Polarity dependent strongly inhomogeneous In-incorporation in GaN nanocolumns.

In this work, GaN/InGaN/GaN nanocolumns (NCs) have been grown by molecular beam epitaxy. Selective area growth (SAG) and self-organized growth (SOG) were performed simultaneously in patterned and unpatterned regions of the same substrate, respectively. The resulting structures show different tip morphologies and structural properties due to the different polarity along the growth direction, namely Ga-polar with r-plane faceted tips for the SAG NCs and N-polar with c-plane top facet for the SOG ones. When growing Ga-polar GaN/InGaN NCs, no indium is incorporated at a substrate temperature of [Formula: see text]°C. Rather, indium incorporation takes place under the same growth conditions on the N-polar NCs. The In-incorporation is investigated by means of nano x-ray fluorescence and diffraction, high-angle annular dark-field scanning transmission electron microscopy and high-resolution transmission electron microscopy.

Phase separation in single In(x)Ga(1-x)N nanowires revealed through a hard X-ray synchrotron nanoprobe.

In this work, we report on the composition, short- and long-range structural order of single molecular beam epitaxy grown In(x)Ga(1-x)N nanowires using a hard X-ray synchrotron nanoprobe. Nano-X-ray fluorescence mapping reveals an axial and radial heterogeneous elemental distribution in the single wires with Ga accumulation at their bottom and outer regions. Polarization-dependent nano-X-ray absorption near edge structure demonstrates that despite the elemental modulation, the tetrahedral order around the Ga atoms remains along the nanowires. Nano-X-ray diffraction mapping on single nanowires shows the existence of at least three different phases at their bottom: an In-poor shell and two In-rich phases. The alloy homogenizes toward the top of the wires, where a single In-rich phase is observed. No signatures of In-metallic precipitates are observed in the diffraction spectra. The In-content along the single nanowires estimated from X-ray fluorescence and diffraction data are in good agreement. A rough picture of these phenomena is briefly presented. We anticipate that this methodology will contribute to a greater understanding of the underlying growth concepts not only of nanowires but also of many nanostructures in materials science.

Spontaneous core­shell elemental distribution in In-rich In(x)Ga1-xN nanowires grown by molecular beam epitaxy.

The elemental distribution of self-organized In-rich In(x)Ga1-xN nanowires grown by plasma-assisted molecular beam epitaxy has been investigated using three different techniques with spatial resolution on the nanoscale. Two-dimensional images and elemental profiles of single nanowires obtained by x-ray fluorescence and energy-dispersive x-ray spectroscopy, respectively, have revealed a radial gradient in the alloy composition of each individual nanowire. The spectral selectivity of resonant Raman scattering has been used to enhance the signal from very small volumes with different elemental composition within single nanowires. The combination of the three techniques has provided sufficient sensitivity and spatial resolution to prove the spontaneous formation of a core­shell nanowire and to quantify the thicknesses and alloy compositions of the core and shell regions. A theoretical model based on continuum elastic theory has been used to estimate the strain fields present in such inhomogeneous nanowires. These results suggest new strategies for achieving high quality nonpolar heterostructures.

Hard X-ray nanoprobe investigations of the subtissue metal distributions within Daphnia magna.

The unique potential of nanoscale elemental imaging of major/minor and trace-level elemental distributions within thin biological tissue sections of the ecotoxicological model organism Daphnia magna is demonstrated by synchrotron radiation nano-X-ray fluorescence (nano-XRF). The applied highly specialized sample preparation method, coupled with the high spatial resolution (∼180 nm) and high X-ray photon flux (6 × 10(11) photons/s) available at the European Synchrotron Radiation Facility (ESRF) ID22NI beamline proved to be critical for the high-quality visualization of (trace-)metal distributions on the submicron level within the target structures of interest. These include the branchial sacs on the thoracic appendages (epipodites) of D. magna, which are osmoregulatory regions where ion exchange occurs. For the main element of interest (Zn), detection limits of 0.7 ppm (3 ag) was reached in fast-scanning mode using an acquisition time of 0.3 s/pixel. As demonstrated, synchrotron radiation nano-XRF revealed the elemental distributions of Ca, Fe, and Zn within this osmoregulatory region on the submicron scale, aiding the exploration of possible detoxification mechanisms of Zn within D. magna at the subtissue level.

Formation of nanostructures in Eu3+ doped glass-ceramics: an XAS study.

We describe the results of x-ray absorption experiments carried out to deduce structural and chemical information in Eu(3+) doped, transparent, oxyfluoride glass and nanostructured glass-ceramic samples. The spectra were measured at the Pb and Eu-L(III) edges. The Eu environment in the glass samples is observed to be similar to that of EuF(3). Complementary x-ray diffraction experiments show that thermal annealing creates ß-PbF(2) type nanocrystals. X-ray absorption indicates that Eu ions act as seeds in the nanocrystal formation. There is evidence of interstitial fluorine atoms around Eu ions as well as Eu dimers. X-ray absorption at the Pb-L(III) edge shows that after the thermal treatment most lead atoms form a PbO amorphous phase and that only 10% of the lead atoms remain available to form ß-PbF(2) type nanocrystals. Both x-ray diffraction and absorption point to a high Eu content in the nanocrystals. Our study suggests new approaches to the oxyfluoride glass-ceramic synthesis in order to further improve their properties.

