Interfacial Ferroelectricity by van-der-Waals Sliding (2010.05182v1)

Abstract: Despite their ionic nature, many layered diatomic crystals avoid internal electric polarization by forming a centrosymmetric lattice at their optimal anti-parallel van-der-Waals stacking. Here, we report a stable ferroelectric order emerging at the interface between two naturally-grown flakes of hexagonal-boron-nitride, which are stacked together in a metastable non-centrosymmetric parallel orientation. We observe alternating domains of inverted normal polarization, caused by a lateral shift of one lattice site between the domains. Reversible polarization switching coupled to lateral sliding is achieved by scanning a biased tip above the surface. Our calculations trace the origin of the phenomenon to a subtle interplay between charge redistribution and ionic displacement, and our minimal cohesion model predicts further venues to explore the unique "slidetronics" switching.

• The paper demonstrates that non-centrosymmetric stacking of h-BN flakes enables reversible and switchable ferroelectric domains.
• Experimental analysis using Kelvin probe force microscopy and simulations validates polarization switching with a 100 mV potential difference.
• Findings pave the way for advanced slidetronic nanodevices and offer new insights into intrinsic ferroelectricity in layered materials.

Interfacial Ferroelectricity by van der Waals Sliding: A Review

The paper "Interfacial Ferroelectricity by van der Waals Sliding" investigates a novel form of ferroelectricity observed at the interface of hexagonal-boron-nitride (h-BN) flakes. This work demonstrates the potential for local and reversible polarization switching, essential for information storage applications at the nanoscale. By strategically controlling the stacking configuration, the authors document the emergence of stable ferroelectric domains, offering insights into the materials' interlayer interactions and potential technological applications.

Summary of Findings

The authors report the emergence of ferroelectric order when h-BN flakes are arranged in a non-centrosymmetric and metastable parallel orientation. This configuration deviates from the typical centrosymmetric structures that usually suppress internal polarization. Key observations include:

• Alternating domains with inverted normal polarization arise due to a lateral shift of one lattice site between domains.
• This interfacial polarization is accompanied and switchable by the lateral sliding motion when driven by a biased scanning tip, demonstrating a potential mechanism for "slidetronics" applications.
• These findings align with theoretical predictions obtained from density functional theory (DFT) and molecular dynamics simulations, which trace the origin of polarization to the complex interplay between charge redistribution and ionic displacement.

The ability to achieve reversible polarization switching signifies a breakthrough in reducing information storage dimensions down to the atomic scale, crucial for next-generation memory devices. This is particularly important as ferroelectricity at the nanoscale often grapples with challenges related to long-range dipole-dipole interactions and surface effects.

Experimental and Computational Approach

• Device Fabrication and Measurements: The experimental setup involves stacking two h-BN flakes with different twist angles to investigate the potential for ferroelectricity. Kelvin probe force microscopy (KPFM) was employed to map the surface potential and infer the polarization states.
• Molecular Dynamics and Simulations: Calculations support the empirical observations, revealing stable polarization and highlighting significant properties of the commensurate AB and BA stacking domains. This corroborates the hypothesis that the observed polarization phenomena result from delicate changes in atomic positions within the lattice.

Key Results and Implications

• The domain dynamics reveal consistent polarization states with a potential difference of around 100 mV between different stacking domains.
• The research substantiates that the intrinsic polarization of h-BN is localized at the interface, unaffected by the substrate or the number of layers in the flakes. This independence suggests an intrinsic property of the interface, opening paths for novel applications in nanoelectronics.
• The paper suggests that similar phenomena may exist in other van der Waals materials, such as transition metal dichalcogenides (TMDs), expanding the scope of research into this domain.

Future Directions

The paper's exploration of interfacial ferroelectricity in 2D materials inaugurates several avenues for future research and engineering applications:

• Materials Exploration: Pursuing analogous studies in other layered materials can expand our understanding of interfacial ferroelectricity and its applicability across different systems.
• Technological Innovations: Tailoring the polar and slidetronic properties of such materials could lead to advancements in non-volatile memory devices and nanomechanical systems.
• Control Mechanisms: Enhancing the control over domain switching, potentially integrating external stimuli such as pressure or electric fields, will further drive the technological relevance of this phenomenon.

Conclusion

The findings of this research offer significant insights into the mechanisms underlying interfacial ferroelectricity in layered materials, especially the role of van der Waals interactions in these settings. Such results pave the way for a deeper understanding and exploitation of nanoscale ferroelectricity, serving as a foundation for future work aiming to integrate these features into mainstream electronics. The unique properties of these ferroelectric domains, along with their reversible control, bring us closer to realizing advanced memory technologies with unprecedented precision and efficiency.