A Study on the Structure, Morphology and Optical Properties of ZnO Nanostructures Films Synthesized using Different Concentrations of Zinc Acetate

Abstract

Researchers are usually looking for simple methods like sol-gel process that leads to possible low cost and pure products and easy film processing on a variety of substrates for synthesizing metal oxides like ZnO nanostructures. The main aim of this study is to investigate the effect of different concentrations of zinc acetate on the structural, morphological and optical properties of Zinc oxide films nanostructures. The different concentrations of zinc acetate are 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and1.0 Moles respectively. The sol-gel method has been used as main step and then using coating technique deposited on ITO glass substrates to synthesize ZnO2 nanostructure. The structural and the surface morphologies of as-synthesized ZnO materials were characterized by X-ray Diffraction, Fourier Transformer Infrared (FTIR) and Scanning Electron Microscopy (SEM). The XRD patterns for the ten samples of as-synthesized established that there is a sharp peak at 2Ɵ =33.5027o corresponding to (111) plane. Interestingly, among the ten samples, only sample ZnO 1.0 M explained the highest intensity of 9950 (a.u) for the sharp peak, which indicated that good crystallinity of the as-synthesized ZnO films samples increase with increasing the concentrations of zinc acetate. The crystal structure of as –synthesized ZnO produced local cubic structure that differed from the majority recent publishing papers which reported the most common for ZnO structure is hexagonal wurtzite. The FTIR resulted that the mean band for the ten samples around 1340 𝑐𝑚−1 is associated with the O-H bending vibration also the location of the absorbtion bands at the positions around 3640〖 cm〗^(-1)and 3910 cm^(-1) , is due to the stretching mode of H-O-H bending vibration of free charge or absorbed water which implies that the hydroxyl groups are retained in ZnO for different concentrations of zinc acetate. The surface morphologies of as-synthesized ZnO film structures have been investigated by Scanning Electron Microscopy (SEM). The SEM images for some samples revealed that the synthesized ZnO films formed like-date nanostructures with smooth surface. Also the results from SEM micrograph established that the size of the like-date nanostructures for sample 1.0 M equal to 11.77 nm where as for sample 0.1 M is equal to 148.38 nm. These results indicated that by increasing the zinc acetate concentrations lead to decreasing the size of nanostructures of as-synthesized ZnO films. The results verified that the nanosizes received from SEM images agree with that calculated from XRD data except samples 1.0 and 0.9 moles. The optical properties; including absorption coefficient, refractive index, extinction coefficient, energy bandgap, real dielectric constant, imaginary dielectric constant and, optical and electrical conductivity were investigated by means of absorption, transmittance and reflectance spectra. The results indicated that themaximum value of the absorption coefficient α is 4.63×103 cm-1 materialized in the U.V region at the peak of wavelength 270 nm corresponding the concentration of 1.0 moalr of zinc acetate wherever α at same wavelength dcrease to 1.34×103 cm-1 for low concentration of 0.1 mole of zinc acetate. The refractive index (n) of the as-synthesized ZnO nanostructures represented a macximum peak at n = 2.159, except samples 0.2 mole and 0.1 M illustrated refractive index of values 2.128 and 2.044 respectively. This result in a good agreement with standard refractive index n= 2.004. Also the result demonstrated that the value of (n) begins to decrease between the wavelengths 306 - 344 nm at the region of the spectrum. This behavior may due to the nature of the sharp absorption of Zinc Oxide nonostructures that lead to an electronic transmission at the absorption edge. Concerning the energy bandgap, the results indicated that the as-obtained ZnO film nanostructures exhibted the hieghest bandgap of 3.889 eV for sample 0.1 molar, where as for sample 1.0 molar it exhibted the lowest value of 3.443 eV, which believed to possess a better coductivty. As a result, the bandgap energy received in this study decreases with increasing the concentration of the zinc acetate dehydrate. In addition, the study established that high magnitude of optical conductivity is found to be 1.34×1011 sec-1 for samples 1.0 M, 0.9 M, 0.8 M and 0.7 M respectively of as-prepared ZnO nanostructures which confirms the presence of very high photo-response. Although, samples 0.1 M, 0.2 M, 0.3 M, 0.4 M , 0.5 M and 0.6 M sharing same broad peak at wavelength of 268 nm, but are represented different optical conductivities 7.48×1010, 9.01×1010, 1.04×1011, 1.17×1011, 1.258×1011 and 1.309×1011 sec-1 respectively. The study confirmed that the electrical conductivity increases with increasng the concentrations of zinc acetate and that means the high concentration could acount as an optimal condition for large electrical conductivity.