Observations of silicon carbide by high resolution transmission electron microscopy

Abstract

High resolution transmission electron microscopy techniques, principally involving direct lattice imaging, have been used as part of a study of the crystallography and phase transformation mechanics of silicon carbide polytypes. In particular, the 3C (cubic) and 6H (hexagonal) polytypes have been examined together with partially transformed structural mixtures. Although direct observation of two-dimensional atomic structures was not possible at an operating voltage of 100 kV, considerable microstructural information has been obtained by careful choice of the experimental conditions. In particular, tilted beam observations of the 0.25 nm lattice fringes have been made in the 3C polytype for two different { 11 1 } plane arrays in order to study the dimensions and coherency of finely-twinned regions together with (0006) and {10T2} lattice images in the 6H polytype which allow the detailed stacking operations to be resolved. Lower resolution lattice images formed with axial illumination have also been used to study the nature of the 3C-+6H transformation and results are presented showing that the transformation interface may originate with fine twinning of the 3C structure followed by growth of the resultant 6H regions. Observations have been made of the detailed stepped structure of this interface together with the stacking fault distribution in the resultant 6H material. The images obtained suggest that tilted beam techniques will be useful for studying the one-dimensional disorder in other S i c polytypes and related ceramic materials. Some of the possible advantages of future observations with high voltage, high resolution instruments are considered. '

The direct identification of stacking sequences in silicon carbide polytypes by high-resolution electron microscopy

“…The materials used in these studies were prepared as described previously (Sawyer & Page, 1978;Smith, Jepps & Page, 1978). Observations were made with a JEM-120CX and a high-resolution goniometer holder.…”

“…Observations were made with a JEM-120CX and a high-resolution goniometer holder. The resolution required for obtaining two-dimensional * The structure of any polytype may be represented by a modified form of the ABC notation (used for close-packed structures), a dash being added to differentiate between tetrahedral sheets in the same spatial position but rotated by ~r (Smith, Jepps & Page, 1978).…”

“…Our recent observations with high-resolution lattice imaging at the 2.5 A level with tilted-beam illumination (Smith, Jepps & Page, 1978) established that essentially one-dimensional information about individual stacking sequences was directly obtainable. The technique has since been applied to observations of a variety of silicon carbide polytypes and it has been possible to identify directly the detailed stacking sequence in longer-period polytypes, and around the vicinity of stacking faults, without recourse to any confirmatory calculations based on postulated trial structures.…”

Pulse laser processing of a SiC/Al-alloy metal matrix composite

“…The TEM microstructural search of the as-received MMC sample revealed the existence of predominantly a-SiC particles (Fig. 18 The fundamental structural unit in all the polytypes is a coordination tetrahedron (either SiC 4 or CSi 4 ). 7).…”

A transmission electron microscopy investigation of SiC films grown on SiC substrates by solid-source molecular beam epitaxy

“…2,3 The polytypes of SiC have been intensively studied and their defect microstructures have been wellcharacterized by means of transmission electron microscopy (TEM). Perfect SiC is generally difficult to grow at low temperatures because of its low stacking fault energy, 16 resulting in formation of a high density of stacking faults each bounded by two partial dislocations within this material. However, use of the large 0.9-eV band-gap difference between the cubic (3C) and hexagonal (4H) SiC polytypes can be fully realized only if layers are grown defect-free in a controlled fashion at lower temperatures because such a regime would be required for modulation doping of future device structures.…”