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Öğe Effect of Si on austenite stabilization, martensite morphology, and magnetic properties in Fe-26%Ni-x%Si alloys(Springer, 2011) Gungunes, H.; Yasar, E.; Dikici, M.The effect of Si on the austenite stabilization, martensite morphology, and magnetic properties in Fe-26%Ni-x%Si (x=3.5, 5, and 6) alloys have been studied by means of transmission electron microscopy (TEM) and Mossbauer spectroscopy techniques. TEM observations reveal that the martensite morphology is closely dependent on the Si content. The volume fraction changes of martensite and austenite phases, the hyperfine magnetic field, and isomer shift values have been determined by Mossbauer spectroscopy. The Mossbauer study reveals that the hyperfine magnetic field, the isomer shift values and the volume fraction of martensite decrease with increasing Si content.Öğe Infrared luminescence of annealed germanosilicate layers(Elsevier Science Bv, 2014) Tokay, M. S.; Yasar, E.; Agan, S.; Aydinli, A.In the light of growing importance of semiconductor nanocrystals for photonics, we report on the growth and characterization of annealed germanosilicate layers used for Ge nanocrystal formation. The films are grown using plasma enhanced chemical vapor deposition (PECVD) and post-annealed in nitrogen at temperatures between 600 and 1200 degrees C for as long as 2 h. Transmission electron microscopy (TEM), Raman scattering and photoluminescence spectroscopy (PL) has been used to characterize the samples both structurally and optically. Formation of Ge precipitates in the germanosilicate layers have been observed using Raman spectroscopy for a variety of PECVD growth parameters, annealing temperatures and times. Ge-Ge mode at similar to 300 cm(-1) is clearly observed at temperatures as low as 700 degrees C for annealing durations for 45 min. Raman results indicate that upon annealing for extended periods of time at temperatures above 900 degrees C; nanocrystals of few tens of nanometers in diameter inside the oxide matrix and precipitation and interdiffusion of Ge, forming SiGe alloy at the silicon and oxide interface take place. Low temperature PL spectroscopy has been used to observe luminescence from these samples in the vicinity of 1550 nm, an important wavelength for telecommunications. Observed luminescence quenches at 140 K. The photoluminescence data displays three peaks closely interrelated at approximately 1490,, 1530 and 1610 nm. PL spectra persist even after removing the oxide layer indicating that the origin of the infrared luminescent centers are not related to the Ge nanocrystals in the oxide layer. (C) 2013 Elsevier B.V. All rights reserved.Öğe Some characteristics of thermally induced martensite in Fe-30%Ni-3.6%Mo alloy(Elsevier Science Inc, 2008) Yasar, E.; Guler, E.; Gungunes, H.; Durlu, T. N.Kinetical, morphological and magnetic characteristics of thermally induced martensite in an Fe-30%Ni-3.6%Mo alloy has been studied by scanning electron microscopy, transmission electron microscopy and Mossbauer spectroscopy. Scanning electron microscope and transmission electron microscope observations revealed the occurrence of both athermal and isothermal martensitic transformation in the alloy. In addition, the magnetic properties of both the austenite and martensite phases were determined by the Mossbauer spectroscopy. The Mossbauer spectra showed a paramagnetic character for the austenite phase and an antiferromagnetic character for the martensite phase. (C) 2007 Elsevier Inc. All rights reserved.Öğe Studies of Al-Ti AHoys by SEM(Amer Inst Physics, 2007) Yildiz, K.; Atici, Y.; Kelioglu, K.; Yasar, E.Al-Ti (1, 2 wt. %) alloys were investigated by Scanning Electron Microscopy (SEM). SEM observations and energy-dispersive x-ray analyses (EDX) showed that the phase structure of Al-Ti (1 %) alloy at 165 mu m/s is composed of Al matrix and C, Ni, Fe and Si particles and the Al-Ti (1 %) alloys at 16 and 8 mu m/s have only the Al matrix and C particles. It was also found that the Al-Ti (2 %) form the Al matrix and intermetallic TiAl.
