Ultrasound assisted synthesis of TiO2–WO3 heterostructures for the catalytic degradation of Tergitol (NP-9) in water

TiO₂–WO₃ heterostructures were synthesized at room temperature, ambient pressure, and short reaction time via a sonochemical approach. TEM and EDX images show that the prepared TiO₂–WO₃ heterostructures consist of globular agglomerates (∼250 nm in diameter) composed of very small (<5 nm) dense particles (WO₃) dispersed inside the globules. The observed less intense monoclinic WO₃ diffraction peak (around 2θ = 22° belonging to (0 0 1) plane) and the high intense hexagonal WO₃ diffraction peak (around 2θ = 28° belonging to (2 0 0) plane) in XRD indicate that there may be phase transition occurring due to the formation of intimate bond between TiO₂ and WO₃. In addition, the formation of such new phase was also observed from Raman spectra with a new peak at 955 cm⁻¹, which is due to the symmetric stretching of W = O terminal. The catalytic activity of TiO₂–WO₃ heterostructures was tested for the degradation of wastewater pollutant containing Tergitol (NP-9) by a process combined with ozonation and it showed two-fold degradation rate compared with ozone process alone.     

Highly sensitive hydrogen detection by medium energy Ne+ impact

Hydrogen atoms on solid surfaces were measured directly by elastic recoil detection analysis (ERDA) using medium energy (100–150 keV) Ne⁺ ions with an excellent sensitivity of (～ 1 × 10¹² H/cm²) without any absorber foils and time-of-flight techniques. An electrostatic toroidal analyzer acquired H⁺ ions with energy around 11 keV recoiled from Si(111)-1 × 1-H surfaces. The H⁺ fraction strongly depends upon emerging angle and takes a value more than 50% at the angle below 70° and a saturated value of 17% at the angle above 80° with respect to surface normal. We detected H atoms on the reduced TiO₂(110) exposed to water molecules at room temperature (2 L) and estimated the absolute amount of H to be ～ 2.0 × 10¹⁴ H/cm² corresponding to ～ 38% (～ 0.38 ML) of the bridging oxygen atoms.     

The generalized Fresnel–Hadamard complementary transformation for asymmetric beamsplitter

Based on the newly developed parameterized coherent-entangled state representation we propose so-called the generalized Fresnel–Hadamard complementary transformation for asymmetric beamsplitter, which is unitary. The new unitary operator plays the role of both Fresnel transformation for a₁ sin θ ? a₂ cos θ and Hadamard transformation for a₁ cos θ + a₂ sin θ, respectively. Physically, a₁ sin θ ? a₂ cos θ and a₁ cos θ + a₂ sin θ could be a asymmetric beamsplitter’s two output fields. We show that the two transformations are concisely expressed in the parameterized coherent-entangled state representation as a projective operator in integration form.     

Epitaxial alloyed films out of the bulk stability domain: Surface structure and composition of Ni3Al and NiAl films on a stepped Ni(1 1 1) surface

We have studied by Spot Profile Analysis Low Energy Electron Diffraction (SPA-LEED) and Auger Electron Spectroscopy (AES) Ni–Al alloyed layers formed by annealing, around 780 K, Al deposits on a stepped Ni(1 1 1) surface. The surface structure and composition of the thin epitaxial Ni₃Al and NiAl films, obtained respectively below and above a critical Al initial coverage θ_c, differ markedly from those of corresponding bulk alloys.The Ni₃Al ordered films form in a concentration range larger than the stability domain of the L1₂ Ni₃Al phase. The NiAl films present a marked distortion with respect to the lattice unit cell of the B2 NiAl phase, which slowly decreases when the film thickness increases.It also appears that the value of θ_c depends on the morphology of the Ni(1 1 1) substrate, increasing from θ_c = 4.5 ML for a flat surface to θ_c = 10 ML for a surface with a miscut of 0.4°. This could be directly related to the presence of steps, which favour Ni–Al interdiffusion.     

