Comparative Raman study of graphene on BaTiO3 (001) and (111) single crystals: Temperature-driven evolution of ferroelectric domains

We investigate how the ferroelectric domains of two single-crystal BaTiO3 (BTO) substrates, oriented along [001] and [111], influence the Raman response of monolayer graphene at varying temperatures. A Raman band around 1445 cm−1, close to the G mode and associated with BTO polarization, enables the simultaneous analysis of charge density in graphene and the organization of ferroelectric domains. Raman mapping reveals a periodic modulation in the frequency of graphene's 2D band, correlated with the BTO polarization-related Raman band for both substrate orientations. This effect is more pronounced for BTO (001), which exhibits strong out-of-plane polarization, whereas it is attenuated for BTO (111) due to polarization deviation. The interaction induces spatial charge variations and p–n junction formation in graphene on BTO (001) at room temperature. The periodic modulation effects vanish above the ferroelectric–paraelectric transition (430 K) for both substrates but reappear upon cooling only for graphene on BTO (111). Upon cooling, the BTO [001]-oriented substrate exhibits an emergent distribution of in-plane-oriented ferroelectric domains, eliminating its influence on the Raman mappings of graphene. This emergent distribution is confirmed by Raman mapping of different bands of the BTO [001] single crystal.