Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Other Erratum To: Mbe-Grown Cdte Layers on Gaas With In-Assisted Thermal Deoxidation(Springer Verlag, 2016) Arı, Ozan; Bilgilisoy, Elif; Özçeri, Elif; Selamet, YusufArticle Citation - WoS: 6Citation - Scopus: 5Mbe-Grown Cdte Layers on Gaas With In-Assisted Thermal Deoxidation(Springer Verlag, 2016) Arı, Ozan; Bilgilisoy, Elif; Özçeri, Elif; Selamet, YusufMolecular beam epitaxy (MBE) growth of thin (∼2 μm) CdTe layers characterized by high crystal quality and low defect density on lattice mismatched substrates, such as GaAs and Si, has thus far been difficult to achieve. In this work, we report the effects of in situ thermal deoxidation under In and As4 overpressure prior to the CdTe growth on epiready GaAs(211)B wafers, aiming to enhance CdTe crystal quality. Thermally deoxidized GaAs samples were analyzed using in situ reflection high energy electron diffraction, along with ex situ x-ray photo-electron spectroscopy (XPS) and atomic force microscopy. MBE-grown CdTe layers were characterized using x-ray diffraction (XRD) and Everson-type wet chemical defect decoration etching. We found that In-assisted desorption allowed for easier surface preparation and resulted in a smoother surface compared to As-assisted surface preparation. By applying In-assisted thermal deoxidation to GaAs substrates prior to the CdTe growth, we have obtained single crystal CdTe films with a CdTe(422) XRD rocking curve with a full-width half-maximum value of 130.8 arc-s and etch pit density of 4 × 106 cm−2 for 2.54 μm thickness. We confirmed, by XPS analysis, no In contamination on the thermally deoxidized surface.Conference Object Citation - WoS: 33Citation - Scopus: 35Effects of Physical Growth Conditions on the Structural and Optical Properties of Sputtered Grown Thin Hfo2 Films(Elsevier Ltd., 2011) Aygün, Gülnur; Cantaş, Ayten; Şimşek, Yılmaz; Turan, RaşitHfO2 thin films were prepared by reactive DC magnetron sputtering technique on (100) p-Si substrate. The effects of O2/Ar ratio, substrate temperature, sputtering power on the structural properties of HfO2 grown films were studied by Spectroscopic Ellipsometer (SE), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrum, and X-ray photoelectron spectroscopy (XPS) depth profiling techniques. The results show that the formation of a SiOx suboxide layer at the HfO2/Si interface is unavoidable. The HfO2 thickness and suboxide formation are highly affected by the growth parameters such as sputtering power, O 2/Ar gas ratio during sputtering, and substrate temperature. XRD spectra show that the deposited films have (111) monoclinic phase of HfO 2, which is also supported by FTIR spectra. XPS depth profiling spectra shows that highly reactive sputtered Hf atoms consume some of the oxygen atoms from the underlying SiO2 to form HfO2, leaving Si-Si bonds behind. © 2010 Elsevier B.V. All rights reserved.Article Citation - WoS: 10Citation - Scopus: 11The Effects of Sb Substitution on Structural Properties in Yba 2cu 3o 7 Superconductors(Springer Verlag, 2011) Akyüz, Gönül B.; Kocabaş, Kemal; Yıldız, Aylin; Özyüzer, Lütfi; Çiftçioglu, MuhsinIn this study, the effects of partial Sb 3+ ion substitutions for the Y sites and the Cu sites on the superconducting properties of YBa 2Cu 3O y (Y123) ceramic superconductors were investigated. The samples were prepared by the conventional solid-state reaction method and the properties of the samples were investigated by means of X-ray diffraction, AC magnetic susceptibility measurements, scanning electron microscope, and energy dispersive X-ray analysis. The critical temperatures were determined to be in the range of 80-92 K for both Systems I and II. It was found that Sb-addition leads to the formation of the non-superconducting YBa 2SbO 6 phase, which has a negative effect on the critical temperature, since the highest critical temperature was measured for pure Y123. However, the increasing substitution level has a negligible effect on the X-ray diffraction analysis peak intensities of the superconducting phases. In addition, SEM images showed that Sb substitution decreases the grain size and modifies