Defect equilibria and partial molar properties of (La,Sr)(Co,Fe)O3−δ

The oxygen nonstoichiometry δ of La_1−xSr_xCo_1−yFe_yO_3−δ (x = 0.6 and y = 0.2, 0.4) was investigated by thermogravimetry in the range 703 ≤ T/°C ≤ 903 and 1E−5 < pO₂/atm < 1. The oxygen deficit increases with increasing T and decreasing pO₂. Electronic conductivities σ were measured as a function of pO₂ in the range 1E−5 < pO₂/atm < 1 at 700 ≤ T/°C ≤ 900. At constant T, a p-type pO₂-dependence of σ is observed. Oxygen nonstoichiometry data are analyzed with regard to the enthalpy and entropy of oxidation ΔH_ox^θ and ΔS_ox^θ, as well as to the partial molar enthalpy and entropy of oxygen with respect to the standard state of oxygen (pO₂^θ = 1 atm), (h_O − H_O^θ) and (s_O − S_O^θ), respectively. For 2.67 ≤ (3 − δ) ≤ 2.79, (h_O − H_O^θ) decreases with increasing δ, while (s_O − S_O^θ) is constant within the limits of error. Defect chemical modelling was performed by an ideal solution model under consideration of three different valence states for B-site ions (Co or Fe). The dependence of σ on δ is modelled, using calculated defect concentrations as functions of δ. Deviations from the ideal behaviour suggest an immobilization of n-type charge carriers by oxygen vacancies.     

Texture analysis of RF-sputtered CeO2 buffer layers and superconducting MOD-YBCO films

CeO₂ buffer layers were deposited on YSZ single-crystal substrates using an RF-sputtering method. The development of crystalline textures of sputtered CeO₂ films at different sputtering pressure and their effects on YBCO films, deposited by Metal Organic Deposition (MOD), were investigated. Both CeO₂ and subsequent YBCO films grew well epitaxially. The relative XRD peak intensities of CeO₂ (2 0 0) to substrate YSZ (2 0 0) increased with deposition pressure in the range of 3–5 mTorr and were inversely proportional to the θ–2θ scan FWHM values of CeO₂ (2 0 0). Also, the reaction layers of BaCeO₃ were thicker in the samples with lower CeO₂ (2 0 0) intensities and poor out-of-plane alignment when CeO₂ were deposited at the lower pressure of 3.3 mTorr. It is noted, however, that the superconducting layer grew well epitaxially on these BaCeO₃ layers, possibly due to the epitaxial relation between CeO₂ and YBCO. The superconducting critical currents of MOD-YBCO films showed an increasing tendency as both the Δ2θ (CeO₂) and BaCeO₃ peak intensities decreased.     

Thermodynamics and kinetics of CO and benzene adsorption on Pt(111) studied with pulsed molecular beams and microcalorimetry

The adsorption and desorption of the system CO/Pt(111) and C₆H₆/Pt(111) at 300 K has been investigated with a pulsed molecular beam method in combination with a microcalorimeter. For benzene the sticking probability has been measured in dependence of the coverage θ. For coverages θ > 0.8 transient adsorption is observed. From an analysis of the time-dependence of the molecular beam pulses the rate constant for desorption is determined to be 5.6 s^? 1. With a precursor-mediated kinetic adsorption model this allows to obtain also the hopping rate constant of 95.5 s^? 1. The measured adsorption enthalpies could be best described by (199 ? 77θ ? 51θ²) kJ/mol, in good agreement with the literature values. For CO on Pt(111) also transient adsorption has been observed for θ > 0.95 at 300 K. The kinetic analysis yields rate constants for desorption and hopping of 20 s^?1 and 51 s^?1, respectively. The heats of adsorption show a linear dependence on coverage (131 ? 38θ) kJ/mol between 0 ≤ θ ≤ 0.3, which is consistent with the desorption data from the literature. For higher coverage (up to θ = 0.9ML) a slope of ?63 kJ/mol describes the decrease of the differential heat of adsorption best. This result is only compatible with desorption experiments, if the pre-exponential factor decreases strongly at higher coverage. We found good agreement with recent quantum chemical calculations made for (θ = 0.5ML).     

