Narrow Results

The lattice structure and electronic properties of perfect and defective CoSi₂ and NiSi₂ have been calculated using an ab initio plane-wave ultrasoft pseudopotential method based on the generalized gradient approximations (GGA). Special attention is paid to the formation energies of the vacancies, which largely depend on the atomic chemical potentials of Si and metal atom: in Si-rich limit, the formation energies of Si and Co vacancies are 2.39 eV and 0.56 eV whilst those are 1.53 eV and 2.29 eV in Co-rich limit in CoSi₂, respectively. For NiSi₂, the formation energies of Si and Ni vacancies are 0.56 eV and 1.25 eV in Si-rich limit and those are 0.04 eV and 2.3 eV in Ni-rich limit.

Nickel-aluminides-reinforced nickel-matrix composites were fabricated from 0.05mm-thick nickel foils and 0.012mm-thick aluminum foils, in a process using a pulsed-current hot pressing (PCHP) equipment, and the effect of reaction temperature on mechanical properties of the composites was investigated. The composites were of laminated structure and composed of Ni and reacted layers containing Ni-aluminides. The chemical composition of the reacted layers was dependent on reaction temperature in the temperature range employed. Tensile testing at room temperature revealed that the reaction temperature evidently influences mechanical properties, including tensile strength, elongation and fracture mode, of the composites. The tensile strength and elongation of composites fabricated at 1373K were 500MPa and 3.8%, respectively. Microstructure observations of fractured specimens revealed that Ni layers of the composite played a significant role in prohibiting the growth of numerous cracks emanating from Ni-aluminides. In the case of composites fabricated at 1373K, in addition, crack propagation between Ni-rich Al-solid-solution layers and cellular Ni₃Al in the Ni-aluminides were prevented by mutual interaction.

In this paper, we use molecular dynamics (MD) simulations and a modified analytic embedded-atom method to investigate the edge dislocation movement without imposed strain at 0 K. The obtained results indicate that the straight lines of the partial dislocations always preserve their original shapes and are parallel to each other during the simulation process. According to the energy of each atom, the positions of both partial dislocation cores are determined. Then the velocities in the period of the relaxation process are investigated in detail. The MD simulations reveal that the MD relaxation time dependence of the edge dislocation mobility is divided into two parts. First, during the initial period ranging from 0 to 6 ps, the relative velocity of the dislocation movement lineally increases with the incremental relaxation time. Second, in the latter period from 6 ps to the end of the simulated process the velocity decreases exponentially as the MD simulation time evolves.

The structure and processes of mass, charge and heat transfer are investigated in an equiatomic Fe–Ni composite fabricated by electroconsolidation using the spark plasma sintering (SPS) technology. The system contains regions of almost pure Fe and Ni, separated by areas with variable concentration of components, formed in consequence of the interdiffusion in the electroconsolidation process. The interdiffusion coefficient of the Fe–Ni system has been revealed to be significantly higher than that of an alloy of a similar composition at the same temperature, which is likely the result of the employed SPS technology and the enhanced diffusion along the grain boundaries. The concentration dependence of the interdiffusion coefficient passes through a maximum at a Ni concentration of $\sim$70 at.%. The electrical and thermal conductivity of the studied system is significantly higher than that of an alloy of the same composition. The temperature dependence of the resistivity of the sample in the range 5–300 K is due to the scattering of electrons by defects and phonons, and the scattering of electrons by phonons fits well to the Bloch–Grüneisen–Wilson relation. The boundaries of the conductivity of the investigated composite correspond to the Hashin–Shtrikman boundaries for a three-phase system, if Fe, Ni and the FeNi alloy are selected as phases.

