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We examine the structure and composition of phase-pure epitaxial α-(Fe1-xVx)2O3 thin films deposited on a-Al2O3(0001) substrates by oxygen-plasma-assisted molecular beam epitaxy for 0⩽x⩽~0.5. The films crystallize in the corundum lattice, with vanadium substituting for iron throughout. Vanadium cations exhibit the expected 3+ charge state in the bulk, but exhibit higher valences nearer to the surface, most likely because of excess oxygen in interstitial sites near the surface. The extent of vanadium oxidation beyond the 3+ state is inversely proportional to x. The gradation of vanadium valence with depth has an impact on local bonding geometries, and could be highly significant in this material's efficiency as a photocatalyst. [ABSTRACT FROM AUTHOR]

We report the spatio-temporal separation of electron and phonon thermal transports in nanostructured magnetic L10 FePt films at the nanometer length scale and the time domain of tens of picosecond, when heated with a pulsed laser. We demonstrate that lattice dynamics measured using the picosecond time-resolved laser pump/X-ray probe method on the FePt (002) and Ag (002) Bragg reflections from different layers provided the information of nanoscale thermal transport between the layers. We also describe how the electron and phonon thermal transports in nanostructured magnetic thin films were separated. [ABSTRACT FROM AUTHOR]

Single crystals of transition metal (TM) doped β-Ga2O3, a wide gap semiconductor system of interest for transparent conductive oxide and diluted magnetic semiconductor applications, have been studied in the dilute, non-interacting limit (≤0.06 cation %). Based on optical absorption, particle induced x-ray emission, and Rutherford backscattering measurements, Mn does not incorporate as well as Cr, and Mn degrades the crystal quality. Using superconducting quantum interference device (SQuID) magnetometry, a Brillouin type paramagnetic magnetization is observed for Mn or Cr doped crystals with an effective number of Bohr magnetons per TM ion of 5.88 ± 0.1 or 3.95 ± 0.1, respectively. A trace ferromagnetic signal is consistent with a very small concentration of secondary phases in the Mn-doped crystal. The position of the edge in x-ray absorption near edge structure (XANES) measurements suggests that the Cr takes the 3+ valence, while a mixture of Mn2+ and Mn3+ are present; based on the absence of a prominent pre-edge feature in the XANES, both TM predominantly occupy an octahedral site in β-Ga2O3. Density functional theory (DFT) results, optical absorption and SQuID data are consistent with this assignment. While the Cr-doped crystal is conductive, the Mn-doped crystal is insulating, which is consistent with the Mn2+/Mn3+ mixed valence, assuming the Fermi level is pinned mid-gap at the Mn 2+/3+ transition level, which is predicted by DFT to be 1.8 eV above the valence band maximum. [ABSTRACT FROM AUTHOR]

Pure anatase TiO2 and CoxTi1-xO2 (0.013 buffer layer. Using 1/2 ML Sr metal to form the silicide allowed the deposition of 10 ML SrTiO3 without oxidation of the Si interface. Epitaxial anatase could be grown on this heterostructure, although use of the oxygen plasma during deposition resulted in significant SiO2 formation. Pure anatase films consisted of epitaxial anatase surface particles on a continuous anatase film. For Co-doped films, Co segregation to surface particles of epitaxial anatase was observed by Auger electron spectroscopy and transmission electron microscopy (TEM); faceting of the particles was observed for low Co doping concentrations. Although no secondary phases containing Co were observed in Co-doped anatase films by x-ray diffraction or TEM, x-ray absorption near edge spectroscopy indicated Co was present in the films as a mixture of Co(0), Co(II), and Co(III). All samples were ferromagnetic at room temperature; for lower Co concentrations, the ferromagnetic remanence (9%) and coercive field (100 Oe) were similar to phase-pure Co:TiO2/LaAlO3. However, the presence of Co(0) under strongly oxidizing growth conditions known to oxidize the Si interface implies that under no deposition conditions can Co metal be eliminated while simultaneously protecting the Si interface from oxidation. [ABSTRACT FROM AUTHOR]

The oxygen-plasma-assisted molecular-beam epitaxy was used to grow the epitaxial ferromagnetic films of Cr-doped TiO2 anatase on LaAlO3 (001). Cr is found to substitute for Ti in the lattice, with uniform distribution throughout the doped region of the film.