Structural,electronic and energetic properties of water adsorbed on β-Si3N4 (0 0 0 1) surface: First-principles calculations

Structural, energetic and electronic properties of water molecules adsorbed on β-Si₃N₄ (0 0 0 1) surface, at various coverages, are investigated using density functional theory. At low coverages (θ ? 0.5), it is found that all H₂O molecules undergo spontaneous dissociation forming hydroxyl (OH) and imino (NH) groups where the reactive sites are identified, a result shown for the first time using ab initio theory. For higher coverages (θ > 0.5), only partial dissociation takes place where some of the molecules stay intact being bound via H-bond in good agreement with experimental findings. The driving force for the water dissociation has been identified to be dangling bonds on lower coordinated N and Si surface atoms showing that not all surface atoms are reactive corroborating with previous experimental findings.     

Geometry dependent resistivity behavior in mesoscopic Bi2Sr2CaCu2O8+δ single crystals

In order to investigate the interaction between Josephson vortices and pancake vortices in a layered Bi₂Sr₂CaCu₂O_8+δ superconductor, c-axis resistivity measurements were carried out on fabricated mesoscopic single crystals for two experimental geometries, when an applied high magnetic field of 14 T is perpendicular (B_ex⊥L) and parallel (B_ex∥L) to the width of sample. In the first case, the angular dependence of the resistance obtained near the ab-plane at T = 30 K exhibited hysteretic non-monotonic behavior with local maxima at θ = 0.6° away from the ab-plane and dips and spikes at θ = 0.2° marking a vortex lock-in transition. In the second geometry (B_ex∥L), instead of a local maximum, peculiar resistance shoulders were observed. At higher temperatures, hysteresis is reduced, while the vortex lock-in transition becomes considerably broader indicating the interaction of pancake and Josephson vortices.     

Optical and electrical properties of Ge-implanted SiO2 layers on n-Si and p-Si

Ge ions of 100 keV were implanted into a 120 nm-thick SiO₂ layer on n-Si at room temperature while those of 80 keV were into the same SiO₂ layer on p-Si. Samples were, subsequently, annealed at 500°C for 2 h to effectively induce radiative defects in the SiO₂. Maximum intensities of sharp violet photoluminescence (PL) from the SiO₂/n-Si and the SiO₂/p-Si samples were observed when the samples have been implanted with doses of 1×10¹⁶ and 5×10¹⁵ cm⁻², respectively. According to current–voltage (I–V) characteristics, the defect-related samples exhibit large leakage currents with electroluminescence (EL) at only reverse bias region regardless of the type of substrate. Nanocrystal-related samples obtained by an annealing at 1100°C for 4 h show the leakage at both the reverse and the forward region.     

Spin reorientation and magnetocrystalline anisotropy of (Nd1−xDyx) Fe14B

Spin reorientation and magnetocrytalline anisotropy of (Nd_1−xDy_x)₂Fe₁₄B (x=0.25, 0.5, 0.75) have been studied from mangetization curves of magnetically aligned powders. In (Nd_1−xDy_x)₂Fe₁₄B, the spin reorientation temperature (T_SR) decreases linearly on increasing Dy-substitution from 135 to 56 K with the ratio of ΔT_SR=−1.11 K/Dy at% in the composition range of 0⩽x⩽0.75. The spin reorientation angle at 4.2 K decreases on Dy-substitution from 30.4° at x=0 to 14.7° at x=0.75. From the investigation of the magnetocrystalline anisotropy at 4.2 K, the disappearance of the spin reorientation for compositions x≳0.85 is expected.     

Densely mapping the phase diagram of cuprate superconductors using a spatial composition spread approach

A novel spatial composition spread approach was used successfully to deposit a 52-member library of La_2?xSr_xCuO₄ (0 ? x ? 0.18) using magnetron sputtering combined with physical masking techniques. Two homemade targets of La₂CuO₄ and La_1.82Sr_0.18CuO₄ were sputtered at a power of 41 W RF and 42 W DC, respectively, in a process gas of 15 mTorr argon. The libraries were sputtered onto LaSrAlO₄ (0 0 1), SrTiO₃ (1 0 0) and MgO (1 0 0) substrates through a 52-slot shadow mask for which a ?20 V substrate bias was applied to prevent resputtering. The resulting amorphous films were post-annealed (800 °C for 1 h then at 950 °C for 2 h) in a tube sealed with oxygen gas. Wavelength Dispersive Spectroscopy (WDS) analysis revealed the expected linear variation of Sr content from 0 to 0.18 with an approximate change of 0.003 per library member. Transport measurements revealed superconducting transitions as well as changes in the quasiparticle scattering rate. These transitions and scattering rate changes were mapped to produce the T-hole concentration phase diagram.     

