Document Type : Research Paper
Authors
Department of Physics, College of Science, University of Diyala, Iraq
Abstract
Keywords
INTRODUCTION
The manganese oxide Mn3O4 has a normal structure with a tetragonal distortion along the C-axis, making it one of the most stable thins in the family. Mn3O4 possesses significant electrical and magnetic characteristics, such as metal-insulator transition materials and huge magneto resistance [1].The metal oxides are used at various technological applications such as solar cells, energy harvesting applications, catalysis, and sensors, and they are very attractive to the scientists because of their promising properties in industry [2],Among the transition metal oxides, manganese exhibits many oxidation states and therefore forms different oxides (MnO, MnO2, Mn2O3, Mn3O4 and Mn5O8) [3] ,The magnetic and transport properties of these materials are closely related to their structures, crystal quality and chemical stoichiometry [4],Manganese oxide nanoparticles with various shapes and exceptional qualities have been synthesized via several innovative and novel methods [5], chemical vapor deposition [6],sol–gel [7],thermal combustion [8],pulsed laser deposition (PLD) technique [9] ,spray pyrolysis technique [10] ,Because to its high uniformity of deposit, low cost, ease of use, and low deposition temperature, spray pyrolysis was one of the most economical methods for creating manganese oxide coatings. [11]. process begins with the preparation of a precursor solution that contains the desired chemical components for the film. This solution is typically prepared by dissolving metal salts, organic compounds, or other precursors in a suitable solvent. The precursor solution is then atomized into fine droplets using a spray nozzle The current study aims to prepare Nano scale films of pure manganese tetragonal oxide doped with nickel oxide to study the effect of The effects of nickel oxide doping on the produced films’ structural, optical and electrical characteristics Their possible usage is the reason behind this in the field of solar cell manufacturing and sensors
MATERIALS AND METHODS
Chemical spray pyrolysis (CSP) method was employed to create thin films of manganese oxide (Mn3O4) doped with nickel oxide (NiO). German-made glass plates from Los Las Company were prepared. The plates were cut into (2.5 × 2.5) cm dimensions and rinsed with distilled water for 4 minutes in an ultrasonic device. After that, they were sterilized with acetone for 4 minutes and then again with distilled water. Finally, they were dried with a special fabric to remove the remaining suspended particles. The oxide solution was prepared by mixing manganese chloride (MnCl2.4H2O) weighing 1.979 g in 100 ml of distilled water. Then, it was placed on a magnetic stirrer for 10 minutes. Then, it was filtered using filter paper. After that, it was deposited using a spray system on the glass plates at a temperature of 350 °C. The pure oxide films were doped with nickel oxide at ratios of (0,1, 3, 5, 7)%. Measurements have been made using a (Shimadzu XRD-6000 Powder) X-ray diffract meter with (Cu Kα) radiation within the available wavelength and range at the Technological University,and To study the effect of manganese oxide(Mn3O4) doping on the (NiO) films and compare the results with established values in standard cards, The spectra of transmittance and absorbance were measured using a (Shimadzu UV-Visible 1900 Spectrophotometer) Equipped with the BPC laboratory located in Baghdad Governorate, Adhamiya area.
RESULTS AND DISCUSSION
X-ray Diffraction (XRD)
The results of the diagnosis using the X-ray diffraction technique for the undoped manganese oxide Mn3O4 films and those doped with nickel oxide with impurity rates of (0, 1, 3, 5, 7)% showed that they have a polycrystalline structure of the tetragonal type, and The films’ X-ray diffraction patterns are displayed in Fig. 1. All prepared, by analyzing these patterns, the locations of the peaks were known We notice the appearance of levels (101,110,103,211,004,303) The prevailing trend of growth is 101 for all films, and there is no change in the prevailing trend with increasing percentages of doping with nickel oxide. It was also found that the outcomes are Most of the time, it matches the typical card with the serial no.(00-001-1127) It has been shown that doping with nickel oxide led to a change in the intensity of the peaks, especially in the dominant direction (101) in the X-ray diffraction pattern compared to the pure Mn3O4 film The intensity of the peak decreases and continues to decrease with increasing doping rates, and this decrease is accompanied by an increase in the width of the middle of the peak (FWHM) This means that the degree of crystallization of the films decreases with increasing doping rates. The decrease in the rate of crystallization can be described. because of the kind of link that is created between the film material’s atoms, or because of the specific heat of the solid body, or resulting from the difference in the melting point in the material’s constituent parts Thus, this decrease leads to the membrane material getting closer to the nano materials [12],[13] We notice that ions (NiO) were introduced into the manganese lattice (Mn3O4), the width of the middle of the peak increased and the intensity decreased after doping (Mn3O4) due to the added nickel ions, which led to a reduction in the crystalline growth of the film.This is because the ionic diameter of the nickel is (0.69 A0) [14] smaller than the ionic diameter of manganese (0.83A0) [15].
Results of Atomic Force Microscopy Tests (AFM)
The results (AFM) for each prepared film are depicted in Figs. 2a-e. The thin film’s topography (Mn3O4) prepared in different proportion (1,3,5,7) % was studied using an atomic force microscope (AFM), which has a high ability to photograph and analyze the surface of thin films and also gives very accurate information about the average particle size, method of their distribution, and surface roughness values We note that the root mean square roughness (RMS) of pure (Mn3O4) and nickel-doped (NiO) As doping ratios increase, films shrink. The reason for this is that the films were formed with nanoparticles, where the particle size decreases with increasing doping ratios. This result is consistent with the difference in particle size obtained from XRD [16].
