Metal films reduced

Ultrathin metal film (UTME) is another widely studied candidate for the transparent electrode in ST-OPV. Metal films are highly conductive and ductile when the thickness of metal film reduces to under 20 nm, it starts... 

Rhenium hexafluoride is used for the deposition of rhenium metal films for electronic, semiconductor, laser parts (6—8), and in chemical vapor deposition (CVD) processes which involve the reduction of ReF by hydrogen at elevated (550—750°C) temperatures and reduced (<101.3 kPa (1 atm)) pressures (9,10). 

Electroless plating rates ate affected by the rate of reduction of the dissolved reducing agent and the dissolved metal ion which diffuse to the catalytic surface of the object being plated. When an initial continuous metal film is deposited, the whole surface is at one potential determined by the mixed potential of the system (17). The current density is the same everywhere on the surface as long as flow and diffusion are unrestricted so the metal... 

The capacitor element in this case is made up of extremely thin metallic films. When a dielectric failure occurs in any of the elements, the current passes through the film. The film, being too thin to sustain the current, fuses only at the point of dielectric puncture clearing the fault quickly. The external fuses remain intact, and so remains the affected element in service. Some manufacturers claim that 10000 such failures and healings may reduce the rating of the element or the unit made up of such elements by barely I %. 

Another problem in the construction of tlrese devices, is that materials which do not play a direct part in the operation of the microchip must be introduced to ensure electrical contact between the elecuonic components, and to reduce the possibility of chemical interactions between the device components. The introduction of such materials usually requires an annealing phase in the construction of die device at a temperature as high as 600 K. As a result it is also most probable, especially in the case of the aluminium-silicon interface, that thin films of oxide exist between the various deposited films. Such a layer will act as a banier to inter-diffusion between the layers, and the transport of atoms from one layer to the next will be less than would be indicated by the chemical potential driving force. At pinholes in the AI2O3 layer, aluminium metal can reduce SiOa at isolated spots, and form the pits into the silicon which were observed in early devices. The introduction of a tlrin layer of platinum silicide between the silicon and aluminium layers reduces the pit formation. However, aluminium has a strong affinity for platinum, and so a layer of clrromium is placed between the silicide and aluminium to reduce the invasive interaction of aluminium. 

Surface films are formed by corrosion on practically all commercial metals and consist of solid corrosion products (see area II in Fig. 2-2). It is essential for the protective action of these surface films that they be sufficiently thick and homogeneous to sustain the transport of the reaction products between metal and medium. With ferrous materials and many other metals, the surface films have a considerably higher conductivity for electrons than for ions. Thus the cathodic redox reaction according to Eq. (2-9) is considerably less restricted than it is by the transport of metal ions. The location of the cathodic partial reaction is not only the interface between the metal and the medium but also the interface between the film and medium, in which the reaction product OH is formed on the surface film and raises the pH. With most metals this reduces the solubility of the surface film (i.e., the passive state is stabilized). 

Chemical reduction is used extensively nowadays for the deposition of nickel or copper as the first stage in the electroplating of plastics. The most widely used plastic as a basis for electroplating is acrylonitrile-butadiene-styrene co-polymer (ABS). Immersion of the plastic in a chromic acid-sulphuric acid mixture causes the butadiene particles to be attacked and oxidised, whilst making the material hydrophilic at the same time. The activation process which follows is necessary to enable the subsequent electroless nickel or copper to be deposited, since this will only take place in the presence of certain catalytic metals (especially silver and palladium), which are adsorbed on to the surface of the plastic. The adsorbed metallic film is produced by a prior immersion in a stannous chloride solution, which reduces the palladium or silver ions to the metallic state. The solutions mostly employed are acid palladium chloride or ammoniacal silver nitrate. The etched plastic can also be immersed first in acidified palladium chloride and then in an alkylamine borane, which likewise form metallic palladium catalytic nuclei. Colloidal copper catalysts are of some interest, as they are cheaper and are also claimed to promote better coverage of electroless copper. 

The significance of corrosion protection has risen sharply in recent years for a number of reasons (1) because of efforts to reduce the metal content of parts (e.g., by using thinner metallic support structures) (2) with the use of new types of equipment and processes involving expensive equipment operated under extreme conditions, such as nuclear reactors and jet and rocket engines and (3) in connection with the development of products having extremely thin metal films, such as printed circuit boards and integrated circuits. 

Johans et al. derived a model for diffusion-controlled electrodeposition at liquid-liquid interface taking into account the development of diffusion fields in both phases [91]. The current transients exhibited rising portions followed by planar diffusion-controlled decay. These features are very similar to those commonly observed in three-dimensional nucleation of metals onto solid electrodes [173-175]. The authors reduced aqueous ammonium tetrachloropalladate by butylferrocene in DCE. The experimental transients were in good agreement with the theoretical ones. The nucleation rate was considered to depend exponentially on the applied potential and a one-electron step was found to be rate determining. The results were taken to confirm the absence of preferential nucleation sites at the liquid-liquid interface. Other nucleation work at the liquid-liquid interface has described the formation of two-dimensional metallic films with rather interesting fractal shapes [176]. 

That the assumption of such spatially separated sites is justified has been demonstrated by experiments using evaporated metal films, acting as catalytic sites [LilO]. In an electrolyte composed of aqueous HF, H202 and ethanol, stain film formation has been observed under and close to evaporated thin films of Au, Pt and Pd, while silicon samples free of metal films showed no PS formation. The metal is assumed to act as a cathodic site, where H202 is reduced to H20 under injection of two holes into the silicon VB. These holes are consumed by the for-... 

Figure 7.6 shows the intensity / that would be detected in the glass at a particular supercritical angle, given an excitation intensity that is not a function of z (e.g., epi-illumination rather than TIR). Only the results for perpendicular dipoles are shown (so that averaging over azimuthal is unnecessary). The result for parallel dipoles is qualitatively similar except that the metal film case would be very much reduced in overall intensity. 

As a result of ion bombardment effects and of their ability to reduce native oxides chemically, chlorocarbon or fluorocarbon gases, rather than pure halogens, are typically used to etch metal films (Table IV). 

Hydrazine reduces heavy metal oxides and their salts to free metals. These reactions are utilized for plating of metal films on plastics and glass ... 

Two different kinds of catalytic metal structure are required. Thick films, which are assumed to be dense, are needed for high-temperature operation and detection of excesss oxidizing or reducing molecules in environments such as exhaust gases. Porous metal films are needed for selective detection of molecules such as NHj, CO, NO, and HC in excess air in environments such as diesel exhausts or flue gases. 

Figure 8.11 Electrochemistry of nanotubes solubilized by direct sodium reduction. Background of the supporting electrolyte solution is shown with dashed line. The star indicates the irreversible anodic peak due to the oxidative stripping of the reduced alkali metal film. 2 mM tetrabutylammonium hydroxide/DMSO working electrode Pt disk (r = 25 pm) data recorded at 298K scan rate 1 V/s. Potentials are referenced to SCE. Reproduced with permission from Ref. 122. Copyright 2008 American Chemical Society.

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