GaP films were grown on offcut Si(001) substrates using migration enhanced epitaxy nucleation followed by molecular beam epitaxy, with the intent of controlling and eliminating the formation of heterovalent (III-V/IV) nucleation-related defects—antiphase domains, stacking faults, and microtwins. Analysis of these films via reflection high-energy electron diffraction, atomic force microscopy, and both cross-sectional and plan-view transmission electron microscopies indicate high-quality GaP layers on Si that portend a virtual GaP substrate technology, in which the aforementioned extended defects are simultaneously eliminated. The only prevalent remaining defects are the expected misfit dislocations due to the GaP–Si lattice mismatch.

Solid-solid displacive, structural phase transformations typically undergo a discrete structural change from a parent to a product phase. Coupling electron microscopy, three-dimensional atom probe, and first-principles computations, we present the first direct evidence of a novel mechanism for a coupled diffusional-displacive transformation in titanium-molybdenum alloys wherein the displacive component in the product phase changes continuously with changing composition. These results have implications for other transformations and cannot be explained by conventional theories.

Electron energy-loss spectroscopy (EELS) and energy dispersive x-ray (EDX) analysis in scanning transmission electron microscopy (STEM) have the ability to produce elemental maps of a specimen at atomic resolution. In this paper we present EELS and EDX maps for the oxygen K-shell in 001 strontium titanate. The results initially seem to be anomalous since substantially more signal is obtained when the STEM probe is above the columns containing both titanium and oxygen than those containing only oxygen. This is at variance with the stoichiometry -the density of oxygen in both types of columns is the same. Using theory, we show that an understanding of the direct contribution to the recorded signal from electrons which have been thermally scattered is the key to understanding these results. We contrast these results to elemental maps of 110 strontium titanate. Whilst the experimental results are not directly interpretable, they are in concert with simulations from first-principles such as those presented in this paper.

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

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