Molecular structures of dicarboxylated viologens (1,1′-bis (7-carboxyheptyl)-4,4′-bipyridinium dibromide molecules, V-(C₇–COOH)₂) on a Cu(100) surface are studied by means of in situ scanning tunneling microscopy (STM) in combination with cyclic voltammetry (CV). Self-assembled monolayers of adsorbed dicarboxylated viologens form during an ongoing charge transfer reaction. Mainly six structures of the organic molecules are observed, including a dot array, metastable phases, stripe patterns, a closed stacking stripe pattern, chloride desorption, and a dimer phase. The molecular structural models for all the structures have been successfully established. The carboxylated viologen molecules in the dicationic state prefer the face-on configuration on the surface and form the dot array phase. The other phases are shown by the radical state of the viologens. The metastable phases show two forms: cluster-like and stripe pattern-like structures. Main features of the metastable phases are face-to-face configurations of the radical viologens in π-stacking form between neighboring parallel bipyridiniums. Hydrogen bonding is considered to be the major factor in constructing the network of the stripe pattern. At a more negative potential, the bilayers of the stripe pattern transform to be a monolayer of the closed stacking stripe pattern because of the enhanced electrostatic force. The closed stacking stripe pattern is stable on the surface until chloride desorption. As the chloride anions desorb from the Cu(100) surface, the disordered dimers transform to an ordered dimer phase on a Cu(100)-1×1 surface due to the hydrogen bonding between neighboring dimer rows.

Magnetic properties and surface structures of Ni/Cu(100) ultrathin films are studied by means of magneto-optical Kerr effect and in situ scanning tunneling microscopy in combination with cyclic voltammetry. At the initial stage of Ni deposition on a Cu(100) electrode, nickel atoms attach onto the steps and the surface shows single atomic steps corresponding to a layer-by-layer growth. For thicker Ni/Cu(100) films, nanometer-size clusters are randomly distributed on the surface showing a three-dimensional island growth. For thinner Ni layers in the coherent region, the magnetic anisotropy energy of the Cl-electrolyte/Ni interface is small. The reduction of squareness of the hysteresis loops is related to the inhomogeneous growth of the Ni layers. For thicker Ni layers in the incoherent region, the negative value of interface anisotropy for the Cl-electrolyte/Ni interface has a strong impact on perpendicular magnetic anisotropy and plays an important role on the reduction of the Ni thickness for spin reorientation transition in the electrolyte condition. By adding Pb additives, the deposition of a Pb wetting layer causes a defaceting phenomenon and the hydrogen evolution reaction is reduced. As the Ni thickness increases, the growth of Ni changes from layer-by-layer to quasi-two-dimensional islands with a flat top layer. With a Pb additive, the spin reorientation transitions of the Ni/Cu(100) system are not significantly influenced. However, due to the change of the growth mode by Pb atoms as a surfactant, the squareness of the hysteresis loops is enhanced for all the Ni thicknesses.

Modifying the interfacial conditions of magnetic layers by capping with overlayers can efficiently enhance the magnetic functionality of a material.

The influences of an Ag buffer layer on the magnetic properties of ultrathin Co/Ge(111) films grown at ambient temperature were studied using the surface magneto-optic Kerr effect technique. Due to the intermixing of Co adatoms and Ge(111) substrate, a nonferromagnetic layer forms at the initial stage of the deposition for Co/Ge(111) films. We demonstrate experimentally that the ferromagnetic inactive layer can be reduced by introducing an Ag buffer layer and the orientation of the easy axis of magnetization remains unchanged. Three magnetic phases have been resolved for Co/Ag/Ge(111) films with a Ag thickness less than 6 monolayers. In the phase diagram, the boundary between ferromagnetic and nonmagnetic regions shifts to a lower Co thickness from 10 to 5 monolayers as the thickness of the Ag layer increases from 0 to 6 monolayers.

A combination of a solution process and the control of the electric potential for magnetism represents a new approach to operating spintronic devices with a highly controlled efficiency and lower power consumption with reduced production cost. As a paradigmatic example, we investigated Co/Pt(111) in the Bloch-wall regime. The depression in coercive force was detected by applying a negative electric potential in an electrolytic solution. The reversible control of coercive force by varying the electric potential within few hundred millivolts is demonstrated. By changing the electric potential in ferromagnetic layers with smaller thicknesses, the efficiency for controlling the tunable coercive force becomes higher. Assuming that the pinning domains are independent of the applied electric potential, an electric potential tuning-magnetic anisotropy energy model was derived and provided insights into our knowledge of the relation between the electric potential tuning coercive force and the thickness of the ferromagnetic layer. Based on the fact that the coercive force can be tuned by changing the electric potential using a solution process, we developed a novel concept of electric-potential-tuned magnetic recording, resulting in a stable recording media with a high degree of writing ability.