Inorganic deposition processes

Kern, W., and Ban, V. S., Chemical Vapor Deposition of Inorganic Thin Films, in Thin Film Processes, (J. Vossen and W. Kern, eds.). Academic Press, New York (1978)... 

Besides the use of solution-based processing for the deposition of inorganic compounds, major developments are taking place in the field of deposition of organic-inorganic hybrid structures. Already indicated was the use of a combination of structured inorganic QDs and organics in the field of photovoltaics,... 

The simple model contained the same inorganic and CO-CH4 oxidation schemes as the detailed model, taken from the MCMv3. The model was completed with heterogeneous loss and dry deposition terms, as described in the following section. The chemical mechanism employed in the simple model contains 75 gas-phase reactions, 9 heterogeneous and 8 deposition processes and is shown in Table 7. 

Chemical vapor deposition (CVD) is a process whereby a thin solid film is synthesized from the gaseous phase by a chemical reaction. It is this reactive process that distinguishes CVD from physical deposition processes, such as evaporation, sputtering, and sublimation.8 This process is well known and is used to generate inorganic thin films of high purity and quality as well as form polyimides by a step-polymerization process.9-11 Vapor deposition polymerization (VDP) is the method in which the chemical reaction in question is the polymerization of a reactive species generated in the gas phase by thermal (or radiative) activation. 

Most solutions used in electrodeposition of metals and alloys contain one or more inorganic or organic additives that have specific functions in the deposition process. These additives affect deposition and crystal-building processes as adsorbates at the surface of the cathode. Thus, in this chapter we first describe adsorption and the factors that determine adsorbate-surface interaction. There are two sets of factors that determine adsorption substrate and adsorbate factors. Substrate factors include electron density, d-band location, and the shape of substrate electronic orbitals. Adsorbate factors include electronegativity and the shape of adsorbate orbitals. 

During the 25-year history of atomic layer deposition several volatile compounds of different chemical nature have been studied for deposition processes. Typically these volatile compounds have been either metals, halides, nitrates or inorganic chelates and, more recently and still relatively rarely, true organometallic compounds. Systematic studies have typically been carried out using metal alkyls and cyclopentadienyl-type compounds. 

It is difficult to design a catalyst that can tolerate deposition of inorganic materials from organically bound sources. Such poison precursors should be removed or stabilized before the catalytic process as described earlier. Pores and pits on the catalyst surface may not trap solid catalyst poisons even if they are very fine. Again, poreless, very small particles are recommended. 

Simultaneous electrodeposition of ZnO and dye molecules from aqueous solution was reported as well to achieve a deeper penetration of the dye molecules into the inorganic film, as compared with those obtained by adsorption of dye molecules by the pre-assembled particles (mostly limited to the top layers). Yoshida and coworkers (2000) conducted such deposition process in an aqueous solution of Zn (N03)2 and eosin Y at 70°C and obtained ZnO/eosin Y dye-sensitized semiconductor films without high temperature annealing. The eosin Y molecules condensed at a sufficiently high concentration at both inside and on the surface of the film, which improved light absorption and IPCE. 

In this section, the fundamentals of chemical vapor deposition process (CVD) are briefly reviewed. For further details on this section, the reader is referred to excellent articles in literature. " Also the differences between polymer and other inorganic (for instance, metallic or ceramic materials) CVD processes are noted. 

Water-free inorganic solvents, such as ammonia, sulfur dioxide, and hydrazine, have been tested in terms of their suitability for electrolytic metal deposition. Liquid ammonia is used for a series of electrolytic metal deposition processes. Besides the low boiling point (- 33 °C) of this solvent its toxicity is disadvantageous. It has been reported that group lA and IIA metals, such as hthium, sodium, magnesium, and beryllium can be deposited from solutions based on ammonia as a solvent [45]. However, only thin or incoherent layers are thus produced [43, 44]. Because it is possible to form anions of molybdenum, lead, selenium, and tellmium in anunonia, these elements can be anodically deposited. Thus, deposition of the semiconductor lead selenide has also been achieved with ammonia as a solvent. 

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