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- ArticleYalnız künye2026Novel fabricated CoxCrxNixFexAlxTixByMnyRz (R: Mo, Ta, W, Hf and Nb; x = 13, y = 5, z = 12) high entropy alloys for nuclear applications: Radiation interaction and structural features
Aygun, Murat; Aygun, Zeynep; Ercan, Ercan; Astam, Aykut
The principal aim of the paper is to produce innovative alloys for the purpose of investigating their structural properties, as well as their capacity for radiation protection. In this regard, novel CoxCrxNixFexAlxTixByMnyRz (R: Mo, Ta, W, Hf and Nb; x = 13, y = 5, z = 12) alloys were synthesized and mean free path, half value layer, effective atomic number, linear and mass attenuation coefficients, atomic and electronic cross sections, fast neutron removal cross section, buildup factors of the alloys were calculated by employing Phy-X/PSD software. Spectroscopic methods (SEM-EDS and XRD) were performed to get structural findings for the alloys. Attenuating effect of fast neutrons are also achieved to be similar as that of photon. The conclusion drawn from this study is that all of the produced alloys, especially CoxCrxNixFexAlxTixByMnyWz, can be considered suitable new shields for applications where high temperatures are experienced. It can be also stated that W improves the radiation protection properties. The study was conducted with the objective of fabricating new high entropy alloys to enhance radiation protection, and with the objective of generating extensive data on the radiation protective and structural properties of the alloys.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2024Tavlama İşleminin SILAR Tekniğiyle Elde Edilen Cu3SnS4 İnce Filmlerin Yapısal ve Optik Özellikleri Üzerine Etkisi
Astam, Aykut; Cemal, Çetin
Cu3SnS4 ince filmler, sıralı iyonik tabaka adsorpsiyonu ve reaksiyonu (SILAR) tekniği kullanılarak cam altlıklar üzerine oda sıcaklığında büyütüldü ve azot atmosferinde farklı sıcaklıklarda tavlanarak büyütme sonrası tavlama işleminin filmlerin yapısal ve optik özellikleri üzerindeki etkileri incelendi. Filmlerin yapısal, yüzey morfolojik ve optik özellikleri X-ışını kırınımı (XRD), taramalı elektron mikroskobu (SEM), enerji dağılımlı X-ışını analizi (EDAX), Raman spektroskopisi ve optik soğurma ölçümleri kullanılarak incelendi. XRD sonuçları, filmlerin tavlama öncesinde tetragonal Cu3SnS4 fazından oluştuğunu, tavlama sıcaklığının arttırılmasının kristal yapının iyileşmesine ve Cu4SnS4, Cu2S ve CuS ikincil fazlarının oluşmasına neden olduğunu ortaya çıkardı. SEM görüntüleri, filmlerin nanometre boyutunda rastgele şekilli parçacıklardan oluştuğunu gösterdi. EDAX ölçümleri Cu, Sn ve S elementlerinin varlığını ve ayrıca tavlama sıcaklığının artmasıyla Sn ve S elementlerinin miktarlarının azaldığını ortaya koydu. Raman spektrumları Cu3SnS4 fazının ve yüksek tavlama sıcaklıklarında Cu4SnS4, Cu2S ve CuS ikincil fazlarının oluşumunu doğruladı. Optik soğurma ölçümlerinden filmlerin direkt geçişlere sahip olduğu ve artan tavlama sıcaklığıyla yasak enerji aralığı değerinin 1.62 eV'dan 1.47 eV'a azaldığı belirlendi.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2024Effect of Hydrothermal Reaction Temperature on the Structural and Optical Properties of CuO Thin Films
Astam, Aykut; Kaya, Ömer
Copper oxides are one of the first semiconductors studied for device applications. In the present work, CuO thin films were deposited on fluorine-doped tin oxide (FTO) substrates via hydrothermal method without using any surfactant and the effects of reaction temperature on the properties of the films were studied. CuO thin films deposited at different reaction temperatures were characterized for their structural and optical properties using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Raman spectroscopy, and optical absorption measurements. XRD results revealed that all the films consisted of polycrystalline CuO with a monoclinic crystal structure without any impurity phase. SEM images showed that chrysanthemum-like structures were formed, the number of which increased with increasing hydrothermal reaction temperature. EDAX measurements proved the existence of Cu and O elements and showed that all the films have Cu/O ratios close to unity. The Raman spectra confirmed the formation of crystalline CuO in all the films. From the optical absorption measurements, the direct forbidden energy gap values of the CuO thin films were found to be between 1.34 eV and 1.41 eV, depending on the hydrothermal reaction temperature.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2024Effect of Substrate Temperature on Structural, Morphological, and Optical Properties of Gallium Oxide Thin Films Deposited by RF-Sputtering
