Pulsed Current Conditions Research Articles

High-power InGaAs/GaAs quantum-well laser with enhanced broad spectrum of stimulated emission

We report the demonstration of an InGaAs/GaAs quantum well (QW) broadband stimulated emission laser with a structure that integrated a GaAs tunnel junction with two QW active regions. The laser exhibits ultrabroad lasing spectral coverage of ∼51 nm at a center wavelength of 1060 nm with a total emission power of 790 mW, corresponding to a high average spectral power density of 15.5 mW/nm, under pulsed current conditions. Compared to traditional lasers, this laser with an asymmetric separate-confinement heterostructure shows broader lasing bandwidth and higher spectral power density.

Pulse Electrodeposition of Amorphous Si Film Anodes for Li-Ion Battery

INTRODUCTIONOver the past two decades, lithium ion batteries have carved a significant market for use in consumer and portable electrical and electronic devices. However, in recent years, the quest for environmentally clean technology in the automotive industry has resulted in a greater demand for increased energy storage capacity and improved performance of Li ion batteries. Silicon shows a high theoretical capacity of ~4212 mAh/g, corresponding to Li22Si5 phase and was identified as promising material to replace graphite (~372 mAh/g) anode which is currently used in the Li-ion batteries. However, during alloying and de-alloying of lithium with the Si anode there is a very large well known volumetric change (~400% volume) leading to colossal mechanical stresses in the electrode causing cracking and consequently loss of inter – particle contact. Hence, there is delamination of the electrode layer leading to rapid capacity fade of battery (1).Nanostructured and amorphous Si synthesized by physical (2,3) and chemical vapor deposition (4) show improved performance but are not economically viable for secondary batteries. Electrodeposition is a very inexpensive process which has been widely studied and used in many industrial applications for plating metals and alloys. Electrodeposition of silicon from organic solvents and ionic liquids on metallic and graphite substrates has previously been reported in the literature (5). Additionally, the electrodeposition technique provides the opportunity to generate films with different morphologies and functional properties by controlling the parameters such as electrolyte composition, applied voltage/current density and time of deposition.In the current study, Si thin films were electrodeposited on copper substrate using galvanostatic and pulse current conditions in an argon environment. Electrochemical investigations were performed on the electrodeposited Si thin films on copper foil which served as the working electrode. A 2016/2025 coin cell assembly in a half cell configuration was used by employing lithium (Li) foil as counter electrode and 1 M LiPF6 in ethylene carbonate and di-ethyl carbonate (EC:DEC = 1:2, by volume) as the electrolyte. The assembled cells were tested by cycling between 0.02 and 1.2 V vs. Li+/Li employing a constant current density. Scanning Electron Microscopy (SEM) studies were performed to study the effect of deposition on the morphology of the Si films before (Fig. 1) and after electrochemical cycling. The electrochemical testing of these films as Li-ion anodes showed stable cycling data with an improvement in the stability of the films. The SEM analysis of the films showed that the films were stable even after running over 100 cycles.

Alteration of corrosion and nanomechanical properties of pulse electrodeposited Ni/SiC nanocomposite coatings

Nickel/silicon carbide composite electrodeposits were prepared on a rotating disk electrode (RDE), under pulse current condition. The effect of pulse parameters, current density, SiC content in the electrolyte on the codeposition of SiC were studied. Afterwards, the effect of codeposited SiC amount was investigated on electrochemical behavior and nanomechanical properties of coatings. The coatings were analyzed with Scanning Electron Microscopy (SEM), linear polarization, nanoindentation and Atomic Force Microscopy (AFM). The Ni–SiC electrocomposites, prepared at optimum conditions, exhibited improved nanomechanical properties in comparison to pure nickel electrodeposits. With increasing current density the morphology changed from flat surface to cauliflower structure. The Ni–SiC electrocomposites exhibited improved nanomechanical properties and corrosion resistances in comparison to pure nickel electrodeposits and these properties were improving with increasing codeposited SiC particles in electrocomposites.

