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Excitation of Kossel patterns by synchrotron radiation
Nuclear Instruments and Methods in Physics Research A 349 (1994) 269-273 North-Holland
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH Section A
Excitation of Kossel patterns by synchrotron radiation HA. Ullrich a, M. Schlaubitz a, F. Friedel a, T. Spann a, J. Bauch a, T. Wroblewski b, S. Garbe `, G. Gaul e, A. Knöchel `,*, F. Lechtenberg e, E. Rossmanith d, G. Kumpat d, G. Ulrich d ° Technische Universität Dresden, Inst. F. Werkstoffwissenschaft, Mommsenstrasse 13, D-01069 Dresden, Germany b HASYLAB at DFSY, Notkestrasse 85, D-22607 Hamburg, Germany ` Inst. f Anorg und Angew. Chemie, Untversadt Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany d Mineralogisch-Petrographssehes Inst., Unwersadt Hamburg, Grindelallee 48, D-20146 Hamburg, Germany
Received 26 July 1993 ; revised form received 24 February 1994
In this article we will report on Kossel experiments by means of synchrotron radiation. To our knowledge this is the first demonstration that Kossel patterns can be observed using fluorescent radiation excited by synchrotron X-rays . Kossel patterns are characterized by the importance of a high degree of information in the determination of the crystal structure, e.g. the orientation matrix, lattice parameter, symmetry elements and the phase of scattering waves into the microstructure of the single crystal under consideration In the first test experiment Cu and GaAs single crystals were investigated .
1 . Introduction The Kossel technique differs from other diffraction techniques in that the interferring radiation does not come from outside the crystal, but has its origin in the fluorescent radiation emitted from atoms of the crystal itself [1]. The X-ray fluorescent radiation from these lattice sources spreads into every direction leaving the crystal to a great extent undiffracted and thus contributes to the background . The far smaller amount is diffracted according to the Bragg equation by the lattice planes with nonzero structure factor . The resulting interferences lie on straight circular cones (Kossel-cones), the half-opening angle being (90 O) and the cone axes coinciding with the normals of the reflecting lattice planes (see Fig. 1) . Therefore, the X-ray film used for detection shows weak interference lines corresponding to cuts through the Kossel-cones on a high intrinsic background . Sharp Kossel lines are obtained if the fluorescence is excited only in a small volume . Excitation of a large volume averages out the lines and reduces the signal to noise ratio. Further background can arise from the radiation generating the fluorescence, which may be electron beams [1], X-rays [2] or proton beams [3-5] . Energy discrimination is neither possible with films nor with most other area detectors; especially the bremsstrahlung produced by an electron beam lowers the contrast . Using characteristic radiation * Corresponding author Tel. +49 40 4123 3982, fax +49 40 4123 2893 .
from X-ray tubes (beam cross-section < 50 win) leads to exposure times of about one day, limiting the sensitivity of the method . Furthermore, we are restricted to a few combinations of elements in the sample and the anode material (like Fe excited by Cu radiation). This restriction does not apply if the intense continuous spectrum of synchrotron radiation is utilized . It should, however, be kept in mind that the spectral flux (photons/bandwidth/time) of synchrotron radiation from a bending magnet is not much higher than that of characteristic radiation from an X-ray tube if the experiment allows the use of a large solid angle . The high collimation of synchrotron radiation is, therefore, a special advantage for Kossel investigations . Intensity can, however, be gained if the energy band pass is increased. The highest number of incoming photons is achieved by using the white spectrum which, however, results in an increase of the background . Whereas both the background arising from the high energy bremsstrahlung produced by the scattering of electrons by the residual gas in the storage ring and the background resulting from radiation scattered along the beam path can be minimized by proper collimation and shielding, this is not possible for the background due to scattering events from the specimen . Even if one profits from the high degree of linear polarization of synchrotron radiation by positioning the film less than an angle at 90 ° to the incoming beam in the plane of the electron beam the background due to the scattering cannot be suppressed completely . Therefore, it would be helpful to reduce the
0168-9002/94/$07 .00 © 1994 - Elsevier Science B.V . All rights reserved SSDI0168-9002(94)00336-6
270
H .-J.
Ullrich et al. /Nucl. Instr. and Meth. in Phys . Res. A 349 (1994) 269-273 X-ray film
synchrotron radiation
capillary
Fig. 3. The set-up of the Kossel experiment using capillary optics . without a monochromator. Two different set-ups were used (see Figs. 3 and 4) .
