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

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RBS Analysis of Mass-transport Process in Au/Cu Film
on Sapphire Treated by Centrifugal Forces
H. Naramoto a) , K. Narumi a) , T. Hao a) , M. Ono a) , S. Okayasu a) ,
S. Sakai a) , Y. Hiraiwa b) , Y. Maeda a, b) and M. Sasase c)
a) Advanced Science Research Center, JAEA,
b) Faculty of Engineering, Kyoto University, c) Department of Research and Development, WERC
The controlled mass-transport is commonly important in
materials science, and the various kinds of efforts have been
made to find out the controlling parameters for that purpose.
Recently, the directional mass transport has been reported
under the application of the centrifugal force in the solid
state, assuming the directional diffusion of vacancies 1) .
For the directional transport, it is important to consider the
symmetry-lowering or the gradient field introduction by the
application of external filed 2) , and this becomes more
pronounced in nm system 3) . Mass-transport process is also
strongly influenced by the lattice imperfections, and the
attention should be paid for the possible introduction of the
lattice defects under the external fields.
In the present study, Au/Cu diffusion couple films were
prepared on -Al 2O 3(0001) substrate with the vacuum
deposition method. The centrifugal force application was
made at 0.61 × 10 6 G (denoted as MG hereafter following
“million-level gravity”) along the direction of the film
pressing to the substrate (+MG) and also along its reverse
(-MG) at 220 C. For a comparison, the same kinds of
samples were treated with the same thermal conditions.
The mass-transport process is quantitatively analyzed with
2.7 MeV 4 He + ion Rutherford Backscattering Spectrometry
(RBS) system at TIARA, and possible microstructure
changes associated with thermal annealing and/or
centrifugal force application are characterized with a
Scanning Transmission Electron Microscope (STEM) at
WERC.
Figure 1 illustrates the results of RBS analysis for the
growth of Cu layer on the surface as a function of
treatment-periods for thermal annealing and also for
centrifugal force application of MG. Even after thermal
Thickness (nm)
60
40
20
0
0
Annealing
+MG
-MG
100 200
Time (min.)
Fig. 1 The thickness changes of the transported Cu
layer on the Au surface as a function of time for the
annealed samples and the samples treated with +MG
and -MG at 220 C.
JAEA-Review 2010-065
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annealing with the same conditions as MG application,
considerable amounts of mass-transport of Cu atoms into the
surface through Au layer is observed. The similar
phenomena was also observed in thin Au/Cu films with the
high epitaxial nature (not shown for the simplicity), but any
evidence of Cu atom localization was not confirmed within
the Au layer in this case. This difference contains the
important suggestion for surface diffusion along cylindrical
4)
microstructures within epitaxial films . It is also
distinguished that the MG application enhances the
mass-transport of Cu atoms into the surface through Au
layer, and the enhancement seems to be expected to be
intensified under the –MG application.
In order to
confirm the
possible
introduction of the
lattice defects
under the
centrifugal force
application, the
microstructure
analysis was made
with STEM.
Figure 2 illustrates
70 nm
0.5 µm µm µm
the typical STEM image of the cross-sectional area in
Au/Cu film after the relevant treatment. In this case, the top
Cu layer thickness amounts to 70 nm. The RBS analysis
contains some ambiguity of possible opening of Au layer so
as to expose the Cu layer directly to the analyzing He + ion
beam, but the present STEM image evidences the Cu atom
transport through Au layer. The growth rate of the Cu
layer on the surface under the application of the +MG and
-MG is higher than that of the thermal annealing. The
different growth rate of the Cu layer under the application of
+MG/-MG suggests the influences of lattice imperfections
on the mass-transport process. The X-Ray Diffraction
(XRD) analysis confirms the non-alloying even under the
employed treatments. In the STEM micrograph, one can
recognize the microstructural changes typically found in
deformed metals, and it is inevitable to consider the
influence of lattice imperfections as a next step.
References
1) T. Mashimo et al., Phil. Mag. Lett. 83 (2003) 687.
2) M. J. Aziz et al., Phys. Rev. B73 (2006) 054101.
3) G. Dehm, Prog. in Mater. Science 54 (2009) 664.
4) A. V. Chechkin et al., Phys. Rev. E 79 (2009) 040105(R).
Cu
Au
Cu
0.5 m
Fig. 2 STEM image of cross-sectional
area in Au/Cu film after treated with
+MG at 220 C for 310 min.