M. Kubota

NEUTRON SCATTERING STUDIES ON MAGNETIC STRUCTURE OF THE DOUBLE-LAYERED MANGANITE LA2-2XSR1+2XMN2O7 (0.30 X 0.50)

Abstract Systematic powder diffraction studies have been carried out to establish the magnetic phase diagram of La 2−2 x Sr 1+2 x Mn 2 O 7 (LSMO327) in a wide hole concentration range (0.30≤ x ≤0.50), using the HERMES diffractometer. LSMO327 exhibits a planar ferromagnetic structure for 0.32≤ x ≤0.38 at low temperatures. A finite canting angle between planar magnetic moments on neighboring planes starts appearing around x ∼0.40 and reaches 180° (A-type antiferromagnet) at x =0.48. At x =0.30, on the contrary, the magnetic moments are aligned parallel to the c -axis.

Alloyed interface formation in the AuSi(111)2 × 1 system studied by photoemission spectroscopy

Abstract Room temperature deposition of gold (Au) on the Si(111)2×1 cleaved surface has been studied by photoelectron spectroscopy using synchrotron radiation. Binding energies of Si(2p) and Au(4f) and the splitting of the Au(5d) signal are changed with increasing coverage in a different manner below and above one monolayer coverage and reach to saturation values at 20–100 monolayers. The Au(4f) binding energy and the Au(5d) splitting at saturation are clearly different from those of pure Au metal. The origin of alloying in the AuSi(111)2×1 system is discussed from these results. A new model, “chemical bonding model” is proposed to explain the initial stage of the metallic overlayer formation in the AuSi(111) system.

Cs on Si(111)2×1: Si surface state and Cs valence state

Abstract Cesium atom adsorption on the Si(111)2×1 surface has been studied by angle-integrated photoemission spectroscopy. It was found that the intrinsic surface state of Si is always present throughout cesium monolayer formation and that the emission from Cs 6s electrons increases at high coverages. The character of cesium adsorption on Si(111)2×1 is discussed.

Unit cell step structures on vapour-grown Cr2S3 single crystals

Abstract Step structures on the (001) plane of as-grown crystalline Cr 2 S 3 that had been prepared by the chemical vapour deposition method have been observed by interference contrast microscopy. Two kinds of steps, with heights of 10.1 and 5.1 A were found. These are respectively due to the unit cell and a half of the unit cell of the crystal. Unit cell steps were seen to occur successively from a screw dislocation with Burgers vector normal to the surface equal to half of a unit cell. The generated steps with height equal to a half of the unit cell coagulated soon into a step with height of one unit cell. By passing other screw dislocations on the surface the unit cell steps combine with them just as expected from the screw dislocation model for monomolecular steps. The unit cell steps split spontaneously into half unit cell steps forming a fork-like step structure. The successively drawn out forking structure weaves an interlaced step pattern on the surface. However, the two interlaced steps annihilate when they meet.

Mechanism of alloy formation due to noble metal deposition on silicon surfaces at room temperature: Chemical bonding model

Abstract Room temperature deposition of noble metals of Au, Ag and Cu on a clean Si(111)2×1 surface is studied through photoemission using synchrotron radiation in order to clarify the phenomenon of room temperature alloyed interface formation (RTAIF) at metal (M)-semiconductor(S) contacts. Ag atoms behave differently on a clean Si(111)2×1 surface from the point of view of the RTAIF, in spite of the fact that Ag belongs to the same group as Au and Cu in the periodic table. As for the phenomenon of the RTAIF, experimental results are examined in the light of the “chemical bonding model” proposed by some of the authors and others.

Core-level photoemission spectra from Cs monolayers on Si(1 1 1)2 × 1

Abstract Band shape in the Cs 4 d core level of cesium atom monolayers adsorbed on Si(1 1 1)2 × 1 has been studied by photoemission spectroscopy using synchrotron radiation. Asymmetry appeared on the low kinetic energy side at high coverages of cesium atoms. This is caused by the energy loss due to the overlayer plasmon in the cesium atom monolayer of photoemitted Cs 4 d electrons.

Photoemission of Cs Valence Electrons from a Cs Monolayer on Si(111) 2×1

The adsorption of Cs atoms on the Si(111) 2×1 surface has been studied by photoelectron spectroscopy using synchrotron radiation. A photoemission peak due to Cs 6s valence electrons is clearly observed at full monolayer coverage by tuning photon energy at around 50 eV over an available energy range from 30 to 130 eV. The peak appears at almost the same initial energy (-1 eV) as that of the surface state of the clean Si(111) 2×1 surface. It is shown that the insulator-metal transition in the Cs monolayer takes place with increasing coverage.

Order-disorder transition on Si(001)

Abstract A phase transition between c(4x2) and 2x1 structures on the Si(001) surface has been observed at 200 K by low-energy electron diffraction. This transition is a second order order-disorder transition of the asymmetric dimer configuration. The streak pattern remains up to well above the transition temperature. The temperature dependence of the width and the length of the streak can be described in terms of the effects of a strong anisotropic coupling between adjacent asymmetric dimers.

Photoemission study of NaF and KF overlayers on GaAs surfaces

Abstract We present a synchrotron radiation photoemission investigation on the adsorption and desorption behaviour of vapour-deposited NaF and KF overlayers on the As-rich GaAs(1OO) and (111) surfaces. The results indicate a strong dependence on the overlayer species and the initial deposition, but not on the GaAs surface structure itself.

Examination of spin fluctuations within the MnO2 layers in a bilayer manganite La1.1Sr1.9Mn2O7

Abstract We have investigated antiferromagnetic (AFM) correlations within the MnO 2 layers in a canted AFM La 1.1 Sr 1.9 Mn 2 O 7 by neutron diffraction study. Intense ferromagnetic (FM) diffuse scattering exists even at room temperature, and the FM correlation grows with decreasing temperature.