Solution deposition

Desmopressin may be given orally, intranasally, SC, or IV. The oral dose must be determined for each individual patient and adjusted according to the patient s response to therapy. When the drug is administered nasally, a nasal tube is used for administration. The nasal tube delivery system comes with a flexible calibrated plastic tube called a rhinyle. The solution is drawn into the rhinyle. One end is inserted into the nostril and the patient (if condition allows) blows the other end to deposit solution deep into the nasal cavity. A nasal spray pump may also be used. Most adults require 0.2 mL daily in two divided doses to control diabetes insipidus. The drug may also be administered via the SC route or direct IV injection. 

The prescribed amount of solution is drawn into the rhinyle. One end is inserted into the nostril, and the patient blows the other end to deposit solution deep into the nasal cavity. 

Fig. 3.13 SEM microstructure of PbTe films electrodeposited at -0.12 V (left) and —0.40 V (right) vs. Ag/AgQ. Deposition solution 0.0001 M HTeOj + 0.05 M Pb + 1 M HNO3. (Reprinted from [215], Copyright 2009, with permission from Elsevier)...

However, an application of thermodynamic control may be complicated by too large difference in binding constant of adsorbed species. The highest concentration of an adsorbate in deposition solution cannot exceed its solubility. The lowest concentration should provide enough high amounts of molecules for formation of a monomolecular layer. For most of compounds and... 

Electrodeposition is not heat and beat , it is not a heat driven reaction. Ideally, electrodeposition involves control of equilibrium by controlling the activity of the electrons at the deposit solution interface, and thus their equilibrium with reactants in solution. 

Not all additives function as inhibitors in electroless deposition solutions. A few additives function to increase the rate of electroless deposition these tend to be... 

Deposition of the mixed monolayer. Deposition solutions were prepared by dissolving octadecylmercaptan [ClsSH] and the respective bipyridinium in a mixture of chloroform and methanol. The electrode was cleaned by heating it in a gas-air flame. After cooling, the electrode was immersed in the deposition solution for 15 - 30 minutes, withdrawn, and rinsed in clean methanol or chloroform. Qualitatively the most reproducible surface redox waves and lowest charging currents during cyclic voltammetry were obtained with a freshly-prepared deposition solution containing 50 mM CiaSH and 10 mM of the bipyridinium in a 1 1 volume ratio of chloroform and methanol. 

We will restrict r to values less than unity, wbicb is necessary to accumulate an Fe deposit. Solution of tbe time derivatives, expressed as F (fraction of liquid remaining in tbe pool), following tbe approach of DePaolo (1981), but cast in terms of fluxes, produces ... 

A comparative smdy of great practical value has been carried out between several Ni-based diffusion barrier properties. Those were produced by means of electroless deposition from nickel sulfate and nickel sulfamate deposition solutions (73). It was concluded on the basis of Auger depth profiling (see Section 13.3) that Ni(P) sulfamate has much better diffusion barrier properties than Ni(P) sulfate. This conclusion is a telling example of the influence of anions on the physical properties of electro-chemically deposited metals. 

CD reactions sometimes proceed via a metal hydroxide intermediate the concentration of OH ions in the solution is particularly important in such cases. Since almost all CD reactions are carried out in aqueous solutions, the pH of the deposition solution will give this concentration. In translating pH into OH concentration, the very temperature-dependent ioiuzation constant of water should be kept in mind, as mentioned previously. The reason for this can be seen from Table 1.2, which gives the OH concentration in water at a pH of 10 (a typical pH value for many CD reactions), calculated from the ionization constant of water, from the relation... 

This rate control can be accomplished by generating the sulphide slowly in the deposition solution. The rate of generation of sulphide, and therefore reaction rate, can be controlled through a number of parameters, in particular the concentration of sulphide-forming precursor, solution temperature, and pH. 

The CdS forms through a number of different possible pathways simple ionic reaction between Cd and sulphide ion topotactic conversion of Cd(OH)2, which may be present in the deposition solution, to CdS by sulphide and decomposition of a complex between Cd (whether as a free ion or as a Cd compound. 

For the cluster mechanism, while growth and termination can be similarly explained, the induction period is less obvious. The hydroxide cluster can start to adsorb on the substrate immediately after immersion of the substrate in the deposition solution, yet experiments have shown that film growth often does not occur for some time. While the reason for this is not clear, it may be connected with the... 

