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The reactions of screw superdislocations or micropipes in silicon carbide single crystals are examined by using synchrotron radiation phase sensitive radiography. The simulation demonstrates that the coalescence of micropipes with opposite-sign Burgers vectors may be realized by their straightforward movement towards each other or their revolution about one another.

Research was conducted to examine coherence-enhanced synchrotron radiology. The investigation revealed that both refraction and edge diffraction can play a role in radiological images taken with coherent synchrotron light and that their relative weight in a given image relies on the experimental geometry, type of specimen and other parameters. This finding could be used to achieve more detailed and complementary radiological information.

Pd atom bonding on a thin layer of silicon intermediate oxidation states was investigated using core level and valence band photoemission spectroscopy. The results showed that the pristine Si intermediate oxidation states alter their configuration and bond metal atoms. Si2P spectrum changes in the chemical shift were observed, along with new peaks whose areas increased with the metal coverage.

We present a simple and highly versatile protocol for polymer ablation: hard x-ray irradiation makes it possible to rapidly depolymerize hyaluronan hydrogels and fabricate three-dimensional network of microchannels. Photodynamic and photochemical analyses show that x-ray irradiation directly cleaves the polymer backbone and the total dose controls the degradation kinetics. This nonthermal ablation protocol may offer opportunities for processing organic polymers and biological materials. [ABSTRACT FROM AUTHOR]

Synchrotron phase sensitive radiography, optical and scanning electron microscopies, and color photoluminescence have been used to study the interaction of micropipes with foreign polytype inclusions in 4H-SiC bulk crystals grown on 6H-SiC substrates. This combination of techniques confirms that micropipes agglomerate at the polytype inclusions and merge into pores. A mechanism for this phenomenon is suggested based on a three-dimensional theoretical model; the inclusion boundaries elastically interact with micropipes, causing them to migrate from the bulk to their equilibrium positions at the polytype boundaries. The turning of micropipes towards the inclusions is experimentally demonstrated, and the reduction of their density in nearby regions is revealed. Supported by experimental observations, our model helps to understand the pore formation and expansion in SiC bulk crystals. [ABSTRACT FROM AUTHOR]

We investigated the room temperature electroless nickel deposition on glass, induced by synchrotron x ray. By irradiating electrolytes with intense x ray the onset time for Ni reduction disappears at high electrolyte pH (>6.0) in sharp contrast with conventional electroless deposition. The time for Ni reduction in irradiated solution also decreases with increase in electrolyte pH. Consequently higher reduction rates in alkaline solutions (pH>8.0) raise the Ni nucleation density during deposition, as illustrated by homogeneous and complete coverage of the substrate by nanoparticles within a short period of 1 min. The enhancement in reduction rate is attributed to high redox efficiency of hydrated electrons produced by x ray as well as their redox potential enhancements under higher electrolyte pH conditions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The ramification of micropipes is observed using scanning electron microscopy, optical microscopy, and synchrotron x-ray radiography. The conditions for the ramification of dislocated micropipes are determined theoretically within a model when the angles between dislocation lines are small. It is shown that the ramification of micropipes into two smaller ones is possible only for micropipes with radii that exceed the equilibrium micropipe radius and is associated with a decrease in the total micropipe surface area. [ABSTRACT FROM AUTHOR]

We investigated the structural evolution of GaN nucleation layers in the initial growth stages on commercial c-plane sapphires with atomic steps at the surface, using field-emission scanning electron microscopy, synchrotron x-ray scattering, and high-resolution electron microscopy. GaN nucleates into islands preferentially on the atomic steps. The initial small islands of 25 Å high have well-ordered cubic sequences and nearly coherent interfacial structures with a large compressive strain of ∼10%. As the islands grow to 50 Å high, the strain is drastically reduced, to less than 1%, by generating misfit dislocations at the interface and forming the six-to-seven matched interfacial structure. Interestingly, stacking faults are developed from the GaN/sapphire interface, which induces a cubic-hexagonal transformation. The changes in the stacking order during the initial growth are investigated quantitatively. [ABSTRACT FROM AUTHOR]