Aksoy Pehlivanoglu, Seval; Bayram, Sinan

In this work, the structural, morphological and optical properties of the eumelanin film fabricated on an FTO substrate were first investigated. Then, the effects of illumination intensitiy on the optoelectronic properties of the device fabricated on p-Si substrate (Eumelanin/p-Si) were investigated. The deposited film was identified as polycrystalline from the XRD pattern. The crystallite size was found to be approximately 13 nm. Surface morphology analysis of the film was carried out using atomic force microscopy (AFM) measurements. The surface roughness value (Rq) of the film was determined to be 55.7 nm. The film’s transmittance in the visible region is approximately 83%. The average refractive index in the visible region was calculated to be 1.39. The value of the eumelanin film was determined using both the Tauc technique and the Kubelka-Munk function. The direct and indirect optical bandgaps of eumelanin were calculated using both the Tauc method and the Kubelka-Munk function. The calculated direct and indirect optical bandgap values are, respectively, 2.79 eV and 1.96 eV for the Tauc method, and 2.65 eV and 1.79 eV for the Kubelka-Munk method. The electronic parameters of Eumelanin/p-Si heterostructure were derived from its characteristics. The charge transport mechanisms controlling the diode behavior of the eumelanin/p-Si structure were investigated and analyzed using the power law relationship. measurements performed at various illumination intensities indicated that the device exhibited photoconductive behavior. All the results obtained from this study demonstrate the potential of eumelanin/p-Si device to be used in photonic applications.

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Yücel, Harun

Due to diffraction patterns in light microscopy, the overlapping of colloid images introduces minor errors in determining particle positions, which affecting the accuracy of observing interactions between colloids near contact. This study quantitatively investigates the errors arising from the overlapping effect in force measurements between two closely positioned colloids using digital video microscopy (DVM). For this aim, computer simulations were conducted to obtain the positions of two optically trapped colloids interacting based on a force model and particle images were generated as a time series using experimental particle intensity profiles for two different particle sizes. These generated images were analyzed using tracking algorithms from the literature and the interaction forces were extracted and compared with theoretical force values. The results demonstrated that diffraction patterns significantly influence the accuracy of particle position detection and interaction force calculations. Large diffraction patterns and intensity fluctuations in an image introduce significant errors. However, these errors can become significantly smaller in the presence of large forces and may therefore be considered negligible.

İncele

Alım, Bünyamin

In this study, it is aimed to investigate alloys that can replace lead and its derivatives in terms of radiation shielding. A new alternative shielding material must have optimum properties that should be present in a protective material. For this purpose, this study focused on the determination of the radiation-shielding characteristics of five different alloys named Tin-Silver, Manganin-R, Hastelloy-B, Hastelloy-X and Dilver-P. The photon interaction parameters (µ, µm, λ, X1/2, σT, σe, Zeff, Neff, σeff and RPE) that give significant information about the radiation shielding capacities of the materials were calculated for the alloys in the energy range from 30 to 1333 keV. The narrow-beam transmission geometry was used to determine these parameters accurately and was adjusted such that the error rate is minimized. The present samples were irradiated with photons of nineteen different photon energies emitted from seven different radionuclides (241Am, 133Ba, 109Cd, 152Eu, 22Na, 137Cs and 60Co). Photon intensities were measured by using two different detectors (Si(Li) and NaI(Tl)) for convenient photon energy regions. Then, these parameters were also calculated theoretically using Phy-X/PSD software in order to compare the experimental and theoretical results. Furthermore, the Rinc/total, Zeq, G-P fitting coefficients (a, b, c, d and XK) and exposure build-up factors (β) for the alloys were calculated using Phy-X/PSD software at photon energy range from 0.015 to 15 MeV. In order to make a significant comparison about the shielding capacities of investigated alloys, the µm values obtained for the alloys were compared with corresponding values of Pb metal, RS 253 glass and Cupero-Nickel alloy. Consequently, the descending order of MAC values in the all surveyed energy region was obtained as Tin-Silver > Manganin-R > Hastelloy-B > Hastelloy-X > Dilver-P. In the low energy region, it was found that the all present alloys have better shielding performances than RS 253 glass and Cupero-Nickel alloy. The experimental results also revealed that the Tin-Silver alloy has 25% better shielding performance than Pb metal in the energy range of 30–88 keV. Finally, it was concluded that Manganin-R alloy could be considered as the most ideal shielding material in the entire photon energies studied along with its other superior features (high density (10.22 g cm−3), high melting point (2500–2600 °C), high tensile strength (560–1150 MPa), high modulus of elasticity (320 GPa) and high specific heat (305 J K−1 kg−1) although the Tin-Silver alloy had the highest µm values among the examined alloys.

