Effect of Annealing on the Structural and Optical Properties of Nanostructured TiO2 Films Prepared By PLD. تأثير التلدين على الخواص التركيبية والبصرية لأغشية أوكسيد التيتانيوم (TiO2) ذات التراكيب النانوية المحضرة بتقنية ترسيب الليزر النبضي (PLD)

1. Republic of Iraq
Ministry of Higher Education and Scientific Research
University of Al-Mustansiriya
College of Education
A thesis submitted By
Sarmad Sabih Kaduory Al-Obaidi
Supervised by
Dr.Ali Ahmed Yousif Al-Shammari
(Assistant Professor)

3. Abstract
 Nanostructured TiO2 thin films are grown by pulsed laser
deposition (PLD) technique on glass substrates. TiO2 thin
films are then annealed at 400-600 °C in air for a period of 2
hours. Effect of annealing on the structural, morphological
and optical properties are studied.
 The results of the X-ray testing show that all nanostructures
tetragonal are polycrystalline, also these results show that
increasing in grain size with increasing of annealing
temperature. The XRD results also reveal that the deposited
thin film and annealed at 400 °C of TiO2 have anatase phase.
Thin films annealed at 500 °C and 600 °C have mixed
anatase and rutile phase.

4.  AFM measurements confirmed that the films grown by this
technique have good crystalline and homogeneous surface.
The Root Mean Square (RMS) value of thin films, surface
roughness increased with increasing annealing temperature.
 From UV-VIS spectrophotometer measurements, the optical
transmission results shows that the transmission over
than ~65% which decrease with the increasing of annealing
temperatures. The allowed indirect optical band gap of the
films was estimated to be in the range from 3.49 to 3.1 eV.
The allowed direct band gap was found to decrease from
3.74 to 3.55 eV with the increase of annealing temperature.
The refractive index of the films was found from 2.1-2.8 in
the range from 350nm to 900nm. The extinction coefficient,
real and imaginary parts of the dielectric constant increase
with annealing temperature.

5. Why titanium dioxide (TiO2)?
Non-toxic, inexpensive, highly photoactive, and easily
synthesized and handled.
 Highly photostable.
 High electro-chemical properties and high chemical stability.
 Wide band gap (Eg 3 eV).
 High refractive index - up to 2.7 (at wavelength of 600nm).
 High dielectric constant and hardness.

6. The Crystal Structure of TiO2
Anatase Rutile Brookite
form is tetragonal form is tetragonal form is orthorhombic
3.9 gm/cm3 4.23 gm/cm3 4.13 gm/cm3
a = b = 3.7710 Å and a = b = 4.5933 Å and a = 9.18 Å, b = 5.447 Å
c = 9.430 Å c = 2.9592 Å and c = 5.145 Å
n= 2.5612 n= 2.605 n= 2.5831

7. Applications of Nanostructured TiO2
 Hydrophilic properties for environmental applications, such
as air purification, sterilization, anti fogging, and self
cleaning.
 Biomedical applications .
 Photocatalysis.

8.  Dye-sensitized solar cells (DSSC).
 TiO2/polymer nanocomposites.
 Gas sensors.

9. Mechanism of Pulsed Laser Deposition
The mechanism of the PLD process can be expressed in three
steps :
 The interaction of the laser beam and target.
 Plasma Plume Formation.
 Nucleation and growth of thin films.

10. Pulsed laser deposition (PLD)
 The target material is
ablated by a Nd: YAG Nd: YAG
Laser.
 The ejected material
forms a plasma plume
and expands across to
the substrate where it is Halogen
deposited as a film.
Lamp
 The substrate is heated
by a halogen lamp.
 A background gas is
used to control the plume
stoichiometry and
dynamics.

11. Aim of the Work
 Initially, the series of samples has been prepared by PLD
technique at different technological conditions on glass
substrates.
 We study the preparation condition such as, substrate
temperature, oxygen pressure, energy laser influence during
deposition, as well as the concentration into the target on
the structure, morphology (Atomic Force Microscopy
(AFM)), and XRD. Also the optical properties for deposited
films.
 Then, we study the effect of annealing temperature on
structural and optical properties of TiO2 films.

