Experimental Method

Aerosols with an average drop size of 1.5 |xm were generated by a (Sonaer Ultrasonic Model 241CST) nebulizer. The aerosol was carried through a conical nozzle into the growth chamber by SF6 gas. The schematic diagram of the laser-assisted spray pyrolysis system is shown in Fig. 2. The droplets and the SF6 gas interact with the focused 10.6 |im wavelength CO2 laser beam at the nozzle. The laser power of 3W used in the experiment was sufficient to increase the temperature of the gas and subsequently the droplets to about 350°C. Approximate value of the gas temperature was measured in a calibration experiment where a thermocouple was placed in front of the gas jet, just outside the laser beam-gas interaction volume. Oxygen was introduced into the growth chamber to promote oxidation of the depositing film. The flow rate and thus the speed of the aerosol into the chamber were controlled by gas flow meters. The pressure inside the chamber was about 700 Torr. Films were deposited on quartz or silicon substrates at a temperature of 300°C. The growth rate of the film depended on the concentration of the precursor. The average growth rate was about 50 nm/min.


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