Non-linear Compensated Dwell Time for Efficient Fused Silica Surface Figuring Using Inductively Coupled Plasma

Atmospheric plasma etching has been increasingly applied in the fabrication of optical elements for high efficiency and near-zero damage to optical surfaces. However, the non-linearity of material removal rate is inevitable because of the thermal effect of inductively coupled plasma (ICP) etching for fused silica. To apply ICP to figure fused silica surface, the time-varying non-linearity between material removal rate and dwell time is analyzed. An experimental model of removal function is established considering the time-varying non-linearity. According to this model, an algorithm based on nested pulsed iterative method is proposed for calculating and compensating this time-varying non-linearity by varying the dwell time. Simulation results show that this algorithm can calculate and adjust the dwell time accurately and remove surface errors with rapid convergence. Surface figuring experiments were set up on the fused silica planar work-pieces with a size of 100 mm (width) × 100 mm (length) × 10 mm (thickness). With the compensated dwell time, the surface error converges rapidly from 4.556 λ PV (peak-to-valley) to 0.839 λ PV within 13.2 min in one iterative figuring. The power spectral density analysis indicates that the spatial frequency errors between 0.01 and 0.04 mm^?1 are smoothed efficiently, and the spatial frequency errors between 0.04 and 0.972 mm^?1 are also corrected. Experimental results demonstrate that the ICP surface figuring can achieve high convergence for surface error reduction using the compensated dwell time. Therefore, the ICP surface figuring can greatly improve surface quality and machining efficiency for fused silica optical elements.     

Combined methane reforming over nano LaNiO<Subscript>3</Subscript> catalyst with modified active surface

In this study, nano catalyst LaNiO₃ with perovskite structure was synthesized using the citrate sol–gel method in the combined methane reforming with CO₂ and O₂ (CRM). The effects of increasing the surface area of the LaNiO₃ perovskite on the catalytic activity were investigated by changing the method of preparing and creating holes in the surface of the samples. Physical and chemical properties of the samples, before and after the reactor test, were determined through ICP, AA, XRD, TGA, TPR, BET, SEM, EDX and TEM techniques. The results of XRD, ICP, AA, SEM, EDX and TEM tests indicated that the citrate sol–gel method is a good way to prepare a homogeneous perovskite LaNiO₃ sample on a scale of nanometers. The results of the TPR test showed using etching in the citrate sol–gel method can produce samples with high stability. The BET results indicated that the surface area of the LaNiO₃ sample tripled with the method suggested in this paper. Changes in preparation method lead to induction time decreasing and temperature increasing. Use of etching in the citrate sol gel method had no significant effect in the results of activity tests versus time reaction at a temperature of 800 °C. TGA curves revealed no production of coke over the process for the produced samples.     

Chemical etching of silicon: Smooth, rough, and glowing surfaces

Scanning Force Microscope images of silicon surface morphology are presented for samples exposed to various oxidizing environments followed by oxide removal. These are contrasted with samples exposed to HNO₃/HF solutions. The former samples consistently produced surface roughness on the order of a few nanometers, while the latter solution exhibited surface roughness of several hundred to over a thousand nanometers. This rough surface is photoluminescent and is known as porous silicon. Careful observation of the onset of the reaction (which is proceeded by a concentration dependent induction period) suggests that the reaction mechanism is autocatalytic; some etchant product species catalyzes the further attack of the surface. Surface features of co-existing fluorescing and non-fluorescing regions emphasize the heavy etching present in the porous silicon region. Local control of the porous silicon formation by a photoinduced etching process is reported for the first time suggesting the possibility of a non-resist lithographic procedure.     

XPS, ICP and DPASV analysis of medieval pottery — Statistical multivariate treatment of data

Medieval ceramic sherds have been studied by inductively coupled plasma (ICP) emission spectroscopy and X-ray photoelectron spectroscopy (XPS) in order to acquire knowledge about technological achievements in pottery production in Apulia during the Middle Ages. The XPS results allow to characterize the surface glazes, which are transparent owing to the presence of PbO or opaque-white in case of Sn addition. The study of coloured glossy surfaces, after an optimized chemical etching, has also shed light on the pigment nature of the painted decorations, whose red colour is to be attributed to the presence of Pb₃O₄ and not of Fe oxides. Quantitative determinations were performed by ICP measurements on samples of differently coloured glazes, clayey slips and ceramic bulks. Pb and Cu, present in one green glaze, were also determined by differential pulsed anodic stripping voltammetry (DPASV). The analytical results were treated by different statistical techniques of multivariate analysis.     

