Manuel J.P. Maneira

Correlation between a-Si:H surface oxidation process and the performance of MIS structures

In order to correlate the MIS devices performance with different surface oxidation methods, AFM, spectroscopic ellipsometry and infrared spectroscopy measurements were performed in a-Si:H films, before and after surface oxidation, using different Ž.Ž . Ž oxidation techniques and oxides: thermal dry in air , wet in H O and by oxygen plasma, while MIS metal-insulator-semicon22 . ductor devices were characterised by IV curves, under dark and AM1.5 illumination conditions. The a-Si:H films were grown by the PECVD technique, in a modified triode configuration reactor to allow a precise control of the ion bombardment during the film deposition. We found that the growth of a thin layer of oxide by chemical processes on the top of the a-Si:H surface can cause changes on the surface morphology that are reflected in the electrical behaviour of the devices. The oxygen plasma treatment, cause the rearrangement of the surface atoms leading to a change of their morphology and to the improvement of the electrical properties of the surface for a MIS applications. 2001 Elsevier Science B.V. All rights reserved. Ž.

In-Situ GIXRD Characterization of the Crystallization of Ni-Ti Sputtered Thin Films

Abstract. The Ni-Ti system is the most popular of the SMA’s because of its large recovery force, a transformation temperature near room temperature and a good oxidation resistance. Although the transformation frequency is low (mainly limited by thermal inertia), a thin film of Ni-Ti coupled with silicon for heat dissipation can produce cycling frequencies much larger than the typical macrosize structures. The thin films can be electrically driven using joule heating, and they demonstrate fast cooling rates because of their large surface-to-volume ratio. The control of film composition and properties has proven difficult in sputter-deposited films, and a deeper study of deposition techniques is needed. Furthermore, the as-deposited films show an amorphous structure and thus have to be heat treated to induce crystallization in order to have the shape memory effect. In the present study, thin films have been prepared by dc and rf magnetron sputtering. The crystallization of these films has been studied by in-situ grazing incidence X-Ray diffraction (GIXRD), allowing us to establish a correlation between the deposition conditions and the tendency for crystallization.

Characterization of Nickel Implanted α-Al2O3

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.

Optical Emission Spectroscopy Study of Magnetron Assisted Ni-Ti DC Sputtering

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.