Structure and composition of sputter-deposited nickel-tungsten oxide films

Films of mixed nickel-tungsten oxide, denoted Ni_xW_1−x oxide, were prepared by reactive DC magnetron co-sputtering from metallic targets and were characterized by Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, X-ray diffractometry and Raman spectroscopy. A consistent picture of the structure and composition emerged, and at x < 0.50 the films comprised a mixture of amorphous WO₃ and nanosized NiWO₄, at x = 0.50 the nanosized NiWO₄ phase was dominating, and at x > 0.50 the films contained nanosized NiO and NiWO₄.     

The photoluminescence of SiCN thin films prepared by C implantation into α-SiNx:H

SiCN thin films were prepared by high-dosage (2 × 10¹⁷ cm^− 2) C⁺ ion implantation into α-SiN_x:H films. The prepared films were then processed by thermal annealing for 2 h at 800 °C, 1000 °C and 1200 °C respectively. The composition and bond structure of SiCN were analyzed by X-ray photoemission spectroscopy, Auger electron spectroscopy, Raman spectroscopy and X-ray diffraction, and photoluminescence. Ternary structure with N bridging C and Si of the film annealed at 800 °C was found. The luminescent properties of SiCN have also been studied by synchrotron radiation at 20 K. Four emission bands were observed, corresponding to 2.95, 2.58, 2.29 and 2.12 eV at 20 K, respectively. In this paper, we report the experimental results and try to explain them.     

Structural and magnetic properties of glass-ceramics containing silver and iron oxide

Glass-ceramics with a nominal composition of 25SiO₂–(50 − x)CaO–15P₂O₅–8Fe₂O₃–2ZnO–xAg (where x = 0, 2 and 4 mol%) have been prepared. Structural features of glass-ceramics have been investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. Magnetic properties were studied using vibrating sample magnetometer and Mössbauer spectroscopy. Ca₃(PO₄)₂, hematite and magnetite are formed as major crystalline phases. The microstructure reveals the formation of 25–30 nm size particles. Mössbauer spectroscopy has shown the relaxation of magnetic particles. Saturation magnetization value is increased with an increase of Ag content up to 4 mol%, which has been attributed to the formation of magnetically ordered particles. The antibacterial response was found to depend on Ag ions concentration in the glass matrix and samples with 4 mol% Ag in glass matrix have shown effective antibacterial activity against Escherichia coli.     

Characterization of electrochemically deposited Cu-Ni black coatings

Electrochemically deposited Cu-Ni black coatings on molybdenum substrate from ethylenediaminetetraacetic acid (EDTA) bath solution are shown to exhibit good optical properties (α=0.94, ε = 0.09). The deposit is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Cu is present in metallic and +2 oxidation states in the as-prepared Cu-Ni black coating, whereas Ni²⁺ as well as Ni³⁺ species are observed in the same coating. Cu and Ni are observed in their metallic state after 10 and 20 min sputtering. X-ray initiated Auger electron spectroscopy (XAES) of Cu and Ni also agrees well with XPS investigations.     

Ti2Al(O,N) formation by solid-state reaction between substoichiometric TiN thin films and Al2O3 (0001) substrates

Titanium nitride TiN_x (0.1 ≤ x ≤ 1) thin films were deposited onto Al₂O₃(0001) substrates using reactive magnetron sputtering at substrate temperatures (T_s) ranging from 800 to 1000 °C and N₂ partial pressures (pN₂) between 13.3 and 133 mPa. It is found that Al and O from the substrates diffuse into the substoichiometric TiN_x films during deposition. Solid-state reactions between the film and substrate result in the formation of Ti₂O and Ti₃Al domains at low N₂ partial pressures, while for increasing pN₂, the Ti₂AlN MAX phase nucleates and grows together with TiN_x. Depositions at increasingly stoichiometric conditions result in a decreasing incorporation of substrate species into the growing film. Eventually, a stoichiometric deposition gives a stable TiN(111) || Al₂O₃(0001) structure without the incorporation of substrate species. Growth at T_s 1000 °C yields Ti₂AlN(0001), leading to a reduced incorporation of substrate species compared to films grown at 900 °C, which contain also Ti₂AlN(101?3) grains. Finally, the Ti₂AlN domains incorporate O, likely on the N site, such that a MAX phase oxynitride Ti₂Al(O,N) is formed. The results were obtained by a combination of structural methods, including X-ray diffraction and (scanning) transmission electron microscopy, together with spectroscopy methods, which comprise elastic recoil detection analysis, energy dispersive X-ray spectroscopy, and electron energy loss spectroscopy.     

