Bucurgat, Mahmut; Özdemir, Ahmet Faruk; Altindal, Semsettin

Different thicknesses of Si3N4 insulator layers were grown on an (Au: Ti)/n-GaAs (MS) reference structure to analyze the effect of these layers with/without illumination on the electrical characteristics and compare the results between these structures. With this motivation, current measurements were made as a function of voltage over +/- 3 V, either in the dark or at 20-100 mW cm- 2 illumination with an increment of 20 mW cm- 2. Some important electric and optoelectronic parameters, such as barrier height at zero bias, ideality factor, saturation current at reverse bias, photosensitivity, photoresponsivity, and detectivity, have been determined using currentvoltage data in relation to illumination intensity. To compare the calculation methods used, the basic electrical parameters, the barrier height at zero bias, the ideality factor, and the series resistance were calculated first using the Thermionic Emission Method and then, alternatively, using Cheung functions. Additionally, the dependence of energy of the interface states was investigated using forward bias current voltage data with the ideality factor and barrier height with/without different intensities of illumination, because of their reordering/restructuring in electric field effects and illumination. The voltage-dependent characteristics of resistance of these structures were also determined from Ohm's Law for each illumination intensity.

Kaya, Selim

This Study aims to evaluate the radiation shielding efficiency of YBa2Cu3O7 and Y3Ba5Cu8O18 superconducting ceramics. In the current study, the radiation shielding efficiency of YBa2Cu3O7 and Y3Ba5Cu8O18 superconducting ceramics were calculated using the EGS4 code and discussed experimentally and theoretically by comparing with XCOM data. The mass attenuation coefficients (μ/ρ) for YBa2Cu3O7 and Y3Ba5Cu8O18 superconductors and their contents was investigated theoretically (EGS4 and WinXcom) and experimentally at gamma-ray energies from 122 to 1332 keV. The theoretical values have been computed in the energy range from 1 keV to 100 MeV using WinXcom program. Then, using the mass attenuation coefficients, it was determined some shielding parameters such as mean free path (MFP), half value layer (HVL), effective atomic number (Zeff), radiation protection efficiency (RPE) and gamma–ray kerma coefficients ((kγ). It has been seen that the theoretical and the empirical results were in agreement. The data and findings from this study can guide further research and development of shielding materials for gamma-ray and neutron shielding applications.

Yuksek, Mustafa; Kaya, Elif Çelenk; Karabulutlu, Nur; Kaya, Ahmet Afşin; Karabulut, Mevlut; Elmali, Ayhan

Unlike the earlier nonlinear optical studies of single walled carbon nanotubes (SWCNTs) which were generally carried out as solvent, in this study, we established to deposit the unsoluble SWCNTs as homogeneous thin films by blending them with phthalocyanines in PMMA host. The structural and morphological features of the thin films were studied by SEM and TEM imaging techniques while the linear, nonlinear-absorptions and carrier dynamic properties of the thin films were investigated with the UV–Vis spectrophotometer, open aperture Z-scan experiments and pump-probe technique, respectively. In addition, the optical limiting performances of the samples were calculated from nonlinear absorption spectra. It was observed that the linear- and nonlinear-absorptions and optical limiting performance of the thin films increased with the mixing of the SWCNT sample with the Pcs complexes. We have clearly explained the mechanisms contributing to the nonlinear optical absorption and optical limiting performances.