Temperature control, spin coating

These films can be prepared by a variety of routes, only a few of which are mentioned here. The original references should be consulted for more practical details. Titanium dioxide is used as an illustrative example below. First, colloidal solutions are prepared, e.g., from titanium isopropoxide. The resultant sol is concentrated under vacuum at room temperature until its viscosity increases. Then it is spin-coated on to suitable supports (e.g., conducting glass) and fired in an oven. The firing temperature critically controls the morphology of the resultant film as discussed elsewhere [300-303]. Films up to several micrometers thick can be prepared by this simple version of the sol-gel technology [304]. Aerosol or spray pyrolysis is a somewhat related approach [305, 306]. 

Although the thickness of spun-coated films may be controlled by the concentration of the polymer in the solution, the spinning rate, and the spin-coating temperature, it is difficult to fabricate thick films and the thickness obviously cannot be monitored during deposition. In addition, no combinatorial fabrication methods have been developed for spun- coated PLEDs (see above). 

The influence of the microstructure on electrieal transport and nonstoichiometry was reported for Ce02, Zr02 Ca bulk [12, 15, 16] and YSZ and ScSZ nanocrystalline thin films [7, 13, 14]. Bulk specimens are usually prepared by pressure-densified processing (l.lGPa, 600°C) from powders of 5nm crystallite size, while nanocrystalline thin films were obtained by the lymeric precursor spin coating technique, which has been proved to be particularly useful for the formation of dense nanocrystalline films at temperatures about 1000°C lower than those required to prepare micrometersized specimens [26]. The uniform distribution of grain size as well as the ability to control the thickness and microstructure of the films prepared by the polymeric precursor method allow comprehensive structure/property studies to be made on nanocrystalline materials [7]. 

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