Microbeam X-ray Diffraction Research Articles

Strong Fibers and Films of Microbial Polyesters

Poly[(R)-3-hydroxybutyrate] (P(3HB)) and its copolymers are accumulated by a wide variety of microorganisms as intracellular carbon and energy material, and are extensively studied as biodegradable and biocompatible thermoplastics. However, these microbial polyesters have not been recognized as practical because of their stiffness and brittleness. Recently, by new drawing techniques, we succeeded in obtaining strong fibers and films from microbial polyesters, produced by both wild-type and recombinant bacteria. The improvement in mechanical properties of the fibers and films is due not only to the orientation of molecular chains, but also to the generation of a zigzag conformation and network structure, formed by fibrillar and lamellar crystals. The structure of strong fibers with a tensile strength over 1.0 GPa was analyzed by micro-beam X-ray diffraction with synchrotron radiation. The strong fibers and films were completely degraded in natural, river freshwater or by extracellular polyhydroxybutyrate depolymerases. In this feature article, the processing, mechanical properties, highly ordered structure and biodegradability of strong fibers and films produced from microbial polyesters are presented.

Structure investigation of narrow banded spherulites in polyhydroxyalkanoates by microbeam X-ray diffraction with synchrotron radiation

Narrow banded structures of spherulites of poly[( R)-3-hydroxybutyrate] (P(3HB)) and its copolymers, with different second monomer unit of 4-hydroxybutyrate, 3-hydroxyhexanoate or 6-hydroxyhexanoate, were investigated by microbeam X-ray diffraction with Fresnel Zone Plate technique in synchrotron radiation (SPring-8). Radial scanning of spherulites were performed in 2 or 4 μm steps with 0.5 μm beam diameter of fine microfocus beam. The X-ray diffraction patterns for P(3HB) homopolymer spherulites showed the change of crystal orientation along the radial direction ( a-axis), while the b- and c-axes rotated around a-axis. The intensities in microbeam X-ray diagrams of spherulites for P(3HB) copolymers changed periodically as function of the distance along the radial direction. The periodicity measured by X-ray diffraction was matched with narrow band spacing (15–25 μm) observed by polarized optical microscopy.

Structural analysis of cell membrane complex of a hair fibre by micro-beam X-ray diffraction

The cell membrane complex in the cuticle of a human hair fibre or a rat whisker is composed of three layers, that is, β, δ and β layers. The X-ray diffraction technique is a powerful tool to investigate the pathway of aqueous molecules and ions across the cuticle. Small-angle scattering experiments using a micro X-ray beam, which can be applied to a cuticle of 5 µm thickness, provide the structural information on the cell membrane complex without interference from other structures. Taking into account the variation of thickness in the δ and β layers, the overall features of the diffraction profile in a small-angle region can be explained satisfactorily. The method makes it possible to analyse the structure of β, δ and β layers without assuming an ambiguous background in the diffraction profile, and was used for the analysis of a human hair fibre and a rat whisker. In a rat whisker, the X-ray diffraction was stronger and the variation in the layer thickness smaller than in a human hair fibre. This may be due to the fact that the rat whisker had not been washed with soap or cosmetically treated, whereas the variation may depend on the lipids or the proteins that each species naturally has. It is proposed that the method represents convenient tool for quantitative analysis to estimate the thickness of δ and β layers in the cell membrane complex.

Shear-induced crystallization in isotactic polypropylene containing ultra-high molecular weight polyethylene oriented precursor domains

Melt blends of short ultra-high molecular weight polyethylene (UHMWPE) fibers and isotactic polypropylene (iPP) were subjected to shear at 145 °C, above the melting point of polyethylene (PE). Structural evolution and final morphology were examined by in situ synchrotron X-ray scattering/diffraction as well as ex situ microbeam X-ray diffraction and high resolution scanning electron microscopy, respectively. Results indicate that the presence of oriented UHMWPE molten domains significantly facilitated the crystallization of iPP and enhanced the initial ‘shish-kebab’ structure leading to the final cylindritic morphology. It is argued that shear flow aligns the fibrillar UHMWPE domains, where the interfacial frictions between PE and iPP effectively retards the relaxation of iPP chains, allowing the aligned iPP chains to create a shish-like structure. Nucleation on the iPP shish initiates the folded chain lamellae (kebabs), which grow perpendicularly to the iPP/PE interface.

