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 5000 Ar/N 2 = 4/2 0.032 nm/s T S = 300 °C TiN(200) Intensity (arb. units) 4000 3000 2000 1000 TiN(111) 70 min - 135.7 nm 55 min - 106.6 nm 40 min - 77.4 nm 30 min - 58.2 nm 20 min - 39.1 nm 10 min - 20.0 nm 0 15 16 17 18 19 20 Scattering angle 2θ (deg) Fig. 3.56: In-situ XRD spectra of pure TiN film sputtered at low growth rate at 300°C. Ion irradiation at a bias of −30 V leads to (100) preferred orientation in pure TiN. Figure 3.57(a) exhibits the development of the net areas of the TiN(111) and TiN(200) diffraction peaks as a function of time. During the initial stages of growth, primarily and oriented grains nucleated and grew. The results show that grains took over at higher thickness values. 1500 0.430 Net area (arb. units) 1250 1000 750 500 250 111 200 Lattice parameter, a 0 (nm) 0.428 0.426 0.424 0.422 a 111 a "111" a 200 a 200 a theory = 0.424 nm 0 0 20 40 60 80 Time (min.) (a) 0.420 0 20 40 60 80 Time (min.) (b) Fig. 3.57: In-situ XRD results recorded as a function of time after start of TiN film growth on thermally oxidized Si(100); (a) The net areas of the Bragg-Brentano 111 and 200 diffraction peaks of TiN, (b) comparison of in-plane lattice constants (a “111” and a 200 ).and off-plane lattice constants (a 111 and a 200 ). Chapter 3 – Results 149
In-situ XRD studies during growth of Ni-Ti SMA films and their complementary ex-situ characterization For a qualitative evaluation of the internal film stress, the off-plane and in-plane lattice parameters of the growing film were determined from the peak positions in Bragg-Brentano, and grazing exit in-plane large angle scattering (GIXS) geometry with an incident angle of 0.2° (where planes perpendicular to the film surface are probed). Figure 3.57(b) shows the comparison of these lattice parameters as a function of deposition time. The film exhibits inplane a 0 values that are slightly smaller than the off-plane ones. This implies a compressive stress that diminishes the in-plane interplanar distance, while because of the Poisson’s effect the interplanar distance expands out of plane. It further shows that for higher thickness values the compressive stress is generally reduced, suggesting that during the 70 min deposition time the film relaxes into a lower stress state. XRR spectra have been taken after each deposition step and later fitted with the Bede Mercury REFS code [157]. The results are shown in Fig. 3.58. From the fitting an average roughness of 1-2 nm is derived. The film exhibits a density of approximately 91% of the bulk density (TiN = 5.43 g/cm 3 ), thus a porosity less than 9%, which is a typical value for physical vapour deposition TiN films. The fitted average deposition rate was 0.032±0.003 nm/s. 91 % of bulk TiN = 4.94 g/cm³ Energy (keV) 400 600 800 1000 1200 Intensity (arb. units) 40 min, 77.4 nm 30 min, 58.2 nm 20 min, 39.1 nm Experimental Best fit RBS yield (cts.) 2000 1500 1000 500 Experimental Simulated 10 min, 20.0 nm 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Incident angle θ (deg) (a) Fig. 3.58: XRR spectra with respective fits for the TiN film deposited on SiO 2 /Si(100) substrate. 0 200 300 400 500 600 700 Channel (b) Fig. 3.59: RBS analysis of pure TiN deposited on SiO 2 /Si(100) substrate showing data from experiment and simulation. The film composition was measured ex situ by RBS confirming the desired stoichiometry (Fig. 3.59). From previous experiments, the total oxygen content of the films should not change when the growth is stopped at regular intervals although, during the stops, Chapter 3 – Results 150
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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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