Nickel Monolayers Research Articles

Extraordinary Catalytic Performance of Nickel Half‐Metal Clusters for Light‐Driven Dry Reforming of Methane

AbstractGlobal warming and the energy shortage due to the burning of fossil fuels are two major challenges. A strategy of light‐driven catalytic dry reforming of methane (DRM) using inexhaustible solar energy has provided an effective approach to tackle these challenges. Loaded metallic Ni nanoparticles have been identified as promising catalysts as alternatives to noble metals for DRM. However, they suffer from quick deactivation caused by severe coking due to thermodynamically inevitable side‐reactions. Herein, a unique nickel half‐metal catalyst of monolayer nickel clusters stabilized by alumina is reported, with 100% atomic utilization efficiency and extraordinary catalytic performance for light‐driven DRM, dramatically different from its counterpart of conventional metallic Ni nanoparticles. It has extremely high specific H2 and CO production rates of 8572.96 and 9614.26 mmol min−1 gNi−1, more than one order of magnitude higher than those of Ni nanoparticles. No detectable coke is formed due to the alteration of kinetic processes for DRM, resulting in the inhibition of coke deposition. It is discovered that light not only significantly enhances catalytic activity, but also enables quick thermocatalytic deactivation to be durable due to the oxidation of carbon species and the desorption of strongly adsorbed CO2 and CO being dramatically promoted by light.

Zn–Ni compositionally modulated multilayered alloy coatings for improved corrosion resistance

ABSTRACT Zinc–Nickel monolayer (single layer) and compositionally modulated multilayer alloy coatings were developed on to mild steel from acidic sulphate bath; and their corrosion performance were studied using potentiodynamic polarization and electrochemical impedance spectroscopy methods. The coating layers were formed galvanostatically by single bath technique, using square current pulses and triangular current pulses. For the best efficiency of the deposits against corrosion, the switched cathode current density and the number of layers were optimized. Under optimized conditions, Zn–Ni multilayer alloy coatings were produced at the current density 3.0/5.0 A dm−2 having 300 layers were ∼65 (square) and ∼48 (triangular) times more corrosion resistant respectively than the single layer alloy coating of the same thickness. Scanning electron microscopy has been employed to investigate, the formation of multilayer alloy coatings as well as the morphology of the surface before and after corrosion studies.

Improved the quality factor and sensitivity of a surface plasmon resonance sensor with transition metal dichalcogenide 2D nanomaterials

In this paper, design and modeling of a surface plasmon resonance (SPR) sensors using transition metal dichalcogenide (TMDC) 2D nanomaterials such as tungsten sulfide (WS2) and graphene with the improvements of the sensitivity and the figure of merit (FoM) are demonstrated. The proposed sensors are based on Kretschmann configuration for the obtaining of the reflectivity using the transfer matrix method (TMM) and Fresnel equations. A monolayer of nickel (Ni) was added between WS2 layers and graphene layers to enhance the sensitivity (S) and FoM of our proposed sensor. The reported sensor exhibits a good angular sensitivity which is improved to the maximum value of 243.31°/RIU. It is noted the SPR sensor sensitivity changes with the variation of the WS2 and graphene layer numbers. Full width half maximum (FWHM) values are minimized to be 7.15°; then, the FoM is reached to be 34.03 RIU−1 which gives better sensing properties in comparison with other published articles.

The Magnetism of a Ni Monolayer on Vanadium: Structure and Exchange Correlation Effects

The influence of structure and exchange correlation on the electronic and magnetic properties of a Nickel monolayer on Vanadium is investigated using the density functional theory with norm-conserving pseudopotentials. The Ni and Ni/V surfaces in the (001) direction have been simulated by using a seven layer slab to calculate the structural, electronic and magnetic properties. The bcc structure of the substrate V induces an artificial bcc structure for the Ni monolayer. This results in a quenching of the Ni surface magnetic moment due to expansion and d band hybridization. The results predict a ferromagnetic p1 × 1 Ni surface with negligible values of moments within the local density approximation (LDA) and the generalized gradient approximation (GGA) exchange correlations. In contrast, there is no agreement for the induced magnetism in the interfacial V layer for the two exchange correlations; the magnetic moment values obtained are ∼zero and 1.32 μB for LDA and GGA respectively.

