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 (a) (b) Fig. 3.7: X-TEM micrographs of the Ni-Ti film grown on naturally oxidized Si(100) without V b ; (a) two types of interfacial reaction products are perceptible in the image (A-NiSi 2 and B-NiSi 2 ), (b) X-TEM micrographs focusing the presence of the B-NiSi 2 in the Si(100) substrate. The main micrograph in Fig. 3.8 shows that A-NiSi 2 silicides grow epitaxially towards the Si substrate with growth fronts {111} resulting in a semi-octahedron shape. A deeper insight into the circled area can be found in the inset of the figure. In the substrate Si oxide layer, it is possible to distinguish the presence of disruptions. The Ti 4 Ni 4 Si 7 compound (identified by cross-section HR-TEM) nucleated between the oxide layer and the A-NiSi 2 . It can be expected that at higher temperatures the tendency would be to grow into the A-NiSi 2 and the Si substrate (as observed by Wu et al. [130]). Between the Ni-Ti film and the oxide layer [the (Si, O)-rich layer, i.e. the native silicon oxide of the Si substrate], another layer can be distinguished (lighter grey in the micrograph). It was possible to conclude, by electron dispersive X-ray spectroscopy (EDX) performed in a sample with analogous interface morphology (3.5.1.2. Ex-situ characterization), that this layer contains not only Ni and Ti but also Si (identified as Ti, Ni, Si in Fig. 3.8). However, the structural analysis by cross-section HR-TEM did not detect the presence of crystalline order. Chapter 3 – Results 107
In-situ XRD studies during growth of Ni-Ti SMA films and their complementary ex-situ characterization Fig. 3.8: X-TEM micrographs of the interface’s morphology obtained on a sample grown on naturally oxidized Si(100) without V b . The main micrograph shows that A-NiSi 2 grows epitaxially towards the Si substrate with growth fronts {111} resulting in a semi-octahedron shape. The inset represents the circled region in HR-TEM. (a) (b) Fig. 3.9: X-TEM micrographs of a sample obtained on naturally oxidized Si(111) substrate (without V b ); (a) overview of the Ni-Ti/Si(111) region, (b) HR-TEM enlargement of the interfacial diffusion zone. Chapter 3 – Results 108
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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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