Deposition of (Iron Oxide) Thin Films by Spray Pyrolysis Method

The growth and characterization of iron oxide thin films by spray pyrolysis method using iron chloride hexahydrate. Iron oxide films deposited on well cleaned glass substrate at different substrate temperatures varying from 250 0 C to 500 0 C in air atmosphere. The characterization of iron oxides films was investigated for their optical and morphological properties by using spectroscopy and Scanning Electron Microscopy. The atomic absorption spectroscopy showed the existence of direct band gap energy nearly 2.18 eV with varying substrate temperature. Optical, structural and morphological observations were showed the film quality was getting better at 350 0 C substrate temperature, also grain sizes were cleared.


Introduction
Iron oxides are employed in various activities, including material science, soil science, industrial chemistry, medicine, chemistry, and corrosion science. This is due to the fascinating magnetic characteristics, crystal shapes, and different compositions of these materials. When it comes to iron, there are three types of iron oxides that may be found in the Earth's crust: hematite (α-Fe2O3), maghemite (γ-Fe2O3) and magnetite (Fe3O4) [1]. Iron oxides are often used in cosmetics to create wall murals and aesthetic adornment for colours [2]. As a result of advances in nanotechnology, a wide range of new applications have emerged [3]. These particles have acceptable magnetic characteristics, minimal cytotoxicity, biodegradability, biocompatibility, chemical stability, decreased particle size, and high surface area [4].
Thermal barriers, corrosion prevention, and optical applications all benefit from the versatility and low cost of thin films. Spray pyrolysis, chemical vapor deposition, chemical bath deposition, pulsed laser deposition, and electron beam deposition are some of the deposition methods available. For thin films, spray pyrolysis is the most straightforward method. Because it's a coating procedure that yields a variety of useful goods, the instrument is simple to use and inexpensive to purchase. Pyrolysis of the substrates results in nearly oxide layers on the substrate surface that are excellently homogenous. The component of the precursor solution is the single factor that determines the attention combination of the deposited layers [5].
Spray pyrolysis is a process for creating thin films, coatings, and dust using high temperatures and high pressures. If you compare spray pyrolysis to other techniques that involve costly materials and laborious processes, spray pyrolysis is the most advantageous option. It allows for the easy production of films using everyday items. The use of porous films and massive quantities of substrates or chemicals is not necessary [6].

Material and Methods
Traditional and versatile spraying methods may be used to produce metal oxide films, and the substrate temperature is necessary.

Film preparation
A 0.01 molar of FeCl3.6H2O was used to prepare the thin films of iron oxides α-Fe2O3, in 50 ml of distilled water. The glass substrates were preheated and then later sprayed for 10s with the obtained clear yellow solution. Prior to that, the solution went through a 0.7 mm nozzle diameter of a pneumatic nebulizer. In order to prevent the glass substrates from excessive cooling, attention was made to ensure that a 5-minutes time span was allocated between each spraying process. The film preparation process to determine the effects of changes in the substrate temperature from 250, 300, 350, 400, 450 to 500 ᵒ C. If the thin-film production is successful, the substrates need to be well cleaned and prepared before to application. The cleaning process ensures that the substrates do not have any contaminants and remain clean. A UV/VIS spectrophotometer is used to calculate the thin film's optical absorption of spray pyrolysis on a glass substrate which is performed at a wavelength ranging between 300 nm and 900 nm. This involves measuring the intensity and dilution of the mean between the source and the detector

Structural, Compositional and Optical Analysis of Iron Oxide Films
XRD is supported by Bragg's Law. Mathematically, Bragg's Law is as follows:

