Graphene on Hexagonal Boron Nitride (1401.5145v2)

Abstract: The field of graphene research has developed rapidly since its first isolation by mechanical exfoliation in 2004. Due to the relativistic Dirac nature of its charge carriers, graphene is both a promising material for next-generation electronic devices and a convenient low-energy testbed for intrinsically high-energy physical phenomena. Both of these research branches require the facile fabrication of clean graphene devices so as not to obscure its intrinsic physical properties. Hexagonal boron nitride has emerged as a promising substrate for graphene devices, as it is insulating, atomically flat and provides a clean charge environment for the graphene. Additionally, the interaction between graphene and boron nitride provides a path for the study of new physical phenomena not present in bare graphene devices. This review focuses on recent advancements in the study of graphene on hexagonal boron nitride devices from the perspective of scanning tunneling microscopy with highlights of some important results from electrical transport measurements.

Graphene on Hexagonal Boron Nitride: A Review

This paper presents a detailed review of the advancements in graphene research, particularly focusing on graphene devices supported by hexagonal boron nitride (hBN) substrates. Since its isolation in 2004, graphene has been at the forefront of materials science research due to its unique electronic properties attributed to its relativistic Dirac charge carriers. However, realizing graphene's full potential for electronic applications necessitates clean fabrication techniques that preserve these intrinsic properties, which is where hexagonal boron nitride substrates offer significant advantages.

Introduction and Motivation

Graphene's promise in electronic devices, coupled with its utility in exploring high-energy physical phenomena, requires substrate choices that maintain its pristine electronic characteristics. hBN emerges as a superior choice over traditional SiO$_2$ substrates due to its insulating, atomically flat nature and cleaner charge environment. Furthermore, hBN introduces new physical phenomena through its interaction with graphene, making it a subject of intensive research within scanning tunneling microscopy (STM) and spectroscopy (STS) realms.

Key Findings and Results

• Substrate Comparisons: Graphene supported on hBN displays markedly reduced surface roughness compared to those on SiO$_2$, facilitating clearer observations of intrinsic electronic properties. The flatter landscape provided by hBN is crucial for unveiling phenomena like long-wavelength LDOS oscillations and edge scattering effects.
• Electronic Properties: hBN creates a superlattice potential essential for uncovering new Dirac points in graphene's band structure. Scanning tunneling spectroscopy confirms the presence of these superlattice Dirac points, whose energies are tunable by adjusting the moiré pattern's wavelength, a function of crystallographic alignment between graphene and hBN.
• Experimental Signatures: The review highlights experimental evidence of superlattice Dirac points through STS measurements showing symmetric dips in LDOS. Moreover, transport measurements suggest enhanced mobility in graphene due to the cleaner charge environment, with significant observance of quantum Hall effects even at reduced magnetic fields.

Implications and Speculative Insights

The paper systematically discusses the implications of graphene on hBN for future electronics, particularly in scenarios demanding high mobility and unique optical characteristics. The presence of superlattice Dirac points opens pathways for novel device architectures and functionalities, exemplified by phenomena like Hofstadter quantization observed in aligned graphene-hBN samples. Additionally, the clean environment presents opportunities to investigate interaction-driven phenomena like atomic collapse in manipulated artificial nuclei composed of adsorbed atomic dimers.

Theoretical and Practical Perspectives

This paper lays crucial groundwork for theoretical models that encapsulate graphene's behavior on periodic potentials, advancing the understanding of electronic band modifications as a consequence of substrate interactions. Practically, the clean graphene devices supported by hBN present scalable opportunities for next-generation electronic device fabrication, potentially integrating other van der Waals materials into complex heterostructures capable of tailored electronic properties.

Conclusion

Graphene on hBN devices represents a promising frontier for both theoretical exploration and practical applications, owing to the superior substrate properties that enable the observation of intrinsic and novel electronic effects. The combination of graphene's unparalleled electronic characteristics with the periodic potential of hBN is instrumental in expanding both the fundamental understanding and industrial applicability of this versatile material.

The observations in this paper underscore the critical role of substrate choice in graphene research, highlighting the transformative potential of hBN in elevating the clarity and functionality of graphene devices for electronic applications. Future developments will undoubtedly leverage these insights, incorporating novel materials and stacking configurations to achieve desired electronic outcomes.