Compositional dependence on the optical properties of amorphous As2 − xS3 − xSbx thin films

In this paper, we report results of the optical properties of thermally deposited As_2 − xS_3 − xSb_x thin films with x = 0.02, 0.07, 0.1 and 0.15. We have characterized the deposited films by Fourier Transform Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The relationship between the structural and optical properties and the compositional variation were investigated. It was found that the optical bandgap decreases with increase in Sb content. The XPS core level spectra show a decrease in As₂S₃ percentage with increase in Sb content. This is confirmed from the shifting of the Raman peak from AsS₃ vibrational mode towards SbS₃ vibrational mode.     

Structural properties of low-temperature grown ZnO thin films determined by X-ray diffraction and X-ray absorption spectroscopy

The epitaxial growth of ZnO thin films on Al₂O₃ (0001) substrates have been achieved at a low-substrate temperature of 150 °C using a dc reactive sputtering technique. The structures and crystallographic orientations of ZnO films varying thicknesses on sapphire (0001) were investigated using X-ray diffraction (XRD). We used angle-dependent X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to examine the variation of local structure. The XRD data showed that the crystallinity of the film is improved as the film thickness increases and the strain is fully released as the film thickness reached about 800 Å. The Zn K-edge XANES spectra of the ZnO films have a strong angle-dependent spectral feature resulting from the preferred c-axis orientation. The wurtzite structure of the ZnO films was explicitly shown by the XRD and EXAFS analysis. The carrier concentration, Hall mobility and resistivity of the 800 Å-thick ZnO film were 1.84 × 10¹⁹ cm^− 3, 24.62 cm²V^− 1s^− 1, and 1.38 × 10^− 2 Ω cm, respectively.     

Crystal structure, thermal analysis and IR spectrometric investigation of bis(o-anisidinium) sulfate (C7H10NO)2SO4

Chemical preparation, X-ray single-crystal, thermal behaviour, and IR spectroscopy investigations are given for a new organic cation sulfate (C₇H₁₀NO)₂SO₄ (denoted BOAS) in the solid state. This compound crystallizes in the monoclinic space group P2₁/c. The unit cell dimensions are: a = 7.010(3) Å, b = 11.142(5) Å, c = 20.770(8) Å, β = 95.27(3)° with V = 1615.4(12) Å³ and Z = 4. The structure has been solved using a direct method and refined to a reliability R factor of 0.047. The title compound consists of a framework of isolated SO₄ tetrahedral interleaved with organic molecules, so as to build isolated ribbons parallel to a-axis. In the present work, we describe the crystal structure, thermal behaviour and IR analysis of this new compound.     

Optical properties of nanocrystalline SnS2 thin films

Thin films of nanocrystalline SnS₂ on glass substrates were prepared from solution by dip coating and then sulfurized in H₂S (H₂S:Ar = 1:10) atmosphere. The films had an average thickness of 60 nm and were characterized by X-ray diffraction studies, scanning electron microscopy, EDAX, transmission electron microscopy, UV-vis spectroscopy, and Raman spectroscopy. The influence of annealing temperature (150-300 °C) on the crystallinity and particle size was studied. The effect of CTAB as a capping agent has been tested. X-ray diffraction analysis revealed the polycrystalline nature of the films with a preferential orientation along the c-axis. Optical transmission spectra indicated a marked blue shift of the absorption edge due to quantum confinement and optical band gap was found to vary from 3.5 to 3.0 eV with annealing temperature. Raman studies indicated a prominent broad peak at ∼314 cm⁻¹, which confirmed the presence of nanocrystalline SnS₂ phase.     