the microstructure development, which makes the samples denser.Article Citation - WoS: 17Citation - Scopus: 19Effect of Compaction Pressure on Structural and Superconducting Properties of Bi-2223 Superconductors(Springer Verlag, 2010) Kocabaş, Kemal; Gökçe, Melis; Çiftçioğlu, Muhsin; Bilgili, ÖzlemIn this work, effects of compaction pressure on the structural and superconducting properties of BSCCO ceramic superconductors were investigated. The study was carried out on two systems which were, System I: Bi 1.7Pb 0.3Sr 2Ca 2Cu 3O y and System II: Bi 1.6Pb 0.3Ag 0.1Sr 2Ca 2Cu 3O y, respectively. Ceramic powders were prepared by conventional solid-state reaction method and sintered at 850°C after compaction at five different pressures in the 150-750 MPa range. Critical temperatures of samples were determined by resistivity-temperature determinations made by four-point probe method in liquid nitrogen conditions. XRD analysis was conducted by powder X-ray diffraction method. Morphology of the grains present in the samples were determined by using scanning electron microscope (SEM) photographs at 2 K× and 2.5 K× magnifications for System I and System II, respectively. Sintered densities of the superconducting ceramics were measured by Archimedes water displacement method and unit cell parameters were additionally obtained from XRD data. T c values for System I was determined to be in the 109-115 K with sample D having the highest T c of 115 K while T c varied in the 104-109 K range and sample B had the highest T c value of 109 K for System II. The transition width, which is a sign of the purity of the samples, was determined to be narrow for both systems. The data obtained from X-ray diffraction measurements have shown that 2223 high-T c phase was dominant in both systems. The determination of the optimum pellet compaction pressure for BSCCO ceramic superconductors was the main purpose of this work. The results of this work indicated that compaction at around 450 MPa improves the superconducting and structural properties of the BSCCO ceramic superconductors. © 2009 Springer Science+Business Media, LLC.Article Citation - WoS: 12Citation - Scopus: 12The Effect of Zn Substitution of Ca in Bipbsrcacuo Superconductors Sintered at 830°c(Springer Verlag, 2009) Kocabaş, Kemal; Şakiroğlu, Serpil; Çiftçioğlu, Muhsin; Ercan, İsmail; Epik, Hakan; Bilgili, ÖzlemThe effect of partial substitution of Ca by Zn in Bi 1.7Pb 0.3Sr 2Ca 2-x Zn x Cu 3O y at x=0.00, 0.05, 0.10, 0.15 and 0.20 levels on the electrical and structural properties was investigated in this work. The characterization of the ceramics prepared by the conventional solid-state reaction method were done by resistance-temperature measurements, XRD, SEM and density analysis. Low levels of Zn substitution of Ca caused significant changes in the properties of the ceramics. The low-T c superconducting properties were enhanced and the fraction of the low-T c (2212) phase were found to increase at x=0.15 level of Zn substitution at 830°C sintering temperature. Zero resistance was observed only in sample D with x=0.15 and the T c was determined as 92 K. The SEM micrographs and the density analysis have shown that this was the densest packed ceramic.Article Citation - WoS: 19Citation - Scopus: 21Microwave Effect on Ion-Exchange and Structure of Clinoptilolite(Springer Verlag, 2007) Akdeniz, Yelda; Ülkü, SemraThe effect of microwave irradiation on the ion exchange degree and structure of clinoptilolite mineral has been examined in comparison with the conventional heat treatment in waterbath. Clinoptilolite-rich mineral from the Western Anatolia, Bigadiç region was used for the experimental study. The mineral was mainly clinoptilolite (80-85%) and additionally, quartz (5-10%), and analcime+mordenite (<5%) were found as co-existing minerals. The mineral was stable towards dehydration and maintains its original structure up to 800°C. The BET and Langmuir surface areas of the sample were found to be 22 and 17m2/g for N2 adsorption and 28 and 22m2/g for Ar adsorption, respectively. For the exchange experiments, clinoptilolite rich mineral was treated with 1N NaCl salt solution both in