For the first experiment with a Cu single crystal, a
capillary with an entrance of about 300 [Lm and an exit diameter of about 100 p,m was used to increase the intensity of the primary synchrotron radiation [6]. The corresponding intensity gain is shown in Fig. 2, revealing a maximum gain of 6 at about 12 .5 keV. Going toward lower and higher energies respectively, the gain factor falls rapidly to a very experiment .
good background reduction for this
The distance between the capillary's end and the sample was approximately 10 mm . The angle of divergence
Fig . 1 . The principles of the Kossel technique. number of photons having a low fluorescent yield. As the absorption coefficient decreases with A3 the spectrum
should be limited to energies near twice the energy of the absorption edge . This high energy cut-off can be accomplished by making use of the total reflection of X-rays inside conical
capillaries. Furthermore, this offers the possibility to use focussing optics to increase the flux on the sample . Low energy radiation (below the absorption edge) may be reduced using appropriate filters.
was calculated in the low energy range at 2 mrad leading to an illuminated area on the sample of 120 ltm diameter . The synchrotron beam was directed towards the specimen (see Fig. 3). Thus a high X-ray output density in the specimen point could be obtained .
Higher energies are required for the second experiment
using GaAs samples. The energy limiting capillary was removed and the synchrotron radiation DORIS III at 4 .5 GeV was reduced by means of the collimators to 100 X 100 p.m2 (see Fig. 4) .
Kossel patterns in the reflection and in the transmission
mode have been measured with both set-ups. We used exposure times from 10 s up to 20 min depending on beam
current, experimental set-up and the substance under inves-
2. Experimental set-up
tigation . Orwo(TF10)- and Agfa(C)-X-ray-films have been
The experiment was performed at the electron storage ring DORIS 111 (4 .5 GeV) at HASY-LAB beamline Fl
applied to record the Kossel patterns .
3. Results
capillary 3001o 100pm 7
In these first experiments using synchrotron radiation to observe Kossel patterns the contrast between the Kossel lines and the background is appreciably higher than in the
s
earlier experiments using X-ray tubes.
X-ray film
0
10
15
20
25
30
Encrgy (keV)
Fig. 2. The gain factor of this capillary.
35
40
synchrotron radiation collimator
Fig. 4. The set-up of the Kossel experiment using a collimator .
H.-J. Ullrich et al. /Nucl. Instr. and Meth. in Phys. Res. A 349 (1994) 269-273
271
Fig. 5. The Kossel pattern of Cu generated with synchrotron radiation.
Fig. 5 shows a Kossel pattern in the reflection mode of
Cu in the vicinity of the [100]-pole . In addition to the Laue spots the Kossel lines are clearly visible as a relatively
large section of the reflex system . The small line width of
By the relative position of Kossel-cones and the measurement of their opening angles the lattice parameter a can be determined with a relative accuracy of Da/a <
the Kossel lines, the distinct doublet separation of the
(420)- and (331)-reflexes and the transition from the re-
flection into the extinction lines indicate a high perfection of the Cu single crystal under investigation.
In Fig. 6 the stereographic projection made by computer simulations is shown. By comparing the observed Kossel patterns with the results of these simulations the orientation of the specimen can be determined .
Fig. 7 shows a Kossel pattern in reflection mode of
GaAs in the vicinity of the [321]-pole. The bright-dark
fields are clearly visible. Fig. 8 shows the computer simulation of the corresponding reflex system .
Since the Kossel-cones are firmly related to the crystal
axes the interference pattern shows very clearly the under-
lying crystal symmetry . This fact allows both the determination of the crystal system (phase identification) and the
fast determination of the orientation of the sample under investigation.
Fig. 6. The computer simulation of the Kossel pattern of Cu .
272
H.-J. Ullrich et aL. INucl. Instr. and Meth . in Phys. Res. A 349 (1994) 269-273
Fig. 7. The Kossel pattern of GaAs generated with synchrotron radiation .
10
-4 .
For copper a = 0.36150 (Aa/a = 1.0 X 10 -4 ) nm
and for GaAs a = 0.56538 (Aa/a = 1.0 X 10 -4 ) nm is obtained . The evaluation of the fine structure of the Kossel lines (line width, bright-dark structure) allows statements about the real structure within the diffraction volume .
Stephan et al . [7,8] have shown that by including the absorption of excited and diffracted radiation and by analy-
sis of the tails of Kossel lines the phase angle of the structure factor can be determined .