Effect of the Polarization Conditions on the Structural Properties of Zinc Dendritic Deposits

The influence of the polarization conditions on growth dynamics and structure of electrolytic zinc dendritic deposits obtained at room temperature from electrolyte with 0.3 mol/l zinc oxide and 4 mol/l sodium hydroxide is studied. The electrodeposition was performed at constant and pulsed current and potential. Constant-current chronopotentiometry was used to determine the surface area of the dendritic deposits in situ. The zinc microstructure was studied with electron microscopy. The deposit surface produced in pulsed current conditions intensively grew during the first 5 minutes of electrolysis and then changed insignificantly. In conditions of potentiostatic electrolysis, the coefficient K, which is the ratio of the deposit surface area to the substrate area, increased linearly with time; in pulsed potential conditions, it increased as a power-law functions. The deposits obtained in potentiostatic conditions show the lowest density that slightly varies with thickness. The density of the deposits crystallized in pulsed current conditions sharply increased upon the completion of active dendrite extension.

Pulsed plasma electrolytic oxidation processes for aeronautical applications and their technical application

A range of aluminium alloys have been treated by plasma electrolytic oxidation in different alkaline electrolytes containing silicate, aluminate, vanadate and other additives, under pulsed current conditions and the dependence of oxide thickness growth rates on variation in electrolyte and operating conditions measured. The oxide morphology was examined by SEM, and coating phase and crystal size analysis was carried out by XRD. Coating hardness varied with anodising current type and electrolyte composition, and the incorporation of dispersed nano silica particles.

Effect of fluoride on plasma electrolytic oxidation of AZ61 magnesium alloy

Plasma electrolytic oxidation has been carried out on AZ61 magnesium alloy in a silicate–phosphate electrolyte under pulsed current conditions. It is shown that the addition of fluoride to the electrolyte reduced localized corrosion that occurred near Al–Mn intermetallic particles before sparking begins. Such corrosion affected the uniformity of the PEO coating. On the other hand, fluoride ions caused significant loss of coating material during coating growth. Irrespective of the fluoride addition, the coatings contained Mg3(PO4)2, amorphous material and possibly MgO. However, fluoride strongly affected the rate of coating growth and the morphology of the coating. The loss of coating material is suggested to be due to the effects of fluoride ions on the intensity of the discharges and melting of the coating.

Chirped InAs/InP quantum-dash laser with enhanced broad spectrum of stimulated emission

We report on the demonstration of 50 nm (full-width at half-maximum) broadband stimulated emission from a chirped AlGaInAs barrier thickness multi-stack InAs/InP quantum dash (Qdash) laser. The 2 μm wide uncoated Fabry-Perot (FP) ridge-waveguide laser exhibits a total power of 0.18 W, corresponding to an average spectral power density of 3.5 mW/nm, under pulsed current conditions. Intentional extended inhomogeneity across the Qdash stacks have been attributed to the enhancement of broadband emission.

Effects of cis-2-butene-1,4-diol additive and pulse current imposition on production of Ni nanocrystalline coatings

Nickel nanocrystalline electrodeposits were produced from a Watts type bath with the addition of cis-2-butene-1,4-diol and simultaneous application of either direct or pulse current conditions. The surface morphology, the preferred orientation, grain size and microhardness of Ni deposits were determined as functions of the concentration of the additive in bath, the type of imposed current and the frequency of imposed current pulses. The combined imposition of predefined pulse current conditions (pulse frequency) and specific additive concentration in the bath leads to specific textural modifications ([211] and [100] preferred crystal orientations) accompanied by considerable nanosized grain refinement of the coatings. The overall experimental data indicate that the production of hard and bright nanostructured deposits could be obtained under pulse current regime and reduced amounts of cis-2-butene-1,4-diol compared to direct plating.

