PhD Thesis_RuiMSMartins.pdf - RUN UNL

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In-situ XRD studies during growth of Ni-Ti SMA films and their complementary ex-situ characterization 110 200 Fig. 3.25: Pole figures of Ni-Ti B2 phase grown on thermally oxidized Si(100) substrate at ≈ 470°C, nominally measured in the Bragg peaks B2(110) and B2(200). The grey arrow indicates the direction of the vapour flux coming from the magnetron with the Ni- Ti target. In order to observe the corresponding reflexions with more detail, sections at ϕ = 0° and ϕ = 90° from the pole figure measured in the Bragg peak B2(110) are shown in Fig. 3.26. ϕ = 0° ϕ = 90° χ _____ → Fig. 3.26: Sections at ϕ = 0° and ϕ = 90° from the measured austenite pole figure of the 110 diffraction plane of the previous figure. Chapter 3 – Results 121
In-situ XRD studies during growth of Ni-Ti SMA films and their complementary ex-situ characterization The results, when compared with schematic theoretical pole figures derived from the stereographic projection of the B2 phase using the CARINE 3.1 software (calculated for 100 and 310 planes, parallel to the film surface) [161], confirm what has been described above. There are different grains with (h00) and (310) planes parallel to the substrate surface. In this section it has been shown that for the Ni-Ti film deposited on thermally oxidized Si(100) substrates, without applying V b , there is a strong preferential stacking on (h00) planes of B2 phase leading to a fibre texture. Nevertheless, after ≈ 540 nm film thickness, a stabilization of the intensity of the B2(200) diffraction peak was observed. This was the result of a gradual change of the growing direction of the columnar crystals; in the present experiments, this inclination favoured the diffraction (in Bragg–Brentano geometry) of the B2(310) peak. This trend was confirmed by ex-situ pole figures measurements and X- TEM observations. The results obtained in situ for the Ni-Ti sample deposited on thermally oxidized Si(100), have shown a considerable reduction of the net area of the B2(110) and B2(200) Bragg-Brentano diffraction peaks, when going from V b = 0 to V b = −45 V. Ex-situ XRD experiments in off-plane Bragg-Brentano geometry detected the presence of the B2(310) diffraction peak, which could not be detected in-situ due to the chamber windows size limitation of the set-up used for the deposition of this sample. The inclination of the columnar crystals favoured the diffraction (in Bragg-Brentano geometry) of the (310) peak of the B2 phase and the stabilization of the intensity of the B2(200) peak, which was observed in-situ during the deposition process. Although this behaviour has also been observed for the Ni-Ti deposition without V b , it is much more pronounced when a V b (−45V) is applied during Ni-Ti film growth. The growth of Ni-Ti at a temperature of ≈ 520°C has shown that, increasing the deposition temperature, the intensity of the B2(200) diffraction peak increased along the deposition process and, therefore, a stabilization of the peak intensity was not observed as it has been for the depositions at ≈ 470°C (without and with a V b of −45V). Ex-situ AES and TEM studies performed on samples obtained without and with V b revealed that the thermally grown SiO 2 layer acts as a diffusion barrier. However, the XRD and X-TEM results suggest the presence of TiO 2 at the interface Ni-Ti/SiO 2 . Chapter 3 – Results 122
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RUI MIGUEL DOS SANTOS MARTINS IN-SI
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ACKNOWLEDGEMENTS The research work
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At CENIMAT, Luís Pereira also carr
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SUMÁRIO O fabrico de películas fi
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LIST OF SYMBOLS AND ABREVIATIONS α
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TABLE OF CONTENTS Introduction ....
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LIST OF FIGURES Fig. 1.1: Power/wei
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Fig. 2.3: Calculated integrated pho
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Fig. 3.25: Pole figures of Ni-Ti B2
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Fig. 3.66: SAED pattern obtained on
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LIST OF TABLES Tab. 1.1: Factors af
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In-situ XRD studies during growth o
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