Zinc oxide (ZnO) nanorods have been synthesized by solution processing hydrothermal method in low temperature using the spin coating technique. Zinc acetate dehydrate, Zinc nitrate hexahydrate and hexamethylenetetramine were used as a starting material. The ZnO seed layer was first deposited by spin coated of ethanol zinc acetate dehydrate solution on a glass substrate. ZnO nanorods were grown on the ZnO seed layer from zinc nitrate hexahydrate and hexamethylene-tetramine solution, and their diameters, lengths were controlled by precursor concentration and development time. From UV-Visible spectrometry the optical band gap energy of ZnO nanorods was calculated to be 3.3 eV. The results of X-Ray Diffraction (XRD) showed the highly oriented nature of ZnO nanorods the hardest (002) peak reflects that c-axis elongated nanorods are oriented normal to the glass substrate. The Field Emission Scanning Electron Microscope (FESEM) was employed to measure both of average diameter of ZnO nanorods, Energy Dispersive X-Ray (EDX) is used to identify the elemental present and to determine the element composition in the samples.
Zinc oxide (ZnO) is inexpensive n-type of semiconductor compound, which has shown promise for commercial applications in photovoltaic cells, [
Nanostructured ZnO is fabricated using various thin film techniques as spray pyrolysis [
In this work ZnO nanorods have been produced by thermal method using the solution, zinc acetate dehydrate in ethanol as a seed layer. The growth of ZnO nanorods, diameter and length are controlled by changing the solution concentration and immersion time in equimolar of zinc nitrate hexahydrate and hexamethylenetetramine (HMTA) in deionized water at a 90 ̊C and their morphologies, preferential orientation and optical properties were examined in particular.
The hydrothermal method synthesis and thin film process arrangement are presented schematically in
was spin coated on the cleaned glass at a spinning speed of 2000 rpm for 20 s with a 10 s wait time, then annealing at 150˚C for 15 min. The procedure was repeated three times, and finally the ZnO seed layer was annealed at 350˚C for 15 minutes. The solution of growing ZnO nanorods was prepared by dissolving equimolar zinc nitrate hexahydrate (Zn(NO3)∙6H2O, Aldrich 98%) and hexamethylenetetramine (HMTA) (C6H12N4, Aldrich, 99%) in deionized (DI) water. The solution concentration was varied from 15 to 35 mM for controlling the ZnO nanorods. The ZnO seed layer deposited on glass was immersed in the solution, where the glass was face down, and the baker was kept at 90˚C for 60, 90, 120, 150, 180 min. Alteration in the immersion time at a given concentration can control the length of the ZnO nanorods. The ZnO nanorods film was rinsed with Deionized water an ethyl alcohol several times. Ultimately, the film was annealed at 450˚C for 30 minutes.
The average diameter and length of the ZnO nanorods were measured by using the field emission scanning electron microscope FESEM (Model: FEI Nova NanoSEM 450). The transmission spectra of the films were measured by a double beam UV/visible (UV-4100) spectrophotometer with a wave length rang 200 nm - 800 nm and the optical band gap was measured from the transmission spectra.
X-Ray Diffraction (XRD) was utilized for the physical construction of the ZnO thin films. XRD patterns were obtained with a (Model: PANalytical X’pert PRO MRD PW 3040) single scan diffractometer with CuKα (λ = 1.54050 Å) radiation and scanning range of 2θ set between 20˚ and 80˚. The diameter and length of ZnO nanorods were measured using field emission scanning electron microscope FESEM (Model: FEI Nova NanoSEM 450). Energy Dispersive X-Ray Spectrometer (EDX) used for quantitative detection of elements in the prepared samples.
where α is the absorption coefficient, hν is the photon energy, Eg is the optical band gap and A is a constant.
This difference is due to the fact the values of band gap Eg depend on many factors, e.g. the granular structure, the nature and concentration of precursors, the structural defects and the crystal structure of the films. Moreover, departures from stoichiometry form lattice defects and impurity stats. Dengue Bao et al. [
The unit cell “a” and “c” of the crystalline ZnO nanorods with (002) orientation is calculated using the relation (2) and (3):
The values obtained for the unit cell a = 3.007 Å and c = 5.21 Å are in a good agreement with those reported in the JCPDS standard data (card no. 80 - 0074). The calculated parameters are given in
From the XRD spectrum, grain size (D) of the film is calculated using debay scherrer formula [
where k is a constant to be taken 0.49 [
The dislocation density (δ), which represents the amount of defects in the crystal, is estimated from the following equation:
Strain ( ) of the thin film is determined from the following formula:
a (Å) | c (Å) | ||
---|---|---|---|
Standard | Calculated | Standard | Calculated |
3.253 | 3.007 | 5.215 | 5.21 |
Plan | d (Å) | FWHM (β)˚ | 2θ˚ | D (nm) | δ × 10−4 (nm)−2 | ε × 10−3 |
---|---|---|---|---|---|---|
002 | 2.6055 | 0.1968 | 34.426 | 44.12 | 5.13 | 8.049 |
The calculated structural parameters of the thin film are presented in
In
Length of ZnO nanorods can also be varied when the immersion time changes in the fixed concentration.
In this work, we have grown ZnO nanorods on glass substrates by solution processing hydrothermal method in low temperature using the spin coating technique. The structural, morphological and optical properties were in-
vestigated. The hydrothermal method is a relatively simple technique: there are many factors which affected the quality of the film. We have optimized different parameters to obtain a good crystalline structure of ZnO nanorods with intense and sharp peak. The optical transmittance is over 80% in the wave length range from 400 nm - 800 nm and the band energy band gap is found to be 3.300 eV. According to XRD results, the as deposited films exhibited a hexagonal wurtized structure with (002) preferential orientation after annealing at 400˚C in air ambiance for 30 min. The XRD pattern consists of a single (002) peak which occurred due to ZnO crystals and grows along the c-axis. The grain size estimated to be 44.46 nm. The average diameter and average length of the ZnO nanorods obtained from the FESEM. The average diameter of ZnO nanorods, which are increasing from (57, 64, 83, 120 and 230 nm) as the precursor concentration increases at 90˚C for immersion time 180 min, and the average length of ZnO nanorods increases from (241, 459, 522, 820 nm and 1.2 µm) when the immersion time was increased at 90˚C for precursor concentration 35 mM. The (EDX) analyses of the samples clearly show that the sample prepared by above route has pure ZnO nanorod phases.