Diffusion Of Nickel Research Articles

Triggering surface nickel diffusion by adsorption of carbon

The dissociation of carbonaceous molecules on the surface of a nano-sized Ni crystal induces deep morphological changes way below the melting temperature, as imaged by Field Ion Microscopy. In this Letter, classical Molecular Dynamics (MD) was used to demonstrate that carbon adsorption triggers Ni surface diffusion. More precisely, single adsorbed carbon atoms, preferentially bound to 5-fold surface sites, enhance thermally activated Ni diffusion. A mechanism is identified by which adsorbed carbon promotes the rupture of surface Ni atoms from their lattice position. This leads to a destabilization of edges between facets of the Ni crystal.

Interface and Wear Resistance of High Frequency Induction Remelted Ni-Based WC Coating

Ni-based WC composite coatings conducted on the surface of 45 steels by free spraying followed with high frequency induction remelting were investigated. The influences of induction remelting time on properties of the coating were discussed. The wear resistance of the coating and the elemental diffusion cross the interface between the coatings and the substrate were analyzed. The compositions and microstructure of the coating before and after a wear test were characterized by scanning electron microscope with energy dispersive X-ray microanalysis. The results indicate that a coating which is free from crackers and pores composed of Ni-based solid solution and dispersed tungsten carbide is obtained by free spraying and induction remelting. The interface is a white lamellar zone. The mutual diffusion of iron and nickel in the interface proves it’s an atomic bonding between the substrate and the coating. The wear mechanisms of the coated sample are abrasive wear and microplowing. The wear resistance of Ni-based WC composite coatings is superior to that of quenched high carbon steels.

Long-term flue gas exposure effects of silica membranes on porous steel substrate

In this work we investigate the long-term effects of exposing an inorganic membrane for 1100 h in a flue gas stream of a coal power plant. Of particular importance, from an industrial testing perspective, was the effect of fly ash deposition, water vapour and acid gases on the integrity of the membrane made of cobalt silica coated on a substrate of 316L steel, with interlayers of 310S steel, yttria-stabilized zirconia and γ-alumina. Subsequent to the flue gas testing, the membrane was characterized for single gas permeance, SEM and EDX spectroscopy. Diffusion of nickel and chromium during sintering was observed at the interface of the 316L/310S steels, resulting in a reduced capacity to withstand corrosion in this area. Single gas permeation testing following flue gas exposure revealed a maximum permeation of 1.85 × 10 −8 mol m −2 s −1 Pa −1 and 2.13 × 10 −8 mol m −2 s −1 Pa −1 for helium and hydrogen respectively, and selectivity of 5.1 and 5.2 for He/N 2 and H 2/CO 2 respectively, was achieved at a pressure difference of 2 × 10 5 Pa (2 bar) at 200 °C. The permeation behavior of the membrane appeared to be altered as a result of flue gas exposure with the membrane displaying a reduced H 2 flux in contrast to an unexposed but otherwise identical membrane which displayed fluxes an order of magnitude higher than the membrane used in the power plant. This change in permeation behavior was thought to be the result of densification of the silica matrix following long-term exposure to flue gas containing water vapour. Micro-fractures in the surface of the cobalt silica gas separation layer were also observed, possibly the result of expansion due to corrosion. However, bulk diffusion was not observed suggesting that the layer was not completely compromised.

Influence of the heating temperature on the properties of nickel doped TiO 2 films prepared by sol–gel method

Formation and properties of nickel doped TiO 2 films prepared by sol–gel method were studied using X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, and energy dispersive X-ray analysis. The results demonstrate that sizes of TiO 2 crystallites increase with increasing heating temperature. Also, at temperatures above 800 ° C diffusion of nickel onto the surfaces results in increased concentrations of nickel compounds on the surfaces. Similar to pure TiO 2 films the light-induced modification of hydrophilicity is observed also in the case of nickel doped TiO 2 films.

