PhD Thesis_RuiMSMartins.pdf - RUN UNL

In-situ XRD studies during growth of Ni-Ti SMA films and their complementary ex-situ characterization
intensity is observed implying that the Ni-Ti film surface becomes fast rougher for such
depositions conditions (the Ni-Ti film was also deposited without applying V b ).
10000
Normalized intensity (cps)
8000
6000
4000
2000
Ni-Ti/MgO(100)
Ni-Ti/MgO(111)
0
0 30 60 90 120 150 180 210 240 270 300
Sputter time (s)
Fig. 3.43: Time-dependent in-situ specular X-ray reflectivity for the first minutes of deposition
of the Ni-Ti films on MgO(100) and MgO(111) substrates (the arrow indicates the moment
when the shutter was closed again).
The in-situ XRD measurements have shown a preferential stacking of (100) planes of
the B2 phase parallel to the substrate surface for the Ni-Ti film deposited on MgO(100)
substrate. The preferential orientation of B2(100) // MgO(100) was very strong and was
maintained as such until the end of the deposition, which lasted for 2 h (≈ 900 nm), as shown
in Fig. 3.44. However, additionally two diffraction peaks located near the B2(200) diffraction
peak were detected suggesting the presence of interfacial reaction products. The peak at
2θ ≈ 25.98° (position at the end of the deposition) reveals the presence of TiO 2 . A clear
identification of the diffraction peak located at 2θ ≈ 24.65° could not be achieved (i.e., Ni 3 Ti
or Ni 3 Ti 2 phase). The peak has then been identified as Ni-rich phase.
In the case of the Ni-Ti film grown on MgO(111) substrate, the in-situ XRD
measurements have shown a preferential stacking of (110) planes of the B2 phase parallel to
the film surface (Fig. 3.45) but, due to the fast increase of the intensity of the diffraction peaks
of the interfacial reaction products (Ni-rich phase and TiO 2 ), it was decided to stop the
deposition 60 min earlier (i.e., with only 69 min deposition time).
Chapter 3 – Results 140