Browsing by Subject "Crystal Structure"

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Open Access
MOCVD growth and optical properties of non-polar (11-20) a-plane GaN on (10-12) r-plane sapphire substrate
(Elsevier, 2010-11-15) Yu, H.; Ozturk, M.; Demirel, P.; Cakmak, H.; Özbay, Ekmel
Non-polar a-plane GaN film with crystalline quality and anisotropy improvement is grown by use of high temperature AlN/AlGaN buffer, which is directly deposited on r-plane sapphire by pulse flows. Compared to the a-plane GaN grown on AIN buffer, X-ray rocking curve analysis reveals a remarkable reduction in the full width at half maximum, both on-axis and off-axis. Atomic force microscopy image exhibits a fully coalesced pit-free surface morphology with low root-mean-square roughness (similar to 1.5 nm). Photoluminescence is carried out on the a-plane GaN grown on r-plane sapphire. It is found that, at low temperature, the dominant emission at similar to 3.42 eV is composed of two separate peaks with different characteristics, which provide explanations for the controversial attributions of this peak in previous studies. (C) 2010 Elsevier B.V. All rights reserved.
Open Access
Structural and microstructural phase evolution during mechano-synthesis of nanocrystalline/amorphous CuAlMn alloy powders
(Elsevier, 2013-11) Amini, R.; Mousavizad, S. M. M.; Abdollahpour, H.; Ghaffari, M.; Alizadeh, M.; Okyay, Ali Kemal
The formation mechanism of Cu-11.5Al-4Mn alloys by mechanical alloying (MA) of pure elemental powders was investigated. During milling, the powder sampling was conducted at predetermined intervals from 1 h to 96 h. The quantitative phase analyses were done by X-ray diffraction and the particles size and morphology were studied by scanning electron microscopy. Furthermore, the microstructure investigation and phase identification were done by transmission electron microscopy. Concerning the results, the nanocrystalline Cu solid solution were formed at short milling times and, by milling evolution, the austenite-to-martensite (2H) phase transformation occurred. Moreover, the formation of considerable amount of amorphous phase and its partial transformation to crystalline phases during the milling process were revealed. It was also found that, by milling development, the powder morphology changes from lamellar to semi-spherical and their size initially increases, then reduces and afterward re-increases.