Bifunctional Electrocatalytic Activity of Bis(iminothiolato)nickel Monolayer for Overall Water Splitting

The bifunctional catalysts for the hydrogen and oxygen evolution reactions (HER and OER) with high efficiency, low cost, and easy integration for future renewable energy systems are highly desirable. Here, on the basis of first-principles calculations, we predicted a two-dimensional (2D) metal–organic framework (MOF) bifunctional electrocatalyst, namely, bis(iminothiolato)nickel (NiIT) monolayer, for overall water splitting. The semi-metallic properties and low HER/OER overpotentials (−0.15/0.50 V) ensure the remarkable electrocatalytic performance of the 2D MOF electrocatalyst. The spatially separated HER and OER active sites with different electronegativities facilitate the electrocatalytic processes. Our findings highlight a promising precious-metal-free bifunctional electrocatalyst for efficient overall water splitting, as well as a novel strategy in catalyst design.

Strongly Enhanced Gilbert Damping in 3 d Transition-Metal Ferromagnet Monolayers in Contact with the Topological Insulator Bi2Se3

Engineering Gilbert damping of ferromagnetic metal films is of great importance to exploit and design spintronic devices that are operated with an ultrahigh speed. Based on scattering theory of Gilbert damping, we extend the torque method originally used in studies of magnetocrystalline anisotropy to theoretically determine Gilbert dampings of ferromagnetic metals. This method is utilized to investigate Gilbert dampings of 3d transition metal ferromagnet iron, cobalt and nickel monolayers that are contacted by the prototypical topological insulator Bi2Se3. Amazingly, we find that their Gilbert dampings are strongly enhanced by about one order in magnitude, compared with dampings of their bulks and free-standing monolayers, owing to the strong spin-orbit coupling of Bi2Se3. Our work provides an attractive route to tailoring Gilbert damping of ferromagnetic metallic films by putting them in contact with topological insulators.

Kane Fermion in a Two-Dimensional π-Conjugated Bis(iminothiolato)nickel Monolayer.

Massless Kane fermions revealed in zinc-blende semiconductors have recently gained interest in the broad study of relativistic materials. In particular, two-dimensional (2D) Kane fermions were expected to be hybrids of pseudospin-1 and -1/2 Dirac fermions. Based on first-principles calculations, we demonstrated that 2D Kane fermions can be realized in a recently synthesized metal-organic framework, namely, bis(iminothiolato)nickel monolayer. A slight compression takes the system from a semimetal to a semiconductor. At the critical strain of ∼1%, the upper and lower conical bands linearize and touch at a single point intersecting a flat band, showing the same dispersion as the pseudospin-1 Dirac-Weyl systems. We adopted a tight-binding Hamiltonian of a line-centered honeycomb lattice to reveal the origins and topology of the electronic band structure. The coexistence of Kane-type and Dirac-type spectra in the bis(iminothiolato)nickel monolayer is expected to benefit the study of multi quasiparticle effects.

Structure and Oxidation Behavior of Nickel Nanoparticles Supported by YSZ(111).

Nickel nanoparticles supported by the yttria-stabilized zirconia (111) surface show several preferential epitaxial relationships, as revealed by in situ X-ray diffraction. The two main nanoparticle orientations are found to have their [111] direction parallel to the substrate surface normal and ∼41.3 degrees tilted from this direction. The former orientation is described by a cube-on-cube stacking at the oxide–metal interface and the latter by a so-called coherent tilt strain-relieving mechanism, which is hitherto unreported for nanoparticles in literature. A modified Wulff construction used for the 111-oriented particles results in a value of the adhesion energy ranging from 1.4 to 2.2 Jm2, whereby the lower end corresponds to more rounded particles and the upper to relatively flat geometries. Upon oxidation at 10–3 Pa of molecular oxygen and 673 K, a NiO shell forms epitaxially on the [111]-oriented particles. Only a monolayer of metallic nickel of the top (111) facets oxidizes, whereas the side facets seem to react more severely. An apparent size increase of the remaining metallic Ni core is discussed in relation to a size-dependent oxidation mechanism, whereby smaller nanoparticles react at a faster rate. We argue that such a preferential oxidation mechanism, which inactivates the smallest and most reactive metal nanoparticles, might play a role for the long-term degradation of solid oxide fuel cells.

CO2 activation and dissociation on the low miller index surfaces of pure and Ni-coated iron metal: a DFT study.

