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    Effects of substrate temperature and post-deposition anneal on properties of evaporated cadmium telluride films
    (Elsevier Science Sa, 2007) Bacaksız, E.; Basol, B. M.; Altunbaş, M.; Novruzov, V.; Yanmaz, E.; Nezir, S.
    The effects of substrate temperature and post-deposition heat treatment steps on the morphology, structural, optical and electrical properties of thin film CdTe layers grown by vacuum evaporation were investigated. Scanning electron microscopy and X-ray diffraction (XRD) techniques were employed to study the structural changes. It was observed that the grain sizes and morphologies of as-deposited layers were similar for substrate temperatures of - 173 degrees C and - 73 degrees C. However, CdTe films produced at a substrate temperature of 27 degrees C had substantially larger grain size and clearly facetted morphology. Annealing at 200-400 degrees C in air did not cause any appreciable grain growth in any of the films irrespective of their growth temperature. However, annealing at 400 degrees C reduced faceting in all cases and initiated fusing between grains. XRD studies showed that this behavior after annealing at 400 degrees C coincided with an onset of a degree of randomization in the originally strong (I 11) texture of the as-grown layers. Optical band gap measurements showed sharpening of the band-edge upon annealing at 400 degrees C and a band gap value in the range of 1.46-1.49 eV Resistivity measurements indicated that annealing at 400 degrees C in air forms a highly resistive compensated CdTe film. All results point to 400 degrees C to be a critical annealing temperature at which optical, structural and electrical properties of CdTe layers start to change. (c) 2006 Elsevier B.V. All rights reserved.
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    Hardness and microstructural analysis of Bi1.6Pb0.4Sr2Ca2−xSmxCu3Oy polycrystalline superconductors
    (Elsevier Science Sa, 2006) Kölemen, U.; Uzun, O.; Yilmazlar, M.; Güçlü, N.; Yanmaz, E.
    Bi1.6Pb0.4Sr2Ca2-xSmxCu3Oy superconductors with nominal substitution parameters x = 0.0, 0.001, 0.005, and 0.1 were prepared by the conventional solid-state reaction powder compacting method. The effects of Sm substitution on the phase formation, microhardness and surface microstructure of the samples were investigated. Phase examination by X-ray diffraction indicated that Sm substitution enhanced the formation of the Bi-2212 phase. Morphological investigations by scanning electron microscope revealed that both the number and size of the voids on the sample surfaces decreased with Sm enrichment. This result was also supported by density measurements of the samples. Additionally, indentation-induced Vickers microhardness testing results in the applied load range 0.245-2.940 N were presented. It was shown that microhardness values decreased non-linearly with increasing applied load in all cases. The experimental results were analyzed using the Kick's law, the Hays-Kendall approach and the modified proportional specimen resistance (PSR) model. The analyses revealed that Kick's law failed to explain the observed variations. Besides, the modified PSR model was more suitable than the Hays-Kendall approach to estimate load independent hardness of BSCCO superconductor. (c) 2005 Elsevier B.V. All rights reserved.