4. Discussion We have demonstrated that Kossel patterns of very
high quality can be obtained by using synchrotron radia-
tion . This technique has various advantages compared to other excitation methods with electron or proton beam : - relatively simple experimental set-up ;
- measurements can be performed in air; - no special preparation of the sample ; - investigation of microstructures ; - short exposure times;
- coupling to material analysis techniques . In order to ensure a comprehensive evaluation of the Kossel patterns (in addition to the determination of the
orientation of the lattice parameter, of the symmetry deviations and of the scattering phase) the experimental and especially the geometrical set-up and its variability must --
134010 .
be optimized.
Further work should, above all, deal with the optimiza-
tion of the band pass by using appropriate combinations of
capillaries and filters, as well as with the special specimen
materials for which electron beam excitation is impossible or excluded (isolators, polymers, biominerals, etc.) . Acknowledgements Fig. 8. The computer simulation of the Kossel pattern of GaAs.
We gratefully acknowledge the financial support of the "Bundesministerium für Forschung und Technologie" as
H.-J Ullrich et al . I Nucl . Instr. and Meth . to Phys. Res. A 349 (1994) 269-273 well as the" Verband der Chemischen Industrie, Fond der Chemischen Industrie" . For technical support we cordially thank the staff at HASYLAB.
References [1] W. Kossel, V. Loeck and H. Voges, Z. Phys . 94 (1935) 139. [2] G. Bormann, Naturwissenschaft 23 (1935) 677. [3] V. Geist, and R. Flagmeyer, Phys . Status Solidi . A 26 (1974) Kl .
273
[4] J.B . Roberto and M. Battermann, J . Appl . Phys . 46 (1975) 936. [5] HA . Ulrich, Proc. 3rd Working Meeting Microprobe 1975, Berlin, Physical Society of the GDR, p. 93 [6] P. Engstroem, S. Larsson, A. Rindby, A. Buttkewitz, S. Garbe, G. Gaul, A. Kn6chel and F. Lechtenberg, Nucl . Instr. and Meth . A 302 (1991) 547 . [7] D. Stephan, W. Blau, HA . Ullrich and G.E .R . Schulze, Kristall und Technik 9 (1974) H.7, 707. [8] D. Stephan, HA . Ullrich and G.E .R . Schulze, Kristall und Technik 11 (1976) H.5, 475.
NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH Section A
Excitation of Kossel patterns by synchrotron radiation HA. Ullrich a, M. Schlaubitz a, F. Friedel a, T. Spann a, J. Bauch a, T. Wroblewski b, S. Garbe `, G. Gaul e, A. Knöchel `,*, F. Lechtenberg e, E. Rossmanith d, G. Kumpat d, G. Ulrich d ° Technische Universität Dresden, Inst. F. Werkstoffwissenschaft, Mommsenstrasse 13, D-01069 Dresden, Germany b HASYLAB at DFSY, Notkestrasse 85, D-22607 Hamburg, Germany ` Inst. f Anorg und Angew. Chemie, Untversadt Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany d Mineralogisch-Petrographssehes Inst., Unwersadt Hamburg, Grindelallee 48, D-20146 Hamburg, Germany
Received 26 July 1993 ; revised form received 24 February 1994
In this article we will report on Kossel experiments by means of synchrotron radiation. To our knowledge this is the first demonstration that Kossel patterns can be observed using fluorescent radiation excited by synchrotron X-rays . Kossel patterns are characterized by the importance of a high degree of information in the determination of the crystal structure, e.g. the orientation matrix, lattice parameter, symmetry elements and the phase of scattering waves into the microstructure of the single crystal under consideration In the first test experiment Cu and GaAs single crystals were investigated .
1 . Introduction The Kossel technique differs from other diffraction techniques in that the interferring radiation does not come from outside the crystal, but has its origin in the fluorescent radiation emitted from atoms of the crystal itself [1]. The X-ray fluorescent radiation from these lattice sources spreads into every direction leaving the crystal to a great extent undiffracted and thus contributes to the background . The far smaller amount is diffracted according to the Bragg equation by the lattice planes with nonzero structure factor . The resulting interferences lie on straight circular cones (Kossel-cones), the half-opening angle being (90 O) and the cone axes coinciding with the normals of the reflecting lattice planes (see Fig. 1) . Therefore, the X-ray film used for detection shows weak interference lines corresponding to cuts through the Kossel-cones on a high intrinsic background . Sharp Kossel lines are obtained if the fluorescence is excited only in a small volume . Excitation of a large volume averages out the lines and reduces the signal to noise ratio. Further background can arise from the radiation generating the fluorescence, which may be electron beams [1], X-rays [2] or proton beams [3-5] . Energy discrimination is neither possible with films nor with most other area detectors; especially the bremsstrahlung produced by an electron beam lowers the contrast . Using characteristic radiation * Corresponding author Tel. +49 40 4123 3982, fax +49 40 4123 2893 .
