Mujdat Caglar

Morphological, optical and electrical properties of CdZnO films prepared by sol–gel method

CdZnO films were deposited by the sol?gel spin coating method onto glass substrates. ZnO, Cd(0.25)Zn(0.75)O, Cd(0.50)Zn(0.50)O, Cd(0.75)Zn(0.25)O, CdO films were deposited using different rates of cadmium acetate dehydrate and zinc acetate dehydrate solutions. These values in parentheses refer to the ratio in solution. The dried and annealing temperatures were selected to be 300??C and 500??C in air, respectively. The XRD patterns show polycrystalline nature. It was observed that the crystal structure changes from wurtzite (ZnO) to cubic (CdO) depending on the Zn and Cd proportions in the CdZnO structure. The optical properties of these films have been investigated by means of the optical transmittance measurement. The absorption band edges of films shift from 3.26 to 2.31?eV. The morphological characterizations of the films have been performed by SEM and AFM. In particular, the clusters formed from the nanostructured particles were shown in the SEM image of the Cd(0.75)Zn(0.25)O film. The electrical measurements show that the CdZnO films have semiconducting behaviour and are very sensitive to light.

Synthesized some 4-(2-thiazolylazo)resorcinol complexes: Characterization, thermal and optical properties

Some transition metal complexes of the type [ML2].nH2O (n=0 or 2) of the title ligand, 4-(2-thiazolylazo)resorcinol, HL (TAR) have been synthesized and characterized by various analytical and physicochemical (elemental, thermal analyses, AAS, electrolytic conductance and magnetic susceptibility measurements) and spectral (UV-vis and IR) techniques for structure determination and optical properties. The complexes have the formulae [ML2] for M=Fe(II), Cu(II) and Zn(II); [CdL2].2H2O. An octahedral structure is proposed for all complexes. IR spectra show that the ligand is coordinated to the metal ions in a tridentate manner with ONN donor sites of the resorcinol OH, azo N and thiazole N. The effect of varying pH and solvent on the absorption behavior of the ligand and complexes has been investigated. The optical constants such as, refractive index, extinction coefficient, dielectric constant were determined for the ligand and its complexes. These parameters changed with different metal complexes. The optical absorption data revealed that the band gap of the films was direct transitions. The optical band gap and Urbach energy of the films were determined using the known theory. The optical dispersion parameters were determined according to Wemple and DiDomenico method.

A spectroelectrochemical study on single-oscillator model and optical constants of sulfonated polyaniline film.

The optical properties of sulfonated polyaniline (SPAN) thin film prepared by electrochemical method have been investigated. Polychromic behavior of SPAN thin film (transparent yellow-green-dark blue) was observed when the cyclic voltammograms were taken between -0.25 V and +1.90 V (vs. Ag/AgCl, sat.) during the growth of polyaniline film. In situ UV-vis spectra of the polymers-indium tin oxide (ITO) glass electrode were taken during the oxidation of the polymers at different applied potentials. The direct band gap values of SPAN thin film changed from 3.771 eV to 3.874 eV with the applied potentials. From in situ UV-vis spectra, the optical constants such as refractive index and dielectric constant of the SPAN thin film were determined. The important changes in absorption edge, refractive index and the dielectric constant were observed due to the applied potentials. The refractive index dispersion curves of the film obey the single-oscillator model and oscillator parameters changed with the applied potentials. The most significant result of the present work is in situ spectroelectrochemical method, which can be used to modify the optical band gaps and constants.

Fabrication and electrical characterization of flower-like CdO/p-Si heterojunction diode

The electrical properties of a flower-like CdO/p-Si heterojunction diode have been investigated in the temperature range 80–400 K. The CdO thin film was deposited on p-type Si using the sol–gel spin coating method. The scanning electron microscope result indicates that the film has a flower-like structure. From the x-ray diffraction result, it is shown that the CdO film has a polycrystalline structure with preferential orientation along the (1 1 1) crystal plane. The optical band gap of the CdO film was found to be 2.57 eV. The ideality factor is n 2 which is due to the presence of non-ideal contact behaviour and the result of inhomogeneity and tunnelling. At lower temperatures, the charge transport mechanism results from the tunnelling mechanism, whereas at higher temperatures, it is controlled by recombination currents. The capacitance–voltage characteristic shows a typical abrupt heterojunction.

Controlled growth of c-axis oriented ZnO nanorod array films by electrodeposition method and characterization.

ZnO nanorod array films were deposited from aqueous solution containing different concentrations (1×10(-2) M and 5×10(-3) M) Zn(NO3)2⋅6H2O and C6H12N4 and at different electrodeposition times (i.e., 15 min, 30 min, 60 min, 120 min and 180 min) using chronoamperometry method on p-Si substrate. Surface morphology and crystal structural properties of ZnO films were investigated by XRD and FESEM to select ZnO films which have optimum properties. The highest TC(hkl) value was observed in (002) plane for the film, which is deposited at 1×10(-2) M and 120 min. It is also observed that the highly oriented nanorods in this film are denser. Additionally, the conductivity type was determined by using Mott-Schottky which is electrochemical impedance spectroscopy method (EIS). On the other hand, to investigate the utility of obtained ZnO on p-Si (p-Si/n-ZnO) as supercapacitor electrode active material, the electrochemical storage properties of p-Si/ZnO was studied by electrochemical impedance spectroscopy and repeating chronopotentiometry methods. It is suggested from electrochemical tests results that p-Si/ZnO is a promising electrode materials for supercapacitor applications that required low voltage (<10 V). Rectifiying behavior was observed from the I-V characteristic of nanorod array n-ZnO/p-Si heterojunction diode. The n value, Io and the ϕb were found to be 5.48, 1.93×10(-8) A and 0.75 eV, respectively.

