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The Mn3Ga Heusler compound and related alloys are the most promising materials for the realization of spin-transfer-torque magnetoresistive memories. Mn-Ga films exhibits perpendicular magnetic anisotropy and high spin polarization and can be used to improve the performance of MgO-based magneto tunneling junctions. The interface between Mn-Ga and MgO films were chemically characterized by hard x-ray photoelectron spectroscopy. The experiment indicated the formation of Ga-O bonds at the interface and evidenced changes in the local environment of Mn atoms in the proximity of the MgO film. We show that the deposition of few monoatomic layers of Mg on top of Mn-Ga film, before the MgO deposition, strongly suppresses the oxidation of gallium. [ABSTRACT FROM AUTHOR]

By using laboratory x-ray photoemission spectroscopy (XPS) and hard x-ray photoemission spectroscopy (HX-PES) at a synchrotron facility, we report an empirical semi-quantitative relationship between the valence/core-level x-ray photoemission spectral weight and electrical conductivity in La1-xSrxMnO3 as a function of x. In the Mn 2p3/2 HX-PES spectra, we observed the shoulder structure due to the Mn3+ well-screened state. However, the intensity at x = 0.8 was too small to explain its higher electrical conductivity than x = 0.0, which confirms our recent analysis on the Mn 2p3/2 XPS spectra. The near-Fermi level XPS spectral weight was found to be a measure of the variation of electrical conductivity with x in spite of a far lower energy resolution compared with the energy scale of the quasiparticle (coherent) peak because of the concurrent change of the coherent and incoherent spectral weight. [ABSTRACT FROM AUTHOR]

Oxygen bonding in La-silicate film with compositional gradient has been characterized by x-ray photoelectron spectroscopy. Based on an analytical model of bridging and nonbridging oxygen, the O 1s spectra arising from La-silicate layer have been deconvoluted with compositionally dependent parameters. For a composition ratio of 1:1 for SiO2 and LaO1.5 on the surface of the La-silicate layer, negative binding energy shifts of 0.35 and 0.10 eV for bridging and nonbridging oxygen, respectively, have been found to well interpret the angle-resolved spectra. The method has also been applied to characterize the temperature dependence of interface reactions at La2O3/Si with in situ processed Pt electrode. SiO4 molecules combined with bridging and nonbridging oxygen atoms have been found to form by high temperature annealing. The thickness of the silicate layer of 0.4 nm at as-deposited state has been found grow up to 2.8 nm after 500 °C annealing. From rough estimation, it has been revealed that 10% of the newly created bridging oxygen atoms by annealing are incorporated into SiO4 network which contain also nonbridging oxygen atoms. [ABSTRACT FROM AUTHOR]

The chemical states of Fe and Pt in in situ annealed L10 structured FePt nanodots formed by self-assembled nanodot deposition method have been systematically investigated by angle resolved x-ray photoelectron spectroscopy. From the Fe3p and the Pt4f core level x-ray photoelectron (XP) spectra, it is evident that both the Fe and Pt of the nanodots were oxidized in the as-grown state. After the in situ annealing under high vacuum, a peak corresponding to metallic Fe begins to appear, and subsequently the metallic peak fraction increased with the increase in the annealing temperature. In line with this, the peak fraction of the respective oxides is drastically decreased. Irrespective of the annealing temperatures, it is inferred from the intensity of the XP spectrum that the Fe atom of the FePt nanodots is highly prone to oxidation than the Pt atom. Nevertheless, the valence band spectra of the as-grown FePt nanodot film clearly depict the presence of metallic Fe–Pt alloy. We would like to explain the results of the core level and valence band XP spectra as follows: only the peripheral Fe and Pt atoms of the as-formed FePt nanodots are bonded to the oxygen of the cosputtered SiO2 matrix, whereas the metallic core of the as-formed FePt nanodots is always preserved. The very good vacuum ambient during postannealing highly promotes the dissociation of oxygen from the metal oxides via reduction reaction. This results into an increase in the fraction of metallic Fe and Pt at the periphery of FePt nanodots and the formation of high quality SiO2 matrix after annealing. Similar results were also observed for the monatomic W as well as Pt nanodots embedded in SiO2 matrix. Hence, this simple, rather effective method of in situ annealing of metal dots dispersed in an insulating matrix can be readily employed in the fabrication of high-density nanodot memory devices. [ABSTRACT FROM AUTHOR]

