Imaging dislocation cores – the way forward

Abstract

Although the sub-angstrom resolution of the modern transmission electron microscope (TEM) has made major contributions to defect structure analysis in many fields (such as oxides, interfaces, nanoparticles and superconductors) it has yielded little direct information on the core structure of dislocations. We suggest that ''forbidden reflection'' lattice images recorded in an ultra-high vacuum TEM in projections normal to the dislocation line could provide interpretable images of cores at atomic resolution. These could answer crucial questions, such as the nature of kinks, core reconstruction and periodicity, the nature of obstacles, and help distinguish obstacle theories of kink motion from the secondary Peierls-valley Hirth-Lothe theory. We give experimental forbidden reflection images and a new image obtained from silicon under UHV conditions with atomically smooth surfaces, whose preparation did not anneal out all dislocations. We also show experimental coherent nanodiffraction patterns and scanning transmission electron microscope (STEM) images recorded with the beam parallel to the core, so that core reconstruction can be expected to introduce a ''half-order'' Laue zone ring. We discuss the contribution that energy-loss spectroscopy from dislocation cores can be expected to make if a nanoprobe beam is used.

Strain fields around dislocation arrays in a Σ9 silicon bicrystal measured by scanning transmission electron microscopy

“…In the current experiment, variations in the diffraction patterns across the grain boundary were observed to ensure the region analyzed did not display significant specimen deformation. Furthermore, information about dislocation core reconstruction is contained in the diffraction pattern [41]. Another advantage of performing GPA in STEM is the possibility to combine strain measurement with the mapping of the chemical composition.…”

The elastic potential energy of a thin foil deformed by an in-plane 60° dislocation

“…This edge-on orientation is, however, not appropriate to reveal kinks along a partial dislocation core because the contrast of a high-resolution TEM image is not sensitive enough to the presence of such a defect. However, a less common technique was proposed to image a partial dislocation at near-atomic scale, able to reveal possible kinks, the so-called ''high-resolution forbidden-reflection electron microscopy (HRFREM)'' technique [5][6][7][8][9]. This technique, which requires preparation of an ultrathin foil with dislocations extended parallel to the free surface of the foil, does not refer to the atom columns.…”

Extended defects generated in the slip plane by moving dislocation in diamond lattice crystals: morphology and properties

“…Indeed it is questionable whether dislocation movement is controlled by obstacles (such as foreign atom) decorating the core, or obstacles of unknown nature [3]. Furthermore, despite the development of modern sub-angstrom resolution transmission electron microscopy techniques very little is known about actual dislocation core structure in elemental semiconductors [4][5][6]. Enormous information about dislocation core structure and electrical and optical properties has been accumulated by indirect methods such as EPR, Hall effect, EBIC, DLTS [1].…”