a microwave unit and waterbath for 10min, 1h and 2h at 80°C. The waterbath treatment with the same conditions was continued for two additional weeks. The chemical composition of the parent and Na-exchanged forms of the clinoptilolite rich minerals were analyzed by using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). Microwave treatment was found to be more rapid and effective for ion exchange compared to conventional waterbath treatment. Additionally, the XRD results reveal that microwave irradiation has zero effect on the structure of the clinoptilolite rich mineral.Article Citation - WoS: 30Citation - Scopus: 35Effect of Temperature and Time on Zinc Borate Species Formed From Zinc Oxide and Boric Acid in Aqueous Medium(American Chemical Society, 2007) Eltepe, H. Emre; Balköse, Devrim; Ülkü, SemraThe effect of temperature and time of heating of zinc oxide and boric acid in aqueous medium on product type, dehydration behavior, crystal morphology, and structure was investigated for the production of flame retardant and smoke suppressant zinc borate. Two different products dehydrated at 140 and 350°C were obtained and characterized by thermal gravimetric analysis, X-ray diffraction, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy.Article Citation - WoS: 6Citation - Scopus: 5Cobalt Coated Substrate for Matrix-Free Analysis of Small Molecules by Laser Desorption/Ionization Mass Spectrometry(Elsevier Ltd., 2009) Yalçın, Talat; Li, LiangSmall molecule analysis is one of the most challenging issues in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. We have developed a cobalt coated substrate as a target for matrix-free analysis of small molecules in laser desorption/ionization mass spectrometry. Cobalt coating of 60-70 nm thickness has been characterized by scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, and laser induced breakdown spectroscopy. This target facilitates hundreds of samples to be spotted and analyzed without mixing any matrices, in a very short time. This can save a lot of time and money and can be a very practical approach for the analysis of small molecules by laser desorption/ionization mass spectrometry.Article Citation - WoS: 11Citation - Scopus: 13Liquid-Phase Oxidation of Carvacrol Using Zeolite-Encapsulated Metal Complexes(American Chemical Society, 2006) Güneş, Alev; Bayraktar, Oğuz; Yılmaz, SelahattinWe report here the use of zeolite-encapsulated metal (salpn) complexes as catalysts in the oxidation reaction of the natural compound carvacrol in acetonitrile with hydrogen peroxide as the oxidant. No previous studies on the oxidation of carvacrol in the presence of metal salpn complexes have been reported. By using a general flexible ligand method, Cr(III), Fe(III), Bi(III), Ni(II), and Zn(II) complexes of N,N′-bis(salicylidene)propane1,3-diamine (H2salpn) encapsulated in NaY zeolite were prepared. All catalysts were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses to confirm the complex encapsulation. The activities of all prepared catalysts for the oxidation of carvacrol and hydrogen peroxide were tested. The performances of all catalysts were compared on the basis of the leaching test results and carvacrol conversions. Thymohydroquinone and benzoquinones were observed as byproducts at high conversions of carvacrol. No product was formed in the absence of a catalyst. Fe(salpn)-NaY catalyst exhibited the highest carvacrol conversion of 27.6% with a yield of 22.0%, followed by Cr(salpn)-NaY catalyst with 23.5% carvacrol conversion and a yield of 17.6%. Other catalysts have shown relatively lower performances in terms of carvacrol conversion and leaching. The Cr(salpn)-NaY catalyst was found to be a more efficient catalyst than others on the basis of leaching and activity tests. With the selected catalyst Cr (salpn)-NaY, the effects of temperature and carvacrol/hydrogen peroxide molar ratio on carvacrol oxidation reactions were investigated. Increasing the temperature from 40 to 60 °C caused an increase in the thymoquinone yield from 6.2% to 16.0%. An increase in carvacrol/hydrogen peroxide molar ratio from 1 to 3 resulted in a decrease in the thymoquinone yield.