László Péter

Laser-induced breakdown spectrometry — applications for production control and quality assurance in the steel industry

Abstract Recent progress in sensitivity and signal processing opened a broad field of application for laser-induced breakdown spectrometry (LIBS) in the steel making and processing industry. Analyzed substances range from top gas of the blast furnace, via liquid steel up to finished products. This paper gives an overview of R&D activities and first routine industrial applications of LIBS. The continuous knowledge of the topgas composition yields information about the blast furnace process. An online monitoring method using LIBS is currently under investigation to measure alkali metals, which influence energy and mass flow in the furnace. Direct analysis of liquid steel reduces processing times in secondary metallurgy. By using sensitivity-enhanced LIBS, limits of detection of approximately 10 μg/g and below were achieved for light and heavy elements in liquid steel. The process control in steel production relies on the results from the chemical analysis of the slag. A prototype of an analytical system was developed using LIBS to analyze slag samples two times faster than with conventional methods. The cleanness of steel is a key issue in the manufacturing of spring steel, thin foils and wires. Microscopic inclusions have to be determined quickly. A scanning microanalysis system based on LIBS was developed with measuring frequencies up to 1 kHz and a spatial resolution of

Preparation and Magnetoresistance Characteristics of Electrodeposited Ni‐Cu Alloys and Ni‐Cu/Cu Multilayers

Galvanostatic electrodeposition was used to produce Ni-Cu alloys and Ni 81 Cu 19 /Cu multilayers by direct current (dc) plating and two-pulse plating, respectively, from a sulfate/citrate electrolyte. For the dc-plated Ni-Cu alloys, the deposition rate and the alloy composition were established as a function of the deposition current density, from which the appropriate deposition parameters for the constituent sublayers of the multilayers could be established. By measuring the resistivity at room temperature in magnetic fields up to H = 7 kOe, anisotropic magnetoresistance (AMR) was found for Ni 81 Cu 19 electrodeposits, whereas both giant magnetoresistance (GMR) and AMR contributions were observed for most Ni 81 Cu 19 /Cu multilayers. Finally, Ni-Cu alloys were also prepared by conventional pulse plating, varying the length of the deposition pulse (on-time) with constant separation (off-time) between the pulses. Clear evidence of a GMR contribution also appeared in these pulse plated Ni-Cu alloys which may be explained by the formation of a Cu enriched layer between the ferromagnetic layers deposited during the cathodic pulses. A quartz crystal microbalance experiment confirmed that an exchange reaction takes place during the off-time. These findings provide useful information on the formation mechanism of multilayers by the two-pulse plating technique.

Giant Magnetoresistance in Co-Cu/Cu Multilayers Prepared by Various Electrodeposition Control Modes

The giant magnetoresistance (GMR) effect was studied on electrodeposited Co-Cu/Cu multilayers of 300 bilayer repeats which were produced in an electrochemical cell with homogeneous current distribution from a bath with two solutes (CoSO 4 ,CuSO 4 ). The preparation employed the conventional potentiostatic/potentiostatic and galvanostatic/galvanostatic, as well as an unprecedented galvanostatic/potentiostatic (G/P) control. We find that the specific deposition parameters rather than the deposition mode itself are decisive for the magnitude of the GMR which could be as high as 10% measured at 1 kOe on substrate-free multilayers in optimized G/P conditions. For this new deposition mode, detailed studies on the dependence of GMR on Co and Cu layer thicknesses as well as the bath pH were performed. No oscillatory behavior of the GMR as a function of the Cu layer thickness could be observed. The results suggest the importance of a Co-dissolution and/or a Co vs. Cu exchange reaction after completing the deposition of each magnetic layer. These reactions lead to the formation of a Cu or Cu-rich interface layer prior to the electrochemical deposition of the actual Cu layer during the subsequent pulse in either deposition mode. It turned out that the properties of this interfacial layer (thickness, degree of chemical intermixing) strongly influence the resulting GMR behavior of the multilayer.