Surface Diffusion Controlled Formation of Nickel Silicides in Silicon Nanowires

� R � 0.75 . The dependence of R on annealing time, t, is close to t 0.5 . The profile of the new phase was described for different combinations of two dimensionless parameters: R/d and Dc/Dsc, where d is the thickness of the high-diffusivity surface layer with diffusion coefficient Dsc, and Dc is the volume diffusion coefficient. After the formation of a continuous layer of a new phase, further growth is controlled exclusively by the interface diffusion of Ni along the nickel silicide surface and Si/Ni2Si interface. The growth kinetics depends on the ratio of diffusion coefficients Dsc/Db, where Db is the interface diffusion coefficient, and may be parabolic or linear. The calculated dependencies were compared with the published experimental results for nickel silicide formation in SiNWs. The analysis performed indicates that surface and interface diffusion of nickel play an important role in the formation of nickel silicides in NWs—a critical finding that should be considered in the design of SiNW FETs.

Preparation of NiO Buffer Layer by Direct Oxygenation of Ni Tape

Recently, Nickel-based alloys are widely used for textured substrates tapes. However, the deposition of oxide buffer layers on nickel tapes is required to stop the diffusion of nickel from the tape to superconducting layer and to improve the mismatch between the substrate and superconducting film. Biaxially textured NiO buffer layer is easily formed on cubic textured nickel tape by the technique called surface oxidation epitaxy. In this work, we developed a direct oxygenating method to make the NiO buffer layer on nickel tape. The nickel tape was directly oxygenated in different atmospheres. It is found that in inert atmosphere, a high quality NiO layer can be formed on the surface of the tape. The oxygenating conditions, including atmospheres and temperatures, and their influence on the structure of the NiO buffer layer, were studied in detail and discussed.

10.1007/s11455-008-2015-5

The depth-concentration profiles of nickel upon diffusion in submicrocrystalline (SMC) molybdenum processed by severe plastic deformation (SPD) have been studied by Auger electron spectroscopy. The coefficients (D b) and activation energies of the grain-boundary diffusion of nickel in SMC molybdenum were determined in a 973–1123 K temperature interval. The results indicate that a difference between the D b values in SMC and coarse-grained molybdenum is related to a nonequilibrium state of grain boundaries in the SPD-processed metal.

Bonding Quality of Copper-Nickel Fine Clad Metal Prepared by Surface Activated Bonding

The effects of surface roughness and heat treatment on the bonding quality of surface-activated bonding (SAB)-treated copper-nickel fine clad metals were investigated. An increase in the surface roughness of the copper layer decreased the peel strength after cladding, indicating that increases in the surface roughness decreased the contact area between the clad materials in the SAB cladding process, unlike conventional cold rolling that induces high deformation. In addition, the peel strength of the clad metals increased up to 7.3 N/mm with decreasing surface roughness of the copper layer after heat treatment. The change in the total sheet resistance of the copper-nickel clad metal with the heat treatment depended on the balance between a decrease in the sheet resistance due to the reduction of dislocation and the increase in the heat treatment temperature, and an increase in the sheet resistance due to the diffusion of nickel in the copper direction. [doi:10.2320/matertrans.M2009354]

