رضية مهدي شاكر الجراح

In this work gas sensor based on a TiO2 nanostructure has been investigated to employ it to detect and measurement percentage of presence of nitrogen dioxide in the air specimen. TiO2 was fabricated using dc magnetron sputtering method, pure Ti (99.99%) used as sputtering target, the oxygen/argon rate flow rate was settled at (50:50 sccm), the chamber presser was controlled to remain it at (0.2 Pa) during the deposition process and direct voltage for the sputtering operation was 1000 V with 100W power. Xray diffraction pattern show that the structure of all TiO2 films is polycrystalline with three phases Anatase, Brookite and Rutile with preferential orientation in the (112) direction. For TiO2 metal oxides, the annealed sensor exhibit variation of the conductance upon exposure to NO2 gas and showing excellent sensitivity. The high sensitivity for NO2 gas can be achieved with annealing the film and the sensitivity of the TiO2 thin films changes linearly with the increase of the gas concentration. The response – recovery time of TiO2 materials to NO2 gas is characterized to be relatively exceedingly short. TiO2 thin films have the highest sensitivity of 95% and exceedingly short response time of 2 s.

In this research, the effect of annealing temperature Ta on the structural and optical properties of ZnO nanostructure which was prepared by spray pyrolysis method, was investigated. ZnO films prepared by spray pyrolysis technique on glass substrate with thickness 300 nm using: Zinc acetate Zn (CH3COO)2•2H2O, with purity of 99.6% and distilled water. After that the films were annealed at various temperatures (673, 7 773 and 873 K). X-ray diffraction studies show that the structure of all ZnO films is polycrystalline with hexagonal wurtizte structure with preferential orientation in the (002) direction. The post-deposition annealing of the film from (R.T to 873) K increases the intensity of (002) peak corresponding to c-axis orientation in addition with the decrease in full width at half maxima (FWHM). The optical measurement showed that the nature of the optical transition has been direct allowed with average band gap energies have tendency to decreases from (3.28 -2.93) eV with increasing of Ta excepted it was increased to 3.21 eV at 773 K. The extent and nature of transmittance and optimized band gap of the material assure to utilize it for photovoltaic applications.

In this research, nanostructure of ZnO film has been fabricated by spraying 0.2M concentration of Zinc salt solution on glass substrate. The Zinc solution was prepared by solves 4.389908g of the Zinc salt in 100 mL of isopropyl alcohol C3H9O. In order to obtain the best optimization in their optical properties via the annealing effect, these films were treated thermally at different temperatures (RT, 200, 300 and 400). Then AFM and XRD tests are employed to examine the structure. According to X-ray diffraction patterns, the structure of all ZnO films is polycrystalline with hexagonal wurtizte structure and preferential orientation in the (002) direction. It also turns out that the annealing process has led to increase the high of the peaks of the x-ray pattern tests which means the structure has been improved. As for the surface morphology, the Atomic Force Microscope (AFM) test results are shown there is uniform distribution of homogeneous with columnar nanostructure grains. The band gap varies between (3.2-3.37 eV) and tendency to rise with annealing temperature have been observed through the optical measurement. The sensing tests showed that linear response with increasing the gas concentration and, the annealing treatment gave rise to the sensitivity and more selectivity for NO2 gas. Moreover, the best sensing performance in term of sensitivity and selectivity has been absorbed by ZnO film that was treated by 300 oC annealing temperature.

The aim of this research was to undertake a study to improve the optoelectronic properties of the CdS/Si Junctions. There are CdS thin films were deposited using a spray pyrolysis technique, this was followed by annealing at various temperatures (400-600) oC, in order to optimize the film properties. X-ray diffraction tests have been demonstrated that the structure of all CdS films are polycrystalline with cubic and hexagonal wurtizte structure together, with preferential orientation in the H(002) and C(111) direction around the c-axis. In addition to new peaks have been appearing with an increase in the intensity of H (002) in x-ray diffraction pattern with increasing annealing temperature to 600 oC.The value of capacitance as a function of reverse bias voltage at 40 KHz frequency has indicated to that these hetero-junctions are abrupt. Moreever, the thermal treatment has been led to increases the built in potential from 0.15 V to 0.62 V, and also expand the width of the depletion layer from 66.6nm to 143.81nm.The increasing of annealing temperature to 500C was led to increase the forward current, and when annealing temperature exceeds 500 the value of the current start falling. In general I-V Measurements for CdS/Si heterojunctions showed typical rectifying characteristic, and the ideality factor varies within the range of (1.31 -1.89).

