Room-Temperature Raman Enhancement in Colloidal 2D PbS Nanosheets

Colloidal two-dimensional (2D) PbS nanosheets exhibit a dramatically enhanced longitudinal optical (LO) phonon Raman signal at room temperature, exceeding the intensity of 0D quantum dots by orders of magnitude. We attribute this giant enhancement to two synergistic mechanisms: spatial phonon coherence across the expansive 2D lattice and broad resonance enhancement enabled by a step-like density of states that strengthens exciton-phonon coupling. While surface oxidation can activate room-temperature Raman scattering in 0D quantum dots, their signal remains significantly weaker than that of pristine 2D nanosheets. Structural coalescence from porous quantum-dot networks to continuous 2D nanosheets directly drives peak sharpening and intensity amplification. Unlocking this robust, non-destructive Raman response provides a key framework to investigate 2D lattice dynamics, which govern hot-carrier relaxation, multiple exciton generation, and superfluorescence in colloidal quantum materials.