Initial formation of contact layers on Ni/SiC samples studied by XPS

This study deals with the quantitative assessment of the coverage and thickness of Ni silicide films formed during annealing of SiC substrates with sputtered thin films of Ni. The analytical approach involves the use of XPS and depth profiling by means of successive ion etchings and XPS analyses. For either 3 or 6 nm initial Ni film thickness, a 10 nm Ni₂Si product is formed. On top of this product, the C released is accumulated in a very thin (1–2 nm) film. In neither case, the Ni₂Si covers the whole surface, although the coverage is almost complete (～90%) in the latter case. For the greater initial Ni‐film thickness of 17 nm, the thickness of the Ni₂Si product corresponds well to the value of 25 nm expected from the Ni/Ni₂Si stoichiometric relationship. This thickness is significantly greater than a critical level and the film covers the whole surface. Carbon is similarly accumulated in a very thin layer on the top surface, although the major part of C (～70%) is found inside the main reaction product layer. Copyright © 2008 John Wiley & Sons, Ltd.     

Bioactivity and mechanical properties of nickel‐incorporated hydrogenated carbon nanocomposite thin films

In this paper, the influence of nickel incorporation on the mechanical properties and the in vitro bioactivity of hydrogenated carbon thin films were investigated in detail. Amorphous hydrogenated carbon (a‐C:H) and nickel‐incorporated hydrogenated carbon (Ni/a‐C:H) thin films were deposited onto the Si substrates by using reactive biased target ion beam deposition technique. The films' chemical composition, surface roughness, microstructure and mechanical properties were investigated by using XPS, AFM, TEM, nanoindentation and nanoscratch test, respectively. XPS results have shown that the film surface is mainly composed of nickel, nickel oxide and nickel hydroxide, whereas at the core is nickel carbide (Ni₃C) only. The presence of Ni₃C has increased the sp² carbon content and as a result, the mechanical hardness of the film was decreased. However, Ni/a‐C:H films shows very low friction coefficient with higher scratch‐resistance behavior than that of pure a‐C:H film. In addition, in vitro bioactivity study has confirmed that it is possible to grow dense bone‐like apatite layer on Ni/a‐C:H films. Thus, the results have indicated the suitability of the films for bone‐related implant coating applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Prefabrication of two-dimensional Ni–W/TiN films on oil-gas X52 steels by pulse electrodeposition

The main aim of this investigation was to prefabricate two-dimensional Ni–W/TiN films on oil-gas X52 steel substrates via pulse electrodeposition (PE). The influences of the TiN content in the bath on the surface morphology, nano-hardness, wear, and corrosion properties of the films were also discussed. The results indicated that the TiN particle size was only ～33 nm in 8 g/L TiN electrolyte, which was ～2.4 times less than that of TiN in 16 g/L solution. The Ni–W/8TiN film exhibited a uniform, smooth surface, and the depression depth and protrusion height were 45.3 nm and 81.7 nm, respectively. Three diffraction peaks at 43.72, 50.78, and 75.26° in the Ni–W/4TiN film emerged as the sharpest and narrowest peaks among the four films. Three XPS peaks for the Ni 2p_3/2 were present at 852.13, 856.35, and 861.87 eV in the Ni–W/8TiN film, corresponding to Ni, Ni²⁺ (Ni(OH)₂), Ni³⁺ (NiOOH) species. Besides, the XPS peak of W 4f_7/2, which located at 33.85 eV belonged to elemental W. The Ni–W/8TiN film had the lowest wear depth and width at 32.1 μm and 5.7 mm, respectively. Only some narrow and shallow scratches were found on the Ni–W/8TiN film surface, showing its outstanding tribological properties among the films tested. In addition, the Ni–W/4TiN film showed the highest mean frictional coefficient of 0.73, which was ～1.6 times more than that of the Ni–W/8TiN film.     

