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.