The (GeTe)1-γ–(Sb2Te3)γ pseudobinary system has, over almost its entire composition range, two kinds of crystalline phase: one is a metastable phase with a NaCl-type structure and the other is a spectrum of stable phases with homologous structures. In the metastable phase, Ge/Sb atoms and intrinsic vacancies occupy the Na sites; on the other hand, Te atoms are located at the Cl sites. These vacancies are produced by following γ/1+2γ to ensure the stoichiometry of the metastable pseudobinary compound. This metastable phase obstinately holds its NaCl-type structure and resists transformation to stable homologous structures, even at high temperatures on the GeTe-rich side of the system. In GeTe (γ=0), the NaCl-type atomic configuration itself is the stable structure. GeTe has, as is well known, a high-temperature cubic phase and a low-temperature rhombohedral phase. This GeTe and the pseudobinary compounds containing a small quantity of Sb2Te3 have their single-phase regions not on the GeTe–Sb2Te3 tie line but at Ge-poor sides off the line: in other words, the Na sites of these off-stoichiometric compounds have some excess vacancies besides the intrinsic vacancies. As Sb2Te3 is further added to GeTe, however, the structural transformation temperature continuously falls and the single-phase region converges on the tie line as the excess vacancies at the Na site disappear, which change its electrical property from metallic to semiconducting conductivity. The low-temperature rhombohedral phase is present up to near γ=0.14. The NaCl-type metastable phase becomes unstable with increased Sb2Te3; after subjecting the compound Ge8Sb2Te11 (γ=0.11) to heat treatment for 15 days at 773 K, a stable homologous structure appeared. [ABSTRACT FROM AUTHOR]

Hard X-ray photoelectron spectroscopy (HAXPES) has been utilized to study chemical state and kinetics of sulfur species in a rubber compound by examining thermally induced changes of S 1s core-level spectra. Two peaks at 2470 and 2472 eV together with the 2479 eV peak from SO42- are resolved in the S 1s spectrum. As the rubber compound is heated at 374, 412, and 440 K, the former two peaks show different thermal behaviors; the peak at 2472 eV is swiftly decreased in its intensity with heating time because of thermal desorption of the sulfur species, whereas the intensity of the 2470 eV peak shows a slight increase especially in the surface region of the rubber compound. On the basis of these thermal behaviors, the peaks at 2470 and 2472 eV are, respectively, associated with S atoms bonded directly to the C atoms and those bonded only to other S atoms. An Arrhenius plot analysis of the 2470 eV peak intensity variation reveals that the S-C bond formation and scission reactions compete with each other with a slightly smaller activation energy in the bond formation than in the bond scission. [ABSTRACT FROM AUTHOR]

We investigated the polyvinylidene fluoride (PVDF)-mediated topotactic fluorination of two perovskite ruthenate thin films with different crystallographic structures, non-layered perovskite SrRuO3 and layered perovskite Sr2RuO4. While the former ruthenate did not react with PVDF, the latter was fluorinated to form Sr2RuO3F2 with a structure that exhibited a largely expanded c-axis. These results indicate that fluorine ions are preferentially inserted into the SrO rocksalt blocks in perovskite ruthenates, and that the oxygen atoms in the precursor oxide were partially removed upon fluorination. Finally, we noted that the Sr2RuO3F2 film was insulating, with a resistivity of 4.1 × 10 Ω cm at 300 K. It should be noted that this resistivity is five orders of magnitude higher than that of the metallic Sr2RuO4 film (6.7 × 10−4Ω cm). [ABSTRACT FROM AUTHOR]