Microstructure and Giant Magnetoresistance of Electrodeposited Co-Cu/Cu Multilayers

Direct current plating, pulse plating, two-pulse plating, and reverse pulse plating were used to produce electrodeposited Co-Cu alloys and Co-Cu/Cu multilayers under galvanostatic control from an electrolyte containing CoSO 4 and CuSO 4 . Atomic force microscopy, X-ray diffraction, and transmission electron microscopy were used to study the sample structure and morphology. Direct current plating resulted in a Co 95 Cu 5 alloy with nearly equal amounts of face-centered cubic (fcc) and hexagonal close packed phases, while all pulsed current methods yielded multilayers with fcc structure, Giant magnetoresistance (GMR) behavior was observed in the multilayers with a maximum magnetoresistance (MR) ratio of about 9% as measured at 8 kOe. The shape of the MR curves and the magnitude of the GMR were very similar, regardless of the sign of the current between the Co deposition pulses. The results of structural studies also confirmed the formation of a multilayer structure for each pulsed electrodeposition mode. The conclusion was that the spontaneous exchange reaction between Co and Cu 2+ is responsible for the formation of a pure Cu layer even under reverse pulse plating conditions. The GMR of the multilayer deposits decreased with increasing bilayer number, due to the deterioration of the microstructure as the deposit grew.

Effect of Current and Potential Waveforms on Sublayer Thickness of Electrodeposited Copper-Nickel Multilayers

Electrodeposition of nickel-copper multilayers has been studied in order to understand the effect of current and potential waveforms on layer thickness and composition of nanostructured metal multilayers. Two simple charge balance models for multilayer deposition have been developed to calculate the amount of the less noble material dissolved from the deposit. The models take into account that the less noble material (here, nickel) may he lost from the deposit due to either anodic dissolution or a displacement reaction. Experimentally, Ni(Cu)/Cu metal multilayers have been deposited from a citrate electrolyte in a vertical flow channel under controlled hydrodynamic conditions. Multilayers were deposited by two different fabrication methods: constant current/ constant potential and constant current/relaxation/constant current method. A match between the experimental data and models was used to calculate the amount of nickel dissolved from the deposit. It was found that about one or four monolayers of nickel are dissolved from the Ni(Cu) layer due dissolution and displacement, respectively. The deposition modes studied lead to different deposit morphology.

Giant magnetoresistance in electrodeposited Co-Cu/Cu multilayers: Origin of the absence of oscillatory behavior

A detailed study of the evolution of the magnetoresistance was performed on electrodeposited Co/Cu multilayers with Cu-layer thicknesses ranging from 0.5 to 4.5 nm. For thin Cu layers up to 1.5 nm, anisotropic magnetoresistance AMR was observed, whereas multilayers with thicker Cu layers exhibited clear giant magnetoresistance GMR behavior. The GMR magnitude increased up to about 3.5–4 nm Cu-layer thickness and slightly decreased afterward. According to magnetic measurements, all samples exhibited ferromagnetic FM behavior. The relative remanence turned out to be about 0.75 for both AMR- and GMR-type multilayers. This clearly indicates the absence of an antiferromagnetic AF coupling between adjacent magnetic layers for Cu layers even above 1.5 nm where the GMR effect occurs. The AMR behavior at low spacer thicknesses indicates the presence of strong FM coupling due to, e.g., pinholes in the spacer and/or areas of the Cu layer where the layer thickness is very small. With increasing spacer thickness, the pinhole density reduces and/or the layer thickness uniformity improves, which both lead to a weakening of the FM coupling. This improvement in multilayer structure quality results in a better separation of magnetic layers and the weaker coupling or complete absence of interlayer coupling enables a more random magnetization orientation of adjacent layers, all this leading to an increase in the GMR. Coercive field and zero-field resistivity measurements as well as the results of a structural study reported earlier on the same multilayers provide independent evidence for the microstructural features established here. A critical analysis of former results on electrodeposited Co/Cu multilayers suggests the absence of an oscillating GMR in these systems. It is pointed out that the large GMR reported previously on such Co/Cu multilayers at Cu-layer thicknesses of around 1 nm can be attributed to the presence of a fairly large superparamagnetic SPM fraction rather than being due to a strong AF coupling. In the absence of SPM regions as in the present study, AMR only occurs at low spacer thicknesses due to the dominating FM coupling.