Growth and characterization of ultrathin carbon films on electrodeposited Cu and Ni

Ultrathin carbon films were grown on different types of metallic substrates. Free‐standing foils of Cu and Ni were prepared by electroforming, and a pure Ni film was obtained by galvanic displacement on a Si wafer. Commercial foil of Ni 99.95% was used as a reference substrate. Carbon films were grown on these substrates by chemical vapour deposition in a CH₄‐H₂ atmosphere. Obtained films were characterized by Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, and ultraviolet photoemission spectroscopy. The XPS at grazing collection angle was used to determine the thickness of carbon films. Depending on the deposition parameters, the films of graphene or graphite were obtained on the different substrates. The uniformity of graphene and its distribution over the sample area were investigated from Raman data, optical images, and XPS chemical maps. The presence of graphene or graphite in the films was determined from the Raman spectra and Auger peak of C KVV. For this purpose, the D parameter, which is a fingerprint of carbon allotropes, was determined from C KVV spectra acquired by using X‐rays and electron beam. A formation of an intermediate layer of metal hydroxide was revealed in the samples with graphene overlayer.     

High oxygen vacancy tin oxide synthesized by combustion chemical vapor deposition (CCVD)

Tin oxide nanotentacles were synthesized by combustion chemical vapor deposition in air. Their surface composition and optical properties were then investigated using X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy. XPS core level spectra indicate that these nanotentacles are of high oxygen vacancy with chemical composition of about SnO_1.6, which is also supported by the Sn Auger parameter. Besides SnO₂, the optical properties of SnO were detected in Raman spectrum. Moreover, two new Raman peaks were found for the SnO₂ phase because of the high oxygen vacancy concentration. Copyright © 2008 John Wiley & Sons, Ltd.     

Nanoporous Ni3S2 Film on Ni Foam as Highly Efficient Electrocatalyst for Hydrogen Evolution in Acidic Electrolyte

In this work, nanoporous Ni₃S₂ film (Ni₃S₂/Ni) is in situ synthesized by direct sulfurization of Ni foam under a mild hydrothermal process. Surprisingly, it is found out that the obtained Ni₃S₂/Ni exhibits outstanding HER activity and excellent stability in acidic electrolyte. The structure and nature of the Ni₃S₂/Ni are analyzed with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscope (FE-SEM). On Ni₃S₂/Ni, the onset potential is only ?6.23 mV (vs. RHE) while the large exchange current density is 790 µA cm^?2 and the Tafel slope is 62.47 mV dec^?1. The experimental results demonstrate the potential of Ni₃S₂/Ni for its replacement of Pt-based catalysts.

     

Synthesis and magnetic properties of octahedral ferrite Ni χ Co1−χ Fe2O4 nanocrystals

A series of Ni doped cobalt ferrite compounds with the formula Ni _χ Co_1−χ Fe₂O₄ where x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 were prepared using a hydrothermal method and subsequently sintered/annealed at 600 °C for 3 h. The influence of the Ni content on the lattice parameter, a, stretching vibration and the magnetization of specimens were subsequently studied. XRD and FTIR were used to investigate structure and composition variations. All samples were found to have a cubic spinel structure. SEM was used to study morphological variations. The results indicate that the average particle sizes are between 30–35 nm with a narrow size distribution along with nanocrystals forming of regular octahedrons. A decrease in the peak to peak line width and increase in resonance field with increasing Ni content were observed from ESR measurements. Based on ESR results, a core-shell type of formation was proposed where the core is made up of undoped CoFe₂O₄ and the shell is Ni²⁺ doped CoFe₂O₄.      

