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Medium Approximation (medium + approximation)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

Spectroscopic ellipsometry study of thin diffusion barriers of TaN and Ta for Cu interconnects in integrated circuits

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2008
S. Rudra
Abstract The objective of this work is to study the optical and electrical properties of tantalum nitride and tantalum barrier thin films used against copper diffusion in Si in integrated circuits using spectroscopic ellipsometry in the VUV and UV,visible range. Single layers of tantalum nitride and bilayer films of Ta/TaN were produced by reactive magnetron sputtering on Si(100) substrates covered with a native oxide layer. Ellipsometric measurements were performed in the energy range from 0.73,8.7 eV and the dielectric functions were simulated using Drude,Lorentz model and effective medium approximation (EMA) in order to obtain information regarding film thickness, film composition, free carrier plasma energy, mean relaxation time and electrical resistivity. The film thickness clearly affects the electrical resistivity and the electron mean free path. It was observed that for films of Ta on TaN even after maintaining the deposition condition suitable for the ,-phase of Ta, it turned out to be a mixture of ,- and ,-phases with higher contribution of the ,-phase. It is shown that even a very small intermixture of two different phases of Ta can be determined accurately using ellipsometry. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magneto-optical, optical and magnetic properties of the Mn1,xFex alloy films

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003
Y. V. Kudryavtsev
Abstract A set of Mn1,xFex alloy films with 0 < x < 1 has been prepared by face-to-face DC sputtering onto glass substrates kept at 293 K. The X-ray diffraction study reveals that an , -Fe phase with bcc-type of structure is the prevailing phase for the Mn1,xFex alloy films with 0.8 < x < 1, while , -Mn,Fe and , -Mn phases are dominant for 0.2 < x < 0.8 and x < 0.2, respectively. The experimental equatorial-Kerr-effect spectra for Mn1,xFex alloy films, which are observed only for x < 0.5, have nearly the same spectral shape (Fe-like), and differ from each other only by the intensity. They are nicely reproduced in the framework of the effective medium approximation by using scaled off-diagonal components of the dielectric function for pure Fe film and measured optical constants for the corresponding alloys. The optical properties of all the investigated alloys can be separated into three groups which are related to different prevailing crystalline structures of alloys. [source]

Investigation of graded index SiOxNy antireflection coating for silicon solar cell manufacturing

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2007
M. Lipi
Abstract An optimization of SiOxNy anti-reflective coatings with graded index layers for silicon solar cells based on the Bruggeman's effective medium approximation is presented. For simulation of reflectance and absorption of graded layer, the experimental optical data of silicon nitride SiNx:H and oxynitride SiOxNy obtained by Low Frequency (440 kHz) Plasma Enhanced Chemical Vapour Deposition (LF-PECVD) were used. We have shown that the graded index oxynitride antireflection coating can reduce the effective reflectance to about 2.5% but the high absorption due to high extinction coefficient compensates this improvement and reduces the short circuit current (Jsc) of the solar cell. The improvement in the Jsc can be obtained for graded SiNxOy layer with smaller value of refractive index of SiNx (n = 2.2). In this case the graded SiOxNy layer is characterized by an abrupt concentration profile and can be considered as a double antireflection coating SiO2/SiNx. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Structural acclimation and radiation regime of silver fir (Abies alba Mill.) shoots along a light gradient

PLANT CELL & ENVIRONMENT, Issue 3 2003
A. CESCATTI
ABSTRACT Shoot architecture has been investigated using the ratio of mean shoot silhouette area to total needle area ( ) as a structural index of needle clumping in shoot space, and as the effective extinction coefficient of needle area. Although can be used effectively for the prediction of canopy gap fraction, it does not provide information about the within-shoot radiative regime. For this purpose, the estimation of three architectural properties of the shoots is required: needle area density, angular distribution and spatial aggregation. To estimate these features, we developed a method based on the inversion of a Markov three-dimensional interception model. This approach is based on the turbid medium approximation for needle area in the shoot volume, and assumes an ellipsoidal angular distribution of the normals to the needle area. Observed shoot dimensions and silhouette areas for different vertical and azimuth angles (AS) are used as model inputs. The shape coefficient of the ellipsoidal distribution (c) and the Markov clumping index (,0) are estimated by a least square procedure, in order to minimize the differences between model prediction and measurements of AS. This methodology was applied to silver fir (Abies alba Mill.) shoots collected in a mixed fir,beech,spruce forest in the Italian Alps. The model worked effectively over the entire range of shoot morphologies: c ranged from 1 to 8 and ,0 from 0·3 to 1 moving from the top to the base of the canopy. Finally, the shoot model was applied to reconstruct the within-shoot light regime, and the potential of this technique in upscaling photosynthesis to the canopy level is discussed. [source]