Browsing by Author "Selvi S."
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Item Improving the resolution of beta scattering spectroscopy(2004) Celiktas C.; Selvi S.; Yegin G.We have examined the performance of a modified beta-ray spectrometer using a pulse shape analyzer/timing single channel analyzer and related electronics, thereby preserving the low energy electron tail in measurement of the scattered electron spectra from an n-type Si wafer target. Comparison of measurements with the scattering spectra calculated by the Monte Carlo program EGS4 indicates good agreement across a significant part of the spectrum, an exception being for the energy region 30-100keV. Re-evaluation of existing scattering cross-sections would be useful, as would possible geometrical effects of the scattering arrangement used herein. Present efforts seek to contribute to the evaluation of electron scattering cross-sections and improvement in theoretical models. © 2004 Elsevier Ltd. All rights reserved.Item High fluence effects on ion implantation stopping and range(2005) Selvi S.; Tek Z.; Öztarhan A.; Akbaş N.; Brown I.G.We have developed a code STOPPO which can be used to modify the more-widely used ion implantation codes to more accurately predict the mean nuclear and electronic stopping power, preferential sputtering and range of heavy ions in monatomic target materials. In our simulations an effective atomic number and effective atomic mass are introduced into conveniently available analytical stopping cross-sections and a better fitting function for preferential sputtering yield is carefully evaluated for each ion implantation. The accuracy of the code confirmed experimentally by comparison with measured Rutherford backscattering spectrometry (RBS) concentration profiles for 130 keV Zr ions implanted into Be to fluences of 1 × 1017, 2 × 10 17 and 4 × 1017 ions/cm2. We find a steady increase in the mean nuclear and electronic stopping powers of the target; the increase in nuclear stopping power is much greater than the increase in electronic stopping power. © 2004 Elsevier B.V. All rights reserved.Item Optical properties of Cu implanted ZnO(2006) Cetin A.; Kibar R.; Ayvacikli M.; Can N.; Buchal Ch.; Townsend P.D.; Stepanov A.L.; Karali T.; Selvi S.Nanoparticles of Cu have been made in zinc oxide crystals by ion implantation. The Cu ions were implanted at 400 keV into the (0 0 0 1) face of a single crystal. After implantation and after post-irradiation annealing there are numerous changes in the luminescence responses which include a variety of green and yellow emission bands. Following annealing at temperatures up to 1000 °C a green luminescence near 525 nm was observed which has been associated with the isolated Cu ions. The changes between as implanted and annealed luminescence signals suggests that the implants generate clustering or nanoparticle formation of Cu but anneals dissociate them. © 2006 Elsevier B.V. All rights reserved.Item Optical properties of Tb implantation into ZnO(2007) Çetin A.; Kibar R.; Ayvacikli M.; Tuncer Y.; Buchal Ch.; Townsend P.D.; Karali T.; Selvi S.; Can N.ZnO [0001] single crystals were implanted at room temperature with 400 keV Tb+ ions at fluences in the range of 1 × 1016-2 × 1017 ions/cm2. Zinc oxide was chosen because of its potential for photonic applications as a semiconductor with high radiation resistance. After implantation and post-irradiation annealing, optical absorption was measured in a UV-VIS-NIR range and radioluminescence spectra were recorded at room temperature. Emission signals were generated by the Tb+ ion implants and intrinsic emission of the ZnO matrix were observed. The implant signal intensities were comparable with the host radioluminescence, even though the implants modify the surface of the crystal. It is suggested that the presence of Tb at high concentration generates stresses which influence the bulk material and also potentially forms precipitates or nanoparticles in the near surface region. Overall ion implantation of ZnO results in strongly modified luminescence. © 2007.Item Luminescent, optical and color properties of natural rose quartz(2007) Kibar R.; Garcia-Guinea J.; Çetin A.; Selvi S.; Karal T.; Can N.Rose quartz is an interesting mineral with numerous impurities that have been studied by scanning electron microscopy (SEM), X-ray fluorescence (XRF), X-ray diffraction (XRD), cathodoluminescence (CL), ion beam luminescence (IBL), radioluminescence (RL), thermoluminescence (TL) and optical absorption (OA). After HF etching, rose quartz from Oliva de Plasencia (Caceres, Spain) shows under SEM the presence of other silicate phases such as dumortierite [Al6.5 - 7 (BO3) (SiO4)3 (O, OH)3]. The OA spectrum of rose quartz suggests that these inclusions are the cause of coloration of rose quartz. The luminescence (CL, IBL, RL, TL) spectra behavior, at both room temperature and lower, confirms that the ∼ 340 nm emission could be associated with Si-O strain structures, including non-bridging oxygen or silicon vacancy-hole centers; the observed ∼ 400 nm emission could be associated with recombination of a hole trapped adjacent to a substitutional, charge-compensated aluminum alkali ion center; the ∼ 500 nm emission could be associated with substitutional Al3 + and the ∼ 700 nm peak could be associated with Fe3 + point defects in Si4 + sites. These results suggest that, while defect properties of rose quartz are not greatly dissimilar to those of purer forms of quartz and silica, further research seems necessary to determine criteria for the evolution of the newly-formed self-organized microstructures in the rose quartz lattice under irradiation. © 2007 Elsevier Ltd. All rights reserved.Item Characterization of Ti + N and Zr ion implanted 316 L stainless steel(2007) Tek Z.; Öztarhan A.; Selvi S.In this study, polished 316LSS stainless steel has been implanted with Ti + N and Zr ions at fluence of 2 × 1017 ions/cm2 and 1 × 1017 ions/cm2, respectively. Ion charge state distributions of Ti + N and Zr were measured by time-of-flight spectrometry, and the mean energies of these ions were determined. The Zr concentration profiles were obtained by Rutherford backscattering spectrometry. The range distribution of ions in implanted and unimplanted samples were evaluated using TRIM and STOPPO programs and the results were compared with the experimental data, which were in good agreement. The influence of the ions on the mechanical behavior of the 316LSS was investigated. The measurements show that after Ti + N implantation; the friction coefficient decreases, the hardness value increases, the wear resistance decreases and after Zr implantation; the friction coefficient decreases, the hardness value increases and the wear resistance increases with respect to an unimplanted sample. © 2007 Elsevier B.V. All rights reserved.Item A comparative study of Ti + N and W ion implantation into Ti-6Al-4V alloy(2007) Tek Z.; Öztarhan A.; Selvi S.The effect of Ti + N hybrid ion implantation and W ion implantation at a dose of 1 × 1017 ions/cm2, and 50 kV and 40 kV extraction voltage on mechanical properties of Ti-6Al-4V samples was studied. Mechanical tests have shown that the friction coefficient decreased with both Ti + N and W ion implantations. It was observed that the Ti + N hybrid ion implanted samples gave better results compared to those of the W ion implanted ones. The results of wear tests showed that both Ti + N hybrid and W ion implanted samples had much better wear resistance compared to unimplanted samples. Hardness values for Ti + N hybrid ion implanted and W implanted samples were much higher than those for unimplanted ones. Ti + N and W ions charge state distributions were measured using time of flight spectrometry. W concentration profiles were obtained by Rutherford backscattering spectrometry. These and the range distribution of ions in implanted and unimplanted samples were evaluated using TRIM and STOPPO programs [S. Selvi, Z. Tek, A. Oztarhan, I. Brown, N. Akbaş 'High fluence effects on ion implantation stopping and range', Nuclear Instruments and Methods in Physics Research B 229 (2005) 60-64; J.F. Ziegler, J.P. Biersack, U. Littmark, (Pergamon, New York, 1985); also http://www.SRIM.org] and the results were compared with the experimental data. © 2007 Elsevier B.V. All rights reserved.Item Luminescence properties of Tb implanted ZnO(2009) Cetin A.; Kibar R.; Selvi S.; Townsend P.D.; Can N.ZnO [0 0 0 1] crystals were irradiated at room temperature with Tb+ ions of 400 keV with fluences from 1×1016 to 2×1017 cm-2. The implanted layer was examined by several methods, including radioluminescence (RL), Rutherford backscattering spectrometry (RBS) and optical spectroscopy. The optical extinction spectra were simulated using Mie scattering theory. Absorption spectra predicted by Mie theory for particles of decreasing diameter were compared with those obtained experimentally. Some qualitative agreement between theoretical and experimental data was achieved. It was also shown that the intensities of the characteristic green emission bands associated with Tb produced by 5 D4 → 7 Fj = 5, 4 transitions have increased about 8 times after annealing. Optical spectroscopy and radioluminescence data have revealed that the ion implantation is a promising tool for synthesizing Tb nanoparticles in the ZnO surface. The Tb nanoparticles exhibit a rather weak plasma resonance. © 2009 Elsevier B.V. All rights reserved.Item Absorption and cathodoluminescence properties of Cu implanted SrTiO3(2010) Kibar R.; Çetin A.; Selvi S.; Can N.Single crystal of SrTiO3 (STO) has been implanted at room temperature with 200 and 400 keV Cu ions to doses ranging from 1×1016 to 1×1017 ions/cm2. The temperature cathodoluminescence (CL) of Cu implanted SrTiO3 has been studied in order to clarify the role of them in luminescence. Therefore CL measurements made on SrTiO3 implanted with metal ions are reported at 300 K with different excitation modulation frequencies. Room temperature ion implantation into surface layer changes low temperature CL signals both in terms of their relative intensities and also modifying the emission spectra. For such a large ion dose the unusual aspect is that the signals are still recognisable. The details of such changes and modifications of emission spectra are reported and discussed. A particularly important result is that the CL demonstrates that the implants cause bulk relaxations of the material that are apparent via the rear face CL. © 2009 Elsevier B.V. All rights reserved.