Structural investigation of MOVPE-Grown GaAs on Ge by X-ray techniques

The selection of appropriate characterisation methodologies is vital for analysing and comprehending the sources of defects and their influence on the properties of heteroepitaxially grown III-V layers. In this work we investigate the structural properties of GaAs layers grown by Metal-Organic Vapour Phase Epitaxy (MOVPE) on Ge substrates – (100) with 6⁰ offset towards – under various growth conditions. Synchrotron X-ray topography (SXRT) is employed to investigate the nature of extended linear defects formed in GaAs epilayers. Other X-ray techniques, such as reciprocal space mapping (RSM) and triple axis ω-scans of (00l)-reflections (l = 2, 4, 6) are used to quantify the degree of relaxation and presence of antiphase domains (APDs) in the GaAs crystals. The surface roughness is found to be closely related to the size of APDs formed at the GaAs/Ge heterointerface, as confirmed by X-ray diffraction (XRD), as well as atomic force microscopy (AFM), and transmission electron microscopy (TEM)

Structural investigation of MOVPE-Grown GaAs on Ge by X-ray techniques

The selection of appropriate characterisation methodologies is vital for analysing and comprehending the sources of defects and their influence on the properties of heteroepitaxially grown III-V layers. In this work we investigate the structural properties of GaAs layers grown by Metal-Organic Vapour Phase Epitaxy (MOVPE) on Ge substrates – (100) with 6⁰ offset towards – under various growth conditions. Synchrotron X-ray topography (SXRT) is employed to investigate the nature of extended linear defects formed in GaAs epilayers. Other X-ray techniques, such as reciprocal space mapping (RSM) and triple axis ω-scans of (00l)-reflections (l = 2, 4, 6) are used to quantify the degree of relaxation and presence of antiphase domains (APDs) in the GaAs crystals. The surface roughness is found to be closely related to the size of APDs formed at the GaAs/Ge heterointerface, as confirmed by X-ray diffraction (XRD), as well as atomic force microscopy (AFM), and transmission electron microscopy (TEM)

High-Resolution X-ray Emission and X-ray Absorption Spectroscopy

In this review, high-resolution X-ray emission and X-ray absorption spectroscopy will be discussed. The focus is on the 3d transition-metal systems. To understand high-resolution X-ray emission and reso-nant X-ray emission, it is first necessary to spend some time discussing the X-ray absorption process. Section II discusses 1s X-ray absorption, i.e., the K edges, and section III deals with 2p X-ray absorption, the L edges. X-ray emission is discussed in, respectively, the L edges. X-ray emission is discussed in, respec-tively, and section V on 2p3s and 2p3d X-ray emission. Section VI focuses on magnetic dichroism effects, and in section VII selective X-ray absorption experiments are discussed. To limit the scope of this review paper, many related topics (for example, EELS, XPS, and resonant photoemission, phonon-oriented inelastic X-ray scat-tering, and X-ray microscopy) will not be discussed. In addition, many aspects of X-ray absorption, such as reflection experiments, diffraction absorption fine structure, and related experiments, will remain untouched. EXAFS will be discussed very briefly, and its X-ray emission analogue EXEFS 69,71 will not be discussed

Nanosized superparamagnetic precipitates in cobalt-doped ZnO

The existence of semiconductors exhibiting long-range ferromagnetic ordering at room temperature still is controversial. One particularly important issue is the presence of secondary magnetic phases such as clusters, segregations, etc... These are often tedious to detect, leading to contradictory interpretations. We show that in our cobalt doped ZnO films grown homoepitaxially on single crystalline ZnO substrates the magnetism unambiguously stems from metallic cobalt nano-inclusions. The magnetic behavior was investigated by SQUID magnetometry, x-ray magnetic circular dichroism, and AC susceptibility measurements. The results were correlated to a detailed microstructural analysis based on high resolution x-ray diffraction, transmission electron microscopy, and electron-spectroscopic imaging. No evidence for carrier mediated ferromagnetic exchange between diluted cobalt moments was found. In contrast, the combined data provide clear evidence that the observed room temperature ferromagnetic-like behavior originates from nanometer sized superparamagnetic metallic cobalt precipitates.Comment: 20 pages, 6 figures; details about background subtraction added to section III. (XMCD

A Structural Model of the Cytochrome c Reductase/Oxidase Supercomplex from Yeast Mitochondria

