Browsing by Subject "Crystalline phasis"

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Open Access
Formation of B19′, B2, and amorphous phases during mechano-synthesis of nanocrystalline NiTi intermetallics
(Elsevier BV, 2014-02) Amini, R.; Alijani, F.; Ghaffari, M.; Alizadeh, M.; Okyay, Ali Kemal
Ni-50Ti shape memory alloy was synthesized by mechanical alloying of the elemental powders mixture under an argon gas atmosphere. The structural and microstructural properties of the alloyed powders were evaluated by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. Moreover, the Vickers microhardness of the powders was estimated at different milling times. According to the results, by milling progression, the amount of the amorphous phase increased considerably and after sufficient milling time (48h), the mechano-crystallization of the amorphous phase into the more stable crystalline phases (i.e. B2 and B19') occurred. It was found that the particles size and microhardness were significantly affected by the formation of the amorphous, B2, and B19' phases. It was also deduced that, by appropriate heating and cooling cycles, the B2 and thermally-induced B19' phases can be created. Furthermore, it was inferred that the formation of undesirable intermetallic phases (particularly NiTi2) during the heating cycle was considerably reduced by milling time evolution. © 2013 Elsevier B.V.
Open Access
Substrate temperature influence on the properties of GaN thin films grown by hollow-cathode plasma-assisted atomic layer deposition
(AIP Publishing LLC, 2016-02) Alevli, M.; Gungor, N.; Haider A.; Kizir S.; Leghari, S. A.; Bıyıklı, Necmi
Gallium nitride films were grown by hollow cathode plasma-assisted atomic layer deposition using triethylgallium and N2/H2 plasma. An optimized recipe for GaN film was developed, and the effect of substrate temperature was studied in both self-limiting growth window and thermal decomposition-limited growth region. With increased substrate temperature, film crystallinity improved, and the optical band edge decreased from 3.60 to 3.52 eV. The refractive index and reflectivity in Reststrahlen band increased with the substrate temperature. Compressive strain is observed for both samples, and the surface roughness is observed to increase with the substrate temperature. Despite these temperature dependent material properties, the chemical composition, E1(TO), phonon position, and crystalline phases present in the GaN film were relatively independent from growth temperature.