Papers by Author: Manuel J.P. Maneira

Abstract: Ni-Ti thin films where the R-phase transformation occurs between 55°C and 30°C, the peak temperature being 40°C, have been produced. These thin films have been grown using a magnetron assisted system of dc sputtering, with a Glow-Discharge Optical Emission Spectroscopy device. The OES technique has been used to investigate the spatial distribution of sputtered atoms from the cathode to the substrate in different operating conditions: Argon pressure of 5 and 9x10 – 4 Torr, without polarization and with – 60 V bias. Structural characterization of the thin films has been made by XRD and the transformation temperatures associated to the shape memory effect have been determined by DSC. A discussion of the optimization of the processing parameters (Argon pressure and polarization) is then presented.

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.