**4.10 Chemical vapor deposition (CVD)**

The CVD technique (**Figure 15**) is a vacuum deposition method used to produce high quality, high-performance thin films. The substrate is exposed to one or more volatile precursors, which react and/or decompose on the substrate

**Figure 15.** *Schematic of the chemical vapor deposition method.*

**Figure 16.** *Schematic of the chemical bath deposition method.*

surface to produce the desired deposit. Frequently, volatile by-products are also produced, which are removed by gas flow through the reaction chamber. A. M. Alotaibi et al. [17] have elaborated TiO2 into SiO2 substrate by mixing 0.5 g of [Ti(OCH2CH2CH2CH3)4] in 20 mL of methanol. The solution was transferred to the reactor and the deposition has been made at 550°C for 40 min. After deposition, the reactor was cooled to room temperature by N2.

## **4.11 Chemical bath deposition (CBD)**

The CBD technique (**Figure 16**) is one of the cheapest methods to deposit stable, adherent, uniform, and hard thin films by immersing substrate in bath. S.V. Kite et al. [18] have succeed to deposed TiO2 thin films by simple chemical bath deposition method onto conducting and non-conducting glass substrates. The solution was prepared with ratio of 1: 2: 8 of titanium tetra isopropoxide (TTIP) as a precursor, propan-2-ol (C3H8O) and ethanol (EtOH) as solvents respectively. Firstly, the TTIP was mixed with C3H8O at constant stirring for 10 min then, EtOH was added. The obtained solution was kept at room temperature with constant stirring to get a clear and homogeneous solution. The substrate was dipped vertically inside the resulting chemical bath for 5 minutes and then substrates pulled out and allowed to dry the step was repeated for 2 to 3 times and finally, the films were rinsed with the distilled water, dried in the oven at 100°C for 2 h then annealed.
