Masaoki Oku

X-ray photoelectron spectroscopy of manganese—oxygen systems

Abstract The Mn 2p, Mn 3s, Mn 3p, and O 1s spectra of various manganese oxides were studied at room temperature, 200 °C, and 400 °C. The binding energies of

X-ray photoelectron spectroscopy of Co3O4, Fe3O4, Mn3O4, and related compounds

Abstract The metal 2p region spectra of the mixed valence spinels, Co3O4, Fe3O4, Mn3O4, and related compounds were studied. The satellite splittings of Co 2p 3 2 for the octahedrally coordinated cobaltous ions are 6.2 eV and those for the tetrahedrally coordinated ones are about 5.3 eV. The Co 2p spectrum for Co3O4 is considered to be the sum of spectra of magnetic cobaltous ions and low-spin cobaltic ions. In the cases of Fe3O4 and Mn3O4, the oxidation states were not clearly distinguished because both the divalent and trivalent ions of iron and manganese are high-spin.

In-situ X-ray photoelectron spectroscopic study of the reversible phase transition between CoO and Co3O4 in oxygen of 10−3 Pa

The temperature dependence of the Co 2p and O 1s XPS spectra for the cobalt-oxygen system was studied in an oxygen atmosphere of 1 × 10−3 Pa. The reversible transition between CoO and Co3O4 was observed between 373 and 973 K. Although bulk thermodynamics predicts a transition temperature of 806 K, the transition occurred at about 620 K. This means that surface compositions or phases of the Co-O system are ruled by surface thermodynamics different from that of the bulk.

On the surface chemical reactions of metal and oxide XPS samples at 300–400° at a high vacuum produced by oil diffusion pumps

Abstract Metal and oxide surface reactions formed by heating in the spectrometer at 300–400° at a vacuum of ca. 10 −9 Torr (oil diffusion pumps) were studied. As a result of spectral observations before and after heating, the metals studied were classified into five groups. In the first group, oxide films on the metal surface are easily evaporated because of the high vapour pressure of oxide; in the second, the oxide films are easily reduced in the spectrometer; in the third, the oxide film formed on the metal is reduced but the bulk oxide is not easily reduced; in the fourth, very stable oxide films are formed and the bulk oxide is also stable; and finally in the fifth, the oxide film formed on the metal is apparently reduced, yet the bulk oxide is very stable.

Final states after Ni2p photoemission in the nickel-oxygen system

Abstract The Ni2p, Ni3p, Li1s and O1s XPS spectra were measured for single crystal NiO and LixNi1−xO, cleaved and scraped, respectively, in a spectrometer. The cleaved surface had Ni2p 3 2 peaks at 853.9 and 855.8 eV with an intensity ratio of 1:1, where the FWHM of the former was smaller than that of the latter. The intensity ratio decreased with doping of lithium. Although these peaks had previously been ascribed to di- and tri-valent nickel ions in their ground states, we interpret them here as follows. The peaks at 854 and 856 eV correspond to the final states of Ni2 p 3d9 L and Ni2 p 3d10 L 2, where the underline denotes an electron hole. An O2p electron hole in the ground state is necessary to give the latter final state. The doping of lithium increases the density of electron holes and the intensity of the latter final state. The spectral profile of Ni3p did not change with the addition of lithium. The binding energies of Li1s from the particle surface and the bulk were 55.5 and 53.5 eV, respectively. The large shift is associated with surface contamination. The O1s spectrum of the cleaved NiO had two peaks at 529.5 and 531.5 eV with an intensity ratio of 1:0.1. The FWHM of the peaks at 529.5 eV for NiO and Li0.3Ni0.70 were 1.0 and 1.7 eV, respectively. The binding energy of the main peak for LiNiO2 was 528.7 eV.

