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This paper reports the relationship between the heat treatments of the CoFeB/MgO/CoFeB/Ta-based magnetic tunnel junction (MTJ) and the chemical bonding state using angle-resolved hard X-ray photoelectron spectroscopy. The redox reaction for B 1s during postannealing was verified for the MTJ without a capping layer by oxidizing the metallic B 1s in CoFeB and reducing the oxidized Fe 2p and Co 2p near the surface. For the MTJ with a capping layer, regardless of the heat treatments, MgO was found to be in a peroxidized state, and the diffusion of O 1s and B 1s exerted by the heat treatments is considered to be controlled by the degree of crystallization of MgO. The composition at the MgO/CoFeB interface changes on account of the heat treatments since the ratio of CoFeB and TaB at the bottom changes as a result of boron diffusion through the grain boundaries in MgO. By postannealing at 400 °C, the peak binding energy of Mg 1s at the surface was found to shift slightly to lower energy toward the stoichiometric MgO. However, the release of the excess oxygen in MgO is suppressed by the crystallization. Since the crystallization of MgO is enhanced by the in situ IR heating, the internal oxygen is more constrained in MgO. An improvement of the tunneling magnetoresistance deterioration observed with an ultrathin MgO is considered to be achieved under the peroxidized state controlled by the crystallinity of MgO. [ABSTRACT FROM AUTHOR]

Rutile-related (tetragonal rutile and monoclinic distorted rutile) ReO2 epitaxial thin films were grown on rutile TiO2 single crystalline substrates by reactive pulsed laser deposition of the Re metal target under a N2O atmosphere. The ReO2 film underwent structural phase transition from the monoclinic to tetragonal phase with the decreasing film thickness, driven by compressive lattice strain from the substrate. X-ray photoelectron spectroscopy and electrical transport measurements revealed that both phases had metallic properties above 25 K. The distinct difference in valence band spectra between the two phases might be due to reconstruction of the band structure dominated by Re 5d t2g. [ABSTRACT FROM AUTHOR]

Soft x-ray-excited angle-resolved photoemission results for nitride films formed using nitrogen–hydrogen radicals on Si(100), Si(111), and Si(110) are reported. The data were obtained using synchrotron radiation, which allowed the Si 2p, N 1s, and O 1s levels to be investigated with the same probing depth. The following main results were obtained: (1) the Si3N4 film is covered with one monolayer of Si–(OH)3N. Its areal density is 15% smaller on Si(111) than on Si(100) and Si (110), (2) the Si3N4/Si interfaces on all three surfaces are compositionally abrupt. This conclusion is based on the observation that no Si atoms bonded with three N atoms and one Si atom were detected, and (3) the observation that the number of Si–H bonds at the Si3N4/Si(110) interface is 38%–53% larger than those at the Si3N4/Si(100) and Si3N4/Si(111) interfaces indicates a dependence of the interface structure on the orientation of the substrate. [ABSTRACT FROM AUTHOR]

The chemical bonding states of boron (B) in shallow P+/N junctions on Si substrates were studied by soft x-ray photoelectron spectroscopy (SXPES). This study revealed three chemical bonding states of B embedded in bulk Si. The concentration profiles of B were successfully determined by combining SXPES with step-by-step etching of Si substrates. The concentration profiles of B thus determined were in good agreement with those determined by secondary ion mass spectroscopy. The concentration profiles of holes were also determined by combining Hall measurements with the step-by-step etching of Si substrates. The concentration profiles of B having the lowest binding energy were found to agree well with the concentration profiles of holes. Therefore, B with the lowest binding energy can be assigned as activated B and those having the middle and highest binding energies can be attributed to deactivated B having chemical bonding states different from that of activated B. [ABSTRACT FROM AUTHOR]