Yildiz, Fevkani; Akcay, Hulya; Astam, Aykut; Kundakci, Mutlu
In this paper, gallium oxide (Ga2O3) thin films at various substrate temperatures (Ts) were grown on Indium Tin Oxide (ITO), glass, p-type silicon by radio-frequency magnetron sputtering (RFMS). We investigated how structural, morphological and optical properties change with various Ts. XRD results of thin films grown on p-type silicon substrate suggest that crystallinity properties of synthesized thin films strongly depend on the Ts. From SEM and AFM analyses of Ga2O3 thin films grown on p-type silicon substrate, it was observed that when the temperature increased, a porous structure appeared, and the grain size changed depending on the Ts. Moreover, obtained results from the absorption measurements, the bandgap energy of Ga2O3 thin films grown on the p-type silicon substrate decreased with increasing substrate temperature.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2023Vertically Well-Aligned ZnO Nanoscintillator Arrays with Improved Photoluminescence and Scintillation Properties
Kurudirek, Murat; Kurudirek, Sinem V.; Hertel, Nolan E.; Erickson, Anna; Sellin, Paul J.; Mukhopadhyay, Sharmistha; Astam, Aykut; Summers, Christopher J.
ZnO nanoarrays were grown via a low-temperature hydrothermal method. Solutions, each with different additive combinations, were prepared and evaluated. The effects of the additives involved in the growth procedure, i.e., ammonium hydroxide and sodium citrate, were studied in terms of the morphological, optical and scintillation properties of the ZnO nanostructures. Measurement of the nanorod (NR) length, corresponding photoluminescence (PL) and scintillation spectra and their dependence on the additives present in the solution are discussed. ZnO NRs grown on a silica substrate, whose UV transmission was found to be better than glass, showed high-quality structural and optical properties. It was found that the addition of sodium citrate significantly reduced defects and correspondingly increased the intrinsic near-band-edge (NBE) UV emission intensity at ~380 nm. To obtain high-quality nanostructures, samples were annealed in a 10% H2 + 90% N2 atmosphere. The anneal in the forming gas atmosphere enhanced the emission of the UV peak by reducing defects in the nanostructure. NRs are highly tapered towards the end of the structure. The tapering process was monitored using time growth studies, and its effect on PL and reflectance spectra are discussed. A good alpha particle response was obtained for the grown ZnO NRs, confirming its potential to be used as an alpha particle scintillator. After optimizing the reaction parameters, it was concluded that when ammonium hydroxide and sodium citrate were used, vertically well-aligned and long ZnO nanoarrays with highly improved optical and scintillation properties were obtained.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2023Hydrothermal synthesis of MnCO3 thin film and its conversion to Mn-oxides by annealing in different atmospheres
Astam, Aykut; İnanç, Cemal Turgay
Transition metal carbonates are of great interest, not only as alternative electrode materials in Li/Zn/Na/K-ion batteries or supercapacitors, but also as solid precursors for the synthesis of transition metal oxides via thermal decomposition. In this work, thin films of MnCO3 were deposited on quartz substrates via a mild one-pot hydrothermal process without using any catalysts or templates and the conversion of these films to manganese oxides through post-deposition thermal annealing for 1 h in air and nitrogen atmospheres was investigated. The films were analyzed by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and optical absorption measurements before and after annealing. The obtained results showed that as deposited films composed of MnCO3 with an impurity phase of Mn3O4 and annealing in air atmosphere caused the conversion of the films to Mn2O3, whereas nitrogen atmosphere led to the conversion to MnO with a secondary phase of Mn3O4. After annealing in both atmospheres, the size and shape of the microcubic structure were mainly retained, except for porosity caused by the release of CO2 and O2 gases. From the analysis of the room temperature optical absorption measurements, direct optical band gaps of the as deposited and air annealed films were determined as 3.27 eV and 2.30 eV, respectively, whereas the nitrogen annealed film was found to have two band gaps of 2.50 eV and 2.71 eV.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2018Interfacial engineering of CuO nanorod/ZnO nanowire hybrid nanostructure photoanode in dye-sensitized solar cell
