Investigation of amorphous Ni0.60Nb0.40 diffusion barriers

Interactions of Ni_0.60Nb_0.40 amorphous alloys with polycrystalline overlayers of gold and copper and single-crystal substrates of silicon. GaAs and GaP were observed with Auger depth profiling. The Ni-Nb layer was deposited by r.f. sputtering and was approximately 5000 Å thick. The overlayers were evaporated to a thickness of 1000 Å. The amorphous metal reacted with the gold overlayers and the GaAs and GaP substrates at temperatures well below the nominal crystallization temperature of 650 °C. The Cu/Ni-Nb/Si system, in contrast, was stable at 600 °C for at least 1 h. Samples were also measured that had been contaminated with approximately 5–10 at.% O. Complete separation of the niobium and nickel into distinct layers was seen. For the samples on silicon substrates this separation was accompanied by the formation of a nickel silicide layer.     

Alkoxide route to La0.5Sr0.5CoO3 epitaxial thin films on SrTiO3

An all alkoxide based sol–gel route was investigated for preparation of epitaxial La_0.5Sr_0.5CoO₃ (LSCO) films on 100 SrTiO₃ (STO) substrates. Films with 20–30 to 80–100 nm thickness were prepared by spin-coating 0.2–0.6 M (metal) solutions on the STO substrates and heat treatment to 800 °C at 2 °C min^− 1, 30 min, in air. The films were epitaxial with a cube-on-cube alignment and the LSCO cell was strained to match the STO substrate of 3.905 Å closely; a and b = 3.894 Å and 3.897 Å for the 20–30 and 80–100 nm films, respectively. The c-axis was compressed to 3.789 Å and 3.782 Å for the 20–30 and 80–100 nm films, respectively, which resulted in an almost unchanged cell volume as compared to polycrystalline film and nano-phase powders prepared in the same way. The SEM study showed mainly very smooth, featureless surfaces, but also some defects. A film prepared in the same way on an -Al₂O₃ substrate was dense and polycrystalline with crystallite sizes in the range 10–50 nm and gave cubic cell dimensions of a_c = 3.825 Å. The conductivity of the ca 30–40 nm thick polycrystalline film was 1.7 mΩcm, while the epitaxial 80–100 nm film had a conductivity of around 1.9 mΩcm.     

Synthesis, structure and luminescent properties of Lu(PO3)3

A new structural type of rare earth metaphosphate, Lu(PO₃)₃, was prepared from high-temperature solution, of which the crystal structure was solved in S.G. of Cc (No.9) and Z = 4 with unit cell dimensions of a = 13.972(3) Å, b = 6.6710(13) Å, c = 9.958(2) Å and β = 127.36(3)°. In Lu(PO₃)₃, [LuO₆] octahedra connect with the non-bridging oxygens on (PO₃)_n infinite zigzag chains that extended along c-axis. The VUV and X-ray excited luminescent properties of undoped and Ln³⁺ (Ln = Ce, Eu, Tb) doped samples were examined, from which the optical band gap was estimated to be 8.3 eV. Besides, in the undoped sample a STE emission within 320–480 nm was observed, which probably be related to oxygen defects. However, in the Lu(PO₃)₃:Ce sample the Ce³⁺ emission was weak and STE emission was totally quenched under hard X-ray excitation.     

HMTTEF.C60-A 2-D close-packed layered compound of C60

The analysis of high resolution synchrotron X-ray powder diffraction data of HMTTEF.C₆₀, (HMTTEF = hexamethylenetetratellurafulvalene) gave a triclinic unit cell with a 9.9297 Å, B = 9.9359 Å, C = 13.1472 Å, = 106.966 °, β = 95.887 ° and γ = 118.252 ° in the space group P . Steric considerations suggest that there is a nearly close-packed layer of C₆₀ molecules in the plane, and HMTTEF molecules are sandwiched between layers of C₆₀. The compound is insulating and weakly paramagnetic and the charge-transfer is small.     

Structure determination of CaMgGeO4

The crystal structure of CaMgGeO₄ is described. CaMgGeO₄, M_r = 200.9, orthorhombic, Pnam, A = 11.285(5) Å, B = 5.016(2) Å, C = 6.435(2) Å, V = 364.36 ų, Dx = 3.664 Mg/m³.λ(MoK_a = 0.71069 Å, F(000) = 384, room temperature, final R = 0.045 for 1752 observed reflections. The structure is isomorphous with CaMgSiO₄ (monticellite).     