Electro-deposition tangsten coating on low activation steel substrates from Na2WO4-ZnO-WO3 melt salt

Tungsten coating is considered as a promising alternative material for plasma facing materials (PFC) in future fusion devices. The electro-deposition of tungsten in Na2WO4-ZnO-WO3 melt at 1173 K on low activation steel substrates was studied in this work. Adherent and smooth tungsten films were deposited under various pulsed current conditions. The crystal structure and microstructure of tungsten deposits were characterized by XRD, SEM and EDX techniques. The results show that pulsed current density and duty cycle have a significant influence on tungsten nucleation and electro-crystallization phenomena. Uniform and smooth tungsten coating with high purity and high adherence is obtained on low active steel substrates as cathodic current density ranges from 35 to 25 mA·cm−2.

Thermal overstress of Cu wire under pulsed current condition

Copper wire introduction in IC industry is showing new and interesting challenges. In this paper, we present the experimental observations and theoretical hypothesis of copper wire degradation under thermal stress in pulsed current condition. The real case is a smart power test vehicle which fails under stress induced by Operating Life Test. Physical failure analysis results and theoretical thermal simulations are reported, as well as a failure mechanism hypothesis, which highlights product/package interaction sensitivity.

Experimental characterization and modelling of electromigration lifetime under unipolar pulsed current stress

The electromigration behaviour of Cu/SiCOH interconnects carrying unipolar pulsed current with long periods (i.e. 2, 16, 32 and 48h) is presented in this study. Experimental observations suggest that the electromigration behaviour during void growth can be described by the ON-time model and that the lifetime of the Cu/SiCOH interconnects is inversely related to the duty cycle. Numerical simulation is carried out to compute the time required to nucleate a void under unipolar pulsed current stress conditions. The time to void nucleation is found to vary proportionally to the inverse square of the duty cycle and is independent of frequency at 1Hz and higher. By computing the stress evolution in interconnects with short length, it was shown that the product of the unipolar pulsed current’s duty cycle and current density, i.e. average current density, is equivalent to the current density of a constant current (D.C.) stress. The simulation results suggest (d·jL)crit as the equivalent critical current density-length product under unipolar pulsed current condition. Both the experimental and simulation results show that duty cycle has an effect on the electromigration lifetime of interconnects carrying unipolar pulsed current.

Formation of Co–Ni alloy coatings under direct current, pulse current and pulse-reverse plating conditions

Co–Ni coatings have been deposited by galvanostatic direct current, unipolar pulse plating and bipolar pulse reverse plating in buffered additive-free sulfate solutions at pH 3 and analyzed for their alloy composition, deposition current efficiency and surface morphology. A main objective is to determine whether the use of pulse or pulse reverse plating can overcome the anomalous behavior of this system whereby cobalt preferentially deposits over nickel even from solutions containing more NiSO 4 than CoSO 4. This study focuses on the use of a plating solution having a NiSO 4:CoSO 4 molar ratio of 2:1 and another bath containing a large excess of NiSO 4 over CoSO 4. Experiments reveal that both pulse plating and pulse reverse plating are unable to significantly alleviate the anomalous behavior in either solution over the range of pulse frequencies, duty cycles and current amplitudes considered in this study, unlike that observed in previous studies when deposition is carried out in chloride-based solutions. On the other hand, significant improvement and better control of coating morphology over that achievable by direct current plating is possible using unipolar pulse plating in particular. Smoother and brighter deposits with finer-grained structures are obtained by increasing pulse duty cycle and frequency and decreasing cathodic pulse amplitude.

Effect of Frequency on Composition and Microstructure of Siliconized Layer Using Pulse Electrodeposition

The siliconized layer on low silicon steel substrate was produced under pulse current conditions from KCl-NaCl-NaF-SiO2molten salt and the effects of frequency on the composition and microstructure were investigated. The results showed that at the same average current density and other experimental conditions, Si content in the surface and the layer thickness decreased with increasing frequency. Low pulse frequency (500 Hz) and high frequencies (1500, 2000Hz) produced coarse grain and bigger surface roughness. There was a flat fine grain structure and a relatively thick (30m) layer when the frequency was 1000Hz. However, the effect of pulse frequency on the structure of the layer was not obvious. The phase structure of the layer was composed of Fe3Si with (110) preferred orientation at all experimental frequencies.

