Papers by Author: Giovanni Bruno

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Authors: M. Karadge, Benedict M.B. Grant, Giovanni Bruno, Javier R. Santisteban, Philip J. Withers, Michael Preuss
Abstract: In this study we present a direct comparison between residual strain measurements carried out on the same inertia friction weld using ENGIN-X at ISIS, UK and the new strain scanner SALSA at ILL, France. ENGIN-X is a time of flight (TOF) instrument, which receives neutrons from a neutron spallation source, while the SALSA Strain-Imager, a high resolution diffractometer, is based at a research reactor source with a continuous neutron flux and is operated with a constant wavelength. The purpose of this study was to demonstrate a confidence in crosscomparing future strain measurements to be performed at ENGIN-X and SALSA. Measurements were carried out on medium size inertia friction welded nickel superalloy test-piece, which show no significant crystallographic texture across the weld line. The results demonstrate that, even though residual stresses determined on SALSA only rely on a single peak analysis (in this case the (111) reflection), the results show excellent agreement with the measurements carried out on ENGIN-X, where strain is determined from multi-peak Rietveld analysis.
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Authors: Tong Ho Kim, Soo Jeong Choi, April S. Brown, Maria Losurdo, Giuseppe Valerio Bianco, Maria M. Giangregorio, Giovanni Bruno
Abstract: Nitride materials are critical for a range of applications, including UV-visible light emitting diodes (LEDs). Advancing the performance, reliability and synthesis of AlGaN/GaN and InGaN/GaN heterojunction devices requires a systematic methodology enabling characterization of key metric like alloy composition, thickness and quality possibly in real time. This contribution reports on the real time characterization of the plasma assisted molecular beam epitaxy of AlGaN/GaN and InGaN/GaN heterostructures. Spectroscopic ellipsometry real time monitoring has revealed a number of key process and material iusses, such as the roughening of the GaN templates depending on plasma exposure during the substrate cleaning step, the composition of the alloy and the growth mode. Parameters like the plasma conditions, the surface temperature and the atomic flow ratio are investigated to understand the interplay process-material composition-structure-optical properties.
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Authors: R. Fernández, Giovanni Bruno, Ru Lin Peng, G. González-Doncel
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Authors: Giovanni Bruno, Maria Losurdo, P. Capezzuto, V. Capozzi, F.G. Lorusso, A. Minafra
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Authors: Maria M. Giangregorio, Giuseppe Valerio Bianco, Alberto Sacchetti, Pio Capezzuto, Maria Losurdo, Giovanni Bruno
Abstract: In this contribution, we address two critical and interesting aspects from both fundamental and technological point of views, which are the polarity of ZnO and the interface reactivity and stability to hydrogen and nitrogen. The effects of atomic hydrogen and nitrogen produced by radiofrequency (r.f. ,13.56 MHz) H2 and N2 plasmas and of temperature on the optical, compositional and structural properties of Zn- and O-polar ZnO have been studied. It is found that Zn-polar ZnO is highly reactive with atomic hydrogen while O-polar ZnO is almost inert. Conversely, both polarities react with nitrogen, with the O-polar ZnO showing a larger reactivity toward N-atoms than the Zn-polarity.
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Authors: Giovanni Bruno, Adele Carradò, B. Dunn, F. Fiori, E. Girardin, Thilo Pirling, F. Rustichelli
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Authors: Jesus Ruiz-Hervias, Giovanni Bruno, Jonas Gurauskis, A.J. Sanchez-Herencia, C. Baudin
Abstract: Residual stress profiles were measured by neutron diffraction in Al2O3/Y-TZP ceramic composites containing 5 and 40 vol.% Y-TZP fabricated by conventional slip casting and by a novel tape casting route. Residual stresses in the zirconia are tensile and increase as its volume fraction decreases. For the alumina matrix, residual stress is compressive and increases with the zirconia volume fraction. In the composite with 5 vol.% zirconia, the processing route does not have an influence on residual stresses. However, in the composite with 40 vol.% zirconia, residual stresses are different in the samples obtained by both processing routes.
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Authors: G. Albertini, Giovanni Bruno, F. Fiori, M. Marcantoni, E. Quadrini, F. Turquier
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Authors: Thilo Pirling, Giovanni Bruno, Philip J. Withers
Abstract: SALSA (Strain Analyser for Large Scale engineering Applications) is a novel instrument for strain imaging at the high flux neutron reactor of the Institut Max von Laue – Paul Langevin (ILL) in Grenoble, France. It is the first of its kind that uses a precise robotic sample stage for sample manipulation. In addition to standard xyz-translation it provides tilts up to ±30° about any horizontal axis. Its load capacity is more than 500 kg and samples up to 1.5 m in length can be scanned with high accuracy. Thanks to a double focusing monochromator and supermirror guide count times are very short. A broad wavelength range, variable beam optics, including radial focusing collimators for high lateral resolution, make it a very flexible instrument for a large variety of strain imaging applications in small and large specimens. The instrument has been commissioned in 2005 and is open for access by a peer review proposal system and as well by industry. The paper describes the important aspects of the instrument and results from the first experiments.
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Authors: Elena Dilonardo, Maria M. Giangregorio, Maria Losurdo, Pio Capezzuto, Giovanni Bruno, Antonio Cardone, Carmela Martinelli, Gianluca M. Farinola, Francesco Babudri, Francesco Naso
Abstract: There has been growing interest in developing new semiconducting polymers for applications in optoelectronics (OLEDs) due to their exceptional processability and appealing characteristic of manipulating electronic and optical properties by tuning of molecular structure and self-assembling. This study is an investigation on the interplay among supermolecular organization and optical properties of thin films of the poly[2-(2-ethylhexyloxy)-5-methoxy]-1, 4-phenylenedifluorovinylene (MEH-PPDFV) conjugated polymer, which has fluorinated vinylene units. This interplay is elucidated exploiting atomic force microscopy, spectroscopy ellipsometry, photoluminescence and electroluminescence. Thin films of MEH-PPDFV have been deposited by drop casting on indium-tin-oxide (ITO), quartz and glass substrates. The dependence of polymer chains self-organization and morphology on substrate surface is presented. Furthermore, it is demonstrated that the presence of F-atoms in the vinylene units of the MEH-PPDFV yields a blue optical band gap with the maximum of the fundamental HOMO-LUMO transition at 331 nm and photoluminescence at 458 nm. The OLED built with the above polymer shows a very stable blue-greenish electroluminescence that is also achieved at 504 nm.
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