Size-Dependent Fracture Strength Of Graphene Nanoribbons And Current-Voltage Characteristics Under Tension Stress

Graphene has received special attention in recent years due to its excellent mechanical, thermal, optical and electrical properties as well as potential applications in the fields of electronics and optoelectronics. Different configurations such as zigzag and armchair nanoribbons can be obtained by cutting the boundaries of graphene. Importantly, graphene nanoribbons(GNRs) have a vast potential prospect for future development in nanoelectronics devices because of their excellent electrical transport properties. Up to date, the research on the strain-dependent electrical transport properties of GNRs is mainly focused on experimental measurements and simulations, while theoretical model from the atomistic origin is still lacking. Moreover, the physical mechanisms on the fracture strength and electrical transport properties of GNRs under the condition of different widths and imposed uniaxial stress remains unclear.Therefore, in this paper, we first calculate the fracture strength of two different configurations of GNRs in terms of first-principles molecular dynamics. Second, we establish an analytical model to address the width dependence of fracture stain and related strength based on the atomic-bond-relaxation theory and discuss the relevant changes of bond identities. Third, we further calculate the I-V characteristics in the two different configurations of GNRs and clarify the corresponding physical mechanism in detail. The achievements are shown as follows:(1) We simulate the fracture properties of two types of GNRs, e.g., zigzag and armchair, in terms of first-principles calculations within the framework of density functional theory(DFT). It is found that the width of nanoribbons greatly affects the fracture strength and fracture strain. Also, the fracture strain of zigzag-GNRs is greater than that of armchair-GNRs. Meanwhile, an analytical model is established to address the width-dependent fracture strain in zigzag-GNRs based on the atomic-bond-relaxation theory.(2) We calculate the electrical transport properties of two types of GNRs in terms of first-principles calculations within the framework of DFT and analyzed the I-V characteristics of GNRs under uniaxial tensile stress. It is shown that when the width of zigzag-GNRs is an odd number, the bias is proportional to the current; while when the width is even, the bias voltage is smaller than the threshold bias voltage(approximately 1.6V), the current is very small, and the current will start to increase until the bias voltage greater than the threshold bias. For the case of armchair-GNRs, we demonstrate that when the width N=3P+2, it exhibits half-metallic properties, and when the width N=3P or 3P+1, it likes semiconductor.(3) Furthermore, based on previous results, the I-V characteristics of GNRs under stress in any direction are calculated. We found that it satisfies the same laws in the two configurations of GNRs, e.g., when the stress is small, the electrical transport properties will be reduced under transverse tension, and it will be improved in the longitudinal tension; while the stress becomes larger, the electrical transport properties of GNRs will be depressed in any direction.