**4.9 Successive ionic layer adsorption and reaction (SILAR) method**

The SILAR technique (**Figure 14**) is a simple, less expensive, and less timeconsuming method for the deposition of binary semiconducting thin films. It is also applicable in the deposition of large-area thin films. V. L. Patil et al. [16] have succeeded to fabricate nanogranular TiO2 thin films by SILAR. In the initial step, glass substrate was immersed vertically in first beaker contains 2.5 ml TiCl3 (pH = 1)

**Figure 14.**

*Schematic of the successive ionic layer adsorption and reaction method.*

in 50 ml double distilled water for 10 s, so that a layer of titanium water complex [Ti(OH)3] was adsorbed on the substrate surface. Then the substrate was rinsed using double distilled water (DDW) for 5 s. Then, the substrate was immersed in third beaker contains 0.1 M NaOH solution with pH = 12 for 10 s in which the adsorbed Ti-species with NaOH forms into stable TiO2 on the substrate. Finally, the TiO2 and adsorbed hydroxide rinsed in the fourth beaker for 5 s. The nanogranular TiO2 thin films shows a good gas sensitivity towards NO2 gas at 50 ppm with good selectivity.
