Researchers from The University of Texas at Austin, University of Pennsylvania and Massachusetts Institute of Technology (MIT) have addressed the question of how lattice dynamics in layered hybrid perovskites are affected by the dimensional engineering of the inorganic frameworks and their interaction with the molecular moieties.
The team tackled this question by using a combination of spontaneous Raman scattering, terahertz spectroscopy, and molecular dynamics simulations. This approach reveals the structural dynamics in and out of equilibrium and provides unexpected observables that differentiate single- and double-layered perovskites.
While no distinct vibrational coherence was observed in double-layered perovskites, an off-resonant terahertz pulse can drive a long-lived coherent phonon mode in the single-layered system. This difference highlights the dramatic change in the lattice environment as the dimension is reduced, and the findings could pave the way for ultrafast structural engineering and high-speed optical modulators based on layered perovskites.
The scientists presented a joint experimental-theoretical study aimed at uncovering the origin of the dynamic structural complexity in two-dimensional hybrid perovskites (2DHPs). By means of steady-state and ultrafast spectroscopy experiments, they identified unique fingerprints that distinguish the structural dynamics of the hybrid lattices in the crossover between quasi-2D and 2D.
They observed that the collective motion of the octahedral cages is substantially enhanced as the number of layers per repeating unit is altered from two to one. These results are rationalized via molecular dynamics (MD) calculations, which provide an atomic-level understanding of the hybrid lattice in and out of equilibrium.