Arc-Enhanced Plasma Machining Technology for High Efficiency Machining of Silicon Carbide

Atmosphere plasma etching methods have been demonstrated efficient in the etching of fused silica or ULE. However, because of the high chemical stability of silicon carbide (SiC), the conventional plasma etching methods seem incapable of obtaining a high material removal rate (MRR). We have found that MRR will be significantly improved while the electric spark appears between the plasma and the SiC surface. As a result, a new plasma source is designed to generate stable arc at the surface. Due to the generation of arc, the MRR of 0.35 mm³/min is obtained, about 10 times as high as the conventional method. In this paper, the removal characteristics and the thermal effect of this method are presented. MRR and the surface temperature are investigated in dependence on plasma parameters: RF power, travel speed of plasma source, SF₆ gas flow and O₂ gas flow. Due to the negligible thermal effect, the surface figuring can be achieved using the conventional dwell time method. The shape error of a flat SiC surface is corrected, verifying the figuring capability and the effectiveness of this method.     

Rapid dissolution of metal in aqueous media using a modified commercial spark source unit

In this preliminary study the feasibility of a modified spark source was investigated as a method of rapidly dissolving solid conductive samples in aqueous media prior to analysis by atomic spectroscopy. The spark source, originally designed for spark emission spectroscopy in air, was modified by the installation of a spark ablation vessel. This spark ablation vessel was designed for spark ablating samples in aqueous solution, such as deionised water. Samples such as mild steel and brass were ablated in 5–10 ml of deionised water for 2–30 s producing a colloidal suspension. The suspension was readily dissolved by adding 100 μl of concentrated HCl or HNO₃. In this paper the spark ablation vessel is described as well as some of the properties of spark ablation in aqueous solutions. Spark ablation rates on mild steel were measured with respect to spark ablation parameters such as applied current (power), polarity and spark time. Using mild steel as a test sample, spark ablation rates varied from 40 μg s⁻¹, with 2.5 A of applied current, to 70 μg s⁻¹ with 10 A of applied current to the electrodes. The feasibility of using this technique for analysing trace levels (μg g⁻¹) of elements in solid samples was also demonstrated for elements such as Ni in brass with inductively coupled plasma mass spectrometry (ICP-MS). Quantification of selected elements (Cr, Ni, Mn and Cu) in a certified alloy (SRM 663) and a non-certified stainless steel showed good agreement between the measured values using spark ablation and the accepted values.     

Current Developments in Optical Emission Spectrometry with High-Frequency and Microwave Induced Plasmas

The state-of-the-art and trends of development with the inductively coupled plasma (ICP) and microwave induced plasmas (MIP) as radiation sources for optical emission spectrometry arc presented. Especially techniques for sample introduction are discussed. Here special reference is given to the use of spark ablation as well as 10 direct sample insertion and slurry atomization for the direct analysis of powder samples. The development in MIP optical emission Spectrometry is shown to center on the improvement of the plasma sources, their characterization and their tailoring to various sampling techniques. Results of the use of pneumatic nebulization of liquids and electrothermal evaporation of dry solution residues will be presented.     

Extraction-back extraction preconcentration in the system based on p-alkylaniline and oil sulfides for determining platinum-group metals and gold by inductively coupled plasma atomic emission spectrometry

A procedure is developed for determining all platinum-group metals (PGM) and gold (10⁻⁷ to 10⁻⁴%). It includes the autoclave digestion of samples with the transfer of metals into a hydrochloric acid medium without losing osmium and ruthenium, group 10- to 20-fold extraction preconcentration of precious metals with the removal of matrix interfering elements to a factor of 10⁵–10⁶, and the analysis of the group back extract of PGM and gold by ICP AES. A method is proposed for the quantitative back extraction of all PGM and gold from a group extract in two steps of consecutively washing the extract with ammonia solutions and thiourea. The procedure is tested on seven GSO samples and technological objects. It is shown that ICP MS can be used for the analysis of group back extracts of PGM and gold.     