DFT study of carbon monoxide adsorption on α-Al2O3(0001)

The adsorption of CO on α-Al₂O₃(0001) was studied using the DFT-GGA computational method and on α-Al₂O₃ powder experimentally by Infra red spectroscopy. The core and valence level regions of α-Al₂O₃(0001) single crystal surface were also studied experimentally. Ar ions sputtering of the surface results in a slight but reproducible decrease in the XPS O2p lines in the valence band regions due to preferential removal of surface (and near surface) O atoms. Core level XPS O1s and Al2p further confirmed oxygen depletion with an associated surface stoichiometry close to Al₂O_2.9. The adsorption energy of CO was computed and found equal to 0.52 eV for θ = 0.25, it decreased to 0.42 eV at θ = 1. The IR frequency of νCO was also computed and in all cases it was blue shifted with respect to gas phase CO. The shift, Δν, decreased with increasing coverage where it was found equal to 56 cm^? 1 for θ = 0.25 and decreased to 30 cm^? 1 for θ = 1. Structural analyses indicated that the change in the adsorption energy and the associated frequency shift is due to surface relaxation upon adsorption. Experimentally the adsorption of CO gave rise to one main IR peak at 2154 cm^? 1 at 0.3 Torr and above. Two far smaller peaks are also seen at lower pressures of 0.03–0.2 Torr at 2189 and 2178 cm^? 1. The isosteric heat of adsorption was computed for the IR band at 2154 cm^? 1 and was found equal to 0.2 eV which did not change with coverage in the investigated range up to θ = 0.6.     

Thermoelectric power of CuCrxVySe4 p-type spinel semiconductors

Structural, electrical and magnetic measurements of polycrystalline CuCr_xV_ySe₄ spinels with x=1.79, 1.64 and 1.49 and y=0.08, 0.22 and 0.45, respectively, are presented. The compounds under study crystallize in regular system of a normal spinel type MgAl₂O₄ structure with the space group symmetry Fd3m. The chromium spins are coupled ferromagnetically and show both strong long- and short-range magnetic interactions evidenced by the large values of the Curie (T_C) and Curie–Weiss (θ_CW) temperatures, decreasing from T_C=407 K and θ_CW=415 K for y=0.08, via T_C=349 K and θ_CW=367 K for y=0.22 to T_C=283 K and θ_CW=293 K for y=0.45, respectively. In all the studied spinels a change of the electrical conductivity character from the semiconductive into the metallic one above 230 K was observed. A detailed thermoelectric power analysis showed a domination of diffusion thermopower component, maximum of phonon drag component at 230 K, a decrease of impurity component with increasing V content, as well as the weak magnon excitations at 40 K.     

Sputter damage in Si surface by low energy Ar+ ion bombardment

The damage distributions in Si(1 0 0) surface after 1.0 and 0.5 keV Ar⁺ ion bombardment were studied using MEIS and Molecular dynamic (MD) simulation. The primary Ar⁺ ion beam direction was varied from surface normal to glancing angle. The MEIS results show that the damage thickness in 1.0 keV Ar ion bombardment is reduced from about 7.7 nm at surface normal incidence to 1.3 nm at the incident angle of 80°. However, the damage thickness in 0.5 keV Ar ion bombardment is reduced from 5.1 nm at surface normal incidence to 0.5 nm at the incident angle of 80°. The maximum atomic concentration of implanted Ar atoms after 1 keV ion bombardment is about 10.5 at% at the depth of 2.5 nm at surface normal incidence and about 2.0 at% at the depth of 1.2 nm at the incident angle of 80°. However, after 0.5 keV ion bombardments, it is 8.0 at% at the depth of 2.0 nm for surface normal incidence and the in-depth Ar distribution cannot be observable at the incident angle of 80°. MD simulation reproduced the damage distribution quantitatively.     

