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Visualization of domain boundaries in Gd2(MoO4)3 single crystals by scanning electron microscope potential contrast
Ultramicroscopy 6 (1981) 6 7 - 7 0 North-Holland Publishing Company
SHORT NOTE VISUALIZATION OF DOMAIN BOUNDARIES IN Gd2(MoO4)3 SINGLE CRYSTALS BY SCANNING ELECTRON MICROSCOPE POTENTIAL CONTRAST K.-P. MEYER and H. BLUMTRITT Institute o f Solid State Physics and Electron Microscopy, Academy of Sciences of the GDR, Halle, GDR
and L. SZCZE~NIAK Institute of Molecular Physics, Polish Academy of Sciences, Poznah, Poland Received 6 October 1980
The domain structure of ferroelectric-ferroelastic Gd2(MoO4)3 (GMO) was first revealed by polarization microscopy [ 1]. Later on also X-ray topography [2], chemical etching [3-5], transmission electron microscopy [6] and decoration by chemical reactions [7] have been applied.
•
f
/
~
In the present note the application of a scanning electron microscope (SEM) for direct visualization of domain boundaries on the surfaces of non-etched GMO crystals is described. The method was first reported by Le Bihan and Sella [8] for domain structure study of BaTiO3. SEM observations of dielectric
i
),
/2Imm
Fig. 1. Comparison of topographic and electric SEM contrast of a domain structure in GMO. The horizontal lines indicate domain boundaries: (a) etched (001) surface, carbon coated; backscattered electrons, Vaee = 25 kV; (b) untreated counter surface; secondary electrons, Vaec = 5 kV.
0304-3991/81/0000-0000/$ 02.50 © North-Holland Publishing Company
68
K..P. Meyer et al. / Domain boundaries in Gd2(Mo04) 3 crystals
specimens normally require a coating of the surface by a conducting layer in order to avoid charging of the specimen due to the electron beam. Le Bihan and Sella, however, showed that by the use of the secondary electron emission mode at low accelerating voltages (Vacc)uncoated dielectric surfaces can be observed without strong charging effects. At accelerating voltages of a few kV an equilibrium of the electron currents impinging on the surface and leaving it can be obtained, and the specimeri does not charge up. The equilibrium voltage V0 depends on the substance and on some other parameters (e.g. angle of incidence and scanning speed). In the ideal case with Vacc = Vo a contrast between antiparallel domains arises due to the difference of surface charge depending on the orientation of spontaneous polarization. If Vacc is slightly different from 1Io the surface is charged due to the electron beam, and only the domain boundaries are visible, namely as bright lines for Vacc < Iio and as dark lines for Vacc > V0. (For a detailed explanation of these effects see [9]). For our experiments GMO single crystals were cleaved perpendicularly to the polar axis. First, two
corresponding (001) faces ("matched faces") were investigated. One of them was chemically etched, carbon-coated and studied in the SEM (fig. la). (In this case the reflective mode was applied.) Parallel domain boundaries and curved antiphase boundaries are to be seen. The SEM image of the non-etched and uncoated counter face was taken in the secondary electron emission mode (fig. lb). The dark lines can be identified as the same domain boundaries visible in fig. 1a. Because the antiphase boundaries separate regions of equal surface charge they do not appear. In fig. 2,part of an untreated surface observed at accelerating voltages of 2.5 and 6 kV, respectively, is shown. The contrast reversal of the four domain boundaries indicates that the equilibrium voltage Vo has a value between 2.5 and 6 kV. (Further experiments showed that Vo ~ 3 kV.) The topographic contrast of high surface steps (bright lines on figs. 2a and 2b intersecting the domain boundaries and marked by arrows) is not changed with variation of Face- This fact supports the conclusion that the observed contrast of domain boundaries is primarily due to the electrical relief of the crystal surface.
f 't
Fig. 2. SEM potential contrast images of an untreated GMO (001) surface; secondary emission mode. The arrows indicate high surface steps: (a) Vacc = 2.5 kV; (b) Vacc = 6 kV.
K.-P. Meyer et al. /Domain boundaries in Gd2fMo04) 3 crystals
69
Conclusion
References
The results show that the method of SEM potential contrast is useful to reveal the domain structure of GMO without any pretreatment of its surface. Thus it can be applied for the study of the dynamic behaviour of the domain structure on the surface of GMO bulk material.
[ 1] H.J. Borchasdt and P.E. Bierstedt, Appl. Phys. Letters 8 (1966) 50. [2] S. Suzuki and M. Takagi, Acta Cryst. A 28 (1972) S183. [31 J. Bohm and H.-D. KiJrsten, Kristall Tech. 6 (1971) 213. [4] J.R. Barkley and W. Jeitschko, J. Appl. Phys. 44 (1973) 938. [5] V.A. Meleshina et al., KristaUografiya 18 (1973) 1218. [6] N. Yamamoto, K. Yagi and G. Honjo, Phil. Mag. 30 (1974) 1161. [7] A. Bhalla and L.E. Cross, J. Mater. Sci. 12 (1977) 2346. [8] R. Le Bihan and C. Sella, J. Phys. Soc. Japan 28 Suppl. (1970) 377. [9] R. Le Bihan and M. Maussion, J. Physique (Paris) 33 (1972) C2-215.
