Effects of temperature and electron energy on the electron-irradiation-induced decomposition of sapphire

The effects of temperature and electron energy on the electron-irradiation-induced decomposition of sapphire have been investigated by in situ transmission electron microscopy (TEM). It was found that the decomposition rate of α-Al₂O₃ increased with increasing irradiation temperature and decreased with increasing acceleration voltage. The core-hole Auger decay process (K–F model), rather than knock-on displacement, is responsible for the decomposition of α-Al₂O₃ under electron irradiation.     

Effect of a nanoporous surface on photoluminescence from nanopatterned GaN thin films fabricated by anodic alumina templates

GaN photonic crystal slabs on InGaN/GaN multi-quantum well light-emitting diodes have been formed by dry etching using nanoporous anodic alumina templates, which have a periodic lattice constant of 105 nm and a hole diameter of 45 nm. The photonic crystal slab shows an enhanced intensity of photoluminescence due to the nanohole pattern array producing Fabry–Perot like interference. A rough surface of nanoholes results in a broad spectrum with a small oscillation, and well-ordered multiple facets of nanoholes results in a relatively sharp spectrum with a large oscillation.     

First-principles pseudopotential study of an aluminium grain boundary containing sulphur atoms

The electronic structure of an aluminium grain boundary with segregated sulphur impurity atoms has been calculated by a first-principles pseudo-potential method. It is found that a sulphur atom bonds to only one of the neighbouring aluminium atoms. This bond is a mixed-character metallic-covalent bond which is stronger than the metallic Al-Al bonds. Electrons that participate in forming this bond are 3p electrons of sulphur but not its 3s electrons. Other Al--S bonds in the boundary contain no covalent character. From the nature of Al--S bonds in the boundary it cannot be decided whether the embrittlement promotion mechanism by sulphur segregation should be classified as a 'bond mobility model' or a 'decohesion model'.     

Evolution of a sharp {110} texture in microcrystalline Fe78Si9B13 during magnetic crystallization from the amorphous phase

The effect of magnetic crystallization on texture evolution and control in nanocrystalline materials has been studied using a melt-spun amorphous Fe₇₈Si₉B₁₃ alloy. The magnetic crystallization was conducted at temperatures ranging from 653 to 853?K in a magnetic field up to 6?T. The temperatures used for magnetic crystallization were chosen on the basis of the Curie and crystallization temperatures of the amorphous phase, and the Curie temperature of the crystallized phase. The resultant microstructure was characterized by X-ray diffraction and FE-SEM/EBSP/OIM techniques. It was found that a sharp {110} texture developed when the amorphous precursor was crystallized at 853?K in a magnetic field of 6?T applied in a direction parallel to the ribbon surface.     

Dissociation of dislocations in MgAl2O4 spinel deformed at low temperatures

Abstract

When spinel is deformed in compression at 400°C along 〈110〉, the primary slip plane is found to be {111} with cross-slip occurring on a {001} plane. A comparison of weak-beam images of dislocations from both systems indicates that all dislocations which belong to the primary slip plane are dissociated out of the {111} plane independent of the character of the dislocation. It is proposed that deformation occurs by motion of dislocations in their dissociated state and that the partial dislocations actually glide on parallel glide planes. Movement of these dissociated dislocations is then accompanied by a concurrent migration of the stacking fault which takes place by a local shuffling of the cations. A stacking fault energy for conservative dissociation at 400°C on {001} of 530±90mJ m^?2 has been determined from weak-beam images of screw dislocations.