Synthesis and properties of NiSn colloids using different metal ratios by CLD

Bimetallic colloidal dispersions of Ni–Sn were prepared by simultaneous co-condensation with organic solvents at 77 K using the chemical liquid deposition (CLD) method. The atoms in a 1:1, 2:1, 3:1, 1:2 and 1:3 ratios were produced by resistive heating and were reacted with 2-propanol, 2-methoxyethanol, ethanol and acetone to produce colloids. The bimetallic films and solids were obtained by evaporation under vacuum at room temperature. The colloids and solids were characterized by several studies, including the stability at room temperature, electrophoresis, ultraviolet-visible spectrophotometry, transmission electron microscopy (TEM), electron diffraction, conductivity, nergy dispersive X-ray analysis, electrophoretic measurements, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and magnetic properties. TEM studies show a size distribution between 6 and 14 nm, depending of the solvent and Ni:Sn ratio. We can observe a high stability for the colloidal dispersion with different solvents (>2 weeks); this is due mainly to the solvation capacity and polarity of the organic molecules. Electrophoretic measurements revealed that the particles are weakly positively charged with a greater Ni percentage. Electron diffraction analysis for the metallic colloids shows the presence of bimetallic compounds as NiSn, Ni₃Sn, Ni₃Sn₄ and tin oxides. XPS analysis was used for the study of the Ni–Sn solid composition, where it was determined that the Ni atoms could be as Ni⁰ and Ni²⁺. The bond energy difference in both species were 0.8 eV; on the other side, Sn atoms showed two peaks, the first associated with Sn⁰ atoms and the second attributed to oxidized species like SnO_x. The conductivity studies showed that when the metal is changed, the electric conductivity properties change too and are associated with the particle size increasing.     

The Ce2Li0.39Ni1.61Si2 structure as a new derivative of the AlB2 family

A new quaternary dicerium lithium/nickel disilicide, Ce₂Li_0.39Ni_1.61Si₂, crystallizes as a new structure type of intermetallic compounds closely related to the AlB₂ family. The crystal–chemical interrelationships between parent AlB₂‐type, BaLiSi, ZrBeSi and the title compound are discussed using the Bärnighausen formalism. Two Ce atoms occupy sites of 3m. symmetry. The remainder, i.e. Ni, mixed Ni/Li and Si atoms, occupy sites of m2 symmetry. The environment of the Ce atom is an 18‐vertex polyhedron and the Ni, Ni/Li and Si atoms are enclosed in tricapped trigonal prisms. The title structure can be assigned to class No. 10 (trigonal prism and its derivatives) according to the Krypyakevich classification scheme [Krypyakevich (1977). In Structure Types of Intermetallic Compounds. Moscow: Nauka]. The electronic structure of the title compound was calculated using the tight‐binding linear muffin‐tin orbital method in the atomic spheres approximation (TB‐LMTO‐ASA). Metallic bonding is dominant in this compound. The strongest interactions are Ni—Si and Ce—Si.     

Interplay of Magnetic Exchange Interactions and Ni?S?Ni Bond Angles in Polynuclear Nickel(II) Complexes

The ability of bridging thiophenolate groups (RS^?) to transmit magnetic exchange interactions between paramagnetic Ni^II ions is examined. Specific attention is paid to complexes with large Ni? SR? Ni angles. For this purpose, dinuclear [Ni₂L¹(μ‐OAc)?I₂][I₅] ( 2 ) and trinuclear [Ni₃L²(OAc)₂][BPh₄]₂ ( 3 ), where H₂L¹ and H₂L² represent 24‐membered macrocyclic amino‐thiophenol ligands, are prepared and fully characterized by IR‐ and UV/Vis spectroscopy, X‐ray crystallography, static magnetization M measurements and high‐field electron spin resonance (HF‐ESR). The dinuclear complex 2 has a central N₃Ni₂(μ‐S)₂(μ‐OAc)Ni₂N₃ core with a mean Ni? S? Ni angle of 92°. The macrocycle L² supports a trinuclear complex 3 , with distorted octahedral N₂O₂S₂ and N₂O₃S coordination environments for one central and two terminal Ni^II ions, respectively. The Ni? S? Ni angles are at 132.8° and 133.5°. We find that the variation of the bond angles has a very strong impact on the magnetic properties of the Ni complexes. In the case of the Ni₂‐complex, temperature T and magnetic field B dependencies of M reveal a ferromagnetic coupling J=?29 cm^?1 between two Ni^II ions (H=JS₁S₂). HF‐ESR measurements yield a negative axial magnetic anisotropy (D<0) which implies a bistable (easy axis) magnetic ground state. In contrast, for the Ni₃‐complex we find an appreciable antiferromagnetic coupling J′=97 cm^?1 between the Ni^II ions and a positive axial magnetic anisotropy (D>0) which implies an easy plane situation.     

