Study of the Relationships Between Optical and Physical Properties for Nanostructure TiO 2 Thin Film

Pulsed Laser Deposition (PLD) technique was performed to deposit the pure Titanium oxide (TiO 2 ) nanoparticles on the glass substrate of temp. (100 - 400°C), using the doubled frequency of Nd: YAG laser wavelength of 532nm at (10) Hz rate, 10 nanosecond duration pulses and a constant laser energy 800 mJ. The optical measurements obtained by UV-Vis transmittance on deposited TiO 2 lms indicate the highest transparency in the visible wavelength region with an average transmittance of 80%. Estimated the relationship between the refractive index of TiO 2 thin lms with substrate temperature was n = 2.49 at 400 oC. Moreover, the calculated empirical relation between the energy gap and refractive index have similar to the work results.


Introduction
The most common material for generations as solar cell as nanostructure and high storage like nanobatteries selected according to durable, low-cost, and eco-friendly depends on the crystal structure features of the materials [1][2][3][4][5]. Titanium dioxide TiO 2 (Titania) is one of the most inexpensive, non-toxic, environmentally friendly and highly e cient semiconductor materials for many applications, including energy and environmental due to its strong oxidizing ability, high resistance to photochemical corrosion and high e ciency in decomposing pollutants that accumulate on surfaces Such as roofs of buildings or windows and surfaces of olfactory cells that affect their e ciency in the future. Nanotechnology, especially using nanostructures such as titanium, provides self-cleaning, transparent and highly conductive surfaces [1,2]. TiO 2 has three crystalline structures: brookite, anatase, and rutile [7]. In addition, particle size plays an important role in nanocrystals for the functioning of solar cells on TiO 2 .
The nanostructured surfaces provide a large surface area, which allows increasing the activity of high absorption of sunlight effects on the recombination dynamics e_/h +, adsorption amount of reaction types and adsorption rate [5][6]. TiO 2 , WO 3 and ZnO have received wide attention lately due to its unique and important properties, Making it great and wide applications in various elds. Suitable for use in photovoltaic elements, dielectrics, capacitors, or gates in photovoltage solar cells, microelectronic devices, biosensors, position sensor anti-re ection coatings, photonic crystal, and photo guides [3], metalbased devices, nano random lasers, and other similar applications [7][8][9][10][11]. Due to the particular qualities of TiO 2 lms with distinct crystal structure, orientation, or shape, controlling TiO 2 lms structure during growth is essential. TiO 2 lms have been created using a variety of techniques, including rotary coating, pulsed laser deposition, anodizing, oxygen plasma-assisted molecular beam ampli cation. PLD technology, for example, has been extensively utilized to build oxide lms because it enables the stoichiometry of the composite material to be achieved. Because the Si substrate is extensively utilized in semiconductor manifacturing, the development of TiO 2 lms on Si by PLD has piqued the curiosity of many researchers and industry professionals' curiosity. TiO 2 nanostructure is a one-of-a-kind material with a greater bandgap of 3.2 eV than rutile, with a bandgap of 3 eV. Because of their various features, such as high refractive index, broad bandgap, and resilience to physical and chemical effects [11,12], anatase and rutile bulk offer potential for use in sensing applications [5].
The electric symmetry in solar cells is used to transport electrons away from the proximity of their initial state, so preventing the relaxation of the cell's electrochemical properties. This results in an energy transfer to excited electrons from photons. The energy transferred to excited electrons increases potential difference, which may be utilized to drive current via an external circuit [13][14][15][16][17][18][19][20][21][22][23][24][25].
In the present study, the pure Titanium oxide (TiO 2 ) nanostructures on glass substrate were synthesized by pulsed laser deposition (PLD) at different temperatures was prepared. Also, evaluation of the relationship between optical and physical properties (optical constants, energy band gap, density and porosity, and refractive index,) of TiO 2 thin lms have been estimated.

Target Preparation
The substrate raises the substrate temperature to 600°C by heater 650W halogen lamp. The temperature was measured of the glass by a K-type thermocouple. The glass dimensions slide each 3 x 2 cm2 area and clean by alcohol using ultrasonic waves supply by co. Cerry PUL 125 device for 15 minutes to remove the contamination and dust from their surfaces. Figure 1 depicts an optical picture of a TiO2 lm that has been deposited on glass via PLD. Figure 1 is a schematic representation of the whole PLD system, including its components in gure 2.

