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32 │방사광과학과기술│
밝은빛 제언
I. WHITE RADIATION TOPOGRAPHY
AT 9D XNMM BEAMLINE
The advantage of the 9D beamline,
fundamentally important to x-ray
topography, is a small angular
divergence of the primary SR beam
w=S/D, where S is the vertical source
size and D the source to sample
distance. Since S and D are equal to
29 μm and 23 m respectively, w=0.16
arcsec. Generally there is gain
in intensity with increased brilliance
if D is reduced. The limit on
reduction of D is the beam height
at the sample, usually about 10 mm.
At the 9D beamline the size of the
beam on the sample is large enough:
100(H) × 10(V) mm2. When D remains
constant, there is gain in the spatial
resolution R in a topograph: R=dS/
D where d is the sample to film (or
detector) distance.
Due to the small source size the
resolution is weakly dependent on
the film to sample distance. For
example, with the above listed
setup parameters the resolution
R=0.13 μm can be achieved for
d=10 cm. It deteriorates to 1μm
at the distance d=1 m.
A. Recording the topograph
In polychromatic radiation many
diffracted beams are observed in a
pattern. They are registered with
large area CCD detector attached
to a motorized arm. The arm can
be moved in both azimuthal and
altitude directions. In the Bragg
geometry the detector plane can
be installed perpendicular to a dif
fracted beam. However in the Laue
geometry this installation is preven
ted by limited rotations of the arm.
High-resolution topographs are
obtained using film. The film cassette
is fixed on the surface of the detector
by tape.
It is desirable to design a casset
te holder, which enables setting the
film perpendicular to the selected
diffracted beam with high precision.
Certain types of films (as, e.g.,
M100) have an emulsion layer on both
sides. This reduces an exposure
time but imposes a requirement
of placing the film strictly
perpendicular to the diffracted
beam. When the diffracted beam
passes through the film at the right
angle, the two images recorded by
the both emulsion layers will coincide
giving sharp topographs. Otherwise,
the topographs will appear blurred.
The holder should also provide
variation of the sample to film distance
for separation reflections.
In addition, the cassette holder
must have another important property.
Up to now, the possibility to mount the
film in the back-reflection mode1,2
has been overlooked and this
deficiency should be corrected.
B. Setting up the crystal
Where the crystal has not
crystallographically oriented edges,
the crystallographic orientation
has to be determined. When the
orientation is known the diffraction
pattern can be solved. Then the
desired set of reflections or a single
reflection can be recorded with the
highest possible resolution. Currently
the goniometer at 9D has limited
rotations about all axes. Under
such conditions, proper design of
Synchrotron radiation topography using poly- and monochromatic x-rays
Tatiana S. Argunova (POSTECH & Ioffe Institute, St. Petersburg, Russia)
VOL.22/NO.2/Summer 2015
33
밝은빛 제언
the sample holder plays an impor-
tant role. When the crystal is small,
it is useful to mount it inside a
suitable metal ring, which is fixed
to the holder. If the holder enables
to rotate the mount manually about the
sample surface normal, one can do
it between the orientation runs
allowed by the goniometer. So one
can avoid repeatable dismounting
crystals.
Since x-ray topographic techniques
are sensitive to strain, rigid mounting
will lead to difficulties. Tapes and
glues which contract on setting
should be avoided. Having at their
disposal 1-2 kinds of mounting
materials which contract very little
on setting would be convenient for
users.
II. MONOCHROMATIC RADIATION
TOPOGRAPHY AT 6C BMI
At 6C BMI beamline the source
with the vertical size S=29μm at the
distance D=35 m provides a very
bright beam with the small angular
divergence: w=0.17 arcsec and long
transverse coherence length, e.g.,
Lt=75 μm for E=20 keV. The wavelength
dispersion is small and has an order
of magnitude ∆λ/(λ= 10-4 - 10-5
when Si crystal-monochromator is
used. By use of Ru/C multilayer
mirror it can be increased up to 3
× 10-3.
The topography technique in
the 6C is in the making. From
the beginning it is important to
design the equipment for doing
experiments in two diffraction
geometries - in the Bragg and
Laue ones. To achieve this goal it
is necessary to mount the sample in
side a ring and fix it to the holder
which enables 360。rotation about
the sample surface normal. Then
one can change the geometry by
rotating the mount around the Bragg
axis.
Rather than fasten a film casset
te to a detector by a tape, a cassette
holder must be constructed. This
requirement is strongly supported
by the fact that the film must always
be set in the same position with
respect to the scattering plane. Only
then one can be sure of the direction
of diffraction vector, which determines
contrast features in a topograph.
III. CONCLUSION
High intensities and good
collimations available in 9D and
6C beamlines are very suit- able
for topography. However some of the
shortcomings should be addressed.
After their elimination the x-ray to
pography techniques at 9D and 6C
will work better for different purposes,
e.g., for dynamic and survey experim
ents, for obtaining information inacce
ssible to laboratory methods and for re
search into new techniques.
―저 자 약 력
Tatiana S. Argunova POSTECH & Ioffe Institute, St. Petersburg,
Russia; Electronic
I have been using Synchrotron Radiation (SR) topography
techniques in 9D and 6C beamlines of PAL in 2014-15. In
the middle 1990s I also used synchrotron facilities in ESRF.
In general, I am a PAL user since 1999. On the basis of
my experience I would like to share some comments on
x-ray topography facilities available at 9D and 6C
참고문헌
[1] Noonan D, McNally P J, Chen W-M, Lankinen A, Knuuttila L, Tuomi T O, Danilewsky A N and Simon R Microelectr J 37 (2006) 13721378.[2] Oriwol D, Carl E-R, Danilewsky A N, Sylla L, Seifert W, Kittler M, Leipner H S Acta Mater. 61 (2013) 69036910.