Three phases in the system Hg1 − xCxBa2CuOy (0.00 ≤ x ≤ 1.00)

Samples of the [Hg_{1 − x}C_x]-Ba₂CuOy system [(Hg,C)-1201] with stoichiometries within the range 0.00≤x≤1.00 were synthesized by a highpressure, high-temperature technique. The sample with X = 0.00 [HgBa₂CuO_4+δ] was non-superconducting with lattice parameters A = 3.8676(2) Å, C = 9.470(1) Å. At low ranges of substitution (0.10≤x≤0.30), the predominant phase was found to be Hg-1201 with identical lattice parameters to those found for X = 0.00. At X = 0.40 the Hg-1201 phase coexists in similar proportions with the phase of mixed [Hg_{1 − x},C_x]-1201 stoichiometry. At X = 0.50, this second phase with lattice parameters A = 3.9271(3) Å, C = 8.676(2) Å is predominant and only traces of the Hg-1201 phase were found. At X = 0.75 the [Hg_{1 − x},C_x]-1201 phase found for X = 0.50 coexists with the CO₃Ba₂CuO_y phase, which is the extreme of the substitution range. This latter was predominant at X = 1.00 with lattice parameters A = 4.0044(3) Å, C = 7.909(1) Å, but at higher pressure than the previous substitutions. This system is constituted of three main phases, HgBa₂CuO_{4 + δ}, Hg_{1 − x}C_xBa₂CuO_y (x ≈ 0.50) and CO₃Ba₂CuO_y, which appear in different proportions according to the percentage of substitution and the applied synthesis pressure.     

Transparent conducting F-doped SnO2 thin films grown by pulsed laser deposition

Transparent conducting fluorine-doped tin oxide (SnO₂:F) films have been deposited on glass substrates by pulsed laser deposition. The structural, electrical and optical properties of the SnO₂:F films have been investigated as a function of F-doping level and substrate deposition temperature. The optimum target composition for high conductivity was found to be 10 wt.% SnF₂ + 90 wt.% SnO₂. Under optimized deposition conditions (T_s = 300 °C, and 7.33 Pa of O₂), electrical resistivity of 5 × 10^− 4 Ω-cm, sheet resistance of 12.5 Ω/□, average optical transmittance of 87% in the visible range, and optical band-gap of 4.25 eV were obtained for 400 nm thick SnO₂:F films. Atomic force microscopy measurements for these SnO₂:F films indicated that their root-mean-square surface roughness ( 6 Å) was superior to that of commercially available chemical vapor deposited SnO₂:F films ( 85 Å).     

New transparent conducting MgIn2O4---Zn2In2O5 thin films prepared by magnetron sputtering

New materials for a transparent conducting oxide film are demonstrated. Highly transparent Zn₂In₂O₅ films with a resistivity of 3.9 × 10⁻⁴ Ω cm were prepared on substrates at room temperature using a pseudobinary compound powder target composed of ZnO (50 mol.%) and In₂O₃ (50 mol.%) by r.f. magnetron sputtering. MgIn₂O₄---Zn₂In₂O₅ films were prepared using MgIn₂O₄ targets with a ZnO content of 0–100 wt.%. The resistivity of the deposited films gradually decreased from 2 × 10⁻³ to 3.9 × 10⁻⁴ Ω cm as the Zn/(Mg + Zn) atomic ratio introduced into the films was increased. The greatest transparency was obtained in a MgIn₂O₄ film. The optical absorption edge of the films decreased as the Zn/(Mg + Zn) atomic ratio was increased, corresponding to the bandgap energy of their materials. It was found that the resistance of the undoped Zn₂In₂O₅ films was more stable than either the undoped MgIn₂O₄, ZnO or In₂O₃ films in oxidizing environments at high temperatures.     

Giant magnetoresistance increase in a hard–soft spin valve structure with the growth of a semiconductor layer

Magnetic and transport properties of a hard–soft spin valve structures have been investigated. A first series of sandwiches composed of an artificial antiferromagnetic (AAF) Co/Ru/Co sandwich decoupled from a soft Fe/Co buffer layer as follows: Fe_{50 Å}/Co_{5 Å}/Cu_{30 Å}/Co_{30 Å}/Ru_{5 Å}/Co_{30 Å}/Cu_{20 Å}/Cr_{20 Å} has been prepared. This sandwich presents a giant magnetoresistance (GMR) of 1.7% and an exchange coupling strength of approximately −1.73 erg/cm². Afterwards, we have grown a second series of sandwiches in which the Cu/Cr capping layer has been replaced by a 15-Å thin semiconductor layer of ZnS, covered by a soft ferromagnetic layer of Co_{5 Å}/Fe_{50 Å}. Surprisingly, the giant magnetoresistance for the last sandwiches has been increased by a factor of 2, up to 4%. To explain this non-expected result, we have performed atomic force microscope imaging at the semiconductor layer surface. The results show that the semiconductor layer is not homogeneous and contains a non-negligible density of pin-holes, that are responsible of a direct magnetic coupling between the upper 30 Å Co layer of the AAF and the Co 5 Å/Fe 50 Å bilayer. This coupling induces a strong asymmetry between the magnetic layers of the AAF and consequently an enhancement of the GMR.     