Layer-by-layer analysis of A4B6 thin-film heterostructures using inductively coupled plasma atomic fluorescence spectrometry (ICP-AFS)

The technique of layer-by-layer analysis of semiconductive A₄B₆ heterostructures using electrochemical etching and inductively coupled plasma atomic fluorescence spectrometry (ICP AFS) is developed. The Norr etching solution and electrochemical oxidation with subsequent dissolution of oxidized layers in acid were used to remove layers of 0.5 to several microns thickness. Pb_1?xEu_xTe/PbTe and Pb_1?xEu_xSe/PbSe heterostructures were analyzed. The Eu content in removed layers was determined by ICP-AFS. The data on Eu depth profiles were used for the evaluation of the Eu diffusion coefficient in this heterostructures to predict the changes of properties along the depth of the structure. The technique can be applied to the analysis of semiconductive heterostructures with different admixtures.     

Layer-by-layer analysis of A4B6 thin-film heterostructures using inductively coupled plasma atomic fluorescence spectrometry (ICP-AFS)

The technique of layer-by-layer analysis of semiconductive A₄B₆ heterostructures using electrochemical etching and inductively coupled plasma atomic fluorescence spectrometry (ICP AFS) is developed. The Norr etching solution and electrochemical oxidation with subsequent dissolution of oxidized layers in acid were used to remove layers of 0.5 to several microns thickness. Pb_1–xEu_xTe/PbTe and Pb_1–xEu_xSe/PbSe heterostructures were analyzed. The Eu content in removed layers was determined by ICP-AFS. The data on Eu depth profiles were used for the evaluation of the Eu diffusion coefficient in this heterostructures to predict the changes of properties along the depth of the structure. The technique can be applied to the analysis of semiconductive heterostructures with different admixtures.     

Inductively Coupled Plasma Etching in ICl- and IBr-Based Chemistries. Part II: InP, InSb, InGaP, and InGaAs

A parametric study of Inductively Coupled Plasma (ICP) etching of InP, InSb, InGaP, and InGaAs has been carried out in ICl/Ar and IBr/Ar chemistries. Etch rates in excess of 3.1 for InP, 3.6 for InSb, 2.3 for InGaP, and 2.2 m/min for InGaAs were obtained in IBr/Ar plasmas. The ICP etching of In-based materials showed a general tendency: The etch rates increased substantially with increasing ICP source power and rf chuck power in both chemistries, while they decreased with increasing chamber pressure. The IBr/Ar chemistry typically showed higher etch rates than ICl/Ar, but the etched surface morphologies were fairly poor for both chemistries.     

Intelligent flow-injection—inductively coupled plasma system for matrix matching

Water samples with variable salinity are analysed by a flow-injection—inductively coupled plasma (ICP) system. The sampling zone approach is used to level the sample and standard saline contents in order to compensate for matrix effects. Calibration graphs for Ca, Mg, Al, Fe, P and Si at three different sodium concentrations are obtained. The sample and standard salinity matching is done automatically by processing the sample sodium signal from the ICP with a microcomputer and adding a suitable amount of sodium. The decision process consists in choosing the appropriate standard solution and adjusting the commutation delay for the sampling zone, using a previously determined time—concentration curve. Sodium interference is minimized, allowing the analysis of water samples with a saline matrix up to 2.5% (w/v) NaCl. The proposed method is suitable for 60 samples h^?1.     

Mechanisms of particle removal from silicon wafer surface in wet chemical cleaning process

A quantitative mechanism of particle removal from silicon wafer surfaces by a wet chemical cleaning process is proposed. The particles are removed from the surface due to the combined effects of chemical etching and a net repulsive interaction between the particle and surface. The mechanism suggests that a critical etching depth, which has been determined theoretically, and an optimal etching rate, which can be determined from etching profile calculation, are required for particle removal. The study will help in the optimization of cleaning processes and formulation of superior cleaning solutions.     

High accuracy in the element analysis by mass spectrometry

Summary Accurate analysis results are a common problem in trace and micro determinations of elements, as found in particular in a number of interlaboratory studies. The difference between precision and accuracy of an analysis is shown in this review and a possible hierarchy of analytical methods is given. Isotope dilution mass spectrometry is the most accurate method of all mass spectrometric techniques. Possible element analyses by isotope dilution mass spectrometry are discussed using different ionization methods in the mass spectrometer (thermal ionization, spark source mass spectrometry, electron impact ionization, ICP and MIP, field desorption mass spectrometry). If MIP-MS and spark source mass spectrometry are applied, the difference between analysis results where the isotope dilution technique is and is not used is shown. The precision and accuracy of spark source mass spectrometry increases significantly when the isotope dilution method is applied. Accurate results by mass spectrometry are shown in comparison with certified values of standard reference materials using food samples, biological samples, geological samples, nuclear reactor materials, metals, and samples from the environment as examples. Possible sources of error by isotope dilution mass spectrometry are discussed. In contrast to the analysis of metal traces, only a few alternative methods can be applied to the trace analysis of non-metals and their anion forming compounds. In this case the production of negative thermal ions in a mass spectrometer in connection with the isotope dilution technique is a useful tool for accurate anion and non-metal analyses.