Novel chiral filament in an achiral W-shaped liquid crystalline compound

Anomalous optical birefringence and optical rotation have been observed in a liquid crystal phase comprising of W-shaped liquid crystal molecules with hydrogen bonds. The texture of this phase exhibits characteristic chiral filaments, which form strongly segregated chiral domains similar to the B4 phase of conventional bent-core mesogens, despite of having no chiral carbon. Based on X-ray microbeam diffraction, polarizing and confocal optical microscope observations, the molecular arrangement in the filament is discussed, and the novel structure different from that in B4 is proposed; the smectic layers form concentric cylinder, on which the c-director of the W-shaped molecules form screw-like and/or polar arrangement, inducing herringbone anisotropic structure and chirality in each filament, as observed in the experiments.

Crystal structure and grain size of Zr oxide characterized by synchrotron radiation microdiffraction

Zirconium oxides formed on Zirclaoy-4 and Zr–1.5Nb (in wt%) were characterized by the microbeam X-ray diffraction using a synchrotron radiation. The phase fraction and the grain size were determined as a function of the position in the oxide. It was found that Zr–1.5Nb showed the better corrosion resistance than Zircaloy-4 in 360°C pure water although the tetragonal phase was more stabilized to a further distance from the metal/oxide interface in the oxide of Zircaloy-4. The calculation of the grain size revealed that the oxide of the Zr–1.5Nb had larger grains than that of Zircaloy-4 with the tetragonal phase being smaller than the monoclinic one. It seems reasonable to suppose that the superior corrosion resistance of Zr–1.5Nb was attributed to the lager grain size of the oxide in which the oxygen diffusion is expected to be lowered when compared to the smaller grain size of the oxide on Zircaloy-4.

Identification of ancient textile fibres from Khirbet Qumran caves using synchrotron radiation microbeam diffraction

Archaeological textiles fragments from the caves of Qumran in the Dead Sea region were investigated by means of X-ray microbeam diffraction on single fibres. This non-destructive technique made the identification of the used plant textile fibres possible. Apart from bast fibres (mainly flax), cotton was identified which was most unexpected in the archaeological context.

Synchrotron x-ray microbeam diffraction from abalone shell

Microstructured biomaterials such as mollusk shells receive much attention at present, due to the promise that advanced materials can be designed and synthesized with biomimetic techniques that take advantage of self-assembly and aqueous, ambient processing conditions. A satisfactory understanding of this process requires characterization of the microstructure not only in the mature biomaterial, but at the growth fronts where the control over crystal morphology and orientation is enacted. In this paper, we present synchrotron microbeam x-ray diffraction (XRD) and electron microscopy observations near the nacre–prismatic interface of red abalone shell. The relative orientations of calcite and aragonite grains exhibit some differences from the idealizations reported previously. Long calcite grains impinge the nacre–prismatic boundary at 45° angles, suggestive of nucleation on (104) planes followed by growth along the c axis. In the region within 100 μm of the boundary, calcite and aragonite crystals lose their bulk orientational order, but we found no evidence for qualitative changes in long-range order such as ideal powder texture or an amorphous structure factor. XRD rocking curves determined the mosaic of calcite crystals in the prismatic region to be no broader than the 0.3° resolution limit of the beamline’s capillary optics, comparable to what can be measured on geological calcite single crystals.

Temperature and Electric Field Dependences of the Local Layer Structure in Anti-Ferroelectric Liquid Crystals Measured by X-Ray Micro-Diffraction

The local layer of the antiferroelectric liquid crystal has been investigated as a function of the temperature near the SmA to SmC A * phase transition by synchrotron X-ray microbeam diffraction. The stripe texture in the SmA phase well above the phase transition temperature is related to the in-plane layer deflection. Just above the phase transition temperature, the clear stripe starts to grow and the local layer structure becomes the combination of the vertical-chevron and the horizontal-chevron. With decreasing temperature in the SmC A * phase, the chevron angle increases. The growth of the chevron structure is explained by the gradual reduction of the layer spacing. The time resolved measurement of the local layer structure in the electroclinic effect is also carried out to characterize the layer response in the SmA phase. The comparison of the chevron structure between the antiferroelectric and the ferroelectric liquid crystal is made.