We fabricated epitaxial thin films of oxygen-vacant Sr2MgMoO6-δ using pulsed laser deposition. The films showed low resistivity of the order of 10-2 Ω cm at 300 K. X-ray diffraction analyses revealed that Mg and Mo ions in the Sr2MgMoO6-δ films were considerably disordered, compared to those in bulk Sr2MgMoO6-δ. The proportion of oxygen vacancies estimated through hard x-ray photoemission measurements was as large as 0.37, and correlated well with the Mg/Mo ordering. [ABSTRACT FROM AUTHOR]

We have synthesized BaFeOx thin films by pulsed-laser deposition followed by low temperature (200 °C) oxidation to BaFeO3. X-ray diffraction indicates that fully oxidized single crystalline BaFeO3 has been formed with a lattice parameter of 3.97 Å, the bulk stoichiometric value. The oxidation state of Fe is confirmed to be 4+ by using hard x-ray photoemission spectroscopy. A ferromagnetic ground state is found with saturation magnetization and Curie temperature of 3.2 μB/formula unit and 115 K, respectively. Unusually, for a uniform cubic ferromagnet, the films are insulating with an optical gap of ∼1.8 eV. [ABSTRACT FROM AUTHOR]

The chemical structures of SiO2/Si interfaces were studied by photoelectron spectroscopy using high-brilliance soft X-ray with photon energy ranging from 500 to 1500 eV at Super Photon ring 8 GeV(SPring-8) and it is able to probe a depth of about 1.2 to 3 nm with energy resolution of 100 meV. On the other hand, high-brilliance hard X-ray with photon energy ranging from 6 to 10 keV is able to probe a depth of about 8.5 to 12.5 nm with energy resolution of 100 meV. Hard photoelectron spectroscopy are particularly useful for studying the composition and the chemical structure of transition layer at high-k dielectric/silicon interface. [ABSTRACT FROM AUTHOR]

Family and twin studies have supported a strong genetic factor in the etiology of obsessive-compulsive disorder (OCD), although the precise mechanism of inheritance is unclear. Clinical and pharmacological studies have implicated the serotonergic and dopaminergic systems in disease pathogenesis. In this cross-sectional study, we have examined the allelic and genotypic frequencies of a Val-158-Met substitution in the COMT gene, a 44-base pair (bp) length variation in the regulatory region of the serotonin transporter gene ( 5-HTTLPR) and the T102C and C516T variants in the serotonin receptor type 2A ( 5HT2A) gene in 79 OCD patients and 202 control subjects. There were no observed differences in the frequencies of allele and genotype between patients and control groups for the COMT, the 5HTTLPR and the T102C 5HT2A gene polymorphisms. In contrast, a statistically significant difference between OCD patients and controls was observed on the genotypic distribution (χ2 = 16.7, 2df, P = 0.0002) and on the allelic frequencies (χ2 = 15.8, 1df, P = 0.00007) for the C516T 5HT2A gene polymorphism. The results suggest that the C516T variant of the 5HT2A gene may be one of the genetic risk factors for OCD in our sample. However, further studies using larger samples and family based methods are recommended to confirm these findings. [ABSTRACT FROM AUTHOR]

The influence of 30 keV He+ ion irradiation on structural, electronic, and magnetic properties of Co2MnSi thin films with a partial B2 order was investigated. It was found that room temperature irradiation with light ions can improve the local chemical order. This provokes changes of the electronic structure and element-specific magnetization toward the bulk properties of a well-ordered Co2MnSi Heusler compound. [ABSTRACT FROM AUTHOR]

The authors have investigated changes in the electronic structures of digitally controlled La0.6Sr0.4MnO3 (LSMO) layers sandwiched between SrTiO3 as a function of LSMO layer thickness in terms of hard x-ray photoemission spectroscopy (HX-PES). The HX-PES spectra show the evolution of Mn 3d derived states near the Fermi level and the occurrence of metal-insulator transition at 8 ML. The detailed analysis for the thickness dependent HX-PES spectra reveals the existence of the less conducting and nonmagnetic transition layer with a film thickness of about 4 ML in the interface region owing to significant interaction through the interface. [ABSTRACT FROM AUTHOR]

