Polycrystalline Ni Foil Research Articles

Observation and Characterization of Vibrationally Active Surface Species Accessed with Nonthermal Nitrogen Plasmas.

Polycrystalline Ni, Pd, Cu, Ag, and Au foils exposed to nonthermal plasma (NTP)-activated N2 are found to exhibit a vibrational feature near 2200 cm-1 in polarization-modulation infrared reflection-absorption spectroscopy (PM-IRAS) observations that are not present in the same materials exposed to N2 under nonplasma conditions. The feature is similar to that reported elsewhere and is typically assigned to chemisorbed N2. We employ a combination of temperature-dependent experiments, sequential dosing, X-ray photoelectron spectroscopy, isotopic labeling, and density functional theory calculations to characterize the feature. Results are most consistent with a triatomic species, likely NCO, with the C and O likely originating from ppm-level impurities in the ultrahigh-purity (UHP) Ar and/or N2 gas cylinders. The work highlights the potential for nonthermal plasmas to access adsorbates inaccessible thermally as well as the potential contributions of ppm-level impurities to corrupt the interpretation of plasma catalytic chemistry.

Two dimensional boron nitride growth on nickel foils by plasma assisted molecular beam epitaxy from elemental B and N sources

The growth of two dimensional sp2-bonded boron nitride (2D-BN) was studied in a plasma-assisted molecular beam epitaxy set-up, using independent boron and nitrogen sources. We studied the growth conditions on polycrystalline Ni foils: B and N respective fluxes, growth temperature and time, which are influencing the surface morphology, stoichiometry and the 2D-BN domain size. Using a B/N precursor flux ratio ≫1 yields films with incorporated boron largely in excess and intermixed with 2D-BN. On the contrary, precursor flux ratios from moderately B-rich to moderately N-rich leads to stoichiometric 2D-BN. The optimum growth temperature is found to be 900 °C, a temperature for which the crystallographic quality is improved compared to lower temperatures thanks to the increased adatom surface mobility although a partial sublimation of BN occurs. Increasing the growth time under the optimized settings shows that the growth does not occur in a layer-by-layer mode, but rather by stacking BN domains on top of each other with a rather slow lateral extension of the domains.

LiOx-modification of Ni and Co3O4 surfaces: An XPS, LEIS and LEED study

LiOx was deposited at room temperature by physical vapor deposition (PVD) on polycrystalline Ni foil and Co3O4(111) thin film, creating uniform model systems well-suited for surface-sensitive characterization by X-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS) or low energy electron diffraction (LEED). In the case of Ni, about 15 layers of LiOx film were grown under the current conditions either stepwise or continuously, with XPS analysis indicating a deposition rate of 0.16 and 0.24 ML/min, respectively. Li 1s and O 1s spectra revealed that Li2O and to a lesser extent LiOH were preferentially formed. The stability of the LiOx films was examined in UHV, upon annealing at 573 K and upon hydrogen reduction at 723 K. On the more reactive Co3O4(111) film grown on Ir(100), the Li accommodation rate was about twice as high, at least within the first minutes of deposition. Post-deposition LEED showed an obscured cobalt oxide diffraction pattern, not unexpected in light of the LiOx deposited. On both substrates, LEIS characterization of Li (≈ 103 eV) was prevented by the high background in this kinetic energy region, due to surface roughness and unspecific scattering. Still, LiOx deposition was evident from the vanished LEIS signals of Ni or Co. The prepared LiOx-modified surfaces may serve as starting point for the future growth of epitaxial LixCoO2 model systems.

Molecular beam epitaxial growth of hexagonal boron nitride on Ni foils

Hexagonal boron nitride (h-BN) was synthesized by molecular beam epitaxy on polycrystalline Ni foils using borazine (B3N3H6) as precursor. Our photoemission analysis shows that several components of boron and nitrogen are detected, suggesting the complex nature of the bonds noticeably at the h-BN/Ni interface. The BN thickness was estimated by photoemission and the BN distribution by time-of-flight secondary ion mass spectroscopy. Due to the catalytic effect of the Ni substrate, this thickness is self-limited in the range 1–2 layers regardless of the borazine dose. A spatially resolved photoemission study was carried out before and after transfer of the h-BN on a Si substrate. It shows that a strong electronic coupling exists at the interface between h-BN and polycrystalline Ni, not only for (111) grains, which disappears after transfer on Si. In addition, we highlight the importance of detecting π plasmons in the photoemission spectra to confirm the hexagonal nature of BN.