Structure of zirconium alloy oxides formed in pure water studied with synchrotron radiation and optical microscopy: relation to corrosion rate

A detailed study was undertaken of oxides formed in 360 °C water on four Zr-based alloys (Zircaloy-4, ZIRLO™, 1 ZIRLO is a trademark of Westinghouse Electric Co. 1 Zr–2.5%Nb and Zr–2.5%Nb–0.5%Cu) in an effort to relate oxide structure to corrosion performance. Micro-beam X-ray diffraction was used along with transmitted light optical microscopy to obtain information about the structure of these oxides as a function of distance from the oxide–metal interface. Optical microscopy revealed a layered oxide structure in which the average layer thickness was inversely proportional to the post-transition corrosion rate. The detailed diffraction studies showed an oxide that contained both tetragonal and monoclinic ZrO 2, with a higher fraction of tetragonal oxide near the oxide–metal interface, in a region roughly corresponding to one oxide layer. Evidence was seen also of a cyclic variation of the tetragonal and monoclinic oxide across the oxide thickness with a period of the layer thickness. The results also indicate that the final grain size of the tetragonal phase is smaller than that of the monoclinic phase and the monoclinic grain size is smaller in Zircaloy-4 and ZIRLO than in the other two alloys. These results are discussed in terms of a model of oxide growth based on the periodic breakdown and reconstitution of a protective layer.

Local layer structures in circular domains of an achiral bent-core mesogen observed by x-ray microbeam diffraction.

The local layer structures have been investigated by x-ray microbeam diffraction in the circular domains of the SmCP phase of a banana-shaped molecule. Originally, the molecules form tilted layers with a certain tilt angle as well as nontilted ones. The application of a low electric field induces a tilted layer with a continuous change of the tilt angle; i.e., the tilted layer gradually changes the tilt angle, finally being upright at the center of circular domains. Upon application of a high electric field, the smectic layer forms a cylindrical-type structure. The layer structure changes from cylindrical to onionlike after turning off the high field.

Relationship between copper concentration and stress during electromigration in an Al(0.25 at. % Cu) conductor line

Synchrotron-based x-ray microbeam fluorescence and diffraction have been used for in situ measurements of Cu concentration and biaxial stress in a 200-μm-long, 10-μm-wide Al(0.25 at. % Cu) conductor line with 1.5-μm-thick SiO2 passivation during electromigration. Measurements over 48 h with T=300 °C and j=1.5×105 A/cm2 show that a stress gradient of 3 MPa/μm develops over the upstream 130 μm of line length where Cu concentration drops below 0.15 at. %, and a 10-μm-long void develops at the cathode end of the line, but little change in stress occurs over the downstream 70 μm of line length where Cu concentration remains above 0.15 at. %. These experimental results have been reproduced by a finite element model in which the downstream Cu transport is accompanied by a counter flow of Al in the upstream direction, and downstream Al motion is blocked where the local Cu concentration is above ∼0.15 at. %. Defect mediated coupling between Al and Cu diffusive flows, e.g., Cu–vacancy binding, is proposed as the cause for the counterflow of Al when the Cu concentration is above the critical concentration, and as the mechanism by which Cu reduces the rate of electromigration damage in Al(Cu) conductor lines.

X-ray Microbeam Diffraction Measurements in Polycrystalline Aluminum and Copper Thin Films

ABSTRACTThermally induced residual strains in polycrystalline Cu and Al films on single crystal Si and glass substrates, respectively, have been examined on a grain-by-grain basis by x-ray microbeam diffraction. The crystallographic orientation and the deviatoric strain tensor, εij*, are determined for each grain by white beam Laue diffraction. From grain orientation mapping and strain tensor measurements, information is obtained about the distributions of strains for similarly oriented grains, about strain variations within single grains, and about grain-to-grain correlations of strains. This type of information may be useful in developing and testing theories for intergrain effects in strain evolution in polycrystals.

