Tom Blanton

Reference materials for the study of polymorphism and crystallinity in cellulosics

Eighty specimens of cellulosic materials were analyzed over a period of several years to study the diffraction characteristics resulting from polymorphism, crystallinity, and chemical substitution. The aim of the study was to produce and verify the quality of reference data useful for the diffraction analyses of cellulosic materials. These reference data can be used for material identification, polymorphism, and crystallinity measurements. Overall 13 new references have been characterized for publication in the Powder Diffraction File (PDF) and several others are in the process of publication.

AN EXAFS STUDY OF PHOTOGRAPHIC DEVELOPMENT IN THERMOGRAPHIC FILMS

Silver K edge extended X-ray absorption fine structure (EXAFS) spectroscopy of films containing silver behenate (AgBeh) in the unprocessed, fully processed, and step-processed states has been performed. The results of the EXAFS analysis indicate that the intensity for the real-space peak for the Ag-O distance ({approx}2.3 {angstrom}) decreases while the real-space peak for the Ag-Ag distance ({approx}2.9 {angstrom}) grows with increasing thermal processing of the film. The changes observed in the real-space EXAFS signal indicate the growth of metallic silver at the expense of AgBeh. The X-ray absorption near-edge spectroscopy (XANES) portion of the signal shows that the absorption edge position varies stepwise, with unprocessed films and pure AgBeh having an edge location at 25 506 eV, films processed from steps 1 through 10 have an absorption edge at 25 508 eV, and the fully processed film has an edge location at 25 512 eV.

MATERIALS CHARACTERIZATION USING A NOVEL SIMULTANEOUS NEAR-INFRARED/X-RAY DIFFRACTION INSTRUMENT

X-ray powder diffraction (XRD) is utilized for the determination of polymorphism in crystalline organic materials. Though convenient to use in a laboratory setting, XRD is not easily adapted to in situ monitoring of synthetic chemical production applications or thin film depositions. Near-infrared spectroscopy (NIR) can be adapted to in situ manufacturing schemes by use of a source/detector probe. Conversely, NIR is unable to conclusively define the existence of polymorphism in crystalline materials. By combining the two techniques, a novel simultaneous NIR/XRD instrument has been developed. During material’s analysis, results from XRD allowed for the determination of the existence of polymorphic phases, and NIR data were collected as a fingerprint for each of the observed polymorphs. These NIR fingerprints allowed for the development of a library, which can be referenced during the use of a NIR probe in manufacturing settings. The NIR/XRD instrument was also used to monitor materials during exposure to ambient air. XRD can detect crystalline phase changes and NIR can monitor solvent loss and/or water uptake.

New neutron time-of-flight (TOF) capability in PDF-4+ relational databases: digitized diffraction patterns and I/I c for quantitative phases analysis

Neutron powder diffraction is a useful tool because elemental scattering contrast is quite different when compared to X-rays. Elements in the periodic table often have quite different scattering amplitudes (the scattering cross sections are not strictly proportional to atomic number, Z and isotope). Unlike standard laboratory X-ray sources, neutrons are available both at nuclear reactors and pulsed sources. These facilities are available world-wide. In this paper, we treat the TOF white beam neutron case. One of the initiatives at the ICDD is to expand the content of the PDF-4+ to include data from facilities outside the in-house X-ray laboratory.

X-RAY DIFFRACTION CHARACTERIZATION OF MOVPE ZnSe FILMS DEPOSITED ON (100) GaAs USING CONVENTIONAL AND HIGH- RESOLUTION DIFFRACTOMETERS

