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 The EDS system of the transmission electron microscope (electron dispersive X-ray spectroscopy technique) was used in order to identify the elements present in the different reaction layers. Figure 3.68 shows the results obtained using the line scan mode along a distance of 430 nm, probing information from the substrate, interface and Ni-Ti film. With this complementary information provided by the EDS measurement it was possible to conclude that the lighter grey layer located between the Ni-Ti B2 structure and the Si oxide native layer has in its composition not only Ni and Ti but also Si (see zone C in Fig. 3.68). This confirmed the diffusion of Si into the alloy and has suggested the presence of ternary silicides. An expected increase of the Ni content in the interface substrate’s side (zone B) was discernible mainly as a result of the formation of NiSi 2 compounds (detected in Fig. 3.67). Nr counts 300 250 200 150 100 O K Si K Ti K Ni K 50 0 0 20 40 60 80 100 120 140 160 180 200 220 240 260 Channel number A B C D 256 channels = 430 nm Fig. 3.68: EDS results obtained using the line scan mode of the transmission electron microscope along a distance of 430 nm, probing information from the substrate, interface and the Ni-Ti graded film. In Fig. 3.69 the interfacial reaction products of the graded film are not all visible because the focus was in the area on the left hand side of the lighter grey layer (film’s region). A dashed line was inserted on top of the thin Si oxide layer as a reference. The goal has been the detection of possible Ti 2 Ni phase. Stemmer et al. [129] mention the formation of a Ti-rich layer with no significant amount of Si that was associated with the Ti 2 Ni compound. This layer adjacent to the Ni-Ti near equiatomic film could be the result of the migration of the Ni Chapter 3 – Results 159
In-situ XRD studies during growth of Ni-Ti SMA films and their complementary ex-situ characterization atoms, which are the main species diffusing to the Si substrate below 600ºC [130]. In the present study, in some areas along the interface, lattice spacings agreeing well with those of Ti 2 Ni were observed between the Ni-Ti film and the lighter grey layer (ternary compound: Ti, Ni, Si). The (111) planes of Ti 2 Ni could be identified by cross-section HR-TEM. They make an angle of ≈ 54.74° with the interface (Fig. 3.69). This observation suggests that the (400) planes are approximately parallel to the interface. A white line on the figure indicates the expected arrangement of the (400) planes. Si(100) 54.74° Ti 2 Ni(400) oxide Fig. 3.69: X-TEM micrograph of the interfacial zone of the Ni-Ti graded film with a black line inserted on top of the thin Si oxide layer as a reference. Lattice spacings agreeing well with those of Ti 2 Ni were observed suggesting that the (111) planes of Ti 2 Ni make with the interface an angle that leads the (400) planes approximately parallel to the interface. As it was mentioned earlier, there are two possible NiSi 2 families (A-precipitates and B-precipitates). In this sample, the formation of B-NiSi 2 precipitates in the Si substrate was also detected (Fig. 3.70). Chapter 3 – Results 160
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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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