Composition depth profile analysis of electrodeposited alloys and metal multilayers: the reverse approach

The reverse depth profile analysis is a recently developed method for the study of a deposit composition profile in the near-substrate zone. The sample preparation technique enables one to separate the deposit and a thin cover layer from its substrate, and the initial roughness of the sample is much smaller than in the conventional sputtering direction. This technique is particularly suitable to study the zones being formed in the early phase of the electrodeposition of alloys. It has been demonstrated with the reverse depth profile analysis that in many cases when one component of an alloy is preferentially deposited, an initial zone is formed that is rich in the preferentially deposited component. This phenomenon is demonstrated for Ni–Cd, Ni–Sn, Fe–Co–Ni, Co–Ni, and Co–Ni–Cu alloys. The composition change is confined to the initial 150-nm-thick deposit, and it is the result of the interplay of the deposition preference and the depletion of the electrolyte near the cathode with respect to the ion reduced preferentially. The reverse depth profile analysis made it possible to compare the measured and the calculated composition depth profile of electrodeposited multilayers. It has been shown that the decay in the composition oscillation intensity in Co/Cu multilayers with the increase of the sputtering depth can be derived from the roughness measured as a function of the deposit thickness.

     

Spontaneous near-substrate composition modulation in electrodeposited Fe–Co–Ni alloys

Conventional and reverse depth profile analysis of electrodeposited Fe–Co–Ni alloys was performed by secondary neutral mass spectrometry (SNMS). It was found that the reverse sputtering method gave a much better depth resolution at the vicinity of the substrate. The reverse SNMS spectra showed that the deposition of Fe–Co–Ni alloys starts with the formation of an Fe-rich zone followed by an increase in Co concentration, then the nickel content increases and a steady-state alloy composition is achieved. At high current density, the initial depth pattern reproduces itself twice before the composition becomes stable. It was concluded that the varying depth profile is a consequence of the anomalous nature of the codeposition of the alloy components, the depletion of the electrolyte with respect to the metal salts, and the dependence of the intensity of the hydrogen evolution on the deposit surface composition.     

Nanoscale Co/Cu Multilayers Investigated by Analytical TEM and AES

 Concentration profiles of sputtered and pulsed laser deposited nanoscale Co/Cu multilayers have been measured by EDXS and EELS line scans in scanning mode at electron microscopic cross section foils and by AES depth profile analysis. The interpretation of the results has been supported by model calculations. After deposition, the pulsed laser deposited multilayers are stronger mixed than the sputtered layers. They decompose during annealing.     

Formation of a tetragonal Cu3Au alloy at gold/copper interfaces

A gold–copper alloy with a nominal composition of Cu₃Au but with a tetragonal (c = 4a) structure is observed to form at Au/Cu interfaces of gold/copper multilayers deposited on amorphous substrates by d.c. magnetron sputtering. The formation of this non‐equilibrium structure (tentatively D0₂₃) under‐ambient conditions is detected by secondary ion mass spectrometry, x‐ray diffraction and high‐resolution cross‐sectional transmission electron microscopy. Co‐sputtering of Au and Cu under similar conditions produces only conventional fcc Cu₃Au alloy phases, suggesting that interfacial confinement plays a significant role in producing the novel Cu₃Au alloy phase in gold/copper multilayers. Copyright © 2003 John Wiley & Sons, Ltd.     

Thermodynamic investigations on the component dependences of high-entropy alloys

In the present research, a study on the thermodynamical properties of the quinary Co–Cu–Cr–Fe–Ni high-entropy alloys and ternary Ca–Sb–Yb is carried out by the models Kohler, Chou’s general solution method (GSM) and Muggianu. The dependences of composition variation on thermodynamic properties, such as enthalpy of mixing of Co–Cu–Cr–Fe–Ni alloys in simple FCC phase are investigated at the temperatures 1273, 1373, and 1473 K. Moreover, a comparison between the results of the three models and those of other theoretical models shows good mutual agreement.     

