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Analytical and Bioanalytical Chemistry (v.363, #2)
Julius Adolph Stöckhardt – a pioneer of applied chemistry by O. Wienhaus (pp. 139-144).
From 1838 to 1847 J. A. Stöckhardt was engaged in teaching and research work at the Königliche Sächsische Gewerbeschule (Royal Saxon Industrial School), Chemnitz – the present-day place of activity of Prof. G. Marx – and from 1847 to 1883 at the Königliche Forstakademie (Royal Academy of Forestry) in Tharandt – the present place of work of the author. J. A. Stöckhardt is acknowledged as the founder of agricultural and forestry experimental stations and research on fume damage (air pollution). His book Die Schule der Chemie (School of Chemistry) was a standard work in many countries over several decades; it was an introduction to this discipline for a great number of young people among them A. v. Bayer, E. Fischer, W. Ostwald, O. Wallach. The merits of this outstanding applied chemist have, surprisingly, not been stressed adequately in previous treatises on the history of chemsitry.
Some topical applications of plasma atomic spectrochemical methods for the analysis of ceramic powders by H. Nickel; J. A. C. Broekaert (pp. 145-155).
The scope of a number of plasma spectrochemical methods for the determination of the main components and impurities in ceramic powders is described. These methods meet the requirements for the analytical characterization of new structural and functional ceramics for modern industrial applications and electronic devices. For ceramic powders, spectrochemical analysis with direct methods as well as analysis subsequent to sample dissolution are discussed. Fusion is a powerful method for the dissolution of ZrO2 ceramic powders, provided the fluxes are pure enough. For determinations in Al2O3, SiC and ZrO2, it will be shown that ICP-MS is very useful. This is especially true for trace analysis after matrix removal. The latter can easily be performed on-line in the case of the analysis of Al2O3 powders. For direct analysis of ceramic powders, the direct insertion of samples into the plasma, spark and arc ablation, laser ablation, electrothermal vaporization and slurry nebulization are discussed. Particular attention is given to the direct analysis of ceramics in powder form (Al2O3, SiC, Si3N4, B4, WC) using ICP-OES with slurry nebulization as well as with direct sample insertion (DSI) and with electrothermal vaporization (ETV). For the two latter methods, the use of chemical modifiers for volatile compound formation will be shown to be of great importance, and its features will be explained using thermochemical considerations.
Experiments to determine the escape probability of photoelectrons by J. Zemek; S. Hucek (pp. 156-159).
A novel experimental method for the assessment of the escape probability of photoelectrons as a function of depth and their mean escape depths is described and illustrated for photoelectrons leaving an aluminium oxide surface. The results are compared with those of the straight line approximation model calculations.
Direct spectrometry of solids in view of information characteristics by K. Flórián; J. Haßler; A. Hudák; M. Matherny (pp. 160-164).
The development of atomic spectrometric methods in recent years is characterized by a remarkable orientation towards direct analysis of solids using various sample introduction techniques in connection with inductively coupled plasma excitation. The old-fashioned direct-current arc excitation with computer-controlled arc current vs. time programming has been studied as an alternative to the above mentioned methods. The influence of different electrode material, different sample preparation mode and working atmosphere on the main figures of merit (precision of the method, dynamic concentration range, determination limit, etc.) have been studied using an evaluation procedure based on the information theory.
Analysis of the spatial distribution of the constituting elements in amorphous solids: Laser ablation with ICP spectrometry by Sabine Rings; Rolf Sievers; M. Jansen (pp. 165-173).
Amorphous materials of the systems Si/B/N/C and Ba/Si/Al/O/C, which are highly resistant against thermal and chemical attack, were analyzed using laser ablation inductively coupled plasma atomic emission (LA-ICP-AES) and mass spectrometry (MS) in order to prove the applicability of these techniques to this special type of materials. Homogeneity was evaluated and the concentrations of the main components were determined with a resolution of 50 μm. A good reproducibility was obtained using one element for internal standardization (0.3–0.7% RSD for Si and Al with Ba as internal standard and about 1.5% for B with Si as internal standard). Scanning white light interferometry employed for the measuring of the crater volumes was tested to support the internal standardization method.
Comparison between different presentations of pore size distribution in porous materials by K. Meyer; P. Klobes (pp. 174-178).