Acknowledgement The authors wish to thank Dr. B. Hilczer (Poznafi) for helpful advice.
SHORT NOTE VISUALIZATION OF DOMAIN BOUNDARIES IN Gd2(MoO4)3 SINGLE CRYSTALS BY SCANNING ELECTRON MICROSCOPE POTENTIAL CONTRAST K.-P. MEYER and H. BLUMTRITT Institute o f Solid State Physics and Electron Microscopy, Academy of Sciences of the GDR, Halle, GDR
and L. SZCZE~NIAK Institute of Molecular Physics, Polish Academy of Sciences, Poznah, Poland Received 6 October 1980
The domain structure of ferroelectric-ferroelastic Gd2(MoO4)3 (GMO) was first revealed by polarization microscopy [ 1]. Later on also X-ray topography [2], chemical etching [3-5], transmission electron microscopy [6] and decoration by chemical reactions [7] have been applied.
•
f
/
~
In the present note the application of a scanning electron microscope (SEM) for direct visualization of domain boundaries on the surfaces of non-etched GMO crystals is described. The method was first reported by Le Bihan and Sella [8] for domain structure study of BaTiO3. SEM observations of dielectric
i
),
/2Imm
Fig. 1. Comparison of topographic and electric SEM contrast of a domain structure in GMO. The horizontal lines indicate domain boundaries: (a) etched (001) surface, carbon coated; backscattered electrons, Vaee = 25 kV; (b) untreated counter surface; secondary electrons, Vaec = 5 kV.
0304-3991/81/0000-0000/$ 02.50 © North-Holland Publishing Company
68
K..P. Meyer et al. / Domain boundaries in Gd2(Mo04) 3 crystals
specimens normally require a coating of the surface by a conducting layer in order to avoid charging of the specimen due to the electron beam. Le Bihan and Sella, however, showed that by the use of the secondary electron emission mode at low accelerating voltages (Vacc)uncoated dielectric surfaces can be observed without strong charging effects. At accelerating voltages of a few kV an equilibrium of the electron currents impinging on the surface and leaving it can be obtained, and the specimeri does not charge up. The equilibrium voltage V0 depends on the substance and on some other parameters (e.g. angle of incidence and scanning speed). In the ideal case with Vacc = Vo a contrast between antiparallel domains arises due to the difference of surface charge depending on the orientation of spontaneous polarization. If Vacc is slightly different from 1Io the surface is charged due to the electron beam, and only the domain boundaries are visible, namely as bright lines for Vacc < Iio and as dark lines for Vacc > V0. (For a detailed explanation of these effects see [9]). For our experiments GMO single crystals were cleaved perpendicularly to the polar axis. First, two
corresponding (001) faces ("matched faces") were investigated. One of them was chemically etched, carbon-coated and studied in the SEM (fig. la). (In this case the reflective mode was applied.) Parallel domain boundaries and curved antiphase boundaries are to be seen. The SEM image of the non-etched and uncoated counter face was taken in the secondary electron emission mode (fig. lb). The dark lines can be identified as the same domain boundaries visible in fig. 1a. Because the antiphase boundaries separate regions of equal surface charge they do not appear. In fig. 2,part of an untreated surface observed at accelerating voltages of 2.5 and 6 kV, respectively, is shown. The contrast reversal of the four domain boundaries indicates that the equilibrium voltage Vo has a value between 2.5 and 6 kV. (Further experiments showed that Vo ~ 3 kV.) The topographic contrast of high surface steps (bright lines on figs. 2a and 2b intersecting the domain boundaries and marked by arrows) is not changed with variation of Face- This fact supports the conclusion that the observed contrast of domain boundaries is primarily due to the electrical relief of the crystal surface.
f 't
Fig. 2. SEM potential contrast images of an untreated GMO (001) surface; secondary emission mode. The arrows indicate high surface steps: (a) Vacc = 2.5 kV; (b) Vacc = 6 kV.
K.-P. Meyer et al. /Domain boundaries in Gd2fMo04) 3 crystals
69
Conclusion
References
The results show that the method of SEM potential contrast is useful to reveal the domain structure of GMO without any pretreatment of its surface. Thus it can be applied for the study of the dynamic behaviour of the domain structure on the surface of GMO bulk material.
[ 1] H.J. Borchasdt and P.E. Bierstedt, Appl. Phys. Letters 8 (1966) 50. [2] S. Suzuki and M. Takagi, Acta Cryst. A 28 (1972) S183. [31 J. Bohm and H.-D. KiJrsten, Kristall Tech. 6 (1971) 213. [4] J.R. Barkley and W. Jeitschko, J. Appl. Phys. 44 (1973) 938. [5] V.A. Meleshina et al., KristaUografiya 18 (1973) 1218. [6] N. Yamamoto, K. Yagi and G. Honjo, Phil. Mag. 30 (1974) 1161. [7] A. Bhalla and L.E. Cross, J. Mater. Sci. 12 (1977) 2346. [8] R. Le Bihan and C. Sella, J. Phys. Soc. Japan 28 Suppl. (1970) 377. [9] R. Le Bihan and M. Maussion, J. Physique (Paris) 33 (1972) C2-215.
Acknowledgement The authors wish to thank Dr. B. Hilczer (Poznafi) for helpful advice.