Multilayered Cu–Ti deposition on silicon substrates for chemiresistor applications

Abstract

On the perspective to develop CuO–TiO₂ MOS, multilayered Cu and Ti thin layers were alternatively deposited on silicon wafers using 25?keV Ar?+?ion beam sputtering and, subsequently, oxidized by thermal annealing in air at 400?°C for 24?h. The deposited films have variable ratios of the Cu and Ti % at. One of the main goal is to obtain such multilayers avoiding the presence of Cu–Ti–O compounds. The samples were characterized in terms of composition (by RBS and SIMS analyses) and morphology (by AFM and SEM investigations). In particular, SIMS maps allows to observe the spatial distribution and thickness of each phase of the Cu/Ti multilayers, and further to observe Cu diffusion and mixing with Ti, as well as phase separation of CuO and TiO₂ in the samples. The reasons of this effect represent an open issue that has to investigated, in order to improve the MOS fabrication.     

Electrodeposition of nanocrystalline Ni–Cu alloy from environmentally friendly lactate bath

A new environmentally friendly electroplating bath for Ni–Cu alloy deposition was developed. Lactic acid was used as a complexing agent. The influence of bath composition, current density, pH and temperature on cathodic polarization, cathodic current efficiency and alloy composition was studied. Different proportions of the two metals were obtained by using different deposition parameters, but at all [Ni²⁺] / [Cu²⁺] ratios studied, preferential deposition of Cu occurred and regular co‐deposition took place. The Ni content of the deposit increased with Ni²⁺ content and current density and decreased with temperature. The surface morphology of the deposited Ni–Cu alloy was investigated using scanning electron microscopy. The crystal structure was examined using the X‐ray diffraction technique. The results showed that the deposits consisted of a single solid solution phase with a face‐centered cubic structure. The crystallite size lies in the range of 12 to 25 nm for as‐plated alloys. Copyright © 2014 John Wiley & Sons, Ltd.     

Backscattering effect in quantitative AES sputter depth profiling of multilayers

AES sputter depth profiles of multilayers with constituents of very different backscattering factors show characteristic distortions in the shape of the intensity–depth profiles. These distortions are quantified by introducing an extension of the local effective backscattering factor concept developed in an earlier paper in the mixing‐roughness‐information depth (MRI) model for profile quantification. The extension is based on a linear superposition of two newly defined parameters, the effective backscattering factors for each interface that are diminished with distance from the respective interface by another characteristic parameter, the mean effective backscattering decay length. As shown for a Ni/C multilayer structure of six alternating layers of Ni (38 nm) and C (25 nm) on a Si substrate, AES intensity depth profiles calculated with the presented modification of the MRI model, yield an excellent agreement with the measured profile after some adjustment of the initial mean effective backscattering decay lengths and, sometimes, after a slight change of the backscattering factors given by the Ichimura–Shimizu relations. The backscattering effect is studied as a function of the single layer thickness. A critical layer thickness can be determined, below which the backscattering influence becomes negligible for typical AES depth profiling results. Copyright © 2007 John Wiley & Sons, Ltd.     

The evolution of growth morphology and corrosion behavior of electrodeposited Ni–P coatings on alumina borate whisker‐reinforced pure aluminum composite

The Ni–P alloy coatings were obtained on alumina borate whisker‐reinforced pure aluminum composite by electro‐deposition. The initial electro‐deposition behavior of the Ni–P alloys on the composite and pure aluminum was studied, respectively. It was found that the composition and the morphology of materials had a distinct effect on the initial electro‐deposition behavior of the Ni–P alloys. The Ni–P alloy coatings preferred to nucleate at the composite as compared with the pure aluminum. Moreover, the Ni–P particles were prone to deposit at the whisker/Al interface in the composite. The Ni–P coatings were barely depositing upon the surface of whisker during the plating process. As the deposition time increased, the Ni–P particles that were deposited on the surface of the composite grew gradually. These Ni–P particles linked to each other and eventually covered the whisker surface. Moreover, it can be found that the surfaces of the composite were gradually covered by Ni–P coatings and the anticorrosion performance of the coated composite increased remarkably with the increase in the deposition time. When the deposition time is 60 min, only the Ni–P diffraction peak could be detected. In this case, the coated composite had significantly better corrosion resistant, which is attributed to the surface of composite was perfectly covered by the Ni–P coatings. Copyright © 2012 John Wiley & Sons, Ltd.     

