Metal deposition displacement

Reproducibility of film preparation and stability of the resulting films are important issues for practical applications. Cleanliness of the IRE before metal deposition can play a decisive role in determining reproducibility. Depending on the conditions, metal films may not be stable and may peel off (36,37). The stability and reproducibility of metal films can be enhanced by evaporating a metal oxide support material (such as AI2O3) prior to evaporation of the desired metal. Contaminants on the IRE are covered or displaced by evaporation of the metal oxide. It was reported that a 50-100-nm-thick AI2O3 layer deposited on a Ge IRE by electron beam physical vapor deposition hardly affected the reflectivity in an ATR experiment. Thin platinum films directly deposited onto it were found to be rather stable under catalytic reaction conditions (26,38). 

Displacement deposition — Displacement deposition (also called cementation) means the electroless -> deposition of a noble metal on a less noble metal. The driving... 

In the displacement of Cu from CuSO by Zn and Cd, and of Ag from AgNC>3 by Zn and Cu (24), rates were found as high as eight times the values expected by comparison with dissolution from smooth cylinders. This was ascribed to enhanced transport by local cell electrolysis, but much of the effect was probably due to roughness caused by the metal deposit. With Zn in 2. 5 x 10" M AgNOg (followed by radiotracer technique) the rate was not abnormal of course very little Agwas deposited. 

As in other chemical processes, temperature significantly influences the rate of deposition during the galvanic displacement. The rate of metal deposition generally increases with an increase in temperature, which is a consequence of the Arrhenius equation ... 

Rotating electrode cells. Cells for industrial applications which utilise rotation of the cathode are either discs or cylinders. They can produce the metal deposit as a powder or a particulate which enables the cell to be operated in a continuous mode when the powder is displaced freely from the electrode surface. 

Porous silicon is a promising template for the preparation of metal nanostructures by eleetroehem-ical deposition. Because porous siheon is a semiconduetive porous electrode, eleetroehemieal deposition of metals oeeurs not only at the bottom of pores but also on the pore wall and pore openings. Thus, the control of electrochemical deposition within porous siheon has been a challenging issue. Eleetroehemieal deposition on porous siheon is influenced by illumination condihons. Metal deposition on porous siheon is possible by displacement deposihon. Many studies have reported on electrochemical deposition of metal for prachcal appheations. In this chapter, electrodeposition under polarization is firstly reviewed. Secondly, displacement deposition on porous siheon is explained. Finally, the microscopic structure formation by electrodeposition on porous siheon is summarized. 

Metal deposition creates a hybrid material of metal and semiconductor and the new material is expected to develop a new function, where microstructuring is cracial. A variety of techniques have been utilized for producing the 2D and 3D stractures. They are controlled physically, mechanically, optically, and electrochemically. Some examples of the 2D or position-selective local deposition are summarized in Table 1. The optical control is only possible on p-type silicon and deposition of less-noble metal. Illumination creates charge carriers and the illuminated spot undergoes deposition. Otherwise, excess free electrons and displacement deposition hinder the selective deposition. 

D structure formation of deposits 3 3D structure formation and deposition control 4 Displacement deposition 2 Electrodeposition 1 Metal deposition 3... 

A deposit of weld metal or displacement of base metal... 

As applied to metals, the series was first established by laboratory experiments to discover which metal would displace others from their salts. Thus a strip of clean zinc immersed in a solution of copper sulphate is soon covered by a deposit of metallic copper while the zinc passes into solution as Zn. This process is really an oxidation-reduction transfer of electrons ... 

Chemical deposition The deposition of a metal film by precipitation where another metal ion displaces the depositing atom in a solution of the metal salt. See also Chemical silvering. 

Electrochonical processes for metal deposition are broadly classified in electrolytic and electroless techniques. The electrolytic method implies the use of an external current source, whereas electroless methods—though relying on an electrochemical mechanism—only require the immersion of the substrate into the plating solution. Electroless methods comprise two essentially different processes, displacement or immersion plating and autocatalytic deposition. In Figure 11.2 the basic functioning of these processes is schematically represented. 

The process known as immersion plating is the simplest and oldest electrochemical technique for metal deposition. Immersion plating is the result of a displacement reaction in which a more noble metal cation is rednced to the elemental state thanks to the oxidation/dissolution of a more active (less noble) metal. A schematic representation of the process is shown in Figure 11.2 the substrate metal S gets oxidized to the ionic state supplying electrons for the reduction of the more noble metal cation... 

Principles Immersion plating resulting from a displacement reaction involving the metal to be coated can continue only as long as the less noble substrate remains accessible to the plating solution, and therefore as plating proceeds, the quantity of A/, deposited, and of A/j dissolved, falls. Dissolution of A/j can be avoided by coupling it with a less noble metal A/, so that only A/j dissolves, i.e, by internal electrolysis. 

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