Ti 2p and Ti 3p X-ray photoelectron spectra for TiO2, SrTiO3 and BaTiO3

Ti 2p and Ti 3p X-ray photoelectron spectra (XPS) were taken for TiO2, SrTiO3 and BaTiO3 single crystals fractured insitu in an electron spectrometer. The inelastic scattering energy loss parts were removed from the observed Ti core level XPS by a deconvolution method using O 1s spectra as a response function. The Ti 2p spectrum for TiO2 has four maxima and it indicates that the final states of the photoemission had quasi continuous energy states. The Ti 2p spectra for SrTiO3 and BaTiO3 had only three maxima. The Ti 3p spectra of the three samples had satellite peaks with energy separation of about 14 eV from the main peaks. The intensity at the higher binding energy side of the main peaks continuously decreased with the relative binding energy from 0 to 8 eV. The spectral features of the Ti 2p and Ti 3p spectra are explained by the charge transfer model after the photoemission.

Low stacking-fault density in ZnSe epilayers directly grown on epi-ready GaAs substrates without GaAs buffer layers

We report a remarkably low stacking-fault density in ZnSe epilayers directly grown on commercial epi-ready GaAs (001) substrates without GaAs buffer layer growth. It is found that proper pregrowth treatments on epi-ready GaAs (001) substrates to obtain clean surfaces are crucial for two-dimensional layer-by-layer growth and suppression of stacking fault generation. Chemical etching using a NH4OH-based solution is found to reduce not only the thickness of the oxide layers but also the ratio of Ga2O3 to As2O3 to about half of that before etching. A clean GaAs (001) surface characterized by a (4×1) reconstruction in the present case is obtained after thermal cleaning followed by Zn pre-exposure. Reflection high-energy electron diffraction intensity oscillations with more than 50 periods are observed even from the very beginning of ZnSe growth on GaAs substrates cleaned as such. The stacking fault density in such a ZnSe layer is in the low-105 cm−2 range.

Ferromagnetism in Transparent Thin Films of Fe-Doped Indium Tin Oxide

Transparent films of Fe-doped indium tin oxide (ITO) were grown at oxygen pressures of 5, 1, 10-1, 10-2, and 10-3 Pa on yttria-stabilized zirconia (001) substrates by a pulsed-laser deposition method. We observed X-ray diffraction peaks from (00h) planes of In2O3 crystalline phase for the films. The films grown at 5 and 1 Pa were paramagnetic and semiconducting, that at 10-1 Pa was ferromagnetic and semiconducting, and those at 10-2 and 10-3 Pa were ferromagnetic and metallic. The Fe-ITO films grown below 10-1 Pa exhibited room-temperature (RT) ferromagnetism. Nanoscale Fe clusters in the highest oxidation state such as γ-Fe2O3 resulted in the RT ferromagnetism.

The effect of the next nearest neighbor ion on the X-ray photoelectron spectra of 2p levels for Co2+, Ni2+ and Cu2+ in MgO

Abstract The X-ray photoelectron spectra of Co, Ni and Cu 2p levels for samples of MxMg1-xO (M = Co, Ni, Cu), CoO, NiO and CuO were compared. The binding energies of metal 2p 3 2 levels did not change with their concentration. The shake-up satellite main peak intensity ratios and FWHM of metal 2p levels for Co2+ and Cu2+ in MgO were smaller than those for CoO and CuO. The Ni 2p 3 2 spectrum for Ni2+ in MgO had no shoulder, unlike NiO. Results indicate that next nearest neighbor ions (metal ions) may influence the final states after photoelectron ejection.

Removal of inelastic scattering part from Ti2p XPS spectrum of TiO2 by deconvolution method using O1s as response function

Abstract Ti2p and O1s XPS spectra of a clean surface of single crystal TiO 2 fractured in situ were taken to study the removal of the inelastic scattering part from the Ti2p spectrum. The features of inelastic scattering peaks in EELS were more influenced by surface than O1s XPS. It indicates that O1s XPS is proper as the response function to deconvolute a Ti2p spectrum. FWHM of the non-energy loss peak of Ti2p 3/2 is smaller than that of O1s. When the raw O1s spectrum is used as the response function, the deconvoluted spectrum has negative intensity values in some regions and beat waves. The replacement of the non-energy loss peak of O1s with narrower Gaussian peak takes off the beat waves. Peak separation of the deconvoluted spectrum reveals that it has six peaks. Two of them are main peaks of Ti2p 3/2 and 2p 1/2 . The others are classified into two kinds of satellite peaks, whose energy separation from the main peaks are 3 and 13 eV. Although the latter satellites have been discussed by many authors, the former satellites are first reported here.