from X-ray tubes (beam cross-section < 50 win) leads to exposure times of about one day, limiting the sensitivity of the method . Furthermore, we are restricted to a few combinations of elements in the sample and the anode material (like Fe excited by Cu radiation). This restriction does not apply if the intense continuous spectrum of synchrotron radiation is utilized . It should, however, be kept in mind that the spectral flux (photons/bandwidth/time) of synchrotron radiation from a bending magnet is not much higher than that of characteristic radiation from an X-ray tube if the experiment allows the use of a large solid angle . The high collimation of synchrotron radiation is, therefore, a special advantage for Kossel investigations . Intensity can, however, be gained if the energy band pass is increased. The highest number of incoming photons is achieved by using the white spectrum which, however, results in an increase of the background . Whereas both the background arising from the high energy bremsstrahlung produced by the scattering of electrons by the residual gas in the storage ring and the background resulting from radiation scattered along the beam path can be minimized by proper collimation and shielding, this is not possible for the background due to scattering events from the specimen . Even if one profits from the high degree of linear polarization of synchrotron radiation by positioning the film less than an angle at 90 ° to the incoming beam in the plane of the electron beam the background due to the scattering cannot be suppressed completely . Therefore, it would be helpful to reduce the
0168-9002/94/$07 .00 © 1994 - Elsevier Science B.V . All rights reserved SSDI0168-9002(94)00336-6
270
H .-J.
Ullrich et al. /Nucl. Instr. and Meth. in Phys . Res. A 349 (1994) 269-273 X-ray film
synchrotron radiation
capillary
Fig. 3. The set-up of the Kossel experiment using capillary optics . without a monochromator. Two different set-ups were used (see Figs. 3 and 4) .
For the first experiment with a Cu single crystal, a
capillary with an entrance of about 300 [Lm and an exit diameter of about 100 p,m was used to increase the intensity of the primary synchrotron radiation [6]. The corresponding intensity gain is shown in Fig. 2, revealing a maximum gain of 6 at about 12 .5 keV. Going toward lower and higher energies respectively, the gain factor falls rapidly to a very experiment .
good background reduction for this
The distance between the capillary's end and the sample was approximately 10 mm . The angle of divergence
Fig . 1 . The principles of the Kossel technique. number of photons having a low fluorescent yield. As the absorption coefficient decreases with A3 the spectrum
should be limited to energies near twice the energy of the absorption edge . This high energy cut-off can be accomplished by making use of the total reflection of X-rays inside conical
capillaries. Furthermore, this offers the possibility to use focussing optics to increase the flux on the sample . Low energy radiation (below the absorption edge) may be reduced using appropriate filters.
was calculated in the low energy range at 2 mrad leading to an illuminated area on the sample of 120 ltm diameter . The synchrotron beam was directed towards the specimen (see Fig. 3). Thus a high X-ray output density in the specimen point could be obtained .
Higher energies are required for the second experiment
using GaAs samples. The energy limiting capillary was removed and the synchrotron radiation DORIS III at 4 .5 GeV was reduced by means of the collimators to 100 X 100 p.m2 (see Fig. 4) .
Kossel patterns in the reflection and in the transmission
mode have been measured with both set-ups. We used exposure times from 10 s up to 20 min depending on beam
current, experimental set-up and the substance under inves-
2. Experimental set-up
tigation . Orwo(TF10)- and Agfa(C)-X-ray-films have been
The experiment was performed at the electron storage ring DORIS 111 (4 .5 GeV) at HASY-LAB beamline Fl
applied to record the Kossel patterns .
3. Results
capillary 3001o 100pm 7
In these first experiments using synchrotron radiation to observe Kossel patterns the contrast between the Kossel lines and the background is appreciably higher than in the
s
earlier experiments using X-ray tubes.
X-ray film
0
10
15
20
25
30
Encrgy (keV)
Fig. 2. The gain factor of this capillary.
35
40
synchrotron radiation collimator
Fig. 4. The set-up of the Kossel experiment using a collimator .
