JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

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Behavior of N Atoms in Nitriding Processes of
Evaporated-Ti Thin Films due to Ion Implantation
Y. Kasukabe a), b) , Y. Watanabe b) , Y. Chen b) , S. Yamamoto c) and M. Yoshikawa c)
a) Center for International Exchange, Tohoku University, b) Department of Metallurgy,
Tohoku University, c) Environment and Industrial Materials Research Division, QuBS, JAEA
It has recently been reported that properties of
non-stoichiometric titanium nitrides (TiNy) such as electrical
conduction, diffusion barrier, wear resistance, catalysis, etc.
depend not only on chemical composition, but also on
orientation relationships between TiNy films and substrates.
Therefore, much interest has been focused on studying
atomistic-growth processes of TiNy films 1) . The purpose
of the present paper is to clarify atomistic-growth processes
of TiNy films due to ion implantation by using in-situ
transmission electron microscopy and electron energy-loss
spectroscopy, along with composition analysis and with the
characterization of the electronic structure by molecular
+
orbital calculation. The ions of N2 with 62 keV are
implanted into deposited Ti films in the 400-kV analytic
high-resolution TEM combined with ion accelerators
installed at JAEA-Takasaki 2) .
+
Nitrogen ions (N2 ) with 62 keV were implanted into the
as-deposited Ti film composed of mainly (110)-oriented
TiHx and ( 03
5)
-oriented hcp-Ti at room temperature,
which results in the epitaxial formation of (110)-oriented
and (001)-oriented TiNy, respectively. In order to elucidate
the atomistic nitriding processes of the epitaxial
transformation of Ti thin films due to N implantation in
detail, DV-Xα MO calculations have been performed for
the Ti19 cluster and Ti19N cluster models shown in Fig. 1(a).
The Ti19 cluster of Fig. 1(a), which does not include a
nitrogen atom indicated by an open circle G, corresponds to
a part of the hcp-Ti structure. The central position G
(O-site) of the octahedron with larger space as formed by
A-F atoms in Fig. 1(a), has lower electron density (~1/5,000
of electron density of A-site). Thus, the O-sites have
smaller repulsion for electrons of N atoms, and admit the
invasion of N atoms, which leads to the formation of a Ti19N cluster in Fig. 1(a). The contour map of the wavefunction
of the mainly Ti3d-N2p bonding orbital, which has the energy
eigenvalue of -5.9715 eV below the Fermi level, is shown in
Fig. 1(b). It can be seen from Fig. 1(b) that strong Ti-N
bonds (A-G and F-G bonds) include the π-like bonds of
Ti3dyz and N2pz orbitals, and that the N2pz orbital interacts
with orbitals of Ti atom denoted by J, but hardly with those
of Ti atom denoted by K. It can be considered that the
interaction of the N2pz orbital with Ti atom, J, leads to the
movement of the nitrogen atom, G, to other neighboring
O-site of the octahedron formed by A, C, D, H, I and J
atoms, midway between the A and J atoms. Since in the
transformed fcc-Ti sublattice after the hcp-fcc
transformation, the site, G, in Fig. 1(a) is not O-sites, the N
atom denoted by G has to move into other O-sites in order to
JAEA-Review 2010-065
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form the TiN y. In other words, the movement (diffusion)
of the N atom in the O-site of hcp to other neighboring
O-site of the octahedron which is maintained during the
hcp-fcc transformation of Ti-sublattice plays an important
role in epitaxial growth of TiN y. Thus, the shift of the F
atom to the center of gravity of the triangle BEF promoted
by the forming of the strong A-G and F-G bonds and the
weakening of the C-B and D-E bonds for Ti 19N, the
inheritance of square atomic arrangement formed by C, D, H
and I atoms, and the movement of the N atom in the O-site
of hcp-Ti to other neighboring O-site of the octahedron
(from G, to other neighboring O-site of the octahedron
formed by A, C, D, H, I and J atoms) can be considered to
be the origin for the hcp-fcc transformation of Ti sublattices
and epitaxial growth of TiN y.
References
1) S. Hao et al., Phys. Rev. B 74 (2006) 035424-1.
2) H. Abe et al., JAERI-Research 96-047 (1996)18p.
(a)
(b)
K
FL =
●:Ti ○:N
L
K
A
G
01
0
Fig. 1 (a) Schematic illustration of the Ti19 cluster and
Ti19N cluster with a nitrogen atom, G. (b) The
contour map of the wavefunction of the mainly
Ti3d-N2p bonding orbital, which are drawn for
the { 21
0}
plane including A, L, F and J atoms in (a).
F
J