Deposition pinhole free

A limitation to the application of SERS to electrochemical systems is the specificity of the enhancement effect to Ag, Au, and Cu. However, since the electromagnetic part of the enhancement is maintained over distances of several nanometers, it has been possible to coat a SERS active metal with a thin layer of another metal that is exposed to the adsorbing molecules and still obtain enhanced signals (69). For example, by constant-current deposition, it is possible to deposit pinhole-free layers of Pd on Au with a thickness corresponding to 3.5 monolayers and to study the adsorption of species on the Pd by SERS. The spectra of adsorbed benzene on such an electrode are shown in Figure 17.2.12 (84). The symmetric ring-breathing mode of benzene adsorbed on Pd appears at 950 cm shifted considerably from that found either for liquid benzene (992 cm ) or for benzene adsorbed on Au (975 cm ). Deuterated benzene (C D ) behaves similarly and shows the expected shift in the band to lower frequency. The attenuation of the enhancement effect with thickness of the Pd overlayer was reported to be only a factor of 4-5 for thicknesses of 3-30 monolayers. 

Advantages 1) Low Temperature 2) Controllable Composition 3) Step Coverage 4) Pinhole Free 5) Fast Deposition Rates 6) Can Produce Graded Interfaces... 

Investigations were conducted to determine whether jet vapor deposition (JVD) could be substituted for EVD, which is capital intensive. JVD is a thin film technique in which sonic gas jets in a low vacuum fast flow serve as deposition sources. Results showed that the YSZ films can be made dense and pinhole free they seal highly porous electrode surfaces and are gas tight. Conductivity needs to be improved, which should be obtainable. The ultimate goal will be to fabricate thin film SOFCs, both electrolyte and the electrodes, in an unbroken sequence of JVD steps. This would also allow the use of alternate metal cathode, such as Ag thin films (19). 

It is possible to inhibit reaction (5) by employing spray pyrolysis to deposit a compact layer of 2 on the Sn02 substrate before deposition of the nanocrystalline 2 film [9,10]. It is, however, relatively difficult to achieve a pinhole-free film. We chose to investigate the electropolymerization of an insulating film on the exposed parts of the Sn02 after the nanocrystalline 2 film has been depos-... 

The elemental Pt(0) Is dispersed throughout the surface polymer as determined by depth profile analysis,(7) and a representation of the interface is given in Scheme V. According to this view there is a certain amount of Pt(0) in contact with the thin SiOx overlayer on the bulk p-type Si. This is a relevant structural feature, since direct deposition of Pt(0) onto photocathode surfaces is known to improve the efficiency for the reduction of H2O to H2> Thus, we expect that, for an interface like that depicted in Scheme V, there will be a certain amount of the H2 evolution occurring by direct catalysis of the reaction of the photoexcited electrons with H2O at the Si0x/Pt(0) interfaces. In the extreme of a uniform, pinhole-free coverage of Pt(0) on p-type Si/SiOx one expects that the photocathode would operate as a buried photosensitive interface and in fact would be equivalent to an external solid state photovoltaic device driving a photoelectrolysis cell with a Pt(0) cathode. 

A pulsed plasma has been used to prepare pinhole-free films from relatively nontoxic N vinylpyrrolidone.323 The pulsing reduced fragmentation of the monomer and cross-linking. This method should be tried with other monomers. Plasmas are often used for the modification of polymer surfaces.324 These methods are relatively rapid and use no solvent. Decorative coatings of TiN and other inorganic compounds can be applied to metals and other inorganic substrates by sputtering, chemical vapor deposition, plasmas, and such, as described in Chap. 4.325... 

This is a commonly applied technique in the microelectronics industry used to deposit thin uniform polymeric films. In this method the polymer, dissolved in a suitable solvent, is dropped onto the substrate whilst it is being spun at high speed. As a result the solution spreads out to form a thin uniform film across the substrate surface which, on evaporation of the solvent, leaves a polymer film over the surface of the substrate. The thickness of the film is determined by the rotation speed and by the viscosity of the polymer solution. The technique is only suitable for coating relatively flat substrates and for the deposition of reasonably thick (1 fim) pinhole-free films. Once deposited the polymer films can be cross-linked by suitable reactive reagents, heat, or light to produce robust, adherent films. 

Insulating films can be formed either by using monomers such as phenol [182, 183] or 1,2-diaminobenzene which yield non-conducting polymers or by overoxidation of conducting polymer films as described above. Insulating polymers, such as poly(phenol), form as thin (0.1 iim range) pinhole-free films at the surface. This allows very thin uniform films to be deposited. Films of... 

Complex substrate modifications involving intermediate layers and palladium alloy deposition methods are often required for superior membrane performance. Modification of a membrane support surface before palladium deposition by sintering on smaller particles can create a smoother surface with smaller pores, facilitating the deposition of a defect-free palladium layer. Nickel microparticles have been sintered together to form a porous support that was sputter-coated with palladium and then copper [118]. Thermal treatment at 700 °C for 1 h promoted reflow to create a durable, pinhole-free membrane with a Pd-Cu-Ni alloy film. In another case, starting with commercially available PSS with a 0.5 pm particle filtration cut-ofF, submicron nickel particles were dispersed on the surface, vacnium sintered for 5 h at 800 °C, and then sputtered with UN [159]. The nickel particles created a smoother surface with smaller pores, so a thinner palladium alloy layer... 

Our experimental results show that the carbon fiber microelectrodes can be encapsulated by electrochemically generated insulator. The encapsulation with Si02 is experimentally demanding and does not yield reliable results. This is presumably due to the fact that the thin layer of silicon is extremely reactive and traces of residual oxygen, present at the electroactive (i.e. to be encapsulated) surface cause the formation of the insulating film which inhibits further deposition of the precursor. Therefore, only very thin layers which were obtained at very slow scan rates within the potential range of —1 V up to —3 V are pinhole free. The inconsistency of the quality of the silicon deposits has been observed also by Tannenberger. ... 

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