Atomic-scale dynamic process of deformation-induced stacking fault tetrahedra in gold nanocrystals

Abstract

Stacking fault tetrahedra, the three-dimensional crystalline defects bounded by stacking faults and stair-rod dislocations, are often observed in quenched or irradiated face-centred cubic metals and alloys. All of the stacking fault tetrahedra experimentally observed to date are believed to originate from vacancies. Here we report, in contrast to the classical vacancyoriginated ones, a new kind of stacking fault tetrahedra formed via the interaction and crossslip of partial dislocations in gold nanocrystals. The complete atomic-scale processes of nucleation, migration and annihilation of the dislocation-originated stacking fault tetrahedra are revealed by in situ high-resolution observations and molecular dynamics simulations. The dislocation-originated stacking fault tetrahedra can undergo migration and annihilation due to mechanical loading in a manner that is not expected in bulk samples. These results uncover a unique deformation mechanism via dislocation interaction inside the confined volume of nanocrystals and have important implications regarding the size effect on the mechanical behaviour of small-volume materials.

Stacking fault tetrahedra in metals

“…Importantly, it was explicitly concluded that vacancies were not involved, and for many years this has been the accepted view for tetrahedra formed in deformed metals. This conclusion is contrary to many statements made in the paper by Wang et al [5]. For example, among other assertions they state:…”

“…Figure 2, which is Figure 2(g) from Wang et al's paper [5], is reproduced below, where the stacking faults on b, c and d were observed to be formed by partial dislocations gliding in from the surface of the nanocrystal.…”

“…2. Diagram, taken from Wang et al [5], showing dislocations of b = bC, dB and cD on the faulted {1 1 1} planes. The notation defining the Burgers vectors of dislocations is that of Thompson [6].…”

Electronically decoupled stacking fault tetrahedra embedded in Au(111) films

“…These defects can occur more frequently in crystalline films that are grown on substrates with different lattice. SFs are typically considered to be undesired defects that lower the film structural properties and therefore much effort is done to avoid their formation12. However, they also show intriguing electronic properties34 that may be exploited if they can be created in a controlled manner.…”

Grain boundary orientation effects on deformation of Ta bicrystal nanopillars under high strain-rate compression

“…Figure 3(a) presents a formation progression of normal bcc structure-SF-twin, in terms of stacking sequences along the close-packed direction [111]: a SF involves only one faulted plane of stacking, 62 while twins involve two or more faulted planes, where the crystal lattice symmetry is broken and the lattice becomes a mirror image of itself. 63 (Stable SFs are observed to nucleate from the GB with h ¼ 0 ; however, twins are observed in grain interiors for all grain orientations, as well as all GBs except for h ¼ 0…”