We have used spin polarized density functional theory calculations to perform extensive mechanistic studies of CO2 dissociation into CO and O on the clean Fe(100), (110) and (111) surfaces and on the same surfaces coated by a monolayer of nickel. CO2 chemisorbs on all three bare facets and binds more strongly to the stepped (111) surface than on the open flat (100) and close-packed (110) surfaces, with adsorption energies of -88.7 kJ mol-1, -70.8 kJ mol-1 and -116.8 kJ mol-1 on the (100), (110) and (111) facets, respectively. Compared to the bare Fe surfaces, we found weaker binding of the CO2 molecules on the Ni-deposited surfaces, where the adsorption energies are calculated at +47.2 kJ mol-1, -29.5 kJ mol-1 and -65.0 kJ mol-1 on the Ni-deposited (100), (110) and (111) facets respectively. We have also investigated the thermodynamics and activation energies for CO2 dissociation into CO and O on the bare and Ni-deposited surfaces. Generally, we found that the dissociative adsorption states are thermodynamically preferred over molecular adsorption, with the dissociation most favoured thermodynamically on the close-packed (110) facet. The trends in activation energy barriers were observed to follow that of the trends in surface work functions; consequently, the increased surface work functions observed on the Ni-deposited surfaces resulted in increased dissociation barriers and vice versa. These results suggest that measures to lower the surface work function will kinetically promote the dissociation of CO2 into CO and O, although the instability of the activated CO2 on the Ni-covered surfaces will probably result in CO2 desorption from the nickel-doped iron surfaces, as is also seen on the Fe(110) surface.

Effect of nickel monolayer deposition on the structural and electronic properties of the low miller indices of (bcc) iron: A DFT study

Metal clusters of both iron (Fe) and nickel (Ni) have been found in nature as active electro-catalytic sites, for example in the enzyme carbon mono-oxide dehydrogenase found in autotrophic organisms. Thus, surface modification of iron with nickel could improve the surface work function to enhance catalytic applications. The effects of surface modifications of iron by nickel on the structural and electronic properties have been studied using spin-polarised density functional theory calculations within the generalised gradient approximation. The thermodynamically preferred sites for Ni adsorption on the Fe (100), (110) and (111) surfaces have been studied at varying monolayer coverages (including 0.25ML and 1ML). The work function of the bare Fe surfaces is found to be of the order (100) ∼ (111)<(110) i.e. 3.80eV∼3.84eV<4.76eV, which is consistent with earlier studies. The adsorption energies show that monolayer Ni deposition is thermodynamically favoured on the (100) and (111) surfaces, but not on the (110) surface. Expansion of the first interlayer spacing (d12) of all three Fe surfaces is observed upon Ni deposition with the extent of expansion decreasing in the order (111)>(110)>(100), i.e. 6.78%>5.76%>1.99%. The extent of relaxation is magnified on the stepped (111) surface (by 1.09% to 30.88%), where the Ni coordination number is highest at 7 compared to 5 on the (100) facet and 4 on the (110) facet. The Ni deposition changes the work functions of the various surfaces due to charge reordering illustrated by charge density plots, where the work function is reduced only on the (110) surface by 0.04eV, 0.16eV and 0.17eV at 1ML, 0.5ML and 0.25ML respectively, with a concomitant increase in the surface dipole (polarity). This result implies enhanced electron activity and electrochemical reactivity on the most stable and therefore frequently occurring Ni-doped (110) facet compared to the clean (110) facet, which has implications for the development of improved Fe electro-catalysts (for example for CO2 activation and reduction). These findings improve our understanding of the role of surface topology and stability on the extent of Ni interactions with Fe surfaces and the extent to which the Fe surface structures and properties are altered by the Ni deposition.

Thermal Joining of Highly Conductive Bonds by Using Reactive Al-Ni Nanofoils

In view of the demand for electrified long-range vehicles, the performance of traction batteries has to be improved. To achieve a high power density, the battery cells must be interconnected with low electrical resistance within the joints. The joining process has to fulfill specific requirements, as the battery cells may only be exposed to very low mechanical and thermal impacts. Joining by using reactive aluminum-nickel nanofoils represents an innovative technology meeting the abovementioned requirements. These foils are multilayered systems consisting of several hundred alternating monolayers of aluminum and nickel, each with a thickness in the nanometer range. Their unique ability is that they can react with temperatures up to 1500 °C for a duration of a few milliseconds upon external ignition. This thermal reaction energy serves as a heat source in the joining process, melting the materials in the interfacial surface. Subsequently, the joining partners solidify and form an adhesive bond when compressed properly. However, these advantageous characteristics are contrasted by complex reaction mechanisms and an unknown interaction of the process parameters. For the industrial application of the joining technology, the requirements for initiating the exothermic reaction must be known. Therefore, the process window and the mechanism of ignition have to be scrutinized. For this purpose, an experimental test setup was developed to generate and monitor short circuit currents to ignite the nanofoils. The amperage as well as the layer composition of the nanofoils were varied within a parameter study. Two independent process windows for a stable ignition were identified for all analyzed nanofoils.

