Identify the chemical and electronic inhomogeneity in optimally Co doped BaFe$_{\mathrm{\mathbf{2}}}${As}$_{\mathrm{\mathbf{2}}}$

Combined scanning tunneling microscopy, spectroscopy and local barrier height (LBH) image studies show that low temperature cleaved optimal doped Ba(Fe$_{\mathrm{1-x}}$Co$_{\mathrm{x}})_{\mathrm{2}}$As$_{\mathrm{2\thinspace }}$single crystals have complicate morphologies, by means of the mixture of the Ba dominated bright patches and As dominated stripes. Although the surface morphologies are different, the superconducting gap maps show same gap width and similar nanometer size inhomogeneity. Based on the spectroscopy and LBH maps, the bright patches and dark stripes variations in the morphologies were identified as Ba or As dominated surface terminations. Magnetic impurities are believed to create local in-gap state and suppressed coherent peaks of the SC. This study will clarify the debate on the terminations of the cleavage surface of the Fe based 122 superconductors. This research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.