Selective deposition

By buffering the metal ion concentration using a chelant, E can be adjusted to and stabilized at values that give desirable properties to the deposit. Selective buffering can sequester the properties of interfering ions or can be used to regulate the potentials of two or more ions to approximately the same value in order to effect codeposition. 

An understanding of gas-phase and surface chemistry is particularly important to the next generation of MOVPE processes involving selective epitaxy [18] and atomic layer epitaxy (ALE) [19]. In the first process, the compound semiconductor is deposited selectively on substrate areas opened in a suitable masking material (e.g., SiOz). This is achieved by operating under conditions where nucleation occurs only on the substrates. Slight variations in processing environment and the presence of impurities can cause nucleation on the mask and result in loss of selectivity. 

As a consequence when the difference between equilibrium potentials of the two half redox reactions is low, the modifying metal, during the preparation of a bimetallic catalyst by direct redox reaction, will be deposited selectively on specific sites of the parent metal (i.e. sites that are highly oxidizable such as comers, edges, etc.). However, the equilibrium potentials are defined by Nemst s law which provides facilities to fit the potential values by changing the concentrations of the oxidized and reduced forms (eqs 2 and 2 ) and so induces selective deposition of the modifier on the parent catalyst. 

Finally, under well-defined experimental conditions (essentially the concentrations), the modifying metal can be deposited selectively on specific sites of the parent metal. Such deposition can significantly influence the selectivity of the bimetallic catalysts [12, 14],... 

If the metal Pt is deposited selectively on one of the two carriers, the graphical representation, % weight Pt /(proportion of alumina in the zeolite-alumina mixture) is a straight line where the ordinate at the origin is an estimate of the Pt concentration level in the zeolite. In the example shown here, the estimated concentration level is 2.5% weight Pt in the zeolite. This graphic representation clearly shows that the impregnation method used enables the platinum to be deposited selectively on the zeolite. 

Figure 3.1. After opening of the contacts or the vias (a) tungsten is deposited selectively (b) followed by the sputter deposition of aluminum (c).

On the solvent-treated silicon surface, the polymeric coating is deposited selectively. Adsorption and nucleation of polymeric microparticles on the silicon surface are nonuniform. These polymer films contain cross-links with the relative high length of the molecular branches. 

Mining is by the open-pit method, and, because of the chemical irregularity of the deposit, selective mining methods have to be employed. Visual distinction between the various grades of ore is difficult, so identification has to be made by determining the two principal contaminants, lime... 

When Cu was electrochemically deposited onto the GaAs surface part of which was modified by the AFM tip, Cu was deposited selectively on the scratched portion. This result may lead to a novel technique for the submicron fabrication. 

When we use a hydrophilic polymer like poly(4-hydroxystyrene) or poly(2-(2-(4-vinyl phenoxy)-ethoxy)-ethanol), which will show hydroxy groups at die surface after reconstruction, we are able to deposit selectively inoiganic materials like titanium dioxideor copper" on these parts. 

Fmther support for the role of hydrophobic interactions in the area-selective adsorption was obtained by reversing the dipping sequence. A single bilayer was adsorbed on a methyl- and hydroxyl-terminated stripe pattern (10 and 5 pm, respectively), in one case starting with the polycation, in the other case with first adsorbing the polyanion. Both substrates were subsequently analyzed by AFM in contact mode. The friction force images (Fig. 8) clearly show a reversal in contrast for both experiments, compared with the template without the polymers, indicating that in both cases one bUayer had been deposited selectively on the methyl-terminated areas. 

TiCU-derived Ti02 is deposited selectively on the photolyzed hydrophilic region of the monolayer. 

Despite the failure of the activation of TCE on clusters observed in TPD, EES experiments of deposited selected clusters of similar sizes were performed. The exclusion of additional molecules and the chemisorption behavior for selected clusters, reduces the origin of possible shifts in peak energy positions in EE spectra to the effect of physisorption induced relaxation shifts. Thus, it allows for uncomplicated comparison of the differences in physisorption on the surfaces and supported clusters (if omitting compensating effects of potential energy and electron relaxation, as discussed in Sect. 2.2.4). 

If the film is deposited selectively on anodic areas, the corrosion potential shifts to more positive values if it is deposited on cathodic areas, the shift is to more negative values and if the film covers both anodic and cathodic areas, there may be only a slight shift in either direction. 

In Composite Deposition technology (CD process) [96], the filler metal for joint formation is derived from a composite powder, a compound consisting of potassium fluoroaluminate flux and Al-Si alloy. The CD powder is deposited selectively and accurately on heat-exchanger components prior to assembly and brazing. 

Tao et al. [214] reported the synthesis of monodispersed silver NPs capped by PVP with regular polyhedral shapes with solely (100) and (111) facets on the fee crystal lattice. Initially, small silver particles (<10 nm) nucleate and develop into nanocubes bound by (100) planes. As the reaction continues, silver deposits selectively onto the (100) nanocrystal facets and various polyhedral shapes capped with (100) and (111) faces can be obtained, depending on the reaction duration (Figure 15.4). It was suggested that the driving force for the selective (100) planes growth is not the adsorption of the capping polymer (PVP) to the (111) planes, but rather the inherent increased stability of the (100) planes [215]. 

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