Grain-Boundary Roughening in Colloidal Crystals

Abstract

In polycrystals, faceted grains may become round and rough at high temperatures. Such a roughening phenomenon remains poorly understood, partly because of the lack of experimental observations. Here, we directly visualize the roughening dynamics of grain boundaries inside thin-film colloidal crystals at the single-particle level using video microscopy. The thermal fluctuations of grain boundaries appear to exhibit both static and dynamic critical-like behaviors, in contrast to the Kosterlitz-Thouless transition in typical free surface roughening. The roughening point shifts towards the melting point as the grain boundary's mismatch angle θ decreases and is preempted by melting when θ < 18°. Counterintuitively, the amplitude of grain-boundary fluctuations decreases above the roughening point. This could be attributed to the observed widening of the grain boundary. The roughening strongly affects the mobility of the grain boundary but not the stiffness. These results provide new guidance for the control of microstructures in polycrystals and further development of roughening theory.

Statistical Mechanics of Low Angle Grain Boundaries in Two Dimensions

“…While previous works have focused on the roughening [16][17][18][19][20], defaceting [5,21], premelting [22,23], and structural phase transitions [24,25] in three-dimensional crystals, recent advances in colloid science [26] and 2d electronic devices [27][28][29] have triggered studies of grain boundaries in 2d crystals, with electronic and thermal properties especially sensitive to lattice imperfections [30][31][32][33][34][35][36][37][38].…”

Imaging how thermal capillary waves and anisotropic interfacial stiffness shape nanoparticle supracrystals

“…This anisotropy plays an important role in governing crystal nucleation and shaping crystals into distinctive morphologies 8 , 41 . Interfacial fluctuations thus depend on both γ (related to interfacial stretching) and the second derivative of γ with respect to surface orientation (related to interfacial bending), which are better characterized by interfacial stiffness (sum of these two contributions 42 , 43 ). Interestingly, in our system, although the lattice orientation of the supracrystal stays unchanged (Fig.…”

Grain-boundary topological phase transitions

“…where B ≡ b/h is the shear coupling factor. A correlation length ξ is introduced here as a wavelength cutoff (21). The KT transition theory suggests that ξ → ∞ for T > T KT (21).…”