TY - JOUR
T1 - Study of graded Ni-Ti shape memory alloy film growth on Si(100) substrate
AU - Martins, Rui M. S.
AU - Schell, Norbert
AU - Mücklich, Arndt
AU - Reuther, Helfried
AU - Beckers, Manfred
AU - Silva, Rui J. C.
AU - Pereira, Luís M. N.
AU - Braz Fernandes, Francisco Manuel
PY - 2008/5
Y1 - 2008/5
N2 - In-situ X-ray diffraction (XRD) was employed to study the effect of the deliberate change of the Ti/Ni ratio during the deposition of Ni-Ti films. Thus, graded films were deposited exhibiting distinctive composition and crystalline structure along the growth direction. The as-sputtered films were ex-situ characterized by Auger electron spectroscopy (AES), cross-sectional transmission electron microscopy (XTEM), and electrical resistivity (ER) measurements (during thermal cycling). In this paper results are presented concerning a film (thickness of ≈∈420 nm) with a Ti-rich composition in the central part (ranging from 50 to ≈60 at.∈%) and near-equiatomic composition in the extremities, following four distinct deposition periods (different Ti target powers). During the initial deposition step (near-equiatomic composition) the Ni-Ti B2 phase starts by stacking onto (h00) planes on the naturally oxidized Si(100) substrate due to the presence of the native Si oxide (2-3 nm). The increase of the power of the Ti target in the second and third steps induced the precipitation of Ti2Ni. When stopping the Ti co-sputtering, Ti 2Ni dissolves and, thus, plays the role of a Ti reservoir for the formation of B2 phase now preferentially stacking onto (110) with the system approaching again the equiatomic composition. The ex-situ study of the morphology of the interface has shown the presence of NiSi2 silicides (A-NiSi2 and B-NiSi2), Ti4Ni 4Si7, Ti2Ni and a non-identified phase constituted by Ni, Ti and Si, most likely amorphous. During thermal cycling, ER measurements revealed phase transitions associated with the B2, R-phase and B19' phases. These type of studies allow the identification of intermediate states during deposition and annealing, and the correlation with the final structure of the film, being useful for the optimisation of the deposition parameters in order to fabricate films with a two-way reversible actuation.
AB - In-situ X-ray diffraction (XRD) was employed to study the effect of the deliberate change of the Ti/Ni ratio during the deposition of Ni-Ti films. Thus, graded films were deposited exhibiting distinctive composition and crystalline structure along the growth direction. The as-sputtered films were ex-situ characterized by Auger electron spectroscopy (AES), cross-sectional transmission electron microscopy (XTEM), and electrical resistivity (ER) measurements (during thermal cycling). In this paper results are presented concerning a film (thickness of ≈∈420 nm) with a Ti-rich composition in the central part (ranging from 50 to ≈60 at.∈%) and near-equiatomic composition in the extremities, following four distinct deposition periods (different Ti target powers). During the initial deposition step (near-equiatomic composition) the Ni-Ti B2 phase starts by stacking onto (h00) planes on the naturally oxidized Si(100) substrate due to the presence of the native Si oxide (2-3 nm). The increase of the power of the Ti target in the second and third steps induced the precipitation of Ti2Ni. When stopping the Ti co-sputtering, Ti 2Ni dissolves and, thus, plays the role of a Ti reservoir for the formation of B2 phase now preferentially stacking onto (110) with the system approaching again the equiatomic composition. The ex-situ study of the morphology of the interface has shown the presence of NiSi2 silicides (A-NiSi2 and B-NiSi2), Ti4Ni 4Si7, Ti2Ni and a non-identified phase constituted by Ni, Ti and Si, most likely amorphous. During thermal cycling, ER measurements revealed phase transitions associated with the B2, R-phase and B19' phases. These type of studies allow the identification of intermediate states during deposition and annealing, and the correlation with the final structure of the film, being useful for the optimisation of the deposition parameters in order to fabricate films with a two-way reversible actuation.
KW - SILICON
KW - R-PHASE TRANSFORMATION
KW - X-RAY-DIFFRACTION
KW - IN-SITU
KW - THIN-FILMS
KW - SPUTTER-DEPOSITION
KW - STRESS
KW - INTERMEDIATE LAYER
KW - MEMS APPLICATIONS
KW - SYNCHROTRON-RADIATION
KW - Electrical Resistivity
KW - Auger Electron Spectroscopy
KW - European Synchrotron Radiation Facil
KW - Ternary Silicide
KW - XTEM Micrograph
UR - http://www.scopus.com/inward/record.url?scp=40949085553&partnerID=8YFLogxK
U2 - 10.1007/s00339-008-4397-2
DO - 10.1007/s00339-008-4397-2
M3 - Article
SN - 0947-8396
VL - 91
SP - 291
EP - 299
JO - Applied Physics A: Materials Science & Processing
JF - Applied Physics A: Materials Science & Processing
IS - 2
ER -