Unsteady hydromagnetic rotating flow of a conducting second grade fluid

The purpose of this work is to investigate the hydromagnetic oscillatory flow of a fluid bounded by a porous plate, when the entire system rotates about an axis normal to the plate. The fluid is assumed to be non-Newtonian (second grade), incompressible and electrically conducting. The magnetic field is applied transversely to the direction of the flow. Such a flow model has great significance not only of its theoretical interest, but also for applications to geophysics and engineering. The resulting initial value problem has been solved analytically for steady and unsteady cases. The analysis of the obtained results showed that the flow field is appreciably influenced by the material parameter of the second grade fluid, the applied magnetic field, the imposed frequency, rotation and suction and blowing parameters. It is observed in a second grade fluid that a steady asymptotic hydromagnetic solution exists for blowing and resonance which is different from the hydrodynamic situation.     

Pulsed laser deposition of non-stoichiometric silicon nitride (SiNx) thin films

Silicon nitride (SiN_x) thin films of various stoichiometries (x) were prepared on Si (100) substrates applying the Nd:YAG (=1064 nm) pulsed laser deposition (PLD) process in the shaded off-axis technique at room temperature. The specific arrangement of this technique with perpendicular target (Si) and substrate surfaces and a metallic screen in between guarantees very low particulate (droplet) deposition and, thus, excellent surface qualities. Compared to the usually used on-axis deposition technique consisting of a parallel arrangement of the target and substrate surface, the coating surface covered with particulates is about 100 times lower reaching a maximum of 0.2% on 400 nm thick films. The variation the N₂ partial pressure affects the nitrogen content and the silicon bonding structure of the films analysed by means of SIMS and XPS, respectively. As a consequence the optical properties (e.g.m refractive index) are tailorable in a wide spectral range between 250 and 1200 nm. PACS 81.15.Fg; 78.20.Ci     

Quantitative SIMS depth profiling of diffusion barrier gate-oxynitride structures in TFT-LCDs

Gate oxynitride structures of TFT-LCDs were investigated by SIMS, and successful solutions are demonstrated to overcome difficulties arising due to the charging effects of the multilayer systems, the matrix effect of the method, and the small pattern sizes of the samples. Because of the excellent reproducibility achieved by applying exponential relative sensitivity functions for quantitative analysis, minor differences in the barrier gate-oxynitride composition deposited on molybdenum capped aluminium-neodymium metallisation electrodes were determined between the centre and the edge of the TFT-LCD substrates. No differences were found for molybdenum-tungsten metallisations. Furthermore, at the edge of the glass substrates, aluminium, neodymium, and molybdenum SIMS depth profiles show an exponential trend. With TEM micrographs an inhomogeneous thickness of the molybdenum capping is revealed as the source of this effect, which influences the electrical behaviour of the device.The production process was improved after these results and the aging behaviour of TFT-LCDs was investigated in order to explain the change in control voltage occurring during the lifetime of the displays. SIMS and TEM show an enrichment of neodymium at the interface to the molybdenum layer, confirming good diffusion protection of the molybdenum barrier during accelerated aging. The reason for the shift of the control voltage was finally located by semi-quantitative depth profiling of the sodium diffusion originating from the glass substrate. Molybdenum-tungsten was a much better buffer for the highly-mobile charge carriers than aluminium-neodymium. Best results were achieved with PVD silicon oxynitride as diffusion barrier and gate insulator deposited on aluminium-neodymium metallisation layers.     

Low energy RBS and SIMS analysis of the SiGe quantum well

The Ge concentration in a MBE grown SiGe and the depth of the quantum well has been quantitatively analysed by means of low energy Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS). The concentrations of Si and Ge were supposed to be constant, except for the quantum well, where the nominal germanium concentration was at 5%. Quantitative information was deduced out of raw data by comparison to SIMNRA simulated spectra. With the knowledge of the response function of the SIMS instrument (germanium delta (δ) layer) and using the model of forward convolution (point to point convolution) it is possible to determine the germanium concentration and the thickness of the analysed quantum well out of raw SIMS data.     

Investigations of corrosion phenomena on gold coins with SIMS

In order to establish a new handling procedure for contaminated coins, the Coin Cabinet and the Conservation Science Department of the Kunsthistorisches Museum, Vienna, initiated a research project on corrosion effects of gold coins. By now, investigations on historic and contemporary coins included optical microscopy, scanning electron microscopy (SEM), Auger electron microscopy (AES), X-ray photoelectron microscopy (XPS), and electrochemical methods showing the distribution of pollutants.This work focuses on secondary ion mass spectrometry (SIMS) investigations merely showing the distribution of electronegative elements, such as sulfur, oxygen, and chlorine on the surface. Sulfur is highly suspected of causing the observed corrosion phenomena, and is indeed enriched near polluting splints. Since SIMS is a destructive method, the investigated samples are test coins with intentionally added impurities. These coins were manufactured in cooperation with the Austrian Mint. They were treated with potassium polysulfide (K₂S_x) for 8 h gaining a rapid corrosion of the surface.SIMS mass spectra, depth profiles, and images were done (a) at non-polluted areas, (b) near polluted areas with slight coloring, and (c) directly at polluting stains showing enrichments of sulfur and chlorine. Due to the success of these investigations further studies on historic coins are intended.     

