Morphologies of silicon crystals solidified on a chill plate

Abstract

Electromagnetically levitated liquid droplets of pure Si or a Si-Ge alloy were cooled to different temperatures and then dropped onto a chill plate of Cu. Droplet oscillations mark the solid/liquid interface during solidification and permit the different crystal morphologies of silicon to be observed on the quenched surface by scanning electron microscopy (SEM). A spherical morphology found on the quenched surface represents the initial stage of crystal growth. Further growth leads to octahedral crystals bounded by {111} faces near equilibrium and to other polyhedra or even faceted dendrites further from equilibrium. The spherical growth can be observed only when the initial melt undercooling is moderately high. The critical size at which spherical crystals start to develop dendritic growth is much bigger than that calculated from the Mullins and Sekerka model, and is bigger than the Coriell and Parker model when kinetic undercooling is taken into account.

Simulation of Intermetallic Solidification Using Phase-Field Techniques

“…Also shown in Figure 3c are contours from throughout the growth so that the evolution of the shape, from initial hexagonal seed to fully continuous dendrite may be observed. The transition of the growth morphology from faceted to continuous with increasing departure from equilibrium is considered a desirable property of the model that closely mimics just such a transition observed in rapid solidification experiments [22,23,24]. Figure 3.…”

Phase-Field Modelling of Intermetallic Solidification

“…It is well established that crystals that grow with faceted morphologies close to equilibrium progressively take on more continuous interface shapes with increasing departures from equilibrium, eventually adopting fully dendritic morphologies. This has been shown for the growth of pure semiconductors [8,9], the Si phase in Al-Si eutectics [10] and for intermetallic phases [11]. Simulation of this particular aspect of faceted growth has however received very little attention.…”

Thermodynamic properties of under-cooled silver melts

“…Specific heat and related thermodynamic properties of under-cooled liquid melts are very important parameters to further research on the mechanism of non-equilibrium solidification and formation of new metastable materials, and these properties are also essential for describing the nucleation and growth phenomena in under-cooling melts [1][2][3][4][5][6]. In the past several decades, the specific heat and related thermodynamic properties of under-cooled metals, alloys and oxides have been investigated, by electromagnetic [7][8][9][10][11][12][13][14][15] and electrostatic [16,17] levitation, whose techniques can easily realize the deep under-cooling of melts.…”