Time-Dependent Structural Phase Transitions of Two-dimensional Intercalated Layered Oxides

We demonstrate time-dependent phase transitions in metal-intercalated 2D layered MoO$_{3}$. Copper metal atoms are chemically intercalated into ultrathin 2D nanocrystalline MoO$_{3}$ using a novel method we developed to intercalate high densities of zero-valent atomic species. In-situ transmission electron microscopy (TEM), operating on a timescale of seconds, and Dynamic TEM, operating on nanosecond time scales show that unique, time-dependent phase transitions can be driven in these two-dimensional layered oxide nanoribbons. Very different structures arise on different time scales, indicating a competition between kinetics and thermodynamics in determining the resulting structure. Control experiments in pure MoO$_{3}$ show no such transitions, thus it appears that the copper intercalant is an essential part of the process. Measurements of the nanosecond-scale transformation are consistent with a local reordering of material within the original unit cell, while the slower transition is characterized by an incommensurate superlattice possibly associated with a charge density wave. This work opens new ground for accessing novel phases of matter in two-dimensional layered nanomaterials.