A Molecular Dynamics Study of the Mechanical Properties of Twisted Bilayer Graphene

Enhancing the Mechanical Stability of 2D Fullerene with a Graphene Substrate and Encapsulation

Recent advancements have led to the synthesis of novel monolayer 2D carbon structures, namely quasi-hexagonal-phase fullerene (qHPC₆₀) and quasi-tetragonal-phase fullerene (qTPC₆₀). Particularly, qHPC₆₀ exhibits a promising medium band gap of approximately 1.6 eV, making it an attractive candidate for semiconductor devices. In this study, we conducted comprehensive molecular dynamics simulations to investigate the mechanical stability of 2D fullerene when placed on a graphene substrate and encapsulated within it. Graphene, renowned for its exceptional tensile strength, was chosen as the substrate and encapsulation material. We compared the mechanical behaviors of qHPC₆₀ and qTPC₆₀, examined the influence of cracks on their mechanical properties, and analyzed the internal stress experienced during and after fracture. Our findings reveal that the mechanical reliability of 2D fullerene can be significantly improved by encapsulating it with graphene, particularly strengthening the cracked regions. The estimated elastic modulus increased from 191.6 (qHPC₆₀) and 134.7 GPa (qTPC₆₀) to 531.4 and 504.1 GPa, respectively. Moreover, we observed that defects on the C60 layer had a negligible impact on the deterioration of the mechanical properties. This research provides valuable insights into enhancing the mechanical properties of 2D fullerene through graphene substrates or encapsulation, thereby holding promising implications for future applications.

Quantifying the local mechanical properties of twisted double bilayer graphene

Nanomechanical measurements of minimally twisted van der Waals materials remained elusive despite their fundamental importance for device realisation. Here, we use Ultrasonic Force Microscopy (UFM) to locally quantify the variation of out-of-plane Young's modulus in minimally twisted double bilayer graphene (TDBG). We reveal a softening of the Young's modulus by 7% and 17% along single and double domain walls, respectively. Our experimental results are confirmed by force-field relaxation models. This study highlights the strong tunability of nanomechanical properties in engineered twisted materials, and paves the way for future applications of designer 2D nanomechanical systems.

Graphene Properties, Synthesis and Applications: A Review

We have evaluated some of the most recent breakthroughs in the synthesis and applications of graphene and graphene-based nanomaterials. This review includes three major categories. The first section consists of an overview of the structure and properties, including thermal, optical, and electrical transport. Recent developments in the synthesis techniques are elaborated in the second section. A number of top-down strategies for the synthesis of graphene, including exfoliation and chemical reduction of graphene oxide, are discussed. A few bottom-up synthesis methods for graphene are also covered, including thermal chemical vapor deposition, plasma-enhanced chemical vapor deposition, thermal decomposition of silicon, unzipping of carbon nanotubes, and others. The final section provides the recent innovations in graphene applications and the commercial availability of graphene-based devices.

The Crack Angle of 60° Is the Most Vulnerable Crack Front in Graphene According to MD Simulations

Graphene is a type of 2D material with unique properties and promising applications. Fracture toughness and the tensile strength of a material with cracks are the most important parameters, as micro-cracks are inevitable in the real world. In this paper, we investigated the mechanical properties of triangular-cracked single-layer graphene via molecular dynamics (MD) simulations. The effect of the crack angle, size, temperature, and strain rate on the Young’s modulus, tensile strength, fracture toughness, and fracture strain were examined. We demonstrated that the most vulnerable triangle crack front angle is about 60°. A monitored increase in the crack angle under constant simulation conditions resulted in an enhancement of the mechanical properties. Minor effects on the mechanical properties were obtained under a constant crack shape, constant crack size, and various system sizes. Moreover, the linear elastic characteristics, including fracture toughness, were found to be remarkably influenced by the strain rate variations.

Molecular dynamics simulations of ion beam irradiation on graphene/MoS2 heterostructure

The interaction between ion irradiation and two-dimensional (2D) heterostructures is important for the performance modulation and application realization, while few studies have been reported. This paper investigates the influence of Ar ion irradiation on graphene/MoS2 heterostructure by using molecular dynamics (MD) simulations. The generation of defects is studied at first by considering the influence factors (i.e., irradiation energy, dose, stacking order, and substrate). Then uniaxial tensile test simulations are conducted to uncover the evolution of the mechanical performance of graphene/MoS2 heterostructure after being irradiated by ions. At last, the control rule of interlayer distance in graphene/MoS2 heterostructure by ion irradiation is illustrated for the actual applications. This study could provide important guidance for future application in tuning the performance of graphene/MoS2 heterostructure-based devices by ion beam irradiation.

Atomic Insights into Fracture Characteristics of Twisted Tri-Layer Graphene

Graphene twistronics have recently gained significant attention due their superconductive behavior as a consequence of their tunable electronic properties. Although the electronic properties of twisted graphene have been extensively studied, the mechanical properties and integrity of twisted trilayer graphene (tTLG) under loading is still elusive. We investigated the fracture mechanics of tTLG with a twist angle of ±1.53° utilizing molecular dynamics simulation. This twist angle was chosen because it is known to exhibit highly superconductive behavior. The results indicate that tTLG does not preserve the excellent mechanical properties typically associated with graphene, with toughness and fracture strain values much lower in comparison. The Young’s modulus was an exception with values relatively close to pristine graphene, whereas the tensile strength was found to be roughly half of the intrinsic strength of graphene. The fracture toughness, fracture strain and strength converge as the crack length increases, reaching 0.26 J/m3, 0.0217 and 39.9 GPa at a crack length of 8 nm, respectively. The Griffth critical strain energy is 19.98 J/m2 and the critical stress intensity factor Kc is 4.47 MPa M1/2, in good agreement with that of monolayer graphene in the experiment. Our atomic insights might be helpful in the material design of twisted trilayer graphene-based electronics.

Monolayer Twisted Graphene-Based Schottky Transistor

The outstanding properties of graphene-based components, such as twisted graphene, motivates nanoelectronic researchers to focus on their applications in device technology. Twisted graphene as a new class of graphene structures is investigated in the platform of transistor application in this research study. Therefore, its geometry effect on Schottky transistor operation is analyzed and the relationship between the diameter of twist and number of twists are explored. A metal–semiconductor–metal twisted graphene-based junction as a Schottky transistor is considered. By employing the dispersion relation and quantum tunneling the variation of transistor performance under channel length, the diameter of twisted graphene, and the number of twists deviation are studied. The results show that twisted graphene with a smaller diameter affects the efficiency of twisted graphene-based Schottky transistors. Additionally, as another main characteristic, the I_D-V_GS is explored, which indicates that the threshold voltage is increased by diameter and number of twists in this type of transistor.

Atomic Structure and Mechanical Properties of Twisted Bilayer Graphene

We studied the atomic structure and mechanical properties of twisted bilayer graphene with a different twist angle using molecular dynamic simulations. The two layers are corrugated after energy minimization. We found two different modes of corrugation. The mechanical properties are tested both in-plane and perpendicular to the plane. The in-plane properties are dominated by the orientation of graphene. The perpendicular properties depend on the twist angle, as the larger the twist angle, the higher the intrinsic strength.