Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 50Citation - Scopus: 52Monitoring the Characteristic Properties of Ga-Doped Zno by Raman Spectroscopy and Atomic Scale Calculations(Elsevier, 2019) Horzum, Şeyda; İyikanat, Fadıl; Senger, Ramazan Tuğrul; Çelebi, Cem; Sbeta, Mohamed; Yıldız, Abdullah; Serin, TülayWe experimentally and theoretically study how the structural and vibrational properties of zinc oxide (ZnO) are modified upon Gallium (Ga) doping. The characteristics of Ga-doped ZnO thin films which are synthesized by sol-gel spin coating method on glass substrates are monitored by using X-ray diffraction (XRD) and Raman scattering measurements. For atomic-level understanding of the experimental findings state-of-the-art density functional theory (DFT) based calculations are also performed. DFT calculations reveal that both the substitution and adsorption of Ga atoms in ZnO are energetically possible and substitutional doping in ZnO is the most favourable scenario. XRD measurements show that all the films are in wurtzite structure and the crystallite size of the films decreases with increasing Ga doping. In addition, Raman analysis show that strong vibrational modes at about 100 and 441 cm(-1) are associated with E-2(low) and E-2(high) phonon branches of ZnO, respectively. While the frequency of the E-2(low) mode downshifts with increasing Ga concentration, the E-2(high) phonon mode is not affected by the Ga doping. Furthermore, E-Ga phonon branch, stemming from the substituted Ga atoms, emerges at low frequencies. It is also seen that the Raman intensity of the E-G(a) peak linearly increases with increasing Ga concentration. Experimental results on the vibrational properties are in good agreement with the ab initio phonon calculations. (C) 2018 Elsevier B.V. All rights reserved.Article Citation - WoS: 42Citation - Scopus: 42Investigation of Humidity Sensing Properties of Zns Nanowires Synthesized by Vapor Liquid Solid (vls) Technique(Elsevier Ltd., 2011) Üzar, Neslihan; Okur, Salih; Arıkan, M. ÇetinZinc sulfide (ZnS) nanostructures were synthesized by vapor-liquid-solid (VLS) method which is based on thermal evaporation. The morphology, chemical composition and crystal structure of ZnS nanostructures were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analyses. The results of these studies revealed that wurtzite ZnS nanowires with diameters in range of 50-400 nm are obtained. In order to investigate the humidity sensing capability, quartz crystal microbalance (QCM) and electrical resistance measurement techniques were carried out at different relative humidity (RH) conditions between 33% and 100% RH at room temperature. QCM results show that the oscillating frequency of ZnS nanowires loaded on QCM crystal decreases in range of 33-84% RH, but increases at 90% and 100% RH. The sensitivity of ZnS nanowires-based sensor (R air/RRH) increases over 1000 times from 33% to 100% RH. These experimental results show that ZnS nanowires have a great potential for humidity sensing applications at room temperature.Article Citation - WoS: 31Citation - Scopus: 40Structural and Magnetic Characterization of Plasma Ion Nitrided Layer on 316l Stainless Steel Alloy(Elsevier Ltd., 2009) Öztürk, Orhan; Okur, Salih; Riviere, Jean PaulIn this study, an FeCrNi alloy (316L stainless steel disc) was nitrided in a low-pressure R.F. plasma at 430 °C for 72 min under a gas mixture of 60% N2-40% H2. Structural, compositional and magnetic properties of the plasma nitrided layer was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and magnetic force microscopy (MFM). The magnetic behaviour of the nitrided layer was also investigated with a vibrating sample magnetometer (VSM). Combined X-ray diffraction, cross-sectional SEM, AFM and MFM, as well as VSM analyses provide strong evidence for the formation of the γN phase, [γN-(Fe, Cr, Ni)], with mainly ferromagnetic characteristics. The uniform nature of the γN layer is clearly demonstrated by the XRD, cross-sectional SEM and AFM analyses. Based on the AFM and SEM data, the thickness of the γN layer is found to be ∼6 μm. According to the MFM and VSM analyses, ferromagnetism in the γN layer is revealed by the observation of stripe domain structures and the hysteresis loops. The cross-sectional MFM results demonstrate the ferromagnetic γN phase distributed across the plasma nitrided layer. The MFM images show variation in the size and form of the magnetic domains from one grain to another.Article Citation - WoS: 18Citation - Scopus: 22Microstructural and Mechanical Characterization of Nitrogen Ion Implanted Layer on 316l Stainless Steel(Elsevier Ltd., 2009) Öztürk, OrhanNitrogen ion implantation can be used to improve surface mechanical properties (hardness, wear, friction) of stainless steels by modifying the near-surface layers of these materials. In this study, a medical grade FeCrNi alloy (316L stainless steel plate) was implanted with 85 keV nitrogen ions to a high fluence of 1 × 1018N2+ / cm2 at a substrate temperature <200 °C in an industrial implantation facility. The N implanted layer microstructures, thicknesses and strengths were studied by a combination of X-ray diffraction (XRD), conversion electron Mössbauer spectroscopy (CEMS), atomic force microscopy (AFM) and nanohardness measurements. AFM was also used for the surface roughness analysis of the implanted as well as polished materials. The CEMS analysis indicate that the N implanted layer is ∼200 nm thick and is composed of ε-(Fe,Cr,Ni)2+xN-like nitride phase with mainly paramagnetic characteristics. The nanohardness measurements clearly indicate an enhanced hardness behaviour for the N implanted layer. It is found that the implanted layer hardness is increased by a factor of 1.5 in comparison to that of the substrate material. The increased hardness resulting from nitrogen implantation is attributed to the formation of ε nitride phase.