This study investigates the impact of initial temperature on the microstructure and mechanical properties of welded components, using molecular dynamics (MD). The stress–strain curves of the welded components, following various initial temperature treatments, revealed a double yielding phenomenon. Notably, there was a significant strain difference of 19.7% between the two yields. When the strain was loaded to the point of doubling yielding, stacking faults and twins covered the aluminum component part, while no such observations were made in the nickel component part. Additionally, tensile cracking occurred in the aluminum component part. The results indicate that treatment at varying initial temperatures alters the internal structure of the welded components. After the material yielded the first time, a significant number of disordered atoms and Shockley partial dislocations emerge, resulting in a substantial buildup of dislocation tangles and reduced dislocation migration rates. Consequently, the material exhibits a phenomenon of double yielding, with dislocation slip and deformation serving as the primary mechanisms. The optimal mechanical properties of the welded components achieved an initial temperature of 200K. Additionally, the effect of tensile temperature on the mechanical properties of the welded components were analyzed, and similar observations of double yielding were made. The significant number of dislocation tangles served as a barrier to dislocation slip, effectively enhancing the material’s mechanical properties. The simulation results provide theoretical support for the development of aluminum–nickel multilayer film self-propagation welding process.

We present the first results concerning the atomic structure and morphology of ultrathin Sb layers deposited on the Ni(111) face in ultrahigh vacuum at the substrate temperature ranging from 150 to 700 K obtained with the use of Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and directional elastic peak electron spectroscopy (DEPES). The AES results indicate that the antimony layer on the Ni(111) at T < 200 K grows in the Frank–van der Merwe mode. For temperature around 250 K, the flat two atomic layer islands ("wedding cakes") seem to grow after completion of the first antimony monolayer. At T ≥ 300 K, a Sb–Ni surface alloy is formed. DEPES measurements indicate that the atomic structure of Sb layers deposited at T = 150 K is completely amorphous, while better and better pronounced maxima appear in DEPES profiles when the sample temperature increases from 300 to 450 K. LEED patterns corresponding to p(1 × 1), p(2 × 2) and structures have been observed for 150 K ≤ T ≤ 250 K. A possible model for the last structure is proposed. After annealing the deposited layer at T > 500K, the structure appears.

In this paper the adsorption of C₆₀ on Li-covered Ni(110) surfaces is investigated by means of Auger electron spectroscopy, low-energy electron diffraction and work function measurements, in ultrahigh vacuum. Deposition of C₆₀ on the 1 × 2 Li-induced Ni(110) surface at 650 K causes the formation of islands with a 4 × 2 structure, where the C₆₀ molecules adsorb along neighboring troughs of the substrate. At higher C₆₀ coverages, the Li-induced 1 × 2 reconstruction of the Ni(110) surface is lifted and a 9 × 3 structure is formed, which finally ends in a semihexagonal structure, as in the case of C₆₀ adsorption on clean Ni(110) surfaces. AES and LEED measurements suggest that charge is transferred from Li to the C₆₀ molecules, which in a rough approximation was estimated to be around one electron per C₆₀ molecule. The above estimated charge transfer to the C₆₀ molecules is substantially smaller than that we have calculated when Li is adsorbed on C₆₀-covered Ni(110) surfaces. Apparently, the order of Li and C₆₀ deposition is very important for the charge transfer and the deposition of Li on C₆₀-covered surfaces provides a substantially greater amount of charge to the C₆₀ molecules.

The electronic properties of very thin Ni films on the SrTiO₃(100)-Fe doped surfaces and their interaction with oxygen have been studied by soft X-rays photoelectron spectroscopy measurements. Nickel starts to become metallic on the surface in the very early adsorption stages. Oxygen adsorption on the nickel covered SrTiO₃(100) surface leads gradually to an almost complete oxidation of the nickel overlayer. The oxidation seems to take place through two different oxidation states, which according to the literature are due to the Ni²⁺ and Ni³⁺ species. The heating of the O/Ni/SrTiO₃ system at 850 K, causes a partial reduction of the nickel overlayer.