ZnSe-based heterostructures grown on GaAs substrates have been investigated for use in pindiode LED applications. ZnSe has a large band gap, 2.76 eV, as well as a near lattice match to GaAs, 5.6688 A vs. 5.6538 A, respectively. In this study a metallorganic vapor phase epitaxy (MOVPE) deposition technique is used to produce doped and undoped thin films of ZnSe on (100) GaAs. Understanding the effect of deposition parameters on the crystallographic quality of the ZnSe films is important for optimizing the performance of these devices. X-ray diffraction is well suited for analyzing epitaxial thin films deposited on single-crystal substrates. In this study, a conventional Bragg-Brentano diffractometer (BBD) has been used to screen samples for phase identification, crystallite size, presence of polycrystalline ZnSe, and initial rocking curve (RC) analysis. A limitation of the conventional diffractometer is that the smallest RC full width at half maximum (FWHM) that can be achieved is 500–600 arc seconds. As deposition parameters are optimized and the RC limit of the conventional diffractometer is reached, analysis is moved to a 4-bounce high-resolution diffractometer (HRD). Although more time for analysis is required, using the HRD has a RC resolution advantage, where RCs of <20 arc seconds are obtained for neat GaAs wafers. Combining the BBD and HRD instruments for analysis of ZnSe films grown on GaAs substrates allows for an efficient means of high sample throughput combined with an accurate measurement of film alignment.

X-ray diffraction analysis of ultrathin platinum silicide films deposited on (100) silicon

X-ray diffraction methods have been used successfully for the analysis of platinum silicide films of 100 A or less in thickness. Conventional X-ray diffraction was utilized for phase identification, planar orientation, and crystalline size determination. Low-angle X-ray specular reflectivity analysis measured film thickness. As the nominal film thickness approached 100 A, it was observed that the deposited platinum film thickness was larger than expected and longer anneal times would be required to ensure homogeneous platinum silicide phase composition.

Powder X-ray diffraction of levothyroxine sodium pentahydrate, C 15 H 10 I 4 NNaO 4 (H 2 O) 5

The room-temperature crystal structure of levothyroxine sodium pentahydrate has been refined using synchrotron powder diffraction data. The compound crystallizes in space group P1 (#1) with a = 8.2489(4), b = 9.4868(5), c = 15.8298(6) A, α = 84.1387(4), β = 83.1560(3), γ = 85.0482(3) deg, V = 1220.071(9) A 3 , and Z = 2. Hydrogen atoms (missing from the previously-reported structure) were included.

Sixty-third Denver X-ray Conference and selected Advances in X-ray Analysis papers for the June Powder Diffraction issue

As part of the 63rd Annual Denver X-ray Conference (DXC), proceedings are published in Advances in X-ray Analysis (AXA). After reviewing 32 XRD (X-ray Diffraction), XRF (X-ray Fluorescence), and related fields AXA papers, five were selected for publication in Powder Diffraction. The five selected papers highlight interesting developments in materials analysis. Together with the regular published papers in this June issue of Powder Diffraction readers are provided with the opportunity to learn about current topics in a variety of materials characterization applications. The five selected AXA papers and authors are:

Sixty-second Denver X-ray Conference and selected papers for the special June Powder Diffraction issue

This issue of Powder Diffraction is comprised of selected papers presented at the 2013 62nd Annual Denver X-ray Conference (DXC). At DXC 16 workshops, 2 poster sessions, a plenary session The 100th Anniversary of X-ray Spectroscopy and 13 special sessions were held, covering the following topics: New Developments in XRD & XRF Instrumentation, Applications of XRD & XRF in the Petroleum Industry, Applied Materials Analysis, High Energy XRD, Stress Analysis, Pair Distribution Function, Polymers, New Developments in Rietveld Analysis, Quantitative Analysis, Applications for Portable XRF, Fusion & Industrial Applications of XRF, Micro XRF, and Trace Analysis. As part of theDenverConference, proceedings are published and from these proceedings, select papers covering XRD, XRF, and other high-energy scattering methods were selected for publication in Powder Diffraction. This issue of Powder Diffraction will provide readers with the opportunity to learn about current topics in a variety of materials characterization applications. The talents of many people are required to make this special issue possible. Besides the authors themselves, we thank the DXC organizing committee members for their reviews of these articles. We would also like to thank the DXC conference coordinator Denise Zulli and Powder Diffraction managing editor Nicole Ernst Boris for all of their hard work in making this publication a reality. We hope you enjoy this compilation of manuscripts and we look forward to seeing you at the 2014 Denver X-ray Conference in Big Sky, Montana, 28 July–1 August, 2014 (www. dxcicdd.com).