Kinetics of Ni2Si growth from pure Ni and Ni(V) films on (111) and (100) Si

The kinetics of Ni₂Si growth from pure Ni and from Ni_0.93V_0.07 films on (111) and (100) silicon has been studied by the combination of He⁺ backscattering, x-ray diffraction, Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) techniques. The activation energies are 1.5 and 1.0 eV for pure Ni and Ni(V) films, respectively while the pre-exponential factors in Ni(V) are 4–5 orders of magnitude smaller than in the pure Ni case. The variations in the measured rates are related to the different grain size of the growing suicide layers. The vanadium is rejected from the silicide layer and piles up at the metalsilicide interface.     

Model of the lattice dynamics and study of the vibronic structure of intracenter transitions in ZnO:Ni+2 crystals

This paper presents a calculation of the defect vibrations induced in a ZnO:Ni crystal by the Ni⁺² impurity. The computations are done by a recursive method in the shell model. Based on the model calculations, the vibronic structure in the absorption spectra of the intracenter d-d transitions in the ZnO:Ni crystal is interpreted. Fiz. Tverd. Tela (St. Petersburg) 40, 2213–2216 (December 1998)     

EPR and optical spectra of Ni2+-VAg in silver chloride and silver bromide

The optical absorption and EPR spectra of Ni²⁺-V_Ag centres in the AgCl:Ni²⁺ and AgBr:Ni²⁺ systems have been investigated theoretically on the basis of the complete energy matrices including the electron–electron repulsion interaction, the ligand field interaction, the spin–orbit coupling interaction, and Zeeman interaction. Because the charge compensation forms a silver ion vacancy (V_Ag) which makes the attractive force acted on the each ligand ion different, it was determined that the Ni–X (X = Cl, Br) distance next to V_Ag is shorter than others for both AgCl:Ni²⁺ and AgBr:Ni²⁺ systems in the tetragonal symmetry. Besides, it was found that the local lattice structure of (NiX₆)^4? clusters in AgCl and AgBr crystals exhibit a compression distortion. This compression distortion may be ascribed to the fact that the Ni²⁺ ion has a smaller ionic radius and more effective charge than the Ag⁺ ion.     

g-factor of the 9/2+ isomeric state in 65Ni from transfer reaction

We report a measurement of the g-factor of the I ^π = 9/2⁺, t _1/2 = 22ns isomer in ⁶⁵Ni. The state of interest was populated and spin-oriented using a single-neutron transfer on an enriched ⁶⁴Ni target. The value, which was obtained, g(9/2⁺,^65m Ni) = - 0.296(3) is well in agreement with the g-factors of the other 9/2⁺ states in the region and with large-basis shell model calculations. The known g-factor of the 9/2⁺ isomer in ⁶³Ni was used in order to verify the strength of the hyperfine field of Ni( Ni) at room temperature.     

Hydrogenation of Zr2Ni

The intermetallic compound Zr₂Ni has been found to take up hydrogen on charging at room temperature. Zr₂(NiFe) H_4.7 and Zr₂(NiFe) H_4.5 show the same structure (CuAl₂ type) as the uncharged compound but with an expanded lattice.Analysis of room temperature spectra in zero and applied fields indicates that the⁵⁷Fe atoms occupy Ni sites in Zr₂(Ni ⁵⁷Fe). Volume expansion effects account for about one third of the increase in isomer shift ( +0.58 mms^–1) observed on hydrogenation. The distribution of hydrogen atoms around the probe³⁷Fe atoms also causes a decrease of 0.23 mms^–1 in the mean value for the quadrupole splitting compared Rith uncharged Zr₂Ni.     

CEMS and SEM studies of the ion-beam mixed Ni−Sn and Al−Sn systems

Metallic¹¹⁹Sn was vapour deposited on Al and Ni substrates to form layers about 40nm thick and subsequently irradiated with 100keV Xe⁺ at fluences 1, 5 and 10·10¹⁵ Xe⁺/cm². Irradiation with 100keV N⁺ at 5·10¹⁶N⁺/cm² fluence was also accomplished on an Al sample on which a layer of 100nm¹¹⁹Sn was previously electrodeposited. Surface evolution of the deposited layers due to irradiation has been observed by SEM and loss of Tin due to sputtering has been evidenced by EDX microanalysis. Changes of chemical structure at the irradiated surfaces have been followed by CEMS: β-Sn, SnO, SnAl₂O₄, SnO₂ and SnAl₂O₅ or β-Sn, dissolved Tin in Nickel, SnO₂, Ni₃Sn and Ni₃Sn₂ phases were recognized on the surface of Aluminium and Nickel substrates respectively.     

