Polycrystalline Ni Foil Research Articles

Probing mesoscopic lattice misorientation by strain gradient crystal plasticity modelling and micro-beam Laue diffraction experiments

A lengthscale and rate-dependent strain gradient crystal plasticity framework was employed to simulate the inter- and intra-granular deformation at the meso- to microscopic level in a large-grained polycrystalline Ni foil. The sample was characterised by micro-beam Laue diffraction experiments. Post-processing of the model was carried out both to forward predict the Laue diffraction patterns on the detector and to perform inverse analysis of the local lattice misorientation in the crystal. The anisotropic broadening of the Laue spots ('streaking') was correctly captured by the simulation and further analysed to reveal the local lattice arrangement.

Dislocation-based plasticity model and micro-beam Laue diffraction analysis of polycrystalline Ni foil: A forward prediction

A physically-based, rate and length-scale dependent strain gradient crystal plasticity framework was employed to simulate the polycrystalline plastic deformation at the microscopic level in a large-grained, commercially pure Ni sample. The latter was characterised in terms of the grain morphology and orientation (in the bulk) by micro-beam Laue diffraction experiments carried out on beamline B16 at Diamond Light Source. The corresponding finite element model was developed using a grain-based mesh with the specific grain orientation assignment appropriate for the sample considered. Sample stretching to 2% plastic strain was simulated, and a post-processor was developed to extract the information about the local lattice misorientation (curvature), enabling forward-prediction of the Laue diffraction patterns. The ‘streaking’ phenomenon of the Laue spots (anisotropic broadening of two-dimensional (2D) diffraction peaks observed on the 2D detector) was correctly captured by the simulation, as constructed by direct superposition of reflections from different integration points within the diffraction gauge volume. Good agreement was found between the images collected from experiments and simulation patterns at various positions in the sample.

Large-scale graphitic thin films synthesized on Ni and transferred to insulators: Structural and electronic properties

We present a comprehensive study of the structural and electronic properties of ultrathin films containing graphene layers synthesized by chemical vapor deposition based surface segregation on polycrystalline Ni foils then transferred onto insulating SiO2/Si substrates. Films of size up to several mm’s have been synthesized. Structural characterizations by atomic force microscopy, scanning tunneling microscopy, cross-sectional transmission electron microscopy (XTEM), and Raman spectroscopy confirm that such large-scale graphitic thin films (GTF) contain both thick graphite regions and thin regions of few-layer graphene. The films also contain many wrinkles, with sharply-bent tips and dislocations revealed by XTEM, yielding insights on the growth and buckling processes of the GTF. Measurements on mm-scale back-gated transistor devices fabricated from the transferred GTF show ambipolar field effect with resistance modulation ∼50% and carrier mobilities reaching ∼2000 cm2/V s. We also demonstrate quantum transport of carriers with phase coherence length over 0.2 μm from the observation of two-dimensional weak localization in low temperature magnetotransport measurements. Our results show that despite the nonuniformity and surface roughness, such large-scale, flexible thin films can have electronic properties promising for device applications.

Surface Microscopy Characterizations of Large Size Graphene Films Grown by Surface Segregation on Ni and Transferred to Si/SiO2 Substrate

We report surface microscopy characterizations of large size graphene films (up to mm) grown on polycrystalline Ni foils and transferred to Si/SiO2. Wrinkles in such films are studied by both atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Local graphitic lattice structures of the films are imaged with atomic-resolution STM and compared with those of the highly ordered pyrolytic graphite (HOPG).

Large-grained and Highly-ordered Graphene Synthesized by Radio Frequency Plasma-enhanced Chemical Vapor Deposition

We have synthesized a very thin graphite film on polycrystalline Ni foil using radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at relatively low temperature. Structural analysis through electron diffraction and Raman spectroscopy demonstrated that the PECVD grown graphite film consists of large grains sized over tens of microns and is highly ordered structure exhibiting Bernal stacking despite of low synthetic temperature of 850oC. Accordingly, the high carrier mobility of 4,500 cm2/Vsec was obtained at room temperature from a monolayer of PECVD grown graphene, which is higher than any reported value of CVD-grown graphene.

Structure, morphology and composition of thin Pd and Ni films deposited by dc magnetron sputtering on polycrystalline Ni and Pd foils

The understanding of atomic and electronic structures is crucial for designing devices. The surface properties of bimetallic systems have been widely studied due to the possibility of applications in different areas, such as catalysis, magnetism, microelectronics and electrochemistry. The objective of this work is studying thin (10 nm) Pd and Ni films on polycrystalline Ni and Pd substrates (Pd/Ni and Ni/Pd), respectively, grown by dc magnetron sputtering. The film structure was investigated by x-ray diffraction (XRD), morphology, by atomic force microscopy and surface composition, and by x-ray photoelectron spectroscopy. The XRD indicated that the Ni/Pd film did not present an ordered structure, while the Pd/Ni had a nanocrystalline structure with a slight structural distortion. Oxide formation was detected for the Ni film, but not for the Pd film.