Kilic, Bayram; Turkdogan, Sunay; Astam, Aykut; Baran, Sümeyra Seniha; Asgin, Mansur; Gur, Emre; Kocak, Yusuf
Developing efficient and cost-effective photoanode plays a vital role determining the photocurrent and photovoltage in dye-sensitized solar cells (DSSCs). Here, we demonstrate DSSCs that achieve relatively high power conversion efficiencies (PCEs) by using one-dimensional (1D) zinc oxide (ZnO) nanowires and copper (II) oxide (CuO) nanorods hybrid nanostructures. CuO nanorod-based thin films were prepared by hydrothermal method and used as a blocking layer on top of the ZnO nanowires’ layer. The use of 1D ZnO nanowire/CuO nanorod hybrid nanostructures led to an exceptionally high photovoltaic performance of DSSCs with a remarkably high open-circuit voltage (0.764 V), short current density (14.76 mA/cm2 under AM1.5G conditions), and relatively high solar to power conversion efficiency (6.18%). The enhancement of the solar to power conversion efficiency can be explained in terms of the lag effect of the interfacial recombination dynamics of CuO nanorod-blocking layer on ZnO nanowires. This work shows more economically feasible method to bring down the cost of the nano-hybrid cells and promises for the growth of other important materials to further enhance the solar to power conversion efficiency.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2017Structural and optical properties of Cu2SnS3 thin films obtained by SILAR method
Astam, Aykut
Cu2SnS3 thin films were obtained by annealing of SILAR deposited films at 350°C for 1 hour in sulphur atmosphere. The structural and optical properties of the films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and optical absorption measurements, before and after annealing. The XRD results showed that the annealing process transformed the crystal structure of the films from amorphous to polycrystalline. SEM images revealed that the surface morphology of films was changed after annealing while EDAX analysis showed that the films were excess in copper concentration before and after annealing. Optical absorption measurements confirmed that the direct band gap of films decreased from 1.27 eV to 1.21 eV with annealing.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2017Graphene-based copper oxide thin film nanostructures as high-efficiency photocathode for p-type dye-sensitized solar cells
Kilic, Bayram; Turkdogan, Sunay; Astam, Aykut; Baran, Sümeyra Seniha; Asgin, Mansur; Cebeci, Hulya; Urk, Deniz
Graphene-based p-type dye-sensitized solar cells (p-DSSCs) have been proposed and fabricated using copper oxide urchin-like nanostructures (COUN) as photocathode with an FeS2 counter electrode (CE). COUN composed of Cu2O core sphere and CuO shell nanorods with overall diameters of 2 to 4μm were grown by a simple hydrothermal method with self-assemble nucleation. It was figured out that the formation of copper oxide core/shell structures could be adjusted by an ammonia additive leading to pH change of the precursor solution. In addition to a photocathode, we also demonstrated FeS2 thin films as an efficient CE material alternative to the conventional Pt CEs in DSSCs. FeS2 nanostructures, with diameters of 50 to 80 nm, were synthesized by a similar hydrothermal approach. FeS2 nanostructures are demonstrated to be an outstanding CE material in p-DSSCs. We report graphene/COUN as photocathode and Pt/FeS2 as CE in p-DSSCs, and results show that the synergetic combination of electrodes in each side (increased interconnectivity between COUN and graphene layer, high surface area, and high catalytic activity of FeS2) increased the power conversion efficiency from 1.56% to 3.14%. The excellent performances of COUN and FeS2 thin film in working and CEs, respectively, make them unique choices among the various photocathode and CE materials studied.