EPR g factors and tetragonal distortion for the isoelectronic Ni and Cu centers in the CuGaSe2 crystal

The EPR g factors, g_|| and g_⊥, for the isoelectronic 3d⁹ ions Ni⁺ and Cu²⁺ at the tetragonal Cu⁺ site of the CuGaSe₂ crystal are calculated from the high-order perturbation formulas based on a two-spin-orbit-parameter model. In the model, both the contributions to g factors from the spin-orbit parameter of central 3d⁹ ion and that of ligand ion are contained. The calculated results appear to be consistent with the experimental values. The tetragonal distortions (characterized by θ−θ₀, where θ is the angle between the metal-ligand bond and C₄ axis, and θ₀≈54.74° is the same angle in cubic symmetry) of Ni⁺ and Cu²⁺ centers, which are different from the corresponding angle in the host CuGaSe₂ crystal and from impurity to impurity, are obtained from the calculations. The difference of the sign of g_||−g_⊥ between the isoelectronic Ni⁺ and Cu²⁺ centers is found to be due to the different tetragonal distortions of both centers in the CuGaSe₂ crystal.     

The use of low energy sims to study the chemisorption of CO on Ni(100) and polycrystalline nickel

Adsorption of CO on Ni(100) has been investigated using secondary ion mass spectrometry (SIMS) and Auger electron spectroscopy at 175 and 295 K. Interaction with polycrystalline nickel was examined at 295, 325 and 365 K. All the secondary ions, Ni⁺, Ni₂⁺, NiCO⁺ and Ni₂CO⁺ show large increases in intensity as CO is adsorbed but there is no simple correlation of the secondary ion species with the sequence of linear and bridge-bonded CO species expected from electron energy loss spectroscopy. Adsorption of CO at 175 K on a hydrogen saturated Ni(100) surface, which is thought to permit only bridge-bonded adsorbed CO, does not result in any enhancement of Ni₂CO⁺. The extent of increases in secondary ion yields after CO adsorption on the nickel surfaces are primarily related to the variations in the heat of adsorption as a function of surface coverage. The presence of more weakly-held species is important in enhancing secondary ion yields.     

Ni2+ emission in SrF2

Luminescence measurements of X-irradiated SrF₂:Ni are reported. After X-irradiation two emission bands have been found. One of them peaked at 293 nm and has an excitation band at 267 nm. The other one at about 770 nm, which is much weaker, has an excitation band at 274 nm. Both emission bands are also observed under X-ray excitation. A comparison with some previous studies of the absorption and thermoluminescence properties of X-irradiated SrF₂:Ni indicates that the emission bands are due to two different kinds of Ni²⁺ centers. The proposed emission mechanisms are similar to those found in CaF₂:Ni.     

Study of the electro-absorption spectrum of a nickel acceptor exciton in a ZnO:Ni crystal based on a calculation of vibrations associated with a Ni+1 impurity

Localized vibrations in ZnO crystals due to the substitution impurity Ni⁺¹ are modeled. The calculations were performed in the shell model using a recursive method for vibrations with A ₁ and E type symmetry. Numerical calculations allowed us to analyze the vibronic structure in the electro-absorption spectra for nickel acceptor excitons in ZnO:Ni. Fiz. Tverd. Tela (St. Petersburg) 41, 986–990 (June 1999)     

Luminescent Ni+ centres and changes of the charge state of nickel ions in ZnS and ZnSe

In addition to Ni²⁺(3d ⁸) with its known internal transitions, Ni⁺(3d ⁹) is identified here by detecting its²E(D)?² T ₂(D) transition in ZnS and ZnSe both in absorption and emission. An analysis of vibronic satellites in these spectra indicates a moderate Jahn-Teller coupling in the² T ₂ ground state. Thermal annealing procedures which raise the Fermi level allow to increase the intensity ratio between the characteristic low-temperature optical bands of Ni⁺ and Ni²⁺. Ionisation and capture processes at these centres are studied by using the intensity of internal transitions as a probe for the concentration of the respective charge state of nickel. They are induced by additional optical irradiation of the samples in various spectral ranges. These photoionisation and radiative recombination processes manifest themselves in absorption, excitation and luminescence spectra as well as in the spectral response of photosensitive EPR signals. In addition to the threshold for the process [Ni²⁺]^x+hv→[Ni⁺]′+e _vb ^/ which had previously been determined, the experiments yield another threshold for the reaction [Ni⁺] +hv→[Ni²⁺]^x+e _cb ^/′ . A well-known but hitherto unsettled emission band of ZnS:Ni is attributed to the radiative recombination which is the reverse of this photoionisation. The corresponding transition in ZnSe:Ni is observed as well.     

