Asymmetry effects in atomically resolved STM images of Cu(014)-O and W(100)-O surfaces measured with MnNi tips

We report on scanning tunneling microscopy (STM) studies of the Cu(014)-O and W(100)-O surfaces using MnNi tips. The STM data demonstrate asymmetry effects in atomically resolved images of W(100)-O as well as a regular apparent doubling of surface atomic features along the {110} direction in Cu(014)-O surface images. A qualitative explanation of the observed features based on tight-binding (TB) and density functional theory (DFT) calculations of the electronic structure of the MnNi tip is presented. The experimentally observed tip-sample distance dependence of atomically resolved images of Cu(014)-O surface and results of DFT and TB calculations show a significant role of different electron orbitals on both the tip and the surface atoms in the STM image formation.