In this paper, we study the adsorption of Ba on the Ni(110) surface at room temperature. The investigation takes place mainly by soft X-ray photoelectron spectroscopy measurements. At low coverage (<0.5 ML), the Ba adatoms are in a partially ionic state, whereas at higher coverage, the barium overlayer becomes metallic. The nonmetal to metal transition is characterized by a new Ba 4d doublet appearing at higher binding energy. This more bound Ba 4d core state is attributed to initial state changes of the electrostatic potential at the atomic core region, due to changes in the hybridization of the Ba atoms from Ba 5d with Ni 3d, to Ba 5d, 6s and 6p states in the metallic phase. The latter states are more spatially extended than the Ba 5d ones, overlapping with the Ni 3d orbitals in the nonmetal and therefore lead to a reduced potential at the core electrons. A strong effect on the Ba 4d binding energy shifts, due to the surface dipole induced by the adsorbate itself, was observed.

Bi₂Te₃ has attracted attention due to its potential applications in the microfabrication of integrated thermoelectric devices. It is also interesting to study the metallization process of this compound. Metallic nanostructures were deposited by means of an electron gun evaporator in ultra high vacuum (UHV) conditions (10^-8 Pa) on the freshly cleaved 0001 surface of the crystal Bi₂Te₃. Measurements were conducted using the commercially available Omicron UHV scanning tunneling microscope (STM). Scanning tunneling spectroscopy (STS) measurements were performed using current imaging tunneling spectroscopy (CITS), and subsequent calculation of the dI/dV maps. Metallic characteristics were observed on nickel islands since early stages of the growth. CITS and dI/dV maps showed distinct contrast between the substrate and metallic islands. Similar contrast was not observed in the case of titanium, most probably due to an intercalation process. Occurring of such a process was confirmed by the appearance of the superlattice structure.

The nickel ion containing Langmuir–Blodgett (LB) multilayer was prepared by transferring first dissolving nickel acetate and the solution was poured into a subphase of ultrapure water and stearic acid-chloroform. The resultant mixture was then spread onto a hydrophilic water or glass plate. Then the multilayer was converted into nickel ultrathin film after chemical reduction by sodium borohydride. The optimized parameters for monolayer formation, such as concentration of subphase, pH value, barrier speed and standing time, were determined by the measurement of the surface pressure–surface area (Π–A) isotherms. The expended areas after deposition with nickel ions inferred the interaction of stearic acid with nickel ion during the formation of monolayer at air–water interface. The optimized parameters for multilayer deposition, such as surface pressure and dipping speed were determined by the measurement of the transfer coefficient. The Fourier transform infrared spectroscopy (FTIR) was used to investigate the interactions of nickel ions with stearic acid at air–water interface and in nickel ion/stearic acid LB film, as well as the metal transformations of nickel ion in ultrathin film. The disappearance of peak at 1689 cm^-1 verified the interactions between stearic acid and nickel ion. The further reduction made the organic phase dissolve and remove from the multilayer mostly. The surface morphologies of the LB multilayer and ultrathin film after reduction were detected by atomic force microscopy (AFM). A uniform and flat surface of nickel ultrathin film within nanometer ranges were obtained after reduction. The particle sizes of nickel were approximately 50 nm.

Using density functional theory calculations with van der Waals corrections, we have investigated the stability and electronic properties of monolayer hexagonal boron nitride (hBN) on the Ni(111) surface. We have found that hBN can bind either strongly (chemisorption) or weakly to the substrate with metallic or insulating properties, respectively. While the more stable configuration is the chemisorbed structure, many weakly bound (physisorbed) states can be realized via growth around an hBN nucleus trapped in an off-registry position. This finding provides an explanation for seemingly contradictory sets of reports on the configuration of hBN on Ni(111).

