Cobalt Substrate Research Articles

Doping the Spin-Polarized Graphene Minicone on Ni(111).

In the attempt to induce spin-polarized states in graphene (Gr), rare-earth deposition on Gr/Co(0001) has been demonstrated to be a successful strategy: the coupling of graphene with the cobalt substrate provides spin-polarized conical-shaped states (minicone) and the rare-earth deposition brings these states at the Fermi level. In this manuscript, we theoretically explore the feasibility of an analogue approach applied on Gr/Ni(111) doped with rare-earth ions by means of density functional theory calculations. Even if not well mentioned in the literature, this system owns a minicone, similar to the cobalt case. By testing different rare-earth ions, not only do we suggest which one can provide the required doping but we also explain the effect behind this proper charge transfer.

Ni–Fe Nanosheets Anchored on Porous Cobalt Substrate towards Oxygen Evolution Reaction

Ni–Fe Nanosheets Anchored on Porous Cobalt Substrate towards Oxygen Evolution Reaction

Investigation of novel suppressor Nitrotetrazolium Blue chloride on cobalt superconformal growth

It is significantly important to develop novel suppressor to achieve cobalt superconformal filling. Linear sweeping voltammetry (LSV) and impedance spectra (EIS) were coupled together to study the effect of novel dye suppressor nitrotetrazolium blue chloride (NBT) on cobalt electrodeposition. The adsorption behavior of NBT on cobalt substrate was investigated by applying density functional theory (DFT) calculation, molecular dynamics (MD) simulation and in situ Raman spectra, while the interaction between NBT and cobalt ions (Co2+) is analyzed based on topology analysis and interaction region indicator (IRI) analysis. Synergistic suppressing mechanism, namely adsorption effect and coordination effect, was proposed to explain the suppressing effect of NBT during cobalt electrodeposition. The cobalt surface morphology analysis under the influence of NBT demonstrates that NBT is of grain refinement, while XRD analysis indicates that the formation of Co hcp (100) is formed preferentially. The superconformal filling of cobalt is achieved in microvias with different diameters. The cobalt layer is of excellent quality due to low surface deposit thickness (SDT). The SDT values are 15.9 μm, 8.8 μm and 4.9 μm for 150 μm, 100 μm and 50 μm.

Effect of Residual Carbon on Spin‐Polarized Coupling at a Graphene/Ferromagnet Interface

AbstractVertical stacks of graphene and ferromagnetic layers are predicted to be efficient spin filters, while the experimentally observed figures of merit systematically remain below the theoretical predictions. According to general consensus, a vaguely defined interface contamination is found responsible for this discrepancy. Here, it is demonstrated how the spin‐polarized electronic structure of single‐layer graphene supported on a ferromagnetic cobalt substrate is affected by the presence of an interfacial carbidic buffer layer, formed by residual carbon present in the Co substrate. It is found that the Co‐C hybridized single‐spin state near the Fermi level disappears upon thermal segregation of bulk carbon at the graphene–Co interface, which determines the electronic decoupling of graphene from the ferromagnetic support and consequently, the suppression of net spin polarization. These observations are shown to be independent of the graphene azimuthal orientation with respect to the high symmetry directions of the substrate. The findings provide clear evidence that the realization of highly polarized spin currents in graphene/ferromagnet heterostacks depends on careful control of the graphene growth process in order to eliminate interfacial carbon.

Recent Advances in Electrodeposition of Copper Ultrathin Films on Cobalt Substrate

As the miniaturization trend in integrated circuits fabrication continues, alternative liner materials in copper interconnects have been actively explored. Cobalt has been widely investigated and employed due to its low resistance at nanoscales, integration compatibility, as well as benefit of improving copper electromigration resistance. However, direct electrodeposition of copper onto cobalt remains less explored due to the stability issue of cobalt in acidic copper damascene process. Subsequent processes of copper seeding and copper electroplating face increasing technical difficulties when widths and aspect ratios of electro-fill features become more challenging.Direct electrodeposition of copper on cobalt has been explored in acidic and alkaline chemistries, both of which were formulated by MacDermid Alpha Semiconductor Solutions. In both cases, well-adherent, nearly-pinhole-free, and ultrathin Cu has been successfully electrodeposited onto cobalt substrate with less than 10% cobalt loss. SEM images in Figure 1 imply uniform dispersion of copper on cobalt. XRF and ICP analysis confirm that the thinnest copper films deposited could be no thicker than 2 nm. Corrosion test in acidic copper plating bath shows that an ultrathin copper layer of thickness less than 2 nm can effectively suppress cobalt dissolution by a factor of three in comparison to non-coated bare cobalt.This work could pave the avenue towards direct copper electrodeposition onto cobalt liner in semiconductor manufacturing for advanced technology nodes. Figure 1. Top-down SEM images. (left) As-received cobalt substrate; (center) Cu of 2 nm nominal thickness electrodeposited on cobalt from an acidic solution; (right) Cu of 2 nm nominal thickness electrodeposited on cobalt from an alkaline solution. All three images have the same scale and scale bars are 200 nm. Figure 1

Электрохимический синтез интерметаллических соединений кобальта с неодимом в хлоридных расплавах.

