Modeling and mitigation of sample relief effects applied to chemistry measurements by the Mars Science Laboratory Alpha Particle X‐ray Spectrometer

The Alpha Particle X‐ray Spectrometer (APXS) onboard the Mars rover Curiosity conducts high‐precision in situ chemical measurements of rocks and regolith. Target surfaces are not always flat and thus can pose issues for interpretations that assume such. Here, we investigate when variable target relief is an important effect to consider for APXS targets. We provide operational recommendations on how to most efficiently study targets of significant changes in surface relief with the rover‐arm‐mounted APXS and Mars Hand Lens Imager camera. Additionally, we deconvolve the chemistry of heterogeneous targets of significant vertical relief encountered along Curiosity's traverse, providing the chemical composition of visible endmembers in the process. Specifically, presented here are the deconvolved endmember compositions of two recent targets. The first is a manganese‐rich, calcium‐rich, and zinc‐rich dark‐toned vein at Garden City that is chemically and visually unique compared with the intermixed light‐toned Ca‐sulfate‐dominated vein. The other target is a weathered Mg‐sulfate‐rich nodule that is unique compared with a previously encountered nodule that had significant nickel enrichment. The distinctly different chemistry both at Garden City and with the Mg‐sulfate‐rich nodules along the traverse provides further evidence for either multiple fluid events or an evolving fluid on the surface of ancient Mars. Copyright © 2017 John Wiley & Sons, Ltd.     

Application of X‐Ray Computerized Tomography to Characterize Particle Retention Within Depth Filters

Local measurements of solid concentration in depth wound cartridge filters using X‐ray computerized tomography (XCT) are described. The filters were contaminated with glass bead particles, which exhibit high contrast in the tomographic images. Segmentation of the successive original slices was applied and solid profile concentrations along the filters were obtained. 3D reconstruction techniques permitted the modeling of the spatial distribution of the solid particles captured by the filters.     

The comparative analytical performance of the Beagle 2 X‐ray Spectrometer for in situ geochemical analysis on Mars

The Beagle 2 X‐ray Spectrometer (B2 XRS) instrument was part of the Beagle 2 Mars lander payload and intended to perform in situ geochemical analyses of geological materials on Mars. The analytical performance of a spare version of the B2 XRS was compared with (1) a portable X‐ray fluorescence (PXRF) spectrometer designed to perform terrestrial fieldwork and (2) a laboratory‐based wavelength‐dispersive (WD‐XRF) system used to produce high quality geochemical data. The criteria used to assess the performance were based on fitting precision, accuracy and detection limit, determined from the analysis of international geochemical reference materials. The fitting precision of the B2 XRS and PXRF was found to be in agreement with the Horwitz function (a benchmark relating the analysed concentration of an analyte to its uncertainty) over 4 orders of magnitude of concentration range from 10^?1 to 10^?5 g/g. The PXRF generally had a better fitting precision than the B2 XRS because of its better resolution. In order of improving accuracy, the spectrometers generally are ranked B2 XRS, PXRF and WD‐XRF for various major and trace elements. A limiting factor in the accuracy of the B2 XRS was the application of the algorithm used for its quantitative analysis. The detection limits for the spectrometers ranked in the same order as the accuracy as a result of improving signal‐to‐noise ratio (SNR) of elemental peaks, which is a direct consequence of improving resolution between these spectrometers. Overall, the B2 XRS was found to have a favourable analytical performance compared to the benchmark spectrometers, despite having met considerable design constraints and qualification tests as a planetary instrument. Copyright © 2009 John Wiley & Sons, Ltd.     

Particle Size Distribution of Nanospheres by Monte Carlo Fitting of Small Angle X‐Ray Scattering Curves

A method for recovering the size distribution of spherical particles from small angle scattering data by using a Monte Carlo interference function fitting algorithm is presented. The method is based on the direct simulation of the small angle scattering data upon the assumption of non‐interacting hard sphere ensembles (“dilute” solution approximation). The algorithm for retrieving the particle size distribution does not require any additional parameters apart from the input of the scattering data. The fitting strategy necessarily implies positive particle size distributions, while preserving the advantage of the indirect transformation method for data desmearing. Furthermore, the present approach does not use any regularisation procedures of the best fit solution and favours smooth particle size distributions. The Monte Carlo procedure has been tested against several simulated cases with various types of mono‐ and bi‐modal size distributions and different noise levels. In the special case of non‐interacting spheres, the Monte Carlo fitting algorithm had the same retrieving ability as the well assessed indirect transformation, structure interference and maximum entropy methods. Finally, the algorithm was applied to retrieve the distribution of spherical nanopowders produced by gas‐to‐particle conversion both as free powder and as reinforcing second‐phase agent in polymer nanocomposites.     