Soft norm-conserving pseudopotential for carbon

A soft, norm-conserving pseudopotential for carbon is presented and its performance tested by calculations on atomic states and on diamond: electronic energy levels of different atomic configurations, equilibrium lattice constant, bulk modulus, and the TA(X) frozen-phonon frequency are accurately reproduced. Convergence of the total energy of diamond with the size of the plane-wave basis set is compared for several frequently used pseudopotentials, and it is shown that calculations with the reported pseudopotential can be performed at considerably lower cost than with the other norm-conserving pseudopotentials, without loosing the accuracy of the latter in predicting structural and dynamical properties. The rapid convergence of the results with the plane-wave cutoff is comparable to the performance of the Vanderbilt's ultrasoft pseudopotentials. The transferability of the pseudopotential to other electronic configurations is discussed. Received 8 September 1999     

Hall effects on the unsteady hydromagnetic oscillatory flow of a second-grade fluid

An exact solution of an oscillatory flow is constructed in a rotating fluid under the influence of an uniform transverse magnetic field. The fluid is considered as second-grade (non-Newtonian). The influence of Hall currents and material parameters of the second-grade fluid is investigated. The hydromagnetic flow is generated in the uniformly rotating fluid bounded between two rigid non-conducting parallel plates by small amplitude oscillations of the upper plate. The exact solutions of the steady and unsteady velocity fields are constructed. It is found that the steady solution depends on the Hall parameter but is independent of the material parameter of the fluid. The unsteady part of the solution depends upon both (Hall and material) parameters. Attention is focused upon the physical nature of the solution, and the structure of the various kinds of boundary layers is examined. Several results of physical interest have been deduced in limiting cases.     

Local Ions Distribution Inhomogeneities in Polymer Based Light Emitting Cells

 In the last years the development of light emitting electrochemical cells on a polymer base has made a great progress. They are extremely interesting due to their low cost, but still, problems concerning the stability and lifetime of these elements remain. The performance of light-emitting electrochemical cells (LEC) is strongly influenced by the inhomogeneous distribution of the three main components (light emitting polymer, ion conductive polymer, ionic molecules) in the device. The local ions distribution of lithium and triflate (short for the CF₃SO₃ ⁻ species) ions in a blend with the ionic conducting polymer poly(ethylene oxide) (PEO) and the conjugated polymer m-LPPP (methyl substituted poly(para phenylene)) throughout the polymer layer has been investigated by secondary ion mass spectroscopy (SIMS). Different combinations of top- and base-electrodes have been investigated and have been found to influence the distribution of the ions strongly. Received January 13, 1999. Revision June 16, 2000.     

Fusion of 2-D SIMS Images Using the Wavelet Transform

 Secondary ion mass spectroscopy (SIMS) is a powerful method for element distribution examination of conducting and semi-conducting surfaces at high spatial resolution and with a high sensitivity. Routine surface analysis produces about 8 to 15 images in a short time, each of which displays the intensity distribution of one mass, thus generating a multispectral SIMS image. Formation of occlusions, segregations, and the overall location of the elements relative to each other, are difficult to recognise when looking at n separate 2-D images. Image fusion is a process whereby images obtained from various sensors, or at different moments of time, or under different conditions, are combined together to provide a more complete picture of the object under investigation. The process of combining SIMS images may be viewed as an attempt to compensate for the inherent effect of SIMS to channel the information obtained from the sample into different images, corresponding to different element phases. The wavelet transform is a powerful method for fusion of images. This work covers the use of wavelet based fusion algorithms on multispectral SIMS images, evaluating the performance of different wavelet based fusion rules on different type of image systems and comparing the results to conventional fusion techniques. An aim of this study is to increase the information, i.e. the number of masses, which can be merged into one image in order to enhance the perception and interpretation of the SIMS surface images.     

Environmental radiation and radioactivity in the vicinity of the Semipalatinsk Test Site

The International Atomic Energy Agency's Mission to Kazakhstan studied the present environmental contamination and the exposure risk from nuclear tests performed at the Semipalatinsk Test Site. On this mission, EML scientists collected in-situ gamma-ray spectra, measured external gamma dose rates, and collected soil samples. With the exception of plowshare areas and near ground zero, all the areas visited had external dose rates within typical environmental levels. Measurements within a 15 km radius of ground zero showed elevated levels of¹³⁷Cs,¹⁵²Eu, and⁶⁰Co. The dose rate within ≈1 km of ground zero ranged from 500 to 30000 nGy·h⁻¹.