Sr-L3M4, 5M4, 5 Auger transitions in SrO, SrF2, SrTiO3, SrSi2 and SrAg were studied by tuning the synchrotron radiation at the Sr2p3/2 absorption edge (∼1945 eV). It was observed that the Sr-L3M4, 5M4, 5 spectator Auger line (∼1645 eV) shifts to higher electron energy side in proportion to the exciting photon energy. Detailed examination of the spectator Auger line showed that the spectral narrowings occur as well. These phenomena are discussed in relation to the localized Sr4d*-dominant states having a band-like character and are interpreted in terms of a new type of the Auger resonant Raman scattering.
A surface effect on the behavior of solid-liquid phase transition is studied by the Landau theory. We calculate the dependence of melting temperature of a small particleon its surface curvature. We show that taking account of the effect of the curvature is essential in understanding the melting process of small particles, particularly when their radii are in the order of nm. The non-linear relationship between a melting point and a reciprocal radius is derived from a difference between the radius-dependence of the “surface-induced melting temperature (Tst)” and that of the “particle melting temperature (Tend).” The calculated results agree satisfactorily with the recent experimental data. We also show that a surface melting state becomes difficult to observe as the particle radius decreases down to a critical value. This is in contrast to the common belief that surface-induced melting becomes more dominant for smaller particles.
A conjugated aromatic compound, 1, 4-bis[β-pyridyl-(2)-vinyl]benzene (P2VB), can be photopolymerized by UV irradiation (topochemical photopolymerization). This reaction is known to be sensitive to the features of the crystal structures of starting compounds. Ultra thin films of P2VB monomer deposited on highly oriented pyrolytic graphite (HOPG) and Au (111) substrates in high vacuum were studied at room temperature in air by scanning tunneling microscopy (STM). On the HOPG substrate, a spindle-like island structure and its molecular structure were observed. On the Au (111) substrate, the for-mation mechanism of the P2VB thin film was of the nucleation and growth type, in the case that the substrate temperature was kept at room temperature during deposition, but was of the monolayer overgrowth type with the substrate temperature up to 40°C. The molecular axis of the first monolayer was parallel to the step direction of Au substrate, indicating that the formation of monolayer is governed by the adsorption of these molecules to the step edge. In spite of the well-ordered structure, however, the obtained lattice constants did not satisfy the topochemical photopolymerization condition probably due to the strong interaction between the molecules and Au (111) reconstructed structure. The result obtained by “simultaneously UV-irradi-ated vacuum deposition” was also presented. In this case, we could observe a structure which may be assigned to poly-P2VB.
Thermal nitridation of clean Si by N2 has been studied by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). It was found that the degree of nitrogen coverage on (111) gradually increases with increasing nitridation temperature and decreases abruptly at around the 7×7 ↔ 1×1 transition temperature, while such a sudden change of coverage was not observed with Si (100) 2×1 surface. This result suggests higher reactivity of N2 with the 7×7 surface than with the unreconstructed 1×1 surface. Furthermore, chemical shifts of Si-2p and N-1s indicates that nitrided regions tend to be condensed forming completely-nitrided (Si3N4) islands with increasing nitridation temperature. These XPS results are evidenced by the behavior of dark and bright regions observed by STM; formation of these regions is strongly suppressed on terraces in the “1×1” temperature range and their dimensions become larger with increasing temperature. The dark regions are assigned from atom resolution images to “8×8” LEED pattern nitrides and the bright regions tentatively to “quadruplet” pattern nitrides.