Characterization of oxide layers on amorphous Mg-based alloys by Auger electron spectroscopy with sputter depth profiling

Amorphous ribbons of Mg-Y-TM-[Ag] (TM: Cu, Ni), prepared by melt spinning, were subjected to electrochemical investigations. Oxide layers formed anodically under potentiostatic control in different electrolytes were investigated by AES and sputter depth profiling. Problems and specific features of characterization of the composition of oxide layers and amorphous ternary or quaternary Mg-based alloys have been investigated. In the alloys the Mg(KL(23)L(23)) peak exhibits a different shape compared to that in the pure element. Analysis of the peak of elastically scattered electrons proved the absence of plasmon loss features, characteristic of pure Mg, in the alloy. A different loss feature emerges in Mg(KL(23)L(23)) and Cu(L(23)VV). The system Mg-Y-TM-[Ag] suffers preferential sputtering. Depletion of Mg and enrichment of TM and Y are found. This is attributed mainly to the preferential sputtering of Mg. Thickness and composition of the formed oxide layer depend on the electrochemical treatment. After removing the oxide by sputtering the concentration of the underlying alloy was found to be affected by the treatment.     

Microdistributions of Electrolytic Alloys and Their Components

Microdistributions of Cu–Ni and Cu–Co alloys electrodeposited from pyrophosphate; Ni–Cu, from sulfate–chloride and pyrophosphate–ammonium; Cu–Zn, from pyrophosphate and cyanide; Cu–Cd, from sulfate and pyrophosphate; and Ni–Cd, Ni–Co–Cd, and Zn–Cd, from sulfate, sulfate–chloride, pyrophosphate, chloride–ammonium, and acetate electrolytes are studied. The coatings' microprofile depends on the kinetics of reduction of each component and mutual influence of electrochemical processes at the cathode. Copper accelerates and cadmium inhibits the reduction of the second component of alloys, no matter the electrolyte type, reduction kinetics, and metal nature. In antileveling conditions, the diffusion-controlled Cu reduction accelerates the reduction of the second component of alloys and ensures deposition of coatings whose microprofiles are more uniform than expected from diffusion limitations only. Depolarizing action of Cu during the Cu–Zn deposition from a cyanide electrolyte can completely neutralize differences in the rates of supply of reduced metal ions; hence a constant chemical composition of the coating over its microprofile. Inhibiting action of the diffusion-controlled Cd deposition provides for leveling properties of electrolytes from which Ni–Cd, Ni–Co–Cd, and Zn–Cd alloys are deposited; the chemical composition of these deposits is nonuniform over their microprofiles.     

A comparison of electrochemical and Auger analysis of the surface composition of platinum-rhodium alloys

Values of the surface composition of platinum-rhodium alloys determined electrochemically, utilizing the potential of the oxygen desorption peak on cyclic voltammograms, have been compared with those obtained by Auger electron spectroscopy (a.e.s.). This comparison confirms that the electrochemical method is applicable to analysis of the surface of cycled as well as untreated homogeneous noble metal alloys. The composition profile in the surface region of cycled electrodes was determined by sputtering of the surface followed by a.e.s. measurements. The rhodium content was found to increase linearly with depth. The depth scale was established from analyses of the metal dissolved during potential cycling. Consideration of the differences between data obtained from the electrochemical and a.e.s. studies leads to the conclusion that the surface zone involved in chemisorption extends over a few atomic layers.     