HRTEM studies of NiNbZr + Ag amorphous‐nanocrystalline composites

Amorphous powder of composition corresponding to Ni60Ti20Zr20 (in at%) was obtained by ball milling in a high-energy mills starting from pure elements. Formation of the amorphous structure was observed already after 20 h of milling, although complete amorphization occurred after 40 h. The microhardness of powders increased from about 30 HV for pure elements to above 400 HV (1290 MPa) after 40 h of milling. Transmission electron microscopy (TEM) allowed to identify nanocrystalline inclusions of intermetallic phases of size 2-10 nm. Uniaxial hot pressing was performed in vacuum at temperature below the crystallization T(x) it is 510 degrees C and pressure of 600 MPa, Mixed amorphous powders and nanocrystalline silver powders were used to form a composite, in which microhardness was near 970 MPa HV and 400 HV for the amorphous phase and nanocrystalline silver, respectively. The compression strength of the composite containing 20 wt% of nanocrystalline Ag powder was equal to 600 MPa and plastic strain was 2%. Microstructure studies showed low porosity of composites of less than 1%, uniform distribution of the silver phase and a transition zone between both components, about 150 nm thick, where diffusion of nickel, niobium and zirconium into silver was observed. High-resolution TEM allowed identifying the structure of nanocrystalline inclusions in the amorphous matrix after hot pressing as either Ni(3)Zr or Ni(17)Nb(3). The identification was performed basing on measurements of angles and interatomic distances using inverse Fourier transformed images with enhanced contrast using Digital Micrograph computer program.

An investigation of the oxidized Ni/InAs interface

Abstract Ni was resistively deposited onto bulk InAs and subsequently oxidized in an O 2 atmosphere. The anneal temperature and time were 450 °C and 2.5 h, respectively. X-ray diffraction of the oxidized Ni/InAs sample revealed the formation of In 3 Ni 2 and In 2 O 3 on the front suggesting inter diffusion of In, Ni and O. NiO was not detected by X-ray diffraction. In a preliminary study, using glass as a substrate, NiO readily formed when using these oxidation parameters. Conductivity measurements of the oxidized Ni/InAs surface revealed a conducting front and insulating rear surface while TEM of the Ni/InAs interface revealed an intermediate amorphous diffusion zone between the “oxidized” Ni layer and the bulk InAs. A closer investigation of the intermediate layer supports the X-ray diffraction results, suggesting compound formation due to diffusion of oxygen and nickel into the substrate, and out-diffusion of In and As from the bulk of the sample. AES was used to further elucidate these results.

Role of titanium in Ti/Ni ohmic contact on n-type 6H-SiC

A set of Ti/Ni metallizations with different thickness of the underlying titanium layer was prepared on 6H-SiC together with structures that contained only pure Ti and Ni. Samples were gradually annealed at 750–1150 °C. Structures Ti(2)/Ni(50) and Ti(100)/Ni(50) showed the lowest contact resistivity, 2 × 10 −4 Ω cm 2 in both cases. For the Ti(2)/Ni(50) structure, low contact resistivity was reached most likely due to reduction of surface oxides on SiC by the thin titanium layer. In the Ti(100)/Ni(50) structure, the titanium layer prevents diffusion of nickel towards SiC and there is a layer containing mainly TiC at the interface with silicon carbide.

Nickel-Boron Nanolayer-Coated Boron Carbide Pressureless Sintering

Sintering of pure B4C and Ni2B nanolayer-coated B4C was studied from 1300° to 1600°C, with the holding time at the peak temperatures being 2 or 10 h. Compacts were made by uniaxial die compaction and combustion-driven compaction. Pure B4C sample shows less sintering at all conditions. Ni2B-coated B4C sample shows more extensive densification, neck formation, and grain shape accommodation. The combustion driven compaction process accelerates sintering by offering higher green density to start with. The Ni2B species on the B4C particle surfaces melts into a nickel–boron-containing liquid phase during heating, remains as liquid during sintering, and then transforms into Ni4B3 and NiB during cooling. High-resolution composition analysis shows that there is no nickel diffusion into bulk B4C during the sintering process. However, there is boron diffusion into the Ni2B coating layer. Carbon diffusion cannot be directly measured but is believed to be a simultaneous process as boron diffusion. A multievent sintering process has been proposed to explain the observations.

Low temperature formation and evolution of a 10 nm amorphous Ni–Si layer on [001] silicon studied by in situ transmission electron microscopy

We investigated low temperature formation of a 10 nm thick amorphous Ni–Si layer after room temperature deposition of a 7 nm Ni layer on [001] Si, by in situ transmission electron microscopy analyses. Instead of a conventional time sequence of phases or an immediate formation of NiSi2 domains, annealing at 220 °C promotes Ni diffusion through a thin interfacial amorphous layer, formed during deposition, into the Si lattice until the entire supply of pure Ni atoms is consumed. High concentration nickel diffusion induces a crystalline-to-amorphous transformation of the original silicon lattice. Further increasing the temperature, in the range between 300 and 350 °C, causes crystalline NiSi2 domains to nucleate and grow within the amorphous matrix.