In this paper, we investigate the influence of temperature on the nickel grain boundary equilibrium segregation of sulfur and the resulting intergranular fracturing susceptibility. Auger electron spectroscopy has been used to study equilibrium segregation of sulfur to the grain boundaries of a metallic nickel, with a mass bulk content of 3.6ppm in sulfur. Samples were first annealed at adequate temperatures for sufficiently large equilibrium time, and then quenched in water at room temperature. The analysis carried out shows a significant increase of sulfur concentration in the grain boundary with decreasing temperature. However, the sulfur content in the grain boundary shows a drastic shrink at 700${}^{\circ }$C. This can be interpreted by the formation of an aggregate sulfide compound in the area of the grain boundaries. At 650${}^{\circ }$C, in situ brittle fracture becomes unworkable and only intragranular fractures are observed. Using the results obtained through the investigation of the grain boundaries by Auger spectroscopy, the standard segregation energy is estimated as $\mathrm{\Delta }{G}_0=-(100÷76)kJ∕mol$.

A method was developed to conveniently and rapidly determine hydrogen peroxide (H₂O₂) in food. The glassy carbon electrode (GCE) modified with agmatine sulfate (AS) easily anchoring nickel ion was attached to AS with polyamine structure. As a result, more Ni${}^{2+}$ was obtained and transformed to Ni(OH)₂/NiOOH on the AS–GCE, which caused the electrode to own much better electrocatalytic performance on H₂O₂. Based on these, the content of H₂O₂ in thin sheet of bean curd sample was detected with standard addition method, by which good results were obtained.

Homoepitaxial growth film for (001), (110) and (111) Ni substrates is investigated by means of molecular dynamics (MD) simulation. Embedded atom method (EAM) is considered to represent the interaction potential between nickel atoms. The simulation is performed at 300K using an incident energy of 0.06eV. In this study, the deposition process is performed periodically and the period, $n$, is relative to a perfect layer filling. The coverage rate of the actual expected level, $L_{(n)}$, can be considered a determinant for thin-film growth of nickel. The $L_{(n)}$ level is the most filled level during the deposition on (001) substrate, while it is the less filled one in the case of (111) substrate. Moreover, the upper level is the one which is responsible for the surface roughness and the appearance time of an upper layer may also be a factor influencing the surface roughness. The deposition on (111) substrate induces the most rigorous surface with a rapid appearance time of the upper layers. The $L_{(n-1)}$ layers are almost completely filled for all substrates. The $L_{(n-2)}$ and lower layers are completely filled for (001) and (110) substrates while for (111) substrate the completely filled layers are $L_{(n-3)}$ and lower ones.

The preparation of ultrathin Ni layer onto the surface of glassy carbon electrode (GCE) by molecule anchoring method was studied in this paper in which two steps were involved: molecule anchoring (GCE-M) and ultrathin Ni layer adsorption (GCE-M-Ni). The result showed that by simply anchoring some molecules (purpald, bismuthiol I, DPTA, EDTA-2Na, ferrotitanium and thiourea) onto the surface of GCE, the adsorption of Ni layer would be improved relatively, thus improving the electrocatalytic ability of GCE toward sucrose, fructose and glucose. It was believed that the anchoring of these molecules helped the following adsorption of Ni layer. Good electrocatalytic characteristics for sugars oxidation of GCE-purpald-Ni were observed in this work with the immediate response, wide linear range from 0$\mu$M to 800$\mu$M and low detection limit down to 0.49$\mu$M for the sensing of total sugar (TS) concentration. The common interfering molecule such as ascorbic acid was proved of no interfering effect on the detection. Also, GCE-purpald-Ni was successfully applied to detect TS concentration in orange juice samples with high recovery rate of more than 85%. It is concluded that the molecule anchoring method can be used to the adsorption of ultrathin Ni layer onto the surface of GCE and works as one of the promising nonenzymatic sensings toward sugars.