Structural investigation of bulk and thin film PLZT using X-ray absorption spectroscopy

Thin film electro-optic and non-linear optical materials are of interest for applications in high-speed integrated optical devices. Materials of the system Pb_1−x/100La_x/100(Zr_y/100 Ti_1−y/100)_1−x/400O₃ or PLZT x/y/(100−y) are attractive since they can be integrated into Si and GaAs substrates using suitable deposition techniques. In this investigation we examine the structural properties of r.f. magnetron sputter-deposited PLZT using X-ray absorption near-edge spectroscopy (XANES). For XANES analysis, four samples were selected: (1) a highly oriented PLZT 28/0/100 film of ≈ 4500 Å deposited on SiO₂; (2) a highly oriented PLZT 28/0/100 film of ≈ 4500 Å deposited on a 2 ωm SiO₂ buffer layer over a Si(100) substrate; (3) a highly oriented PLZT 28/0/100 film of ≈4500 Å deposited on Al₂O₃ (1 02); and (4) a commercial ceramic wafer of PLZT 9/65/35. The XANES experiments were performed at the Stanford Synchrotron Radiation Laboratory (SSRL) using electron yield and fluorescence techniques. Data was taken at the Ti K-edge (4966.4eV) and compared to reference spectra. Of the reference spectra, the Ti K-edge spectra of the PLZT most closely resemble perovskite (SrTiO₃). The surface and bulk thin film are similar and all the 28/0/100 spectra resemble the spectra of 9/65/35, indicating similar cubic perovskite structures for these materials.     

An electron diffraction study of the ZnIn2Se4 crystal structure: A novel phase

A novel layered-structure ZnIn₂Se₄ phase has been obtained. Texture electron diffraction patterns aid in the identification of a crystal structure with lattice parameters a = 4.045 Å and c = 52.29 Å, space group R m, and z = 4.5. Crystal electron diffraction patterns displayed superstructural reflection, thus indicating a √3-fold increase in the a parameter. The similirity of reflection locations and intensities both on the crystal rotation electron diffraction pattern and on texture electron diffraction patterns showed that no phase transition occurred on specimen pounding. Electrophysical and optical parameters (E_g = 1.68 eV; N = 8 × 10²² m^-3; = 0.1Ωm) are studied at 300 K. The Hall coefficient is constant (R_H = 7.2 × 10^-5m³C^-1, mobility μ = 8 × 10^-3m²V^-1s^-1 at 200–300 K.     

Crystal structure and spectroscopic studies of NaGd(PO3)4

Single crystals of gadolinium–sodium polyphosphate NaGd(PO₃)₄ were grown for the first time using a flux method and characterized by X-ray diffraction. This phosphate crystallizes in a monoclinic system with P2₁/n space group and with the following unit-cell dimensions: a = 9.767(3) Å, b = 13.017(1) Å, c = 7.160(2) Å, β = 90.564(5)°, V = 910.3(4) Å³ and Z = 4. The crystal structure was solved from 3451 X-ray independent reflections with final R(F²) = 0.0219 and R_w(F²) = 0.056 refined with 164 parameters (). The atomic arrangement can be described as a long chain polyphosphate organization. Two infinite (PO₃)∝ chains with a period of eight tetrahedra run along the [0 1 1] direction. The structure of NaGd(PO₃)₄ consists of GdO₈ polyhedra sharing oxygen atoms with phosphoric group PO₄. Each Na⁺ ion is bonded to eight oxygen atoms.     

