Research On Mechanical Properties And Temperature Dependent Charicteristics Of Graphene-Substrate System

Graphene has unique properties and wide application prospect, which makes it become a hot topic in the field of condensed matter and materials, and causes great concern of the industry. However, there are many important scientific and engineering problems associated with the mechanical properties of graphene to be solved during the preparation, transfer and application of graphene, and in-depth study on the mechanical properties of graphene can effectively promote its progress and development of basic research and industrialization. In this thesis, some mechanical properties of graphene and graphene/substrate system are studied using nanoindentation, nano-scratch and temperature-dependent Raman experiments, with the corresponding means of molecular dynamics simulation. The main contents and results are as follows:Based on the introduction of molecular dynamics simulation, the tensile mechanical properties (such as ultimate strength, ultimate strain and elastic modulus) of graphene are studied systematically under the influence of temperature, defects and strain rates. As the temperature increases, the mechanical properties are reduced; Defects make ultimate strength and ultimate strain reduce significantly; High strain rates make mechanical properties increase; Mechanical properties of hydrogenated graphene are lower than that of graphene.The properties and mechanism of nanoindentation of suspended graphene are systematically studied under the influence of the factors such as temperature, loading rate, defects, radius of graphene and radius of indenter. Sink-in phenomenon appearing in the AFM experiment of graphene and its followings nanoindentation behavior are studied, revealing that there is strong van der Waals force in the interface between the graphene and the substrate, which is sufficient to avoid slip and ensure clamped boundary conditions of suspended graphene during nanoindentation process; On the basis of suspended graphene, nanoindentation properties of graphene/copper foil substrate are studied, finding that graphene can dramatically extend the elastic contact field of copper foil substrate, effectively increase its normal carrying force, and has obvious enhancement of mechanical properties of the metal surface. Through the nanoindentation experimental study of graphene/copper foil substrate, the drop-down phenomenon of normal load and serious continuous wave phenomenon in the indentation curve are first discovered, and both phenomena indicate that the presence of graphene has important effects on the nanoindentation mechanical behavior of copper foil.The nanofriction charicteristics of suspended graphene and graphene/copper foil substrate systems are studied, finding that the presence of graphene reinforces the contact stiffness of copper foil, expands the scope of low friction force, and the friction force is dependent on the nanoindentation depth rather than the number of graphene layers. Nanofriction experiments confirm that graphene effectively reduces the friction coefficient of the metal material surface.Finally, temperature-dependent characteristics of Raman spectra of graphene on three different substrates (copper foil, glass and SiO2) are studied. Both the G and 2D modes exhibit significant red shift as temperature increases, and the values of temperature coefficients are also extracted when graphene is on different substrates. This study provides useful results of mechanical interaction between graphene and the substrate in the growth process of graphene.