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Paper des Monats
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Clear evidence of the effects caused by hydrogen, introduced in different forms in an analytical glow discharge source (GDS) operated with argon, is presented for the different matrix elements copper, stainless steel, titanium, aluminium and silicon. When hydrogen is present even in small quantities in argon, not only are there significant changes in the emission line intensities of most elements (analyte and plasma species), but also new spectral features, such as emission bands of new compounds (hydrides of sputtered sample constituents) and a continuous background in the range ~220440 nm. Moreover, the discharge current (the dependent parameter in our experiments) decreases with increasing hydrogen concentration. Different modes of hydrogen introduction, externally in gaseous form or sputtered as a sample constituent, cause very similar effects in terms of discharge current, line intensity (of analyte and plasma gas) and emission continua, which implies similar changes in the discharge processes in the two cases. The excitation of the hydrogen continuum appears to quench the population of the argon metastables (11.55 and 11.72 eV) and, consequently, other elementary processes in the plasma in which the argon metastables take part, but to a different extent for each analyte.
The influence of hydrogen contained in a sample or otherwise introduced into a glow discharge source (GDS) is here extensively experimentally presented for the case of copper as a sample by means of the addition of small quantities of molecular hydrogen (<1% relative partial pressure) to the argon carrier gas. The progressive addition of molecular hydrogen causes different intensity changes particular to the individual lines of different species such as atomic (Cu I) and ionic (Cu II) copper, and also atomic (Ar I) and ionic (Ar II) argon. Some interesting features of the emission spectrum of hydrogen such as its line, band and even continuum spectrum are observed. It was also found that the depth resolution becomes worse even at very low concentrations of hydrogen.
Low-energy BO and BO2 emission from H2BO3 sputtered in a low-pressure high-frequency SNMS plasma
(1999)
Background corrected secondary neutral energy spectra derived from Cu powder pellets with H3BO3, MgO, Al2O3, TiO2, Y2O3 and ZrO2, show energy distributions being more or less typical for collision cascades in the cases of the metal ions M+, of O+ at energies >5 eV above the ion generation potential, and of the molecules Cu2+, AlO+, TiO+, YO+ and ZrO+, whereas the larger parts of the energy distributions of BO+and BO2+exhibit a similar shape as the Ar+plasma gas ions. From this, and from the background of the low decomposition and melting temperatures of H3BO3 and B2O3, respectively, we conclude that the detected BO and BO2 molecules have been emitted with thermal energies in processes implying lower energies than collision cascades. Evidence was found that the same holds for HBO2 and H2BO2. In order to obtain relative correction factors for MO+ molecular ion intensities, electron impact ionization cross sections have been calculated for the light MO molecules using the binary-encounter Bethe (BEB) formula, and for the respective metal M atoms by means of the semiempirical Lotz formula. For the heavy MO molecules YO and ZrO, cross sections have been estimated using the Thomson formula. The comparison of corrected relative MO/M and M/Cu intensities yields evidence that thermal (H)BOx emission amounts to the same order of magnitude as B emission from collision cascades, and that this situation is comparable to the high yield of MO molecules emitted in collision cascades from oxides with high M masses. Since the normal energy window of an HF-plasma secondary neutral mass spectrometer does not accept particles with originally thermal energies, it is concluded that these findings are relevant for quantification.
Glow discharge optical emission spectroscopy (GD-OES) is briefly reviewed, with particular reference to topics relevant to the application field of near surface and thin film analysis. The special needs and requirements for thin film analysis, in contrast to coating and bulk analysis, are pointed out. A task list is developed which shows the requirements of further developments to the technique and the fundamentals. The state-of-the-art is presented in measurement technique, GD source control and design, the effect of traces of molecular gases, correction and quantification procedures, contributions of modelling and, finally, reference materials for thin film analysis.
The analysis of thin layers of thickness 100 nm has become a new field of application for glow discharge optical emission spectroscopy (GDOES). In this paper an overview is given of the experiences and possibilities gained by the authors in later years at their research, development and application of GDOES.
During GDOES analysis of a multilayer system the depth resolution was determined using the inverse maximal slope method. Under optimized discharge conditions a depth resolution of 25 nm at 100 nm depth was achieved. The gas flow in a Grimm-type source for glow discharge mass spectrometry (GDMS) was simulated and a correlation between calculated pressure and crater shape was found. Cleanness of the sample and source turned out to be essential for a fast stabilization time and reduction of the influence of light elements and molecules. Thereby, a 10 nm layer at the top surface of a sample could be quantified. Apart from the influence of density, the reflectivity of the sample surface is discussed. It is shown that a high sample reflectivity can cause up to 100% more light to be measured by the spectrometer.
Scanning electron microscopes are usually equipped with energy-dispersive X-ray detectors for electron probe microanalysis. This widespread analytical method allows investigators to determine the elemental composition of specimens with a spatial resolution of about 1 µm. However, owing to the electron-specimen interaction, the emitted spectra reveal, in addition to characteristic lines, also a high level of continuous bremsstrahlung background. As a result, elements with low concentrations cannot be identified. The minimum detection limit can be diminished by two orders of magnitude if the characteristic lines are excited as fluorescence by an additional x-ray source. In this case, the emergence of bremsstrahlung is considerably reduced. Combining a high-brilliance microfocus x-ray tube with efficient polycapillary optics enables one to realize an experimental arrangement for performing local fluorescence analysis at the same point where the electron beam hits the sample. The polycapillary optics under consideration focuses the emitted x-radiation onto focal spots between 30 and 100 µm in diameter. Count rates of several thousands cps have been achieved. Elemental maps have been obtained by means of the motorized specimen stage of the microscope. Copyright © 2005 John Wiley & Sons, Ltd.
An international interlaboratory comparison of the measurement capabilities of four National Metrology Institutes (NMIs) and one Designated Institute (DI) in the determination of the chemical composition of thin Fe-Ni alloy films was conducted via a key comparison (K-67) of the Surface Analysis Working Group of the Consultative Committee for Amount of Substance. This comparison was made using XPS (four laboratories) and AES (one laboratory) measurements. The uncertainty budget of the measured chemical composition of a thin alloy film was dominated by the uncertainty of the certified composition of a reference specimen which had been determined by inductively coupled plasma mass spectrometry using the isotope dilution method. Pilot study P-98 showed that the quantification using relative sensitivity factors (RSFs) of Fe and Ni derived from an alloy reference sample results in much more accurate result in comparison to an approach using RSFs derived from pure Fe and Ni films. The individual expanded uncertainties of the participants in the K-67 comparison were found to be between 2.88 and 3.40 atomic %. The uncertainty of the key comparison reference value (KCRV) calculated from individual standard deviations and a coverage factor (k) of 2 was 1.23 atomic %.
Sol-gel preparation of calcium titanium phosphate: viscosity, thermal properties and solubility
(2012)
Calcium titanium phosphate (CTP) was prepared by the sol–gel route in order to prepare suitable coatings. This work addresses the question of how to prepare stable CTP sols. Their rheological properties as a function of process parameters like solid loading and water content are investigated. It was found that an increased solid loading as well as an increased water content lead to an increased initial viscosity as well as a more pronounced ageing induced viscosity rise. In addition, the thermal behavior of the resulting xerogels was analyzed. Furthermore, we studied the ion release behavior of the xerogels when brought in contact with water. Results suggest that calcium titanium phosphate shows a diffusion controlled ion release mode with a preferential release of Ca.