RDL Kalıcı Kaydıİncele - Conference ObjectYalnız künye2016Effect of thickness on electrical properties of SILAR deposited SnS thin films
Akaltun, Yunus; Astam, Aykut; Cerhan, Asena; Çayir, Tuba; Akkus, B.; Dogan, G.S.; Mutlu, R.B.C.; Yalcin, L.S.; Oktem, Y.
Tin sulfide (SnS) thin films of different thickness were prepared on glass substrates by successive ionic layer adsorption and reaction (SILAR) method at room temperature using tin (II) chloride and sodium sulfide aqueous solutions. The thicknesses of the films were determined using spectroscopic ellipsometry measurements and found to be 47.2, 65.8, 111.0, and 128.7nm for 20, 25, 30 and 35 deposition cycles respectively. The electrical properties of the films were investigated using d.c. two-point probe method at room temperature and the results showed that the resistivity was found to decrease with increasing film thickness.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2016Conversion of SILAR deposited Cu3Se2 thin films to Cu2-xSe by annealing
Astam, Aykut; Akaltun, Yunus; Yildirim, Muhammet
Thin films of copper selenide were deposited onto glass substrates using SILAR method at room temperature and annealed at 573 K for an hour in nitrogen atmosphere. As-deposited and annealed films were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, Raman spectroscopy, and optical absorption measurements. X-ray diffraction studies revealed that annealing the films in nitrogen atmosphere led to conversion of the tetragonal Cu3Se2 phase to cubic Cu2-xSe phase. Scanning electron microscopy images showed a considerable change in the morphology of the films and energy dispersive X-ray analysis demonstrated a reduction in selenium content with annealing. Typical Raman spectra of copper selenide thin films were obtained from the as-deposited and annealed films. Using optical absorption measurements, direct band gap energies of Cu3Se2 and Cu2-xSe phases were found to be 2.72 eV and 2.15 eV, respectively.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2016Preparation of carbon nanotube/TiO2 mesoporous hybrid photoanode with iron pyrite (FeS2) thin films counter electrodes for dye-sensitized solar cell
Kilic, Bayram; Turkdogan, Sunay; Astam, Aykut; Ozer, Oguz Can; Asgin, Mansur; Cebeci, Hulya; Urk, Deniz; Mucur, Selin Pravadili
Multi-walled carbon nanotube (MWCNT)/TiO2 mesoporous networks can be employed as a new alternative photoanode in dye-sensitized solar cells (DSSCs). By using the MWCNT/TiO2 mesoporous as photoanodes in DSSC, we demonstrate that the MWCNT/TiO2 mesoporous photoanode is promising alternative to standard FTO/TiO2 mesoporous based DSSC due to larger specific surface area and high electrochemical activity. We also show that iron pyrite (FeS2) thin films can be used as an efficient counter electrode (CE), an alternative to the conventional high cost Pt based CE. We are able to synthesis FeS 2 nanostructures utilizing a very cheap and easy hydrothermal growth route. MWCNT/TiO2 mesoporous based DSSCs with FeS2 CE achieved a high solar conversion efficiency of 7.27% under 100 mW cm-2 (AM 1.5G 1-Sun) simulated solar irradiance which is considerably (slightly) higher than that of A-CNT/TiO2 mesoporous based DSSCs with Pt CE. Outstanding performance of the FeS2 CE makes it a very promising choice among the various CE materials used in the conventional DSSC and it is expected to be used more often to achieve higher photon-to-electron conversion efficiencies.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2016Produce of graphene/iron pyrite (FeS2) thin films counter electrode for dye-sensitized solar cell
Kilic, Bayram; Turkdogan, Sunay; Ozer, Oguz Can; Asgin, Mansur; Bayrakli, Ozge; Surucu, Gokhan; Astam, Aykut; Ekinci, Duygu
Dye-sensitized solar cells (DSSCs) provide a low cost alternative to the conventional solar cells due to their easy and inexpensive device fabrication steps. Generally, F:SnO2 (FTO) conductive glass with a thin layer coating of platinum (Pt) is used as a counter electrode (CE) in DSSCs. Since Pt is rare and therefore expensive metal, we were looking for a way to produce a new counter electrode based on graphene/iron pyrite (FeS2) thin films as an alternative to the Pt:FTO. In combination with a TiO2 mesoporous photoanode and an I3−/I- redox electrolyte, graphene/FeS2 CE based DSSC shows η=7.43% energy conversion efficiency under 1 sun illumination (100 mW/cm2, AM 1.5G) which is approximately 16.1% higher than conventional Pt CE (η=6.40%). External Quantum Efficiency (EQE) is found to be shifted upward when graphene/FeS2 is used as CE in the place of Pt CE. The excellent performance of the graphene/FeS2 CE makes it a very promising alternative to costly Pt in DSSCs.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2014An investigation on SILAR deposited CuxS thin films