The authors measure the difference of core-level binding energy shifts for Si 1s and Si 2p, ΔE1s-ΔE2p, for various Si compounds using high-resolution high-energy synchrotron radiation. They find that the ΔE1s-ΔE2p values are in very good correlation with the dielectric constant values of the Si compounds. Using this relation, they deduce the local dielectric constant for each of the Si intermediate oxidation states formed at the SiO2/Si interface. The results are in good agreement with values predicted by a first-principles calculation. [ABSTRACT FROM AUTHOR]

Using the high-brilliance synchrotron radiation at SPring-8, we determined the electron escape depths in approximately 1-nm-thick low-temperature oxide layers, which were formed on Si(100) at 300 °C using three kinds of atomic oxygen and that in approximately 1-nm-thick thermally grown oxide layer formed in 1 Torr dry oxygen at 900 °C by measuring angle-resolved Si 2p photoelectron spectra at the photon energy of 1050 eV. The results indicated that the electron escape depths in the three kinds of low-temperature oxide layers were 18%–24% smaller than that in the thermally grown oxide layer. Furthermore, the electron escape depth in the thermally grown oxide layer, whose thickness was close to that of the structural transition layer, was 7% smaller than that in bulk SiO2. [ABSTRACT FROM AUTHOR]

We have developed a new electron-ion coincidence apparatus combined with synchrotron radiation in order to examine the various ion desorption mechanisms related to the Auger process induced by core excitation. Photon stimulated ion desorption (PSID) of a poly-methylmethacrylate (PMMA) thin film has been investigated by this apparatus. The PSID of PMMA induced by carbon core excitation has been examined using Auger electron yield, total ion yield, resonant Auger electron, and Auger electron-photoion coincidence (AEPICO) spectra. The spectrum of the total ion yield divided by the Auger electron yield shows that the desorption efficiency is largely increased at the resonant excitation of carbon 1s electron in the O-CH[sub 3] side chain to σ[sup *](O-CH[sub 3]) orbital. In AEPICO measurement, H[sup +] and CH[sub n][sup +] (n=1-3) ions are observed at various resonant excitations. The AEPICO signal intensity depends on the Auger electron energy. Particularly, the CH[sub 3][sup +] ion desorption in coincidence with Auger electron at 270 eV shows strong enhancement with σ[sup *](O-CH[sub 3]) resonant excitation. The results of the resonant Auger spectra and AEPICO yield spectra demonstrate the relation of the ion desorption mechanism to the bonding/antibonding character and localized character of the excited σ[sup *](O-CH[sub 3]) orbital and the Auger final state. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We studied the charge-orbital ordering in the superlattice of charge-ordered insulating Pr0.5Ca0.5MnO3 and ferromagnetic metallic La0.5Sr0.5MnO3 by resonant soft x-ray diffraction (RSXD) and hard x-ray photoemission spectroscopy (HXPES). A temperature-dependent incommensurability is found in the orbital ordering by RSXD. In addition, a large hysteresis is observed that is caused by phase competition between the insulating charge ordered and metallic ferromagnetic states. No magnetic phase transitions are observed in contrast to pure Pr0.5Ca0.5MnO3 thin films, confirming the unique character of the superlattice. Mn HXPES spectra revealed a hysteresis in the metalicity, supporting the picture of phase competition. The deviation from the commensurate orbital order can be directly related to the decrease of ordered-layer thickness that leads to dimensional crossover from three-dimensional to two-dimensional orbital ordering. [ABSTRACT FROM AUTHOR]

Lattice instability of off-stoichiometric Ni-Mn-Ga based ferromagnetic shape memory alloys with different valence electron concentrations (e/a's) has been studied by utilizing hard X-ray photoelectron spectroscopy. Comparison of two alloys with different e/a's suggests that a rigid band model is not applicable to explain the different martensitic transition temperatures. It is revealed that the specimen with larger e/a shows larger density of the Ni 3d eg states near the Fermi energy compared to specimen with lower e/a. The results can be reasonably explained by the band Jahn-Teller effect. [ABSTRACT FROM AUTHOR]