1,511 research outputs found
Ion-implantation-caused special damage profiles determined by spectroscopic ellipsometry in crystalline and in relaxed (annealed) amorphous silicon
We previously developed a fitting method of several parameters to evaluate ion-implantation-caused damage profiles from spectroscopic ellipsometry (SE) (M. Fried et al., J. Appl. Phys., 71 (1992) 2835). Our optical model consists of a stack of layers with fixed and equal thicknesses and damage levels described by a depth profile function (coupled half Gaussians). The complex refractive index of each layer is calculated from the actual damage level by Bruggeman effective medium approximation (EMA) using crystalline (c-Si) and amorphous (a-Si) silicon as end-points. Two examples are presented of the use of this method with modified optical models. First, we investigated the surface damage formed by room temperature B+ and N+ implantation into silicon. For the analysis of the SE data we added a near surface amorphous layer to the model with variable thickness. Second, we determined 20 keV B+ implantation-caused damage profiles in relaxed (annealed) amorphous silicon. In this special case, the complex refractive index of each layer was calculated from the actual damage level by the EMA using relaxed a-Si and implanted a-Si as end-points. The calculated profiles are compared with Monte Carlo simulations (TRIM code); good agreement is obtained
Determination of complex dielectric functions of ion implanted and implantedāannealed amorphous silicon by spectroscopic ellipsometry
Measuring with a spectroscopic ellipsometer (SE) in the 1.8ā4.5 eV photon energy region we determined the complex dielectric function (Ļµ = Ļµ1 + iĻµ2) of different kinds of amorphous silicon prepared by selfāimplantation and thermal relaxation (500āĀ°C, 3 h). These measurements show that the complex dielectric function (and thus the complex refractive index) of implanted aāSi (iāaāSi) differs from that of relaxed (annealed) aāSi (rāaāSi). Moreover, its Ļµ differs from the Ļµ of evaporated aāSi (eāaāSi) found in the handbooks as Ļµ for aāSi. If we use this Ļµ to evaluate SE measurements of ion implanted silicon then the fit is very poor. We deduced the optical band gap of these materials using the DavisāMott plot based on the relation: (Ļµ2E2)1/3 ā¼ (Eā Eg). The results are: 0.85 eV (iāaāSi), 1.12 eV (eāaāSi), 1.30 eV (rāaāSi). We attribute the optical change to annihilation of point defects
Surface disorder production during plasma immersion implantation and high energy ion implantation
High-depth-resolution Rutherford Backscattering Spectrometry (RBS) combined with channeling technique was used to analyze the surface layer formed during plasma immersion ion implantation (PIII) of single crystal silicon substrates. Single wavelength multiple angle of incidence ellipsometry (MAIE) was applied to estimate the thickness of the surface layer. The thickness of the disordered layer is much higher than the projected range of P ions and it is comparable with that of protons.\ud
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Another example of surface damage investigation is the analysis of anomalous surface disorder created by 900 keV and 1.4 MeV Xe implantation in 100 silicon. For the 900 keV implants the surface damage was also characterized with spectroellipsometry (SE). Evaluation of ellipsometric data yields thickness values for surface damage that are in reasonable agreement with those obtained by RBS
Structural working conditions of journalism in Egypt, Kenya, Serbia and South Africa: Empirical findings from interviews with journalists reporting on democratisation conflicts
Journalistic practices, role perceptions and ethics in democratisation conflicts: Empirical findings from interviews with journalists in Egypt, Kenya, Serbia and South Africa
Non-destructive characterization of nitrogen-implanted silicon-on-insulator structures by spectroscopic ellipsometry
Silicon-on-insulator (SOI) structures implanted with 200 or 400 keV N+ ions at a dose of 7.5 Ć 1017cmā2 were studied by spectroscopic ellipsometry (SE). The SE measurements were carried out in the 300ā700 nm wavelength (4.13-1.78 eV photon energy) range. The SE data were analysed by the conventional method of using appropriate optical models and linear regression analysis. We applied a seven-layer model (a surface oxide layer, a thick silicon layer, upper two interface layers, a thick nitride layer and lower two interface layers) with good results. The fitted parameters were the layer thickness and compositions. The results were compared with data obtained from Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy. The sensitivity of our optical model and fitting technique was good enough to distinguish between the silicon-rich transition layers near the upper and lower interfaces of the nitride layer, which are unresolvable in RBS measurements
Comparative investigation of damage induced by diatomic and monoatomic ion implantation in silicon
The damaging effect of mono- and diatomic phosphorus and arsenic ions implanted into silicon was investigated by spectroscopic ellipsometry (SE) and high-depth-resolution Rutherford backscattering and channeling techniques. A comparison was made between the two methods to check the capability of ellipsometry to examine the damage formed by room temperature implantation into silicon. For the analysis of the spectroscopic ellipsometry data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and volume fractions of the amorphous silicon component in the layers) by linear regression. The depth dependence of the damage was determined by both methods. It was revealed that SE can be used to investigate the radiation damage of semiconductors together with appropriate optical model construction which can be supported or independently checked by the channeling method. However, in case of low level damage (consisting mainly of isolated point defects) ellipsometry can give false results, overestimating the damage using inappropriate dielectric functions. In that case checking by other methods like channeling is desirable
High-temperature catalyst for catalytic combustion and decomposition
A robust, high temperature mixed metal oxide catalyst for propellant composition, including high concentration hydrogen peroxide, and catalytic combustion, including methane air mixtures. The uses include target, space, and on-orbit propulsion systems and low-emission terrestrial power and gas generation. The catalyst system requires no special preheat apparatus or special sequencing to meet start-up requirements, enabling a fast overall response time. Start-up transients of less than 1 second have been demonstrated with catalyst bed and propellant temperatures as low as 50 degrees Fahrenheit. The catalyst system has consistently demonstrated high decomposition effeciency, extremely low decomposition roughness, and long operating life on multiple test particles
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