Characterization of electrodeposited Co + Ni alloys by application of the ALSV technique Professor Aleksandar Despic to commemorate his 70th birthday

Anomalous codeposition of Co and Ni onto a gold RDE was investigated in a solution containing simple sulfate salts with the addition of sodium citrate. It was shown that the dependence of the percentage of Co in the deposit on the percentage of Co in the bath follows the shape found in the literature, with the percentage of Co in the deposit being slightly higher than in electrolytes containing pure simple salts. Alloy layers of different composition, electrodeposited at constant charge Q_dep = 1 C cm⁻² (thickness 0.34 μm) were submitted to anodic dissolution at a sweep rate of 1 mV s⁻¹ (ALSV technique) in a solution of 1 M NaCl, pH 2. All samples were found to dissolve through a single anodic peak, indicating that both constituents of the alloy dissolve simultaneously. Alloys with higher Ni content (above 40at.%) were found to dissolve at potentials more positive than the potential of pure Ni dissolution as a consequence of the Gibbs energy change of formation of electrodeposited solid solution type Co + Ni alloys. The composition of electrodeposited alloys was determined by the atomic absorption technique. An attempt was made to obtain a correlation between the peak potentials of anodic dissolution of alloy samples and the composition of alloys, to determine the composition of the alloy from the peak potential of its dissolution. It is found that such a correlation can be used only for strictly defined conditions of alloy deposition and dissolution, caused by the contribution of the Gibbs energy change of formation of electrodeposited alloys. Also, the presence of a CoNi₃ ordered structure in the system is not detected as a separate ALSV peak, but its existence could be the cause of the shape of the Gibbs energy change with composition of the alloy for alloys electrodeposited at low current density.     

Nanotechnology – a challenge for solid state analysis

The characterisation of nanoscaled structures is an essential part of nanotechnology. Using nanoscaled Co/Cu multilayers as an example of magnetoelectronic devices, the dependence of the layer formation mechanism on the deposition method (pulsed laser deposition and sputtering) is shown. The evolution of the thermal deterioration of Co (2 nm)/Cu (2 nm) multilayers during annealing can be understood using a combination of Monte-Carlo simulations and observations of intermediate steady states. It is shown that analytical TEM, especially energy-filtered imaging, is excellently qualified for this kind of characterisation.     

Inter‐diffusion effects in as‐deposited Al/Ni polycrystalline multi‐layers

Al/Ni multi‐layers, deposited by magnetron sputtering at room temperature have been studied by complementary techniques; XPS, sputter depth profiling, electron‐induced X‐ray emission spectroscopy (XES) and X‐ray diffraction (XRD). XPS depth profile technique evidenced an atomic diffusion dominated by Ni atoms. Moreover, the Ni diffusion results in the formation of an amorphous phase with a stoichiometry close to the Al₃Ni aluminide. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of electrolyte and agitation on the anomalous behavior and morphology of electrodeposited Co–Ni alloys

This study continues previous work which showed that the anomalous behavior of Co–Ni deposition could be alleviated or eliminated through use of cyclic voltammetry (CV) or pulse reverse (PR) plating. The research focuses on aspects not considered in this previous work: the effects of the anion and agitation in the plating bath. A comparison is made of Co–Ni electrodeposition using the CV and PR techniques in sulfate and chloride baths at pH 3 containing equimolar Co(II) and Ni(II) concentrations under both stirred and unstirred conditions. The anomalous behavior can be significantly suppressed and even eliminated with current efficiencies above 90 % through use of PR plating, in particular, but only if carried out in a chloride solution under quiescent conditions. Both metal ion reduction during the cathodic portion and oxidation of the coating during anodic polarization are accelerated in the chloride solution relative to that in the sulfate solution. Electrolyte agitation exacerbates anomalous deposition and reduces the current efficiency by enhancing mass transport of Co(II) and H⁺ to and from the electrode. The origin of anomalous deposition and effects of the chloride ion are examined in terms of coordination chemistry and ligand field theory. This analysis suggests that oxidation of the Co–Ni coating in the chloride solution during anodic polarization of the PR and CV cycles when cobalt preferentially dissolves is crucial to suppressing the anomalous behavior. Examination of the coatings shows that the anion type, degree of agitation of the electrolyte, and electroplating technique significantly affects their microstructure and roughness.     