12. Experimental
Work

13. Experimental work
Thin films
By PLD
Annealing films at
:400 oC, 500 oC&
600 oC
Thickness Structural Optical
of thin films Properties Properties
Optical T, A, α, Eg, n,
interferometer XRD & AFM kₒ,εr, εi & ζ
method

14. Target preparation of TiO2
(a) before (b) after
The target before and after being

15. Parameters Used
 Laser model: Q-switched Nd: YAG Laser Second Harmonic
Generation (SHG).
 Laser wavelength 532 nm.
 Energy density 0.4 J/cm2.
 Pulse duration 10 ns.
 Substrate temperature of 300 °C.
 Pressure of 10-2 mbar.

16. Pulsed Laser Deposition (PLD)

17. Nanostructured TiO2 Thin films

18. Characterization measurements
1. Thickness measurement

19. Characterization measurements
2. X-ray Diffraction (XRD)
Shimadzu 6000 made in Japan

20. Characterization measurements
3. Atomic Force Microscopy 4. Optical measurements
(AFM)

21. Results

22. X-ray Diffraction
• All the films were polycrystalline. • Good agreement with JCPD data card
• Films annealed at 500 °C and 600 °C have mixed anatase and rutile phase structure.

23. Table 1: Lattice constants and interpllanar spacing of TiO2 films.
Temperature 2θ Interplanar Lattice constant Å
(hkl) c/a
( oC) (degree) spacing, d Å a c
As-deposited 25.27 A(101) 3.15 3.3439 /
2.842
at 300 37.83 A(004) 2.37 / 9.5050
25.2 A(101) 3.53 3.8 /
400 37.81 A(004) 2.37 / 9.5098 3.502
48.1 A(200) 1.89 3.7803 /
25.17 A(101) 3.53 3.8 /
37.79 A(004) 2.38 / 9.5147
500 3.503
48.12 A(200) 1.89 3.7788 /
27.47 R(110) 3.24 4.5881 /
25.11 A(101) 3.54 3.8170 /
37.72 A(004) 2.38 / 9.5317
600 48 A(200) 1.89 3.7877 / 2.497
27.41 R(110) 3.25 4.5979 /
54.35 R(211) 1.68 / 2.9484

24. Full Width at Half Maximums (FWHM) decreases with increasing of annealing temperature
Grain size increase with increasing of annealing temperature
Values of texture coefficient decrease with increasing of annealing temperature
Table 2: The obtained result of the structural properties from XRD for TiO2 thin films.
Main
Temperature 2θ Stress Ss Strain δ
(hkl) FWHM Grain Texture Tc
( oC) (degree) (GPa) 10-3)
Size (nm)
As-deposited 25.27 A(101) 0.450 19.02
0.218 0.9354 1.813
at 300 37.83 A(004) 0.440 19.94
25.2 A(101) 0.421 20.19
400 37.81 A(004) 0.098 0.4225 0.412 21.27 1.126
48.1 A(200) 0.410 22.16
25.17 A(101) 0.352 24.16
37.79 A(004) 0.400 21.94
500 -0.019 0.084 1.154
48.12 A(200) 0.349 25.99
27.47 R(110) 0.334 25.59
25.11 A(101) 0.301 28.25
37.72 A(004) -0.435 1.8709 0.288 30.43
600 48 A(200) 0.338 26.88 0.952
27.41 R(110) 0.315 27.13
0.849 3.640
54.35 R(211) 0.293 31.85

25. Atomic Force Microscopy (AFM)

26. AFM
Table 3: Morphological characteristics
from AFM images for TiO2 thin film.
• The root mean square
Root Mean Square
Temperature (oC)
Roughness average
(RMS)
(RMS) and surface
(nm)
(nm)
roughness increased
As-deposited at
46.5 60.5
300 with increasing of
400 76.6 95
annealing temperature
500 84.3 105
600 88.6 114

