Recently materials with promising thermoelectric properties were discovered among the clathrates. Transport data has indicated that these materials have some of the characteristics of a good thermoelectric, namely a low thermal conductivity and a high electrical conductivity. Based on synchrotron powder and conventional single crystal x-ray diffraction data we have determined the charge density distribution in Sr8Ga16Ge3O using the Maximum Entropy Method. The MEM density shows clear evidence of guest atom rattling, and this contributes to the reduction of the thermal conductivity. Analysis of the charge distribution reveals that Sr8Ga16Ge30 contains mixed valence alkaline earth guest atoms. The Sr atoms in the small cavities are, as expected, doubly positively charged, whereas the Sr atoms in the large cavities appear negatively charged. The MEM density furthermore suggests that the Ga and Ge atoms may not be randomly disordered on the framework sites as found in the conventional leastsquares refinements.

Results of high-energy synchrotron radiation experiments are presented demonstrating the advantages of the high-resolution atomic Pair Distribution Function technique in determining the structure of materials with intrinsic disorder.

High-energy, high-flux x-rays from a third-generation synchrotron source were used to measure average elastic strains in the bulk of 1.5 mm thick composites consisting of a copper matrix reinforced with 7.5 vol.% molybdenum particles. From the evolution of lattice strains in both phases during uniaxial tensile deformation, the internal load transfer between phases and reinforcement damage were characterized during elastic and plastic deformation of the composite. The graininess of the diffraction rings, which is related to the Bragg peak broadening, was quantified as a function of applied stress and related to plastic deformation in the matrix.

We present our recent progress in using synchrotron x-ray surface scattering techniques to study several different aspects of ordering at liquid-liquid interfaces. (1) We present measurements of the interfacial width at the water-alkane interface for a series of different chain length alkanes. The width for the shortest chain length studied is in agreement with capillary wave theory. However, significant deviations occur for longer chain lengths, indicating the presence of molecular ordering at the interface. (2) Under appropriate conditions, a surfactant monolayer forms at the interface between water and a hexane solution of a fluorinated surfactant. Reflectivity measurements that probe the electron density profile normal to the interface provide information about the surfactant ordering. This monolayer undergoes a solid to gas transition as a function of temperature. Diffuse scattering near the transition reveals the presence of islands. (3) Equilibrium interfaces between two aqueous phases containing PEG (polyethylene glycol) and potassium phosphate salts can be studied. We present studies of coherent capillary wave fluctuations between two interfaces of a thin film of this biphase system. We also demonstrate that biological macromolecules can be trapped and studied at this aqueous-aqueous interface.

Grazing incidence x-ray diffraction (GIXD) measurements were performed to determine the effects of SP-B1.25, the N-terminus peptide of lung surfactant specific protein SP-B1.25, on the structure of palmitic acid (PA) monolayers. In-plane diffraction shows that the peptide fluidizes a portion of the monolayer, but does not affect the packing of the residual ordered phase. This implies that the peptide resides in the disordered phase, and that the ordered phase is essentially pure lipid. The quantitative insights afforded by this study lead to a better understanding of the lipid/protein interactions found in lung surfactant systems.

We present the first resonant x-ray reflectivity measurements from a liquid surface. The surface structure of the liquid Hg-Au alloy system just beyond the solubility limit of 0.14at% Au in Hg had previously been shown to exhibit a unique surface phase characterized by a low-density surface region with a complicated temperature dependence. In this paper we present reflectivity measurements near the Au LIII edge, for 0.2at% Au in Hg at room temperature. The data are consistent with a concentration of Au in the surface region that can be no larger than about 30at%. These results rule out previous suggestions that pure Au layers segregate at the alloy surface.

High resolution adsorption isotherms, temperature programmed desorption (TPD), x-ray diffraction (XRD) and x-ray absorption near edge spectroscopy (XANES) methods were used to investigate the interaction of SO2 with high quality MgO powders. The results of these investigations indicate that when SO2 is deposited on MgO in monolayer quantities at temperatures near 100K both SO3 and SO4 species form that are not removed by simply pumping on the pre-dosed samples at room temperature. TPD and XANES studies indicate that heating of pre-dosed MgO samples to temperatures above 350 °C is required for full removal of the SO3/SO4 species. XANES measurements made as a function of film thickness indicate for coverages near monolayer completion that the SO4 species form first.