To a first approximation, films can be deposited by CD on any surface (this is one of the advantages of CD). Of course, there will be certain obvious exceptions, such as substrates that are unstable in the deposition solution (this is rarely a problem, in practice) or dirty substrates. In several studies, CdS has been shown to form quite adherent films on Teflon, and this attests to the ability of CD to form films on a wide range of substrates. An important advantage of CD is that the shape of the substrate is usually not important - very irregularly-shaped substrates can be used. 

Thiourea (SC(NH2)2) This solution will slowly precipitate sulphur (seen as a fine white precipitate—white instead of the usual yellow of sulphur possibly due to size quantization of the finely divided precipitate ). However, it can usually be kept over a period of weeks or even months in a stoppered bottle without major adverse effects, although for optimum reproducibility a fresh solution may be preferred. If a prepared stock solution is used, filtration of this solution before use will minimize the presence of sulphur particles in the deposition solution such particles can act as nucleation centers and accelerate precipitation in the solution. 

STEP 3 PREPARATION OP THE DEPOSITION SOLUTION. Solution Compositions, even based on exactly the same constituents as stated earUer, vary widely from one literature source to another. We give a typical average composition and discuss the effect of variations from this composition. 

The prepared solution will slowly deposit Se as a black precipitate over a period of weeks. Also, the solution is considerably less stable than thiourea. If kept out of excessive contact with air, it will be usable for about a month if high reproducibility of the deposition kinetics is not important. However, it is important to be aware of the slow decomposition and loss of reactivity of this reactant. If a freshly made NaiSeSOs solution is used to deposit CdSe, the reaction will proceed much faster than if an aged solution is used this fact should be taken into account in preparing the overall deposition solution. 

STEP 3 PREPARATION OP THE DEPOSITION SOLUTION. As for CdS, the Conditions can be very variable. The following is a typical deposition solution, but re-... 

STRUCTURE. CdSe forms the same three crystal stractures as described earlier for CdS. The main difference between the CD films of the two materials is that, while CdS can be commonly found in both the wurtzite and sphalerite forms, CdSe is more commonly deposited in the cubic zincblende form. Mixtures of the two forms have been reported in some cases, particularly when a visible Cd(OH)2 precipitate is present in the initial deposition solution. 

HgS films have also been deposited from more conventional deposition solutions using thiourea and the tetraiodide complex of mercury—a strong complex—in alkaline solution. Both these and the previous films showed an optical absorption with a gradual absorption onset at 700 nm and a sharp one at 400 nm. 

Chemical deposition films of PbS and PbSe are generally not strongly textured. One report has described (200) textured PbS films on glass if H2O2 is present in the deposition solution. 

The participation of Cd(OH)2 in the deposition of CdS (and other metal chalcogenides) has been demonstrated or suggested on many occasions. Kitaev et al. presented a theoretical thermodynamic treatment of the Cd " /ammonia/ thiourea system to show when Cd(OH)2 should be present as a solid phase in the deposition solution [36]. A graphical representation of this analysis is shown in Eigure 3.1. This graph is based on two equilibria the solubility product of Cd(OH)2 and the stability constant of the ammonia (ammine) complex of Cd. Consider first the former ... 

Betenekov et al. [39] used an isotopic tracer technique to show that, for then-range of solution compositions, the initial deposition involved adsorption of Cd(OH)2 on the glass substrate. At the beginning of the reaction, only Cd was observed to form on the substrate and this was interpreted to be due to Cd(OH)2, since any other insoluble Cd compounds that might be formed from the deposition solution (containing CdCl2, NaOH, NH4OH, and thiourea dissolved in water) were expected to contain either S or C. However, they concluded that the deposition proceeded, not by reaction between Cd(OH)2 and sulphide formed by decomposition of thiourea, but rather by decomposition of a Cd(OH)2-thiourea complex (see Sec. 3.3.3.1). 

Growth of various semiconductors onto certain single-crystal substrates has resulted in epitaxial growth in a number of cases. This epitaxy has been well studied for CdS deposition by Lincot et al. [59-63]. Although the epitaxy requires a certain degree of lattice matching between semiconductor and substrate, chemical interactions between the constituents of the deposition solution and the substrate are important as well (discussed in more detail in Chap. 4). It is a reasonable assumption that epitaxial deposition occurs via an ion-by-ion process. Indeed, it has... 

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