https://hdl.handle.net/20.500.12809/235 2026-04-19T12:13:40Z 2026-04-19T12:13:40Z Özden, Pınar Özden, Şadan Pakma, Osman Özenç, Mehmet Emin Avcı, Nejmettin Afşin Kariper I. https://hdl.handle.net/20.500.12809/11025 2023-10-17T12:15:29Z 2023-01-01T00:00:00Z

Electrical and photoresponse properties of metal–polymer–semiconductor device with TMPTA interface material Özden, Pınar; Özden, Şadan; Pakma, Osman; Özenç, Mehmet Emin; Avcı, Nejmettin; Afşin Kariper I. is study presents the pioneering fabrication of a metal–polymer–semiconductor (MPS) device, where trimethylolpropane triacrylate (TMPTA) was employed as the interface material for the first time. TMPTA offers significant advantages in terms of optoelectronic device fabrication and encapsulation, owing to its high light transmittance. The device was thoroughly characterized employing scanning electron microscopy (SEM) and electrical measurements, including current–voltage (I– V) and capacitance–voltage (C– V) analyses. The fabricated device demonstrated a notably elevated rectification ratio of 3000 along with a low reverse bias saturation current. Subsequently, the ideality factor and junction barrier potential were calculated to be 3.65 and 0.79 eV, respectively. Due to the low viscosity of the TMPA interface material, it was calculated that a series resistance of 6.7 kΩ calculated in the forward-bias region as a result of obtaining a thickness of approximately 200 nm by means of employing SEM measurements. The photodiode behavior of the device was shown through I– V measurements conducted under diverse illumination intensities. The observed exponential relationship between the photocurrent and illumination intensity strongly suggests the prevalence of the nanomolecular reassembly mechanism within the device. Additionally, frequency- and voltage-dependent capacitance measurements unveiled the substantial impact of state densities and series resistance effects at the interfaces of semiconductor–polymer and metal–semiconductor, resulting in noteworthy alterations in the device’s performance

2023-01-01T00:00:00Z Coşkun, Atilla Irmak, Ali Ekber Altan, Barış Ak, Yavuz Selim Coşkun, Arıçtan Tulga https://hdl.handle.net/20.500.12809/10914 2023-08-23T12:00:21Z 2023-01-01T00:00:00Z

Tuning the magnetic and magnetocaloric properties of a compound via mixing (1–x).La0.67Ca0.33MnO3 +x.La0.67Sr0.33MnO3 (x = 0, 0.25, 0.50, 0.75, 1): Composite materials or composite compounds? Coşkun, Atilla; Irmak, Ali Ekber; Altan, Barış; Ak, Yavuz Selim; Coşkun, Arıçtan Tulga This study aims to optimize the magnetic and magnetocaloric properties of composite materials (or compounds) produced by mixing different ratios of two manganite compounds having different structural, magnetic, and magnetocaloric properties. The parent compounds were prepared using the sol–gel production method and the ultrasonic bath mixing technique was involved to prepare desired composite materials. SEM analyses revealed that the parents and composite materials have the same surface morphologies except for their grain sizes. EDS analyses were performed to identify the possible/candidate phases in the composite materials. These candidate phases are involved in refining XRD data. The fact that the Curie temperatures (TC) of the composite materials were found to be much higher than those of the parent compounds was another proof that composite compounds were obtained instead of composite materials by using the ultrasonic bath mixing technique. Although the TC of the composite compounds was higher than those of the parent compounds, the maximum magnetic entropy values were found to vary between the maximum magnetic entropy valuesof the parent compounds.

2023-01-01T00:00:00Z Kuru, Fatma Çoban, Mustafa Burak Erkarslan, Uğur Dönmez, Adem Oylumluoğlu, Görkem Aygün, Muhittin Kara, Hülya https://hdl.handle.net/20.500.12809/10879 2023-08-11T10:55:32Z 2023-01-01T00:00:00Z

Improved photoluminescence properties of one-dimensional (1D) composite fibers of Ho@PVP and Yb@PVP prepared by electrospinning Kuru, Fatma; Çoban, Mustafa Burak; Erkarslan, Uğur; Dönmez, Adem; Oylumluoğlu, Görkem; Aygün, Muhittin; Kara, Hülya Two new Holmium3+ and Ytterbium3+ compounds, {Ho(4cba)3(phen)(H2O)} (1) and {Yb(4cba)3(phen)} (2) (4cba = 4-Cyanobenzoic acid, phen = 1,10-Phenanthroline) were synthesized. These compounds were then incorporated into a Polyvinylpyrrolidone (PVP) matrix at different concentrations (5 wt% to 25 wt%) using an electrospinning technique, resulting in the formation of 1D luminescent composite fibers, Ho@PVP and Yb@PVP. The products were analyzed using various characterization techniques to determine their structures and morphologies. A comprehensive study was conducted to investigate the thermal and photoluminescence properties of these composite nanofibers in comparison to their pure compounds. The findings revealed signif-icant enhancements in the photostability and thermal stability of the composite nanofibers due to the solid environment provided by PVP for the compounds. Furthermore, it was observed that the composite nanofibers exhibited notably superior the thermal-stability and the photo-stability when compared to their pure compounds.

2023-01-01T00:00:00Z Coşkun, A. Tulga Ak, Y. Selim Güleç N. Akça, Gönül Ekicibil A. Coşkun, Atilla https://hdl.handle.net/20.500.12809/10775 2023-06-13T08:09:10Z 2023-01-01T00:00:00Z

A comparative study of magnetic, and magnetocaloric properties of different transition metal-doped La0.67Sr0.33AO3 (A: Mn, Co, Cr, and Fe) samples Coşkun, A. Tulga; Ak, Y. Selim; Güleç N.; Akça, Gönül; Ekicibil A.; Coşkun, Atilla In the present work, structural, magnetic, and magnetocaloric properties of La0.67Sr0.33AO3 (A: Mn, Co, Cr and Fe) samples were examined. XRD analyses revealed that all samples produced by the sol–gel method and subjected to the same grinding and heat treatment steps crystallized in the perovskite crystal structure. In order to examine the magnetic behavior of the samples, temperature-dependent magnetization (M(T)) measurements were carried out. It was found that La0.67Sr0.33MnO3, which has the highest magnetization value, has the highest Curie temperature (T C = 368.2 K). In order to determine the magnetic phase transition order and calculate magnetic entropy change (- Δ SM) value, field-dependent magnetization (M(H)) measurements in the transition temperature region were carried at zero field-cooled (ZFC) and field-cooled (FC) processes. The maximum magnetic entropy change (-ΔSMmax) of La0.67Sr0.33MnO3 sample was calculated as 1.5 Jkg−1 K−1 under 1 T magnetic field change. La0.67Sr0.33CoO3 sample, in which antiferromagnetic (AFM) and ferromagnetic (FM) interactions coexist, exhibits a paramagnetic (PM)-FM phase transition at 244.1 K. At 1 T magnetic field change, the (-ΔSMmax) was found to be 0.145 Jkg−1 K−1 for this sample. La0.67Sr0.33CrO3 and La0.67Sr0.33FeO3 samples showed weak FM properties due to the different magnetic interactions originating from the ions in the B-sites of the samples. The magnetic phase transition is second-order for all samples.

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