X-ray Mapping (x-ray + mapping)

Distribution by Scientific Domains

Selected Abstracts

Spatially resolved X-ray diffraction as a tool for strain analysis in laterally modulated epitaxial structures

A. Wierzbicka
Abstract Spatially resolved X-ray diffraction (SRXRD) is applied for micro-imaging of strain in laterally modulated epitaxial structures. In GaAs layers grown by liquid phase epitaxial lateral overgrowth (ELO) on SiO2 -masked GaAs substrates a downward tilt of ELO wings caused by their interaction with the mask is observed. The distribution of the tilt magnitude across the wings width is determined with ,m-scale spatial resolution. This allows measuring of the shape of the lattice planes in individual ELO stripes. If a large area of the sample is studied the X-ray imaging provides precise information on the tilt of an individual wing and its distribution. In heteroepitaxial GaSb/GaAs ELO layers local mosaicity in the wing area is found. By the SRXRD the size of microblocks and their relative misorientation were analyzed. Finally, the SRXRD technique was applied to study distribution of localized strain in AlGaN epilayers grown by MOVPE on bulk GaN substrates with AlN mask. X-ray mapping proves that by mask patterning strain in AlGaN layer can be easily engineered, which opens a way to produce thicker, crack-free AlGaN layers with a higher Al content needed in GaN-based laser diodes. All these examples show that high spatial and angular resolutions offered by SRXRD makes the technique a powerful tool to study local lattice distortions in semiconductor microstructures. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Neutron Activation Analysis, Atomic Absorption and X-Ray Fluorescence Spectrometry Review for 2006,2007

L. Paul Bdard
These mature analytical techniques do not show any change in publication level from the previous two years and AAS remains dominant in terms of the number of publications. The last two years have seen fewer technical improvements than in the previous review period. Some interesting papers dealing with uncertainty and quality assurance in INAA were published during 2006,2007. It is suggested that photon activation should be reconsidered because the source of electron accelerators has recently improved. A technique to preconcentrate Se for INAA determination has also been proposed. In the case of AAS, papers on analyte preconcentration continue to be more abundant than those relating to instrumental modification. Sample preparation for AAS is also active and ultrasound-assisted leaching shows some promising applications. There were an unusual number of reviews concerned with AAS and those important to geological samples are cited here. A technique to preconcentrate Cr in water is presented and a new device to determine As and Se is showing some potential uses. Confocal X-ray mapping continues to show interesting developments. One group developed a technique to perform XRF inside an oyster and an interesting application of ,-XRF mapping of sediments is presented. Determination of platinum-group elements (at ,g g1 concentrations) can be carried out very quickly with an improved XRF technique. [source]

Prograde metamorphic sequence of REE minerals in pelitic rocks of the Central Alps: implications for allanite,monazite,xenotime phase relations from 250 to 610 C

Abstract The distribution of REE minerals in metasedimentary rocks was investigated to gain insight into the stability of allanite, monazite and xenotime in metapelites. Samples were collected in the central Swiss Alps, along a well-established metamorphic field gradient that record conditions from very low grade metamorphism (250 C) to the lower amphibolite facies (,600 C). In the Alpine metapelites investigated, mass balance calculations show that LREE are mainly transferred between monazite and allanite during the course of prograde metamorphism. At very low grade metamorphism, detrital monazite grains (mostly Variscan in age) have two distinct populations in terms of LREE and MREE compositions. Newly formed monazite crystallized during low-grade metamorphism (<440 C); these are enriched in La, but depleted in Th and Y, compared with inherited grains. Upon the appearance of chloritoid (,440,450 C, thermometry based on chlorite,choritoid and carbonaceous material), monazite is consumed, and MREE and LREE are taken up preferentially in two distinct zones of allanite distinguishable by EMPA and X-ray mapping. Prior to garnet growth, allanite acquires two growth zones of clinozoisite: a first one rich in HREE + Y and a second one containing low REE contents. Following garnet growth, close to the chloritoid,out zone boundary (,556,580 C, based on phase equilibrium calculations), allanite and its rims are partially to totally replaced by monazite and xenotime, both associated with plagioclase ( biotite staurolite kyanite quartz). In these samples, epidote relics are located in the matrix or as inclusions in garnet, and these preserve their characteristic chemical and textural growth zoning, indicating that they did not experience re-equilibration following their prograde formation. Hence, the partial breakdown of allanite to monazite offers the attractive possibility to obtain in situ ages, representing two distinct crystallization stages. In addition, the complex REE + Y and Th zoning pattern of allanite and monazite are essential monitors of crystallization conditions at relatively low metamorphic grade. [source]

Noble Metal Decoration and Alignment of Carbon Nanotubes in Carboxymethyl Cellulose

Mallikarjuna N. Nadagouda
Abstract A facile microwave method (MW) is described that accomplishes alignment and decoration of noble metals on carbon nanotubes (CNT) wrapped with carboxymethyl cellulose (CMC). Carbon nanotubes such as single- and multi-walled, and Buckminsterfullerene (C-60) are well dispersed using the sodium salt of CMC under sonication. Addition of respective noble metal salts then generates noble metal-decorated CNT composites at room temperature. However, aligned nanocomposites of CNTs could only be generated by exposing the above nanocomposites to MW irradiation. The CNT composites are characterized using scanning electron microscopy, energy dispersive X-ray analysis, X-ray mapping, transmission electron microscopy, and UV-visible spectroscopy. The general preparative procedure is versatile and provides a simple route to manufacturing useful metal-coated CNT nanocomposites. [source]