Effect of both deposition temperature and indium doping on the properties of sol-gel dip-coated SnO2 films.

Using indium chloride as an In source, In-doped SnO(2) films were fabricated by sol-gel method through dip-coating on borofloat glass substrates. The undoped SnO(2) films were deposited in air between 400 and 600 °C to get optimum deposition temperature in terms of crystal quality and hence In-doped SnO(2) films were deposited in air at 600 °C. The effect of both deposition temperature and In content on structural, morphological, optical and electrical properties was investigated. The crystalline structure and orientation of the films were investigated by X-ray diffraction (XRD) and surface morphology was studied by a field emission scanning electron microscope (FESEM). The compositional analysis of the films was confirmed by energy dispersive X-ray spectrometer (EDS). The absorption band edge of the SnO(2) films shifted from 3.88 to 3.66 eV with In content. The van der Pauw method was used to measure the sheet resistance of the films. The sheet resistance was affected significantly by deposition temperature and In content.

XPS Studies of Electrodeposited Grown F-Doped ZnO Rods and Electrical Properties of p-Si/n-FZN Heterojunctions

The chemical composition of the electrodeposited undoped and F-doped ZnO (FZN) rods was investigated by X-ray photoelectron spectroscopy (XPS). These results confirmed the existence of F as a doping element into ZnO crystal lattice. The p-Si/n-ZnO and p-Si/n-FZN heterojunction diodes were fabricated and their electrical properties were investigated. Some parameters belong to these diodes such as ideality factor (n), barrier height (źB), and series resistance (Rs) which were calculated from the current-voltage (I-V) curves that exhibited rectifying behavior by using thermionic emission theory, Nordeźs function, and Cheungźs method. There is a good agreement between the diode parameters obtained from different methods.

The electrical modulus and other dielectric properties by the impedance spectroscopy of LaCrO3 and LaCr0.90Ir0.10O3 perovskites

We have prepared LaCrO3 (LCO) and 10% Ir doped LCO samples by the solid state reaction method and studied the electrical modulus and the other dielectric properties of the samples by means of the impedance spectroscopy in the −100 °C to 100 °C range, with steps of 20 °C. It has been clearly observed that the dielectric properties change due to Ir doping. The absolute dielectric constant value of Ir doped LCO has decreased and this reduction was attributed to decreasing Cr6+ ions which may play a vital role in space charge polarization and charge hopping. A plateau region appeared in the temperature-dependent real electrical modulus M′ versus f curves of the pure LCO sample while almost no plateau region is visible in the Ir doped LCO sample. The temperature-dependent imaginary modulus M′′ versus f curves has two peaks at each temperature; one of the peaks is at low frequency and the other at the high frequency region, which shifts through higher frequency region with increasing temperature. This originates from free charge accumulation at the interface with the increase of the temperature. Furthermore, it has been seen that the Ir doped LCO sample has higher impedance and resistance values than the undoped LCO sample at the same frequency and temperature. This phenomenon was attributed to doped Ir ions behaving like a donor in LCO because LCO is a p-type compound. Moreover, the activation energy values of 0.224 eV and 0.208 eV for LCO and of 0.161 eV and 0.265 eV for the Ir doped LCO have been obtained from the slopes of the ρdc vs. (kT)−1 curves, respectively. Also the activation energies were calculated from the slopes of the fmax vs. (kT)−1 curves and the obtained results from low frequency region were in good agreement with ρdc vs. (kT)−1 ones.

Influence of Irradiation Time on Structural, Morphological Properties of ZnO-NRs Films Deposited by MW-CBD and Their Photodiode Applications

Microwave-assisted chemical bath deposition (MW-CBD) was used to deposit zinc oxide nanorods (ZnO-NRs) films by using different microwave irradiation time. The films exhibit a good crystallinity having a hexagonal wurtzite phase formation. Although the dominant preferred orientation was not observed for the ZnO-5 and ZnO-10, ZnO-8 showed (002) preferred orientation. The emission scanning electron microscope (FESEM) showed almost randomly oriented hexagonal nanorods on the surface. A slight decrease in the length of the observed hexagonal nanorods due to the increase in the irradiation time was observed, changing from 550 nm to 300 nm. The p-Si/n-ZnO-NRs heterojunction photodiodes were fabricated. The current-voltage characteristics of these photodiodes were investigated under dark and different illumination intensity. An increase in the reverse current with increasing illumination intensity confirmed that the fabricated photodiodes exhibited a photoconducting behavior. In addition, the barrier height and series resistance values of the photodiodes were determined from capacitance-voltage measurements.

Preparation, structural and morphological properties of nanostructure ZnO films by sol gel spin coating

In preset study, the sol-gel method was used to deposit ZnO films and silicon substrates were used as substrate. The effects of deposition temperature on the structural and morphological properties of ZnO films were investigated. X-ray diffraction (XRD) measurement showed that the ZnO films were crystallized in the hexagonal wurtzite phase and presented a preferential orientation along the c-axis. The current-voltage (I-V) characteristics of the diode were performed using a KEITHLEY 2400 sourcemeter. The pn heterojunction diode was fabricated and the diode parameters were determined from the analysis of the measured dark current-voltage curves. Rectifying behavior was observed from the I-V characteristics of these heterojunction diodes.