Abstract
<jats:p>Controlling crystallographic registry is central to semiconductor heteroepitaxy, yet how epitaxial domains reorient and fluctuate once crystalline order first becomes detectable remains unresolved. Here, we use time-resolved transmission electron microscopy to simultaneously track the twist angle and coherently ordered area of individual MoS2 domains on graphene and the curved graphitic surfaces of carbon nanohorns, complemented by structural analyses spanning nanometre to submicrometre length scales. The smallest resolvable domains, with coherently ordered areas of approximately 1.5 nm2, preferentially adopt orientations near 30°. As their coherently ordered areas increase, individual domains progressively reorient towards 0° and their angular fluctuations diminish, revealing a size-dependent narrowing of the accessible orientational range. Under non-equilibrium formation conditions, however, near-30° orientations can persist to submicrometric dimensions, consistent with kinetic trapping of long-lived interfacial configurations. These observations establish coherent domain size as a key determinant of orientational preference and fluctuation amplitude, whereas kinetic pathways influence the persistence of non-equilibrium orientations. The crossover is consistent with finite-size competition between edge contributions and registry-dependent interfacial energetics, modulated by kinetic barriers. By resolving dynamic orientational pathways inaccessible to ensembleaveraged measurements, our results provide a mechanistic basis for twist-selective growth of twodimensional heterostructures.</jats:p>