Revisiting the Twin Plane Re-entrant Edge Growth Mechanism at an Atomic Scale by Electron Microscopy

Abstract

We conducted an extensive electron microscopy study on surface and defect structures of boron suboxide/ suboxycarbide platelets by examining them under various imaging conditions, e.g., side-view and top-view perspectives. It was determined that a twin plane re-entrant edge mechanism was responsible for the growth process at an atomic scale. Moreover, this thorough investigation provided an opportunity to resolve several critical issues regarding this otherwise wellknown growth mechanism for metallic nanostructures. In this study, the platelets contained multiple {001} twin lamellae parallel to basal planes and their side faces were mainly enclosed by {101} facets. Vertical growth was heterogeneously nucleated of {001}-type growth twins that were confined at the corners. In lateral growth, nucleation sites were greatly extended to twin reentrant edges around all side faces. No secondary growth twins were introduced during lateral growth because {101}-type side faces were not twin planes. This work clearly establishes that surface structures of twinned platelets determine nucleation behaviors on basal/side faces and thus control the final morphology, which is relevant to the shape control of metal nanoplates.

Embedding Ba Monolayers and Bilayers in Boron Carbide Nanowires

“…For example, prior studies showed that the formation of an impurity-based surficial “amorphous” films 1 (SAFs, as a type of surface complexions, where the term “complexion” refers to the thermodynamic equilibrium state of an interface; noting that this type of complexion is neither completely crystalline nor fully amorphous despite of being named as SAFs 1 ) - can change faceted particles into nanospheres 2 or stabilize anisotropic morphology 3 . Specifically, we have recently demonstrated that adding barium oxide as an additive along with the iron-rich catalyst can help to control the growth of B-C-O nanowires 4 and nanoplatelets 5 6 7 to achieve unique morphologies and high yields; here, we further demonstrated that the controlled anisotropic growth is related to the formation of barium-enriched surface complexions.…”

“…Stacking faults were frequently observed in boron-rich crystals and they were considered to arise from the instability in the iron boride catalysts, which assisted the continual nucleation of (001) ledges 7 . In some cases, we also observed trapped bilayers stabilized at stacking faults, similar to the situation of impurity segregation at grain boundaries 17 (see Fig.…”

Effect of Si Content on the Morphology Evolution of the Si Primary Dendrites in Al-Si Alloy Solvent Refining Process

“…Based on the above results, it is clear that the growth pattern of Si primary dendrites has been changed as increasing the Si content in the Al-Si alloy. Generally, on solidi cation of the Al-Si hypereutectic alloy, the growth of plate-like Si primary dendrites lies on (111) planes and in [211] directions, where it occurs by the twin plane re-entrance edge (TPRE) mechanism [24]. Figure 8(a) illustrates schematically the growth model of the plate-like Si primary dendrites.…”

“…Generally, the plate-like Si primary dendrites have a sharp tip morphology along < 211 > fast growth direction [24], which would be easily broken due to its fragile property, especially surrounded by plenty of neighboring grains. The broken tip usually has small size (< 0.5 mm, as shown in Fig.…”

An Order–Disorder Transition in Surface Complexions and Its Influence on Crystal Growth of Boron-Rich Nanostructures

“…Experimental Section. Boron-containing low-dimensional materials were prepared with high reproducibility by a high-temperature solid state processing (that was referred to as “sintering” in prior studies, ,,− despite the fact that it is not the same as the sintering processing as conventionally defined in ceramics), with a starting precursor of BaO, B, and Fe 3 O 4 in a molar ratio of 1.04:16.11:1. First, the starting powder was ground to fine particles with the addition of 0.1 mL glycerol to assist the high yield growth .…”