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Metal oxide thin films used in different applications are mostly ruled by their properties. Among these, Copper oxide (CuO) films have been investigated as a promising material for many applications. Copper oxide is an important P-type transition metal-semiconductor and it is suitable material for terrestrial applications, because of its nontoxic and abundantly available semiconducting material which can be easily synthesized using low cost methods. CuO has a monoclinic structure and direct band gap value of 1.3-2.1eV. CuO are of interest in various technological areas such as solar photovoltaic, photodetectors, gas sensors, bio-sensors, super capacitors and energetic materials.
CuO thin films can be prepared by various liquid and vapour phase methods such as chemical vapour deposition, electrodeposition, SILAR, sol-gel, sputtering, spray pyrolysis, thermal oxidation and nebulizer spray pyrolysis etc., Of these jet spray prolysis have several advantages such as high purity, excellent control of uniformity. To make this study cost effective, a simple inexpensive jet nebulizer spray technique is employed for preparing CuO thin films.
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Various studies of deposition parameters effect on CuO films properties have been investigated such as substrate temperature, molarity, precursor solution and doping. However, the influence of volume of the solution on the properties of CuO thin films have been reported very few. The main purpose of this work is to synthesize nano-structured CuO thin films by acting on different volume of the prepared solution.
A Jet- nebulizer spray pyrolysis system consists of a nebulizer unit, hot plate with heater, temperature controller, compressor unit and ‘L” shaped glass tube.
The CuO thin films were deposited on ultrasonic cleaned glass substrate by Jet- nebulizer spray pyrolysis method. Cleaning of the substrate plays vital role in the film deposition. At first the glass substrates rinsed in a mixed solution of nitric acid and distilled water for 15 min. Then it was well cleaned through running water. Secondly, the substrates were sunk in an acetone bath following ultrasonic cleaning for 30 min. Finally substrates were dried
CuO thin films were sprayed on glass substrate using three volumes of the prepared solution 3ml, 4ml and 5ml. In this work, copper (II) nitrate [Cu (NO3)2. 3H2O] was dissolved in double distilled water. The prepared solution was stirred using a magnetic stirrer for 1 hour. The substrate temperature was managed at 4500C and it was controlled by temperature controller. The distance between the glass tube nozzle and the substrate fixed at 5cm. The airflow rate was controlled and sprayed on a heated substrate by carrier gas pressure. The heated substrate was maintained at 4500C. After deposition, all the films were left on the top of hot plate to cool naturally for room temperature.
The Structural properties of CuO thin films were obtained using X-ray diffraction (XRD) (Shimadzu, Japan) in the 2θ range from 20o to 70o. The average crystallite size was calculated by Scherrer’s equation. The optical characterizations of the films were studied using UV-Vis spectrometer (Jasco, Japan) in the wavelength range 300-1100nm. The variation in surface morphology was analyzed using a field-emission scanning electron microscope (FESEM). The presence of elements in the film was confirmed by the energy dispersive analysis from X-ray spectroscopy (EDAX). The DC electrical properties of the CuO thin films were studied using Keithley electrometer (6517-B).
The impact of volume on the structural properties of prepared CuO thin films by varying volume from 3ml to 5ml. The obtained XRD patterns of the films for different volume reveals that the prepared CuO thin films are monoclinic crystal phase in nature. The primary peaks of 2θ value 32.60, 35.50, 38.70 and 52.70 corresponding to (110), ( ), ( ) and (020) planes were observed for all the films. The analysed diffraction peaks confirmed with the values available in the JCPDS card No. 89-5899 for monoclinic crystal phase of CuO thin films.
In favour to strengthen the structural analysis, the average crystallite size was evaluated from full width half maximum (FWHM) value by using Scherrer’s formula.
Where the full width is half maximum, is the Bragg angle, is the X-rays wavelength, D is the evaluated crystallite size. The average crystallite size of the different films varies from 18 to 23 nm prepared by jet nebulizer spray pyrolysis method using different volumes are depicted in table.
As a result, the crystallite sizes are increased for 3ml and 5ml then it decreased for 4ml. It clearly observed that the volume of the solution play a vital role in the controlling of crystallite size. The micro-strain variations and the average crystallite size are shown in the fig.3. G. Korotcenkov reported that the decrease in strain indicates the decrease in lattice imperfection and thus the formation of high quality thin films. The result revealed that the 4ml of volume provide a crystalline nature in the present study.
