Stacking faults in ultra-thin films of silver on Al(111) investigated by medium energy ion scattering

Medium energy ion scattering has been used to investigate depositions of 0.2, 1.4, 3.5 and 4.8 ML of silver onto Al(111). Energy profiles indicate alloying to the extent that aluminium is still visible after the deposition of 4.8 ML. From assessments of the visibility, blocking dips and fits using VEGAS simulations it is shown that the first two layers continue the fcc stacking but after that hcp and fcc twin-type stacking faults occur. The 1.4 ML structure is consistent with a mixed structure of 85% fcc and 15% hcp indicating that some silver occupies a third layer. The blocking curve from the structure formed by 3.5 ML equivalent deposition can be simulated by 56% fcc, 32% hcp and 12% fcc twin and that from 4.8 ML by 59% fcc, 23% hcp and 18% fcc twin. This provides direct evidence of the incidence of hcp stacking when silver is deposited onto Al(111) in the range between 2 and 5 ML.     

A New Insight into Cobalt Metal Powder Internal Field 59Co NMR Spectra

The authors present a new approach of internal field ⁵⁹Co NMR spectra assignment leaving apart from “usual” decomposition on “pure” hcp and fcc stackings, and a set of stacking faults (sfs) sf₁–sf₅ with a certain lines position. The authors propose including into consideration not only cobalt structural features as well as its magnetic nature due to the strong ferromagnetism in Co metal. The last fact supposes an existence of different magnetic species such as magnetic domains, domain walls, and single-domain particles, thereby helping to spectral lines assignment according to both structural and magnetic origin. The examined sample contains fcc and hcp resonance peaks in both domains and domain walls giving the hcp to fcc ratio equal to 1.9, as well a significant amount of Co sfs, or Co in loose coordination, up to 10 %. The research exhibits a good agreement of all implemented techniques.     

The electronic structures of commensurate Ru(0001)–(3 × 3)–4Kr and Ru(0001)–(5 × 5)–Kr using density functional theory

We have calculated the minimum energies for each of three positionings of the adatom unit cells for Ru(0001)–(3 × 3)–4Kr (high Kr coverage) and for Ru(0001)–(5 × 5)–Kr (low Kr coverage). The differences between the results for the low and high-coverage cases may clarify puzzles posed by the experimental results of Narloch and Menzel. The low-coverage solution converges to a structure having Kr in the top site at a height of 3.09 Å above the substrate with the adsorption energy 185 meV. In the high-coverage case, adatom unit cells with a corner Kr at top, fcc hollow, and hcp hollow locations are found to have nearly the same adsorption energy of 175 meV. The height of the corner atom above the substrate is found to be 3.35, 3.54, and 3.50 Å for the top, fcc hollow and hcp hollow sites, respectively. These results are explained by demonstrating that there is an enhancement of the substrate electronic density of states at krypton orbital energies in the low-coverage case.     

Growth and characterization of CoSi2 films on Si (1 0 0) substrates

In the present work, a special solid phase epitaxy method has been adapted for the preparation of CoSi₂ film. This method includes an epitaxial growth of Co films on Si (1 0 0) substrate, and in situ annealing of the Co/Si films in vacuum. It has been found that at the substrate temperature of 360°C, fcc cobalt film grows epitaxially on the Si (1 0 0) surface. The crystallographic orientation relations between fcc Co film and Si substrate determined from the electron diffraction result are: (0 0 1) Co//(0 0 1) Si, [1 0 0] Co//[1 1 0]Si. Upon annealing at temperatures range from 500 to 600°C, Co film reacts with Si substrate and transforms into CoSi₂. The CoSi₂ films prepared by this way are characterized by XTEM, XPS and AFM.     

Hyperfine Interaction Studies on Y, Zr, Nb, Mo, Rh, In and Xe in Co

Nuclear magnetic resonance on oriented nuclei and modulated adiabatic fast passage on oriented nuclei measurements were performed on several 4d and 5sp impurities in polycrystalline Co(fcc) foils and Co(hcp) single crystals. The hyperfine fields of Y and Zr in Co(fcc), the hyperfine fields of Y, Zr, Nb, Mo, Rh, In and Xe in Co(hcp), the electric field gradients of Zr, Nb and In in Co(hcp), and the nuclear spin-lattice relaxations of Zr, Nb, Rh and In in Co(hcp) were determined. The dependence of the hyperfine fields and electric field gradients in Co(hcp) on the angle between the magnetization and the c axis was investigated in most cases. The magnetic-field dependence of the spin-lattice relaxation was studied for Nb, Rh and In in Co(hcp), applying the magnetic field perpendicular to the c axis. The known hyperfine interaction parameters of the 4d and 5sp impurities in Co(fcc) and Co(hcp) are summarized. The new results provide a more detailed picture of the hyperfine interaction in Co.     