The electrodeposition of neodymium on a cobalt substrate in a chloride-fluoride melt NaCl-KCl — 10 wt. % NaF — 5 wt. % NdF3was studied. It is shown that during electrolysis, a coating with a crystal size of 2–5 microns is formed. Microanalysis of the coating determined the electrocrystallization of the intermetallic compounds Co17Nd2 and Co5Nd on a cobaltsubstrate.

Tribological characteristics of electrical discharge coated layers using quarry dust suspension

In this research, a coating layer was formed on the tungsten carbide cobalt (WC-Co) substrate surface by using electrical discharge coating (EDC) with waste quarry dust powder suspension. The tribological test was carried out by using a micro pin-on-disc tribometer at a constant normal load (10N) and sliding speed (5 mm/s). The surface roughness, Vickers micro-hardness, coefficient of friction (CoF), wear weight loss, wear scar depth and wear track morphology of the coating layer were investigated and compared with the original surface of the WC-Co substrate in this study. The results indicated that under coating conditions of 5 A of peak current (Ip) and 300 μs of pulse on time (Ton), the Vickers micro-hardness increased by 28%, and the surface roughness, CoF, wear weight loss, and wear scar depth of coating layer reduced by 29%, 61%, 79%, 63%, respectively compared with the original WC-Co substrate. These results demonstrated that the coating layers produced by EDC with quarry dust waste powder suspension had good wear resistance, which could be beneficial to the cutting tool, mold and die industries.

Experimental and Theoretical Investigation of the Copper (II)/Co Cementation Reaction

Cobalt is a potential candidate as an adhesion layer in the copper metallization for its low resistivity and high thermal stability.(1) The electrodeposition of copper onto the cobalt substrate is a promising technique for the next generation interconnects. However, the cementation reaction of copper (II)/Co creates an irregular interface, and it’s not possible to apply the mature copper damascene plating technique.(2) In this work, we studied the Copper (II)/Co cementation reaction using a rotating disk electrode (RDE) and developed a continuum model to gain insight into the copper (II)/Co cementation reaction.Experimental section: a thin film of cobalt is firstly plated on the Pt RDE in a three-chamber cell filled with the electrolyte containing 50 mM CoSO4 and 0.5M H3BO3 (pH =2.6). A constant current is applied for a certain period of time (0.7 mA, 20 s) while the electrode is rotating at 700 rpm. The electrode is designated as Co/Pt electrode. After the deposition, the Co/Pt electrode is washed by ultrapure water and dried by nitrogen before it’s moved to another three-chamber cell. The electrode is immersed into the electrolyte containing 10mM CuSO4 and 50mM Na2SO4 while rotating at 900 rpm. The open-circuit potential is recorded in the whole process to identify the species and possible relations on the electrode surface.Figure 1 is the chronopotentiogram of a cobalt film reacting with copper(II) solution. As shown, fresh cobalt is replaced by the Cu in stage a, and a temporary equilibrium is reached in stage b, where the surface is a layer of newly formed metallic copper. A phase transition between copper and copper oxide is observed in stage c, and stage d represents a layer of CuOx, which is a dark color. (3) The intercept between stage and stage b will be used to extract the rate constant of the cementation reaction for modeling study. H.-S. Lu, J.-X. Wang, X. Zeng, F. Chen, X.-M. Zhang, W.-J. Zhang and X.-P. Qu, Electrochemical and Solid-State Letters, 15, H97 (2012).W.-Z. Xu, J.-B. Xu, H.-S. Lu, J.-X. Wang, Z.-J. Hu and X.-P. Qu, J Electrochem Soc, 160, D3075 (2013).J. Xiong and I. M. Ritchie, Hydrometallurgy, 16, 301 (1986). Figure 1

Obtaining of Nd-Co films by electrolysis in a chloride-fluoride melt

The electrodeposition of neodymium on a cobalt substrate in a chloride-fluoride melt NaCl-KCl-10 wt.% NaF-5 wt.% NdF3 was studied. It is shown that during electrolysis, a coating with a crystal size of 2-5 microns is formed. Microanalysis of the coating determined the electrocrystallization of intermetallic compounds Co17Nd2 and Co5Nd on a cobalt substrate.