We report a charge-transfer mechanism in tuning of magnetism of Nd-substituted Gd5-xNdxSi4 (x=1 and 2.5) compounds. The X-ray absorption near edge structure measurements demonstrated that Nd substitutions for Gd induce charge transfer of 5d electrons from Gd to Nd. The charge transfer weakens spin-orbital coupling of Gd but strengthens that of Nd. Consequently, the magnetization responses of the substituted compounds to low magnetic fields are increased while their saturation magnetization is reduced. Electronic structure calculations showed that the charge transfer stabilizes a ferromagnetic and a ferrimagnetic structure in the compounds with x = 1 and 2.5, respectively, but that it does not change the 5d–3p hybridization significantly. It is suggested that the charge transfer of 5d electrons may occur in other rare earth-substituted Gd5Si4 compounds allowing for tuning of their magnetism. [ABSTRACT FROM AUTHOR]

Deals with a study which examined the use of x-ray reflectivity and variable-energy positrons to determine density and defects of thin metal films. Difficulties in measuring density values of thin films; Relationship between defect size and density of thin films; Advantages of using nondestructive methods in studying thin deposited films.

Studies the interface structure and reactions of nickel-chromium alloy and aluminum thin film bilayers using glancing-angle x-ray reflectivity and extended x-ray-absorption fine structure techniques. Sample preparation and x-ray measurements; Results; Discussion.

Provides information on the findings of synchrotron radiation measurements using glancing-angle x-ray reflectivity to study copper aluminum thin film interfaces. Model of the concentration profile and roughness; Amount of copper in the aluminum layer; Density profiles obtained from fitting the reflectivity data from aluminum/oxygen/copper at various annealing temperature.

Presents a study which presented results from a glancing angle extended x-ray absorption fine structure (EXAFS) technique to investigate the structure of tungsten-carbon multi layers and the effects of moderate annealing. Method used in preparing the multi layer samples and performing the glancing angle experiments; Overview of the log of reflectivity versus angle obtained from a sample; Summary of the results of the EXAFS study.

Presents a study that made extended x-ray absorption fine structure (EXAFS) measurements while simultaneously exciting x-ray standing waves in a multilayer structure. Enhancement of the EXAFS signal from selected regions within the multilayer unit cell; Application of the technique to a nickel-titanium (Ni-Ti) multilayer; Quantity of Ni-Ti intermixing.

Iron is unstable as an oxygen evolution electrode in alkaline media. Thus, relatively expensive nickel-based electrodes are used in industrial alkaline water electrolysis. We show that an iron substrate can be rendered stable and electrocatalytically active for the oxygen evolution reaction by nano-scale surface modification with nickel. The electrocatalytic activity of such a surface-modified iron electrode is comparable to the recently-reported nickel-based catalysts. The electrocatalytic activity is due to a 50-nanometer layer of a high-surface area α-nickel hydroxide on the iron electrode. The nickel modification renders the iron electrode electricallyconductive, prevents dielectric breakdown, and thus endows anodic stability. The electrocatalytic activity is unchanged even after 1000 hours of continuous operation. The temperature of preparation is critical, as excessive dehydration of the hydroxide layer results in nickel ferrite formation and a drastic reduction in electrocatalytic activity. We report significant insight into the surface chemical composition and structure of the catalyst layer by X-ray Absorption Spectroscopy, Photoelectron Spectroscopy, and Transmission Electron Microscopy. Electrochemical kinetics analysis suggests that surface hydroxo-intermediates react with the hydroxide ions from the solution to evolve oxygen. Thus, the surface-modified iron substrates present an opportunity for improving the performance and reducing the cost of alkaline water electrolysis systems. [ABSTRACT FROM AUTHOR]