Ni/nano-TiO2 Composite Electrocoatings: Correlation Between Structural Characteristics Microhardness and Wear Resistance

Abstract Nanocomposite coatings were obtained by electrochemical codeposition of TiO2 nano-particles (mean diameter 21 nm, Degussa P25) with nickel, from an additive-free Watts type bath. Pure Ni and composite Ni-TiO2 coatings were electrolytically deposited under both direct and pulse current conditions and an extended region of electrolysis conditions (pH, current density, TiO2 loading in the bath). Pure Ni deposits were produced under the same experimental conditions for comparison. The aim of this study was to correlate the observed structural characteristics of the coatings (crystallographic orientation and grain size of nickel matrix,) and incorporation percentage with the resulting microhardness values and tribological behavior. Overall, the data have demonstrated that when attributing the observed strengthening effect of composites, not only grain refinement and dispersion strengthening mechanisms, but also preferred crystalline orientation should be taken into consideration. The variation of the wear rate is directly associated with the microhardness variations and consequently, governed by the same parameters that determine the synergistic strengthening mechanism proposed. Pure and composite coatings with [110] crystalline orientation exhibited the highest microhardness values and wear resistance.

Resistance to localized corrosion of pure Ni, micro- and nano-SiC composite electrodeposits

The aim of this work was the production and characterization of composite Ni matrix electrodeposits. Pure Ni, micro- and nano-SiC Ni matrix composite deposits have been produced from a Watts’s-type electroplating bath under both direct (DC) and pulse current (PC) conditions. The obtained deposits have been characterized regarding their microstructure by scanning electron microscopy (SEM) observations on both top surface and cross-section and their SiC content by energy-dispersive X-ray spectrometry (EDXS) and glow discharge optical emission spectrometry (GDOES) analyses. The resistance to localized corrosion has been evaluated by exposing the samples in a salt spray cabinet and performing visual observation as well as electrochemical impedance spectroscopy (EIS) measurements every five days. Both the use of PC and the codeposition of the nanoparticles lead to a grain refinement of the Ni matrix. The use of the PC did not influence in a significant way the resistance of the pure Ni deposits to the localized corrosion. The incorporation of micro-SiC led to a decrease of the corrosion resistance for the deposits produced under DC, while the microcomposites produced under PC presented a corrosion resistance comparable to the pure Ni deposits. The nanocomposites presented the highest corrosion resistance due to the more compact and fine-grained microstructure. EIS revealed the presence of a localized corrosion attack earlier than the visual observation, giving useful information about the failure mechanism.

Texture and Mechanical Properties of Electrodeposited Copper Thin Films

Influence of the electrodepositing parameters e.g. applied electric current as variable on texture formation and on mechanical properties of copper thin films was studied. Experiment was done for copper deposition from sulphate bath under galvanostatic and pulse current. It was found that copper layers exhibits different texture depending on applied current conditions during electrodepositing process. Pulse and direct current conditions leads to different texture of electrodeposited copper. Texture of electrodeposited copper coatings and mechanical properties could be correlated. It was found that, texture indexes although are not complex information about texture could be used for analysis of such correlation in technological process.