Synthesis of uniform nanometer-thick graphite film on polycrystalline Ni substrate with ultrafine grains

When a polycrystalline Ni foil is used as the substrate for the chemical vapor deposition synthesis of multilayer-graphene or nanometer-thick graphite films (NGFs), these films always exhibit uneven morphologies and qualities on Ni grains with different orientations. In this study, we fabricated a carbon-supersaturated Ni foil (ss-Ni foil) to function as a carbon source through an ultrafast cooling process (∼180 °C/s), while an additional Ni film was sputtered on the ss-Ni foil to act as a buffer layer and a new surface for NGF growth. By re-annealing the Ni film/ss-Ni foil system at a low temperature (∼650–800 °C) within a short duration, NGF can rapidly form on the Ni film owing to the high supersaturation degree of the ss-Ni foil. The grain growth of the Ni film is limited by the low-temperature growth process, and the ultrafine grains of Ni film averaged the grain orientation effect from the Ni foil. The NGF formed on the Ni film/ss-Ni foil showed a significant improvement in thickness and quality uniformity, and we studied the influences of Ni film thickness as well as re-annealing temperature and time on the diffusion of carbon in the Ni film/ss-Ni foil system and summarized the growth mechanism.

Semi-transparent graphite films growth on Ni and their double-sided polymer-free transfer

Nanorange thickness graphite films (NGFs) are robust nanomaterials that can be produced via catalytic chemical vapour deposition but questions remain regarding their facile transfer and how surface topography may affect their application in next-generation devices. Here, we report the growth of NGFs (with an area of 55 cm2 and thickness of ~ 100 nm) on both sides of a polycrystalline Ni foil and their polymer-free transfer (front- and back-side, in areas up to 6 cm2). Due to the catalyst foil topography, the two carbon films differed in physical properties and other characteristics such as surface roughness. We demonstrate that the coarser back-side NGF is well-suited for NO2 sensing, whereas the smoother and more electrically conductive front-side NGF (2000 S/cm, sheet resistance − 50 Ω/sq) could be a viable conducting channel or counter electrode in solar cells (as it transmits 62% of visible light). Overall, the growth and transfer processes described could help realizing NGFs as an alternative carbon material for those technological applications where graphene and micrometer-thick graphite films are not an option.

A way to improve the uniformity of nanometer-thickness graphite film synthesized on polycrystalline Ni substrate: From large grain to small grain

A pellicle is an important part of mask protection in extreme ultraviolet (EUV) lithography, and nanometer-thickness graphite film (NGF) is an ideal material for pellicle fabrication. In our previous work, we synthesized large-scale NGF on polycrystalline Ni foil by a “two-stage” chemical vapor deposition process with an EUV transmittance of 79 ± 2%. The nonuniformity of EUV transmittance is mainly caused by the thicker NGF formed on the Ni grain boundaries (GBs). Here, we present a simple and cost-effective method to weaken the effects of the Ni GBs by sputtering thin Ni films onto Ni foils. The Ni film provides smaller grains with high GB density so that the non-uniformity of NGFs caused by Ni GBs was averaged out by the large EUV beam size. We investigated the grain growth of Ni films with different thicknesses, and 1-μm Ni film/Ni foil had the minimum average grain size of ∼6 μm. The NGF synthesized on it showed a higher EUV transmittance with better uniformity of 86.3 ± 0.9%. Fullerenic CC and sp3 CC bonding were detected by the X-ray photoelectron spectroscopy, and the NGF on the Ni GBs showed a higher defect density.

Graphene–Ni(111) Synergy Influencing Crystalline Orientation, Grain Morphology and Magnetic Properties of Poly-Ni

Among many metal catalyst surfaces, graphene growth on Ni(111) is highly facile owing to the least lattice mismatch between the two. Although the influence of crystalline orientation of Ni on the quality and properties of graphene is known, the effect of this growth on the catalyst surface is not well studied. In the present study, we have investigated this aspect by growing twisted multilayer graphene on polycrystalline Ni foil by a modified CVD process and examined the Ni surface carefully by employing a host of experimental techniques. X-ray diffraction measurements clearly indicate enhancement in the (111) orientation following graphene growth which is corroborated by the electron backscatter diffraction maps. There is an overall increase in the grain size as well, as evidenced by electron microscopy. Further, the ferromagnetic Curie temperature of Ni exhibits a downward shift of up to ∼80 K as also does saturation magnetization, by ∼0.06 μB. The changes in properties are accompanied by unusual morphological events on the Ni surface which include sharpening and interlocking of grain boundaries and cleavage formation. The above observations clearly point to a synergetic effect that manifests at the graphene–Ni(111) interface, the twisted layers only amplifying the effect.