X-ray photoelectron diffraction (XPD) in combination with hard X-ray photoelectron spectroscopy (HAXPES) has been used to study the structure of buried layers in thin multilayer films. A detailed layer-by-layer investigation was performed using the element-specific, local-probe character of XPD. In the present work, angular-resolved HAXPES at a photon energy of 7.94 keV photon energy was used to investigate a Cr/Mn62Ga38/Mg/MgO multilayer system. Differences in the angular distributions of electrons emitted from Mn and Ga atoms revealed that the structure of Mn62Ga38 changes from L10 towards D022 for increasing annealing temperatures. A c/a ratio of 1.81 ± 0.06 was determined for the buried Mn62Ga38 layer in a D022 structure from the XPD experiment. The improvement of the structural order of the Mn62Ga38 layer is accompanied by an improvement of the structure of the overlying MgO layer. [ABSTRACT FROM AUTHOR]

Thin films of the proposed topological insulator LuPdBi-a Heusler compound with the C1b structure-were prepared on Ta-Mo-buffered MgO(100) substrates by co-sputtering from PdBi2 and Lu targets. Epitaxial growth of LuPdBi films was confirmed by X-ray diffraction and reflection high-energy electron diffraction. The root-mean-square roughness of the films was as low as 1.45 nm, even though the films were deposited at high temperature. The film composition is close to the ideal stoichiometric ratio. The valence band spectra of the LuPdBi films, observed by hard X-ray photoelectron spectroscopy, correspond very well with the ab initio-calculated density of states. [ABSTRACT FROM AUTHOR]

The present work reports on the experimental investigation of electronic structure and transport properties of the proposed topological insulator PtLuSb. The electronic structure was investigated by means of polarization dependent hard x-ray photoelectron spectroscopy. The valence band spectra exhibit a linear behavior close to the Fermi energy, as is typical for massless electrons. The transport properties are similar to that of a gapless semiconductor with low carrier concentration. This compound also exhibits an exceptionally high Hall mobility. At low temperatures, the magnetoresistance changes linearly with the applied magnetic field, whereas it exhibits a quadratic nature at high temperatures. A tentative relation between linear magnetoresistance and high mobility is discussed. [ABSTRACT FROM AUTHOR]

Epitaxial thin films of Mn3-xCoxGa were grown on MgO by magnetron co-sputtering with different Co content. Dependent on the Co content tetragonal or cubic structures are obtained. The composition dependence of saturation magnetization MS and uniaxial magnetic anisotropy Ku in the epitaxial films were investigated. A high magnetic anisotropy Ku of 1.2 MJ m-3 was achieved for the Mn2.6Co0.3Ga1.1 film with low magnetic moment of 0.84 μB. The valence band spectra of the films were investigated mainly by hard x-ray photoelectron spectroscopy. The evidence of sharp states in the cubic case, which are smeared out in the tetragonal case, proof the existence of a van Hove singularity that causes a band Jahn-Teller effect accompanied by a tetragonal distortion. These differences are in well agreement to the ab-initio calculations of the electronic structure. [ABSTRACT FROM AUTHOR]

The electronic band structure of thin films and superlattices made of Heusler compounds with NiTiSn and NiZr0.5Hf0.5Sn composition was studied by means of polarization dependent hard x-ray photoelectron spectroscopy. The linear dichroism allowed to distinguish the symmetry of the valence states of the different types of layered structures. The films exhibit a larger amount of "in-gap" states compared to bulk samples. It is shown that the films and superlattices grown with NiTiSn as starting layer exhibit an electronic structure close to bulk materials. [ABSTRACT FROM AUTHOR]

The thermoelectric properties of a Heusler compound with NiZr0.5Hf0.5Sn composition were studied. A comparison of the properties of a single crystal and a polycrystal was carried out by measurements of the electrical conductivity, Seebeck coefficient, and thermal conductivity. The transport properties are directly compared to the valence band electronic structure measured by photoelectron spectroscopy. The single crystal shows a higher figure of merit (ZT = 0.1) at room temperature which originates from the high electrical conductivity that is mediated by 'in-gap' states observed by photoemission spectroscopy. [ABSTRACT FROM AUTHOR]