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Hohe Richtigkeit in der Elementanalyse durch Massenspektrometrie

Zusammenfassung Richtige Analysenergebnisse sind ein allgemeines Problem bei der Spuren- und Mikrobestimmung der Elemente, wie sich vor allem immer wieder im Rahmen von Ringanalysen herausstellt. Der Unterschied zwischen Reproduzierbarkeit und Richtigkeit eines Analysenergebnisses wird in diesem Übersichtsartikel aufgezeigt und eine mögliche Hierarchie von Methoden aufgestellt. Im Bereich der Massenspektrometrie gilt die Isotopenverdünnungsanalyse als diejenige Methode, mit der die richtigsten Ergebnisse erhalten werden können. Für die Anwendung verschiedener Ionisationsmethoden im Massenspektrometer (Thermionisation, Funkenquellen-Massenspektrometrie, Elektronenstoßionisation, ICP und MIP, Felddesorptions-Massenspektrometrie) werden die Möglichkeiten der Elementanalyse durch die Isotopenverdünnungstechnik diskutiert. Bei Verwendung der MIP-MS und der Funkenquellen-Massenspektrometrie wird auch der Unterschied zwischen Ergebnissen, die mit und ohne Isotopenverdünnungsanalyse erhalten werden, aufgezeigt. Dabei ergibt sich für die Funkenquellen-Massenspektrometrie eine wesentliche Verbesserung der Analysenergebnisse, wenn die Isotopenverdünnungsmethode angewendet wird. Anhand von Beispielen (Lebensmittelproben, biologische Proben, geologische und kerntechnische Proben, Metalle, Umweltproben) wird die Richtigkeit der massenspektrometrischen Ergebnisse verdeutlicht, wobei häufig ein Vergleich zu zertifizierten Werten von Standard-Referenzmaterialien gegeben wird. Mögliche Fehlerquellen der Isotopenverdünnungsanalyse werden diskutiert. Da bisher zur Bestimmung von Anionen- und Nichtmetallspuren nur vergleichsweise wenige Verfahren zur Verfügung stehen, hat sich hier die Erzeugung negativer Thermionen in einem Massenspektrometer bei gleichzeitiger Anwendung der Isotopenverdünnungsanalyse bewährt.

     

Radiological chronometry of uranium metal samples

Radiological chronometry is an important tool in nuclear forensics that uses several methods to determine the length of time that has elapsed since a material was last purified. One of the chronometers used in determining the age of metallic uranium involves measuring the fractional ingrowth of ²³⁰Th from its parent ²³⁴U with the assumption that the uranium metal contained no impurities, especially thorium, when it was purified. The affects of different etching procedures were evaluated for the removal of surface oxidation with three different types of uranium metal samples to determine whether the etching procedure affects the radiological age. The sample treated with a rigorous etching procedure had exhibited the most reliable radiological age while less rigorous etching yields a radiological age from 15 years to hundreds of years older than the known age. Any excess thorium on the surface of a uranium metal sample presents a bias in age determination and the sample will appear older than the true age. Although this research demonstrates the need for rigorous surface etching, a bias in the radiological age could have arisen if the uranium in the metal was heterogeneously distributed.     

Inductively Coupled Plasma Etching in ICl- and IBr-Based Chemistries. Part I: GaAs, GaSb, and AlGaAs

High-density plasma etching of GaAs, GaSb, and AlGaAs was performed inICl/Ar and IBr/Ar chemistries using an Inductively Coupled Plasma (ICP)source. GaSb and AlGaAs showed maxima in their etch rates for both plamachemistries as a function of interhalogen percentage, while GaAs showedincreased etch rates with plasma composition in both chemistries. Etchrates of all materials increased substantially with increasing rf chuckpower, but rapidly decreased with chamber pressure. Selectivities >10 forGaAs and GaSb over AlGaAs were obtained in both chemistries. The etchedsurfaces of GaAs showed smooth morphology, which were somewhat better withICl/Ar than with IBr/Ar discharge. Auger Electron Spectroscopy analysisrevealed equirate of removal of group III and V components or thecorresponding etch products, maintaining the stoichiometry of the etchedsurface.     

