Influence of the electrical parameters on the fabrication of copper nanowires into anodic alumina templates

Metallic copper nanowires have been grown into the pores of alumina membranes by electrodeposition from an aqueous solution containing CuSO₄^.and H₃BO₃ at pH 3. In order to study the influence of the electrical parameters on growth and structure of nanowires, different deposition potentials (both in the region where hydrogen evolution reaction is allowed or not) and voltage perturbation modes (constant potential or unipolar pulsed depositions) were applied. In all cases, pure polycrystalline Cu nanowires were fabricated into template pores, having lengths increasing with the total deposition time. These nanowires were self-standing, because they retain their vertical orientation and parallel geometry even after total template dissolution.However, the electrical parameters influence the growth rate, length uniformity and crystal size of the nanowires. Continuous electrodeposition resulted in higher growth rates but less uniform lengths of nanowires grown inside different membrane pores, whilst a square pulse deposition produced a slower growth but quite uniform lengths. Also the grain size, of the order of 50 nm, was slightly influenced by the potential perturbation mode.     

Magnetic characteristics of thin Ni films electrodeposited on n-Si(1 1 1)

The nanocrystalline Ni films were grown on n-Si(1 1 1) substrate by pulsed electrodeposition in non-aqueous NiCl₂ + methanol solution. The frequency of potential pulse was modulated during the deposition of Ni onto Si substrates. When the frequency varies from 20 to 900 Hz, the average size of Ni nanocrystallites varied in the ranges from 48 to 130 nm. In these cases, all Ni films have grown through a three-dimensional instantaneous nucleation followed by diffusion-limited growth. From X-ray diffraction measurement, it has been found that Ni(1 1 1) grows preferentially on the Si(1 1 1) substrates. The magnetic hysteresis loops for as-deposited films were measured by using VSM. As the angle θ between film plane and applied magnetic field varies from 0 to 90, the coercivity (H_c) and squareness (S) obtained from the magnetic hysteresis loops showed an opposite behavior. With the increase in θ, H_c increased but S decreased near linearly. We have also investigated the variation of H_c as a function of Ni nanocrystallite’s size. From VSM measurement, we could observe that the coercivities for the magnetic field applied perpendicular and parallel to the film plane increase up to the average size of 86 nm but begin to decrease over this size.     

Corrosion behaviour of AISI 304 stainless steel with Cu coatings in H2SO4

The work addresses the influence of cementation and electrodeposition of copper coatings on the corrosion resistance of AISI 304 stainless steel immersed in 30 wt.% H₂SO₄ at temperatures of 25 and 50 °C. Corrosion process was evaluated by gravimetric tests, DC measurements and electrochemical impedance spectroscopy (EIS). The specimen surfaces were analysed by scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. The corrosion performance of AISI 304 stainless steel in sulphuric acid solution was greatly improved by copper coatings. The amount of copper deposited by the cementation process was sufficient to protect the stainless steel of corrosion. A greater amount of copper obtained by electrodeposition treatments does not supply further improvement in the corrosion behaviour. The improved corrosion resistance is related to copper dissolution at the initial stages of immersion tests and the presence of Cu²⁺ in the solution, which makes the medium more oxidizing, increasing the stability of the passive layer. In addition, the presence of copper at the surface reduces the overpotential of cathodic reaction, enabling the transition from an active region to the passive one.     

Evaluation of copper Chemical-Vapor-Deposition films on glass and Si(100) substrates

Thin films of pure copper have been deposited on glass and Si(100) substrates using copper acetylacetonate [Cu(acac)₂] and copper HexaFluoroAcetylacetonate [Cu(HFA)₂] sources. A thermal, cold-wall, reduced pressure (3325–5985 Pa) Metal-Organic Chemical Vapor Deposition (MOCVD) process was employed. The effect of H₂O vapor on the grain size, deposition rate, and resistivity was examined. Electrical resistivities of 2.4 cm for copper films deposited on Si(100) and 3.44 cm for copper films deposited on glass at substrate temperatures of 265° C and a [Cu(acac)₂] source temperature of 147° C with the use of H₂O vapor were measured. When [Cu(HFA)₂] was used, the substrate temperature was 385° C and the source temperature was 85° C. An activation energy for the copper film deposition process was calculated to be 22.2 kJ/mol in the case of the [Cu(acac)₂] source. A deposition rate of 11 nm/min was obtained with Cu(acac)₂ as the source and the rate was 44.4 nm/min with the Cu(HFA)₂ source; both were obtained with the use of H₂O vapor. No selectivity was observed with either source for either substrate. The deposited films were fully characterized using XRD, LVSEM, SAXPS, and RBS.     