Comparison of sliding wear behaviour of pulse electrodeposited Ni–Cu nanocrystalline alloys and Ni–Cu/Cu multilayers

This study presents a comparison of tribological properties of electrodeposited nanolayered Ni–Cu/Cu multilayers and nanocrystalline Ni–Cu alloys. In this work, nanocrystalline Ni–Cu alloys containing 35·8 and 26·0 wt-%Cu with grain sizes of 12·8 and 6·6 nm respectively were chosen for wear tests in which the tribological performances of these alloys were compared with Ni–Cu/Cu multilayers: [Ni–Cu (4·5 nm)/Cu (1·97 nm)]n (30·4 wt-%Cu) and [Ni–Cu (7·8 nm)/Cu (1·97 nm)]n (20·2 wt-%Cu) respectively. All the test samples were electrodeposited under pulsed current conditions on polished stainless steel substrates keeping total thickness fixed at ∼10 μm. Reciprocating dry sliding experiments of these samples at a constant normal load in the range 3–11 N were performed in ball on plate geometry keeping the amplitude fixed at 0·001 m. The obtained average coefficient of friction of nanocrystalline alloys was found to be slightly inferior compared to that of multilayers. On the other hand, the wear rate of nanocrystalline alloys was lower than that of multilayers under identical conditions. Higher hardness and lower elastic modulus of nanocrystalline alloys compared to that of multilayers was found to be responsible for the observed wear rate variation.

The effects of pulse plating variables on morphology and corrosion behavior of Zn–Fe alloy coatings

Considerable researches have been focused on zinc–iron (Zn–Fe) alloy coatings due to their superior characteristics among zinc alloy electrodeposits in recent years. The corrosion behavior of these coatings depends on the phase structure and morphology of the Zn–Fe deposits. In this work the effects of pulse plating variables such as current density, off-time, frequency and pulse modes on the morphology and phase structure of Zn–Fe deposits was studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectrometry (EDS) analysis. The corrosion behavior of these coatings was measured by means of polarization curves and Neutral salt spray tests. It was shown that pulse reverse coatings exhibit excellent resistance to corrosion in comparison with normal pulse and direct current conditions.

Pulse Electrolysis for the Production of Hard Ni/TiO<sub>2</sub>-ZrO<sub>2</sub> Composite Coatings

The electrolytic codeposition has drawn interest as an alternative method for the preparation of metal matrix composite electrocoatings with improved properties. Moreover, the application of a current periodically varied by time during electrodeposition, i.e. pulse current (p.c.), instead of the commonly used direct current (d.c.), has been proved to lead to the preparation of surfaces with well-defined properties. In this work, Ni/TiO2-ZrO2 composite electrocoatings were produced under direct and pulse current conditions. The synergetic action of both the pulse application and the simultaneous codeposition of the two different types of particles on the structure, the morphological characteristics and the microhardness of the composite electrocoatings, were studied. Concerning their mechanical behaviour, it was found that the Ni/TiO2-ZrO2 deposits prepared by pulse electrolysis are characterized by Vickers microhardness threefold harder than the d.c. ones.

Electrodeposition of CuNiW alloys: thin films, nanostructured multilayers and nanowires

Electrodeposition operating conditions were determined for the deposition of copper–nickel–tungsten alloys and compositionally, multilayered deposits. Multilayered alloys with one layer rich in Cu and the other layer rich in NiW were fabricated as both thin films and nanowires. The electrolyte contained 0.6 M Na3C6H5O7, 0.2 M Na2WO4, 0.3 M NiSO4 and variable CuSO4 concentration at a pH of 8 adjusted with ammonium hydroxide at 70 ± 2 °C. The deposit composition and current efficiency were characterized using rotating cylinder electrodes with and without a Hull configuration. Addition of Cu(II) to the electrolyte lowered the tungsten partial current density and hence the W wt% in the deposit. Thin film multilayered alloys, with a modulation in composition, were fabricated with pulse current deposition and conditions to selectively etch one layer was determined with a view towards fabricating nanotemplates. Nanowires with modulated composition were also demonstrated, electrodeposited into alumina nanoporous templates. However, the nanowire deposition was confounded by the formation of oxide during the modulation, and results herein recommend that the potential of the more noble step be more negative than −0.9 V versus SCE to avoid this situation, despite metallic alloy formation in unrecessed electrodes.