The chemical composition and structure of ZrO/W (100) surface were examined by means of X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) in order to understand the lowering mechanism of work function on the surface. Deposition of several monolayers of zirconium onto a clean W (100) surface and following heating in oxygen ambience caused a decrease in work function and oxidation of zirconium, which was accompanied by change of the LEED, pattern. After the heating in oxygen, the crystal was flash-heated under a UHV condition at an elevated temperature. This treatment caused a chemical change from ZrO2 to Zr-O complex. The concentration of Zr-0 complex increased as the flashing temperature was raised, and at the same time, the LEED pattern changed from p (2×1) to c (4×2) pattern. The formation of Zr-O complex and the emergence of the c (4×2) pattern accompanied the lowering of work function to 2.7 eV. Stability of the Zr-O layer at a high temperature of 1800 K was also confirmed by XPS analysis at the temperature.
The hydrogen mediated growth process of Cu films on Si(111) surfaces is observed by medium energy ion scattering (MEIS), RHEED and AES. At room temperature, the role of hydrogen is not so prominent in the growth process. At high temperatures, however, formation of islands is observed. This indicates that the surface diffusion of Cu atoms is enhanced by the hydrogen termination.
The energy distribution of a scanning X-ray probe for XPS, which is equipped with an elliptical mirror monochromator, has been simulated by employing the optical ray tracing method with numerically described Al Kα X-ray and the rocking curve of α-quartz estimated by dynamical diffraction theory. For the evaluation of the validity simulation results, Fermi edge and 3d5/2 photoelectron spectra of silver were measured by a scanning XPS apparatus. From the simulation results, it was found that the peak energy of diffracted X-ray beam shifted to low energy region when X-ray beam size is increased, however the peak widths of energy distribution curves slightly increased with X-ray beam size. Using the simulated widths and an estimated apparatus function, those results were compared with the experimentally obtained energy widths of silver Fermi edge spectra by Al Ka excitation. The simulation results were in agreement with experimental results. In addition, the relationship between X-ray beam position on the anode and diffracted X-ray energy distribution was also investigated. The shift of peak energy of diffracted X-ray beam was proportional to the distance on the anode from the focal point of elliptical mirror monochromator in energy dispersive direction. Since the simulation results were in good agreement with experimental data, it is concluded that this kind of simulation is effectively used for estimating the beam shape and energy distribution of the diffracted X-ray beam.
We have investigated the structure and magnetic property of manganese stearate films prepared by Langmuir-Blodgett (LB) method. From the (00l) Bragg peak of the X-ray diffraction pattern, it is found that the films deposited on quartz substrates are Y-type LB film and Mn2+ ions in the film are arranged two-dimensionally with a lattice spacing of about 48.8 Å. The angular dependence of the (00l) Bragg peak intensity obtained from the structure factor of manganese stearate LB films calculated is consistent with the experimental data. Using SQUID magnetometry, the magnetic moment of the films was measured down to 1.7 K with applied magnetic field of 100 Oe perpendicular to the film surfaces. The susceptibility behaves according to the Curie-Weiss law in high temperature ranges and gradually deviates from the law below about 20 K. Comparing the magnetic moments measured at 1.7 K with two different applied magnetic fields perpendicular and parallel to the film surface, we observed magnetic anisotropy.
A novel cylindrical mirror analyzer (CMA) has been developed to obtain standard spectra in Auger electron spectroscopy. We obtained Auger electron spectra of gold, nickel, and soot (carbon). For gold, the details of the spectra are shown and the possible Auger transitions are identified for the whole range of energy by subtracting a background of assumed simple polynomial function. The total range spectra of nickel and soot are reported for the primary accelerating voltages ranging 1-5000V. In other words, the spectra of true secondary electron, Auger electron, loss electrons which excited shell electron and plasmon, and elastically backscattered primary electron are shown. It is found that the carbon (soot) as evacuated always presents clean surface without any ion sputtering treatment and the surface is quite stable.
The interaction between a planar SiO2 surface and a Si3N4 probe of AFM was measured in aqueous solutions of cationic surfactant homologues CH3(CH2)n-1 N(CH3)3Br (n=12∼18). The potential profiles changed with the surfactant concentrations. In the high concentration region, the mechanical strength of the adsorbed layer was examined by applying an excess pressure from the probe.