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Etching characteristics of screw and edge dislocations on the cleavage plane of BiSb single crystals
Surface Technology, 21 (1984) 379 - 381
379
ETCHING CHARACTERISTICS OF SCREW AND EDGE DISLOCATIONS ON THE CLEAVAGE PLANE OF Bi-Sb SINGLE CRYSTALS
R. C. SHAH, C. F. DESAI, G. R. PANDYA and V. P. BHATT Physics Department, Faculty of Science, Maharaja Sayajirao University of Baroda, Baroda, 390002 (India) (Received August 15, 1983)
Summary The chemical etchant used in the present study is capable of revealing screw and edge dislocations which both intersect and lie in the cleavage plane of Bi-Sb single crystals. It was shown that the etch pattern produced by the m o t i o n of dislocations allows edge and screw dislocations to be distinguished between.
1. Introduction The chemical etching technique is widely used to delineate dislocations which intersect the crystal surface. With a suitable etchant it is also possible to reveal other defects such as impurities, vacancies and dislocations in the plane of observation. Moreover, edge and screw dislocations which intersect the surface can be distinguished by the use of a sequential etching method. However, this m e t h o d is not very suitable for metallic crystals because of the high density and very small size of the etch pits (compared with the pits on non-metallic crystals). In this paper we report the use of an etchant to distinguish between screw and edge dislocations, which both lie and are inclined to the surface, by studying the geometry o f the etch pattern and motion of the dislocation pits.
2. Experimental details Single crystals o f Bi-Sb (1 - 20 at.% Sb) were grown by the horizontalzone-melting m e t h o d [1]. After the two components had been mixed, the ingot was zone levelled by several zone-melting passes in alternate directions. The final pass was used to obtain the single crystal. The Bi-Sb crystal has a (111) cleavage plane. For the etching tests, freshly cleaved slices were used. 0376-4583/84/$3.00
© Elsevier Sequoia/Printed in The Netherlands
380 The specimen was etched for a few seconds in the etchant (described in Section 3), cleaned in running water, rinsed in acetone and finally air dried. The etch pattern was studied using a Vickers projection microscope.
3. Results and discussion The dislocation etchant used for the present study consists of 7 parts of tartaric acid (saturated aqueous solution), 4 parts of HNO3 (70% AnalaR grade) and 2 parts of H20 [1]. The use of the etching technique to study dislocation motion is well known. In the present study the active slip system is {111)(1:~0). The { l l f ) , ( 1 i l ) and ( f l l ) slip planes intersect the (111) observation plane along the [ 1 i 0 ] , [ i 0 1 ] and [011] directions, which are also the slip directions. The etch pits formed by the above etchant have three sides parallel to these directions. A dislocation motion would hence be revealed by the shift of an etch pit along one of its sides. Figure 1 is a photomicrograph of an etched trace produced by the dislocation m o t i o n along the ( l l g J direction and not along the usual {1i0) direction. Such a motion is possible only for a screw dislocation since the m o t i o n of an edge dislocation would always produce the trace along the (1i0) direction as it cannot move out of the {11i~ slip plane. Thus the edge and screw dislocations could be distinguished by the nature of the motion of the etch pits. Since the screw dislocation can move in any direction provided that it remains parallel to its initial orientation, it is possible to observe its motion in directions other than the (112~ direction. A typical example is illustrated in Fig. 2, where the initial and final positions of the dislocation are revealed by fiat-bottomed and point-bottomed etch pits. The m o t i o n of dislocation in this case is along the (213) direction. Apart from the screw and edge dislocations inclined to the (111) cleavage plane, the etchant is also capable of revealing dislocations which lie in the
Fig. 1. Etch pit motion along the [112] direction. (Magnification, 356x.) Fig. 2. Etch pit motion along the [213] direction. (Magnification, 765x.)
381 cleavage plane by producing etch grooves. Figure 3 shows etch grooves observed on the cleavage plane together with some isolated etch pits. Most of these etch grooves are nearly parallel to the {119.) direction, implying that these grooves are due to edge dislocations since the [11~.] direction is perpendicular to the [ 1 i 0 ] slip direction. Similarly, the etch grooves parallel to the slip direction reveal screw dislocations lying in the surface (Fig. 4).
Fig. 3. Etch grooves along the [11~.] direction. (Magnification, 765x.) Fig. 4. Etch grooves parallel to the [ 110 ] slip direction. (Magnification, 231X.) Thus, using this etchant it is possible to distinguish between screw and edge dislocations. It is worthwhile to mention that, in Bi-Sb crystals, a large number of etch grooves are produced by this etchant on the (111) plane, indicating a tendency of the dislocations to be oriented parallel to the (111) plane. Moreover, the screw dislocations in the present study are also highly mobile compared with the edge dislocations.