Metallization of Ge(0 0 1)-p(2 × 1) surface as result of thermal fluctuations

We present a theoretical study of the metallization of Ge(0 0 1)-p(2 × 1) surface which is observed in experimental data. We have considered the connection between thermal fluctuation of this surface structure and its metallic properties. To this end we have performed long-time MD-DFT simulations. The obtained results show that thermal fluctuation of the Ge(0 0 1)-p(2 × 1) structure may cause its metallization which in not necessary connected with a flip-flop motion of dimer atoms. It was shown that the metallization of the Ge(0 0 1)-p(2 × 1) surface takes place when the dimer buckling angle is reduced to around 11°. In the case of our simulations the considered surface system remained in the metallic state for 25% of the simulation time. We have also found that the metallic state of the fluctuating Ge(0 0 1)-p(2 × 1) surface is built up by dangling bonds of the dimer atoms shifted up (D_up) and down (D_down).     

Magnetic and magneto-optical properties of MnSb films on various substrates

Magnetic and magneto-optical properties of MnSb films with different crystalline orientations on various semiconductors of GaAs(1 0 0), GaAs(1 1 1)A, B, and sapphire(0 0 0 1) have been measured by a vibrating sample magnetometer (VSM) and a home-made magneto-optical Kerr effect (MOKE) system. All these samples have their easy axes in the plane and show ferromagnetic properties. Among these samples, the film on GaAs(1 1 1)B has the lowest coercive force H_c and the largest squareness (SQ) value, whereas the film on GaAs(1 0 0) shows the largest H_c and the lowest SQ value. A large Kerr rotation angle of about 0.3° was observed at a wavelength of λ=632.8 nm for the film on sapphire in the field applied both parallel and perpendicular to the film plane. However, the MnSn films on other substrates do not have an observable Kerr rotation. The dynamic effect of the hysteresis was also measured using our MOKE system. As the frequency of applied magnetic field increases, the loop rounds off at the corners and the loop area increases.     

Recombination luminescence of CsI(Tl) under electron pulse irradiation

The luminescence kinetics of CsI(Tl) exposed to an electron pulse irradiation (E_e = 250 keV, t_1/2 = 10 ns, j = 2 ÷ 160 mJ/cm²) has been studied. It has been discovered that the slow emission rise is due to hole V_k–Tl⁰ recombination luminescence at temperature from 100 to 160 K and electron–V_kA recombination, where electrons released from single Tl⁰ at temperature from 180 to 300 K. The effect of Tl concentration on both processes has been investigated.     

Magneto-oscillations in a trapezoidal two-dimensional electron gas grown over GaAs wires

In this work we investigate a nonplanar two-dimensional electron gas (2DEG) that allows study of the electronic behaviour in random and sign-alternating magnetic fields. Shubnikov–de Haas oscillations were studied by measuring the magnetoresistance at different angles φ between the field and the substrate. We find that at low magnetic field the position of the oscillation peaks followsB_p ∼ Bsin (φ − θ), where θ is the angle between the field and the facets that effectively contribute to magnetoresistance. This is due to the fact that electrons follow different paths depending on the realization of a specific magnetic field.     

Effective demagnetizing factors in ferromagnetic resonance equations

A simple method of deriving effective demagnetizing factors (N_x^e,N_y^e) for the use of Kittel's ferromagnetic resonance formula is reported. The effective demagnetizing factors are expressed by an anisotropy energy (G) and a static field direction (θ,φ). By this derivation method, the resonance equations of thin films having a uniaxial or a four-fold anisotropy are obtained when a static field is rotated in the film plane. Six arrangements are calculated: (1) perpendicular anisotropy, (2) in-plane anisotropy, (3) cubic-crystal (0 0 1) face, (4) cubic-crystal (0 1 1) face, (5) cubic-crystal (1 1 1) face, and (6) oblique anisotropy films.