27. Optical Properties
1. Optical Transmission (T)
Average transmittance of as-deposited TiO2 films is about 65% in the near-infrared region
For all the films transmittance decreases with increasing of annealing temperature

28. Optical Properties
2. Optical Absorption (A)

29. Optical Properties
3. Optical Absorption Coefficient (α)
The absorption coefficient (α) is increasing with the annealing temperature increasing

30. Optical Properties
4. Optical Energy Gap (Eg)

31. Optical Properties
4. Optical Energy Gap (Eg)
•
Table 4: Shows allowed direct band gap and
allowed indirect band gap for different From table 4. it can be
annealing temperatures of TiO2 thin films. observed that (Eg) is
decreasing with the
Allowed direct Allowed indirect
increasing of annealing
Temperature (oC) band band
gap (eV) gap (eV)
temperature for all
films.
As-deposited at 300 3.74 3.49
400 3.7 3.39
500 3.68 3.35
600 3.55 3.1

32. Optical Properties
5. The values of the refractive index 6. Extinction coefficient (Ko) increasing
(n) for the films of different with increasing of annealing
annealing temperatures vary in the temperature.
range from 2.1 to 2.8.

33. Optical Properties
7. The Dielectric Constants (Ԑ Ԑ
r, i)
• Real part and imaginary part increases when the annealing temperature
increasing.

34. Optical Properties
8. Optical Conductivity (σ)
• The optical conductivity of the films increases with increasing of annealing
temperature.

35. Conclusion
 The XRD results reveal that the deposited thin film and annealed at 400 C of TiO2
have a good nanocrystalline tetragonal anatase phase structure. Thin films annealed
at 500 C and 600 C have mixed anatase and rutile phase structure.
 The AFM results show the slow growth of crystallite sizes for the as-grown films and
annealed films from 400 to 600 C. The root mean square (RMS) is found to increase
from 50.5 to 114 nm as the annealing temperature is increased up to 600 C.
 The average transmittance (T) of deposited TiO2 films is about 65% in the near-
infrared region. The film annealed at 600 C has the least transmittance among the
films, therefore; the film is good to be detector within ultra-violet region range. The
optical absorption coefficient (α) of TiO2 films is about (α>104cm-1), thus absorption
coefficient has higher increase at wavelength (λ<400 nm). This converts to a large
probability that direct electronic transition will happen.

36. Conclusion
 Also optical properties of TiO2 thin films show that the films have allowed direct
transition and allowed indirect transition. Increasing of the annealing temperature
for all films cause a decrease in the optical band gap value and an increase in the
optical constants (refractive index (n), extinction coefficient (Ko), real (εr) and
imaginary (εi) parts of the dielectric constant).

37. Future Work
 Effect of annealing on the electrical properties of nanostructure TiO2
films prepared by PLD.
 Study of structural, optical and electrical properties of nanocrystalline
TiO2 films prepared by Chemical Spray Pyrolysis.
 Studying the effect of different preparation conditions on the
photolumincent efficiency and Scanning Electron Microscopy (SEM)
of the prepared samples.
 Study of nanostructured TiO2 thin films prepared by PLD for gas
sensor applications.

38. Publications
 “Annealing Effect on the growth nanostructured TiO2 thin films by
pulsed laser deposition (PLD),” Accepted at Journal of Eng. & Tech.,
University of Technology, No: 3291, (27/11/2012).
 “Synthesis of nanostructured TiO2 thin films by pulsed laser
deposition (PLD) and the effect of annealing temperature on structural
and morphological properties,” Accepted at Ibn Al-Haitham Jour. for
Pure and Appl. Sci., University of Baghdad, No: 3/1791, (9/12/2012).
 “Study of Annealing Effect on the Some Physical Properties of
Nanostructure TiO2 films prepared by PLD,” Journal of the college of
the education, Al-Mustansiriya University, (2012), (constraint of
bespreading).

39. T H ANK Y U
iO2
For Listening