Astam, Aykut; Akaltun, Yunus; Yildirim, Muhammet
A copper sulfide thin film was deposited on glass substrate by successive ionic layer adsorption and reaction method at room temperature, using cupric sulfate and sodium sulfide aqueous solutions as precursors. The structural, surface morphological, optical, and electrical properties of the as-deposited film were investigated via X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, optical absorption, and d.c. 2-point probe methods. The film was found to be amorphous, dense, and uniform. Average atomic percentage of Cu:S in the as-deposited film was calculated as 63:37. The band gap energy of copper sulfide thin film was found to be 2.14 eV and the resistivity was 10-2ω cm at room temperature. The effect of annealing on crystal structure was also studied and reported. X-ray diffraction patterns revealed that annealing the film at various temperatures slightly improved the crystallinity. By using thermoelectric power measurement, p-type electrical conductivity was determined for as-deposited and annealed samples..
RDL Kalıcı Kaydıİncele - Review ArticleYalnız künye2009Annealing and light effect on structural, optical and electrical properties of CuS, CuZnS and ZnS thin films grown by the SILAR method
Ali Yildirim, M.; Ateş, Aytunç; Astam, Aykut
CuS, Cu0.6Zn0.4S and ZnS thin films were grown by successive ionic layer adsorption and reaction (SILAR) method on glass substrates at room temperature. The annealing temperature effect on the crystal structure, optical band gap and the light effect on the electrical properties of these films have been investigated. Scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques were used for the investigation of structural properties of films. The SEM and XRD studies showed that the films are covered well with glass substrates and exhibit polycrystalline characterization. Using the absorption measurements, the band gap energies for CuS, Cu0.6Zn0.4S and ZnS thin films were found as 2.03, 2.14 and 3.92 eV at room temperature, respectively. The two-point-probe method was used for the investigation of electrical properties of films and it was found that the current increase with increasing light intensity and increasing rate in illuminated 500 W cm-2 films was greater than in others. There is an important increasing in the current values of the CuS and Cu0.6Zn0.4S films which have annealed at 400 °C. But the annealed ZnS thin film has less current values than the as-grown film. This is the first study which led to deposition of the CuZnS thin films by using the SILAR method.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2007Annealing and light effect on optical and electrical properties of ZnS thin films grown with the SILAR method
Ates, Aytunc; Yildirim, M. Ali; Kundakci, Mutlu; Astam, Aykut
Zinc sulphide (ZnS) thin films were grown on glass substrates by the Successive Ionic Layer Adsorption and Reaction (SILAR) technique at room temperature and ambient pressure. Surface morphologies of grown films were characterized using scanning electron microscopy (SEM). The crystal structure and crystal size of the thin films were characterized by the X-ray diffraction (XRD) method and found that the films exhibit polycrystalline characterization. The optical absorption measurements were done as a function of the temperature at 10-320 K temperature range. Using absorption measurements, the band gap energies were calculated at 10 and 320 K, as 3.83 and 3.72 eV, respectively. The annealing temperature effect on optical band gap and the light effect on the electrical properties of ZnS thin films were investigated and it was found that the current increased with increasing light intensity. The annealed films were found have more resistance than the as-grown film.
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