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

argunova@mail.ioffe.ru

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.