Biomedical applications of the ESRF synchrotron-based microspectroscopy platform.

Very little is known about the sub-cellular distribution of metal ions in cells. Some metals such as zinc, copper and iron are essential and play an important role in the cell metabolism. Dysfunctions in this delicate housekeeping may be at the origin of major diseases. There is also a prevalent use of metals in a wide range of diagnostic agents and drugs for the diagnosis or treatment of a variety of disorders. This is becoming more and more of a concern in the field of nanomedicine with the increasing development and use of nanoparticles, which are suspected of causing adverse effects on cells and organ tissues. Synchrotron-based X-ray and Fourier-transformed infrared microspectroscopies are developing into well-suited sub-micrometer analytical tools for addressing new problems when studying the role of metals in biology. As a complementary tool to optical and electron microscopes, developments and studies have demonstrated the unique capabilities of multi-keV microscopy: namely, an ultra-low detection limit, large penetration depth, chemical sensitivity and three-dimensional imaging capabilities. More recently, the capabilities have been extended towards sub-100nm lateral resolutions, thus enabling sub-cellular chemical imaging. Possibilities offered by these techniques in the biomedical field are described through examples of applications performed at the ESRF synchrotron-based microspectroscopy platform (ID21 and ID22 beamlines).

Nano-X-ray absorption spectroscopy of single Co-implanted ZnO nanowires.

We report on the local structure of single Co-implanted ZnO nanowires studied using a hard X-ray nanoprobe. X-ray fluorescence maps show uniform Zn and Co distributions along the wire within the length scale of the beam size. The X-ray fluorescence data allow the estimation of the Co content within the nanowire. Polarization dependent X-ray absorption near edge structure shows no structural disorder induced neither in the radial nor axial directions of the implanted nanowires after subsequent annealing. Co2+ ions occupy Zn sites into the wurtzite ZnO lattice. Extended X-ray absorption fine structure data reveal high structural order in the host lattice without distortion in their interatomic distances, confirming the recovery of the radiation damaged ZnO structure through thermal annealing.

Study of metallic components of historical organ pipes using synchrotron radiation X-ray microfluorescence imaging and grazing incidence X-ray diffraction.

A comparative study of the composition and microstructure of two different brass alloys from reed pipes, one from a Spanish baroque organ and the other from a modern one, was carried out. This study allowed us to determine the procedure followed to produce the brass used to make ancient reed pipes. Moreover the distribution and correlation of lead and other trace elements present into the main component of the brass, the copper and zinc phases, of the historical tongues and shallots were established. This chemical composition was compared with that of a tongue from a twentieth-century organ. The whole study was accomplished using a combination of laboratory and synchrotron radiation techniques. X-ray fluorescence was the technique used to obtain elemental and chemical imaging of the main phases and the trace elements at a sub-micrometer scale.

X-ray absorption near-edge structure of GaN with high Mn concentration grown on SiC.

By means of x-ray absorption near-edge structure (XANES) several Ga(1-x)Mn(x)N (0.03

High-resolution angular beam stability monitoring at a nanofocusing beamline.

Two semi-transparent imaging beam-position monitors developed at the ESRF have been installed at the micro-analysis beamline ID22 for monitoring the angular stability of the X-ray beam. This system allows low-frequency (10 Hz) angular beam stability measurements at a submicroradian range. It is demonstrated that the incoming macro-beam angular fluctuations are one of the major sources of focal spot instabilities downstream of the Kirkpatrick-Baez mirrors. It is also shown that scanning the energy by rotating the so-called fixed-exit monochromator induces some unexpected angular beam shifts that are, to a large extent, deterministic.

New cryogenic environment for beamline ID22 at the European Synchrotron Radiation Facility.

A compact minicryostat has been well adapted on the hard x-ray microprobe ID22 of the European Synchrotron Radiation Facility. For variable low-temperature investigations, its special technical design provides precise scanning microscopy and allows easy access for multiple detection modes. Based on x-ray excited optical luminescence technique on the micrometer scale, details of the equipment, its temperature calibration, and typical results are described. Data collections from InAs quantum heterostructures support the excellent thermal performance of the novel cryogenic device.

ID22: a multitechnique hard X-ray microprobe beamline at the European Synchrotron Radiation Facility.

The ID22 beamline is dedicated to hard X-ray microanalysis allowing the combination of fluorescence, spectroscopy, diffraction and tomography techniques in a wide energy range from 6 to 70 keV. The recent installation of an in-vacuum undulator, a new sample stage and the adaptation of various focusing optics has contributed to a great improvement in the capabilities of the beamline, which is now accessed by a wide user community issued from medical, earth and environmental science, archaeology and material science. Many applications requiring low detection limits for localization/speciation of trace elements together with structural analysis have been developed at the beamline on the (sub)micrometer scale. The possibility of combining simultaneously different analytical probes offers the opportunity of a thorough study of a given sample or scientific problem. This paper presents a review of the recent developments of the beamline and a detailed description of its capabilities through examples from different fields of applications.