We present an x-ray scattering study of the oxidation of AIN/sapphire films into λ-A12O3 upon annealing. Epitaxial AIN/Sapphire(0001) transforms into nano-crystalline epitaxial λ-A12O3 during annealing at temperatures above 800°C in air. The crystalline orientational relation between the λ-Al2O3 and AIN are < 111 > // < 0001 > in the film normal direction, and < 110 > // < 1120 > in the film plane direction. The domain size of the spinel λ-A1203 crystalline is smaller than 50 Å in both out-of-plane and in-plane directions. The XPS depth profiles of the oxide film showed that the film is composed of aluminum and oxygen, and the atomic concentration ratio is about 2:3.

We have used the intensity and tunability of a synchrotron x-ray source in order to access the buried interface between a glass substrate and a liquid crystal thin film. We find that for energy of 9.4kev, the x-rays can penetrate a 0.22mm substrate. Grazing Incidence x-ray Scattering has been used to study the alignment of the films as a function of depth and temperature. Our results indicate the presence of both a chevron structure and a structure similar to the helical twist-grainboundary (TGB) phase. Some films have a disordered interfacial layer. This technique can be applied in the study of semiconductor devices as well as surfactant film interfaces.

The structural properties of Si/SiGe quantum wires, which were grown by local solid source molecular beam epitaxy through a Si3N4/SiO2 wire-like shadow mask, were investigated by means of high resolution x-ray coplanar and x-ray grazing incidence diffraction, as well as by transmission electron microscopy. High resolution x-ray coplanar diffraction was used to obtain the average in-plane strain in Si/SiGe wires before and after removing the Si3N4/SiO2 shadow mask. x-ray grazing incidence diffraction measurements were performed to obtain information on the shape of the wires and on the depth-dependent strain relaxation. A finite element method was used to calculate the strain distribution in the Si/SiGe wires and in the Si substrate which clearly show the influence of the Si3N4/SiO2 shadow masks on the strain status of the Si/SiGe wires in agreement with the experimental data.

Titanium-induced structural modifications in thin waveguide layers of lithium niobate have been investigated by grazing incidence diffraction and complementary thin film techniques. The study was focused on the high-temperature phase transformation in this system and its influence on the lattice parameter changes, depending on the annealing time.

Synchrotron radiation at the European Synchrotron Radiation Facility has been used to characterize oxide thin films and multilayers grown by metal organic chemical vapor deposition (MOCVD). Reflectometry measurements were performed in the low angle region to get information on the quality of film/substrate and film/film interfaces of the heterostructures. The experimental data were compared to simulated spectra. High angle diffraction experiments were performed on superlattices of (BaTiO3/SrTiO3)15 and (La2/3Sr1/3Mn03/SrTiO3)15. The multilayers are oriented with the [001] direction perpendicular to the substrate plane. The 001 diffraction peaks were recorded up to the 008 one. The satellite peaks observed for both types of multilayers indicate the good coherence over the whole stacking. For the (BaTiO3/SrTiO3)15 systems, the diffraction peaks were particularly well resolved even for the highest order (008 peak), showing excellent epitaxial quality with abrupt interfaces for periods up to 16 nm.

A newly developed synchrotron instrument – the so-called 3D X-ray microscope – is presented. The instrument is placed at the Materials Science beamline at ESRF and dedicated to local μm scale structural characterization within bulk materials. In this paper, emphasis is on in situ studies of thermomechanical processing. The potential of the instrument for characterization of single nuclei and grains is described and discussed based on both first results and planned experiments.

High energy synchrotron radiation is employed for residual strain measurements from local gauge volumes within the bulk of polycrystalline materials. The longitudinal spatial resolution is defined by placing a narrow imaging slit behind the sample and recording the intensity distribution on a position sensitive detector. It is shown that the sample to slit distance can be increased without sacrificing longitudinal resolution by applying a reconstruction technique. Hence, space is provided for large samples and sample environments. The reconstruction technique is described and validated by measuring the residual strain profile of a shot-peened Al sample. A longitudinal gauge length of 95 üm is achieved at 52 keV with a sample to slit distance of 10 cm.