Formation and electronic properties of oxide and sulphide films of Co, Ni and Mo studied by XPS

Dry O2 oxidation up to 4008C, water immersion at room temperature or H2S sulphidation at 4008C forms oxide or sulphide films on polycrystalline Co and Ni foils. X-ray photoelectron spectra (XPS) of the Co 2p and Ni 2p core levels and valence band (VB) structure changes allow the identification of the chemical state of such films and their electronic properties. They are compared with the films obtained on Mo in similar conditions. Ni appears less reactive than Co during O 2 or water oxidation and is considered as a more noble metal. Dry oxidation mainly induces CoO while water immersion induces formation of CoO(OH). For Ni, phases like Ni2O3, Ni(OH)2 and/or NiO(OH) are the most probable products, respectively. H2S sulphidation always produces a sulphur-rich Co or Ni phase. The VB response to sulphidation of the three studied metals shows that Co or Ni sulphides are potential electron-donors to MoS2. Such results are relevant to the synergy observed in hydrotreating catalysis with these sulphides. q 1999 Elsevier Science B.V. All rights reserved.

The Spreading Kinetics of Ag–28Cu(L) on Nickel(S): Part II. Area of Spread on Surfaces Plated with Electrolytic Ni

Furnace brazing is commonly used in the electronic industry to attach I/O pins, lid-seal rings, and heat spreaders to cofired multilayer ceramic packages. Despite the widespread industry usage of electrolytic and electroless Ni coatings to render base metal surfaces wettable by braze fillers, there is no fundamental treatment of “brazeability” in the published literature that can be used by the materials technologist to design coatings for a given application. In this study, dynamic hot stage microscopy is used to establish the parameters that control the spreading of eutectic Ag–Cu braze on surfaces plated with electrolytic Ni. The effects of plating thickness, substrate type, plating annealing, and the braze thermal cycle are considered. A braze spreading mechanism developed for polycrystalline Ni foil in Part I of this study is linked to Ni-plated surfaces through consideration of differences in microstructure. Eventual extension of this improved understanding to surfaces plated with electroless Ni–B and Ni–P deposits will result in shortened product design time and improved manufacturing process control.

Structure of nickel layers in NiC multilayer coatings: Influence of annealing

The structure of NiC multilayer and single nickel layer samples has been analyzed before and after annealing, using two techniques: fluorescence EXAFS (FIEXAFS) at the NiK edge and Cu K α reflection. Annealing at a temperature of 450 °C resulted in a change in the structure of the nickel layers from amorphous like to crystalline like. A reduction of the Bragg reflectivity by a factor of 7 was also found. Comparison between the EXAFS data of the annealed sample and of a nickel foil show a difference in the amplitude of the EXAFS. This is ascribed to a non-Gaussian atomic distribution of the backscattering atoms in the annealed sample around their average positions, whereas the atomic distribution in the (polycrystalline) Ni foil is a Gaussian one. From the annealing experiments we conclude that no irreversible changes take place in the structure of the nickel layers at temperatures below 200 °C.

Structure of Nickel Layers in Ni-C Multilayer Coatings: Influence of Annealing

The structure of Ni-C multilayer and single nickel layer samples has been analyzed before and after annealing, using two techniques: fluorescence EXAFS (F1EXAFS) at the Ni-K. edge and CuKα reflection. Annealing at a temperature of 450°C resulted in a change in the structure of the nickel layers from amorphous like to crystalline like. A reduction of the Bragg reflectivity by a factor of 7 was also found. Comparison between the EXAFS data of the annealed sample and of a nickel foil show a difference in the amplitude of the EXAFS. This is ascribed to a non-Gaussian atomic distribution of the backscattering atoms in the annealed sample around their average positions, whereas the atomic distribution in the (polycrystalline) Ni foil is a Gaussian one. From the annealing experiments we conclude that no irreversible changes take place in the structure of the nickel layers at temperatures below 200°C.

Magnetic imaging by atomic force microscope (invited) (abstract)

A new method of imaging the surface of magnetic samples on a submicron scale is described and the observation of magnetic domain walls is presented. Measurements in air on a Co-Ni recording media, polycrystalline Ni foil and rapidly quenched alloys are shown. This magnetic microscope is based on the idea of measuring magnetic forces with the recently developed atomic force microscope (AFM). Forces acting on a tip are recorded by the measurement of the deflection of a lever to which this tip is attached. In order to measure ultra small forces (less than nN), the spring constant of the lever has to be small and the deflection of the lever has to be measured with great sensitivity, i.e., by using interferometry or scanning tunneling microscopy (STM). The lever is made from ferromagnetic Ni foil with an integrated, electrochemically etched tip. Different measuring modes of the AFM are described. The images obtained by the AFM using a para- or ferromagnetic tip and by the STM are compared. Furthermore, the results obtained by the magnetic AFM on Co-Ni recording media are compared with previous studies by scanning electron microscopy with polarization analysis (SEMPA).