Table 1. Structural parameters of CuO thin films
Volume
2θ (degree)
FWHM
(Degree)
Crystallite size
(D) (nm)
Average thickness
(nm) Micro strain
(Ԑ)
Dislocation density
(δ)
(×1015 lines m-2)
3ml 38.7547 0.43660 19 105 0.0017 2.68404
4ml 38.7277 0.45180 18 109 0.0018 2.87466
5ml 38.7527 0.36610 23 120 0.0015 1.88724
The optical transmittance studies of thin films reveals the amount of energy transmitted by the material sprayed on the film. The transmittance of CuO thin films prepared by jet nebulizer spray pyrolysis with different volumes. The optical transmittance spectra were analysed for CuO thin films in 300-1200nm wavelength range using UV- visible spectrophotometer. All the prepared films showed transparency from 20% to 685%. The highest transmittance of CuO thin film was observed at lowest volume 3ml. As the incident wavelength increases from 400-1200nm, the optical transmittance was found to decrease with an increase in volume. As a result it is well know that the optical transmittance depends on the volume of the solution which strongly influences on the optical properties of the films.
The absorption of CuO thin films deposited with different volume as shown in fig.5. It is revealed that CuO thin film absorption was high in the ultra violet region and low in the visible region. The absorption plot clearly showed that when the volume increases the absorbance of the CuO thin films were also increased. The highest absorbance value was observed at highest volume 5ml.
The band gap of the CuO thin films was calculated from the absorption values of the different volumes. As CuO is a direct band gap material, the absorption co efficient can be related to the band gap energy (Eg) through tauc’s relationship by using the following formul is the absorption coefficient which can be calculated using below formula =2.303 A/t (5).
Where A is the absorbance value and t is the thickness of the CuO films. The relationship between and showed in the fig.6. The value of optical energy band gap (Eg) is estimated from the value of intercept of the straight line at =0 by plotting against. According to tauc plot the value of the energy band gap for CuO thin films was calculated 2.15eV, 1.93eV and 1.85eV for 3ml, 4ml and 5ml respectively.
Surface morphological and chemical composition of the prepared CuO thin film were investigated by the field emission scanning electron microscopy (FESEM) and Energy dispersive X-ray analysis (EDAX). According the obtained results by FESEM indicate how the morphological properties vary with respect to volume of the CuO thin film. The prepared CuO films are well covered and adhered to the substrate with good homogeneity. EDAX spectra of prepared CuO thin films expose the presence of copper (Cu) and oxygen (O) along with other elements from the substrate. From the inset atomic concentrations of Cu and O were observed using EDAX analysis.
The DC electrical conductivity of CuO thin films was measured using two probe setup of Keithley electrometer 6517-B under room temperature. The current values were observed for different applied voltages from 1 to 10V the current values were increases gradually with increasing applied voltages. The DC conductivity for CuO thin films for different volumes were calculated using the following formula.
Where V is applied voltage, I is current, d is inter-probe distance and A is cross sectional area of the film. The I-V characteristics of CuO thin films for different volumes show in the fig.9a. The result revealed that the conductivity of the CuO thin film is increased for 4ml and decreased for 5ml.
In this work, CuO thin films with different volumes were prepared using simple and cost-effective jet nebulizer spray pyrolysis method. The effect of volume on structural, optical, and morphological properties of CuO thin film has been investigated. The structural investigations confirmed all the films are monoclinic crystal phase in nature. From XRD diffraction analysis the crystallite size was calculated.
The crystallite size varies from 19, 18 and 23nm for 3ml, 4ml and 5ml respectively. The optical investigation revealed that optical transmittance of CuO thin films were decreased with increasing volume. The highest transmittance of CuO thin film was observed at lowest volume of 3ml. The absorption analysis clearly showed that when the volume increases the absorbance of the CuO thin films were also increased. All CuO thin films have direct band gaps and have strong absorption in visible region.
The observed band gap values for CuO thin films 2.15eV, 1.93eV and 1.85eV for 3ml, 4ml and 5ml respectively. FESEM images show all CuO films are well covered and adhered to the substrate with good homogeneity. The DC electrical conductivity of the prepared films reveals that the conductivity of the CuO thin film is increased for 4ml and decreased for 5ml. Finally, we concluded that the different volume plays a vital role in the modification structural, optical, morphological and electrical properties of CuO thin films.
Exploring Effects of Solution Volume on CuO Thin Films: Structural, Optical, and Electrical Properties. (2024, Feb 06). Retrieved from https://studymoose.com/document/exploring-effects-of-solution-volume-on-cuo-thin-films-structural-optical-and-electrical-properties
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