Papers by Author: Eduardo Alves

Abstract: Due to their interesting properties copper-based materials have been considered appropriate heat-sinks for first wall panels in nuclear fusion devices. The concept of property tailoring involved in the design of metal matrix composites has led to several attempts to use nanodiamond (nDiamond) as reinforcement. In particular, nDiamond produced by detonation has been used to reinforce copper. In the present study, powder mixtures of copper and nDiamond with 20 at. % C were mechanically alloyed (MA) and consolidated via hot extrusion or spark plasma sintering (SPS). The hardness evolutions as well as the structural characterization of as-milled nanocomposite powders and consolidated samples are reported. Density measurements indicate that the consolidation outcome varies significantly with the process used. Transmission electron microscopy (TEM) inspection of the extrusion consolidated sample revealed bonding at the interface between copper and nDiamond particles. The nDiamond size distribution was determined from TEM observations. The results obtained are discussed in terms of consolidation routes.

Abstract: Transparent conducting Al doped ZnO films have been deposited by dc magnetron sputtering on glass and polymer substrates at room temperature. Depositions have been carried out from an AZOY (contains a small amount of Y2O3 in addition to Al2O3 and ZnO) target under different conditions such as working pressure, substrate bias voltage and oxygen flow rate. The crystallinity of the Al doped ZnO films has been improved by using low-energy-ion bombardment. Likewise, the use of either the rotation or the static mode of the substrate during deposition influences the crystallinity and therefore the optical parameters and the electrical resistance of the films. Increasing the thickness of the films reduces the threshold strain at which the films can be deformed without provoking significant changes on their electrical properties.

Abstract: In this work we studied the structural properties of SiGe alloys with different Ge molar compositions co-implanted with manganese and arsenic ions. The ions were implanted at room temperature to fluences of 1×1015, 5×1015 and 1×1016 cm–2 and energies of 170 keV (Mn) and 200 keV (As) in order to achieve the overlap of the implanted profiles. The alloys were studied with Rutherford Backscattering/Channeling spectrometry (RBS/C) and X-ray Diffraction (XRD) techniques. After implantation the implanted region (150 nm) turns into amorphous according with RBS/C. The evolution of the lattice parameter was studied using XRD. The annealing at 550°C induces the recrystallization of the amorphous layer for the sample implanted with the lower fluence and the full recovery is complete after annealing at 700°C. The samples implanted with higher fluences did not reveal any noticeable recovery. The Mn and As profiles do not exhibit significant changes during the annealing at 550oC.

Abstract: The Hotbird is a state of the art X-ray laboratory for advanced materials characterisation, installed at ITN since 1999. Several major improvements in its capabilities have been implemented. On the one hand, new hardware developments have extended the applications that can be studied and on the other hand, new software has enabled both enhanced automated control of the system, and improved data analysis that leads to extraction of further precise information from the data. One improvement was the implementation of the x-ray reflectometry (XRR) technique, which is a major expansion of the Hotbird capabilities. XRR is well-suited to characterise film thickness and roughness with high resolution. Furthermore, several optics improvements, such as a Göbel mirror and monochromators were introduced. The combination of this optics allows one to use either a higher intensity beam (orders of magnitude better) or a higher resolution beam configuration. A new high-temperature chamber was developed, which allows one to perform in-situ experiments with excellent temperature control up to 800 °C, in all possible configurations. Data simulation/fitting analysis software for XRR was developed. Also, to control the diffractometer and perform experiments, a new user-friendly software package was developed. In order to illustrate the Hotbird capabilities improvements, several experimental examples will be described.

Abstract: Quaternary GaInAsSb films alloys were grown by MOVPE technique on GaSb substrates with different growth conditions such as substrate orientation and thickness. The composition of the films determines their bandgap, and also how well they are lattice matched to the substrate. It is thus essential to determine it accurately, which is not a trivial task in this system. The composition of the samples was studied with a combination of Particle Induced Xray Emission (PIXE) and Rutherford Backscattering Spectrometry (RBS) experiments. The RBS experiments were done with a 2 MeV 4He+ or H+ ion beam, according to the thickness of the films, and were used to determine the thickness of the samples. The PIXE experiments were performed at grazing angle conditions and provided accurate elemental composition information. It was found that for thin layers (300 nm) there is a dependence of In incorporation into the matrix according to the substrate orientation, although this tendency was not found for thicker films (24m).

Abstract: Monolayer (ML) thick Ge deposition on (100) Si substrates by molecular beam epitaxy (MBE) technique using an ultrathin SiO2 interlayer has been studied by ion beam analysis and photoluminescence (PL). The dependence of the Ge layer growth mode on the amount of the deposited Ge and the SiO2 thickness has been investigated. Atomic hydrogen treatment has been performed in order to passivate non-radiative recombination channels and to enhance the PL intensity. We conclude the formation of Ge quantum dots for the sample with the thickest Ge and SiO2 layers (9 Å and 1 ML, respectively).

Abstract: Erbium doped nanocrystalline silicon thin films were produced by reactive magnetron r.f. sputtering. Their structural and chemical properties were studied by micro-Raman, spectroscopic ellipsometry and Rutherford backscattering spectroscopy. Films with different crystalline fraction and crystallite size were deposited by changing the deposition parameters. The impact of the composition and structure of Erbium ions environment on the 1.5 µm photoluminescence is discussed.

Abstract: High temperature phase transformations in EUROFER reduced activation ferritic martensitic (RAFM) steel were studied in-situ by means of X-ray diffraction. Results show that, during slow cooling, the austenite to ferrite transformation takes place around 755 oC. Full transformation of the austenitic phase into pure martensite is observed for cooling above 5 oC/min. This transformation was found in samples annealed at 950 oC for 3 h and quenched in liquid nitrogen. TEM analyses reveal a high concentration of carbides along the grain boundaries of the martensitic structure. The thermal expansion coefficient derived from the measurements was 12.7x10-6 K-1.

Abstract: Ga0.81In0.19As0.14Sb0.86 layers were grown on (100)-Te doped GaSb substrates 2º missoriented towards (110), (111)A and (111)B directions by metalorganic vapour deposition (MOVPE) at 540 °C. X-ray reciprocal space maps done in symmetric (224) and asymmetric (115) directions show a super-lattice structure due to the phase separation with a 5 nm period and independent of substrate orientation. The x-ray maps show different stage of relaxation of the films and in same cases an interdiffusion region near the substrate. Despite of the phase separation, channelling experiments with H ions as projectiles showed a good quality of the films. Channelling experiments show that the crystalline quality gets worse with increasing the In and As concentration.

Abstract: Optical and structural properties of single crystalline α-Al2O3 were changed by the implantation of high fluences of Ni ions. Sapphire single crystals with <0001> orientation were implanted at room temperature with 150 keV nickel ions. Implantation fluences were in the range 0.3×1015 to 1.8×1017 cm-2. After implantation the optical absorption spectra reveal the presence of a band peaking in the region 300 - 500 nm, depending on the retained fluence. This is usually related to the presence of metallic particles. X-ray diffraction (XRD) studies show the presence of metallic Ni after implantation. Annealing in oxidizing atmosphere promotes the ecrystallization of the host matrix along with the formation of NiAl2O4 as deduced from Rutherford Backscattering Spectrometry (RBS) and confirmed through XRD. In vacuum the particles formed are metallic like with some Ni spinel also present. The control of the implantation fluence, temperature and annealing atmosphere allows tailoring the component phases.