Ta/Ni/Ta multilayered ohmic contacts on n-type SiC

The interface formation, electrical properties and the surface morphology of multilayered Ta/Ni/Ta/SiC contacts were reported in this study. It was found that the conducting behavior of the contacts so fabricated is much dependent on the metal layer thickness and the subsequent annealing temperature. Auger electron spectroscopy (AES) and X-ray diffraction analyses revealed that Ni₂Si and TaC formed as a result of the annealing. The Ni atoms diffused downward to metal/SiC interface and converted into Ni₂Si layer in adjacent to the SiC substrate. The released carbon atoms reacted with Ta atoms to form TaC layer. Ohmic contacts with specific contact resistivity as low as 3 × 10⁻⁴ Ω cm² have been achieved after thermal annealing. The formation of carbon vacancies at the Ni₂Si/SiC interface, probably created by dissociation of SiC and formation of TaC during thermal annealing, should be responsible for the ohmic formation of the annealed Ta/Ni/Ta contacts. The addition of Ta into the Ni metallization scheme to n-SiC restricted the accumulation of carbon atoms left behind during Ni₂Si formation, improving the electrical and microstructure properties.     

Sequence of phase formation during solid-state synthesis in Al/Ni films (Al: Ni = 60: 40 at %)

The structure formed during solid-state synthesis in thin bilayer Al/Ni films with the ratio Al: Ni = 60: 40 (at %) has been investigated. The films were obtained by thermal evaporation in vacuum with a residual pressure of 10^?5–10^?6 Torr. Solid-state synthesis was performed by diffusion reaction. The sequence of phase formation upon vacuum annealing of bilayer Al/Ni films has been established: Al + Ni → Al₃Ni + Ni (T _ann = 180°C) → Al₃Ni₂ (T _ann = 220°C).     

Structures and binding energies for complexations of different spin states of Ni+ and Ni2+ to aromatic molecules

Abstract

Density functional theory calculations, using the B3LYP parameterisation, were performed to determine structures, vibrational frequencies, and binding energies for complexation of Ni⁺ and Ni²⁺ cations with benzene and naphthalene molecules and clusters. The calculations employed the Stuttgart basis set with ECP pseudo potentials for the Ni cations and basis sets of at least triple ζ plus polarisation, and diffuse quality for C and H. The effect of electron correlation on non-bonded interactions was accounted for by the Grimme GD3 dispersion correction. Counterpoise computations were made for BSSE. Comparison between experiment and theory provide fascinating new insight into the bonding for these prototypical organometallic (OM) complexes. These structures have a sandwich topology, indicating major structural reorganisations occuring when benzene or naphthalene interact with Ni cations. Adiabatic electron affinities and ionisation potentials agree well with experiment when available. Binding energies were also determined, providing insight into the stability of the complexes. The results presented here provide important information for future studies to address additional investigations of both problems of the electronic structure properties of these complexes, as well as the role of the polycyclic aromatic hydrocarbons (PAHs) in the interstellar medium (ISM) and soot formation in combustion. The Ni⁺/Ni²⁺ + aromatic organometallic bonding is of the same order of stability as an aromatic C–H bond. Such bonding modifies the IR spectrum of the complexed aromatic molecules by enhancing the 3.3?μm feature and decreasing the C–H bands in the 11–12?μm range (γ C–H). Organometallic complexation reactions may contribute significantly to metal depletion in the ISM.     

FMR and TEM Studies of Co and Ni Nanoparticles Implanted in the SiO<Subscript>2</Subscript> Matrix

Fused silica plates have been implanted with 40 keV Co⁺ or Ni⁺ ions to high doses in the range of (0.25–1.0) × 10¹⁷ ions/cm², and magnetic properties of the implanted samples have been studied with ferromagnetic resonance (FMR) technique supplemented by transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. The high-dose implantation with 3d-ions results in the formation of cobalt and nickel metal nanoparticles in the irradiated subsurface layer of the SiO₂ matrix. Co and Ni nanocrystals with hexagonal close packing and face-centered cubic structures have a spherical shape and the sizes of 4–5 nm (for cobalt) and 6–14 nm (for nickel) in diameter. Room-temperature FMR signals from ensembles of Co and Ni nanoparticles implanted in the SiO₂ matrix exhibit an out-of-plane uniaxial magnetic anisotropy that is typical for thin magnetic films. The dose and temperature dependences of FMR spectra have been analyzed using the Kittel formalism, and the effective magnetization and g-factor values have been obtained for Co- and Ni-implanted samples. Nonsymmetric FMR line shapes have been fitted by a sum of two symmetrical curves. The dependences of the magnetic parameters of each curve on the implantation dose and temperature are presented.     