Diffusion of Titanium and Nickel in B2 NiTi

Diffusion of both titanium and nickel was measured in the near stoichiometric Ni-49.4at.%Ti alloy with the B2 ordered structure. The radiotracer technique and the 44Ti and 63Ni isotopes were applied in the temperature interval from 900 to 1300 K. The penetration profiles were determined by precision parallel grinding or by ion beam sputtering at larger and smaller penetration depths, respectively. Titanium and nickel diffusivities were found to follow linear Arrhenius dependencies with the pre-exponential factors of 2.710-7 and 4.710-9 m2/s and the activation enthalpies of 205 and 143 kJ/mol, respectively. A vacancy mediated diffusion mechanism is suggested to provide diffusion of both nickel and titanium in the compound NiTi.

Phase composition and electrical characteristics of nickel silicide Schottky contacts formed on 4H–SiC

4H–SiC Schottky diodes with nickel silicide contacts were formed by consecutive deposition of a titanium adhesion layer, 4 nm thick, and nickel, 100 nm thick, followed by annealing at temperatures between 600 and 750 °C. It was found that contacts with barrier heights of 1.45 eV which consist mainly of single nickel monosilicide (NiSi) phase were formed in the 600–660 °C temperature range, while annealing at around 750 °C led to the formation of Ni2Si Schottky contacts with barrier heights of 1.1 eV. Annealing at intermediate temperatures resulted in the nucleation of Ni2Si grains embedded in the NiSi film which were directly observed by micro-Raman mapping. It was shown that the thermodynamically unfavourable NiSi phase appeared in the 600–660 °C temperature range due to control of the Ni–SiC solid-state chemical reaction by nickel diffusion through the titanium diffusion barrier.

Synthesis of Nickel Mono-Silicide Nanowire by Chemical Vapor Deposition on Nickel Film: Role of Surface Nickel Oxides

We synthesized nickel mono-silicide nanowires (NiSi-NWs) on electron-beam-evaporated Ni films with SiH4/H2 gases in a chemical-vapor-deposition chamber, and studied the growth mechanism of NiSi-NW by investigating various synthesis conditions. Results show that NiO and Ni2O3 phases coexist on nickel surface and agglomerate after heating and the initial growth of NiSi-NW is triggered by the Ni2O3. The effects of these surface nickel-oxides on NiSi-NW growth were investigated, and a synthesis model based-on vapor–liquid–solid mechanism with the aid of nickel diffusion to initiate NiSi-NW synthesis is proposed. It is also found that the diameter of NiSi-NW is mainly controlled by the synthesis temperature and the activation energy of NiSi-NW formation is estimated to be 1.72 eV.

Phase Inhomogeneity and Electrical Characteristics of Nickel Silicide Schottky Contacts Formed on 4H-SiC

Nickel silicide Schottky contacts were formed on 4H-SiC by consecutive deposition of a titanium adhesion layer, 4 nm thick, and nickel, 100 nm thick, followed by annealing at temperatures from 600 to 750 °C. It was found that contacts with barrier heights of 1.45 eV, consisting mainly of NiSi phase, formed in the 600-660 °C temperature range, while annealing at around 750 °C led to the formation of Ni2Si phase with barrier heights of 1.1 eV. Annealing at intermediate temperatures resulted in the nucleation of Ni2Si grains embedded in the NiSi film which were directly observed by micro-Raman mapping. It was concluded that the thermodynamically unfavourable NiSi phase appeared in the 600-660 °C temperature range due to the fact that the solid state chemical reaction between Ni and SiC at these temperatures is controlled by nickel diffusion through the titanium barrier.