We experimentally investigate the room temperature ferromagnetism observed in insulating Co doped anatase TiO2 thin films grown by sputter deposition. The Co was uniformly incorporated in the lattice as Co(II) with no evidence of Co metal. A series of annealing treatments were carried out to optimize the ferromagnetic ordering and a saturation moment of 1.1 μB/Co atom at 300 K was obtained with UHV annealing at 450 °C. Both as-deposited and annealed films were highly insulating at room temperature. Results show that the ferromagnetism is strongly dependent on the number and distribution of oxygen vacancies in the Co:TiO2 lattice. [ABSTRACT FROM AUTHOR]

Epitaxial ferromagnetic films of Cr-doped TiO2 anatase (CrxTi1-xO2-x/2) were grown on LaAlO3(001) using oxygen-plasma-assisted molecular-beam epitaxy. Cr K-shell x-ray absorption near-edge spectroscopy shows that the formal oxidation state of Cr is +3 throughout the films, with no evidence for either elemental Cr or half-metallic CrO2. Cr is found to substitute for Ti in the lattice, with uniform distribution throughout the doped region of the film. The Cr-doped anatase films exhibit room-temperature ferromagnetism aligned in-plane, with a saturation magnetization of ∼0.6 μB/Cr atom. [ABSTRACT FROM AUTHOR]

Presents a study which determined the position of zirconium within the unit cell of samarium[sub2]cobalt[sub17] using extended x-ray-absorption fine-structure spectroscopy. Experimental details; Results and discussion; Conclusion.

Presents a study which deflected an electron beam, which is propagating nearly parallel to the interface between two materials of different mean inner Coulomb potential, towards the material with the largest Coulomb potential. Sample preparation; Energy analysis of the deflected electrons; Conclusion.

Complex oxides exhibit a wide range of crystal structures, chemical compositions and physical properties. The underlying drivers determining the complicated structure–composition–property phase diagrams are the relative positions and orbital overlaps between the metal cations and the oxygen anions. Here we report a combined experimental and theoretical investigation of the structure and bonding in a series of lanthanum chromium oxides prepared by molecular beam epitaxy. Of particular interest is the charge state and local coordination of the Cr. We have stabilized LaCrO3, LaCrO4 and La2CrO6 films by controlling the three elemental fluxes during deposition, and have carried out X-ray diffraction, X-ray photoemission, and X-ray absorption spectroscopy, as well as first-principles calculations, to determine structure, charge state, chemical bonding, and electronic structure. Significant changes in bonding character and orbital interaction are revealed with decreasing ligand symmetry from octahedral to tetrahedral Cr coordination. Both LaCrO4 and La2CrO6 with tetrahedrally coordinated Cr show strong pre-edge features in the Cr K-edge near-edge structure whereas LaCrO3 with octahedrally coordinated Cr exhibits very weak pre-edge features. The origin of these pre-edge features is discussed based on various selection rules and ligand symmetry. We also demonstrate an increase in cation–anion orbital hybridization and a decrease in long-range ligand coupling induced by this symmetry reduction. These in turn result in dramatic modifications of the macroscopic optical and magnetic properties. [ABSTRACT FROM AUTHOR]

Heat-assisted magnetic recording is one of the most promising approaches to achieve extremely high density magnetic recording. A laser is used to temporarily heat the recording media film to render its switching field to become lower than the magnetic field of the writing head. After writing, the film material is cooled down to room temperature for data storage. In this dynamic writing process, the challenge is to tailor and optimize the time resolved structural/thermal/magnetic properties of the media films and their correlations during/after the laser heating. In this paper, the four dimensions of current progress in HAMR media research, i.e., structure, magnetic properties, thermal properties and time, are briefly overviewed and discussed. Their correlations are also emphasized. [ABSTRACT FROM PUBLISHER]