STM investigations of pristine gold(111) at low temperature and surface-supported magnetic clusters

The electronic properties of surfaces can be quite different from bulk electronic properties. Some causes of these differences are reduced dimensionality and symmetry. This thesis work is centered around a series of local spectroscopic studies of the surface of a gold (Au) crystal, both pristine and in the presence of magnetic clusters. The purpose of this work is to better understand low dimensional electronic behavior, as well as magnetism in surface-supported atomic scale structures. These studies were carried out using a custom-designed ultrahigh vacuum scanning tunneling microscope, operating at low temperature. Local STM spectroscopic measurements were used to spatially resolve the electronic structure of the Au(111) surface at low temperature. From these measurements, the long-range herringbone reconstruction on Au(111) is seen to act as a superlattice for surface state electrons, creating a new band-structure and modulated surface electronic density. These observations are quantitatively explained by an extended Kronig-Penney model. In order to study the electronic properties of magnetic clusters at the nanometer lengthscale, magnetic atoms were deposited onto the surface of Au(111). STM spectroscopy of individual cobalt atoms reveals a narrow resonance at the Fermi energy that is identified as the Kondo effect—the predicted response of a magnetic impurity in a metal host. The variation of this Fermi energy resonance with interatom separation was studied using atomic manipulation to vary the spacing between magnetic atoms. In the case of cobalt atoms, the resonance is shown to remain unchanged until the distance between the atoms becomes less than 4 Å, at which point the resonance either vanishes or is greatly reduced. In the case of nickel atoms, a more elaborate behavior is observed. Possible interaction mechanisms between the impurities and their implications on the magnetism of nano-clusters are explored.