Elastic moduli of nanocrystallites in carbon fibers measured by in-situ X-ray microbeam diffraction

The in-plane Young’s modulus and the shear modulus of carbon nanocrystallites were investigated during in-situ tension tests of single carbon fibers by X-ray diffraction using the shift of the 10 band in the meridional direction and the change in the azimuthal width of the 002 reflection. The limiting value for the Young’s modulus was found to be 1140 GPa, which is higher than the value for graphite obtained from macroscopic specimens, but coincides with recent measurements on nanotubes. Furthermore, the shear modulus was evaluated using a uniform stress approach and was found to increase with increasing misorientation of the crystallites. It turns out that both the in-plane Young’s modulus and the shear modulus are not constant, but dependent on the orientation parameter.

Synchrotron Microbeam Diffraction Study of the Microstructure and the Chemical Composition in a Monocrystalline Ni-Base Turbine Blade After a Thermomechanical Mission Test

High-performance turbine blades composed of monocrystalline Ni-base γ/γ′ superalloys are often protected by coatings to resist the high-temperature corrosive atmosphere environment applications. During applications severe thermal and mechanical loads cause drastic and complicated changes in the microstructure and the chemical composition, also combined with strong lateral gradients of both temperature and stress. Microbeam X-ray diffraction experiments with a spatial resolution of about 5 μm enabled the determination of both the microstructural and the chemical composition gradients within material volumes of the sizes of the order of about 1 mm3 or smaller. The high angular and spatial resolution was achieved by a special focusing technique using a Bragg–Fresnel focusing monochromator at the BM5 beamline of the ESRF synchrotron at Grenoble. The X-ray diffraction experiments were complemented and supported by electron microscopy investigations of the microstructure and the chemical composition.

Microbeam X-ray Diffraction Analysis of Human Tooth Enamel from EDJ to Enamel Surface

Microbeam X-ray Diffraction Analysis of Human Tooth Enamel from EDJ to Enamel Surface

Scanning X-ray microdiffraction of complex materials: Diffraction geometry considerations

Complex fiber composites such as biological materials frequently exhibit local fiber textures which can be determined quantitatively by scanning X-ray microdiffraction techniques. The experimental necessity of keeping the illuminated diffraction volume fixed usually leads to complex diffraction patterns, depending on the orientation of the fiber axis with respect to the direction of the primary X-ray beam. Here, an analytical expression is derived that relates the azimuthal intensity distribution measured with an area detector to the orientation distribution of the fibers within the specimen. The validity of the relation is demonstrated for a single flax fiber, which was investigated by microbeam X-ray diffraction using synchrotron radiation.

Microbeam X-ray diffraction measurement of strain

Microbeam X-ray diffraction measurement of strain

Novel applications of X-ray analysis to microelectronic materials and devices

X-ray analysis has been important for advanced understanding of many microelectronic materials. Examples described in this paper are drawn from work on metal conductor lines and on semiconductors. In situ studies of Al and Al(Cu) conductor lines by X-ray microbeam diffraction and fluorescence have been used to test models and to obtain key parameters for electromigration in polycrystalline metals and alloys. EXAFS and high resolution X-ray diffraction have given information about local strains, defect complexes and deformation potentials in studies of group III, IV, and V impurities in silicon. Real-time high resolution diffraction measurements of optically induced structural changes in GaAlAs:Sn and GaAlAs:Si have provided tests for structural models of the DX-center. Some of these examples illustrate advances in X-ray analysis made possible by high brightness synchrotron X-ray sources.

Submicron x-ray diffraction and its applications to problems in materials and environmental science

The availability of high brilliance third generation synchrotron sources together with progress in achromatic focusing optics allows us to add submicron spatial resolution to the conventional century-old x-ray diffraction technique. The new capabilities include the possibility to map in situ, grain orientations, crystalline phase distribution, and full strain/stress tensors at a very local level, by combining white and monochromatic x-ray microbeam diffraction. This is particularly relevant for high technology industry where the understanding of material properties at a microstructural level becomes increasingly important. After describing the latest advances in the submicron x-ray diffraction techniques at the Advanced Light Source, we will give some examples of its application in material science for the measurement of strain/stress in metallic thin films and interconnects. Its use in the field of environmental science will also be discussed.