Σ3 Twin Research Articles

The Influence of Grain Boundary Inclination on the Structure and Energy of Σ3 Twin Boundaries in Copper

ABSTRACTIn a combined theoretical and experimental study, the energies and structures of Σ3 [011] twin boundaries in Cu were investigated. The atomic structures and the grain boundary energies were calculated using the Embedded Atom Method (EAM). Grain boundary energies of welded Cu bicrystals of the same boundary orientations were also obtained by the thermal grooving technique. The atomic structure of the symmetric {211} incoherent twin boundary (SITB) was investigated by High Resolution Transmission Electron Microscopy (HRTEM). Calculated grain boundary energies γb plotted against the inclination angle Φ of the boundary plane relative to the {111} coherent twin boundary (CTB) plane show a mininmm for the CTB (Φ = 0°) and a second minimum at Φ = 82°. This dependence on the inclination is also confirmed by the measured energies. Common to all calculated boundary structures is a microface 11 ing into CTB and SITB segments with a symmetric orientation of the adjacent crystals. Additionally, strong relaxations occur for the grain boundaries near the second energy minimum. This relaxation can be interpreted as a sequence of stacking faults located almost perpendicular to the mean boundary plane. They are terminated by partial dislocations which form a small angle boundary. The most apparent feature of these structures is a bending of the {111} planes running across the boundary. The structural properties were confirmed by HRTEM.

On dislocation reactions in F.C.C. Σ3 twin boundaries

Two prototypes of dislocation reactions in Σ3 twin boundaries in aluminium are discussed in terms of dualistic models: (i) reactions among “similar” glissile dislocations and (ii) reactions involving “dissimilar” sessile dislocations. Whereas the former introduce free lines and flexible networks, the latter lead to rigid lines, loops and ledges. It is demonstrated that the reactions can be handled by means of the dualistic modelling method, and it is concluded that, owing to (i) and (ii), twin boundaries are obstacles to moving crystal dislocations and are unlikely to be overcome by simple direct penetration.

Crystal Growth Study of Silicon and Germanium Wafers Used for Photovoltaic Devices

AbstractTo develop the EPR material quality, electrical and structural charact erizations were executed by EBIC, LBIC, TEM, ECP and X diffraction. Two interface types were observed; some interfaces parallel and constitued by Σ3 and Σ9 twins, show low electrical activity; other are curved with no defined index and higher electrical activity. Some orientations such as (111),(220),(331) appear more frequently.

Characterization of polycrystalline germanium by EBIC

Abstract The electron-beam-induced-current (EBIC) mode of a scanning electron microscope has been used to characterize the electrical activity of the grain boundaries in germanium. The boundaries have also been characterized from a structural point of view using electron channelling patterns (ECP) and X-ray topography. The low-angle boundaries in Ge polycrystals show an EBIC contrast C which increases when the beam energy increases, while the Σ3 twins do not show a significant activity even when there is a deviation from the coincidence orientation. The collection efficiency η of Schottky contacts has been measured. Both C and η measurements cannot be quantitatively analysed using previously existing models. The basic ideas which should lead to a better modelling are discussed.

The use of moiré techniques to measure rigid body displacements

SummaryThe relative advantages and disadvantages of a variety of experimental electron microscopical techniques for the measurement of rigid body displacements are considered. The principles of the application of a moiré method of great simplicity and high potential accuracy are then further discussed as are the experimental difficulties associated with the superposition of suitable reference latices on a substrate. The method is then applied to obtain an upper limit for the rigid body displacement at {111} Σ3 twin boundaries in stainless steel.