Effect of electronic state of ions on the electrochemical properties of layered cathode materials LiNi1−2x Co x Mn x O2

The cathode materials of the composition LiNi_{1 − 2x} Co _x Mn _x O₂ (x = 0.1, 0.2. 0.33) synthesized from the Ni, Co, Mn mixed hydroxides and LiOH by using mechanical activation method are studied. It is shown that all synthesized compounds have layered structure described by the space group R-3m. With the decreasing of the nickel content the cell volume and the degree of structure disordering decrease. According to XPS data, the electronic main state of d-ions at the prepared samples’ surfaces corresponds to Ni²⁺, Co³⁺, and Mn⁴⁺. An increase in the nickel content leads to the increase of the Ni2p _3/2 and Co2p _3/2 binding energy, which points to the change in the Me-O bond covalence. According to magnetic susceptibility measurements data, the nickel ions in LiNi_0.6Co_0.2Mn_0.2O₂ exist in the two oxidation states: Ni²⁺ and Ni³⁺. It is shown that this sample has the highest specific discharge capacity (∼170 mAh/g). The positions of redox peaks in the differential capacitance curves depend on the sample composition: with the increasing of nickel content they are shifted toward lower voltages. Based on the paper presented in the IX International Conference “Basic Problems of Energy Conversion in Lithium Electrochemical Systems” (Ufa, 2006).     

Synthesis of Ni–Ru Alloy Nanoparticles and Their High Catalytic Activity in Dehydrogenation of Ammonia Borane

We report the synthesis and characterization of new Ni_xRu_1?x (x=0.56–0.74) alloy nanoparticles (NPs) and their catalytic activity for hydrogen release in the ammonia borane hydrolysis process. The alloy NPs were obtained by wet‐chemistry method using a rapid lithium triethylborohydride reduction of Ni²⁺ and Ru³⁺ precursors in oleylamine. The nature of each alloy sample was fully characterized by TEM, XRD, energy dispersive X‐ray spectroscopy (EDX), and X‐ray photoelectron spectroscopy (XPS). We found that the as‐prepared Ni–Ru alloy NPs exhibited exceptional catalytic activity for the ammonia borane hydrolysis reaction for hydrogen release. All Ni–Ru alloy NPs, and in particular the Ni_0.74Ru_0.26 sample, outperform the activity of similar size monometallic Ni and Ru NPs, and even of Ni@Ru core‐shell NPs. The hydrolysis activation energy for the Ni_0.74Ru_0.26 alloy catalyst was measured to be approximately 37 kJ mol^?1. This value is considerably lower than the values measured for monometallic Ni (≈70 kJ mol^?1) and Ru NPs (≈49 kJ mol^?1), and for Ni@Ru (≈44 kJ mol^?1), and is also lower than the values of most noble‐metal‐containing bimetallic NPs reported in the literature. Thus, a remarkable improvement of catalytic activity of Ru in the dehydrogenation of ammonia borane was obtained by alloying Ru with a Ni, which is a relatively cheap metal.     

