Eric Dooryhee

Probing the structure of heterogeneous diluted materials by diffraction tomography

The advent of nanosciences calls for the development of local structural probes, in particular to characterize ill-ordered or heterogeneous materials. Furthermore, because materials properties are often related to their heterogeneity and the hierarchical arrangement of their structure, different structural probes covering a wide range of scales are required. X-ray diffraction is one of the prime structural methods but suffers from a relatively poor detection limit, whereas transmission electron analysis involves destructive sample preparation. Here we show the potential of coupling pencil-beam tomography with X-ray diffraction to examine unidentified phases in nanomaterials and polycrystalline materials. The demonstration is carried out on a high-pressure pellet containing several carbon phases and on a heterogeneous powder containing chalcedony and iron pigments. The present method enables a non-invasive structural refinement with a weight sensitivity of one part per thousand. It enables the extraction of the scattering patterns of amorphous and crystalline compounds with similar atomic densities and compositions. Furthermore, such a diffraction-tomography experiment can be carried out simultaneously with X-ray fluorescence, Compton and absorption tomographies, enabling a multimodal analysis of prime importance in materials science, chemistry, geology, environmental science, medical science, palaeontology and cultural heritage.

Revealing the powdering methods of black makeup in Ancient Egypt by fitting microstructure based Fourier coefficients to the whole x-ray diffraction profiles of galena

Galena (PbS) is a major ingredient in ancient Egyptian eye makeup. The microstructure of PbS in Egyptian cosmetic powders is used as a fingerprint and is matched with the microstructures produced artificially in geological galena minerals. The microstructure of PbS is determined by x-ray diffraction peak profile analysis in terms of dislocation density, crystallite size, and size distribution. High-resolution powder diffractograms were measured at the ESRF Grenoble synchrotron source with high resolution and high peak-to-background ratios. The Fourier coefficients of the first nine measured reflections of galena are fitted using physically based Fourier coefficients of strain and size functions. Strain anisotropy is accounted for by the dislocation model of the mean square strain. The x-ray data are supplemented by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) micrographs, and are compared with archaeological documents. It enables us to describe the procedures of eye makeup ...

Association of indigo with zeolites for improved color stabilization.

The durability of an organic color and its resistance against external chemical agents and exposure to light can be significantly enhanced by hybridizing the natural dye with a mineral. In search for stable natural pigments, the present work focuses on the association of indigo blue with several zeolitic matrices (LTA zeolite, mordenite, MFI zeolite). The manufacturing of the hybrid pigment is tested under varying oxidizing conditions, using Raman and ultraviolet–visible (UV-Vis) spectrometric techniques. Blending indigo with MFI is shown to yield the most stable composite in all of our artificial indigo pigments. In the absence of defects and substituted cations such as aluminum in the framework of the MFI zeolite matrix, we show that matching the pore size with the dimensions of the guest indigo molecule is the key factor. The evidence for the high color stability of indigo@MFI opens a new path for modeling the stability of indigo in various alumino-silicate substrates such as in the historical Maya Blue pigment.

Sensitivity of synchrotron radiation x-ray diffraction to the chemical ordering in epitaxial perovskite multilayers

The present work shows that the chemical ordering in (BaTiO3∕SrTiO3)N chemical-vapor-deposition-grown superlattices can be reliably estimated by synchrotron radiation x-ray diffraction (XRD). XRD (00l) diagrams for l=1–8 have been simultaneously simulated using a unique set of parameters describing the stack with a model based on periodic structural and chemical profiles. The relative sensitivity of the (00l) reflections to the atomic concentrations of Sr and Ba is presented: the SrTiO3 and BaTiO3 scattering factors partially compensate each other for the l odd, and their respective contributions in the (007) reflection can be disentangled. Using this property, an accuracy as good as 5% can be obtained regarding the Ba and Sr atomic concentrations. Synchrotron radiation reflectivity was performed, and the simulation confirms the observed large atomic interlayer diffusion. Moreover, energy electron loss spectroscopy measurements at the barium and the strontium edges give a very good agreement with the diff...

Robust Nanostructure from High Throughput Powder Diffraction Data

Modern materials under study for next generation technologies in energy conversion and storage, environmental remediation, and health are highly complex, often heterogeneous and nano-structured. Here we refer to these as real materials. A full understanding of the structure requires us to go beyond crystallography and to study the local structure, which is a major experimental and theoretical challenge [1].

Combining characterization techniques at the NSLS-II

The National Synchrotron Light Source II (NSLS-II) is a US Department of Energy Office of Science Basic Energy Science new scientific user facility, located at Brookhaven National Laboratory (BNL), New York. NSLS-II’s mission is to address critical scientific grand challenges in energy security, advanced materials synthesis and manufacturing, environment, and human health. NSLS-II started operations in October 2014 with a handful of beamlines and since then, has been rapidly ramping up its science and user programs, as well as continuing the development of new beamlines and associated scientific capabilities. The NSLS-II will provide a wide range of in situ and operando spectroscopy-microscopy and tomographic techniques combined with structural characterization techniques, in the soft, tender and the hard X-ray energy range. An increasing number of science cases require to combine techniques, in particular spectroscopic, scattering and imaging techniques that help examine the structure-function relationships that occur at different scales (Å-m; sec-months; >1 attoL) in complex systems or in hierarchical, heterogeneous systems, either in bulk or in thin films or in spatially-resolved gauge volumes. Structural information may be addressed by diffraction for long-range atomic structure, by Pair Distribution Function & Extended X-ray Absorption Fine Structure Spectroscopy for short-to-mid range, and by Small-angle X-ray Scattering for larger scale structure. This talk will outline such scientific opportunities at the NSLS-II, with emphasis on the program at the X-ray Powder Diffraction (XPD) beamline, enabling such new tools as in situ PDF, combined DRIFTS+XRD and Modulation Enhanced Diffraction (MED).

Tracking Cation Migration in Catalysts by Modulated Enhanced Powder Diffraction

Mixtures of Cu-Fe oxides are used for numerous industrial catalytic processes including the Water-gas shift reaction (WGS: CO + H2O > CO2 + H2). In this work we measure the structural changes of CuFe2O4 under redox (oxidizing and reducing) and WGS reaction conditions. A key component associated with the catalytic properties of this material is the reversible transfer of Cu in and out of the spinel structure during the reaction. The WGS reaction is the most active when Cu is metallic and on the surface of the spinel which has become Fe3O4. The reversible nature of the Cu migration preserves the activity of the catalyst and protects the Cu species from deactivation. We investigate the cation migration process from the octahedral site inside the spinel to the surface as Cu metal, using modulation measurements that perturb the dynamic structural properties of the spinel structure in a time resolved manner. The experiments termed MED [1] involve the switching of co-reactants (i.e. CO -> O2 -> CO -> O2) so that the residence time of specific adsorbates can be controlled, thus we can probe directly the role of the reactant and the redox sensitivity in the migration of the Cu cation. We demonstrate how distinguishable this technique is from previous steady-state measurements. The powder patterns are averaged over several cycles of gas (CO/H2/O2) variations. Phase-sensitive detection is applied to demodulate the data, picking up structural changes which occur in phase with reactant in-flow variations. Oscillations of the diffracted signal can be observed at the stimulation frequency ω, but also at the harmonic 2ω. Therefore the Fourier analysis of the components provides selective access to partial diffraction contributions otherwise merged into one average diffraction signal. This work is supported by the BNL LDRD program and experiments were performed at the APS and at the NSLS.