Synthesis and formation mechanism of Ag–Ni alloy nanoparticles at room temperature

Ag–Ni nanoparticles were prepared with a chemical reduction method in the presence of polyvinylpyrrolidone (PVP) used as a stabilizing agent. During the synthesis of Ag–Ni nanoparticles, silver nitrate was used as the Ag⁺ source while nickel sulfate hexahydrate was used as Ni²⁺ source. Mixed solutions of Ag⁺ source and Ni²⁺ source were used as the precursors and sodium borohydride was used as the reducing agent. Five ratios of Ag⁺/Ni²⁺ (9:1, 3:1, 1:1, 1:3, and 1:9) suspensions were prepared in the corresponding precursors. Ag–Ni alloy nanoparticles were obtained with this method at room temperature. Scanning electronic microscope (SEM), energy dispersive spectrum (EDS), high resolution transmission electron microscope (HRTEM) were used to characterize the morphology, composition and crystal structure of the nanoparticles. The crystal structure was also investigated with X-ray diffraction (XRD). In all five Ag/Ni ratios, two kinds of particle structures were observed that are single crystal structure and five-fold twinned structure respectively. Free energy of nanoparticles with different crystal structures were calculated at each Ag/Ni ratio. Calculated results revealed that, with identical volume, free energy of single crystal particle is lower than multi-twinned particle and the difference becomes smaller with the increase of particle size; increase of Ni content will lead the increase of free energy for both structures. Formation of different crystal structures are decided by the structure of the original nuclei at the very early stage of the reduction process.     

Effect of N 2 + ion implantation on the oxidation behaviour of Fe50Ni50 alloy

The high temperature oxidation behavior of Fe₅₀Ni₅₀ alloy foils implanted with 100 KeV N₂ ⁺ ions at a different dose values is studied by using the technique of conversion electron Mössbauer spectroscopy (CEMS). It has been shown that the implanted foils exhibit considerable adherence of scales and higher oxidation resistance as compared to the virgin foils. This excessive adherence of scales to the surface and higher resistance to oxidation of implanted samples is attributed to nickel enrichment in the surface layers. Various oxides of Fe, Ni and Fe?Ni are identified from the hyperfine interaction parameters of the corresponding CEMS spectra and also from x-ray diffraction measurements.     

Strong green luminescence of Ni2+-doped ZnS nanocrystals

ZnS nanoparticles doped with Ni²⁺ have been obtained by chemical co-precipitation from homogeneous solutions of zinc and nickel salt compounds, with S^2- as precipitating anion, formed by decomposition of thioacetamide (TAA). The average size of particles doped with different mole ratios, estimated from the Debye–Scherrer formula, is about 2–2.5 nm. The nanoparticles could be doped with nickel during synthesis without altering the X-ray diffraction pattern. A Hitachi M-850 fluorescence spectrophotometer reveals the emission spectra of samples. The absorption spectra show that the excitation spectra of Ni-doped ZnS nanocrystallites are almost the same as those of pure ZnS nanocrystallites (λ_ex=308–310 nm). Because a Ni²⁺ luminescent center is formed in ZnS nanocrystallites, the photoluminescence intensity increases with the amount of ZnS nanoparticles doped with Ni²⁺. Stronger and stable green-light emission (520 nm) (its intensity is about two times that of pure ZnS nanoparticles) has been observed from ZnS nanoparticles doped with Ni²⁺. Received: 18 December 2000 / Accepted: 17 March 2001 / Published online: 20 June 2001     

Spin states of Ni3+ ions in PrSrAl1−x Ni x O4 ceramics

Solid solutions PrSrAl_1−x Ni _x O₄ have been synthesized and studied by electron paramagnetic resonance (EPR). It is shown that atx≤0.2 the Ni³⁺ ions may be present both in the high- and low-spin states. Asx increases, the part of high-spin centers increases as well. Models of the paramagnetic centers accounting for micro-heterogeneous structure of these ceramics are proposed. The observed features of the temperature dependence of the EPR signals are explained by the interaction of the nickel ions with fast-relaxing Pr³⁺ ions.     

有机金属化学气相沉积法制备的Ni/Al2O3纳米复合材料的氢吸附

研究了通过有机金属化学气相沉积技术及单源分子前躯体方法制备的Ni/Al₂O₃纳米复合材料的氢吸附(存储). 在冷壁的有机金属化学气相沉积反应器中,通过降解Ni(acac)₂粉末基底上的[H₂Al(OtBu)]₂制备的Ni/Al₂O₃纳米复合材料. 通过X射线粉末衍射、扫描电镜、透射电镜以及能量色散型X射线荧光光谱等技术表征该复合材料. 采用自制Sievert's设备研究该复合材料的氢吸附(存储),可以储存约2.9%(重量比)的氢.