Tsugio Miyagawa

Surface segregations during epitaxial growth of Fe/Au multilayers on GaAs(001)

The epitaxial growth process of Fe/Au multilayers on GaAs(001) substrates at temperatures of between 300 and 573 K has been studied using reflection high-energy electron diffraction and Auger electron spectroscopy. The growth mode is identified as the layer-by-layer type. Surface segregations of As, Ga, Fe or Au atoms that constitute substrates and underlayers were observed during the growth processes of these multilayers, depending on the deposition condition. These surface segregations can be removed by sputter etching for a short period, and resegregation is not observed afterwards. Differences in the mechanisms of these and conventional surface segregations are discussed.

Microscopic processes in deposition-concurrent surface segregation

Abstract During the epitaxial growth process of Fe and Au films on GaAs(001)-4×6, we observed various types of deposition-concurrent surface segregation (DCSS). We have investigated the microscopic processes of DCSS using the in situ observation techniques of reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). The process of DCSS consists of two stages, the initial segregation stage in which deposited atoms react with a substrate to initiate a segregation and the continuous segregation stage which subsequently keeps the segregated atoms atop the film surface without being buried under later deposited atoms. An atomistic model for the continuous segregation stage has been proposed. We have discussed the application of the DCSS phenomenon to surfactant-mediated epitaxy techniques.

Mössbauer spectra and structures of Fe/Fe-N multilayered films formed by Fe sputtering and ECR nitrogen plasma exposure

Abstract Fe/Fe-N multilayered films were prepared by an alternation of Fe sputtering and Electron Cyclotron Resonance (ECR) nitrogen plasma exposure, and the films were investigated by 57 Fe Conversion Electron Mossbauer Spectroscopy (CEMS). ECR nitrogen plasma exposure of the sputtered Fe layers generated fine crystal ϵ-Fe 2-3 N and Fe 2 N grains, rather than thermally stable γ′-Fe 4 N. The Fe/Fe-N multilayered films has a periodic structure of [α-Fe]/[ϵ-Fe 2-3 N and Fe 2 N], and showed good soft magnetic properties.

Growth of Bi/Sb Superlattice

The present work describes the growth at room temperature of Bi, Sb and Bi-12 at.%Sb films on glass substrates and a Bi/Sb 40-layer superlattice film on a single-crystal Si (111) substrate. Thin-film X-ray diffractometer measurements strongly show the (003) orientation of these films. Four peaks are observed in small-angle X-ray diffraction measurements of the Bi/Sb superlattice film and indicate good periodicity. Direct transmission electron microscopy (TEM) observations also clearly show the superlattice structure.

RHEED Investigation of the Au(001)–p(2×2)–As Structure Induced by the Deposition-Concurrent Surface Segregation of As

We observed the p(2×2) structure on the surface of Au(001) during the epitaxial growth of Fe/Au multilayers on GaAs(001). This structure disappeared after removal of the segregated As atoms by sputter etching for a short period, and transformed to a hexagonal structure of the 5×1 type, the well-known surface reconstruction of the clean Au(001) surface. When the deposition of Au was conducted on sputter-etched clean surfaces of Fe(001), the surface structure was of the 5×1 type instead of p(2×2). These results show that the p(2×2) structure is induced by the surface segregation of As on Au surfaces during the deposition. The p(2×2) structure transformed to 1×1 after depositing less than 0.4 ML of Fe atoms. The correlation between the process of the deposition-concurrent surface segregation and the observed surface structure is discussed.

Magnetic properties of Fe‐Zr‐Co/Fe‐Zr‐Co‐N multilayered films

Fe‐Zr‐Co/Fe‐Zr‐Co‐N soft magnetic multilayered films were alternately prepared by Fe‐Zr‐Co alloy sputtering and electron cyclotron resonance plasma nitridation, and their magnetic properties and thermal stability were investigated. Co addition to Fe‐Zr/Fe‐Zr‐N multilayered films was effective in improving the magnetic properties of these films. The soft magnetic properties of these films demonstrated outstanding thermal stability, and it was observed that the hyperfine field Hint increased up to that for pure Fe‐Co alloy by heat treatment. Under the optimum preparation conditions, values for saturation flux density Bs of 2.02–2.06 T, coercivity Hc of 75–90 A/m, and relative permeability μ’≥3100 (at 20 MHz) were obtained in Fe84Zr8Co8/Fe84Zr8Co8‐N and Fe76Zr8Co16/Fe76Zr8Co16‐N multilayered films after annealing at 873 K for 3.6 ks.

Epitaxial Growth of Bi/Sb Superlattice

The present work describes the heteroepitaxial growth at room temperature of a Bi/Sb superlattice film, for the first time, on a single-crystal cleaved BaF2(111) substrate. Four peaks were observed in small-angle X-ray diffraction of the Bi/Sb superlattice film, denoting good periodicity. In situ reflection high-energy electron diffraction (RHEED) observations show epitaxial growth after 60 layers of superlattice deposition. Cross-sectional transmission electron microscopy (TEM) observations also show the single-crystal image and diffraction pattern.

Magnetic properties of Fe/Fe-N and Fe/Cu-N multilayered films having intermediate layers containing nitrogen

The structures and magnetic properties of Fe/Fe-N and Fe/Cu-N multilayered films having intermediate layers containing nitrogen were investigated. Fe/Fe-N films formed by alternate Fe sputtering and electron cyclotron resonance (ECR) nitrogen plasma exposure had Fe layers containing approximately 3 at% nitrogen, the /spl alpha/-Fe(110) lattice spacing being larger than that of pure iron. This expansion of the /spl alpha/-Fe(110) lattice spacing was observed after Fe deposition. The Fe layers containing a little nitrogen improved the soft magnetic properties. Fe/Cu-N multilayered films formed by the alternation of Fe sputtering and Cu-N nitrogen reactive sputtering also showed expansion of the /spl alpha/-Fe(110) lattice spacing and reduction of the Fe crystallite size with increasing partial N/sub 2/ gas pressure (PN/sub 2/) during Cu-N reactive sputtering. The Fe/Cu-N multilayered films achieved minimum coercivity at PN/sub 2/=7%. >