Optical properties
From the Fig. 3 we notice that the transmittance increases with increasing wavelength for all prepared films and continues to increase until it stabilizes at wavelengths (1100 nm). We notice that the transmittance increases with increasing doping percentages and its highest value is at 3% Then the transmitted values began to decrease with increasing rates of doping with nickel oxide, and its value was lower in the pure state. The increase in transmitted values causes manganese oxide’s structure to alter due to the addition of nickel electrons, which improves the quality of the crystals and crystal homogeneity, and the reduction in transmittance as nickel levels rise concentration is due to absorption. Free carrier and ratios in granular boundaries [17] The reason for the increase in the transmittance spectrum with increasing wavelength is that the incident photons do not have sufficient energy to excite the material’s electrons and thus they are transmitted. Likewise, films have a high transmittance that indicates photon absorption, and this often occurs by moving from one beam to another, and this is consistent with the results of the researcher [18]
From Fig. 4 we notice that absorbance has an opposite behavior to transmittance, as absorbance is large at short wavelengths, and as the wavelength increases, the absorbance decreases, being its lowest value at the wavelength (1100 nm) The absorbance decreases with increasing doping rates, and its lowest value is at 3% and its highest value is in the pure state. The cause is that the incident photon’s energy is less than the amount of the optical energy gap of the semiconductor. Therefore, the photon cannot excite the electron and move it from the band of valence to the band of conduction,and This agrees with B.Sahin at.el [19]. We also note that there is a difference in the absorbance values of all films at each wavelength due to the homogeneity, the nature of the structure, and the difference in local levels within the energy gap due to crystalline defects, This is consistent with the researcher’s results [20]
It is the ability of a material to absorb light. The absorption coefficient (α) for manganese oxide films doped with nickel oxide was calculated using the Eq. 1. Fig. 5 shows the absorption coefficient for all prepared thin films as a function of the energy of the incident photon. We notice from the results that the absorption coefficient values increase slowly at low photon energies and gradually increase more quickly with increasing incoming photon energies until they approach α ≥ 10-4 cm-1 from the basic absorption edge region. The absorption coefficient values continue to increase For the highest incident photon energies that exceed Eph < Eg for all prepared films, this leads to the possibility of allowing electronic transitions between the valence and conduction bands at that energy. High values of the absorption coefficient, which are greater than 10-4 cm-1,indicate the possibility of a permissible direct transmission, while values less than 10-4 cm-1 indicate an impermissible direct transmission [21]. The behavior of the absorption coefficient changes with doping ratios and moves to the absorption edge towards higher photon energies, which leads to an increase in the energy gap values The reason for this is due to the occupation of substitution or replacement sites in the manganese oxide lattice by nickel [22].
The crystal structure of the prepared films is the basis for determining the optical energy gap values. Using the Eq. 2 at the value of the constant r = 1/2, the values of the optical energy gap for direct transitions allowed for all prepared films were calculated. Through the graphic relationship (αhν)2 and photon energy hν,a straight line was drawn after the basic absorption edge to intersect the axis of the incident photon energy at the point (αhν)2 = 0 Thus, the intersection point represents the value of the optical energy gap of the prepared films. Fig. 6 shows the energy gap values within the range (2.65 - 2.95) eVfor the prepared films. We notice that the energy gap values change with the doping ratios of the NiO concentration, as we notice an increase in the energy gap values. The reason is that increasing the doping leads to the formation of local levels within the energy gap and near the conduction band, and thus the basic absorption edge moves to higher energy levels, and as a result, the electrons in the valence band will be displaced to a higher energy to cross these levels [23,24].
Fig. 7 shows the refractive index values as a function of the incident photon energy. For all prepared films, the refractive index values were calculated using the Eq. 3 We conclude that the refractive index values increase with increasing doping ratios for the prepared films and with increasing photon energy, and then decrease towards higher photon energy. Reflectivity and an increase in absorption coefficient values as a result of direct electronic transfer are the causes of this decline. As the concentration of a substance rises, the refractive index falls (NiO) from 1 % to 3 %,where (NiO) acts as a mediator, i.e. participates in the components of the lattice. Then the refractive index increases with an increase in the concentration of (NiO) from 3 % to 7 %,where nickel acts as a catalyst in the lattice [25].
The extinction coefficient is plotted against the incident photon’s energy in Fig. 8 for all prepared films from the Eq. 4. The extinction coefficient was computed (Ko). The figures show the similarity between the extinction coefficient curves with the absorption coefficient curves, where based on the findings, the extinction coefficient was computed.. Absorption coefficient. We note that the maximum the high photon locations are where the extinction coefficient values are found, after which the extinction coefficient values decrease We notice a decrease in the extinction coefficient because the process of doping with nickel oxide leads to the donor level creation inside the energy gap, and these levels will lead to a decrease in the extinction coefficient [26,27]
CONCLUSION
The results of X-ray diffraction measurement demonstrated that the thin manganese oxide films doped with nickel oxide and prepared by chemical spray pyrolysis method have a tetragonal and polycrystalline structure and the dominant trend is (101). Through diagnosis with an atomic force microscope (AFM), it was shown that all the prepared films had a nanostructure and that root mean square values and surface roughness would both decline. It was observed through optical examinations that the transmittance of the films will rise in tandem with rising doping levels,while the absorbance decreases, and the optical energy gap, absorption coefficient, and refractive index increase with increasing photon energy. We see that when photon energy increases, the extinction coefficient values drop.
CONFLICT OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this manuscript.
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