Electroless plating can be used to prepare metal particle/CaCO₃ composite powder, but the use of noble metal as catalytic site would increase the cost. In this work, we adopt the combined 3-amino-propyltriethoxysilane (KH550) modification and NiCl₂ activation to coat CaCO₃ powder by a uniform layer of Ni particles/polymer brush which acts as non-noble metal catalyst, then, a low-cost electroless plating to prepare Cu particle/CaCO₃ composite powder was developed. Results showed hydrolyzed KH550 coated on the CaCO₃ surface in the form of polymer brush. The active group on the polymer brush surface could chemisorb Ni${}^{2+}$ and then Ni particles/polymer brush was attached on its surface. The Ni particle/polymer brush structure acted as catalytic site and could catalyze electroless copper plating on its surface. The $M_{\mathrm{\text{plated particle}}}∕M_{(\mathrm{\text{plated particle}}+{\mathrm{\text{CaCO}}}_3)}$ is 1%, its average diameter is about 100nm. This means that the dependable technology has great potential application in preparing metal inorganic powder at a low cost.

The life of the components operating under various high-temperature environments decreases due to the activation of different failure mechanisms. High-temperature oxidation and erosion are the two prominent mechanisms that lead to the degradation of materials, resulting in the premature failure of the components. This paper has emphasized the failure and performance analysis of nickel-based coatings formulated by using different thermal spraying techniques. Nickel-based coatings like Ni–Cr, Ni₃Al, Alloy-718, NiCrAlY, NiCrBSi and Ni-based composite coatings showed excellent resistance against the high-temperature conditions. This study helps to select specific thermal spray techniques and coating composition against high-temperature erosion and oxidation conditions.

As a material widely used in aerospace and energy development, the surface quality of nickel and its alloy will need to be improved urgently. Electrochemical polishing, as a surface treatment method, can smoothen the metal surface and improve its corrosion resistance. Strict environmental regulations have given rise to new electrochemical polishing techniques. In this paper, the electrochemical polishing of nickel was carried out using resin particles wetted by deep eutectic solvent (DES) as polishing medium. The surface morphology and roughness of polished nickel were characterized by scanning electron microscopy (SEM) and optical profilometer. In addition, electrochemical polarization curve and electrochemical impedance spectroscopy (EIS) were used to test the corrosion behavior of polished specimens in 3.5wt.% NaCl solution. The results show that the surface morphology of polished nickel shows grain boundary characteristics. The surface roughness Ra can be reduced from 0.612$\mu$m to 0.0913$\mu$m (under 30V voltage polishing 1h), and the corrosion current density can be reduced from 27.30$\mu$Acm${}^{-2}$ to 12.15$\mu$Acm${}^{-2}$. Pitting potential in the polarization curve indicates that the pits at the grain boundaries are corroded due to the influx of corrosive chloride ions. This polishing method combines the resin with DES which can reduce the production of polishing liquid waste while avoiding the use of harmful acid-base electrolytes and effectively reduce the surface geometry uneven degree, improving the surface corrosion resistance.

Transverse vibration of nickel coated carbon nanotubes is investigated by using molecular dynamics simulations. The simulations are carried out for armchair and zig-zag carbon nanotubes with various lengths. Uncoated and nickel coated carbon nanotubes having same lengths are analyzed and their vibrational behaviors are compared. Free transverse vibrations of nickel coated carbon nanotubes are modelled by using a two-phase local–nonlocal Euler–Bernoulli beam model and solved by finite element method. Nonlocal parameter of the beam model is calibrated based on molecular dynamics simulation results. It is seen that for the same length diameter ratio, the nickel coated carbon nanotubes have similar vibrational characteristics with the uncoated carbon nanotubes but their natural frequencies are smaller than the uncoated ones. Also, it is shown that by using proper nonlocal parameters for each radius length ratio, the two-phase local–nonlocal Euler–Bernoulli beam model can successfully predict the natural frequencies of both short and long nanotubes. Besides natural frequencies and mode shapes, the clustering of nickel atoms depend on simulation temperature which is discussed during oscillation of nickel coated carbon nanotubes.