Mechanical and wear characterization of electroless nickel mono and bilayers and high boron-mid phosphorus electroless nickel duplex coatings

Abstract The mechanical and wear properties of electroless nickel monolayer, bilayers and duplex NiP/NiB coatings were investigated in the as deposited state. Bilayers and duplex coatings, constituted of two layer of 10 μm each, were prepared according to four distinct configurations (NiB/NiP; NiP/NiB; NiB/NiB and NiP/NiP). Single layer coatings from each electroless nickel bath with a thickness of 20 μm were also synthesized and analyzed in this work: mid phosphorous NiP (nickel-phosphorus) and high boron NiB (nickel-boron). The microhardness, roughness and wear resistance of electroless nickel duplex coatings were compared with electroless NiP and NiB coatings of similar thickness. The hardness characteristics of duplex coatings are really influenced by the high hardness of NiB coatings: the hardness of pure NiP coatings was 550 HV while the presence of NiB coating as underlayer allowed to reach 738 HV. SEM observations of the cross-sections of the nickel duplex coatings also reveal that coatings are uniform with proper compatibility between layers.

Monolayer Nickel Cobalt Hydroxyl Carbonate for High Performance All-Solid-State Asymmetric Supercapacitors.

The emergence of atomically thick nanolayer materials, which feature a short ion diffusion channel and provide more exposed atoms in the electrochemical reactions, offers a promising occasion to optimize the performance of supercapacitors on the atomic level. In this work, a novel monolayer Ni-Co hydroxyl carbonate with an average thickness of 1.07 nm is synthesized via an ordinary one-pot hydrothermal route for the first time. This unique monolayer structure can efficiently rise up the exposed electroactive sites and facilitate the surface dependent electrochemical reaction processes, and thus results in outstanding specific capacitance of 2266 F g(-1). Based on this material, an all-solid-state asymmetric supercapacitor is developed adopting alkaline PVA (poly(vinyl alcohol)) gel (PVA/KOH) as electrolyte, which performs remarkable cycling stability (no capacitance fade after 19 000 cycles) together with promising energy density of 50 Wh kg(-1) (202 μWh cm(-2)) and high power density of 8.69 kW kg(-1) (35.1 mW cm(-2)). This as-assembled all-solid-state asymmetric supercapacitor (AASC) holds great potential in the field of portable energy storage devices.

Nickel-vanadium monolayer double hydroxide for efficient electrochemical water oxidation.

Highly active and low-cost electrocatalysts for water oxidation are required due to the demands on sustainable solar fuels; however, developing highly efficient catalysts to meet industrial requirements remains a challenge. Herein, we report a monolayer of nickel–vanadium-layered double hydroxide that shows a current density of 27 mA cm−2 (57 mA cm−2 after ohmic-drop correction) at an overpotential of 350 mV for water oxidation. Such performance is comparable to those of the best-performing nickel–iron-layered double hydroxides for water oxidation in alkaline media. Mechanistic studies indicate that the nickel–vanadium-layered double hydroxides can provide high intrinsic catalytic activity, mainly due to enhanced conductivity, facile electron transfer and abundant active sites. This work may expand the scope of cost-effective electrocatalysts for water splitting.

Underpotential Deposition of Nickel on Cu2o Films and Its Effects on Reactivity and Stability of Cu2o Films

