Near-atomic images of interfaces between twin-related lamellae in a synthetic 6<Emphasis Type="Italic">H</Emphasis>-SiC sample |
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| Authors: | G Agrosì G C Capitani E Scandale G Tempesta |
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| Institution: | 1.Dipartimento Geomineralogico,Università degli Studi di Bari Aldo Moro,Bari,Italy;2.Dipartimento di Scienze Geologiche e Geotecnologie,Università degli Studi di Milano Bicocca,Milan,Italy |
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| Abstract: | Transmission Electron Microscopy (TEM) and High Resolution TEM (HRTEM) investigations were used to study a complex micro-structure
of twin-related lamellae of 15R SiC polytype, in syntactic coalescence with 6H-SiC. The analysis of the local stacking microstructure by means of HRTEM revealed that the perfect structure of 15R polytype, (23)3 was locally interrupted by numerous adjoining stacking faults parallel to (0001) with stacking of the coupled (22) and (33)
bilayers superimposed on the twin boundaries. HR images taken exactly across both the twin boundaries showed a zig-zag pattern
(23) that switched to (32) by a twin coherent interfaces or, alternatively, a zig-zag pattern (32) which passed to (23) through
an isolated (33), 6H like sequence. The selected area electron diffraction (SAED) patterns taken exactly above both the twin interfaces indicate
classifying of the twin found in this study as a “Friedelian” reticular merohedric twinning. However, two indistinguishable
twin operations matched the observed features: a reflection through rational plane (0001), and 180°-rotation around 0001].
Since individual Si and C atoms and even the SiC bilayer polarity could not be established from these HR images, the real
twin law was deduced by taking into account that the coherent structural match at the interface could be guaranteed only by
a 180°-rotation around 0001]. In order to explain the origin of the planar defects found in this sample, the growth mechanism
and the influence of the low-energy stacking faults were considered. |
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