Microstructures and electrical conductivity of nanocrystalline ceria-based thin films

Ceria-based thin films are potential materials for use as gas-sensing layers and electrolytes in micro-solid oxide fuel cells. Since the average grain sizes of these films are on the nanocrystalline scale (< 150 nm), it is of fundamental interest whether the electrical conductivity might differ from microcrystalline ceria-based ceramics. In this study, CeO₂ and Ce_0.8Gd_0.2O_1.9−x thin films have been fabrication by spray pyrolysis and pulsed laser deposition, and the influence of the ambient average grain size on the total DC conductivity is investigated. Dense and crack-free CeO₂ and Ce_0.8Gd_0.2O_1.9−x thin films were produced that withstand annealing up to temperatures of 1100 °C. The dopant concentration and annealing temperature affect highly the grain growth kinetics of ceria-based thin films. Large concentrations of dopant exert Zener drag on grain growth and result in retarded grain growth. An increased total DC conductivity and decreased activation energy was observed when the average grain size of a CeO₂ or Ce_0.8Gd_0.2O_1.9−x thin film was decreased.     

Laser deposition of amorphous diamond films from liquid aromatic hydrocarbons

6 H₅CH₃, C₆H₆, and C₆H₅CH(CH₃)₂) to pulsed visible laser radiation of a copper vapor laser (λ=510.6 nm). The X-ray Auger electron spectroscopy (XAES), reflection high energy electron diffraction (RHEED), and Raman analysis are employed to characterize the deposited films. The sp³ fraction in deposited films amounts to 60–70% and depends on the precursor. The average film thickness on a glass substrate is about 100 nm. The films show excellent adherence, are transparent in the visible and have microhardness of 50–70 GPa, as measured by nanoindentor. Received: 28 September 1998 / Accepted: 13 January 1999     

Effects of peak current density on the mechanical properties of nanocrystalline Ni-Co alloys produced by pulse electrodeposition

Cobalt content, grain size, microhardness and tensile strength of nanocrystalline Ni-Co deposits produced from a solution containing saccharin and cobalt sulfate at constant electrodeposition conditions (pulse on-time T_on at 1 ms and pulse off-time T_off at 15 ms) but varying the peak current density J_p were investigated. It is found that an increase in J_p makes the deposit Co content lower, colony-like morphology more obvious, grain size smaller, and hardness and tensile strength higher. All of the facts are believed to result from the higher overpotential and nucleation rates caused by the J_p increase. But its further increase could lead to reduction in the hardness and tensile strength. Peak current densities in the range of 100-120 A dm⁻² are recommended for the preparation of nanostructured Ni-Co alloy deposits with grain sizes in the range of 15-20 nm, containing 7-8% Co, possessing hardness of 590-600 kg mm⁻² and tensile strength of 1180-1200 MPa—significantly higher than the strength of pure nickel deposit which is produced by the similar method and gets similar grain size.     

Nanocrystalline Ni-B coating surface strengthening pure copper

An electroless deposition technique is used to synthesize nanocrystalline Ni-B coating in strengthening the surface of pure copper. The microstructure and some properties of Ni-B coating are studied. It is practicable to coat a uniform and continuous nanocrystalline Ni-B hardening layer on copper surface by this technique, Ni₂B and Ni₃B are formed in the Ni-B coated layer during heat treatment, and the average grain size of nanocrystalline Ni-B coating is about 42-65 nm and properties of the prepared copper alloys are also improved.     