Deposition of TiO2 Thin Film by PLD
The TiO2 lms were prepared under vacuum (10-3 Torr) at laser power of 800 mJ with different temperatures ranging from (100-400) °C by using two background gases, active gas and inert gas, in order to achieve the desired properties (O 2 &Ar). The con guration of the substrate mounts, and objective inside the chamber in relation to the laser beam is seen in Figure 2. Q-switching Nd:YAG SHG laser beam focused on the surface at a 45-degree angle to the surface of the target.

Characterization:
A Shimadzu dual-beam UV-VIS spectrophotometer (SP8001) was used to measure the optical properties of the TiO 2 lms were deposited on glass (transmittance and absorption) under various conditions. For each scan, a background correction was taken. The absorption coe cients for lms at different wavelengths can be calculated using the transmittance and absorption data. Which was used to de ne the bandgap, for example. The average thickness of the lms prepared using the optical method (laser light interference) was measured at about 150 nm.

Transmission and Absorption
According to the results of the UV-Vis spectrophotometer measurements of TiO2 lms optical transmittance on the glass formed by PLD, the transmittance is highly dependent on the temperature of the substrate, as seen in gure 3. uncovered that the transmittance is highly dependent on the temperature, as shown by the. It is average transmittance of the TiO2 lm exceeded 85 percent in the infrared region of the spectrum, which is where it was tested. This demonstrates that TiO2 lm may be used as the material of a solar cell after being recycled. When the temperature of the substrate is raised, it is seen that there is a modest reduction in the optical transmittance of all of the studied lms [26]. The optical absorption are located at (0.55,0.65,0.75,0.85) %, which corresponds to temperatures of (300,200,400, and 100) C, respectively, and are measured in per cent. Figure 4 Enhancement It can be seen from the transmission ndings that absorbance is highly dependent on the ambient temperature. Further investigation showed that the TiO2 absorbance coatings rise with rising substrate temperature, except when the temperature is 400 degrees Celsius or below.

Refractive Index (n):
From equation one and gure 5, the refractive index is measured by using equation 1. The shape of the curves with a wavelength of the refractive index as a function of wavelength of TiO 2 lms in gure 5 are the same curves as transmittance curves because both relations are increased with high temperatures, as gure 5. The index of refractive for TiO2 is rising with high temperatures. From gure conclude the refractive index at wavelength λ = 550 nm is equal ( 2.11, 2.88, 2.80 and 2.49) of the lms with substrate temperatures of (100, 200, 300 and 400 ) o C respectively, coincident results with reference [27].
According to [28], the enhanced results may contribute to the rise in packing change and density in the crystal structure, and the increase in results has been linked to the promotion of crystal growth.
The conclusion that various of the refractive index with a wavelength of the deposited TiO 2 / glass is explained in gure 5. TiO2 refractive index was found to be n = 2.49 at the λ = 550 nm at 400 o C agreement this result with reference [27] for TiO 2 lms by PLD technique.
The relation between the refractive index of TiO 2 lm with substrate temperature is illustrated as shown in gure 6.
To conclude the TiO 2 lm density (ρ) in the unit gram/cm 3 , can be used the following expression (ρ = (n f -0.91933) / 0.42751) .….. (2) where the n f is the refractive index of the TiO 2 , lms. This expression can conclude the relationship between substrate temperatures and TiO 2 lm density explained in Figure 7.
The density of the deposited TiO 2 lm is calculated at λ = 550 nm by the above expression and is equal to be ρ = 3.6881 g/cm 3 [27][28][29].

Conclusion
The current study has created crystalline TiO2 thin lms that have been effectively deposited onto a glass substrate using PLD. Because of their excellent transmittance, these thin lms have the potential to be used as windows in solar cell manufacturing. The optimal substrate temperature is equivalent to 400 degrees Celsius, and the optimum transmittance of TiO2 lm is around (80%) for thickness 150nm. The link between the temperature of the substrate and the refractive index of TiO2 thin lms was attempted to be calculated. Increasing the substrate temperature to 400 degrees Celsius results in a rise in refractive index to n = 2.49. Conclusion: At 400 degrees Celsius, the density of the formed TiO2 sheets is determined to be 3.6881 grammes per cubic centimetre, which is expected to be homogeneous.

Declarations
Acknowledgements: The authors would like to express their gratitude to the Applied Sciences Department and the (NAMR) Center at the Baghdad Institute of Technology for their nancial and technical assistance.

Ethics declarations:
Funding: Not applicable.
Con icts of Interest: The authors declare no con ict of interest.          Explain the density ρ verse of substrate temperature of TiO 2 thin lms.