H.-J. Ullrich et al. /Nucl. Instr. and Meth. in Phys. Res. A 349 (1994) 269-273
271
Fig. 5. The Kossel pattern of Cu generated with synchrotron radiation.
Fig. 5 shows a Kossel pattern in the reflection mode of
Cu in the vicinity of the [100]-pole . In addition to the Laue spots the Kossel lines are clearly visible as a relatively
large section of the reflex system . The small line width of
By the relative position of Kossel-cones and the measurement of their opening angles the lattice parameter a can be determined with a relative accuracy of Da/a <
the Kossel lines, the distinct doublet separation of the
(420)- and (331)-reflexes and the transition from the re-
flection into the extinction lines indicate a high perfection of the Cu single crystal under investigation.
In Fig. 6 the stereographic projection made by computer simulations is shown. By comparing the observed Kossel patterns with the results of these simulations the orientation of the specimen can be determined .
Fig. 7 shows a Kossel pattern in reflection mode of
GaAs in the vicinity of the [321]-pole. The bright-dark
fields are clearly visible. Fig. 8 shows the computer simulation of the corresponding reflex system .
Since the Kossel-cones are firmly related to the crystal
axes the interference pattern shows very clearly the under-
lying crystal symmetry . This fact allows both the determination of the crystal system (phase identification) and the
fast determination of the orientation of the sample under investigation.
Fig. 6. The computer simulation of the Kossel pattern of Cu .
272
H.-J. Ullrich et aL. INucl. Instr. and Meth . in Phys. Res. A 349 (1994) 269-273
Fig. 7. The Kossel pattern of GaAs generated with synchrotron radiation .
10
-4 .
For copper a = 0.36150 (Aa/a = 1.0 X 10 -4 ) nm
and for GaAs a = 0.56538 (Aa/a = 1.0 X 10 -4 ) nm is obtained . The evaluation of the fine structure of the Kossel lines (line width, bright-dark structure) allows statements about the real structure within the diffraction volume .
Stephan et al . [7,8] have shown that by including the absorption of excited and diffracted radiation and by analy-
sis of the tails of Kossel lines the phase angle of the structure factor can be determined .
4. Discussion We have demonstrated that Kossel patterns of very
high quality can be obtained by using synchrotron radia-
tion . This technique has various advantages compared to other excitation methods with electron or proton beam : - relatively simple experimental set-up ;
- measurements can be performed in air; - no special preparation of the sample ; - investigation of microstructures ; - short exposure times;
- coupling to material analysis techniques . In order to ensure a comprehensive evaluation of the Kossel patterns (in addition to the determination of the
orientation of the lattice parameter, of the symmetry deviations and of the scattering phase) the experimental and especially the geometrical set-up and its variability must --
134010 .
be optimized.
Further work should, above all, deal with the optimiza-
tion of the band pass by using appropriate combinations of
capillaries and filters, as well as with the special specimen
materials for which electron beam excitation is impossible or excluded (isolators, polymers, biominerals, etc.) . Acknowledgements Fig. 8. The computer simulation of the Kossel pattern of GaAs.
We gratefully acknowledge the financial support of the "Bundesministerium für Forschung und Technologie" as
H.-J Ullrich et al . I Nucl . Instr. and Meth . to Phys. Res. A 349 (1994) 269-273 well as the" Verband der Chemischen Industrie, Fond der Chemischen Industrie" . For technical support we cordially thank the staff at HASYLAB.
References [1] W. Kossel, V. Loeck and H. Voges, Z. Phys . 94 (1935) 139. [2] G. Bormann, Naturwissenschaft 23 (1935) 677. [3] V. Geist, and R. Flagmeyer, Phys . Status Solidi . A 26 (1974) Kl .
273
[4] J.B . Roberto and M. Battermann, J . Appl . Phys . 46 (1975) 936. [5] HA . Ulrich, Proc. 3rd Working Meeting Microprobe 1975, Berlin, Physical Society of the GDR, p. 93 [6] P. Engstroem, S. Larsson, A. Rindby, A. Buttkewitz, S. Garbe, G. Gaul, A. Kn6chel and F. Lechtenberg, Nucl . Instr. and Meth . A 302 (1991) 547 . [7] D. Stephan, W. Blau, HA . Ullrich and G.E .R . Schulze, Kristall und Technik 9 (1974) H.7, 707. [8] D. Stephan, HA . Ullrich and G.E .R . Schulze, Kristall und Technik 11 (1976) H.5, 475.