Magnetic Properties of Grain Boundaries of Nanocrystalline Ni and of Ni Precipitates in Nanocrystalline NiCu Alloys

Perturbed γγ-angular correlation spectroscopy (PAC) was used to investigate nanocrystalline Ni and NiCu alloys, which are prepared by pulsed electrodeposition (PED). Using diffusion for doping nanocrystalline Ni with ¹¹¹In four different ordered grain boundary structures are observed, which are characterized by unique electric field gradients. The incorporation of ¹¹¹In on substitutional bulk sites of Ni is caused by moving grain boundaries below 1000 K and by volume diffusion above 1000 K. The nanocrystalline NiCu alloys prepared by PED are microscopically inhomogeneous as observed by PAC. In contrast, this inhomogeneity cannot be detected by X-ray diffraction. The influence of the temperature of the electrolyte, the current density during deposition, and the optional addition of saccharin to the electrolyte on the homogeneity of nanocrystalline NiCu alloys was investigated. This revised version was published online in September 2006 with corrections to the Cover Date.     

Microstructure, magnetic and magnetoimpedance properties in electrodeposited NiFe/Cu and CoNiFe/Cu wire with thiourea additive in plating bath

Magnetic thin films of NiFe and CoNiFe alloys were electrodeposited from three different deposition baths onto copper wires of 100-μm diameter. The magnetic and magnetoimpedance (MI) properties of the samples along with their microstructure were investigated as a function of thiourea additive concentrations (C_T) in the plating bath. For all intermediate frequencies, the MI ratio increased with thiourea concentration in plating bath up to a critical concentration of 80 mg/l and then decreased considerably. The change in MI with thiourea concentration in electrodeposition bath was attributed to the grain size reducing action of thiourea, which in turn enhances the soft magnetic properties of the films. At higher concentration of thiourea, the sulfur inclusion increased the magnetic softness and MI value enhanced considerably. The origin of MI lies in the combined effect of domain wall motion and spin rotation, which contributes to permeability. Inductance spectroscopy (IS) was used to evaluate the magnetic characteristic of the samples by modeling coated wires in terms of equivalent electrical circuit; namely parallel LR (inductance and resistance) circuit in series with series LR circuit. The domain wall motion was found to be greatly affected by thiourea addition in the bath, which was revealed through the study of variation of these circuit parameters. The domain wall motion thereby affects the magnetic softness of samples, which is reflected in the MI enhancement.     

Raman scattering studies of polycrystalline 3C-SiC deposited on SiO2 and AlN thin films

This paper describes the Raman scattering characteristics of the Raman spectra of 0.4- and 2.0-μm-thick polycrystalline (poly) 3C-SiC on AlN /Si and SiO₂/Si by using atmosphere pressure chemical vapor deposition (APCVD) with hexamethyldisilane (HMDS) and carrier gases (Ar+H₂). In the Raman spectra for all growth temperatures, the D and G peaks of nanocrystalline graphite were measured. The C/Si rate of poly 3C-SiC deposited in (Ar+H₂) atmosphere was higher than that in H₂ gas, although HMDS C/Si rate is 3. The biaxial stresses of 2.0-μm-thick 3C-SiC on SiO₂ and AlN, which was deposited at the growth temperature of 1180 °C after annealing AlN at 800 and 1100 °C, were calculated as 428 and 896 MPa, respectively. Therefore, poly 3C-SiC should admix with nanocrystalline graphite due to the addition of Ar gas and poly 3C-SiC on SiO₂ should be better than on AlN for harsh environmental MEMS applications.     

Electrochromic properties of nanocrystalline WO3 thin films grown on flexible substrates by plasma-assisted evaporation technique

Thin films of Tungsten trioxide (WO₃) were deposited on ITO-coated flexible Kapton substrates by plasma-assisted activated reactive evaporation (ARE) technique. The influence of growth and microstructure on optoelectrochromic properties of WO₃ thin films was studied. The nanocrystalline WO₃ films grown at substrate temperature of 250°C were composed of vertically elongated cone-shaped grains of size 65 nm with relative density of 0.71. These WO₃ films demonstrated higher optical transmittance of 85% in the visible region with estimated optical band gap of 3.39 eV and exhibited better optical modulation of 66% and coloration efficiency of 52.8 cm²/C at the wavelength of 550 nm.     

