Control and Theoretical Modeling of the Growth Process of AlN Six-fold and Multifold Armed Dendritic Crystals

Abstract

Through a combinatorial approach involving theory and experiments, this study investigated the mechanism of the dendritic growth of AlN microcrystals during the combustion of Al + 0.1AlF3 + kAl2O3 powder mixtures under nitrogen-rich conditions. The experimentally observed morphology of the dendritic AlN crystals is characterized by the six-fold branches that developed outward within an equatorial plane and secondary dendrites that grew above and below the equatorial plane. The physical mechanisms that lead to the shape-controlled synthesis of AlN dendritic crystals were studied through experimental analysis and theoretical investigation including density functional theory (DFT) calculation and phase-field (PF) crystal growth modeling. Based on the DFT-calculated surface energy values, an energy minimization argument was used to construct the AlN nucleus. PF crystal growth modeling provides the details of the sequential crystallization process of the dendritic AlN crystals. The results of this study provide a complete understanding of the shape-controlled growth of AlN crystals, which aids the rational growth design of AlN and other relevant compounds.

Morphological diversity of AlN nano- and microstructures: synthesis, growth orientations and theoretical modelling

“…After 500 steps, dendritic arms began to grow, and at 1000 steps, six dendritic arms with side-branches were formed (Figure 13(B, a)). The phase field modelling results were in good agreement with the experimental results of the same authors (Figure 13(B, b)) [173].…”

“…After 500 steps, dendritic arms began to grow, and at 1000 steps, six dendritic arms with side-branches were formed (Figure13(B, a)). The phase field modelling results were in good agreement with the experimental results of the same authors (Figure13(B, b))[173].Kobayashi developed a scheme for the solidification of a pure substance in an undercooled melt by replacing the sharp interface moving boundary with a diffuse interface scheme[167,174]. This scheme possessed striking simplicity and turned out to be identical to the theoretical concept that is now known as phasefield.…”

“…Therefore, to limit the growth of the side branches, latent heat F should be small. The phase-field growth of a number of seeds in a single calculation domain according to the number of time-steps was reported in [173]. For a single seed, nucleation and growth occurred at the centre of the calculation domain.…”

“…B. Shape of dendritic crystals obtained via (a) phase field modelling; (b) combustion experiments [173]. …”