Electrodeposited deposition mechanism

It was reported recently [216] that optical-quality PbTe thin films can be directly electrodeposited onto n-type Si(lOO) substrates, without an intermediate buffer layer, from an acidic (pH 1) lead acetate, tellurite, stirred solution at 20 °C. SEM, EDX, and XRD analyses showed that in optimal deposition conditions the films were uniform, compact, and stoichiometric, made of fine, 50-100 nm in size, crystallites of a polycrystalline cubic structure, with a composition of 51.2 at.% Pb and 48.8 at.% Te. According to optical measurements, the band gap of the films was 0.31 eV and of a direct transition. Cyclic voltammetry indicated that the electrodeposition occurred via an induced co-deposition mechanism. 

Although electroless deposition seems to offer greater prospects for deposit thickness and composition uniformity than electrodeposition, the achievement of such uniformity is a challenge. An understanding of catalysis and deposition mechanisms, as in Section 3, is inadequate to describe the operation of a practical electroless solution. Solution factors, such as the presence of stabilizers, dissolved O2 gas, and partially-diffusion-controlled, metal ion reduction reactions, often can strongly influence deposit uniformity. In the field of microelectronics, backend-of-line (BEOL) linewidths are approaching 0.1 pm, which is much less than the diffusion layer thickness for a... 

One of the major benefits of the ECALE methodology is that it breaks compound electrodeposition into a series of identical cycles and each cycle into a set of individual steps. Each step is examined and optimized independently, resulting in increased control over deposit structure, composition, and morphology. Better understanding of the individual steps in the deposition mechanism should allow the electrochemical formation of high-quality thin films of compound semiconductors. 

Mechanism of Superconformal Electrodeposition. Two mechanisms for supercon-formal deposition in the presence of additives were proposed ... 

Rodriguez-Torres etal. [235] have used ammonia-containing baths for Zn-Ni alloy electrodeposition on Pt. Zinc and nickel species exist in the form of [Zn(NH3)4] + and [Ni(NH3)6] " complexes in such solutions. The deposition at pH 10 was investigated and compared with deposition from ammonium chloride baths at pH 5. The Ni content in the alloys was found to be 40-60% higher from the ammonia-containing bath than from the acidic baths. The deposition mechanism was found to be affected by complexation of the metal cations by ammonia. 

An in depth study of the deposition mechanism was carried out by Sun et al. who studied the 1 1 [EMIMJCl/ZnCf system at various temperatures on glassy carbon (GC), nickel and platinum electrodes [106], The GC electrode required the largest overpotential for deposition. The stripping process showed a single peak on GC, whereas on Ni two oxidation processes were observed, separated by ca. 0.6V. Itwas proposed that the more positive oxidation process corresponded to the dissolution of an intermetallic compound formed during electrodeposition. 

The same authors also investigated zinc electrodeposition from acidic and alkaline electrolytes without and with inhibitors [6.82-6.86]. It was suggested that the deposition mechanism involves an autocatalytic step... 

Conductive polymers may be synthesized via either chemical or electrochemical polymerization methods. Electrodeposition of conductive polymers from electrolytes is, thus, feasible provided that the depositing polymer is not soluble in the electrolyte.206 Conductive polymers can be deposited from the electrolytes containing the monomers via either electrooxidation or electroreduction, based on the monomer type used. Similar to that of metals, the electrodeposition of polymers is based on nucleation and growth. The deposition mechanism involves oxidation of monomers adsorbed on the electrode surface, diffusion of the oxidized monomers and oligomerization, formation of clusters, and eventually film growth.213... 

Electrophoretic Deposition (EPD) is a forming process where charged particles are consolidated on a substrate in a DC electric field (14). This field causes the particles to move, and deposit on, the oppositely charged electrode (Figure 9.9). EPD is a combination of two processes, i.e. electrophoresis and deposition. Electrophoresis controls the motion of the charged particles in the electric field while the deposition mechanisms control the buildup of the dense particle layer on the electrode. EPD should not be confused with electrodeposition, where ions are deposited and discharged at the electrode. 

The effect of deposition potential on the thickness of electrodeposited silane films was first demonstrated by Mandler and coworkers [2]. They found that the thickness of MTMS films increased as the potential of the cathode was made more negative, as shown in Figure 12.4. This could be explained by the enhanced OH generation at more negative potentials due to the electrochemical reduction of O2 and H2O. Similar trend was observed in many later reports, and it affirms the deposition mechanism as suggested in the previous section [21,36]. They also pointed out that much thicker films were electrodeposited on gold than on indium tin oxide (ITO) electrode under the same deposition conditions. This confirms that the deposition is affected by the kinetics of electrochemical OH generation rather than the electrophoretic effect... 

Other researchers prepared Gd203 by electrodepositing Gd(OH)3 from a nitrate solution and then sintering at 700 °C for 3 h [111, 112]. The authors used a cathodic pulse current method where t =10 ms and t (f = 10 ms. The deposition mechanism was still a base generation method ... 

Annealing of electrodeposited copper reduces the mechanical properties. As an example, the tensile strength has been reported to decrease from 275-330 MN/m to 180-255 MN/m on heating at above 300°C while the hardness of deposits obtained in the presence of addition agents may drop from as high a value as 300 HV to 80 HV after annealing at 200° C. 

Despite the large differences in respect of other mechanical properties, it has been established that the wear resistance of copper deposits, which is markedly inferior to, for example, that of electrodeposited nickel, is not significantly affected by either type of bath or addition agents. 

A major advantage of the electroless nickel process is that deposition takes place at an almost uniform rate over surfaces of complex shape. Thus, electroless nickel can readily be applied to internal plating of tubes, valves, containers and other parts having deeply undercut surfaces where nickel coating by electrodeposition would be very difficult and costly. The resistance to corrosion of the coatings and their special mechanical properties also offer advantages in many instances where electrodeposited nickel could be applied without difficulty. 

In searching to formulate a mechanism of CuInSc2 phase formation by one-step electrodeposition from acid (pH 1-3) aqueous solutions containing millimolar concentrations of selenous acid and indium and copper sulfates, Kois et al. [178] considered a number of consecutive reactions involving the formation of Se, CuSe, and Cu2Se phases as a pre-requisite for the formation of CIS (Table 3.2). Thermodynamic and kinetic analyses on this basis were used to calculate a potential-pH diagram (Fig. 3.10) for the aqueous Cu+In-i-Se system and construct a distribution diagram of the final products in terms of deposition potential and composition ratio of Se(lV)/Cu(ll) in solution. 

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