Influence of ultrasonic combined supercritical-CO2 electrodeposition process on copper film fabrication: Electrochemical evaluation

Introducing ultrasound irradiation to the electrodeposition process can significantly improve the physical and chemical properties of deposited films. Meanwhile, the beneficial effects from supercritical-CO_2, such as high diffusivity, high permeability, low surface tension, etc., would improve the electrodeposition process with better surface quality. In the shed of the light, the present work deals with the preparation of copper (Cu) films using the integrated techniques, i.e., ultrasonic-assisted supercritical-CO₂ (US-SC-CO₂) electrodeposition approach. For comparison, Cu films were also prepared by normal supercritical-CO₂ (SC-CO₂) and conventional electrodeposition methods. To investigate the characteristics of Cu films, surface morphology analysis, roughness analysis, X-ray diffraction studies (XRD), Linear polarization, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were performed. In this work, EIS analysis was utilized for interfacial charge transfer resistance analysis with 5 mM [Fe(CN)₆]^−3/−4 redox system and corrosion analysis with 3.5 wt% NaCl solution. The observed results revealed that the film prepared with the US-SC-CO₂ method have superior properties than those produced by normal SC-CO₂ and conventional methods. Due to the combination of US-SC-CO₂, the cavitation implosion occurs rapidly that enriches the deposited film quality, such as sufficient grain size, smoother surface, enhanced corrosion resistance, and charge carrier dynamics. On the other hand, the ultrasound effect with SC-CO₂ helped to remove the weakly adhered metal ions on the electrode’s surface.     

Growth of nanocrystalline TiO2 films by pulsed-laser-induced liquid-deposition method and preliminary applications for dye-sensitized solar cells

A novel technique, the pulsed-laser-induced liquid-deposition (PLLD) method, has been employed to grow nanocrystalline TiO₂ films on fluorine-doped tin-oxide-coated (FTO) glass substrates at room temperature. The PLLD method was implemented by directing a pulsed laser into a liquid precursor and depositing the photosynthesized nanocrystalline TiO₂ on an FTO glass substrate immersed in the liquid precursor. The as-grown nanocrystalline TiO₂ films were found to have a rutile crystal structure and consist of a number of flower-like TiO₂ crystal units arrayed together on the FTO glass substrate. Each of the flower-like TiO₂ crystal units was composed of many nanostructured TiO₂ whiskers, and their building blocks were found to be bundles of TiO₂ nanorods with diameter of about 5 nm. The growth of these TiO₂ nanorods is highly anisotropic, with the preferential growth direction along [001]. As-grown nanocrystalline TiO₂ films were annealed at 450°C in air for 30 min for the applications of dye-sensitized solar cells, and the nanostructured characteristics with good porosity were preserved after annealing. A preliminary dye-sensitized solar cell was built based on the annealed nanocrystalline TiO₂ film. The results suggest that the PLLD method is a promising technique for growing nanocrystalline TiO₂ films for photovoltaic applications.     

Grain size effect on the universality of AC conductivity in SnO2

Nanocrystalline tin oxide (SnO₂) material with different grain sizes was synthesized by using a chemical precipitation method. This material was characterized by using the X-ray diffraction and transmission electron microscopy. The electrical properties of compressed nanocrystalline SnO₂ were studied by using impedance spectroscopy. AC conductivity data for SnO₂ material having grain sizes between 9 and 34 nm were analyzed using a power law. The exponent n is found to be 0.5 for bulk (34 nm) and unity for material with grain size below 18 nm. The results show a universal behavior for very low average grain sizes and the non-universal behavior for larger grain sizes even at room temperature.     