We have used submicron-resolution white x-ray microbeanis on the MHATT-CAT beamline 7-ID at the Advanced Photon Source to develop techniques for three-dimensional investigation of the deformation microstructure in a 20% plane strain compressed Al(0.2%)Mg tri-crystal. Kirkpatrick-Baez mirrors were used to focus white radiation from an undulator to a 0.7 × 0.7 μm2 beam that was scanned over bi- and tri-crystal regions near the triple-junction of the tricrystal. Depth resolution along the x-ray microbeam of less than 5 microns was achieved by triangulation to the diffraction source point using images taken at a series of CCD distances from the microbeam. Computer indexing of the deformation cell structure in the bi-crystal region provided orientations of individual subgrains to ∼0.01°, making possible detailed measurements of the rotation axes between individual cells.

The surface and the center average textures (macrotexture) of plates of many alloys differ substantially, and nondestructive methods for determining the depth of different texture components would be very useful in various applications. This report evaluates one method based on recording microbeam transmission Laue patterns as a function of sample-detector separation and on tracing the diffracted rays back to their physical origin. Polychromatic synchrotron x-radiation and absorption edge filters are used. Results from sections of Al-Li 2090 T8E41 plates are reported, and limitations of the ray tracing technique are discussed

We have used synchrotron radiation x-ray microdiffraction to study the microstructure and strain variation of copper interconnects. Different types of local microstructures have been found in different samples. Our data show that the Ti adhesion layer has a dramatic effect on Cu microstructure. On site electromigration test has been conducted and strain profile along the same interconnect line was measured before and after this electrical stressing. Cu fluorescence scan was used to find the mass variations along the line. Voids and hillocks can be clearly identified in this scan. x-ray micro-diffraction was used to measure the strain change around the interesting regions.

Attenuation- and phase-contrast microtomography using synchrotron radiation is applied to different samples demonstrating the advantages and limits of the two different contrast mechanism. Photon energies in the range of 8-25 keV and 60-100 keV are used. Scanning techniques employing a 2-dim. x-ray detector allow for investigation of larger specimens at high spatial resolution.

We have obtained the x-ray phase contrast images of the activated carbon/carbon (AC/C) composite used as electrodes in an electric double-layer capacitor (EDLC). To improve the spatial resolution, the beam size of x-ray transmitted from a sample were expanded by using asymmetric Bragg diffraction (asymmetric factor b) of analyzer crystal. Since the analyzer crystals were placed in (+, -) arrangements in both vertical and horizontal directions, the total magnification factor was 1/b2 for each direction. By using the 511 asymmetric Bragg diffraction of Si (100) analyzer with an asymmetric factor of 0.207, we could obtain the magnification factor of about 23.3. We applied this optical system to the AC/C composite. The phase contrast image corresponding to the carbon particles with the diameter of about 10 μm could be detected with the spatial resolution of 5 μm. Furthermore, we also obtained realtime images of bubble formation and movement during the overcharging of an EDLC with the time resolution of 30 frames number per second.

X-ray diffraction topography was used to investigate the relationship between subsurface damage, near-surface microstructure, and fracture strength in a series of sapphire modulus of rupture (MOR) bars which had been fabricated to proof test fabrication processes. The strength of the bars was determined by failure in four point bending. The tensile surface of the bars was also examined using optical microscopy and non-contacting surface profilometry. Both show that the bars have good surface finish, with a typical RMS roughness of 0.7 nm. No correlation was found between RMS surface finish and fracture strength. Although the bars appeared to be indistinguishable, topographs taken prior to fracture testing revealed that they are of two distinct types. Type 1 has an oriented microstructure consisting of a pattern of linear features running the length of the bars. Type 2 was typical of well-polished sapphire, containing individual dislocations and occasional damage from handling. We attribute the Type 1 microstructure to fabrication damage that was not removed by subsequent processing and/or polishing. Fracture strength data showed that the Type I (damaged) bars had strengths less than 70 % of the bars without damage. Topography is sensitive to near-surface damage that can be correlated to fracture strength. Neither low magnification optical microscopy nor conventional surface finish statistics could be correlated to strength.