Large-scale nanometer-thickness graphite films synthesized on polycrystalline Ni foils by two-stage chemical vapor deposition process

In this work, large-scale (120 × 120 mm) nanometer-thick graphite films (NGFs) were synthesized on polycrystalline Ni foils using a “two-stage” chemical vapor deposition (CVD) process. An intermediate cooling process was included in the CVD process; this process affected the isothermal graphene growth, which is explained using a growth model. We mainly studied a graphite film with the thickness of ∼40 nm and the good thickness uniformity was characterized by atomic force microscopy (AFM), Raman spectroscopy and extreme ultraviolet (EUV) mapping. The graphite formed on the Ni grain boundary was analyzed by transmission electron microscopy (TEM). The relationships between the thickness, optical and electrical properties of the NGF and growth temperature were also studied.

Characterization and anticorrosion properties of carbon nanotubes directly synthesized on Ni foil using ethanol

In this work, we describe the direct growth of carbon nanofilaments by the catalytic decomposition of ethanol on untreated polycrystalline Ni foil. Our work focuses on the effects of synthesis conditions on the growth of the carbon nanofilaments and their growth mechanism. Direct growth of carbon nanotubes (CNTs) is more favorable on lower-purity Ni foil. The highest yield was obtained at approximately 750°C. The average diameter of the CNTs was approximately 20–30nm. Raman spectra revealed that the increase of H2 concentration in the carrier gas and synthesis temperature induced the growth of better-graphitized CNTs. Additionally, we investigated the anticorrosion properties of as-prepared products under simulated seawater conditions. The corrosion rate of the CNT/Ni foil system was maximally 50–60 times slower than that of the as-received Ni foil, indicating that the CNT coating may be a good candidate for corrosion inhibition.

(Invited) Fabrication and Dielectric Properties of BaTiO3 Thin Films on Polycrystalline Ni Foils

The BaTiO3 (BTO) thin films were deposited on polycrystalline Ni foils using a chemical solution approach. We show that the interface between the BTO film and the Ni foil plays a critical role in determining the dielectric and magnetoelectric (ME) properties of this flexible assembly. A pretreatment process of nickel foils with hydrogen peroxide (H2O2) solution has been conducted to form thin nickel oxide layers on the surfaces for the growth of BTO films. Both the concentration of H2O2 solution and the pretreated time were found to strongly affect the dielectric constant of BTO films, which is likely to be related to the evolution of nickel oxide at the interface during the growth of BTO films. The growth dynamics was systematically studied to optimize the single phase BTO films with good dielectric properties. Our results have demonstrated that not only a well-controlled interface between the BTO film and the Ni substrate can be achieved, but also an good dielectric and ME performance can be accomplished.

(Invited) Fabrication and Dielectric Properties of BaTiO3 Thin Films on Polycrystalline Ni Foils

The BaTiO3 (BTO) thin films were deposited on polycrystalline Ni foils using a chemical solution approach, polymer-assisted deposition. We show that the interface between the BTO film and the Ni foil plays a critical role in determining the dielectric and ferroelectric properties of this flexible assembly. A pretreatment process of nickel foils with hydrogen peroxide (H2O2) solution has been conducted to form thin nickel oxide layers on the surfaces for the growth of BTO films. A rapid thermal post-annealing in oxygen would also strongly affect the electric properties of the as-prepared thin films. The growth dynamics was systematically studied to optimize the single phase BTO films with good dielectric and ferroelectric properties.

Diagnostics of nanodisperse polycrystals based on the polarization bremsstrahlung of relativistic electrons

The spectra of polarization bremsstrahlung are measured in the backscattering geometry during the interaction of 7-MeV electrons with a polycrystalline Ni foil. Measurement is conducted under conditions such that the size of the region of coherent X-ray radiation scattering in a target is on the order of 10 nm. The obtained results make it possible to suggest that using polarization bremsstrahlung as a new method for the diagnostics of the atomic structures of nanodisperse polycrystals is effective.

Role of the interface on the magnetoelectric properties of BaTiO3thin films deposited on polycrystalline Ni foils

BaTiO3 (BTO) thin films were deposited on polycrystalline Ni foils using a chemical solution approach. We show that the interface between the BTO film and the Ni foil plays a critical role in determining the magnetoelectric (ME) properties of this flexible assembly, which is likely to be related to the evolution of nickel oxide at the interface during the growth of BTO films. Our results have demonstrated that not only a well-controlled interface between the BTO film and the Ni substrate can be achieved, but also an ME voltage coefficient as large as 90 mV cm−1 Oe−1 can be accomplished.