Enhancement of coercivity with reduced grain size in CoCrPt film grown by pulsed laser deposition

We report a pulsed laser deposition (PLD) growth of VMn/CoCrPt bilayer with a magnetic coercivity (H_c) of 2.2 kOe and a grain size of 12 nm. The effects of VMn underlayer on magnetic properties of CoCrPt layer were studied. The coercivity, H_c, and squareness, S, of VMn/CoCrPt bilayer, is dependent on the thickness of VMn. The grain size of the CoCrPt film can also be modified by laser parameters. High laser fluence used for CoCrPt deposition produces a smaller grain size. Enhanced H_c and reduced grain size in VMn/CoCrPt is explained by more pronounced surface phase segregation during deposition at high laser fluence.     

Crystal microstructure of annealed nanocrystalline Chromium studied by synchrotron radiation diffraction

The microstructure of electrodeposited nanocrystalline chromium (n-Cr) was studied by using synchrotron radiation (SR) diffraction, SEM, TEM, and EDX techniques. The as-prepared n-Cr samples show the standard bcc crystal structure of Cr with volume-averaged column lengths varying from 25 to 30 nm. The grain growth kinetics and the oxidation kinetics were studied by time resolved SR diffraction measurements with n-Cr samples annealed at 400, 600, and 800 °C. The grain growth process is relatively fast and it occurs within the first 10 min of annealing. The final crystallite size depends only on the annealing temperature and not on the initial grain size or on the oxygen content. The final volume-averaged column lengths observed after 50 min annealing are 40(4), 80(1), and 120(2) nm for temperatures 400, 600, and 800 °C, respectively. It is shown that annealing ex situ of n-Cr at 800 °C both under vacuum and in air gives a grain growth process with the same final crystallite sizes. The formation of the Cr₂O₃ and CrH phases is observed during annealing.     

Investigation on upconversion photoluminescence of Bi3TiNbO9:Er:Yb thin films

Bi₃TiNbO₉:Er³⁺:Yb³⁺ (BTNEY) thin films were fabricated on fused silica by pulsed laser deposition. It was demonstrated that different laser fluence and substrate temperature during growth of BTNEY upconversion photoluminescence (UC-PL) samples control the film’s grain size and hence influences the UC-PL properties. The average grain size of BTNEY thin films deposited on fused silica substrates with laser fluence 4, 5, 6, and 7 J/cm² are 30.8, 35.9, 40.6, and 43.4 nm, respectively. The 525 nm emission intensities increase with the deposition laser fluence and the emission intensities of BTNEY thin film deposited under 700 and 600 °C are almost 24 and 4 times, respectively, as strong as those of samples under 500 °C. The grain size of BTNEY thin film increases with the increasing temperature. UC-PL of BTNEY films is enhanced by increasing grain size of the films.     

Room temperature mechanical behaviour of a Ni-Fe multilayered material with modulated grain size distribution

To gain fundamental insight into the relationship between length scales and mechanical behaviour, Ni-Fe multilayered materials with a 5-μm-layer thickness and a modulated grain size distribution have been synthesized by pulsed electrodeposition. Microstructural studies by SEM and TEM reveal the alternating growth of well-defined layers with either nano (d = 16 nm) or coarse grains (d ≥ 500 nm). Room temperature tensile tests have been performed to investigate the mechanical response and understand the underlying deformation mechanisms. Tensile test results and fractographic studies demonstrate that the overall room temperature mechanical behaviour of the multilayered material, i.e. strength and ductility, is governed primarily by the layers containing nanocrystalline grains. The measured properties have been discussed in the context of modulated grain structure of the multilayered sample and contribution of each grain size regime to the overall strength and ductility.     

Grain growth in ultrafine titanium powders during sintering

Grain growth behaviour of fine (∼3 μm) and attrition milled nanocrystalline (∼32 nm) titanium powers during sintering have been studied. The activation energies of grain growth (Q _g) in fine titanium were found to be 192.9 and 142.4 kJ/mol at lower and higher temperature ranges, respectively. The nanocrystalline titanium showed very low values of Q _g (54.6 kJ/mol) at lower temperatures and it increased to 273.2 kJ/mol at higher temperatures. The constant (n) in nano Ti system was found to have unusually very high values of 6.5–8.2. The grain boundary rotation along with the diffusional processes could be the grain growth mechanism in nanocrystalline and in fine titanium powders.