Microstructure of MgB2 thin film deposited on r-plane sapphire substrate by co-evaporation method

The microstructural features of MgB2 thin film deposited by co-evaporation method have been investigated by transmission electron microscopy (TEM). MgB2 thin films were deposited on r-plane sapphire substrate. The critical temperature of this film was measured to be similar to 28 K with Delta T-c of about 5 K. XRD data reveal that MgO is the major second-phase in MgB2 film. The surface morphologies have been observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Cross-sectional TEM images also showed that the MgB2 thin films deposited on r-plane sapphire substrate contained secondary phase such as MgO. Besides, according to the results of selected-area electron diffraction (SAD) patterns and high-resolution TEM (HRTEM) images, the MgB2 thin films deposited on the r-plane sapphire substrate comprised minor amount of the amorphous phase regions. The structural features of second-phase such as MgO and amorphous phase, crystal orientation across the interface. and defects in the cross-sectional direction were characterized with STEM-EDS and HRTEM. The correlation between superconducting properties and the MgB2 thin films microstructures are briefly discussed. (C) 2009 Elsevier B.V. All rights reserved.