Characterizations of sprayed TiO 2 and Cu doped TiO 2 thin films prepared by spray pyrolysis method

TiO 2 and TiO 2 :Cu films were deposited by spray pyrolysis (SP). X-ray diffraction reveals that deposited films have a polycrystalline structural. The AFM image of the surface reveals that roughness and root mean square affected by doping. Optical transmission of films was found to decrease from 94 % to 84 % with the as the doping percentage increase to 3. Optical bandgap (E g ) of TiO 2 thin film was 3.947eV. The bandgap is shifted to lower energies upon doping.


Experimental
TiO 2 and TiO 2 : Cu films were grown by SP.A solution contains 0.05 M of Ti (CH 3 COO) 2 •2H 2 O and 100 ml of deionized water DW was utilized to maintain the solution.0.1M of (Cu (NO 3 ) 2 .3H 2 O) resolved in DW as a dopant with volumetric percentage 1 and 3. Table 1 offers the optimal status.Gravimetric measurements were employed for estimating the film thickness, the results were 350± 35 nm.Transmittance spectra was obtained via Shimadzu spectrophotometer.XRD is utilized to gain film structure, whilst the AFM is gained to set films morphology.

Base temperature 450°C
Base to spout distance 29cm Spraying rate 5 mL/min Spraying time 8 S Pause interval 1 min

Topography surface analysis
Figures (3, 4 and 5) show the surface morphologies of the deposited films.It can be seen by AFM images that the films were noncompact morphology and non-cracks and offered a granular nanostructure with grain size ~ 100 nm.Surface average roughness (R a ) increased with Cu dopant concentration.R a and root mean square (R rms ) of intended films are offered in Table 3. R rms and R a are affected by doping.As can be seen that Cu content was more than its solubility in TiO 2 , so formation of CuO is possible, leading to higher roughness [37].

Optical properties analysis
Experimental measurements are commonly presented in relation to the percentage transmittance (T), as defined in Equation [38][39][40]: Where I o and I is the initial light intensity, the light intensity following its passage through the specimen.Fig. 6.Display the difference in transmittance T upon wavelength of undoped TiO 2 and TiO 2 : Cu thin films.It is seen from Fig. 6, that films prepared at 3% Cu doping show a transmission of greater than 80 % in Vis and NIR area.It is found that transmittance decreases with the increase of Cu due to an increment in amorphous nature of doped films [41].
The absorption coefficient (α) is gained from Eq. 5 [42][43][44]  = 2.303(  ⁄ ) (5) Fig. 7. display α that was slowly increased in the high wavelength and then sharply increased near the absorption edge.Hence, the α value depends on Cu doping and decreases as Cu content rises.The variation of absorption might be due to defect centers [45].The energy gap E g is obtained by Tauc's relation [46][47][48].
(ℎ) = �ℎ −   � 1/2 (6) Where A is a constant, h  is photon energy.E g was obtained from Fig. 8, Their value is 3.974 eV, which agrees with the reported values.For 1 % and 3% Cu doping the direct bandgap of the film was (3.947and 3.86) eV [49,50].So it is clear that for Cu doping affect bandgap value of TiO 2 thin films.These values were agreed with the reported values [51,52].

Fig. 8 .
Fig. 8. Direct band gaps of the deposited films films.

Table 2 .
S par of intended films.

Table 3 .
Average particle size, Ra and Rrms for pure and Cu doped TiO 2 .