Pyridinic-Type N-Doped Graphene on Cobalt Substrate as Efficient Electrocatalyst for Oxygen Reduction Reaction in Acidic Solution in Fuel Cell.

In this study, we use density functional theory to investigate the catalytic activity of graphene (G), single vacancy defective graphene (GSV), quaternary N-doped graphene (NGQ), and pyridinic N-doped graphene (NGpy, 3NGpy, and 4NGpy) on Co(0001) substrate for an oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). The results show pyridinic N-doped graphene on a Co support exhibited better performance than the NGQ on a Co support and free-standing systems. According to the results, ORR intermediates (*OOH, *O, and *OH) become more stable due to the presence of a Co substrate. The single pyridinic (3NGpy) layer placed on Co(0001) is the most active site. The overpotential for Co/3NGpy is rather higher compared to pure Pt(111) catalyst (0.65 V). Therefore, pyridinic N-doped graphene with a cobalt support could be a promising strategy to enhance the ORR activity of N-doped graphene in PEMFCs.

Electron Spin-Polarization Dependent Damage to Chiral Amino Acid l-Histidine.

The damage of approximately monolayer films of l-histidine by low-energy spin-polarized electrons (SPE) ejected from a magnetized cobalt substrate has been probed using X-ray photoelectron spectroscopy (XPS). Average damage cross sections for N-containing motifs of l-histidine are 25-30 and 2-5 Mb for zwitterions and neutral molecules, respectively. The magnetization direction of the substrate, which controls the ejected SPE helicity, was reversed in situ, and statistically significant differences in the damage cross sections of 10-30% were measured between positive and negative electron helicities. This is the first measurement of spin dichroism (SD) in an amino acid. The differential cross sections suggest that inelastic scattering of SPE with chiral molecules could contribute to the persistence of one enantiomer vs the other under certain irradiation conditions, particularly for the zwitterionic species.

Controlling βSn grain orientations in electronic interconnects with single-crystal Cobalt substrates

The reliability of electronic solder joints is strongly influenced by βSn grain orientations. Single-crystal Cobalt substrates were used to control βSn nucleation and grain orientations in solder joints. On (0001)Co, (112¯0)Co, (101¯0)Co, and (11¯02)Co, interfacial αCoSn3 crystals that are potent to catalyze βSn nucleation exhibited strong textures with 2–5 symmetric orientations featuring reproducible orientation relationships (ORs) with the Co. Preferred ORs and orientation selections of αCoSn3 were examined by exploring i) thermodynamic stabilities of interfaces represented by interfacial atomic matches and work of adhesion and interfacial energies calculated based on density functional theory (DFT) and ii) crystal growth kinetics indicated by the angle between (100)CoSn3 and the substrate plane. In sharp contrast to the innumerable grain orientations in joints on commonly used substrates, dramatically reduced orientations are attributed to the strongly textured αCoSn3, on which βSn grains nucleated by fixed ORs. On (112¯0)Co, the total number of orientations including twinned grains were reduced to 20. On (101¯0)Co, none of the βSn orientations exhibit the c-axis perpendicular to the substrate (i.e. parallel to the electron flow direction), which should reduce fast diffusion paths across the joint and improve the reliability of solder joints.

Thermal stability of polycrystalline diamond compact sintered with boron-coated diamond particles

The polycrystalline diamond compact (PDC), which consists of a polycrystalline diamond layer on a tungsten carbide (WC)/cobalt (Co) substrate, is extensively utilized as drilling bits. However, the poor thermal stability due to the graphitization and oxygen susceptibility of diamond severely limits the application of PDCs to high-temperature drilling work. In this study, a new PDC with improved thermal stability is successfully synthesized with boron (B)-coated diamond particles, which forms a uniform boron carbide (B4C) barrier. The as-received B4C phase acts as a protective barrier, which enhances the initial graphitization and oxidizing temperatures to 800 °C and 780 °C, respectively, which are ~100 °C and ~30 °C higher than those (700 °C and 750 °C) of the PDC sintered with uncoated diamond particles. The B4C barrier protects diamond grains from direct contact with the Co phase, prohibiting the cobalt-catalytic graphitization. In addition, the oxidation of the B4C barrier occurs prior to that of the diamond grains, which inhibits the PDC from oxidation.

