Kazuhisa Sueoka

Scanning Tunneling Microscopy Study of Surface Structure and Magnetism of Fe Thin Films Grown on MgO (001)

Substrate preparation procedure dependence of the growth morphology and magnetic properties of 25 ML bcc-Fe(001) thin films epitaxially grown on MgO(001) substrates in a wide range of growth temperature was investigated by means of scanning tunneling microscopy (STM) and superconducting quantum interference device (SQUID). The growth morphology of Fe thin films was uniform both on a polished and on an annealed substrate, but nonuniform on a cleaved substrate. It was very difficult to obtain a flat Fe thin film on the cleaved substrate, and the film became discontinuous at or above a growth temperature of 493 K. At a growth temperature of 550 K, atomically defined terraces of Fe thin films were formed on the annealed substrate but were not formed on the polished substrate. A continuous film grown on the annealed substrate at a temperature of 593 K has a less magnetic anisotropy. The other continuous films have low coercivity of about 8 Oe and a biaxial magnetic anisotropy. The dependency of the growth morphology and magnetic properties of Fe thin films upon substrate preparation procedures concerning the presence of step-terraces on the substrate surface is discussed.

Scanning Tunneling Microscopy Observation of Epitaxial bcc-Fe(001) Surface

We report the first atomic-resolution scanning tunneling microscopy (STM) image of epitaxial bcc-Fe(001) films grown on MgO(001) substrates. A 50-A-thick Fe film grown at a growth temperature of 550 K formed square pyramidal islands with atomically flat terraces. The terraces were found to range between 5 nm and 20 nm in width separated by monoatomic high steps. The film exhibited a (1×1) unreconstructed structure at a film thickness below 19 A; however, a reconstructed surface was found on thicker films. The atomic-resolution STM image and low energy electron diffraction (LEED) observation indicated that the reconstructed structure is a c(2×2) structure.

Atomically Resolved Imaging of a NiO(001) Surface

Metal oxides are of great technological importance because of the variety of applications in which they are involved. One example is their use in catalysis. The surface structure of metal oxides has thus been the subject of much investigation. However, the low conductivity inherent in metal oxides makes it difficult to measure surface structure using electron beams or by STM. NC-AFM provides atomically resolved images of semiconducting or conducting surfaces and even insulators. NC-AFM enables the direct surface imaging of metal oxides on an atomic scale. The forces detected by NC-AFM originate from several kinds of interaction between the surface and the tip, including in some cases magnetic interactions. Theoretical studies predict that shortrange magnetic interactions such as the exchange interaction enable NC-AFM to image magnetic moments on an atomic scale.