The research aim of this work is to develop a simple and highly sensitive optical biosensor for detection of mycotoxins. This sensor is built on a planar waveguide operating on the polarization interferometry principle, i.e., detecting a phase shift between p- and s-components of polarized light developed during the binding of analyte molecules. The operation of the proposed sensor is similar to that of a Mach–Zehnder interferometer, while its design is much simpler and it does not require splitting the waveguide into two arms. The refractive index sensitivity of the polarization interferometer sensor was in the range of 5200 radians per refractive index unit (RIU). Several tests were conducted to detect ochratoxin A (OTA) at different concentrations in direct immunoassay with specific antibodies immobilized in the sensing window. The lowest concentration of OTA of 0.01 ng/mL caused a phase shift of nearly one period. The results obtained prove high sensitivity of the sensors, which are capable of detecting even lower concentrations of mycotoxins at the ppt (part-per-trillion) level.

Cadmium Sulphide (CdS) thin films are produced using spray pyrolysis deposition technique. Films are annealed in air at 400, 500, and 600 K of 1 h. It characterized by X-Ray Diffraction (XRD), Atomic Force Microscope (AFM) and optical properties of CdS. XRD shows that these films are polycrystalline in nature with cubic and hexagonal crystalline structure. The crystallite size, microstrain, and dislocation density were measured. AFM shows that the total substrate surface is finely covered with uniformly distributed spherical shaped grains. Optical transmittance was shown that direct transition with band gap energy was decreased between 2.44 to 2.27 eV with annealing.

In this work, a heterojunction TiO2 on Si base has been made by use the D.C magnetron sputtering method with Ti target and oxygen plasma. The film was deposited on Si wafer and then undergone to the annealing process at various annealing temperatures were employed to assess film properties. The capacitance with reverse bias has been measured as a function of bias voltage at frequency 10 kHz, and these measurements have indicated the width of the depletion layer (W) surges with increasing of annealing temperature. The current–voltage characteristic It turned out through the current–voltage graph of TiO2/Si heterojunction the forward current at dark changes with change of applied voltage, in demeanor concordant with recombination-tunneling model. The results have shown that the dark current rises with growth of Ta. Also under illumination condition its clear to show there is a positive correlation relationship between the photocurrent and Ta.

Abstract: The ZnxCd1-xS thin films prepared by chemical bath and deposited on glass substrates. A procedure to make optical quality thin films of ZnxCd1-xS has been investigated. Structural and optical properties of ZnxCd1-xS thin films with x = (0.2, 0.5 and 0.7) and T= (300, 423 and 473) K were synthesised-sized. The structural investigation indicates that they have polycrystalline structure. The crystalline size and degree of preferential orientation were found to be increased with the increase of Zn concentration (x) and annealing temperature. Optical data are recorded in the wavelength range 200-1000nm. In addition, the absorption coefficient is determined and correlated with the photon energy to estimate the band gap. Plots of (αhν)2 versus (hν) yield a straight line indicating direct transition occurs with optical band gap energies in the range) 3.3-3.5( EV. It is also found with increase annealing temperature and Zn content the band gap of the films increases. Refractive indices and extinction coefficients have been evaluated.

Abstract: Thin Films of pure and Zn doped CdTe have been prepared by the thermal evaporation method onto glass substrates at 500 nm film thickness. Real and imaginary ( ) part of dielectric constant, ac conductivity (σac) and cole - cole diagram of thin films for Zn ratios (00, 0.02, 0.04, 0.06 and0.08) have been studied in different substrate temperature as a function of the frequency range (102Hz - 106 Hz). The results indicated that the dielectric constant increases with the increase of Zn concentration, but it decreases with the increase of frequency. The mechanism of Ac conductivity matches with the correlated barrier hoping model. From cole-cole diagram, the polarization and the relaxation time increase with the increase Zn concentration.