Study of the structural and optical properties of GaPN thin films grown by magnetron RF sputtering

GaP_1−xN_x thin films were deposited on glass substrates by RF sputtering employing a nitrogen-argon atmosphere in a partial pressure of 2×10⁻² Torr. We varied the growth temperature in the range 420-520 °C. The film's optical properties were studied by transmittance and absorbance spectroscopy. Characterization by scanning electron microscopy in cross-sectional view, atomic force microscopy, and X-ray diffraction was performed to determinate the film thickness, surface morphology, and crystal structure, respectively. Raman spectroscopy was employed to analyze the structural properties of samples. The GaP_1−xN_x films presented a cubic polycrystalline structure with a preferential orientation along the [1 1 1] direction. By varying the growth conditions we were able to change the band gap energy between 1.35 and 1.98 eV.     

Spectroscopic studies of large sheets of graphene oxide and reduced graphene oxide monolayers prepared by Langmuir-Blodgett technique

Graphene oxide (GO) sheets prepared by chemical exfoliation were spread at the air-water interface and transferred to silicon substrates by Langmuir-Blodgett technique as closely spaced monolayers of 20-40 μm size. Hydrazine exposure followed by annealing in vacuum and argon ambient results in the formation of reduced graphene oxide (RGO) monolayers, without significantly affecting the overall morphology of the sheets. The monolayer character of both GO and RGO sheets was ascertained by atomic force microscopy. X-ray photoelectron spectroscopy supported by Fourier transform infrared spectroscopy revealed that the reduction process results in a significant decrease in oxygen functionalities, accompanied by a substantial decrease in the ratio of non-graphitic to graphitic (sp² bonded) carbon in the monolayers from 1.2 to 0.35. Raman spectra of GO and RGO monolayers have shown that during the reduction process, the G-band shifts by 8-12 cm^− 1 and the ratio of the intensities of D-band to G-band, I(D)/I(G) decreases from 1.3 ± 0.3 to 0.8 ± 0.2, which is in tune with the smaller non-graphitic carbon content of RGO monolayers. The significant decrease in I(D)/I(G) has been explained by assuming that substantial order is present in precursor GO monolayers as well as RGO monolayers obtained by solid state reduction.     

Estimation of oxidation states of AlOx barriers in a tunneling junction by inelastic electron tunneling spectroscopy

Co/AlO_x/Co with AlO_x barriers of various oxidation states were fabricated and investigated using inelastic electron tunneling (IET) spectroscopy and X-ray photoelectron spectroscopy (XPS). XPS revealed that AlO_x oxidized for 8 h contained an inhomogeneous distribution of metallic Al, whereas AlO_x oxidized for 24 h contained a homogeneous distribution. The inhomogeneous and homogeneous distributions of metallic Al corresponded to asymmetric and symmetric IET spectra, respectively. These junctions showed peaks at ± 0.03 V. AlO_x oxidized for 168 h contained no metallic Al, and this junction had no peaks, suggesting that peaks at ± 0.03 V originate from metallic Al.     

Structural, thermal, magnetic and electrical studies of the iron oxophosphate Rb7Fe7(PO4)8O2·2H2O

