J. Szade

X-ray examination, electrical and magnetic properties of R3Co single crystals (R≡Y, Gd, Dy and Ho)

Single crystals of Y3Co, Gd3Co, Dy3Co and Ho3Co were obtained by the Czochralski method from a levitated melt. A description of the crystal growth technology is given. The crystal quality was examined by X-ray methods. Electrical resistivity and magnetic susceptibility have been measured. Y3Co exhibits Curie-Weiss behaviour with μeff = 1 μB (formula unit)−1. It is the first evidence for the existence of a magnetic moment on cobalt atoms in such a low concentration region. Gd3Co, Dy3Co and Ho3Co show an effective moment that is enhanced by 1 μb relative to the theoretical value for R3Co, assuming that only the R3+ ions contribute a magnetic moment equal to the free ion value. A negative curvature of the temperature-dependent electrical resistivity ϱ(T) is observed in the lower temperature range. For higher temperatures dρdT is small, especially for Gd3Co (5.5 × 10−8Ω m K−1).

Visible-light photocatalytic activity of nitrogen-doped NiTiO3 thin films prepared by a co-sputtering process

Nickel titanate (NiTiO3) thin films were grown by a radio frequency magnetron co-sputtering process using metal (Ni and Ti) targets on fused quartz substrates at a substrate temperature of 400 °C. Annealing of as-deposited (amorphous) films was performed at 1100 °C for 2 hours to realize a stable crystalline phase. The effect of the Ti target power (200 and 250 W) and nitrogen doping on the structural, morphological and optical properties of post-annealed NiTiO3 thin films were investigated besides photocatalytic activity under visible light irradiation. X-ray diffraction measurement on the films revealed a pure ilmenite phase at 250 W Ti power. Preferential orientation changed from [104] to [110] as Ti power increased from 200 to 250 W. Raman studies on NiTiO3 thin films showed almost all the active modes (5Ag + 5Eg) of a crystalline structure. Two different microstructures were observed by scanning electron microscopy, films showed rounded (250 nm) grains at 200 W Ti target power while facet forms (500 nm) develop in the films deposited at 250 W. Chemical bonding and valence states of the involved ions such as Ni 2p, Ti 2p and O 1s were investigated by X-ray photoelectron spectroscopy. Nitrogen doping modifies the rms roughness from 12 nm to 17 nm as demonstrated on 200 W grown films and contributes also to modify the indirect optical band gap from 2.50 to 2.43 eV in films obtained at 250 W Ti target power. As a crucial role of nitrogen doping, photocatalytic activity in a broad visible light range was observed with a good efficiency for the degradation of methylene blue by nitrogen doped NiTiO3 thin films.

Electronic structure investigation of Gd intermetallics

Several Gd compounds within the Gd-Ag, Gd-Au, Gd-In, and Gd-Si series were investigated with the use of x-ray photoelectron spectroscopy. The temperature dependence of the magnetic susceptibility was measured for some of the compounds over a large temperature range to obtain accurate values of the effective magnetic moments. The chemical shifts of the core-level photoemission lines were analysed. The shift of the Gd core levels has been found to be independent of the compound stoichiometry within a Gd-M series. The valence band structure close to the Fermi level is also characteristic for each Gd-M group of compounds and may be related to their magnetic properties.

Structural and optical characterization of ball-milled copper-doped bismuth vanadium oxide (BiVO4)

Copper-doped BiVO4 nanoparticles were synthesized by a mechano-chemical method under optimized conditions to obtain a monoclinic scheelite structure. The crystal structure and its evolution with doping were investigated by X-ray powder diffraction, micro-Raman spectroscopy, field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HRTEM). Spherical shape particles with sizes ranging between 40 and 160 nm, which possess a monoclinic scheelite structure, were obtained. From the structural data analysis, it can be observed that the particle size decreases and distortions occur as the copper content increases in doped BiVO4. Chemical bonding and valence states of the Bi-4f, V-2p, O-1s and Cu-2p ions were investigated by XPS which revealed the location of Cu ions in the host lattice of BiVO4 in agreement with EPR investigations. UV-visible absorption experiments showed a broad band in the visible range with a small shift of the energy band-gap from 2.41 eV for undoped BiVO4 to 2.34 eV for 10 at.% Cu–BiVO4. Additional absorption band shoulders and widening of the optical absorption spectrum in the visible range with a well crystalline monoclinic scheelite structure pave the way for efficient visible light-driven photocatalytic activity. Photocatalytic measurements reprinted in supplementary data.