Thermal grain-boundary grooving in bicrystal thin solid films having strong anisotropic surface Gibbs free energy represented by the modified cycloid-curtate function

The variational non-equilibrium thermodynamic method is further extended to give full coverage for the tilted grain-boundary (GB) configuration with respect to the sidewalls of a bicrystal thin solid film having strong anisotropic specific surface Gibbs free energy associated with the singular directions (faceting, vicinal planes). A set of critical computer simulation experiments supported by the generalized longitudinal force diagrams is performed on the asymmetrically disposed (inclination) bicrystal thin metallic films having four- and six-fold anisotropic specific surface Gibbs free energy to demonstrate the various GB-groove root topologies caused by the grain-boundary grooving under the surface drift-diffusion driven by the capillarity forces (thermal grooving). In the computer simulations, the strongly anisotropic surface-specific Gibbs free energy associated with the cusp regions is represented by the modified cycloid-curtate function (MCCF) as a basis (generator) for the Dirac delta distribution function on the Wulff construction, which involves not only the Wulff surface roughness (WSR) parameter (anisotropy constant) but also the Wulff surface topography (WST) index (shape parameter) that may be used as a metric for the temperature roughening phenomenon. A special computer run is also designed using the realistic structural and physicochemical properties in order to simulate the thermal groove profiles of cube-textured pure nickel tape {Ni—99.99 wt%} annealed four hours in vacuum at 800 °C, and observed by the atomic force microcopy (AFM). The experimental line width fitting procedure applied to the simulation profile subjected to the self-similarity transformation, which resulted in almost perfect replication of the experimental digitized AFM photography, has yielded a mean surface (mass) diffusivity of nickel about 5.7×10 −13 m 2/s (800 °C), which is in excellent quantitative agreement with the diffusivity relationship at T⩾1300 K reported in the literature on relatively contaminated surfaces, and obtained by high-precision profilometry measurements of the decay of capillary modes associated with the wide surface scratches.

Nickel diffusion in polycrystalline CuInSe 2 thin films with a fiber texture

Nickel diffusion in CuInSe 2 thin films was studied in the temperature range 430–520 °C. Thin films of copper indium diselenide (CuInSe 2) were prepared by selenization of CuInSe 2–Cu–In multilayered structure on glass substrate. A thin film of Nickel was deposited and annealed at different temperatures. Surface morphologies of the Ni diffused and undiffused CuInSe2 films were investigated using scanning electron microscope. The alteration of Nickel concentration in the CuInSe 2 thin film was measured by Energy Dispersive X-Ray Fluorescence (EDXRF) technique. These measurements were fitted to a complementary error function solution and the diffusion coefficients at four different temperatures were evaluated. The diffusion coefficients of Ni in CuInSe 2 films were estimated from concentration profiles at temperatures 430–520 °C as D = 1.86 × 10 − 7 (cm 2 s − 1 )exp[− 0.68( eV)/kT].

Formation of PTCDI-Based Metal Organic Structures on a Au(111) Surface Modified by 2-D Ni Clusters

The adsorption of PTCDI (3,4,9,10-perylene-tetracarboxylic diimide) onto a Au(111) surface templated by two-dimensional (2-D) Ni clusters has been investigated by scanning tunneling microscopy (STM). We found that the nickel coverage has a significant effect on the distribution and stability of the characteristic hydrogen bonding phase of PTCDI and that a range of novel PTCDI-based aggregates can occur. Porous metal organic frameworks can be generated from diffusion of nickel from 2-D clusters. Close-packed Ni-PTCDI structures can result from incorporation of nickel into domains of the hydrogen bonding phase or rearrangement of porous frameworks after annealing treatments. Annealing Ni/Au(111) surfaces of low PTCDI coverage to higher temperatures leads to the formation of one-dimensional (1-D) molecular chains. We discuss the likely composition of the observed structures and the key role that nickel plays in their stabilization.