46 research outputs found
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Interface reaction characterization and interfacial effects in multilayers
The performance of multilayer structures as x-ray, soft x-ray and extreme ultraviolet optics is dependent on the nature of the interfaces between constituent layers. Interfacial structure and the interaction between atoms at interfaces have also been demonstrated to have significant impact on the physical properties of multilayer materials in general and thus on their performance in other applied areas. As short summary of the approaches to characterization of interfaces in multilayer structures is presented as background. Two new techniques for the experimental evaluation of interfacial structure and interfacial structure effects are then considered and examples presented. Model calculations for one of these techniques which support the experimental results are also presented. In conclusion these results are reviewed of and an assessment of their implications relative to multilayer development given
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Interface reaction characterization and interfacial effects in multilayers
The performance of multilayer structures as x-ray, soft x-ray, and extreme ultraviolet optics is dependent an the nature of the interfaces between constituent layers. Interfacial structure and the interaction between atoms at interfaces have also been demonstrated to have significant impact on the physical properties of multilayer materials in general and thus in their performance in other applied areas. As short summary of the approaches to characterization of interfaces in multilayer structures is presented as background. Two new techniques for the experimental evaluation of interfacial structure and interfacial structure effects are then considered and examples presented. Model calculations for one of these techniques which support the experimental results are also presented. In conclusion these results are reviewed of and an assessment of their implications relative to multilayer development given
Sputter Deposition of Semiconductor Superlattices for Thermoelectric Applications
Theoretical dramatic improvement of the thermoelectric properties of materials by using quantum confinement in novel semiconductor nanostructures has lead to considerable interest in the thermoelectric community. Therefore, we are exploring the critical materials issues for fabrication of quantum confined structures by magnetron sputtering in the lead telluride and bismuth telluride families of materials. We have synthesized modulated structures from thermoelectric materials with bilayer periods of as little as 3.2 nm and shown that they are stable at deposition temperatures high enough to grow quality films. Issues critical to high quality film growth have been investigated such as nucleation and growth conditions and their effect on crystal orientation and growth morphology. These investigations show that nucleating the film at a temperature below the growth temperature of optimum electronic properties produces high quality films. Our work with sputter deposition, which is inherently a high rate deposition process, builds the technological base necessary to develop economical production of these advanced materials. High deposition rate is critical since, even if efficiencies comparable with CFC based refrigeration systems can be achieved, large quantities of quantum confined materials will be necessary for cost-competitive uses
Measurements of laser-hole boring into overdense plasmas using x-ray laser refractometry(invited)
Copyright 1999 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments, 70(1), 543-548, 1986 and may be found at http://dx.doi.org/10.1063/1.114938
X-ray standing wave and reflectometric characterization of multilayer structures
Microstructural characterization of synthetic periodic multilayers by x-ray
standing waves have been presented. It has been shown that the analysis of
multilayers by combined x-ray reflectometry (XRR) and x-ray standing wave (XSW)
techniques can overcome the deficiencies of the individual techniques in
microstructural analysis. While interface roughnesses are more accurately
determined by the XRR technique, layer composition is more accurately
determined by the XSW technique where an element is directly identified by its
characteristic emission. These aspects have been explained with an example of a
20 period Pt/C multilayer. The composition of the C-layers due to Pt
dissolution in the C-layers, PtC, has been determined by the XSW
technique. In the XSW analysis when the whole amount of Pt present in the
C-layers is assumed to be within the broadened interface, it l eads to larger
interface roughness values, inconsistent with those determined by the XRR
technique. Constraining the interface roughness values to those determined by
the XRR technique, requires an additional amount of dissolved Pt in the
C-layers to expl ain the Pt fluorescence yield excited by the standing wave
field. This analysis provides the average composition PtC of the
C-layers .Comment: 12 pages RevTex, 10 eps figures embedde
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High-Resolution Hard X-Ray and Gamma-Ray Spectrometers Based on Superconducting Absorbers Coupled to Superconducting Transition Edge Sensors
We are developing detectors based on bulk superconducting absorbers coupled to superconducting transition edge sensors (TES) for high-resolution spectroscopy of hard X-rays and soft gamma-rays. We have achieved an energy resolution of 70 eV FWHM at 60 keV using a 1 x 1 x 0.25 mm{sup 3} Sn absorber coupled to a Mo/Cu multilayer TES with a transition temperature of 100 mK. The response of the detector is compared with a simple model using only material properties data and characteristics derived from IV-measurements. We have also manufactured detectors using superconducting absorbers with a higher stopping power, such as Pb and Ta. We present our first measurements of these detectors, including the thermalization characteristics of the bulk superconducting absorbers. The differences in performance between the detectors are discussed and an outline of the future direction of our detector development efforts is given
Effect of stress-triaxiality on void growth in dynamic fracture of metals: a molecular dynamics study
The effect of stress-triaxiality on growth of a void in a three dimensional
single-crystal face-centered-cubic (FCC) lattice has been studied. Molecular
dynamics (MD) simulations using an embedded-atom (EAM) potential for copper
have been performed at room temperature and using strain controlling with high
strain rates ranging from 10^7/sec to 10^10/sec. Strain-rates of these
magnitudes can be studied experimentally, e.g. using shock waves induced by
laser ablation. Void growth has been simulated in three different conditions,
namely uniaxial, biaxial, and triaxial expansion. The response of the system in
the three cases have been compared in terms of the void growth rate, the
detailed void shape evolution, and the stress-strain behavior including the
development of plastic strain. Also macroscopic observables as plastic work and
porosity have been computed from the atomistic level. The stress thresholds for
void growth are found to be comparable with spall strength values determined by
dynamic fracture experiments. The conventional macroscopic assumption that the
mean plastic strain results from the growth of the void is validated. The
evolution of the system in the uniaxial case is found to exhibit four different
regimes: elastic expansion; plastic yielding, when the mean stress is nearly
constant, but the stress-triaxiality increases rapidly together with
exponential growth of the void; saturation of the stress-triaxiality; and
finally the failure.Comment: 35 figures, which are small (and blurry) due to the space
limitations; submitted (with original figures) to Physical Review B. Final
versio
Closed-Form transformation between geodetic and ellipsoidal coordinates
We present formulas for direct closed-form transformation between geodetic coordinates(Φ, λ, h) and ellipsoidal coordinates (β, λ, u) for any oblate ellipsoid of revolution.These will be useful for those dealing with ellipsoidal representations of the Earth's gravityfield or other oblate ellipsoidal figures. The numerical stability of the transformations for nearpolarand near-equatorial regions is also considered