The paper reports a comprehensive study of metal-organic polymers consisting of diamino-benzoquinonediimine (QDI) ligands coordinated with Co or Cr atoms synthesized under ultra-high-vacuum conditions on Au(111) surface. A combination of integral x-ray absorption spectroscopy with local-probe inelastic electron tunneling, corroborated by multiplet simulations of the x-ray spectra as well as the inelastic tunneling spectra enabled us to determine magnetic properties of the polymers, including the magnitude and orientation of the magnetic moments at Co and Cr atoms. The simulations of the inelastic tunneling spectra, measured with STM tips functionalized with a nickelocene molecule acting as a spin detector, were performed on an equal footing with the multiplet simulations of the x-ray absorption spectra. This was made possible thanks to a new theory introduced in the paper.
Scanning tunneling spectroscopy with a functionalized tip. Left: cartoon of the experiment – a spin with known properties is attached to the tip of the microscope and an unknown spin is adsorbed on the surface. Middle: measured tunneling current for different distances and different voltages between tip and surface. Right: result of a theoretical model of inelastic tunneling through two interacting spins (the closer they are, the more they interact). By comparing theory and experiment, it is possible to determine the energies of the individual states (Ψi) of the system coposed of the two coupled spins, and from there, the properties of the originally unknown spin.