Chemisorption of carbonyl sulfide (OCS) on Ni between 77 and 293 K

The chemisorption of OCS on polycrystalline Ni foil, in the 77–293 K temperature range, was investigated by XPS, UPS and AES electron spectroscopies. At all temperatures studied, chemisorption was found to be dissociative yielding absorbed S and gas phase CO. The reaction is found to be strongly exothermic with a low activation energy.

Properties of nitrogen implanted nickel foils

Surface nitride layers about 90 nm thick have been formed on high‐purity, polycrystalline Ni foils by ion implantation under ultrahigh‐vacuum conditions. Fluences were 5.5–8.0×1017 N+2/ cm2 at 80 keV. The substrate was free of impurities as judged by Auger electron spectrosopy (AES). AES depth profiles were used to determine the depth distribution in as‐implanted and annealed samples. As‐implanted N has a two‐peaked profile with maxima at the surface and at about 45 nm. Annealing at T <250 °C increases the surface N concentration, decreases the concentration between the maxima, decreases the 45‐nm maxima, and broadens it toward larger depths. Small amounts of C on the surface at the start of implantation significantly alter the N depth distribution. These effects are consistent with terms of recent model calculations.

Temperature jump method in molecular beam relaxation spectrometry applied to catalytic decomposition of CH 3OH on polycrystalline Ni foil

A new modification of molecular beam relaxation spectrometry (MBRS) is described: the temperature jump method for studying catalytic surface processes on metal foils. The temperature of the catalyst foil is maintained by direct ohmic heating; a constant particle beam is directed towards the catalyst surface. A jump of the surface temperature caused by a high current pulse generates a response of the fluxes of desorption. The decay of the desorption intensity after the temperature jump contains the relaxation times of the elementary steps involved. The mathematical treatments of unimolecular and bimolecular surface reactions, of sequences of two and three unimolecular steps and of a sequential reaction accompanied by the redesorption of the reactant are given. The application of the new method is shown by a study of the catalytic decomposition of CH 3)OH on polycrystalline Ni: CO and H 2 are the sole reaction products. The limit of the catalytic activity — apart from the low sticking probability of the reactant — must be seen in the abstraction of the first methyl hydrogen from the transient methoxy species. In the temperature range between 320 and 550 K the reaction mechanism can be described as follows: ▪ Rate constants in dependence from surface temperature T are: k 1 = 4.2 × 10 4 exp ( −22.4 RT kJ mol ) s −1; k 3 = 2.4 × 10 9 exp ( −75 RT kJ mol ) s −1; k 4 = 1.2 × 10 13 exp ( −104 RT kJ mol ) s −1; η = 0.2. Typical surface residence times of the intermediates are: 110 ⩾ τ 1 ⩾ 15 ms at 320 ⩽ T ⩽ 450 K; 210 ⩾ τ 3 ⩾ 6 ms at 450 ⩽ T ⩽ 550 K; 98 ⩾ τ 4 ⩾ 6 ms at 450 ⩽ T ⩽ 500 K.

Temperature jump method in molecular beam relaxation spectrometry applied to catalytic decomposition of CH 3OH on polycrystalline Ni foil

Temperature jump method in molecular beam relaxation spectrometry applied to catalytic decomposition of CH 3OH on polycrystalline Ni foil

Deposition of columnar and laminar forms of carbon on polycrystalline nickel foils

Two distinct forms of carbon in terms of morphology and crystallinity have been produced on polycrystalline Ni foils by pyrolysis of propene (50 Torr). A thick layer (up to 10 μm) of columnar carbon ( d (0002) = 3.40 A ̊ ; E a = 33 Kcal/mole ) was obtained within the temperature region 320–380°C. From 380–800°C a thin layer of laminar graphite ( d (0002) = 3.36 A ̊ ; E a = 16 kcal/mole ) was formed. As a consequence of the temperature gradient along the length of the foils in these experiments both forms of carbon could be produced simultaneously. Bulk diffusion and surface diffusion mechanisms have been proposed to account for the growth of the columnar and laminar products respectively. At ~700°C migration of Ni metal particles to the cooler foil edges occurred and resulted in the formation of non-graphitic filaments. Preliminary studies with butadiene have revealed similar deposition characteristics and activation energies to those of propene.

Bulk Diffusion of Carbon-14 through Polycrystalline Nickel Foil between 350 and 700°C

The bulk diffusion of C-14 through polycrystalline Ni foil was investigated in the temperature range of 350 to 700°C. A thin Ni foil was bombarded by a molecular beam of acetylene tagged with C-14. A masking device situated very close to the ribbon surface shielded part of the surface from this beam, producing a well-defined pattern of high and low concentration of absorbed acetylene on the top surface of the foil. After diffusion annealing, this pattern would appear on the underside of the ribbon. Autoradiographic techniques were used to obtain radiation intensities from both surfaces. The ratio of these intensities determined bulk diffusion coefficients after the method of Kryukov. Most previous data had been obtained at temperatures of 700°C or higher. There is acceptable agreement between these data and the higher-temperature experiments of the present work. However, the present results show an activation energy of approximately 20 kcal/mole from 350 to 700°C, while there is substantial evidence that above 700°C the activation energy for this process is of the order of 40 kcal/mole.