Our studies on crystal facet and reactivity relationship suggest that the (111) face of Cu2O films electrodeposited from pH 12 cupric lactate solution is a preferred surface for photogeneration of H2 from water, owing to its polar O2--termination. In order to prevent photodecomposition of this Cu2O surface, which is initiated by interaction of the terminal O2- and H+ (Cu2O + 2H+ + 2e- --> 2Cu0 + H2O), while maintaining the attraction of H+ to the surface and potentially catalyzing H2 generation, we have attempted to deposit a monolayer of nickel via underpotential deposition (UPD). Underpotential deposition on oxides has not been explored much unlike the underpotential deposition on metals as a monolayer deposition method. Nickel was deposited on Cu2O films from a 0.08 M nickel acetate solution by applying various potentials for 1 min at room temperature. The Cu2O films with nickel deposited were dissolved in HNO3, and then the quantities of the deposited nickel at the various potentials were determined with atomic absorption spectrometry (AAS). The AAS results indicate that the underpotential deposition at -0.2 V vs. SCE (the calculated Nernst potential of the nickel solution is -0.49 V vs. SCE) deposited nickel that is equivalent to a 23 % monolayer coverage, corresponding to 60 kJ stronger interaction of Ni2+(aq) with O2- at Cu2O surface than with bulk Ni surface, as predicted for the polar Cu2O (111) face. For the estimate of the 100 % coverage of Cu2O surface, the atomic radius of Ni (124 pm) was used as well as the surface roughness of 1.09 obtained by atomic force microscopy measurements. At -0.3 V vs. SCE, more than a monolayer of nickel (205 %) was deposited. According to the x-ray photoelectron spectroscopy (XPS), the binding energy (BE) of Ni 2p3/2 electron changed from 855 eV for -0.2 V vs. SCE UPD sample to 851 eV for -0.3 V vs. SCE UPD sample. Since the BEs of 854.6 eV and 852.6 eV have been assigned for Ni2+ and Ni0, respectively, the XPS data indicate that the full reduction of nickel at the Cu2O surface occurs at potentials more negative than -0.2 V vs. SCE. The effects of underpotentially deposited nickel on the activity and stability of Cu2O films will be compared with respect to the deposition potential.

Computer simulation of the thermal stability of nickel films on two-layer graphene

The structure and the dynamic and mechanical properties of monolayer nickel films deposited on two-layer graphene are studied in the temperature range 300 < T < 3300 K by the molecular-dynamics method. A part of the Ni atoms remains on the graphene sheet even at T = 3300 K for both one- and two-sided coatings. The radial distribution functions of the upper and lower metal films differ significantly even at T = 300 K. The temperature dependence of the horizontal and vertical components of the self-diffusion coefficient of a one-sided nickel film exhibits a jump above 1800 K. No similar specific feature was observed for a two-sided coating of graphene with this film. The stress components acting in the nickel-film plane disappear with an increase in temperature for a shorter time in the case of one-sided coating.

Ultra-precision grinding of optical glasses using mono-layer nickel electroplated coarse-grained diamond wheels. Part 2: Investigation of profile and surface grinding

After finishing the precision conditioning of mono-layer nickel electroplated coarse-grained diamond wheels with 151μm (D151), 91μm (D91) and 46μm (D46) grain size, resp., profile and surface grinding experiments were carried out on a five-axis ultra-precision grinding machine with BK7, SF6 optical glasses and Zerodur glass ceramic. A piezoelectric dynamometer was used to measure the grinding forces, while an atomic force microscopy (AFM), white-light interferometer (WLI)) and scanning electron microscope (SEM) were used to characterize the ground surface quality in terms of micro-topography and subsurface damage. Moreover, the wear mechanics of the coarse-grained diamond wheels were analyzed and the grinding ratio was determined as well, in aiming to evaluate the grinding performance with the conditioned coarse-grained diamond wheels. Finally, the grinding results were compared with that of the fine-grained diamond wheels with regard to the ground specimen surface quality, process forces and wheel wear as a function of stock removal. The experimental results show that the precision conditioned coarse-grained diamond wheels can be applied in ductile mode grinding of optical glasses with high material removal rates, low wheel wear rates and no dressing requirement yielding excellent surface finishes with surface roughness in the nanometer range and subsurface damage in the micrometer range, demonstrating the feasibility and applicability of the newly developed diamond grinding technique for optical glasses.

Ultra-precision grinding of optical glasses using mono-layer nickel electroplated coarse-grained diamond wheels. Part 1: ELID assisted precision conditioning of grinding wheels

In order to realize ultra-precision grinding of optical glasses with mono-layer nickel electroplated coarse-grained diamond grinding wheels, a novel conditioning technique was developed using copper bonded diamond grinding wheels with grain sizes of 15μm (D15) and 91μm (D91), respectively, as conditioners for truing of diamond wheels with grain sizes of 46μm (D46), 91μm (D91) and 151μm (D151), respectively. During the conditioning process, the conditioners were continuously dressed by means of electrolytic in-process dressing (ELID). A force transducer was used to monitor the conditioning force while a coaxial optical distance measurement system was used to monitor the wheel run-out. In addition, a white-light interferometer (WLI) and a scanning electron microscope (SEM) were used to characterize the successively modified diamond grain morphologies of the conditioned wheels both directly and by a replication technique. The experimental results show that with optimized conditioning parameters, the developed conditioning technique can be applied for truing of coarse-grained diamond wheels within the abrasive layer achieving a constant wheel peripheral envelop surface exhibiting flattened diamond grains with a run-out <2.5μm, which is a prerequisite for introducing coarse-grained diamond wheels into ultra-precision machining of brittle and hard-to-machine materials.

