Figure 1: Chromium atoms in Pb(111).
From: Mapping the orbital structure of impurity bound states in a superconductor
(a) Constant-current STM image of three Cr atoms in the Pb(111) surface (V=4 mV, I=10 pA, 12 × 12 nm2). The atom apparent height is 50 pm for these imaging conditions. (b) Result of a full DFT relaxation showing that the most stable position of a Cr atom (blue) is at a subsurface site (Pb atoms in yellow). (c) Top view of the local atomic surroundings of the embedded Cr atom, composed by seven Pb atoms all at a distance of ∼3±0.2 Å. The four largest Pb atoms are surface atoms. The relaxed Cr atom lies in a pseudo-FCC position, displaced towards two Pb atoms, which are slightly lifted above the surface plane. The resulting cluster resembles a distorted octahedron with an extra atom at one vertex.
