Deformation-Induced Phase Transformations in Gold Nanoribbons with the 4H Phase

Abstract

The mechanical stability of metallic nanomaterials has been intensively studied due to their unique structures and promising applications. Although extensive investigations have been carried out on the deformation behaviors of metallic nanomaterials, the atomic-scale deformation mechanism of metallic nanomaterials with unconventional hexagonal structures remains unclear because of the lack of direct experimental observation. Here, we conduct an atomic-resolution in situ tensile-straining transmission electron microscopy investigation on the deformation mechanism of gold nanoribbons with the 4H (hexagonal) phase. Our results reveal that plastic deformation in the 4H gold nanoribbons comprises three stages, in which both full and partial dislocations are involved. At the early deformation stage, plastic deformation is governed by full dislocation activities. Partial dislocations are subsequently activated in regions that have undergone full dislocation gliding, leading to phase transformation from the 4H phase to the face-centered cubic (FCC) phase. At the last stage of the deformation process, the volume fraction of the FCC phase increases, and full dislocation activities in the FCC regions also play an important role.

Two-Dimensional Metal Nanostructures: From Theoretical Understanding to Experiment

“…88 Surface stress may also trigger the transformation from hcp to fcc phases during the plastic deformation process. 254 These phenomena in phase transformation 255 were also observed for metals with morphologies other than 2D nanostructures 256,257 or in the bulk form. 258 Silver may form thick and triangular 2D nanostructures because of the formation of twin defects.…”

“…, Ag) can induce a transformation from hcp to fcc crystalline phases . Surface stress may also trigger the transformation from hcp to fcc phases during the plastic deformation process . These phenomena in phase transformation were also observed for metals with morphologies other than 2D nanostructures , or in the bulk form …”

Structural Transformation of Unconventional-Phase Materials

“…19,63 In a recent study, together with Han, Liao, and other co-workers, we investigated the phase transformation behavior of Au nanoribbons with unconventional 4H phase under external mechanical stress. 26 After the deformation of a 4H-Au nanoribbon induced by tensile strain (Figure 2e,f), a 4H-to-fcc phase transformation was observed in the fracture tip, along with the formation of twin boundaries (Figure 2g). Song et al demonstrated a reversible 2H−1T′ phase transformation of MoTe 2 via tensile strain generated from an atomic force microscope (AFM) tip.…”

“…Specifically, the identification of the structural evolution of unconventional-phase materials would lead to deep fundamental understanding of their structural stabilities and transformation mechanisms, providing important guidance to the stabilization strategy of unconventional phases and the exploration of their future applications. 1,19,20 Taking Au as an example, the transformation mechanisms from the unconventional 4H phase to the thermodynamically stable face-centered cubic (fcc) phase in Au nanostructures under diverse conditions, e.g., heating, 24 high pressure, 25 deformation, 26 electron beam irradiation, 27 etc., have been systematically investigated with the aid of various in situ techniques. Moreover, fine control over the transformation of unconventional-phase starting materials also represents an efficient approach toward the preparation of unconventional structures that normally cannot be obtained from conventional starting materials.…”

“…As an important fundamental phenomenon, the structural transformation of materials, which is associated with the change of their different structural parameters, including phase, composition, shape, facet, etc., under diverse external conditions, has drawn much research attention from both theoretical and experimental aspects. − In the transformation processes, the structure of starting materials plays a crucial role in determining the transformation pathway and modulating the resultant structures of intermediates and/or products. − Recently, increasing efforts have been devoted to the investigation of the structural transformation of starting materials with unconventional phases, which can not only unravel their thermodynamic stabilities in potential applications but also offer effective strategies for the synthesis of other unconventional-structured materials. Specifically, the identification of the structural evolution of unconventional-phase materials would lead to deep fundamental understanding of their structural stabilities and transformation mechanisms, providing important guidance to the stabilization strategy of unconventional phases and the exploration of their future applications. ,, Taking Au as an example, the transformation mechanisms from the unconventional 4H phase to the thermodynamically stable face-centered cubic (fcc) phase in Au nanostructures under diverse conditions, e.g., heating, high pressure, deformation, electron beam irradiation, etc., have been systematically investigated with the aid of various in situ techniques. Moreover, fine control over the transformation of unconventional-phase starting materials also represents an efficient approach toward the preparation of unconventional structures that normally cannot be obtained from conventional starting materials. ,− For instance, metastable intermediates and/or unconventional-structured products have been identified and obtained during the structural transformation of various amorphous starting materials, such as amorphous Pd–Ni–P alloy, amorphous Nb 2 O 5 , and amorphous Pd nanoparticles, demonstrating the feasibility of material synthesis via such transformation approaches.…”