A new iron oxophosphate of composition Rb₇Fe₇(PO₄)₈O₂·2H₂O has been synthesized and studied by X-ray diffraction, TG and DTA analysis, magnetic susceptibility, neutron diffraction, Mössbauer spectroscopy and ionic conductivity. This compound crystallizes in the monoclinic system with the P2₁/c space group and the unit cell parameters a = 8.224(8) Å, b = 22.162(6) Å, c = 9.962(6) Å and β = 109.41(8)°. Its structure is built up from Fe₇O₃₂ clusters of edge- and corner-sharing FeO₅ and FeO₆ polyhedra. Neighboring clusters are connected by the phosphate tetrahedra to form a three-dimensional framework. The Rb⁺ cations and the water molecules are occupying intersecting tunnels parallel to a and c. The presence of water molecules was confirmed by TG and DTA analysis. The magnetic susceptibility measurements have shown the existence of antiferromagnetic ordering below 22 K with a weak ferromagnetic component. Additionally, these measurements show evidence for a strong magnetic frustration characterized by |θ/T_N| ≈ 12. Powder neutron diffraction study confirms the presence of a long range antiferromagnetic order coupled to a weak ferromagnetic component along the b-axis. The strongly reduced magnetic moments extracted from the refinement support the existence of a magnetically frustrated ground state. The Mössbauer spectroscopy results confirmed the presence of only Fe³⁺ ions in both five and six coordination. The ionic conductivity measurements led to activation energy of 0.81 eV, a value that agrees with the obtained for other rubidium phosphates.     

Synthesis, crystal structure and infrared study of LiEr(PO3)4

A single-crystal X-ray diffraction analysis has been performed on LiEr(PO₃)₄ prepared by the flux method. The compound crystallizes in the monoclinic system with space group C2/c and cell parameters: a = 16.262(2), b = 7.032(1), c = 9.549(2) Å and β = 125.95(1)°. The crystal structure was refined based on 1272 independent reflections with I > 2σ(I). Final values of the reliability factors were improven considerably: R(F²) = 0.0180 and wR(F²) = 0.0490. The LiEr(PO₃)₄ structure is characterized by infinite chains (PO₃)_n, extending parallel to the b direction. The ErO₈ dodecahedra and LiO₄ tetrahedra alternate on two-fold axes in the middle of four (PO₃)_n chains. The vibrational study by infrared absorption spectroscopy is reported.     

Synthesis and characterization of Ni1−xZnxFe2O4 spinel ferrites from tailored layered double hydroxide precursors

In this paper, a series of pure Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrites have been synthesized successfully using a novel route through calcination of tailored hydrotalcite-like layered double hydroxide molecular precursors of the type [(Ni + Zn)_{1 − x − y}Fe_y²⁺Fe_x³⁺(OH)₂]^x+(SO₄²⁻)_x/2·mH₂O at 900 °C for 2 h, in which the molar ratio of (Ni²⁺ + Zn²⁺)/(Fe²⁺ + Fe³⁺) was adjusted to the same value as that in single spinel ferrite itself. The physico-chemical characteristics of the LDHs and their resulting calcined products were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy. The results indicate that calcination of the as-synthesized LDH precursor affords a pure single Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrite phase. Moreover, formation of pure ferrites starting from LDHs precursors requires a much lower temperature and shorter time, leading to a lower chance of side-reactions occurring, because all metal cations on the brucite-like layers of LDHs can be uniformly distributed at an atomic level.     

Core-level X-ray photoemission spectral shift through the successive phase transitions in layered TlInS2

Temperature-dependent change in core-level electronic structures of the layered semiconductor-ferroelectric TlInS₂ with incommensurate phase has been investigated by means of X-ray photoemission spectroscopy. The temperature dependence of the relative peak position for each core level (Tl 4f, In 3d and S 2p) is found to differ very much in the regions bordering each other at the normal-incommensurate phase transition point of 218 K. The obtained data suggest that the charge distribution in TlInS₂ dramatically changes upon passing from the normal phase (T > 218 K) to the spatially modulated incommensurate phase (T < 218 K).     