Experimental study of polarization bremsstrahlung from small-grained polycrystals

The spectrum of polarization Bremsstrahlung is measured in backscattering geometry for 7-MeV electrons and a polycrystalline Ni foil without texture. The average size of grains in the foil is 300 nm. The results show the possibility of using a new method in the diagnostics of the atomic structure of polycrystalline materials with nanosized grains. The method is based on measuring the coherent component of polarization Bremsstrahlung.

Graphene production by dissociation of camphor molecules on nickel substrate

A chemical vapor deposition (CVD) process for the production of continuous-high quality-graphene layers based on camphor decomposition on polycrystalline Ni foil, is demonstrated. In situ X-ray diffraction at the pyrolysis temperature of the Ni foil indicates the presence of dominant Ni <111> grains which play an important role in the carbon nucleation and growth. The topography of the grown graphene layers is studied by scanning electron microscopy and atomic force microscopy which show that the Ni surface is covered by continuous and wrinkled graphene carpets. Raman spectroscopy reveals the high quality of the graphene film which appears to be only a few monolayers thick. X-ray photoelectron spectroscopy indicates the existence of graphitic layers and the absence of any spectral features associated with carbides (NixC). The proposed CVD process is a sufficient method for large scale production of graphene films.

A study of the key parameters, including the crucial role of H2 for uniform graphene growth on Ni foil

In this work we present a low-cost, scalable technique to fabricate few-layer graphene films via ambient pressure chemical vapor deposition (CVD) on a low-cost commercial polycrystalline Ni foil. Critical parameters including Ni thickness, cooling rate, and polycrystalline crystallographic orientation have been explored to understand the graphene formation mechanism and to obtain controlled carbon growth. We have studied the effect of operating conditions such as the synthesis time and feed composition, as well as the key role played by H2. The effect of the foil position in the reactor with respect to the feed flow was reported: the back Ni surface, not exposed to the feed flow, shows an increased carbon deposition with respect to the front one. An increase of the segregation and precipitation phenomena, as a function of the cooling rate and under Ni thickness increase was observed. By decreasing the synthesis time, it is possible to obtain 1L on areas showing an increased Ni(111) diffraction peak intensity. By varying the hydrogen concentration it is possible to control the final graphene formation on the nickel surface, obtaining quite uniform 2–3-layer graphene.

Optimized growth and dielectric properties of barium titanate thin films on polycrystalline Ni foils

Barium titanate (BTO) thin films were deposited on polycrystalline Ni foils by using the polymer assisted deposition (PAD) technique. The growth conditions including ambient and annealing temperatures were carefully optimized based on thermal dynamic analysis to control the oxidation processing and interdiffusion. Crystal structures, surface morphologies, and dielectric performance were examined and compared for BTO thin films annealed under different temperatures. Correlations between the fabrication conditions, microstructures, and dielectric properties were discussed. BTO thin films fabricated under the optimized conditions show good crystalline structure and promising dielectric properties with ∊r ∼ 400 and tan δ < 0.025 at 100 kHz. The data demonstrate that BTO films grown on polycrystalline Ni substrates by PAD are promising in device applications.

Stencil mask methodology for the parallelized production of microscale mechanical test samples

A new methodology to parallelize the production of micromechanical test samples from bulk materials is reported. This methodology has been developed to produce samples with typical gage dimensions on the order of 20-200 μm, and also to minimize the reliance on conventional focused ion beam fabrication methods. The fabrication technique uses standard microelectronic process methods such as photolithography and deep-reactive ion etching to create high aspect ratio patterned templates-stencil masks-from a silicon wafer. In the present work, the stencil mask pattern consists of a linear row of tensile samples, where one grip of each sample is integrally attached to the bulk substrate. Once fabricated, the stencil mask is placed on top of a pre-thinned substrate, and the pattern and substrate are co-sputtered using a broad ion beam milling system, which ultimately results in the transfer of the mask pattern into the substrate. The methodology is demonstrated using a Si stencil mask and a polycrystalline Ni foil to manufacture an array of metallic micro-tensile samples.

Synthesis of graphenes on Ni foils by chemical vapor deposition of alcohol with IR-lamp heating

We report the synthesis of single-layer graphenes on polycrystalline Ni foils by alcohol-based chemical vapor deposition (CVD) with IR-lamp heating. Heating with an IR lamp allows fast cooling and a reduction in the overall CVD time because of the rapid thermal processes in the heating and cooling stages. Spatially resolved Raman spectroscopy shows that single-layer graphenes are synthesized by CVD of alcohol with IR-lamp heating. The effects of the reaction temperature and alcohol type on the number of layers and graphene quality are investigated.