Frequency dependent electrical conductivity and dielectric relaxation behavior in amorphous (90V2O5–10Bi2O3) oxide semiconductors doped with SrTiO3

We report on the experimental results of frequency dependent a.c. conductivity and dielectric constant of SrTiO₃ doped 90V₂O₅–10Bi₂O₃ semiconducting oxide glasses for wide ranges of frequency (500–10⁴ Hz) and temperature (80–400 K). These glasses show very large dielectric constants (10²–10⁴) compared with that of the pure base glass (≈10²) without SrTiO₃ and exhibit Debye-type dielectric relaxation behavior. The increase in dielectric constant is considered to be due to the formation of microcrystals of SrTiO₃ and TiO₂ in the glass matrix. These glasses are n-type semiconductors as observed from the measurements of the thermoelectric power. Unlike many vanadate glasses, Long's overlapping large polaron tunnelling (OLPT) model is found to be most appropriate for fitting the experimental conductivity data, while for the undoped V₂O₅–Bi₂O₃ glasses, correlated barrier hopping conduction mechanism is valid. This is due to the change of glass network structure caused by doping base glass with SrTiO₃. The power law behavior (σ_ac=A(ω^s) with s<1) is, however, followed by both the doped and undoped glassy systems. The model parameters calculated are reasonable and consistent with the change of concentrations (x).     

Crystal structure, thermal analysis and IR spectroscopic investigation of (C6H9N2)H2XO4 (X = As, P)

Crystals of 2-amino-4-methylpyridinium dihydrogenmonoarsenate (C₆H₉N₂)H₂AsO₄ and 2-amino-4-methylpyridinium dihydrogenmonophosphate (C₆H₉N₂)H₂PO₄ have been prepared and grown at room temperature. These materials are isotypic with the following unit cell dimensions (C₆H₉N₂)H₂AsO₄: a = 12.4415(5) Å, b = 6.8224(3) Å, c = 11.3524(5) Å, Z = 4, V = 963.60(6) Å³; (C₆H₉N₂)H₂PO₄: a = 12.4410(9) Å, b = 6.7165(3) Å, c = 11.3417(5) Å, Z = 4, V = 925.09(10) Å³. The common space group is Pnma. The structure of these compounds has been determined by X-ray data collection on single crystals of (C₆H₉N₂)H₂AsO₄ and (C₆H₉N₂)H₂PO₄. Due to the strong hydrogen-bond network connecting the H₂XO₄ groups, the anionic arrangement must be described as a linear organization. The chains composed by the macroanion spread along the b-direction, approximately centered by x = 0 and 1/2. All atoms of the structure, except one oxygen atom, are located in the mirror planes situated at y = 1/4 and 3/4, imparting an internal mirror symmetry to the anionic and the cationic entities. The linear macroanions are crossed by organic cations lying in mirrors perpendicular to the b-direction; this atomic arrangement is then described by a three-dimensional network of hydrogen bonds, built up by two types, O–HO bonds inside the chains and N–HO bonds linking adjacent chains. The thermal properties of both compounds are investigated as well as the IR properties supported by group theoretical analyses.     

Synthesis, structure refinement and characterization of tetrahydrated acid gadolinium diphosphate HGdP2O7·4H2O

Synthesis and single crystal structure are reported for a new gadolinium acid diphosphate tetrahydrate HGdP₂O₇·4H₂O. This salt crystallizes in the monoclinic system, space group P2₁/n, with the following unit-cell parameters: a = 6.6137(2) Å, b = 11.4954(4) Å, c = 11.377(4) Å, β = 87.53(2)° and Z = 4. Its crystal structure was refined to R = 0.0333 using 1783 reflections. The corresponding atomic arrangement can be described as an alternation of corrugated layers of monohydrogendiphosphate groups and GdO₈ polyhedra parallel to the () plane. The cohesion between the different diphosphoric groups is provided by strong hydrogen bonding involving the W4 water molecule.

IR and Raman spectra of HGdP₂O₇·4H₂O confirm the existence of the characteristic bands of diphosphate group in 980–700 cm⁻¹ area. The IR spectrum reveals also the characteristic bands of water molecules vibration (3600–3230 cm⁻¹) and acidic hydrogen ones (2340 cm⁻¹). TG and DTA investigations show that the dehydration of this salt occurs between 79 and 900 °C. It decomposes after dehydration into an amorphous phase. Gadolinium diphosphate Gd₄(P₂O₇)₃ was obtained by heating HGdP₂O₇·4H₂O in a static air furnace at 850 °C for 48 h.     