Electrochemical properties of spinel-type manganese oxide/porous carbon nanocomposite powders in 1 M KOH aqueous solution

Spinel-type manganese oxide/porous carbon (Mn₃O₄/C) nanocomposite powders have been simply prepared by a thermal decomposition of manganese gluconate dihydrate under an Ar gas flow at above 600 °C. The structure and texture of the Mn₃O₄/C nanocomposite powders are investigated by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) equipped scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), selected area-electron diffraction (SA-ED), thermogravimetric and differential thermal analysis (TG-DTA) and adsorption/desorption of N₂ gas at ?196 °C. The electrochemical properties of the nanocomposite powders in 1 M KOH aqueous solution are studied, focusing on the relationship between their structures and electrochemical capacitance.In the nanocomposite powders, Mn₃O₄ nano particles approximately 5 nm in size are dispersed in a porous carbon matrix. The nanocomposite powders prepared at 800 °C exhibit a high specific capacitance calculated from cyclic voltammogram of 350 and 600 F g^?1 at a sweep rate of 1 and 0.1 mV s^?1, respectively. The influence of the heating temperature on the structure and the electrochemical properties of nanocomposite powders is also discussed.     

Electronic structure and optical properties of BaMoO4 powders

Barium molybdate (BaMoO₄) powders were synthesized by the co-precipitation method and processed in microwave-hydrothermal at 140 °C for different times. These powders were characterized by X-ray diffraction (XRD), Fourier transform Raman (FT-Raman), Fourier transform infrared (FT-IR), ultraviolet–visible (UV–vis) absorption spectroscopies and photoluminescence (PL) measurements. XRD patterns and FT-Raman spectra showed that these powders present a scheelite-type tetragonal structure without the presence of deleterious phases. FT-IR spectra exhibited a large absorption band situated at around 850.4 cm⁻¹, which is associated to the Mo–O antisymmetric stretching vibrations into the [MoO₄] clusters. UV–vis absorption spectra indicated a reduction in the intermediary energy levels within band gap with the processing time evolution. First-principles quantum mechanical calculations based on the density functional theory were employed in order to understand the electronic structure (band structure and density of states) of this material. The powders when excited with different wavelengths (350 nm and 488 nm) presented variations. This phenomenon was explained through a model based in the presence of intermediary energy levels (deep and shallow holes) within the band gap.     

Geometric and magnetic properties of Co/Pd system

We measured geometric and magnetic properties of Co films on the Pd(1 1 1) surface by X-ray photoelectron diffraction (XPD), X-ray magnetic circular dichroism (MCD) at the Co L_2,3 edge, and the surface magneto-optical Kerr effect (SMOKE) measurements. Co thin films are found to grow incoherently with fcc island structure on the smooth Pd(1 1 1) substrate. Comparison of MCD and SMOKE measurements of Co thin films grown on rough and smooth Pd(1 1 1) surfaces suggests that perpendicular remnant magnetization and Co orbital moment are enhanced by the rough interface. Pd capping layer also induces perpendicular orbital moment enhancement. These observations indicate the influence of hybridization between Co 3d and Pd 4d at the interface on the magnetic anisotropy.     

Structural and magnetic properties of Co50Ni50 powder mixtures

In the present work, morphological, structural, thermal and magnetic properties of nanocrystalline Co₅₀Ni₅₀ alloy prepared by high energy planetary ball milling have been studied by means of scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry. The coercivity and the saturation magnetization of alloyed powders were measured at room temperature by a vibration sample magnetization. Morphological observations indicated a narrow distribution in the particle and homogeneous shape form with mean average particle size around 130 μm². The results show that an allotropic Co transformation hcp→fcc occurs within the three first hours of milling and contrary to what expected, the Rietveld refinement method reveals the formation of two fcc solid solutions (SS): fcc Co(Ni) and Ni(Co) beside a small amount of the undissolved Co hcp. Thermal measurement, as a function of milling time was carried out to confirm the existence of the hcp phase and to estimate its amount. Magnetic measurement indicated that the 48 h milled powders with a steady state particles size have the highest saturation (105.3 emu/g) and the lowest coercivity (34.5 Oe).     

Characterisations of CoCu films electrodeposited at different cathode potentials

Structural and magnetic properties of CoCu films electrodeposited on polycrystalline Cu substrates were investigated as a function of cathode potential used for their deposition. The compositional analysis, performed by energy dispersive X-ray spectroscopy, demonstrated that an increase in the deposition potential results in an increase in Co content of CoCu films. The crystal structure of the films was studied using the X-ray diffraction (XRD) technique. It was observed that they have a face centred cubic (fcc) structure, but also contain partly hexagonal close-packed phase. XRD results revealed that the (1 1 1) peak of fcc structure splits into two as Co (1 1 1) and Cu (1 1 1) peaks and the peak intensities change depending on the deposition potential and hence the film composition. The magnetic measurements were carried out at room temperature using a vibrating sample magnetometer. The magnetic findings indicated that coercivity decreases and saturation magnetisation increases with the increase of Co:Cu ratio caused by the deposition potential and also all films have planar magnetisation.     