The different presentations of the pore size distribution derived from the gas adsorption method and the mercury porosimetry are connected with some problems. This concerns especially the use of the logarithmically differential pore volume distribution. The incorrect application of this distribution to bimodal pore systems involves the danger of an apparent overemphasizing of larger pores. This effect may also occur using the incremental pore size distribution in case the experimental point spacing considerably increases towards the larger pore radii. The pore volume density distribution defined as the linear derivative of the cumulative pore volume curve with respect to the pore radius has been found the most convenient form among the various kinds of pore volume distribution presentations. It has been shown that the direct comparison between this distribution and the logarithmically differential pore volume distribution is not allowed. Nevertheless, there is a clear connection between these definitions for the pore size distribution so that they are completely equivalent.
Chemical analysis of thin films by means of SS-MS, GD-OES, and XPS demonstrated at Ir-Si thermoelectrica by R. Kurt; V. Hoffmann; R. Reiche; W. Pitschke; K. Wetzig (pp. 179-184).
Analytical methods with low detection limits were used for the investigation of Ir-Si thin films, the physical properties of which vary strongly with the chemical composition and the amount of impurities. It is demonstrated how to solve chemical characterization of different thermoelectric Ir-Si thin films by spark source mass spectrometry (SS-MS), glow discharge optical emission spectroscopy (GD-OES) and X-ray photoelectron spectroscopy (XPS). The combined use of the three different facilities allows the quantification of impurities of elements of the entire periodic system in the ppm range (down to 30 at.-ppm in dependence on the element) incorporated in thin film samples. Additional information about the in-depth distribution of elements or specifically bonded species can be achieved with a high depth resolution.
15N CP/MAS NMR as an instrument in structure investigations of organosilicon polymers by E. Brendler; E. Ebrecht; B. Thomas; G. Boden; T. Breuning (pp. 185-188).
15N solid state NMR without enrichment is rarely used because of the low sensitivity and low natural abundance of this nucleus. As demonstrated on different nitrogen-containing polysilanes and polysilazanes, it can be shown that with the CP/MAS technique spectra can be obtained in good quality and within acceptable measuring time. Three main different nitrogen sites – NSi3, NSi2H and NSiH2– can be observed as well as changes in the intensities of these sites with reaction and tempering conditions. Thus the spectra give valuable additional information for a better understanding of the structures and their changes within the investigated systems.
Ultra-thin PTCDA layers studied by optical spectroscopies by R. Kaiser; M. Friedrich; T. Schmitz-Hübsch; F. Sellam; T. U. Kampen; K. Leo; D. R. T. Zahn (pp. 189-192).
3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) was deposited using organic molecular beam deposition (OMBD) onto various substrates, i.e. mica(0001), Au(111) layers on mica, and Se-passivated GaAs(100). Layer thicknesses were from 2 to 30 nm. Reflectance and transmittance measurements were performed in order to identify PTCDA absorption features and find suitable laser wavelengths for subsequent Raman investigations. Despite the low thicknesses the Raman spectra reveal strong scattering by the molecular vibrational modes, in particular above 1200 cm–1. Frequency shifts of various modes in the layers from their values in PTCDA source material may indicate the influence of the substrates. Similar shifts were also observed in infrared spectra of the same materials.
Influence of relative humidity in sensing halogenated hydrocarbons with Reflectometric Interference Spectroscopy (RIfS) by S. Kaspar; F. Rathgeb; D. Nopper; G. Gauglitz (pp. 193-196).
For stand-alone sensor systems apart from defined laboratory circumstances sensors are required, which show a high stability against perturbing environmental influences like the relative humidity (r.h.). We present a portable sensor system, which is capable to quantify tetrachloroethene (TCE) in humid air. The system works highly reproducible and shows only negligible cross-sensitivity towards relative humidity. This allows a single calibration valid from 0 to 80% r.h.. Therefore, referencing with an extra sensor for humidity is not necessary. Binary mixtures of TCE and freone R113 were quantified for 0 and 40% r.h. with a root mean square error of prediction of approximately 3% with respect to the maximum concentration of TCE and R113. The sensitive elements used in the experiments consisted of thin polymer films on glass substrates. The measurements were performed with the optical measurement technique RIfS (Reflectometric Interference Spectroscopy).