We report the hard x-ray (hv=7.94 keV) core level photoemission spectroscopy to determine the depletion layer profile in Nb-doped SrTiO3/(La,Ba)MnO3 n-p+ diode structures. The Sr 2p3/2 spectra were detected penetrating even through (La,Ba)MnO3 over layer with thickness of 20 nm. The spectrum for a 0.01 wt % Nb doped SrTiO3 diode exhibited large shift to lower binding energy, whereas the spectrum for a 0.5 wt % Nb doped SrTiO3 diode exhibited small shift with broader width. The depletion layer lengths were experimentally estimated as 182 nm for 0.01 wt % one and 15 nm for 0.5 wt % one, respectively, in good agreement with semiconductor theory. [ABSTRACT FROM AUTHOR]

The effect of Ti substitution by Sc on the thermoelectric properties of the Heusler compounds NiTi0.3-xScxZr0.35Hf0.35Sn (where 00.3Zr0.35Hf0.35Sn showed n-type conductivity with a Seebeck coefficient of -288 μV/K at 350 K, while under Sc substitution the system switched to p-type behavior. A maximum Seebeck coefficient of +230 μV/K (350 K) was obtained by 4% Sc substitution, which is the highest value for p-type thermoelectric compounds based on Heusler alloys. The electronic structure was studied by photoelectron spectroscopy excited by hard x-ray synchrotron radiation. Massive in gap states are observed for the parent compound. This proves that the electronic states close to the Fermi energy play a key role on the behavior of the transport properties. Especially, they are responsible for the high, negative Seebeck coefficient of the parent compound. [ABSTRACT FROM AUTHOR]

This work reports on hard x-ray photoelectron spectroscopy (HAXPES) of CoFeB based tunnel junctions. Aim is to explain the role of the boron diffusion for the observed improvement of the tunneling magnetoresistance ratio with increasing annealing temperature. The high bulk sensitivity of HAXPES was used as a nondestructive technique to analyze CoFeB–MgO–CoFeB magnetic tunnel junctions. The investigated samples were processed at different annealing temperatures from 523 to 923 K. Hard x-ray core level spectroscopy reveals an enforced diffusion of boron from the CoFeB into the adjacent Ta layer with increasing annealing temperature. The dependence of the tunneling magnetoresistance on the annealing temperature is explained by the combined effects of an improved crystalline structure together with a change in the spin polarization at the Fermi energy caused by the removal of boron from the CoFeB layer and Ta diffusion at high annealing temperature. [ABSTRACT FROM AUTHOR]

We investigated the electronic states in amorphous In–Ga–Zn–O films with high carrier concentrations by optical absorption and hard x-ray photoelectron spectroscopy (HX-PES). Films having different Hall mobilities were prepared and their annealing effects were examined. All HX-PES spectra showed Fermi edge structures and extra subgap densities of states (DOSs). Tail-like structures observed in the optical spectra originate from subgap DOSs (>1020 cm-3) near valence band maximas (VBMs). Subgap DOSs near VBMs provide a reason why In–Ga–Zn–O thin film transistors show hard saturation in off states and are difficult to operate in an inversion p-channel mode. [ABSTRACT FROM AUTHOR]

The authors measured soft x-ray-excited angle-resolved photoemission from Si 2p, N 1s, and O 1s core levels, and valence band for nitride films formed on Si(100), Si(111), and Si(110) using nitrogen-hydrogen radicals with the same probing depth. The Si3N4/Si interfaces formed exhibited an almost abrupt compositional transition. Furthermore, the crystal orientation of Si substrate affects the total areal density of subnitrides but not the valence band offset at the Si3N4/Si interface. [ABSTRACT FROM AUTHOR]

