Towards predictive modelling of near-edge structures in electron energy loss spectra of AlN based ternary alloys

Although electron energy loss near edge structure analysis provides a tool for experimentally probing unoccupied density of states, a detailed comparison with simulations is necessary in order to understand the origin of individual peaks. This paper presents a density functional theory based technique for predicting the N K-edge for ternary (quasi-binary) nitrogen alloys by adopting a core hole approach, a methodology that has been successful for binary nitride compounds. It is demonstrated that using the spectra of binary compounds for optimising the core hole charge ($0.35\,\mathrm{e}$ for cubic Ti$_{1-x}$Al$_x$N and $0.45\,\mathrm{e}$ for wurtzite Al$_x$Ga$_{1-x}$N), the predicted spectra evolutions of the ternary alloys agree well with the experiments. The spectral features are subsequently discussed in terms of the electronic structure and bonding of the alloys.Comment: 11 pages, 9 figures, 1 tabl

Dislocation Nucleation and Propagation in Semiconductor Heterostructures

This paper considers misfit dislocation nucleation and propagation in dilute magnetic semiconductor heterostructures in the CdTe-ZnTe-MnTe system. It is shown that, where the deposit is in tension, 1/2 \u3c 110 \u3e dislocations with inclined Burgers vectors propagate by glide along interfacial \u3c 110 \u3e directions and may dissociate giving intrinsic stacking faults. In cases where the deposit is in compression, 1/2 \u3c 110 \u3e dislocations show no evidence of dissociation and propagate by extensive cross-slip to give networks of dislocations close to interfacial \u3c 100 \u3e directions. Evidence for dislocation sources in ZnTe/GaSb films is presented. ZnTe films contained stacking fault pyramids, single Frank faults and a new type of diamond defect are present at densities up to about 107 cm-2. Analysis showed that the diamond defects, which were four-sided defects on {111} planes with \u3c 110 \u3e edges, were of vacancy type with 1/3 \u3c 111 \u3e Frank Burgers vectors and intrinsic stacking faults. Although faulted defects showed no tendency to grow by climb, evidence is given for an unfaulted reaction in which a glissile 1/2 \u3c 110 \u3e dislocation is generated. This new model for dislocation nucleation is discussed

Study of pinholes and nanotubes in AlInGaN films by cathodoluminescence and atomic force microscopy

Cathodoluminescence (CL) in the scanning electron microscope and atomic force microscopy (AFM) have been used to study the formation of pinholes in tensile and compressively strained AlInGaN films grown on Al2O3 substrates by plasma-induced molecular beam epitaxy. Nanotubes, pits, and V-shaped pinholes are observed in a tensile strained sample. CL images show an enhanced emission around the pits and a lower intensity at the V-shaped pinholes. Rounded pinholes appear in compressively strained samples in island-like regions with higher In concentration. The grain structure near the pinholes is resolved by AFM. (C) 2004 American Institute of Physics

Compositional variations in In0.5Ga0.5N nanorods grown by molecular beam epitaxy

The composition of InxGa1 − xN nanorods grown by molecular beam epitaxy with nominal x = 0.5 has been mapped by electron microscopy using Z-contrast imaging and x-ray microanalysis. This shows a coherent and highly strained core-shell structure with a near atomically sharp boundary between a Ga-rich shell (x∼0.3) and an In-rich core (x∼ 0.7), which itself has In- and Ga-rich platelets alternating along the growth axis. It is proposed that the shell and core regions are lateral and vertical growth sectors, with the core structure determined by spinodal decomposition

Usoi Tripura basic vocabulary

The composition of InxGa1 − xN nanorods grown by molecular beam epitaxy with nominal x = 0.5 has been mapped by electron microscopy using Z-contrast imaging and x-ray microanalysis. This shows a coherent and highly strained core-shell structure with a near atomically sharp boundary between a Ga-rich shell (x∼0.3) and an In-rich core (x∼ 0.7), which itself has In- and Ga-rich platelets alternating along the growth axis. It is proposed that the shell and core regions are lateral and vertical growth sectors, with the core structure determined by spinodal decomposition

Composition and strain relaxation of In x Ga1−x N graded core–shell nanorods

Two In x Ga1−x N nanorod samples with graded In compositions of x = 0.5–0 (Ga-rich) and x = 0.5–1 (In-rich) grown by molecular beam epitaxy were studied using transmission electron microscopy. The nanorods had a wurtzite crystal structure with growth along 0001 and core–shell structures with an In-rich core and Ga-rich shell. Energy-dispersive x-ray analysis confirmed grading over the entire compositional range and showed that the axial growth rate was primarily determined by the In flux, and the radial growth rate by the Ga flux. There was no evidence of misfit dislocations due to grading, but the strain due to the lattice mismatch between the In-rich core and Ga-rich shell was relaxed by edge dislocations at the core–shell interface with Burgers vectors a and

Calcitization of aragonitic bryozoans in Cenozoic tropical carbonates from East Kalimantan, Indonesia

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Managing dose-, damage- and data-rates in multi-frame spectrum-imaging

As an instrument, the scanning transmission electron microscope is unique in being able to simultaneously explore both local structural and chemical variations in materials at the atomic scale. This is made possible as both types of data are acquired serially, originating simultaneously from sample interactions with a sharply focused electron probe. Unfortunately, such scanned data can be distorted by environmental factors, though recently fast-scanned multi-frame imaging approaches have been shown to mitigate these effects. Here, we demonstrate the same approach but optimized for spectroscopic data; we offer some perspectives on the new potential of multi-frame spectrum-imaging (MFSI) and show how dose-sharing approaches can reduce sample damage, improve crystallographic fidelity, increase data signal-to-noise, or maximize usable field of view. Further, we discuss the potential issue of excessive data-rates in MFSI, and demonstrate a file-compression approach to significantly reduce data storage and transmission burdens