Polymer films metal-containing, deposition

The activation of nonconducting materials by the deposition of metal-containing polymer films could improve the autocatalytic metallization process by eliminating the aqueous etching and sensitizing steps. In addition, substrates that are hard to etch and activate by the aqueous process could be plated by this technique. 

By the process described above, a plasma film could be obtained that had high enough electrical conductivity to allow direct electrodeposition of copper. The bulk resistivity of film measured by a four-point probe was 2.6 x 10 " ohm-cm for the copper-containing polymer film when deposition was stopped after 18 min at HOW. This value is critical if a uniform electrolytic deposit is to be obtained. For safety, deposition was carried out until a total film thickness of 150nm was obtained, giving a nearly pure metallic layer thick enough to allow subsequent electroplating. 

There are a number of ways of attaching a monolayer of redox molecules to an electrode surface.10 Multilayered films can be obtained by deposition of a polymer containing redox centers. These may be attached to the polymer backbone covalently, electrostatically, or coordinatively if the redox center contains a transition metal. 

Such bilayers can conveniently be built up by successive electropolymerization of complexes containing ligands with vinyl substituents, e.g. 4-vinylpyridine or 4-vinyl-4 -methyl-2,2 -bipyridyl. The films may be deposited on metallic or semiconductor electrodes (e.g. Pt, glassy carbon, Sn02, Ti02). More efficient metailation of the films is obtained by polymerization of coordinated ligand than by subsequent metailation of a preformed polymer film. An alternative to discrete films would be a copolymer with distinct redox sites, or a combination of a single polymer film with a copolymer film in a bilayer device. 

Film deposition refers to the preparation of polymer (organic, organometallic, and metal coordination) films which contain the equivalent of many monomolecular layers of electroactive sites. As many as 10 monolayer-equivalents may be present [9]. The polymer film is held on the electrode surface by a combination of chemisorptive and solubility effects. Since the polymer film bonding is rather nonspecific, this approach can be used to modify almost any type of... 

The Ni and Pt complexes can also be incorporated into polymer films of quaternized poly(vinylpyridine) (PVP) and deposited onto the transparent electrode (84). Photocurrents are enhanced to microamps (pA), an increase that may be attributed to either the effect of immobilization of the complexes near the electrode surface or an increase of the excited-state lifetimes in the polymer matrix. However, the effective concentrations of the complexes in this study were much greater than for the acetonitrile solutions in their earlier work. The polymer films are not stable to continuous photolysis, and voltammograms of the films are quite sensitive to anions used in the supporting electrolyte. The system can be stabilized by using a polymer blend of PVP and a copolymer containing quaternary ammonium ion and including [Fe(CN)6]4- in the electrolyte solution (85). Upon irradiation of the visible MLCT bands of [M(mnt)2]2 (M = Ni, Pt), photocurrents are produced. The mechanism (Scheme 4) is believed to involve photooxidation of the metal bis(dithiolene) triplet state by the Sn02 electrode, followed by [Fe(CN)6]4 reduction of the monoanion, with completion of the ET cycle as ferricyanide, Fe(CN)6 3, diffuses to the other electrode and is reduced. 

Although most metal-containing polythiophenes have been synthesized by electropolymerization on an electrode surface, there are many reasons to chemically synthesize these polymers. Chemical synthesis may allow isolation of soluble polymers, enabling complete solution characterization (GPC, light scattering, NMR, etc.) and facilitating conductivity studies. Moreover, it can enable improved thin-film preparation and film deposition onto nonconducting substrates. Finally, monomers that are unsuitable for electropolymerization may be polymerized by chemical methods. 

A recent XPS study [276] on the interactions between PAN films and silver cations revealed that the more reduced form of the polymer was capable of depositing silver metal from 0.1 M AgNOj. For the intrinsically more oxidized polymer with open-circuit potential greater than the formal potential of silver deposition (0.115 eV), a metal-polymer complex was formed. In a parallel development, it was found that by coupling the metal reduction process in acid solutions with an increase in the intrinsic oxidation state of a N-containing polymer, such as PAN or PPY, and the subsequent re-protonation and reduction of the intrinsically Oxidized polymer in acid media, spontaneous and sustained reduction of precious metals (such as Au and Pd) to their elemental form can be readily achieved... 

Thin-film metal (metal oxide)/polymer nanocomposites with different inorganic phase contents were obtained by using the cold-wall vacuum co-deposition technique. A range of metals was shown to be applicable to form nanocomposite thin films with PPX, i.e., Al, Ti, Pd, and Sn. AFM studies show the metal nanoparticles to have a size of 7-50 nm. Within the composite the polymer forms more or less spherical globules with a maximum size of about 200 nm. The interfacial regions between neighbouring polymeric spherulites contain nanoparticles of the inorganic filler. 

When metal particles are isolated in a polymer so that the interaction between them can be neglected, the conductivity of a composite is determined by that of a polymer matrix. In such composites, metal nanoparticles can only inject carriers into a polymer but do not influence substantially the conductivity process [59], This is the case of metal-PPX films prepared by the cryochemical vapor deposition teclmique if such films contain metal or semiconductor nanocrystals in amounts less than 4—5 vol. % [30]. The conductivity of such composites follows classical olmfic current-voltage relationship [30] and Arrheiuus dependence on temperature [57]. At higher metal contents the mechaiusm of conductivity in synthesized composite films changes under influence of the interparficle interaction. In PPX films containing Pb nanoparficles in amounts from 5 to 10 vol. %, the dependence of current I on voltage U looks like In / [30]. This dependence is characteristic for a... 

As such exemplary experimental material, plasma polymer thin films with embedded silver particles are selected [3]. These films were made by simultaneous or alternating plasma polymerization and metal evaporation. The films can be deposited as multilayers consisting of two polymer thin films and a nanoparticle-containing film between these films. Because of the two plasma polymer layers on either side, the particles are completely embedded in a homogeneous media. The multilayer systems are very appropriate for determining particle size and investigating the interface between metal particles and plasma polymer matrix, because here metal nanoparticles are embedded in one plane. This allows a simple determination of the particle size and shape in the TEM. 

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