Some recent papers!

May 6, 2010

[1] Structural and compositional homogeneity of InAlN epitaxial layers nearly lattice-matched to GaN

J M Manuel et al

A group of InAlN films was fabricated by molecular beam epitaxy and investigated by X-ray diffraction, transmission electron microscopy and element nano-analyses. All top InxAl1−xN layers have compositions around lateral lattice-matching to GaN (x ≈ 0.18) and are pseudomorphic. For a growth rate of 350 nm h−1, each InAlN film separated into two sublayers with different In/Al-ratios. Micrographs reveal sharp transitions both at the InAlN/GaN and at the InAlN/InAlN interfaces. In contrast to these separated layers, an optimized epitaxy using an AlN interlayer and a lower growth rate, 100 nm h−1, enabled the fabrication of a single-phase InxAl1−xN layer on GaN, homogeneous on a nanoscopic scale.

[2] Microstructural stability in multi-alloy systems: Nanostructured two-phase, dual alloy multilayers

X Pan et al

Interdiffusion and microstructural stability in multilayers consisting of two nanostructured two-phase alloys were investigated using phase field simulations. A prototype ternary system containing a miscibility gap was used as the model system. Alloys with various compositions within the miscibility gap were chosen to form 20 μm bilayer repeating units in the multilayers. The initial microstructures in the alloys were produced by spinodal decomposition, which yielded a uniform distribution of precipitates having an average diameter of about 50 nm. Two types of multilayers were investigated; one in which the alloys in the repeating unit had the same matrix phase and the other in which the alloys had a different matrix phase. In general the microstructural instability measured as the size of the reaction zone increased with the increase in composition difference between the two initial alloys and in atomic mobility difference between the diffusing species. In particular, when the matrix phase was the same a precipitate-free zone (i.e. a single-phase layer) and a coarse interconnected precipitate zone formed at the interface between the two alloys, while when the matrix phase differed two precipitate-free zones formed at the interface. The microstructural instabilities were analyzed in terms of variations in the effective diffusivity with composition, which produced a singularity in the diffusion path at the initial alloy interface. The instability caused the diffusion path to exit the two phase region of the phase diagram and enter the single phase region.

[3] The Shape of Bubble in He Implanted Cu and Au

Q Wei et al

Bubble evolution under thermal annealing has been studied in He implanted Cu and Au by in situ transmission electron microscopy (TEM). We show that, under the minimum energy requirement of system, the bubble developed into an octahedron ( or truncated octahedron) shape consisting of {111} planes in the manner predicted by the Wulff construction. Nonspherical shape of bubbles and sessile dislocations along the edges of octahedron provide a barrier to Ostwald ripening and migration of bubbles, leading to the low mobility of bubble under thermal annealing.

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