Mitochondrial respiratory chain complexes are arranged in supercomplexes within the inner membrane. Interaction of cytochrome c reductase (complex III) and cytochrome c oxidase (complex IV) was investigated in Saccharomyces cerevisiae. Projection maps at 15 Å resolution of supercomplexes III2 + IV1 and III2 + IV2 were obtained by electron microscopy. Based on a comparison of our maps with atomic x-ray structures for complexes III and IV we present a pseudo-atomic model of their precise interaction. Two complex IV monomers are specifically attached to dimeric complex III with their convex sides. The opposite sides, which represent the complex IV dimer interface in the x-ray structure, are open for complex IV-complex IV interactions. This could lead to oligomerization of III2 + IV2 supercomplexes, but this was not detected. Instead, binding of cytochrome c to the supercomplexes was revealed. It was calculated that cytochrome c has to move less than 40 Å at the surface of the supercomplex for electron transport between complex III2 and complex IV. Hence, the prime function of the supercomplex III2 + IV2 is proposed to be a scaffold for effective electron transport between complexes III and IV.

Evidence from scanning tunneling microscopy in support of a structural model for the InSb(001)-c(8×2) surface

In this letter we present evidence from scanning tunneling microscopy studies in support of a recently proposed structural model for the indium-terminated c(8×2) surface of InSb(001). This structural model, by Norris and co-workers, is based on a surface x-ray diffraction study [Surf. Sci. 409, 27 (1998)], and represents a significant departure from previously suggested models for the c(8×2) reconstruction on any (001) surface of the common III–V semiconductor materials. Although filled state images of the InSb(001)-c(8×2) surface have previously been published, empty states image of sufficient quality to extract any meaningful information have not previously been reported. The observations are in excellent agreement with the recently proposed model for this surface reconstruction

Synchrotron radiation: science & applications

This general talk is devoted to briefly introduce the main uses and applications of synchrotron radiation. An initial introduction will be dedicated to describe a synchrotron as a Large Facility devoted to produce photons that will be used to carry out excellent science. The five outstanding main characteristics of synchrotron radiation are: i) High brilliance and collimation ii) Wavelength tunability iii) Beamsize tunability iv) Defined polarization v) Time structure vi) (Partial) coherence These properties will be illustrated through selected examples ranging from biomedicine (f.i. determination of the crystal structure of macromolecules from tiny crystals or cryo- nano tomography of individual cells by soft X-ray transmission microscopy) to materials science (f.i. experiments of powder diffraction of materials under high pressure in diamond-anvil-cells), from cultural heritage (f.i. the study of degradation of pigments in paints by X-ray absorption spectroscopy) to cements (f.i. the hydration chemistry of eco-cements followed by in-situ powder diffraction), and from basic research on magnetic materials (f.i. ferromagnets where the magnetism of individual metal transition elements are selectively followed by X-ray Magnetic Circular Dicroism) to industrial applications on chocolate (f.i. small X-ray scattering as function of temperature of the polymorphs of cacao).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Synthesis of titanium dioxide nanoparticles and their application for simultaneous photocatalytic oxidation of As(III) and sorption of As(V)

In this study, the effectiveness of TiO2 nanoparticles in removing arsenic species from water was enhanced by the photocatalytic oxidation by conversion of As(III) to As(V), which adsorbs more strongly onto the solid phase of adsorbent than As(III). Anatase nanoparticles were synthesized by using sol-gel method and the synthesized nanoparticles were characterized by X-ray diffraction and scanning electron microscopy. Batch adsorption experiment was carried out to analyze As(III) removal capacity of the anatase nanoparticles with and without presence of photocatalytic oxidation reaction. The maximum % of removal of As(III) was found ~56% at pH 6, respectively, when 1 g l-1 anatase nanoparticles were used at the As0 1 ppm without presence of photocatalytic oxidation reaction. In contrast, over 94.7% As(V) have been removed by anatase nanoparticles in a period of 120 min UV-light irradiation. Using photocatalytic oxidation process, As(III) removal from water was improved by UV-irradiation

Time-resolved in situ studies on the formation mechanism of iron oxide nanoparticles using combined fast-XANES and SAXS

The reaction of iron chlorides with an alkaline reagent is one of the most prominent methods for the synthesis of iron oxide nanoparticles. We studied the particle formation mechanism using triethanolamine as reactant and stabilizing agent. In situ fast-X-ray absorption near edge spectroscopy and small-angle X-ray scattering provide information on the oxidation state and the structural information at the same time. In situ data were complemented by ex situ transmission electron microscopy, wide-angle X-ray scattering and Raman analysis of the formed nanoparticles. The formation of maghemite nanoparticles (gamma-Fe2O3) from ferric and ferrous chloride was investigated. Prior to the formation of these nanoparticles, the formation and conversion of intermediate phases (akaganeite, iron(II, III) hydroxides) was observed which undergoes a morphological and structural collapse. The thus formed small magnetite nanoparticles (Fe3O4) grow further and convert to maghemite with increasing reaction time