XPS- and AES-investigations of electron and ion beam induced effects on SK16 glass surfaces

Summary Electron beam induced effects in the near surface region of SK16 glass samples (44% SiO₂, 25% B₂O₃, 28% BaO, 3% other) have been studied using Auger electron spectroscopy (AES) with 3 keV primary electrons at different current densities (4.7 mAcm^–2–75 mAcm^–2). It was found that the SiO₂ and B₂O₃ constituents dissociate during electron bombardment to form binding structures which are characteristic for elemental Si and B, respectively. To investigate the influence of the ion beam irradiation on the binding structure, the glass samples were bombarded with Ar⁺ ions of different kinetic energies (0.5 keV–5 keV), followed by XPS analysis. In comparison to the XPS signal of a virgin SK16 surface from a sample fractured in situ under UHV conditions, the FWHM of the photoelectron peaks were found to increase with the bombarding ion energy. Subsequent Auger spectra revealed that the ion bombardment also caused a dissociation of the SiO₂ and B₂O₃ components. Depending on the ion energy, a constant ratio between elemental and oxidized binding form is obtained.     

Influence of the alloying effect on nickel K-shell fluorescence yield in Ni–Si alloys

Alloying effects on the K-shell fluorescence yield ω_K of nickel in Ni–Si binary alloy system have been studied by energy dispersive X-ray fluorescence. It is found that ω_K increases from pure Ni to Ni₂Si and then decreases from Ni₂Si to NiSi. These results are discussed in terms of d-occupation number on the Ni site and it is concluded that electronic configuration as a result of p-d hybridization explain qualitatively the observed variation of ω_K in Ni–Si alloys.     

Investigation of multiplet splitting of Fe 2p XPS spectra and bonding in iron compounds

Ferrous (Fe²⁺) and ferric (Fe³⁺) compounds were investigated by XPS to determine the usefulness of calculated multiplet peaks to fit high‐resolution iron 2p_3/2 spectra from high‐spin compounds. The multiplets were found to fit most spectra well, particularly when contributions attributed to surface peaks and shake‐up satellites were included. This information was useful for fitting of the complex Fe 2p_3/2 spectra for Fe₃O₄ where both Fe²⁺ and Fe³⁺ species are present. It was found that as the ionic bond character of the iron —ligand bond increased, the binding energy associated with either the ferrous or ferric 2p_3/2 photoelectron peak also increased. This was determined to be due to the decrease in shielding of the iron cation by the more increasingly electronegative ligands. It was also observed that the difference in energy between a high‐spin iron 2p_3/2 peak and its corresponding shake‐up satellite peak increased as the electronegativity of the ligand increased. The extrinsic loss spectra for ion oxides are also reported; these are as characteristic of each species as are the photoelectron peaks. Copyright © 2004 John Wiley & Sons, Ltd.     

Synthesis of Mixed Silylene–Carbene Chelate Ligands from N‐Heterocyclic Silylcarbenes Mediated by Nickel

The Ni^II‐mediated tautomerization of the N‐heterocyclic hydrosilylcarbene L²Si(H)(CH₂)NHC 1 , where L²=CH(C?CH₂)(CMe)(NAr)₂, Ar=2,6‐iPr₂C₆H₃; NHC=3,4,5‐trimethylimidazol‐2‐yliden‐6‐yl, leads to the first N‐heterocyclic silylene (NHSi)–carbene (NHC) chelate ligand in the dibromo nickel(II) complex [L¹Si:(CH₂)(NHC)NiBr₂] 2 (L¹=CH(MeC?NAr)₂). Reduction of 2 with KC₈ in the presence of PMe₃ as an auxiliary ligand afforded, depending on the reaction time, the N‐heterocyclic silyl–NHC bromo Ni^II complex [L²Si(CH₂)NHCNiBr(PMe₃)] 3 and the unique Ni⁰ complex [η²(Si‐H){L²Si(H)(CH₂)NHC}Ni(PMe₃)₂] 4 featuring an agostic Si? H→Ni bonding interaction. When 1,2‐bis(dimethylphosphino)ethane (DMPE) was employed as an exogenous ligand, the first NHSi–NHC chelate‐ligand‐stabilized Ni⁰ complex [L¹Si:(CH₂)NHCNi(dmpe)] 5 could be isolated. Moreover, the dicarbonyl Ni⁰ complex 6 , [L¹Si:(CH₂)NHCNi(CO)₂], is easily accessible by the reduction of 2 with K(BHEt₃) under a CO atmosphere. The complexes were spectroscopically and structurally characterized. Furthermore, complex 2 can serve as an efficient precatalyst for Kumada–Corriu‐type cross‐coupling reactions.     

