Yasemin 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.

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 deposition parameters on the structural properties of ZnO nanopowders prepared by microwave-assisted hydrothermal synthesis.

ZnO nanopowders were synthesized via microwave-assisted hydrothermal method at different deposition (microwave irradiation) times and pH values. The effects of pH and deposition (microwave irradiation) time on the crystalline structure and orientation of the ZnO nanopowders have been investigated by X-ray diffraction (XRD) study. XRD observations showed that the crystalline quality of ZnO nanopowders increased with increasing pH value. The crystallite size and texture coefficient values of ZnO nanopowders were calculated. The structural quality of ZnO nanopowder was improved by deposition parameters. Field emission scanning electron microscope (FESEM) was used to analyze the surface morphology of the ZnO nanopowders. Microwave irradiation time and pH value showed a significant effect on the surface morphology.

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.

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.

Effect of Substrate Temperature on The Structural and Optical Properties of Non‐doped ZnO Thin Films

Transparent conducting non‐doped zinc oxide (ZnO) thin films have been deposited by the spray pyrolysis method at different substrate temperatures. X‐ray diffraction spectra of the films have shown that the films are polycrystalline and hexagonal wurtzite in structure. From these spectra, grain size and texture coefficient (TC) are calculated. The analytical method for calculating lattice constants is used to calculate a and c for the films. The preferred orientation of non‐doped ZnO thin films was changed with substrate temperature. The average optical transmittance of non‐doped ZnO thin films was over 80% in the visible range. The optical band gap and optical constants of the non‐doped ZnO thin films were evaluated as dependent on the substrate temperatures. The substrate temperature have a significant effect on structural and optical properties of the non‐doped ZnO thin films..

Synthesis and Photodiode Characterization of Novel Twisted Carbazole Derivatives with 1,3,5-Benzene Core

In this study, considering the information given in the literature the Ullman and Suzuki-Miyaura coupling reactions were carried out using carbazole, 1,3,5 tribromo benzene and aryl boronic acid. The synthesized novel carbazole derivative (CPF4) were characterized by 1H NMR and 13C NMR. The photophysical and thermal properties of the synthesized novel carbazole derivatives CPF4 were investigated Graphene oxide (GO) doped CPF4/p-Si photodiodes were fabricated. The electrical properties of these photodiodes were characterized by current–voltage (I−V) and capacitance–voltage (C−V) measurements. The photocurrent properties of the diode were studied under various illumination intensities. The photoresponse properties of the diodes increased with GO content. The results indicate that CPF4:GO/p-Si heterojunctions can be used as a photodetector for optoelectronic applications.

FESEM, XRD and DRS studies of electrochemically deposited boron doped ZnO films

Abstract In this study, the effect of boron (B) incorporation into zinc oxide (ZnO) has been investigated. The undoped, 2 at.%. and 4 at.% B doped ZnO films were deposited on p-type silicon (Si) substrates by electrodeposition method using chronoamperometry technique. Electrochemical depositions were performed by applying a constant potentiostatic voltage of 1.1 V for 180 min at 90 °C bath temperature. To analyze the surface morphology, field emission scanning electron microscopy (FESEM) was used and the results revealed that while a small amount of boron resulted in smoother surface, a little more incorporation of boron changed the surface morphology to dandelion-like shaped rods on the whole surface. By using X-ray diffraction (XRD) analysis, the crystal structures of the films were detected and the preferred orientation of the ZnO, which exhibited polycrystalline and hexagonal wurtzite structure, changed with B doping. For the estimation of the optical band gap of obtained films, UV-Vis diffuse reflectance spectra (DRS) of the films were taken at room temperature and these data were applied to the Kubelka-Munk function. The optical band gap of ZnO narrowed due to incorporation of B, which was confirmed by red-shift.