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Abstract: A series of Co-doped BaFe2−x Co x As2 (0≤x≤0.32) single crystals have been grown by self-flux method. Study of X-ray diffraction indicates that the lattice parameter c of the crystals decrease linearly with the increase in Co-content added to the initial mixtures. The segregation coefficient of Co related to Fe is determined to be ∼0.78. The values of superconducting transition temperature T c are found to increase to about 1–3K by post growth annealing at high temperature, which should result from the improved crystallinity due to the release of residual strain in the samples. In addition, we demonstrate that the annealing atmosphere of Ar, air or vacuum has an identical effect on the enhancement of T c . Due to inhomogeneous Co distribution, a broad transition temperature width ΔT c is observed and discussed for the over-doped samples. [Copyright &y& Elsevier]

Abstract: Sub-steps and defects of the {100} planes of Cu2+-doped L-arginine phosphate monohydrate (LAP) crystals are observed by atomic force microscopy. Formation of sub-steps is not due to the stacking faults but a result of single LAP: Cu2+ molecule acting as growth unit. Two-dimensional (2D) nuclei with the same height as sub-steps occur on the step-edges. Impurities of Cu2+ ions cause steps bunch and macrosteps formation. Liquid inclusions in the form of long channels form when the macrosteps lose their stability. Numerous small 3D growth hillocks are found in the channels. The extra stress induced by the 3D islands can result in dislocations and steps mismatches. [Copyright &y& Elsevier]