Enhanced high-temperature cycle performance of LiFePO4/carbon batteries by an ion-sieving metal coating on negative electrode

LiFePO₄/mesocarbon microbead (MCMB) cells of which the carbon electrodes were, respectively, coated with different metal layers were characterized for their charge/discharge cycle performance at 55 °C. The examined metals included Au, Cu, Fe, Ni, Co, and Ti, and the superficial layers were 30–50 nm in thickness and deposited by vacuum sputtering. It was found that the presence of a either Au or Cu layer remarkably reduces capacity fading, while the rest metals only accelerate fading. There was observed a consistent trend between the capacity fading rate and the amount of the soild-electrolyte-interphase (SEI) deposition; the faster the capacity fading, the greater amount of SEI materials appearing on the surface of cycled carbon electrode. Microscopic and composition analyses indicates that the superficial Au and Cu layers act as a sieve to collect the Fe ions that result form erosion of LiFePO₄ before they diffuse into the interior of the carbon electrode, and that the so-deposited Fe particles do not show the tendency to catalyze the SEI formation, as in contrast to those directly deposited on the carbon surfaces.     

Properties of electrodeposited ni/cu multilayer structures

The interface structure and magnetic properties of electrodeposited Ni/Cu multilayers have been investigated. The layer thickness of both Cu and Ni range from 200 to 6000Å. The Ni and the Cu layers are polycrystalline with a dominant (111) fibre texture. The magnetization and M-H loops of the samples were determined using a vibrating sample magnetometer (VSM). Ferromagnetic resonance (FMR) was observed at 9.8 GHz. The linewidth of the granular multilayer is attributed either to some roughness or to small fluctuations of magnetization and is about 1.5 kOe when the applied magnetic field is in the plane of the film.     

Cathodic deposition of ternary In+As+Sb alloys and formation of InAsxSb1−x

In+As+Sb alloys have been deposited onto Ni and Ti cathodes from tartaric acid solutions at pH 2. Homogeneous deposits of composition suitable for achieving InAs_xSb_1−x can be obtained from this medium. The As-to-Sb ratio can be controlled by properly selecting solution composition and deposition potential.X-ray photoelectron spectroscopy and X-ray diffraction analyses show that formation of III–V compounds occurs at room temperature. In reacts preferentially with As rather than with Sb, but crystalline phases formed at room temperature are Sb-rich. After annealing the In+As+Sb alloys at 250°C, the composition calculated from cell parameters appears similar to that measured by energy-dispersive X-ray analysis, suggesting that the entire deposit has been converted into the InAs_xSb_1−x crystalline phase.     

The Structural Fate of Individual Multicomponent Metal‐Oxide Nanoparticles in Polymer Nanoreactors

Multicomponent nanoparticles can be synthesized with either homogeneous or phase‐segregated architectures depending on the synthesis conditions and elements incorporated. To understand the parameters that determine their structural fate, multicomponent metal‐oxide nanoparticles consisting of combinations of Co, Ni, and Cu were synthesized by using scanning probe block copolymer lithography and characterized using correlated electron microscopy. These studies revealed that the miscibility, ratio of the metallic components, and the synthesis temperature determine the crystal structure and architecture of the nanoparticles. A Co‐Ni‐O system forms a rock salt structure largely owing to the miscibility of CoO and NiO, while Cu‐Ni‐O, which has large miscibility gaps, forms either homogeneous oxides, heterojunctions, or alloys depending on the annealing temperature and composition. Moreover, a higher‐ordered structure, Co‐Ni‐Cu‐O, was found to follow the behavior of lower ordered systems.