Polytype Transformation by Replication of Stacking Faults Formed by Two-Dimensional Nucleation on Spiral Steps during SiC Solution Growth

Abstract

Polytype transformations on the 4H-SiC(0001) Si face during top-seeded solution growth have been investigated by transmission electron microscopy and micro-Raman spectroscopy. 4H-, 15R-, and 6H-SiC were grown on the 4H-SiC(0001) Si face via spiral growth. Once a polytype transformation from 4H-SiC to 15R-or 6H-SiC occurs, the polytype rarely returns to 4H-SiC. Just before the polytype transformation, a disturbance in the stacking sequence involving the introduction of stacking faults was observed. A polytype transformation during spiral growth can be understood in terms of the replication of stacking faults due to twodimensional nucleation of a single bilayer on the spiral steps. This polytype transformation model shows good agreement with observed polytype transformation pathways as well as the disturbance in the stacking sequence at the interface between 4H-SiC and 15R-SiC.

Fractal MTW Zeolite Crystals: Hidden Dimensions in Nanoporous Materials

“…In summary,weproposed the conceptual structural model of MTW zeolite spiral plates driven by the screw dislocation region, which is confirmed by the features of surface spiral contours,s crew dislocation core,a nd hollow core structure. Different from nanoporous materials with high symmetry (for example,C HA/AEI, [15] SiC ceramic [2,19] ), the special growth mode in this MTW zeolite plate involves the collaborative manner of frequent intergrowth along (310) plane and propagation of SFs along the vertical dimension. Thedimensional change of nanosized zeolite rods via iterative deformation twinning and intrinsic intergrowth procedure is an ovel strategy toward hierarchical materials with interconnected abundant pore structures (Supporting Information, Figures S53-S55).…”

“…Different from nanoporous materials with high symmetry (for example,C HA/AEI, [15] SiC ceramic [2,19] ), the special growth mode in this MTW zeolite plate involves the collaborative manner of frequent intergrowth along (310) plane and propagation of SFs along the vertical dimension. Different from nanoporous materials with high symmetry (for example,C HA/AEI, [15] SiC ceramic [2,19] ), the special growth mode in this MTW zeolite plate involves the collaborative manner of frequent intergrowth along (310) plane and propagation of SFs along the vertical dimension.…”

“…Such dislocation structures have been widely captured in dense-phase materials,s uch as metal oxides and alloy compounds, [1] ceramics, [2] carbon nanotubes, [3] and even ice. Ther ecursive division of branches in the networks is treated as aself-similarity in fractal geometry.Additionally, the branching patterns are assembled by these fractal structures following as elf-similarity law.O nt he other hand, the pivot to form spiral structure of crystal lies in the generation of as crew dislocation to break the symmetry of crystal growth and promote the anisotropic nanostructures.…”

“…Ther ecursive division of branches in the networks is treated as aself-similarity in fractal geometry.Additionally, the branching patterns are assembled by these fractal structures following as elf-similarity law.O nt he other hand, the pivot to form spiral structure of crystal lies in the generation of as crew dislocation to break the symmetry of crystal growth and promote the anisotropic nanostructures. Such dislocation structures have been widely captured in dense-phase materials,s uch as metal oxides and alloy compounds, [1] ceramics, [2] carbon nanotubes, [3] and even ice. [4] Comparatively,i nf ramework materials,t he complex dimension can be individually established:1 )a hierarchal architecture formed by self-repeating pillared MFI [5] or rational intergrowth of FAUn anosheets, [6] and 2) as piral structure in which spiral contour can be observed on the flat surface of various crystals,f or instance,L TA,S TA-7 (SAV), CHA/AEI, ZnPO 4 -Sodalite,a nd ZnPO 4 -Faujasite.I nf act, although the screw dislocation core structure was predicted on the atomic scale of the LTAz eolite by Walker and coworkers, [7] thereal nature of these frameworks remain elusive.…”

Evolution of threading screw dislocation conversion during solution growth of 4H-SiC

“…Details of the growth configuration are given in Ref. 13. High purity silicon (11 N) was placed in a graphite crucible and heated to the growth temperature under a high-purity Ar gas flow.…”