Self-assembly of tetracyanonaphtho-quinodimethane (TNAP) based metal-organic networks on Pb(111): Structural, electronic, and magnetic properties

We use scanning tunneling microscopy and spectroscopy to investigate structural and electronic properties of tetracyanonaphtho-quinodimethane (TNAP) based metal-organic networks on a superconducting Pb(111) surface. At low temperatures, the TNAP molecules form densely packed islands. When deposited at room temperature, Pb adatoms are incorporated into fourfold bonding nodes with the TNAP molecules leading to long-range ordered porous structures. Co-deposition of NaCl with TNAP yields a Na source for an ionically bonded Na-TNAP structure. Fourfold bonding motifs are also created by Fe atoms with the cyano terminations of TNAP. However, the structures are irregular and do not sustain the formation of long-range ordered networks. Some Fe centers with molecules surrounded in a local C2 symmetry exhibit Shiba states as a fingerprint of a magnetic interaction with the superconducting surface.