Effect of Current and Potential Waveforms on GMR Characteristics of Electrodeposited Ni(Cu)/Cu Multilayers

In a previous paper [W. R. A. Meuleman, S. Roy, L. Peter, and I. Varga, J. Electrochem. Soc., 149, C479 (2002)], the electrodeposition of Ni(Cu)/Cu multilayers from a citrate electrolyte has been discussed. In the present work, an X-ray diffraction (XRD) study and the magnetoresistance characteristics of the same multilayers are described. For Cu layer thicknesses above about 2 nm, satellite reflections due to multilayer periodicity could be observed. The grain sizes as deduced from the broadening of the XRD lines were between 10 and 15 nm. A clear giant magnetoresistance (GMR) behavior was observed at Cu thicknesses above 2 nm for the constant current/constant potential series where galvanostatic and potentiostatic control was used for the deposition of the magnetic and nonmagnetic layer, respectively. However, the maximum GMR at 8 kOe was around -0.3% only. For the constant current/relaxation/constant current series in which both layers were deposited under galvanostatic control with a zero current interval in between, only a very weak indication for the GMR contribution could be detected besides the dominating anisotropic magnetoresistance. Interface intermixing due to the Ni vs. Cu exchange reaction, electrolyte pH, (111) orientation of the deposit, and very small crystallite sizes have been considered as possible sources leading to the poor GMR.

Speciation without chromatography : Part I. Determination of tributyltin in aqueous samples by chloride generation, headspace solid-phase microextraction and inductively coupled plasma time of flight mass spectrometry

An analytical procedure was developed for the determination of tributyltin in aqueous samples. The relatively high volatility of the organometal halide species confers suitability for their headspace sampling from the vapour phase above natural waters or leached solid samples. Tributyltin was collected from the sample headspace above various chloride-containing matrices, including HCl, sodium chloride solution and sea-water, by passive sampling using a polydimethylsiloxane/divinylbenzene (PDMS/DVB)-coated solid-phase microextraction (SPME) fiber. Inductively coupled plasma time-of-flight mass spectrometry (ICP-TOFMS) was used for detection following thermal desorption of analytes from the fiber. A detection limit of 5.8 pg ml–1(as tin) was realized in aqueous samples. Method validation was achieved using NRCC PACS-2 (Sediment) certified reference material, for which reasonable agreement between certified and measured values for tributyltin content was obtained.

Ferromagnetic and Superparamagnetic Contributions in the Magnetoresistance of Electrodeposited Co-Cu/Cu Multilayers

Co-Cu/Cu multilayers with Cu layer thickness ranging from 0.37 to 3.45 nm were deposited by galvanostatic/potentiostatic method from electrolytes with 5-200 mM Cu 2 + concentration. The composition analysis revealed an increasing Cu content of the magnetic layers with c(Cu 2 + ). Magnetoresistance up to 8 kOe was measured for each sample. Samples with a thin Cu layer (i.e., 0.37 nm) exhibited anisotropic magnetoresistance. At higher Cu layer thicknesses, giant magnetoresistance was observed. The higher the Cu 2 + concentration, the smaller the slope of the magnetoresistance curves at low magnetic field and the higher the saturation field. Magnetoresistance curves were quantitatively separated into ferromagnetic and superparamagnetic contributions. While the ferromagnetic portion of the magnetoresistance varied with the Cu layer thickness in the same way, the superparamagnetic contribution was higher, the larger the Cu content of the magnetic layer. The size of the superparamagnetic regions decreased with increasing Cu content of the magnetic layers. The copper layer thickness dependence of the magnetoresistance properties could be elucidated by accounting for both the asymmetric nucleation of Co on Cu and vice versa and the variation of the Cu content of the magnetic layers. General conclusions on the electrodeposition of magnetic/nonmagnetic multilayers have also been drawn.

Magnetothermopower and magnetoresistance of single Co-Ni/Cu multilayered nanowires

The magnetothermopower and the magnetoresistance of single Co-Ni/Cu multilayered nanowires with various thicknesses of the Cu spacer are investigated. Both kinds of measurement are performed as a function of temperature (50–325 K) and under applied magnetic fields perpendicular to the nanowire axis, with magnitudes up to −15% at room temperature. A linear relation between thermopower S and electrical conductivity σ of the nanowires is found, with the magnetic field as an implicit variable. Combining the linear behavior of the S vs σ relation and the Mott formula, the energy derivative of the resistivity is determined. In order to extract the true nanowire materials parameters from the measured thermopower, a simple model based on the Mott formula is employed to distinguish the individual thermopower contributions of the sample. By assuming that the nondiffusive thermopower contributions of the nanowire can be neglected, it is found that the magnetic-field-induced changes of thermopower and resistivity are equivalent. The emphasis in the present paper is on the comparison of the magnetoresistance and magnetothermopower results and it is found that the same correlation is valid between the two sets of data for all samples, irrespective of the relative importance of the giant magnetoresistance or anisotropic magnetoresistance contributions in the various individual nanowires.