A Review on Mechanics and Mechanical Properties of 2D Materials - Graphene and Beyond (1611.01555v1)

Abstract: Since the first successful synthesis of graphene just over a decade ago, a variety of two-dimensional (2D) materials (e.g., transition metal-dichalcogenides, hexagonal boron-nitride, etc.) have been discovered. Among the many unique and attractive properties of 2D materials, mechanical properties play important roles in manufacturing, integration and performance for their potential applications. Mechanics is indispensable in the study of mechanical properties, both experimentally and theoretically. The coupling between the mechanical and other physical properties (thermal, electronic, optical) is also of great interest in exploring novel applications, where mechanics has to be combined with condensed matter physics to establish a scalable theoretical framework. Moreover, mechanical interactions between 2D materials and various substrate materials are essential for integrated device applications of 2D materials, for which the mechanics of interfaces (adhesion and friction) has to be developed for the 2D materials. Here we review recent theoretical and experimental works related to mechanics and mechanical properties of 2D materials. While graphene is the most studied 2D material to date, we expect continual growth of interest in the mechanics of other 2D materials beyond graphene.

• The paper presents a comprehensive review of mechanical properties in 2D materials using advanced experimental techniques and theoretical models.
• The paper reveals that controlled defect introduction can increase graphene's elastic modulus and influence fracture mechanics in polycrystalline structures.
• The paper highlights practical applications in flexible electronics, nanolubrication, and biomedical devices driven by engineered 2D material mechanics.

Insightful Overview of Mechanics and Mechanical Properties of 2D Materials – Graphene and Beyond

In recent years, two-dimensional (2D) materials have garnered immense interest due to their unique properties and potential applications in diverse fields ranging from electronics to biomedical devices. This paper reviews the mechanics and mechanical properties of 2D materials, focusing primarily on graphene, but also exploring other materials such as transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), and phosphorene. The implications of mechanical properties for practical applications are critically examined, providing a comprehensive understanding of their role in the integration and performance of 2D-based systems.

Elastic and Inelastic Properties

The paper begins by detailing the elastic properties of 2D materials, exploring advances in experimental techniques such as AFM nanoindentation and pressurized blister tests that allow the measurement of in-plane Young's modulus and bending moduli. Graphene demonstrates an impressive in-plane stiffness and elasticity, but the presence of defects and thermal rippling significantly influences these properties. Recent findings highlight a controversial increase in graphene's elastic modulus upon controlled defect introduction, sparking debate around thermal fluctuations' role.

The inelastic properties section considers defects, strength, and fracture mechanics. Graphene's strength, arising from its defect-free nature, is notably high, with its potential applications highlighted in protective coatings and reinforcement materials. The review extends to fracture toughness, a critical metric for engineering applications. In polycrystalline forms, graphene exhibits a pseudo Hall-Petch behavior, where the strength may inversely relate to grain size due to defect topology.

Coupling with Other Physical Properties

The interplay between mechanical deformation and other physical phenomena such as electronic, optical, and thermal properties is meticulously examined. Strain engineering emerges as a powerful technique, enabling modulation of electronic properties like band gaps in semiconductors. Graphene’s pseudo-magnetic fields (PMFs) induced by mechanical strains suggest novel routes for electronic device platforms. Furthermore, 2D materials under mechanical constraints exhibit phase transitions, essential for phase-change memory devices.

Interfacial Mechanics: Adhesion and Friction

Interfacial properties, crucial for 2D material applications, are analyzed through adhesion and friction experiments. Techniques such as blister and island blister tests provide insights into adhesion energies, which are found to vary vastly with substrate surface conditions and environmental factors. Graphene’s adhesion energies have significant implications for reliable integration in composite materials. The paper also investigates friction, revealing complexities due to chemical modifications and substrate interactions, which impact performance in nanolubrication applications.

Practical Applications and Future Trends

The paper dives into synthesis and transfer mechanisms crucial for fabricating large-area 2D materials. Wet and dry transfer methods are explored, with fracture mechanics concepts playing a role in improving process efficiency. Graphene origami and kirigami are highlighted for their applications in creating highly flexible and stretchable electronic devices.

Biomedical uses are addressed, with 2D materials bridging the gap between rigid electronics and biological systems due to their flexibility and bio-compatibility. Graphene's capabilities in developing epidermal electronics and neural interfaces are underlined, reflecting its potential in future technological advances.

Conclusion and Research Directions

In conclusion, the review underscores the indispensable role of mechanics in the paper and application of 2D materials. Future research directions proposed include further exploration into the influence of temperature and ripple mechanics on elastic properties, the development of multi-physics theoretical models, and a deeper understanding of mixed-mode adhesion and friction interactions. The paper invites continued investigation into engineering the unique properties of 2D materials for innovative applications, recognizing a potential transformative impact on flexible electronics and more.

The intricate relationship between mechanics and the multifaceted properties of 2D materials presents both challenges and opportunities, demanding advanced research to harness their full potential.