Electronic excitations induced climb of dislocations in swift heavy ion irradiated AlN and AlxGa1−xN

International audienceRecent work has shown that electronic excitations play a role in the creation of optical point defects in AlN although the material had been considered during a long time as insensitive to electronic energy loss and radiolysis. We address here an indirect observation of the effect of electronic excitations on point defect in AlN. Unprecedented climb of screw dislocations under swift heavy irradiation in irradiated AlN is studied. This is a sign to point defect diffusion towards the dislocation, which allows the increase of the length of the dislocation line. It is demonstrated that the climb, thus the point defect creation and/or their mobility is mainly induced by electronic excitations. This happens above an electronic stopping power threshold much lower than the one for ion track formation in AlN. This climb of dislocation was also observed for the same irradiation conditions in AlxGa1−xN (x = 0.5; 0.7; 0.8)

Fullerene irradiation leading to track formation enclosing nitrogen bubbles in GaN material

International audienceGallium nitride was irradiated with fullerene projectiles having an electronic stopping power above the threshold required to promote ion track formation. The structural and chemical changes induced by fullerene irradiation were studied through Transmission Electron Microscopy (TEM). High resolution TEM inquiries were performed to identify the structural order along the ion tracks and the strain induced in the lattice neighboring the ion tracks. The TEM investigation pointed out local amorphization inside the whole tracks and High Resolution TEM studies in the track periphery evidence local stress in the wurtzite structure. Chemical investigations were carried out by STEM Electron Energy Loss Spectroscopy (EELS) to describe the chemical order in the neighboring and inside the ion path. Ga/N stoichiometry is essentially maintained in the track core, whereas an oxidation is detected in the ion track, at the surface. Furthermore, the nitrogen k near-edge fine structure investigation reveals the encapsulation of nitrogen bubbles inside the ion tracks

Formation of bimetallic FeBi nanostructured particles: Investigation of a complex growth mechanism

cited By 7International audienceMagnetic bimetallic Fe-Bi composites, synthesized by decomposition of organometallic precursors under amine borane and dihydrogen, formed regular nanospheres with mean diameter of 150 ± 30 nm. The nanospheres display a core-shell like chemical distribution in which bismuth is mainly concentrated in the core, as demonstrated through elemental mapping X-ray energy dispersive spectroscopy while the shell is formed by aggregated 3 nm wide iron nanoparticles. The close environment of the different elements was analyzed through complementary techniques such as extended X-ray absorption fine structure, wide-angle X-ray scattering, and 57Fe Mössbauer and X-ray photoelectron spectroscopies. Despite their iron-rich shell, the Fe-Bi nanospheres present both good magnetic properties and enhanced resistance to oxidation during air exposure. To uncover the growth mechanisms leading to the formation of this compound, a series of samples taken at different steps of the synthesis process was analyzed. The role of metallic iron to promote the reduction of the bismuth precursor from the early stages of the synthesis is emphasized. Remarkably, this process promotes the formation of a metastable Fe-Bi nanoalloy. © 2012 American Chemical Society

Desempenho radicular de mudas de eucalipto produzidas em diferentes recipientes e substratos Root performace of eucalyptus stecklings, produced in different containers and substrates

O trabalho teve como objetivo verificar o desempenho, em sacolas, de clones de eucalipto, produzidos em diferentes recipientes e substratos, com ênfase na persistência das deformações radiculares originadas no viveiro e na produção de raízes. As mudas foram produzidas em tubetes (50 cm³) e em blocos prensados (40 x 60 x 7 cm - 16.800 cm³), sendo utilizados como substratos: casca de arroz carbonizada com casca de eucalipto, bagaço de cana com torta de filtro; e turfa. As mudas, com 90 dias, foram transplantadas para sacos plásticos (20 L), com solo da área de plantio. O experimento foi conduzido em delineamento inteiramente casualizado, em esquema fatorial 2 x 7, constituído por dois clones (híbridos naturais de Eucalyptus grandis Hill ex Maiden e E. saligna Smith) e sete tratamentos, com variação de recipientes e substrato, com quatro repetições, constituídas por quatro plantas. Dois meses após o transplantio, as plantas foram avaliadas quanto ao crescimento em diâmetro ao nível do solo, altura da parte aérea, número de raízes emitidas, comprimento, área superficial e deformação do sistema radicular. As plantas originadas de mudas produzidas em blocos prensados apresentaram melhor desempenho nas avaliações realizadas em relação às dos tubetes. As deformações radiculares causadas por recipientes de paredes rígidas tendem a persistir após a fase de viveiro.<br>The objective of this work was to evaluate the performance after the planting of eucalyptus stecklings, produced in different containers and substrates, with emphasis in root production and deformations. The stecklings were produced in tubes (50 cm³) and in pressed blocks (40 x 60 x 7cm -16800 cm³), and used as substrates: carbonized rice husk and eucalyptus husk; sugarcane bagasse and sugarcane filter cake; and peat. At ninety days the stecklings were transplanted to plastic bags (20 L), with soil from the planting area. This experiment was set in a completely randomized design, arranged in a 2 x 7factorial, constituted by two clones (natural hybrid of Eucalyptus grandis Hill ex Maiden and E. saligna Smith) and seven treatments, with variation of containers and substrates, with four replicates, constituted by four plants. At two months, the cuttings were evaluated considering their root collar diameter, height, number, length and superficial area of emitted roots, and system root deformations. The plants originated of stecklings produced in pressed blocks presented better performance than the tubes ones. The root deformations caused by containers persist after the nursery stage