Analysis of diphenylarsinic acid in human and environmental samples by HPLC–ICP‐MS

A simple, rapid and robust analytical method for determining diphenylarsinic acid in human and environmental samples was developed based on a combination of hydrophilic polymer‐based gel‐permeation high‐performance liquid chromatography (HPLC) and inductively coupled plasma mass spectrometry (ICP‐MS). Hair and nail samples were digested with alkali, and liberated diphenylarsinic acid (derivative) was extracted with diethyl ether, redissolved in water and injected for HPLC–ICP‐MS analysis. Human urine, groundwater and water extracts from soils were injected for HPLC–ICP‐MS directly after filtration. Using the method, diphenylarsinic acid in a solution was quantified in 7 min duration for an analysis with a detection limit of sub‐nanograms per milliliter. The method has been applied to groundwater arsenic pollution recently uncovered in Japan. Copyright © 2005 John Wiley & Sons, Ltd.     

Untersuchungen zur atomspektroskopischen spurenanalyse in AIIIBV-halbleiter-mikroproben—III: Untersuchungen zur schichtabtrennung und zur spurenanalyse in dünnen GaAs schichten

Three methods for stripping thin layers of GaAs have been compared with regard to depth of layer and reproducibility. They are (1) chemical etching with methanolic bromine solution, (2) mechanical separation with a microtome, (3) chemical etching after a preliminary amperostatic anodic oxidation. Conditions were optimized. The depth of strip was 0.4 μm for chemical etching, 1 μm for the mechanical separation and 0.02 μm for the anodic oxidation method. Thus the anodic oxidation is specially suitable for profile analysis, and the mechanical method for investigation of thicker layers; chemical etching lies between them. The trace elements in the micro samples thus obtained were determined by d.c. are atomic-emission spectrography (AES) and atomic-absorption spectrometry with electrothermal atomization in a graphite tube (AAS). The absolute and relative detection limits of AAS for the 0.1–0.2 mg micro samples were on average better by an order of magnitude than those of AES. The advantage of AES lies in the possibility of simultaneous determination of several elements. in der Möglichkeit der Simultanbestimmung mehrerer Elemente.     

Preparation of Porous Hollow SiO2 Spheres by a Modified St?ber Process Using MF Microspheres as Templates

Using the surface charged and acid dissolvable melamine formaldehyde (MF) microspheres as sacrificial hard templates, silica coated MF core?Cshell composite microspheres, denoted as MF@SiO₂, were synthesized via a surfactant-assisted sol?Cgel process by using tetraethyl orthosilicate (TEOS) as silica source. Hollow SiO₂ spheres with mesoporous shells were then obtained after selective removal of the MF cores and the pore directing surfactant by hydrochloric acid etching or calcinations in air. Interesting shrinkage phenomena were observed in both the hollow products derived from hydrochloric acid etching and calcinations. The influence of the ratio of MF sphere to TEOS and the removal method of the MF core on the size of the hollow spheres, the shell thickness and the shell surface roughness have been studied. The composition, the thermal stability, the morphology, the surface area and pore size distribution, the wall thickness and adsorption properties of the hollow spheres derived from hydrochloric acid etching and calcinations were also investigated and compared based on the FTIR, SEM, TEM, TGA, Nitrogen adsorption?Cdesorption and spectrophotometer techniques or measurements.     

Validation of the determination of copper and zinc in blood plasma and urine by ICP MS with cross-flow and direct injection nebulization

The simultaneous determination of copper and zinc in human plasma and urine by inductively coupled plasma mass spectrometry (ICP MS) is discussed. The performances of a cross-flow nebulizer and a direct-injection nebulizer (DIN) were compared. Flow-injection-DIN-ICP MS analysis of clinical samples using 1-2 mul samples was optimized. Isobaric interferences were discussed and were demonstrated to be eliminated for the (65)Cu and most of the Zn nuclides. The need for standard addition to compensate for signal suppression in the case of some serum samples was indicated. Results obtained by ICP MS using calibration with aqueous standard solutions were found to be in good agreement with those obtained by flame AAS for a batch of real blood plasma and urine samples. The methods developed were validated by analysis of several standard reference materials.