On the 40th anniversary of the journal X‐Ray Spectrometry

This journal, X‐Ray Spectrometry, celebrates its 40th anniversary this year. The state of the publications on X‐ray spectral analysis from 1972 onward is considered. The distribution of materials over countries is presented, as published in X‐Ray Spectrometry for 40 years, in 5‐year time intervals: 1972–1976, 1977–1981, and so on. The participation of Russian scientists contributing to the publications in this journal is discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Structure and Stability of PEG‐ and Mixed PEG‐Layer‐Coated Nanoparticles at High Particle Concentrations Studied In Situ by Small‐Angle X‐Ray Scattering

Ligand‐layer structure and stability of gold nanoparticles (AuNP) coated with α‐methoxypoly(ethylene glycol)‐ω‐(11‐mercaptoundecanoate) (PEGMUA) layers and mixed layers of PEGMUA and 11‐mercaptoundecanoic acid (MUA) at high AuNP concentrations are studied in situ by small‐angle X‐ray scattering (SAXS). The thickness of the ligand layer is modified by the molecular weight of the PEG‐ligands (2 and 5 kDa), and the PEG‐grafting density is decreased by coadsorption of MUA. The response of the conjugates to a pressure of up to 4 kbar is probed. The results indicate strongly hydrated PEG layers at high grafting densities. The stability of the mixed ligand‐layer conjugates is lower. This is most probably due to enhanced interparticle PEG–PEG interactions at lower grafting densities. The presented study demonstrates that a detailed structural characterization of polymer ligand layers in situ and in response to external stimuli is possible with SAXS.     

Nuclear Uptake of Gold Nanoparticles Deduced Using Dual‐Angle X‐Ray Fluorescence Mapping

Studies into the cell nucleus' incorporation of gold nanoparticles (AuNPs) are often limited by ambiguities arising from conventional imaging techniques. Indeed, it is suggested that to date there is no unambiguous imaging evidence for such uptake in whole cells, particularly at the single nanoparticle level. This shortcoming in understanding exists despite the nucleus being the most important subcellular compartment in eukaryotes and gold being the most commonly used metal nanoparticle in medical applications. Here, dual‐angle X‐ray flouresence is used to show individually resolved nanoparticles within the cell nucleus, finding them to be well separated and 79% of the intranuclear population to be monodispersed. These findings have important implications for nanomedicine, illustrated here through a specific exemplar of the predicted enhancement of radiation effects arising from the observed AuNPs, finding intranuclear dose enhancements spanning nearly five orders of magnitude.     

In Situ Synchrotron X‐Ray Techniques for Real‐Time Probing of Colloidal Nanoparticle Synthesis

Solution‐phase synthesis of colloidal nanoparticles with precisely tailored properties is one of the fastest growing research topic and represents the most critical foundation to implant nanotechnology in a variety of areas to boost performance of traditional systems. Comprehensive understanding of the nucleation and growth mechanisms involved in the formation of colloidal nanoparticles is very important to realize rational design and synthesis of well‐tailored nanoparticles and requires appropriate in situ techniques to probe the kinetics of the synthetic reactions. Synchrotron hard X‐rays represent a class of promising probes for solution‐phase reactions due to their strong penetration in ambient environment and solutions. This review completely summarizes the in situ synchrotron X‐ray techniques emerged in the recent years for real‐time probing nanophase evolution of colloidal nanoparticles. Typical examples of colloidal nanoparticle syntheses are discussed in detail to shed the light on the advantages and disadvantages of individual techniques.     

Determination of the Surface Facets of Gold Nanorods in Wet‐Coated Thin Films with Grazing‐Incidence Wide Angle X‐Ray Scattering

This work studies the surface facets of gold nanorods (AuNRs) in wet‐coated nanoparticle thin films with synchrotron‐light‐based grazing‐incidence wide angle X‐ray scattering (GIWAXS), which provides statistically relevant results on many nanoparticles. Air‐brush spraying deposits the monodisperse AuNRs into sparse monolayers where the long axis of rods is parallel to the substrate surface. It is found that the crystalline facets of individual AuNRs in the sparse monolayer are all in the same orientation, as indicated by narrow azimuthal widths of (200) reflections, over a macroscopic scale comparable to the substrate. This alignment is probably due to the rods' sitting on high‐index surface facets such as (520) and (250). A quantitative analysis of the angles between bulk facets and the surface facets leads to a “nested‐octagon” model for the cross sections of AuNRs: shell octagon with high‐index crystalline facets (520), (5‐20), (2‐50), (‐2‐50), (‐5‐20), (‐520), (‐250), and (250), and core octagon consisting of low‐index crystalline facets (100), (1‐10), (0‐10), (‐1‐10), (‐100), (‐110), (010), and (110).     

X‐ray spectromicroscopy with the scanning transmission X‐ray microscope at BESSY II

Using the scanning transmission X‐ray microscope at BESSY II, colloidal structures from a Chernozem soil have been studied with a spatial resolution around 60 nm and a spectral resolution of 1700 at the K‐absorption edge of carbon. Elemental mapping has been used to determine the distribution of organic matter within the colloidal structures. Spectra have been extracted from image stacks to obtain information about the chemical state. For the analysis of the latter, principal component analysis and cluster analysis have been applied. It was possible, for example, to discriminate clay particles against organic components.