Electronic structure and magnetism of ferromagnetic GdTiSi and GdTiGe

Crystal structure and temperature dependence of magnetic susceptibility and electrical resistivity have been determined for GdTiSi and GdTiGe. Both compounds order ferromagnetically and for GdTiGe TC is 374 K which is a very high value for such kinds of compounds. The electronic structure for both compounds has been investigated by photoelectron spectroscopy and compared with calculations performed using the TB-LMTO method. A very good agreement with experiment was obtained, especially for GdTiGe. A strong hybrydization between the d states from Gd and Ti was found and a significant polarization of the Ti 3d electrons in GdTiGe was obtained which may be related to the enhanced indirect exchange between Gd magnetic moments.

Formation of bioactive coatings on Ti–13Nb–13Zr alloy for hard tissue implants

In an attempt to increase the bioactivity of a vanadium-free titanium alloy, Ti–13Nb–13Zr, the plasma electrolytic oxidation (PEO) process for surface modification was utilised. Select samples were subjected to further treatment, either thermal or alkali. The morphology, chemical composition, and phase composition of the treated Ti–13Nb–13Zr alloy were investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was observed that during the anodic process under sparking discharge conditions, the simultaneous incorporation of calcium and phosphorus in the forming oxide layer occurs. The resulting layers were porous and exhibited the typical morphology for layers formed during the PEO process. After the alkali treatment of samples oxidised at 150 V, a gel-like titanate layer was formed. The bioactivity investigations in simulated body fluid (SBF) solution indicated that after anodising at 150 V and following alkali treatment the Ti–13Nb–13Zr alloy exhibits osteoinductive properties. The approach presented here may be applied for fabricating Ti–13Nb–13Zr-based implants for hard tissue regeneration.

Photoelectron spectroscopy and magnetism of some gadolinium intermetallic compounds

Abstract X-ray photoelectron spectroscopy was used to investigate Gd intermetallic compounds: GdCu, GdAg, Gd2In and GdAl2. The measured electron density of states close to the Fermi level was compared with the magnetic properties of these compounds. The exchange splittings of the gadolinium 4s and 5s levels were analysed and found to be about the same for the investigated compounds. For GdCu the present results were compared with the existing band structure calculation.

Characteristics of sputter-deposited TiN, ZrB2 and W2B diffusion barriers for advanced metallizations to GaAs

Abstract The sputter deposition of TiN, ZrB 2 and W 2 B thin films were studied in order to develop the process parameters for advanced metallizations to GaAs devices. Thin films of TiN, ZrB 2 and W 2 B were deposited on both bare and AuZn-metallized (100) GaAs substrate in magnetron sputtering systems. The resistivity and stress in as-deposited thin films were examined and related to deposition conditions. The film microstructure and composition of grown compounds were determined by X-ray diffraction, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It was observed that metal boride films were polycrystalline or amorphous depending on the sputtering conditions. Diffusion barrier properties were analyzed by Rutherford backscattering spectroscopy (RBS) technics.

Electronic structure and magnetism of Gd5(Si, Ge)4 compounds

Abstract The electronic structure of Gd5Si4, Gd5Si2Ge2 and Gd5Ge4 was investigated with X-ray photoelectron spectroscopy (XPS) and compared to the results of magnetic susceptibility and electrical resistivity measurements. High-temperature magnetic susceptibility exhibits anomalies for all the compounds. Various magnetic transitions, present in the compounds, manifest in the electrical resistivity in different ways. The details of the electronic structure, obtained from the XPS measurements, are discussed with respect to the GdSi, GdGe bonding, and charge transfer.

Crystal structure, magnetic and electrical properties of YFe4Al8 single crystals

Abstract Single crystals of YFe 4 Al 8 were obtained by the Czochralski method from a levitated melt. Their quality was checked by the Berg-Barrett and Laue methods. The electrical resistivity and the magnetic susceptibility were studied. Besides the antiferromagnetic transition at 195 K, weak ferromagnetism was observed below 100 K.