nλ=2dsinθ
(1) d is the distance between crystalline planes, θ is the Bragg angle from which the X-ray diffracted, and λ is the wavelength of the X-ray. Crystal lattice spacing affects the angle at which incident X-rays are diffracted. Peak Positions in the diffraction pattern provide information on the size and shape of the unit cell, whereas Peak Intensities provide information on the density of electrons inside the unit cell, i.e. the locations of atoms. It is possible to determine the pattern by looking at the Miller indices (hkl) for each peak. Inter-planar spacing dhkl may be estimated using Bragg's relation from XRD patterns for (hkl) plane.
In order to establish the preferred crystal orientation of the sprayed iron oxide coatings, XRD analysis was used. Comparing 2 θ values and intensities helped identify the crystal phases. It is clear from the diffraction pattern that the films' crystal structure is polycrystalline.
Experiments using FeCl3.6H2O yielded the following results: In this case, d is the lattice constant, and hkl is a miller index. The lattice constant 'a' is confirmed to be the same orientation in (320) and (410) based on the results of these calculations. Fe3O4 is the most common source of γ-Fe2O3.  (Fig.1) shows that the crystallinity level changes with substrate temperature; the best crystallinity was observed at 350 oC. According to this, the peak height of the film sprayed at substrate temperature 300 oC is the lowest showed diminishing crystallinity, which means that the crystalline defects are greatly increased for this substrate temperature. Decreasing Full width half maximum and increasing peak height indicate improving crystallinity level. For all sprayed iron oxides, the preferred direction trend is (320 peaks are not significantly affected when the substrate temperature changes, but peak intensities are. Up to a substrate temperature of 350 oC, peak intensities increase. It was proof that crystallinity was rising. The iron oxides film was sprayed at 350 oC, and the XRD pattern was (Fig 2). Although the crystallographic orientation cannot be determined by the XRD patterns, they can be used to determine the crystallite size (D), grain size, dislocation density, and strain.
The crystallite sizes of each sample were estimated by using the Debye-Scherrer formula; = . (2) The microstrain (Ɛ) value of the sprayed iron oxide films was calculated from equation (3): Where β is the full width at half maximum (FWHM) of the diffraction peaks.  increases are attributable to high crystallinity and shrinking grain boundaries. The rise in crystallinity is found to be directly proportional to the increase in grain size, the increase in diffraction peak intensities, and the narrowness of the full width half maximum.     Figure 6: Variation of ( ℎ ) 2 with photon energy ℎ for α-Fe2O3 films at substrate temperature 350 0 C for FeCl3.6H2O.
The spray pyrolysis process is used to grow and characterize iron oxide layers. Optical and structural measurements revealed that the film quality was improving at 350 o C substrate temperature. nebulizer with an atomizing frequency of 1.67 MHz was used to atomize the chemical solution into the stream of fine droplets. From the intake side, the chloride precursor solution was poured into the vessel. The vibration of the transducer produced the aerosol. The hot substrate was applied with the nebulized spray that rises in the column. However, as previously said, we disagreed with our findings concerning XRD pattern outcomes; our preferred temperature is The XRD patterns of iron oxide thin films produced by ultrasonic spray pyrolysis on quartz substrate at various deposition temperatures are shown in the results. The film formed on quartz at Ts =400 o C was found to be amorphous, but the film deposited at Ts =500 o C was found to be crystalline. The results reveal that increasing the substrate temperature promotes the diffusion of atoms absorbed on the substrate and speeds the migration of atoms to more energyefficient places, resulting in increased crystallinity.
(8) demonstrated the energy band gap and optical transmittance spectra of Fe2O3 thin films in the preceding study (8). We used the Tauc's connection to determine the direct band gap. This study found similar results, and the optical band gap can be calculated by projecting the linear region to the energy axis. α -Fe2O3 films or nanoparticles can be generated by direct or indirect transition, as well as several other described methods (4, 9). The obtained direct band gap values in this study were quite close to the value provided by (10). And had a greater band gap than the film deposited at 500 • C, which could be attributable to an increase in crystallinity with increasing substrate temperature, which leads to fewer defects and a better crystal structure.
Furthermore, as previously reported by, the predicted band gap for the Fe2O3 nanopowder was found to be about 2.5 eV. (11).
The present study used a chemical spray approach to deposit nickel-doped zinc oxide thin films In another study by (13), they found quality crystal rather than we reported the electrochemical supercapacitor performance Hematite α-Fe2O3 thin films prepared by spray pyrolysis from a non-aqueous medium.
(12) investigated the crystalline quality of Fe2O3 thin films spray deposited at various temperatures using the same procedure as we did; X-ray diffraction (XRD) analysis was performed, and the findings are reported.  substances like γ-Fe2O3, Fe3O4, or organic impurities were discovered. The peak (104) intensity was observed to be substrate temperature-dependent. Additionally, it has been found that the peak (104) intensity increases as substrate temperature rises, reaches a maximum value at 350 °C, and then falls. An improvement in the crystallinity of the Fe2O3 thin films is indicated by the increase in peak (104) intensity.

Conclusions
In this work, iron oxide thin films are deposited by spray pyrolysis method using ferrum compounds such as FeCl3.6H2O. The summary of this study is the investigation of the role of ferrum compounds on the structural, optical and morphological properties of iron oxide films.
The sprayed solution was prepared by FeCl3.6H2O (0.1M) and distilled water. Iron oxide films deposited on well cleaned glass substrate at different substrate temperatures varying from 250 o C to 500 o C in air atmosphere. Also, we couldn't cover the films we did with FeCl3.4H2O, so we haven't conducted any of these techniques by XRD, SEM, EDX results show that when the temperature it reaches 350 o C the film will be clear and it greater available in this temperature for the FeCl3.6H2O, we have band gap 2.18 eV. We have found that Fe2O3 thin film exhibit a polycrystalline having (320), (410), (200) and (444) plans of high peak intensities.