Semiconducting and structural properties of CrSi2 A-type epitaxial films on Si(111)

Chromium disilicide (CrSi₂) films 1 000 Å thick have been prepared by molecular beam epitaxy on CrSi₂ templates grown on Si(111) substrate. The effect of the substrate temperature on the structural, electrical and optical properties of CrSi₂ films has been studied by transmission and scanning electron microscopies, optical microscopy, electrical resistivity and Hall effect measurements and infrared optical spectrometry. The optimal temperature for the formation of the epitaxial A-type CrSi₂ film have been found to be about 750°C. The electrical measurement have shown that the epitaxial A-type CrSi₂ film is p-type semiconductor having a hole concentration of 1 × 10¹⁷cm⁻³ and Hall mobility of 2 980 cm² V⁻¹ s⁻¹ at room temperature. Optical absorption coefficient data have indicated a minimum, direct energy gap of 0.34 eV. The temperature dependence of the Hall mobility (μ) in the temperature range of T = 180–500 K can be expressed as μ = 7.8 × 10¹⁰T⁻³cm²V⁻¹s⁻¹.     

Infrared optical properties of Bi2Ti2O7 thin films by spectroscopic ellipsometry

Bi₂Ti₂O₇ thin films have been grown directly on n-type GaAs (1 0 0) by the chemical solution decomposition technique. X-ray diffraction analysis shows that the Bi₂Ti₂O₇ thin films are polycrystalline. The optical properties of the thin films are investigated using infrared spectroscopic ellipsometry (3.0–12.5 μm). By fitting the measured ellipsometric parameter (Ψ and Δ) data with a three-phase model (air/Bi₂Ti₂O₇/GaAs), and Lorentz–Drude dispersion relation, the optical constants and thickness of the thin films have been obtained simultaneously. The refractive index and extinction coefficient increase with increasing wavelength. The fitted plasma frequency ω_p is 1.64×10¹⁴ Hz, and the electron collision frequency γ is 1.05×10¹⁴ Hz, and it states that the electron average scattering time is 0.95×10⁻¹⁴ s. The absorption coefficient variation with respect to increasing wavelength has been obtained.     

Optical properties of a-(Se70Te30)100−x(Se98 Bi2)x thin films

Measurements of optical constants (absorption coefficient, refractive index, extinction coefficient, real and imaginary part of the dielectric constant) have been made on a-(Se₇₀Te₃₀)_100−x (Se₉₈Bi₂)_x thin films (where x=0, 5, 10, 15 and 20) of thickness 2000 Å in the wavelength range 450–1000 nm. It is found that the optical bandgap decreases with the increase of Se₉₈Bi₂ concentration in the a-(Se₇₀Te₃₀)_100−x(Se₉₈Bi₂)_x system. The value of refractive index (n) decreases, while the extinction coefficient (k) increases with increasing photon energy. The results are interpreted in terms of concentration of localized states varying effective Fermi level.     

Crystal structure and characterization of [2,5-(CH3O)2C6H3NH3]4P4O12·2H2O

The preparation, crystal structure, TG–DTA analysis and spectroscopy investigation are reported for the 2,5-dimethoxy phenyl ammonium cyclotetraphosphate dihydrate [2,5-(CH₃O)₂C₆H₃NH₃]₄P₄O₁₂·2H₂O. This new compound is triclinic P with unit cell dimensions: a = 7.438(5) Å, b = 11.841(7) Å, c = 12.354(4) Å,  = 96.61(4)°, β = 98.35(4)°, γ = 102.60(6)°, Z = 1 and V = 1038.0(1) Å³. Its crystal structure has been determined and refined to R = 0.049, with 5128 independant reflections. The structure can be described by rows of P₄O₁₂ ring anions along the a axis; between these rows are located the organic groups, connected to them by hydrogen bonds.     

Structure and electrical properties of boron-added (Ba,Sr)TiO3 thin films fabricated by the sol-gel method

Thin films of Ba_xSr_1−xTiO₃ (BST, with x=0.5) were fabricated on a RuO₂/Ru/SiO₂/Si substrate by the spin coating of the multicomponent sol prepared using metal alkoxides. Boron alkoxide was intentionally introduced to establish a better microstructure and to reduce the leakage current. AFM indicated that a crack-free uniform microstructure having a smooth surface was gradually developed with increasing boron content. The relative dielectric permittivity of the 250-nm thick BST thin films fired at 700°C decreased with increasing content of boron, from 420 for the undoped film to 190 for the 10 mol% boron-added film at 1 MHz. This observation was interpreted in terms of a serial capacitance composed of the perovskite BST grain and the interfacial B₂O₃ glassy phase having a low dielectric permittivity. The leakage current density (J) also decreased with the amount of boron added. The leakage current for the applied voltage greater than 1 V showed a linear variation of logJ with E^1/2 at room temperature, suggesting that the interface-controlled Schottky emission was the dominant conduction process for the BST thin films fabricated on the RuO₂ electrode.