Quantitative Auger electron spectroscopy of PtSi and Pd2Si

Summary Quantitative AES analysis has been carried out on PtSi and Pd₂Si using dN(E)/dE spectra. The concentration ratios are determined by elemental sensitivity factors after correcting for matrix and sputter effects. In the case of matrix correction an improved correction procedure has been developed which considers effects created by different atomic densities, electron backscattering, electron attenuation and peak shapes. The concentration ratios X_metal/X_Si deduced from measurements of mechanically cleaned sample surfaces agree very well with the nominal bulk values of the silicides. Ion bombardment creates strong intensity and line shape changes of the Auger signals. Therefore, in case of sputtered silicide surfaces, both matrix and sputter effects must be corrected.     

Optical transitions,XPS, electronic states in NiPS3

We have measured the optical absorption below the fundamental threshold, the normal-incidence reflectivity between 1.5 and 30 eV and the X-ray photoemission spectra of NiPS₃. Shake-up satellites present at the Ni 2p and 3p core levels are strong evidence for the ionicity of the NiS bonds. We have also derived a qualitative molecular orbital model of NiPS₃ in which the trigonal crystal field splits the P and S 3p_xp_y-3p_a states, and strong covalent hybridization between P and S p_xp_y orbitals leads to covalent electronic bonding. Ni is envisaged as a divalent ion which plays little role in the electronic bonding and its 3d levels are localized, lying near the top both of the valence states. This model accounts well for both the valence band XPS data and the low energy optical transitions. Our model should represent, at the center of the Brillouin zone but not at the boundaries, the energy level sequence in NiPS₃ and other related MPX₃ layer-type compounds where M Co²⁺, Mn²⁺, Fe²⁺, Zn²⁺ and X is sulfur or selenium.The XPS spectra and optical properties of NiPS₃ have been obtained and interpreted on a qualitative molecular orbital model in which the Ni is a divalent positive ion which plays little role in the bonding. Evidence for such ionicity appears in the optical properties and XPS satellite structures, as well as in the magnetic properties. The model should represent qualitatively the band structure at the center of the Brillouin zone, but not at the boundaries. It should also be valid for other compounds similar to NiPS₃, i.e. those with other metals in place of Ni and those with Se in place of S.     

On the structural and magnetic properties of the ternary silicides Ce6M1.67Si3 (M=Co, Ni) and Ce5Ni1.85Si3

Contrary to that reported previously, the ternary silicide “Ce₆Ni₂Si₃” does not exist. The melting of this alloy, followed or not by annealing, leads to the existence of the two new ternary compounds, Ce₆Ni_1.67Si₃ and Ce₅Ni_1.85Si₃. The investigation of these ternary silicides based on nickel and Ce₆Co_1.67Si₃ by X-ray diffraction on single crystal reveals an ordered distribution between Ni (or Co) and Si atoms. The nickel or cobalt positions in the chains of face-shared octahedra of cerium are not fully occupied with a strong delocalisation of their electron density. The structural investigations of these compounds confirm that the “Ce₆Ni₂Si₃” and “Ce₅Ni₂Si₃” structural type have to be rewritten as Ce₆Ni_2−xSi₃ and Ce₅Ni_2−xSi₃. Magnetisation and specific heat measurements evidence a magnetic ordering at 3.8(2) K for Ce₆Ni_1.67Si₃ and a heavy fermion behaviour for Ce₆Co_1.67Si₃.