An AFM Evaluation of Rhenium-Nickel Electrodeposit Nucleation on Copper

The electrodeposition of rhenium and rhenium alloys is well documented both in acidic1-5 and alkaline6,7 solutions. The effect of complexing agents as well as the catalytic effect of divalent nickel ions has also been extensively investigated2-4. It has been shown that Re-Ni electrodeposits consist of alternating layers of Ni-rich and Re-rich phases2. However, a detailed explanation of the origin of such layers as well as the electrodeposit nucleation process is still missing. The objective of the present work is threefold. First, we seek to elucidate the nucleation mechanism of Re-Ni alloys. AFM will be used to document the formation and growth of electrodeposit nuclei and delineate the progressive vs. instantaneous nucleation mechanism. Second, the multilayered structure of the Re-Ni deposits will be addressed by documenting the formation of the initial layer and its evolution over time. Finally, nickel deposits will be used as substrates for pure rhenium electrodeposition to test the hypothesis that a strike layer of nickel is necessary to promote the deposition of pure rhenium.Galvanostatic pulse methods were used to electrodeposit pure nickel and pure rhenium salts separately from citrate solutions on (111) single crystal copper substrates as well as mica-supported copper films. The results are compared with the electrodeposition behavior of Re-Ni bath mixtures. A very small time scale is needed to deposit a monolayer of nickel. Distinct differences in frictional force of the initial deposit nuclei was captured by AFM. Figure 1 shows the difference in frictional force between a bare copper surface (111) and nickel deposit on a copper (111) surface. Nickel was deposited electrochemically by exposing a copper surface (111) to a 96 mM nickel sulfamate solution under galvanostatic polarization for 1 ms at -53.0 mA/cm2. The spots observed in the frictional image are attributed to islands of nickel atoms that are too thin to be detected in the topography mode. Acknowledgements The authors gratefully acknowledge the financial support from AFOSR under grant FA9550-10-1-0520. References 1) S. Szabó and I. Bakos, J. Electroanal. Chem., 492, 103 (2000). 2) A. Naor, N. Eliaz, and E. Gileadi, Electrochim. Acta, 54, 6028 (2009). 3) A. Naor, N. Eliaz, L. Burstein, and E. Gileadi, Electrochem. and Solid-State Letters, 13, D91 (2010). 4) A. Naor, N. Eliaz, and E. Gileadi, J. Electrochem. Soc., 157, D442 (2010). 5) E. Méndez, M. F. Cerdá, A. M. Castro Luna, C. F. Zinola, C. Kremer, and María E. Martins, J. Colloid. Int. Sci., 263, 119 (2003). 6) L. E. Netherton and M. L. Holt, J. Electrochem. Soc., 99, 44 (1954). 7) A. Vargas-Uscategui, E. Mosquera and L. Cifuentes, Electrochim. Acta, 109, 283 (2013). 8) A. Duhin, A. Inberg, N. Eliaz, and E. Gileadi, Electrochim. Acta, 56, 9637 (2011).

Influence of low energy Ar-ion bombardment on monolayer Ni/W(1 0 0)

The changes in the morphological and structural properties of monolayer nickel thin films on tungsten induced by low energy Ar+ ion bombardment at varying fluencies have been explored using scanning tunneling microscopy and low energy electron diffraction, respectively, in this work. ~1 monolayer (ML) nickel films were grown on W(100) by electron beam evaporation under ultra high vacuum conditions at room temperature. It was found that the pseudomorphic growth observed in as-grown films was disrupted by the ion bombardment process with additional phases of Ni appearing in the ion bombarded samples. Increase in bombardment time lead to a pronounced phase transition to the hcp phase of Ni. Also, the ion bombardment induced the formation of larger nanostructures (with increasing particulate sizes) from the epitaxial monolayer in the as-deposited sample. Further, the magnetization and magnetic orientation were studied and it was observed that the bombardment induced a weak ferromagnetism in as-grown paramagnetic Ni film.