Reference 1 v.P. Bhatt and G. R. Pandya, J. Phys. C, 6 (1973) 36.
379
ETCHING CHARACTERISTICS OF SCREW AND EDGE DISLOCATIONS ON THE CLEAVAGE PLANE OF Bi-Sb SINGLE CRYSTALS
R. C. SHAH, C. F. DESAI, G. R. PANDYA and V. P. BHATT Physics Department, Faculty of Science, Maharaja Sayajirao University of Baroda, Baroda, 390002 (India) (Received August 15, 1983)
Summary The chemical etchant used in the present study is capable of revealing screw and edge dislocations which both intersect and lie in the cleavage plane of Bi-Sb single crystals. It was shown that the etch pattern produced by the m o t i o n of dislocations allows edge and screw dislocations to be distinguished between.
1. Introduction The chemical etching technique is widely used to delineate dislocations which intersect the crystal surface. With a suitable etchant it is also possible to reveal other defects such as impurities, vacancies and dislocations in the plane of observation. Moreover, edge and screw dislocations which intersect the surface can be distinguished by the use of a sequential etching method. However, this m e t h o d is not very suitable for metallic crystals because of the high density and very small size of the etch pits (compared with the pits on non-metallic crystals). In this paper we report the use of an etchant to distinguish between screw and edge dislocations, which both lie and are inclined to the surface, by studying the geometry o f the etch pattern and motion of the dislocation pits.
2. Experimental details Single crystals o f Bi-Sb (1 - 20 at.% Sb) were grown by the horizontalzone-melting m e t h o d [1]. After the two components had been mixed, the ingot was zone levelled by several zone-melting passes in alternate directions. The final pass was used to obtain the single crystal. The Bi-Sb crystal has a (111) cleavage plane. For the etching tests, freshly cleaved slices were used. 0376-4583/84/$3.00
© Elsevier Sequoia/Printed in The Netherlands
380 The specimen was etched for a few seconds in the etchant (described in Section 3), cleaned in running water, rinsed in acetone and finally air dried. The etch pattern was studied using a Vickers projection microscope.
3. Results and discussion The dislocation etchant used for the present study consists of 7 parts of tartaric acid (saturated aqueous solution), 4 parts of HNO3 (70% AnalaR grade) and 2 parts of H20 [1]. The use of the etching technique to study dislocation motion is well known. In the present study the active slip system is {111)(1:~0). The { l l f ) , ( 1 i l ) and ( f l l ) slip planes intersect the (111) observation plane along the [ 1 i 0 ] , [ i 0 1 ] and [011] directions, which are also the slip directions. The etch pits formed by the above etchant have three sides parallel to these directions. A dislocation motion would hence be revealed by the shift of an etch pit along one of its sides. Figure 1 is a photomicrograph of an etched trace produced by the dislocation m o t i o n along the ( l l g J direction and not along the usual {1i0) direction. Such a motion is possible only for a screw dislocation since the m o t i o n of an edge dislocation would always produce the trace along the (1i0) direction as it cannot move out of the {11i~ slip plane. Thus the edge and screw dislocations could be distinguished by the nature of the motion of the etch pits. Since the screw dislocation can move in any direction provided that it remains parallel to its initial orientation, it is possible to observe its motion in directions other than the (112~ direction. A typical example is illustrated in Fig. 2, where the initial and final positions of the dislocation are revealed by fiat-bottomed and point-bottomed etch pits. The m o t i o n of dislocation in this case is along the (213) direction. Apart from the screw and edge dislocations inclined to the (111) cleavage plane, the etchant is also capable of revealing dislocations which lie in the
Fig. 1. Etch pit motion along the [112] direction. (Magnification, 356x.) Fig. 2. Etch pit motion along the [213] direction. (Magnification, 765x.)
381 cleavage plane by producing etch grooves. Figure 3 shows etch grooves observed on the cleavage plane together with some isolated etch pits. Most of these etch grooves are nearly parallel to the {119.) direction, implying that these grooves are due to edge dislocations since the [11~.] direction is perpendicular to the [ 1 i 0 ] slip direction. Similarly, the etch grooves parallel to the slip direction reveal screw dislocations lying in the surface (Fig. 4).
Fig. 3. Etch grooves along the [11~.] direction. (Magnification, 765x.) Fig. 4. Etch grooves parallel to the [ 110 ] slip direction. (Magnification, 231X.) Thus, using this etchant it is possible to distinguish between screw and edge dislocations. It is worthwhile to mention that, in Bi-Sb crystals, a large number of etch grooves are produced by this etchant on the (111) plane, indicating a tendency of the dislocations to be oriented parallel to the (111) plane. Moreover, the screw dislocations in the present study are also highly mobile compared with the edge dislocations.
Reference 1 v.P. Bhatt and G. R. Pandya, J. Phys. C, 6 (1973) 36.