Engineering and Technology Journal

First,ZnO nanorod s were su ccessfu lly synthesized by simple evaporation
method,u sing single stage controllable horizontaltu be fu rnace and qu artz tu be withou tcatalyst.The ZnO nano powd erwas mix ed with (10 and 20%)of TiO2 powd er(weightratio),then ZnO -TiO 2 thickfilms were synthesized u singsimple,low-cost efficient screen print techniqu e. The thick films were heated at 500 C ˚ for one hou rto remove the organic bind erand anyimpu rities.The prepared thickfilms were examined withX -Ray,and FESEM to stu d y the stru ctu raland morphology of the films,the X -ray results show that the films are polycrystalline with sharp and high intensity peaks indicating
high crystalinity of the product.The FESEM pictures show nanorods with diameters less than 100 nm and several micrometers in length
of ZnO withTiO 2 nanoparticles.ZnO -TiO 2 device was built up by electroding the thick films.The I-V characterization of the films were
studied in dark and light,then photo detection parameters were estimated and it was found to be efficient and high response in UV range detection

This study we don't use any catalyst or buffer layer before the reaction by hydrothermal method was used to prepare ZnO nano rods and flowerlike. The process has taken place inside Teflon lined stainless steel autoclave with volume 50 ml (homemade). ZnO nano rods and flowerlike were successfully synthesized using ZnO nanoparticles (20 nanometer) and NaOH (concentrations 3M) was the starting materials for the chemical reaction under stirring. The suspension was transferred into a Teflon lined sealed stainless steel autoclave and kept at 90 0C for 24 h,48 h and 72 h. The influence of the synthesis process on the morphology, the crystallinity and structural properties are studied by X-ray diffraction and field emission scanning electron microscope (FE-SEM), the experimental pattern of the films show that diffraction peaks can be assigned to the Wurtzite hexagonal-shaped ZnO as shown in the FE-SEM pictures, also the morphology of the films studied by atomic force microscope shows that the prepared thick films have high roughness specially for the powder prepared 46 h .

The electrospinning technique was used to fabricate 1D nanofibers of Zinc Oxide (ZnO). Polyvinylpyrrolidone (PVP) ̸ zinc acetate Nano fibers electrospun using solution containing PVP dissolved in ethanol and zinc acetate in distilled water were mixed, followed by calcination at 500°C for 3hours to remove the polymer. XRD pattern show the hexagonal wurtzite structure of ZnO NFs without any impurities. FESEM pictures show a network of nanofibers with diameters less than 100 nm and several micrometers in length of ZnO, these nanostructures increase the ratio of surface area to volume and improve the physical properties of the materials. The Photoluminescence (PL) of the films was studied and the energy gap and the optical properties were estimated. A photoconductor device was constructed by electroding the films with silver conducting electrode (IDE) using screen print method, The result shown that the resistance of the nanofiber films decrease dramatically when exposes to UV light. In addition, the change of conductivity with the change of wavelengths was studied also the photoconductivity was examined under different bias voltage.

In this work, it was examined mechanisms that control internal cooling device (nano-homojunction diode)depending on thermoelectric Peltier effect, resulting in structures that are optimized thermal management. Peltier coefficient for short-length diode is theoretically investigated. It is found that the cooling power is governed by the carrier concentration, current density and the ratio of n-type region width to p-type region width. It has been determined the optimum value of the cooling power at the junction of ZnO in the optimum density at doping symmetrically on a certain value.The cooling power, temperature difference (temperature between the contact and the junction) and dimensionless figure of merit are found in this material for different thicknesses, then comparing between them. It has been simulated the homojunction diode using a MATLAB software with numerically calculated the Peltier coefficient for each layer in these diodes.It has been found that nano-homojunction introduce a significant improvement in the internal cooling performance.

Polycrystalline films ZnO has been grown onto glass substrates by chemical spray pyrolysis (CSP) method. They were given heat treatment at different temperatures and constant time and for different times with constant temperature in air. The change in structural and optical properties was studied by means of X-ray diffraction (XRD), SEM, and optical absorption measurements. Structural analysis by X-ray diffraction pattern showed annealed ZnO film has high-orientation along c - direction (0 0 2), which remained the same with different heat treatment. The lattice constants of ZnO thin films were also obtained from XRD data. It is found that, with the increase of different heat treatments, the lattice constant a increases from 3.208 Å to 3.254 Å, and c increases from 5.125 Å to 5.219 Å. Where at higher annealing temperature and time the lattice constant c and a approach from bulk value. Other orientations corresponding to (1 0 0) and (1 0 1) are presented with very low relative intensities as compared to that of (0 0 2) plane. The transparency is increasing with increasing annealing temperature and time due to decreasing in films thickness with increasing annealing temperature and time. Change in bandgap energy from 3.2 to 3.01 eV was observed for different heat treatments.

In this paper preparation of good quality transparent conductive ZnO thin films by post-oxidation of vacuum evaporated Zn, on glass and silicon (p-type) as substrates, the oxidation was achieved in a short time (90 sec) which is known as rapid thermal oxidation. One growth parameter has been considered to specify the optimum conditions the film thickness are (200,300,400 &500 nm).
The XRD spectra revealed a high oriented grain in the (002) lattice system which is hexagonal wurtzite and proved that the ZnO films have a polycrystalline structure. Also, the morphological properties of ZnO films show that all films have a homogeneous surface morphology and it appears, to change significantly as a function of thickness.The energy gap of ZnO films decreases as the thickness increases. The FTIR spectra indicate the existence of the distinct characteristic absorption peak at 472.56cm-1 for Zn-O stretching mode.
Study of effect I-V and C-V measurements of ZnO films with the increase thickness. The photovoltaic properties confirmed that the photovoltaic depends strongly on the bias voltage and the amount of current produced by a photovoltaic device which is directly related to the number of photons absorbed. C-V results demonstrated that the fabricated heterojunction is of abrupt type. Also, the width of the depletion layer (w) follows the same behavior (V_bi ) decreased while the charge carrier density (N_d ) was increased with the thickness increase.

In this work a colloid of nanocrystalline ZnO particles is prepared by
chemical method, and then sprayed on porous silicon substrate which is prepared
by electrochemical etching under a current density of 15mA/cm2 for 10 min. The
initial radius of the ZnO particles is found to be (2.2 nm). FTIR spectra exhibit the
presence of Zn – O bond which indicates the formation of ZnO particles. Also
spectra reveals the formation of SiHx (x=1-2) and Si-O bond which indicates the
presence of porous layer. High performance rectifying was obtained, with high
photoresponsivety of 0.54 A/W at 400 nm. The corresponding quantum efficiency
was 166.7%.The results show that ZnO on porous silicon (PS) structures will act as
good candidates for making highly efficient photodiodes.