Epitaxial ferri(ferro)magnetic Fe3-xZnxO4 thin films (x=0–0.9) were prepared using a pulsed-laser deposition technique. The electrical conductivity and magnetic properties of Fe3-xZnxO4 thin film were systematically modulated for the entire range of Zn substitution. Anomalous Hall coefficient measurements revealed the presence of spin-polarized carriers at room temperature. Valence band spectra obtained by hard x-ray photoemission spectroscopy revealed that the density of states near the Fermi level was reduced with an increasing Zn concentration of x. These results indicate that this system will serve as a tunable ferromagnetic semiconductor with a strong electron correlation. [ABSTRACT FROM AUTHOR]

Although amorphous InGaZnO4 has intensively been studied for a semiconductor channel material of thin-film transistors in next-generation flat-panel displays, its electronic structure parameters have not been reported. In this work, the electron affinities (χ) and the ionization potentials (Ip) of crystalline and amorphous InGaZnO4 (c-IGZO and a-IGZO) were measured using bulk-sensitive hard x-ray photoelectron spectroscopy. First, the χ and Ip values of c-IGZO and a-IGZO thin films were estimated by aligning the Zn 2p3/2 core level energies to a literature value for ZnO, which provided χ = 3.90 eV and Ip = 7.58 eV for c-IGZO and 4.31 eV and 7.41 eV for a-IGZO. It was also confirmed that the escape depth of the photoelectrons excited by the photon energy of 5950.2 eV is 3.3 nm for a-IGZO and large enough for directly measuring the interface electronic structure using a-IGZO/c-Si heterojunctions. It provided the valence band offset of ∼2.3 eV, which agrees well with the above data. The present results substantiate that the a-IGZO/c-Si interface follows well the Schottky-Mott rule. [ABSTRACT FROM AUTHOR]

In a previous work, we examined subgap states in highly doped amorphous In-Ga-Zn-O (a-IGZO) films by hard x-ray photoelectron spectroscopy (HX-PES) and found they had subgap electronic states above the valence band maximum (VBM) with the densities > 5 × 1020 cm-3 and just below the Fermi level with the densities > 5 × 1019 cm-3 [K. Nomura, T. Kamiya, H. Yanagi, E. Ikenaga, K. Yang, K. Kobayashi, M. Hirano, and H. Hosono, Appl. Phys. Lett. 92, 202117 (2008)]; however, their electron densities (Ne > 3 × 1019 cm-3) are rather high and not compatible with rational properties required for active channel layers in thin-film transistors (TFTs). In this work, we report the effects of Ne and thermal annealing on the subgap states in order to provide the data useful for actual TFTs. It was found that the low-Ne a-IGZO films had extra subgap states above VBM similar to the previous report, but their densities were as small as ∼2.0 × 1020 cm-3 for the highly resistive, wet-annealed a-IGZO films. Angle-dependent HX-PES revealed that the subgap states above VBM concentrate in the surface region. The O 1s peak indicated that the wet annealing suppressed the generation of subgap states by terminating these states with -OH bonds. The subgap states below EF were observed commonly in all the samples including ZnO, crystalline (c-) IGZO and a-IGZO. It is concluded that these states below EF are neither related to the disordered structures of a-IGZO nor to their TFT characteristics. It is considered that these states are related to the metastable states created by the high-energy photons in vacuum. [ABSTRACT FROM AUTHOR]

A correction is offered for the article Erratum: "Angle-Resolved Phototelectron Study on the Structures of Silicon Nitride Films and Si3N4/Si Interfaces Formed Using Nitrogen-Hydrogen Radicals" in a previous issue.

Epitaxial semiconducting NiYBi thin films were directly prepared on MgO(100) substrates by magnetron sputtering. The intensity ratio of the (200) and (400) diffraction peaks, I(200)/I(400) = 2.93, was close to the theoretical value (3.03). The electronic structure of NiYBi was calculated using wien2k, and a narrow indirect band gap of width of 210 meV was found. The valence band spectra of the films obtained by linear dichroism in hard x-ray photoelectron spectroscopy exhibit clear structures that are in good agreement with the calculated band structure of NiYBi. [ABSTRACT FROM AUTHOR]