Laser cladding process of Cobalt and Nickel based hard-micron-layers on 316L-stainless-steel-substrate

ABSTRACTIn the present study, two different types of coatings such as Cobalt (Co-Cr-W-C) and Nickel (Ni-Cr-B-Si-C) based layers have produced using a high power of Ytterbium-doped yttrium aluminum garnet (Yb:YAG) disk laser on 316L stainless steel substrate. Then the coatings were analyzed to expose their phase characterization, microstructure, and hardness using X-ray diffraction analysis, electron microscopes and microhardness tester. Further, tribo-test has performed through a ball-on-plate machine to analyze the wear properties of coatings. Besides, worn-surfaces of cladding and surface roughness have examined. The results showed that both Cobalt and Nickel based cladding have exhibited a dendrite homogeneous structure with some changes in shape and grain size due to higher cooling rates. XRD results indicate that the mixing of a γ-Co peak with other metastable phases such as Cr7C3 and Cr23C6 were noticed on Cobalt coating and γ-Ni rich matrix was the most dominant peak in Nickel-based coating. Microhardness of the cladding layers has remarkably increased than the substrate. The wear performance of Nickel cladding has increased than Cobalt cladding and substrate sample, which reveals that Nickel-based laser cladding plays a role in wear resistance. The analyzed wear track indicates that adhesion and abrasion were the two major wear mechanisms.

Syntheses and Catalytic Hydrogenation Performance of Cationic Bis(phosphine) Cobalt(I) Diene and Arene Compounds

AbstractChloride abstraction from [(R,R)‐(iPrDuPhos)Co(μ‐Cl)]2 with NaBArF4 (BArF4=B[(3,5‐(CF3)2)C6H3]4) in the presence of dienes, such as 1,5‐cyclooctadiene (COD) or norbornadiene (NBD), yielded long sought‐after cationic bis(phosphine) cobalt complexes, [(R,R)‐(iPrDuPhos)Co(η2,η2‐diene)][BArF4]. The COD complex proved substitutionally labile undergoing diene substitution with tetrahydrofuran, NBD, or arenes. The resulting 18‐electron, cationic cobalt(I) arene complexes, as well as the [(R,R)‐(iPrDuPhos)Co(diene)][BArF4] derivatives, proved to be highly active and enantioselective precatalysts for asymmetric alkene hydrogenation. A cobalt–substrate complex, [(R,R)‐(iPrDuPhos)Co(MAA)][BArF4] (MAA=methyl 2‐acetamidoacrylate) was crystallographically characterized as the opposite diastereomer to that expected for productive hydrogenation demonstrating a Curtin–Hammett kinetic regime similar to rhodium catalysis.

Improved Copper Damascene Wires Using Direct Plate on Cobalt Process

We preset an electrochemical damascene fill process for copper which is capable of direct nucleation and fill on a cobalt substrate. This process preserves the benefits of a cobalt liner while simultaneously reducing problems inherent in the use of a PVD copper seed on small interconnect features. The process depends upon the use of an additive which enhances the action of traditional damascene suppressors. This enables improved nucleation on the Co substrate without sacrificing the ability of the bath to produce the bottom-up fill typical of damascene Cu plating. We demonstrate good fill across a wafer on a thin, resistive cobalt substrate, producing lines with better electrical properties than a control created using PVD seed followed by a traditional damascene process. As integrated circuit features get smaller, the use of electrochemical copper metallization for interconnects has become more challenging. A major reason for this is the requirement for a PVD copper seed layer on top of a cobalt liner to enable traditional damascene plating. In very small features, the seed layer takes up a substantial portion of the feature volume. This produces a serious risk of voids as either the PVD itself or subsequent electrodeposition can close off the feature top before it has been filled with metal. One way to extend the manufacturability of copper interconnects is to eliminate the PVD copper deposition step entirely and instead plate directly on the cobalt liner. Direct plating of copper onto cobalt is a challenging problem. Cobalt dissolves readily in acidic solutions used for damascene Cu plating. Further, the reduction potential of Cu(II) is such that it will galvanically corrode Co substrates exposed to it. Copper has been successfully plated on cobalt, but previous attempts use heavily complexed alkaline baths to preserve the cobalt substrate. Unfortunately, both high pH and heavily complexed copper inhibit the ability of traditional damascene additives to produce good bottom up fill. Our approach to this problem has been to use an additive which improves the nucleation of Cu on Co not by complexing the Cu in the bulk solution, but by improving the ability of damascene suppressor molecules to quickly and effectively inhibit Cu plating on newly created Cu surfaces. This fast inhibition makes it more favorable for Cu nuclei to expand across the Co surface rather than growing in a more perpendicular direction. The faster passivation of the surface with Cu in turn dramatically reduces Co corrosion loss to the bath. Because this behavior is produced using traditional damascene additives, bottom up fill can be established after nucleation occurs if plating conditions are properly chosen. Good nucleation and fill on a 36nm pitch structure can be seen in the benchtop scale fill progression tests shown in Figure 1. Nucleation is slightly rougher than is observed when plating on a Cu substrate, but fill ability is sufficient to compensate. A Sabre electrodeposition tool from Lam Research was used to scale this process up to 300mm wafer plating. In Figure 2 electrical data statistics from these wafers are compared with similar results form a pair of control wafers plated using traditional damascene process on a PVD Cu substrate. A portion of this work was performed by the Research Alliance Teams at various IBM Research and Development facilities. Figure 1