AtıfScopus57·WoS49·OpenAlex58

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Bayram, Ozkan; Guney, Harun; Ertargin, Mehmet Emrah; Igman, Erdal; Simsek, Onder

In this study, the effect of Cu doping on the optical, structural and wettability properties of the nanostructured Cu-doped Mn3O4 (CMO) thin films obtained by using successive ionic layer adsorption and reaction technique was systematically investigated. The optical, morphological, structural and wettability properties of the nanostructured CMO films were determined using scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–Vis spectroscopy, and water contact angle (WCA) measurements. There were significant differences in the crystal structure of the nanostructured CMO thin films. The Cu doping disrupted this structure of pure (undoped) Mn3O4 films and caused the formation of the porous structure. Optical properties such as extinction coefficient, refractive index, and dielectric constants and optical band gap, were determined for nanostructured CMO films. Compared with pure films, the band gap of Cu-doped films decreased from 2.06 to 1.71 eV with increasing Cu concentration. The dielectric constants of the films showed that the nanostructured CMO films have a transparent structure. At 300 nm wavelength, the dielectric constants of pure Mn3O4 films were 2.22 while the calculated dielectric constants at increasing doping concentrations were 3.55, 2.41 and 2.25. It was also found from the WCA measurements that the thin films were hydrophilic in character and the WCA values for the nanostructured CMO thin films were measured as 24, 29 and 40 of degree.

AtıfScopus23·WoS22·OpenAlex26

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Yudar, H. Hakan; Korkmaz, Şadan; Özen, Soner; Şenay, Volkan; Pat, Suat

This study focused on the characterization and properties of transparent and conductive indium tin oxide (ITO) thin films deposited in argon atmosphere. ITO thin films were coated onto glass substrates by radio frequency (RF) magnetron sputtering technique at 75 and 100 W RF powers. Structural characteristics of producing films were investigated through X-ray diffraction analysis. UV–Vis spectrophotometer and interferometer were used to determine transmittance, absorbance and reflectance values of samples. The surface morphology of the films was characterized by atomic force microscope. The calculated band gaps were 3.8 and 4.1 eV for the films at 75 and 100 W, respectively. The effect of RF power on crystallinity of prepared films was explored using mentioned analysis methods. The high RF power caused higher poly crystallinity in the produced samples. The thickness and refractive index values for all samples increased respect to an increment of RF power and were calculated as 20, 50 nm and 1.71, 1.86 for samples at 75 and 100 W, respectively. Finally, the estimated grain sizes for all prepared films decreased with increasing of 2θ degrees, and the number of crystallite per unit volume was calculated. It was found that nearly all properties including sheet resistance and resistivity depend on the RF power.

AtıfScopus11·WoS10·OpenAlex11

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Hasar, Ugur Cem; Barroso, Joaquim José; Kaya, Yunus; Ertugrul, Mehmet; Bute, Musa; Catalá-Civera, José M.

A two-step measurement procedure has been proposed for measurement of complex permittivity of dielectric materials using one-port reflection measurements. In the procedure, as a first step, a graphical method is applied to analyze on the complex reflection-coefficient plane the general pattern of dielectric behavior of the sample. Then, as a second step, optimization algorithms are utilized for retrieving electrical properties of samples. The procedure requires measurement of complex reflection scattering parameters of at least two samples with different lengths. It has been validated by X-band measurements of three polyvinyl chloride samples with lengths 5, 10, and 20 mm.

AtıfScopus14·WoS13·OpenAlex15

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