Influence of surface morphology on the oxidation of metal electrodes studied by in-situ grazing incidence x-ray diffractometry by Sadagopan Sathiyanarayanan; Mario Sahre; W. Kautek (pp. 197-201).
The successful application of in-situ grazing incidence x-ray diffractometry (GIXD) for the investigation of oxidation processes at copper electrodes in pH 12 electrolytes is demonstrated. A penetration/escape depth of about 1 μm could be detected for a smooth polycrystalline copper foil and an x-ray incidence angle of 1.7°. Oxide layers generated at overpotentials less than about 0.5 V in respect to the equilibrium formation potentials of Cu2O or CuO, respectively, showed a dependence of the crystalline oxide formation on the defect density of the copper substrate. Highly disordered ground or polished specimens exhibited an order of magnitude higher GIXD reflexes from crystalline Cu2O than electrodeposited copper. Beyond overpotentials of 0.5 V, this epitaxial information for the Cu2O crystal growth became irrelevant. Further, GIXD turned out to be an appropriate tool to monitor atmospheric corrosion processes under thin humidity films with oxygen access. When oxygen diffusion through the polymer window membrane is allowed, oxygen reduction led to the concurrent formation of a crystalline CuO phase coexisting with amorphous Cu(OH)2 and Cu2O, though the potential was kept in the region of Cu2O.
Phase relations in the system V/Nb/O. V. Investigation of mixed crystals V1-xNbxO2 by H. Oppermann; F. von Woedtke; T. Reich; M. A. Denecke; H. Nitsche; M. Doerr (pp. 202-205).
Mixed crystals V1-xNbxO2 exist over the whole area of the quasibinary line VO2-NbO2. The existence of Nb5+ beside V3+ and V4+ on the V-rich side and V3+ beside Nb5+ and Nb4+ on the Nb-rich side of the mixed crystals is demonstrated by XANES-measurements. The compound VNbO4(V0.5Nb0.5O2) is described as a double oxide with vanadium only as V3+ and niobium only as Nb5+. At this point the electric resistivity of the solid solution shows a maximum.
Force measurements on hydrophobized silica surfaces by using AFM by G. Hüttl; K. Heger; V. Klemm; J. Theissig; W. Wagner; E. Müller (pp. 206-208).
Force measurements between SiO2 surfaces with and without adsorbed phenyl groups in aqueous media using the atomic force microscope (AFM) are compared. An oxidized silicon tip and an oxidized silicon wafer were hydrophobized with phenyl groups, and the long-range attraction induced by hydrophobation is shown in force vs. distance curves. The observed differences prove that the silanol groups of the unmodified SiO2 surface are replaced by the phenyl groups.
Preparation and characterisation of chromium and sodium tantalate layers by anodic spark deposition by F. Schlottig; J. Schreckenbach; G. Marx (pp. 209-211).
A plasma-electrochemical synthesis was used to prepare chromium and sodium tantalate layers. These layers were deposited on a tantalum anode surface as ceramic compounds from aqueous electrolytes. The typical pore structure morphology of the tantalate layer was characterised by SEM as well as fractures which provide evidence of an intimate contact between layers and substrate. An XRD-study showed that the layers are composed of a mixture of Ta2O5 and either NaTaO3 or CrTaO4 depending on the electrolyte composition. Quantitative characterisation by EPM indicated higher chromium and tantalum concentrations on the electrolyte/layer interface than at the layer/tantalum interface. The chemical state of tantalum was investigated by means of XPS.
Characterization of thin metastable vanadium oxide films by Raman spectroscopy by J. P. Schreckenbach; Klaus Witke; Diethard Butte; Günter Marx (pp. 211-214).
Thin films are potentiodynamically generated on vanadium in Ba2+/acetate electrolyte systems at high voltages. The influence of the anodic potential up to 400 V on the composition and structure of the about 500 nm thin anodic conversion films are investigated. Raman spectroscopy indicates that different film types depend on the electrochemical process parameters. The relationship between the Raman laser excitation power and the amorphous or microcrystalline film structure is also discussed. Beside metastable disordered structures the films contain crystalline phases of V2O5, V4O9 and barium vanadate, respectively.