Abstract: UV photoconductive detector was fabricated by the deposition of TiO2 film on silicon by dc magnetron sputtering. Pure oxygen and Argon were used as the reactive and sputtering gases respectively. The gases were mixed prior to the admission in the sputtering chamber [oxygen flow 10, 20, 30, 40 and 50 s.m (stander centimeter cubic per minute) with constant argon flow]. The structure properties of TiO2 thin films were investigated by means of X-ray diffraction. X-ray diffraction (XRD) patterns showed three phases Rutile, Anatase and Brookite . The ratio between these phases changed and depended on oxygen flow. The deposited TiO2 film was coated by nanosheet of polyamind polymer to improve the photoresponsivity of the detector and to reduced the response time of the TiO2 UV detector to about 170 μs. The final device was tested with high speed pulsed nitrogen laser. The spectral responses of TiO2/Si junction were studied. The maximum value of responsivity occurred at wavelength equals to 385 nm. The responsivity, quantum efficiency and specific detectivity increased with increasing of the oxygen flow, while the noise equivalent power decreased with increasing the oxygen flow. It has been observed that the best spectral response occurs when the oxygen flow equal to 50 s.m and we can say that this value of oxygen flow is the optimum condition for TiO2 photoconductive detector preparation.

ABSTRACT: AlxIn1-xSb nanocrystals have been studied using ab-initio calculations. The electronic properties were simulated using different core atoms ( usualy 8, 16, 54 and 64). The calculations uesd showed a that the concentration increament effects on the crystal size. All calculations were done using Gaussian 03 code with Hartree-Fock calculation with the GGA approximation.

Abstract The objective of this research is studying the effects of film thickness on the structural and optical properties for nano ZnO films prepared by d.c magnetron sputtering technique on glass substrates. Thicknesses (t) of ZnO thin films were altered by varying the deposition time from 45 min to 90 min (t=75,150,200 and 250) nm and are determined using optical method. The X-ray diffraction spectra show that ZnO thin films are polycrystalline with the hexagonal structure and show a good c-axis orientation perpendicular to the substrate. The most preferential orientation is along the (002) direction for all sputtered deposited ZnO films, in addition another peaks appear at thickness 200 and 250 nm with orientations in (102) and (110) planes. General observations indicate that microstructure parameters, such as grain size, depend sensitively on the thickness of the film. The optical properties of nano ZnO thin films have been investigated by UV/VIS spectrometer and the band gap values are found to be with the range of 3.27 eV to 3.44eV.The ZnO film of all thickness has transmittance over 85% in the visible region, and the refractive index is about 2.1.

ABSTRACT The objective of this research is investigating the effect of the thickness on the structural and electrical properties for nano ZnO thin films prepared by d.c magnetron sputtering on glass substrates. The deposition parameters such as power, target to-substrate spacing, substrate temperature and sputtering gas composition, self-heating of the substrate in plasma during film deposition were investigated. Thicknesses (t) of nanoZnO thin films are altered by varying the deposition time from 45 min to 90 min (t=50,100,150 and 200 nm) and was determined using optical method. Crystal structure were investigated by mean of a X-ray diffraction (XRD), it was found that all the films have peak located at 2θ ≈ 34.4o with hkl (002), in addition there were another peaks appear at thickness 100 nm, 150 nm and 200 nm .The crystalline was increased with increasing (t). The grain size increased from 9.462 nm to 11.8522 nm as the film thickness increased from 50 to 200nm. General observations indicate that microstructure parameters, such as grain size, depend sensitively on the exact nature of the deposition conditions. The d.c conductivity (σ) for nano ZnO thin films has been studied as a function of thicknesses. From all samples we can be noticed that the resistivity (ρ) increased with increasing the temperature and film thickness, while the activation energies decreased. The carrier concentration and mobility have been studied.