Chemical solution deposition achievements

Wafers of YBCO thin films are prepared for microwave applications. Thermal coevaporation is used as the commercial deposition method. With this method substrates of about 20 x 20 cm can be coated at rates of 20-30 nm/min. A double-sided deposition can be achieved in two deposition steps. The sol-gel method as well as the chemical solution deposition method are promising with respect to lower production costs. Detailed information on applications is given in [2.81] (Table 4.2-26)... 

Downscaling of chemical solution deposition routes to deposit films of a thickness lower than 100 nm can be achieved in two ways either by reducing the concentration of the precursor or by deposition of a smaller number of layers (Figure 24.5). The film thickness increases linearly with the number of layers, if... 

Nonetheless, macroscopically addressable ultrathin film P(L)ZT capacitors have been prepared by chemical solution deposition [35]. The precursor solution is based on the inverted mixing order hybrid sol-gel route, using alkoxides and acetates in butanol, acetic acid, and methanol [36]. To achieve functional capacitors, film quality was the first important fector. Islanding was observed for individual layers deposited from highly dilute precursors (0.025 and 0.01 M) however, deposition of multilayers solves this problem. For example, an eightlayered film obtained with a 0.01 M precursor yields a thickness of 20nm, and results in 10% of functional electrodes (see Figure 24.6). 

Chemical solution deposition Low cost, large-area deposition, stoichiometry control, uniformity, tailoring the solution chemistry Multiple coatings, difficult to achieve epitaxiallity... 

Apart from the promise of low cost, molecnlar photovoltaic materials offer the distinct advantages of compatibility with flexible substrates and, uniquely, the potential to vary the colour of photovoltaic modules by altering the chemical structure. Although compatibility with flexible substrates is possible with some thin-fdm inorganic photovoltaic materials, it is more easily and naturally achieved via solution deposition of extremely thin layers. Tuning of colour via molecular structure is a property unique to molecular semiconductors and is of particular value in building integration, where colonr is of aesthetic importance, and in dual-function applications, snch as photovoltaic windows, where a semi-transparent structure is required. 

In polymer systems, the combination of properties of different components is achieved in a multitude of ways. For example, polymer layers of different functionalities are applied on a polymer substrate by spraying, casting, dip coating, or spreading with a doctor blade. Polymer coatings can be combined with layers of nonpolymeric materials applied from solutions or suspensions of the coating material or precursors thereof, or deposited via vapor phase using physical and chemical vapor deposition. 

The techniques of graft polymerization have been developed for liquid as well as gas phase. One of the polymerization techniques comprises impregnation of cellulose by a solution of conjugated monomers, followed by soaking in a relevant initiator. Chemical vapor deposition (CVD) of poly(3,4-ethylenedioxythiophene) is another, solvent-less technique, used for thin layer deposition of conjugated polymer on fibers [33]. Three CVD methods have been developed physical vaporization CVD [34, 35], plasma-enhanced CVD [36], and thermally initiated CVD [37, 38]. However, low conductivity is achieved when dopants are not used. 

The chemical bath deposition (CBD) process uses a controlled chemical reaction to achieve the deposition of a thin film by precipitation. CBD has been used to prepare ZnS films (by route C). In a typical experiment, substrates are immersed in an alkaline solution containing the chalcogenide source, the metal ion and added base. A chelating agent is also added, in order to control the hydrolysis of the metal ioa The process rehes on the slow release of ions into an alkaline solution in which the free metal ion is buffered at a low concentration. 

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