Synthesis, structure and dielectric properties of a rare earth double perovskite oxide Ba2CeTaO6

A rare earth double perovskite oxide barium cerium tantalate, Ba₂CeTaO₆ (BCT) is synthesized by solid-state reaction. The X-ray diffraction pattern of the sample at room temperature (25 °C) shows monoclinic structure, with the lattice parameters, a = 9.78 Å, b = 9.02 Å and c = 4.27 Å and β = 93.8°. A scanning electron micrograph shows the formation of grains with average size ∼ 2 μm. Impedance spectroscopy is applied to investigate the ac electrical properties of BCT in a temperature range from 303 to 673 K and in a frequency range from 100 Hz to 1 MHz. Complex-impedance-plane plots show grain contribution for BCT. The frequency-dependent electrical data are analyzed in the framework of the conductivity and modulus formalisms. The frequency-dependent conductivity spectra follow a power law. The conductivity at 110 Hz varies from 3.5 × 10⁻⁷ S m⁻¹ to 1.2 × 10⁻² S m⁻¹ with increasing temperature from 303 to 673 K, respectively. The scaling behaviour of M″ and Z″ suggest that the relaxation describes the same mechanism at various temperatures.     

Characterization and magnetic properties of Sm- and Gd-substituted CoFe2O4 nanoparticles prepared by forced hydrolysis in polyol

Pure nanoparticles of the CoFe_2−xRE_xO₄ (RE = Gd, Sm; x = 0.0, 0.1) system have been prepared by forced hydrolysis in polyol. The insertion of Sm³⁺ and Gd³⁺ cations into the cobalt ferrite structure has been investigated. X-ray micro-analysis (EDX) shows that the RE contents are close to the nominal ones. X-ray diffraction (XRD) evidences a cell size increase with slight distortions in the spinel-like lattice indicating the entrance of RE³⁺ ions. Micro-Raman spectroscopy confirms the cubic inverse-spinel structure and rules out the existence of impurities like hematite. Magnetic measurements (SQUID) show important differences in the magnetic properties of the unsubstituted and substituted particles. All the particles are superparamagnetic at room temperature and ferrimagnetic at low temperature. However, their main magnetic characteristics appear to be directly dependent on the RE content.     

A structural and corrosion study of triethoxysilyl and perfluorooctyl functionalized polyhedral silsesquioxane nanocomposite films on AA 2024 alloy

A tri-functional polyhedral oligomeric silsesquioxane (POSS) based silane precursor R_xR_yR_z(SiO_3/2)_n (x + y + z = n = 6, 8, 10, ….) bearing 3-(N-(3-triethoxysilylpropyl)ureido)propyl, isooctyl and perfluoropropyl groups was synthesized and investigated as corrosion protective coating for AA 2024 alloy. Infrared reflection-absorption (IR RA) combined with X-ray photoelectron spectroscopy and atomic force microscopy provided information about partial self-assembling of coatings having a fluorine enriched upper layer with a low surface energy (γ^tot = 12.37 mN/m). The structural changes that accompanied corrosion produced under chronocoulometrical conditions were assessed from ex-situ IR RA spectra. A new band at 1690-1700 cm^− 1 appeared above the corrosion potential, and was assigned to the formation of amidonium ions and consequent relaxation of urea-urea associations.     

Growth and characterization of nitrogen-doped TiO2 thin films prepared by reactive pulsed laser deposition

Nitrogen-doped titanium dioxide (TiO₂) thin films were grown on (001) SiO₂ substrates by reactive pulsed laser deposition. A KrF* excimer laser source (λ = 248 nm, τ_FWHM ≅ 10 ns, ν = 10 Hz) was used for the irradiations of pressed powder targets composed by both anatase and rutile phase TiO₂. The experiments were performed in a controlled reactive atmosphere consisting of oxygen or mixtures of oxygen and nitrogen gases. The obtained thin film crystal structure was investigated by X-ray diffraction, while their chemical composition as well as chemical bonding states between the elements were studied by X-ray photoelectron spectroscopy. An interrelation was found between nitrogen concentration, crystalline structure, bonding states between the elements, and the formation of titanium oxinitride compounds. Moreover, as a result of the nitrogen incorporation in the films a continuous red-shift of the optical absorption edge accompanied by absorption in the visible spectral range between 400 and 500 nm wavelength was observed.