Growth and characterization of multilayer hot-filament chemical vapor deposition diamond coatings on WC–Co substrates

The diamond coating of tungsten carbide (WC)–cobalt (Co) hard metals has been the focus of various research activities mainly due to growing interest in diamond-coated tools for industrial machining of different materials. In this work, multilayered diamond coatings have been grown on pretreated tungsten carbide–cobalt substrates by hot-filament chemical vapor deposition. Two types of multilayer coatings have been prepared: (a) three-layer (alternating nanocrystalline diamond and microcrystalline diamond films) and (b) five-layer (alternating ultrananocrystalline and microcrystalline diamond films). The morphology, roughness, structure, thickness, adhesion of these coatings have been investigated using atomic force microscopy, field emission gun scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, nanoindentantion and Rockwell C indentation tests at 600 N load. Raman spectra of the two types of samples exhibited sharp characteristic bands of nanocrystalline diamond and a centered peak at 1340 cm−1. The displacement of this peak in relation to the natural diamond peak (1332 cm−1) can be attributed to graphitic inclusions in diamond grain boundaries and the thermal coefficient mismatch of the multilayer coating–substrate system. Roughness surface measurements showed very smooth surfaces for both samples. Although the substrate has a high binder content, the results show that well-adhered chemical vapor deposition diamond multilayer coatings were produced.

Modeling of plasma-enhanced chemical vapor deposition growth of graphene on cobalt substrates

Two complementary modeling approaches (1D and 2D) are developed to explain the temperature-dependent growth kinetics of PECVD graphene formation on cobalt substrate. The gas temperature and the species concentrations are predicted for different process conditions by involving gas-phase and surface reaction mechanisms which consist of 15 gas species, 43 gas reactions, 10 surface species and 34 surface reactions. The influence of the growth temperature, the microwave power and the methane flow rate, affecting the gas species mole fractions in the reactor and the surface coverage is evaluated. The numerical results clearly indicate that the hydrogen atoms play an important role in the graphene growth in microwave plasma systems. A global sensitivity analysis is then performed in order to understand the basic mechanisms that lead to the transport of reactants by gas diffusion from the main gas stream through the boundary layer providing insight regarding the growth of graphene on the cobalt substrate.

Oxidation-resistant CoCrAl coatings fabricated by electrodeposition in combination with electrophoretic deposition

CoCrAl coatings are one type of overlay MCrAl coatings (M = Ni, Co, Fe or their combinations), which are normally fabricated by technologies of thermal spray and physical vapor deposition. In the work, CoCrAl coatings have been fabricated by a two-step method, which integrates electrophoretic deposition (EPD) and eletrodeposition (ED). The result shows that a pre-EPDed coating on a pure cobalt substrate consisting of CrAl and Cr nanoparticles mixture can be further EDed with Co from the EPD coating/cobalt substrate interface, forming a novel type CoCrAl nanocomposite coating. Oxidation of Co9Cr6Al and Co12Cr12Al coatings (by weight percentage) in air at 900 °C indicates that both coatings are alumina formers but the coating with higher nanoparticle content forms the continuous alumina layer in a shorter time, leading to a lower oxidation rate.

Giant magnetoresistance switching in multilayer graphene grown on cobalt

Magnetic multilayer devices, showing large magnetoresistance (MR) effects, have revolutionized magnetic sensing and data storage sectors over the last few decades. Two-dimensional van der Waals layered materials are relatively new entrants in this area, and these materials can give rise to large MR effects with diverse physical origins. Here we report observation of giant MR switching (∼10 orders of magnitude) in multilayered graphene grown on cobalt (Co) substrates, which persists even at room temperature. The origin of this effect is linked with weak interlayer coupling of the graphene stacks, which gives rise to an ‘interlayer MR’ effect. This effect is found to be robust against some degree of inhomogeneity in the graphene stack, making it an attractive platform for the emerging area of flexible magnetic sensorics.