The geometries of coadsorbate layers of O and H on Ru(0 0 1): How well can quantitative LEED see hydrogen atoms?

Using a CCD LEED system for the collection of IV data with low beam damage, and full dynamical as well as tensor LEED calculations, we have determined the geometries of the (2 × 2)-(O + 3H) and the (2 × 2)-(O + H) coadsorbate structures on Ru(0 0 1). We show that here quantitative LEED can locate the H atoms very well. Not only their sites (hcp in the first, fcc in the second case), but also the Ru–H spacings and changes in the first two substrate layers are clearly determined. We argue that this success is due to the relatively large data range and to the smaller H mobility compared to pure H layers caused by their repulsive lateral interactions with the oxygen atoms.     

Effects of Zr impurity on microscopic behavior of Hf metal

Hf metal with ∼ 3 wt% Zr impurity has been reinvestigated by perturbed angular correlation (PAC) spectroscopy using a LaBr₃(Ce)–BaF₂ detector set up to understand the microscopic behavior of this metal with temperature. From present measurements, five quadrupole interaction frequencies have been found at room temperature where both pure hcp fraction (∼33%) with 12 nearest neighbor Hf surrounding the probe ¹⁸¹Hf atom and the probe–impurity fraction (∼33%) corresponding to 11 nearest neighbor Hf plus one dissimilar Zr atom are clearly distinguished. At room temperature, the results for quadrupole frequency and asymmetry parameter are found to be ω_Q=51.6(4) Mrad/s, η=0.20(4) for the impurity fraction and ω_Q=46.8(2) Mrad/s, η=0 for the pure fraction with values of frequency distribution width δ=0 for both components. At 77 K, only 1 NN Zr impurity (∼93%) and pure hcp (∼7%) components have been found with a value of δ ∼ 10% for the impurity fraction. A drastic change in microstructural configuration of Hf metal is observed at 473 K where the impurity fraction increases to ∼ 50% and the pure hcp fraction reduces to ∼ 15% with abrupt changes in quadrupole frequencies for both components. The pure fraction then increases with temperature and enhances to ∼50% at 973 K. In the temperature range 473–973 K, quadrupole frequencies for both components are found to decrease slowly with temperature. Using the Arrhenius relation, binding energy (B) for the probe–impurity pair and the entropy of formation are measured from temperature dependent fractions of probe–impurity and pure hcp in the temperature range 473–773 K. The three other minor components found at different temperatures are attributed to crystalline defects.     

在不同的退火温度下钴注入二氧化钛结构与磁性

选用能量为180 keV,温度为623 K,注入4×10¹⁶ cm^-2剂量的钴离子束注入TiO₂样品.在不同的退火温度下,用高分辨的扫描电镜、同步辐射X射线衍射、卢瑟福背散射/沟道实验和超导量子干涉仪,分别对样品进行结构与磁性的测试. SR-XRD和HRTEM测试结果表明: 在Co注入TiO₂后,形成了钴的体心立方(hcp)相和面心立方(fcc)相,且在TiO₂中,钴-纳米粒子也已经形成. 随着退     

NMR studies of cation transport in the crystalline ion conductors MCF3SO3 (M = Li,Na) and Li7TaO6

In this contribution we present studies on the mechanism of ion transport in crystalline solid electrolytes employing a range of different solid state nuclear magnetic resonance (NMR) experiments. The first part is devoted to the elucidation of a possible correlation of cation transport and anion reorientation in the dynamically disordered rotor phases of alkali trifluoromethane sulfonates MCF₃SO₃ (M = Li, Na) employing ⁷Li, ¹³C, ¹⁷O and ²³Na NMR line shape analysis, whereas the second part focuses on the tracking of cation diffusion pathways in the hexaoxometalate Li₇TaO₆ utilizing ⁶Li 1D and 2D exchange MAS NMR approaches.     

