Decher, based on polyelectrolytes. If a solid substrate with ionic groups at the surface is dipped into a solution of a complementary polyelectrolyte, an ultrathin, essentially monomolecular film of the polyion is adsorbed [340]. The adsorption is based on pairing of surface bound ionic sites with oppositely charged ions, bound to the macromolecule. The polymers adsorb in an irregular flattened coil structure and only part of the polymer ions can be paired with the surface ions (Figure 29a). Ionic sites which remain with small counterions provide anchor points for a next layer formed by a complementary polyelectrolyte [342,343]. This way multilayer polyelectrolyte films can be prepared layer-by-layer just by dipping a suitable substrate alternately in an aqueous solution of polyanions and polycations. The technique can be employed with nearly all soluble charged polymers and results in films with a... 

Both crystalline [168] and amorphous [169] alloys are considered as precursors in the preparation of HTSC films. Atomic-level uniformity of the component distribution in metallurgical alloys can be achieved. One more type of metal precursor, the oxidation of which gives good results under relatively mild conditions, are multilayer polymetallic coatings with nanometer-thick layers [170], Similar compositions are also the most frequently used type of precursors in the technology of semiconductors [171]. 

In the next example (Example 2), a different approach for the preparation of zeolite films will be presented. This method was first proposed by Iler in 1979,11321 and involved the assembly of charged nano-sized particles layer by layer to form multilayer films based on electrostatic interaction, hence called the layer-by-layer (LBL) self-assembly technique. 

The excess amount of material used is removed between steps. The LbL technique is easy to carry out and very versatile. Because of this, a great range of polyelectrolytes, biopolymers (proteins and nucleic acids), lipids, and inorganic particles have been used as building blocks in the preparation of multilayer composite films [64, 65], and in the fabrication of micro- and nanometo-sized capsules, the latter introduced in 1998 by Donath and Caruso [66-68]. 

Metal organic chemical vapor deposition (MOCVD) is a promising method for the preparation of thin films. Metal/silicon multilayers with a single layer thickness of 1-10 nm, as used for soft X-ray mirrors [1,2], demand very smooth layers (roughness < 0.5 nm). 

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