Hofer, W. A.Palotas, K.Rusponi, S.Cren, T.Brune, H.2009-04-142009-04-142009-04-14200810.1103/PhysRevLett.100.026806https://infoscience.epfl.ch/handle/20.500.14299/37239WOS:00025247120007012057We demonstrate that the giant spin contrast observed by scanning tunneling microscopy for double-layer Coislands on Pt(111) is caused by adsorbates at the apex of the Cr-coated W tip. The most likely candidate, in ab initio simulations, is hydrogen. Here, the electron charge is highly polarized by the adjacent Cr layers. The hydrogen adsorption site is shown to change from hollow to on top due to the electric field at the tip apex, created by the tunnel voltage.Surface Electronic and Atomic StructureSpectroscopySpin-Polarized STMtext::journal::journal article::research article