单层单晶石墨烯与柔性基底界面性能的实验研究

单晶石墨烯具有更优异的力学及电学性能,有望成为新一代柔性电子器件的核心材料.因此,有必要从实验的角度精细分析化学气相沉积法制得的大尺度单晶石墨烯与柔性基底复合结构的界面力学行为.本文通过显微拉曼光谱实验方法测量了不同长度的单层单晶石墨烯/PET(聚对苯二甲酸乙二醇酯)基底的界面力学性能参数及其在长度方向上界面边缘的尺度效应.实验给出了石墨烯在PET基底加载过程中与基底间黏附、滑移、脱黏三个界面状态的演化过程与应力分布规律.实验发现,单晶石墨烯与柔性基底间由范德瓦耳斯力控制的界面应变传递过程存在明显的边缘效应,并且与石墨烯的长度有关.界面的切应力具有尺度效应,其值随石墨烯长度的增加而减小,而石墨烯界面传递最大应变以及界面脱黏极限则不受试件尺度的影响.

Experimental study on interfacial mechanical behavior of single-layer monocrystalline graphene on a stretchable substrate

Monocrystalline graphene is expected to become a core material for the next-generation flexible electronic device, owing to its superior mechanical and electrical properties. Therefore, it is essential to analyze the interfacial mechanical property of the composite structure composed of large-scale monocrystalline graphene, prepared by chemical vapor deposition (CVD), and flexible substrate in experiment. Recent years, micro-Raman spectroscopy has become a useful method of micro/nano-mechanics for the experimental investigations on the properties of low-dimensional nanomaterials, such as carbon nanotube (CNT), graphene, molybdenum disulfide (MoS₂). Especially, Raman spectroscopy is effectively applied to the investigations on the mechanical behaviors of the interfaces between graphene films and flexible substrates. Among these researches, most of the measured samples are small-scale monocrystalline graphene films which are mechanically exfoliated from highly oriented pyrolytic graphite, a few ones are the large-scale single-layer polycrystalline graphene films prepared by CVD. There is still lack of study of the large-scale single-layer monocrystalline graphene. In this work, micro-Raman spectroscopy is used to quantitatively characterize the behavior of interface between single-layer monocrystalline graphene film prepared by CVD and polyethylene terephthalate (PET) substrate under uniaxial tensile loading. At each loading step from 0 to 2.5% tensile strain on the substrate, the in-plane stress distribution of the graphene is measured directly by using Raman spectroscopy. The interfacial shear stress at the graphene/PET interface is then achieved. The experimental result exhibits that during the whole process of uniaxial tensile loading on the PET substrate, the evolution of the graphene/PET interface includes three states (adhesion, sliding and debonding). Based on these results, the classical shear-lag model is introduced to analyze the interfacial stress transfer from the flexible substrate to the single-layer graphene film. By fitting the experimental data, several mechanical parameters are identified, including the interface strength, the interface stiffness and the interface fracture toughness. The Raman measurements and result analyses are carried out on the samples whose single-layer graphene films have different lengths. It is shown that the stress transfer at the graphene/PET interface controlled by the van der Waals force has obvious scale effect compared with the graphene length. The interface strength, viz. the maximum of the interfacial shear stress, decreases with the increase of the graphene length. While the graphene length has no effect on the debonding strain or the strain transfer limit of graphene/PET interface. Combining with other previous studies of the large-scale single-layer graphene shows that the mechanical parameters of the interface between graphene and flexible substrate have no relation no matter whether the graphene is monocrystalline or polycrystalline.