Dipole Behavior Modulation Through Interface Relaxation in Artificially Designed 2D/3D Heterostructure

Dipoles, as elements that allow control of dielectric materials, play a crucial role in implementing logic, memory, energy storage, micro-electromechanical systems, and wireless communication. These dipoles can be modulated by designing heterostructures, enabling the control of properties such as poling direction and poling speed. However, lattice mismatch and differences in thermal expansion coefficients hinder the creation of single-crystalline heterostructures, deteriorating dipole controllability as well as insulating performance. Freestanding nanomembranes can be exfoliated from the host substrate, enabling single-crystalline artificial heterostructures by adopting 2D layers, thereby overcoming the limitation. By stacking these materials, tailored heterostructures with novel functionalities are engineered. Nevertheless, since the behavior at these interfaces differs from that of covalent bonds, a more comprehensive fundamental study of their interfaces is necessary for effective dipole engineering.<br/>In this talk, we discuss the relaxation at the 2D/3D van der Waals (vdW) interface and its impact on artificial 2D/3D heterostructures using single-crystalline and freestanding BaTiO₃ nanomembranes (SBTO). Due to the differences in dielectric constant and conductivity between SBTO and 2D layers, charge accumulation at the vdW interface was induced because of Maxwell-Wagner (MW) relaxation. To evaluate the effect of the relaxation at the interface according to the supporting layer, we chose 2D conducting (graphene), 2D semiconductor (MoS₂), and 2D insulator (<i>h-</i>BN). The <i>h-</i>BN/SBTO heterostructure induced stronger charge accumulation because of the low conductivity and high dielectric constant of <i>h</i>-BN, acting as a screener for dielectric polarization in the crystal. However, the large amount of charge accumulation suppressed the maximum polarization. In contrast, the MoS₂/SBTO heterostructure provided higher maximum polarization and relatively low remnant polarization, enabling giant energy storage performance. Such charge accumulation at discontinuous gaps can offer new physical phenomena based on fundamental physics of the dipoles, providing new insights for various multifunctional platforms.