Microstructural aspects of the hcp-fcc allotropic phase transformation induced in cobalt by ball milling

A detailed correlation between microstructure evolution and allotropic phase transformations occurring in Co when subjected to ball milling has been carried out. After short-term milling, the starting mixture of hcp + fcc Co develops into an almost pure hcp phase. However, for longer milling times, plastic deformation introduces large amounts of stacking faults, especially of twin type, in the hcp structure. As a consequence, some of the hcp Co is converted back into fcc and the hcp unit cell is progressively anisotropically distorted. After long-term milling, a steady 'pseudo-equilibrium' state is observed, where all microstructural parameters, including the fcc percentage, tend to level off. However, the milling intensity can still be adjusted to increase further the stacking-fault probability and, consequently, the amount of fcc Co in the milled powders. The results imply that the stacking-fault formation, rather than the local temperature rise or crystallite size reduction associated with the milling process, is the main mechanism governing the hcp-fcc transformation.     

Formation of CuS with flower-like,hollow spherical,and tubular structures using the solvothermal-microwave process

CuCl₂ · 2H₂O and CH₃CSNH₂ were dissolved in ethylene glycol, and followed by the addition of NaOH to form solutions with different pH values. Reactions proceeded in surfactant-free solutions contained in an acid digestion bomb using a microwave irradiation at different conditions. Pure CuS (hcp) with flower-like, hollow spherical, and tubular structures were detected, and had the same vibration wavenumber at 474 cm⁻¹. They displayed two emission peaks at 411, and 432 nm. The formation of CuS with different morphologies was proposed according to the analytical results.     

Temperature-dependent 29Si NMR resonance shifts in lightly- and heavily-doped Si:P

Careful NMR measurements on a very lightly-doped reference silicon sample provide a convenient highly precise and accurate secondary chemical shift reference standard for ²⁹Si MAS-NMR applicable over a wide temperature range. The linear temperature-dependence of the ²⁹Si chemical shift measured in this sample is used to refine an earlier presentation of the paramagnetic (high-frequency) ²⁹Si resonance shifts in heavily-doped n-type silicon samples near the metal–nonmetal transition. The data show systematic decreases of the local magnetic fields with increasing temperature in the range 100–470 K for all samples in the carrier concentration range from 2×10¹⁸ cm⁻³ to 8×10¹⁹ cm⁻³. This trend is qualitatively similar to that previously observed for the two-orders of magnitude larger ³¹P impurity NMR resonance shifts in the same temperature and concentration ranges. The ²⁹Si and ³¹P resonance shifts are not related by a simple scaling factor, however, indicating that impurity and host nuclei are affected by different subsets of partially-localized extrinsic electrons at all temperatures.     

The influence of Eu3+ doping on photoluminescent properties of red emitting phosphor YInGe2O7:Eu3+ by microwave assisted and conventional sintering method

This paper describes an investigation of the crystalline morphology and photoluminescent properties of YInGe₂O₇ powders doped with different Eu³⁺ concentrations using microwave assisted sintering and conventional sintering. X-ray powder diffraction analysis confirmed the formation of monoclinic YInGe₂O₇ structure as YInGe₂O₇:Eu³⁺ powders were sintered at 1200 °C in microwave furnace for 1 h, and the raw material phase of Y₂O₃ was observed when Eu³⁺ concentration was below 30 mol%. Scanning electron microscopy showed microwave assisted sintering results in smaller particle size and more uniform grain size distribution. In the photoluminescent (PL) studies, the concentration quenching effect was observed under the excitation at 393 nm, but not under the excitation at CTS band. The ⁵D₀→⁷F₂ transition (620 nm), exhibits a non-exponential decay behavior as YInGe₂O₇:Eu³⁺ powders were sintered by microwave with the Eu³⁺ concentration higher than 50 mol%.     

Surface modification of Ni and Co metal nanowires through MeV high energy ion irradiation

Nickel (Ni) and cobalt (Co) metal nanowires were fabricated by using an electrochemical deposition method based on an anodic alumina oxide (Al₂O₃) nanoporous template. The electrolyte consisted of NiSO₄ · 6H₂O and H₃BO₃ in distilled water for the fabrication of Ni nanowires, and of CoSO₄ · 7H₂O with H₃BO₃ in distilled water for the fabrication of the Co ones. From SEM and TEM images, the diameter and length of both the Ni and Co nanowires were measured to be ∼ 200 nm and 5–10 μm, respectively. We observed the oxidation layers in nanometer scale on the surface of the Ni and Co nanowires through HR–TEM images. The 3 MeV Cl²⁺ ions were irradiated onto the Ni and Co nanowires with a dose of 1 × 10¹⁵ ions/cm². The surface morphologies of the pristine and the 3 MeV Cl²⁺ ion-irradiated Ni and Co nanowires were compared by means of SEM, AFM, and HR–TEM experiments. The atomic concentrations of the pristine and the 3 MeV Cl²⁺ ion-irradiated Ni and Co nanowires were investigated through XPS experiments. From the results of the HR–TEM and XPS experiments, we observed that the oxidation layers on the surface of the Ni and Co nanowires were reduced through 3 MeV Cl²⁺ ion irradiation.