Influence of gamma radiation on structural and optical properties of Fe 2 O 3 thin films prepared by chemical spray technique

. The purpose of this research is studying the effect of gamma radiation on the structural and optical properties of iron oxide Fe 2 O 3 thin films. The technique used for prepared the thin films was thermal chemical spray. The effect of Co 60 irradiation on the structural and optical properties of the thin films was investigated. The crystal structure were studied by XRD pattern. The surface tested from crack and defect was looke by used microscope image. The absorption and transmission spectra by used UV/VIS for the as deposited and irradiated thin films. The energy gap and absorption coefficient were studied. It's found that the energy gap for the un-irradiated sample was 2.3 eV and than after exposed to gamma radiation at (25,50,75,100 and 125) Gy the energy gap decreased and above 5o Gy was increasing. The absorption coefficient increased until (12x10 4 ) cm -1 at 50 Gy and than was decreasing to (2x10 4 ) cm -1 at 125 Gy. The effect of radiation on the structural and optical properties was positive at the levels of irradiation used.


INTRODUCTION
The researchers has been interest in metal oxides as suitable materials for solar cell, photoelectron and another applications in electrical advices field [1]. The study effect of radiation on the properties of thin film consider an important studies on the metal oxide. The radiation was used for this purpose such as X-ray, gamma ray and Beta particles [2]. The study optical properties of Fe 2 O 3 thin films are important for characteristics to evaluation its optical and photo catalytic activity, which possible indicated to use the thin films in suitable application [3]. In the recent past the effect gamma radiation on the optical, electrical and micro structural of some metal oxide thin films has been done [2,4,5,6,7].
In this work Fe 2 O 3 thin films had been prepared by used chemical spray paralysis, which is consider one of the important methods to prepared thin films [8,9]. And then study the optical and structural properties of Fe 2 O 3 thin films before and after irradiation by gamma rays at high exposures level.

EXPERIMENTAL DETAIL
Ferric oxide Fe 2 O 3 thin films were prepared by chemical spray paralysis techniques and deposited on glass substrates at dimensions (2.5x2.5x)cm 2 . The main components set up of the system is showed in the schematic diagram of figure (1). The prepared chemical solutions is pumped through the metal nozzle at rate flow from (1 to 2) ml/minute, the gas pressure to carrier chemical solution was nitrogen gas.   The substrate before deposed the thin film was cleaned by dipping in distilled water and then are ultrasonically cleaned in methanol for 10 min and then soaked in distilled water. Finally dried and polished with smooth paper. After preparation of samples and sure they without defects and cracks by used optical microscope and then samples had been exposed to source of gamma radiation type Co-60 at rate dose 8 Gy/min in the room temperature, wherein the average of doses was (25,50,75,100 and 125) Gy. The optical transmission spectra of Fe 2 O 3 thin films were obtained in the ultraviolet and visible region by using (UV-1650Pc) shimadzu software 1700-1650, UV-visible recording spectra photometer), (Philips), Japanese company in wavelength range (200-1100 nm).

RESULTS AND DISCUSSIONS
Surface image of the all samples were shown in figure (2). For all samples the image is shown that surface was free defect crack and homogeneous. Figure (3) shown the X-ray diffraction of all samples irradiated, it's clear that the results of the all films of Fe 2 O 3 irradiated have polycrystalline structure, also its found that the irradiation with gamma radiation led to high diffraction peaks and increased in the intensity, which is indicated the Fe 2 O 3 thin films become more polycrystalline, and that due to the effect of radiation on the lattice crystal, which is led to increase grained regularity and decrease the grain size. That is mean the gamma radiation work as well as annealing treatment, which is causing broken the bond of the irregular arrangements and turning the thin films to more arrange systematic [2]. This is increasing with increased of radiation dose.

Fig (3): X-ray diffraction pattern of Fe 2 O 3 thin films at different levels of gamma radiation.
The optical absorption and transmission spectra for all samples with and without irradiation shown in figure (4,5) respectively. Clearly the exposure to gamma radiation causes change in the shape of optical absorption consequently led to change in optical transmission and reflections spectra. The values of the absorption coefficient in figure (6) shown as exponential and dependence on the photon energy which is indicated to change in absorption coefficient with the exposure to the gamma radiation, wherein the absorption coefficient is increasing until 50 Gy and then decreased with increasing the radiation exposure. This is changed in the optical absorption, transmission and absorption coefficient is due to increase the energy width of band tails of the localized states, which can be attributed to the induced effects of gamma-ray [2].

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ILCPA Volume 63   (2). Clearly the optical band gap is decreasing from 2.3 eV to 1.7 eV for the radiation dose 50 Gy. This decrease in optical band gap belong the increase in the energy width of the band tails of localized state. During irradiation the defect are created within the thin films and at the same time the defect also annihilated, this creation and annihilated at low dose radiation the annihilated is more from creation of defects, therefore the optical bandgap was decreasing but above 50 Gy the creation of defects become more than annihilated [2], so the optical bandgap is increasing with high rate dose.

CONCLUSION
The optical and structural propert were studied for Fe 2 O 3 thin films which prepared by chemical spray technique as deposited and exposure to various dose from gamma radiation. The results shown that the optical band gap was decreasing with increase the dose rate until appointee level of gamma radiation and then increasing with increasing the dose rate, the structure of Fe 2 O 3 enhanced with increase of gamma dose, this indicate that the high dose of radiation negative effect on the optical proportions of the Fe 2 O 3 thin films.