Investigation of the influence of defects on the nanomechanical properties of graphene by multifrequency atomic force microscopy

在这个项目中，将开发一种将面外和面内定向的力学样品属性可视化的方法。因此，将实现一种基于扫描力显微镜的多频技术，其中用于地形采集的反馈参数是类似于间歇接触模式的悬臂梁弯曲本征模的幅度。此外，第二个弯曲和扭转振动被光热激发。弹性相互作用和耗散相互作用可以从相应模式的频移和激励幅度中提取出来。该方法将用于石墨烯，以确定这种特殊材料的基面上的纳米机械性能。本文以人工诱导缺陷对材料力学性能的影响为研究对象。特别需要解决的问题是：引入SP3缺陷和空位后，石墨烯的局部弹性模数是如何变化的。在石墨烯的纳米和微观力学性能之间建立经验关系是否可行？这对于评估石墨烯是否适合作为电子和机械设备的元件尤为重要。此外，还应研究缺陷的纳米力学性能是否在特定环境中因老化而随时间发生变化。

In this project, a method will be developed that visualizes mechanical sample properties directed out-of-plane and in-plane. Thus, a scanning force microscopy based multifrequency technique will be realized where the feedback parameter for the topographical acquisition is the amplitude of the flexural eigenmode of the cantilever similar as for the intermittent contact mode. In addition, a second flexural and a torsional oscillation is photothermally excited. The elastic and dissipative interactions can be extracted from the frequency shift and excitation amplitude of the respective modes. The method will be employed on graphene to determine the nanomechanical properties across the basal plane of this extraordinary material. The change of the mechanical properties with artificially induced defects is the object of investigation. In particular the following question should be addressed: How does the local elastic modulus of graphene change by the introduction of sp3-defects and vacancies. Is it feasible to establish an empirical relationship between nanoscopic and microscopic mechanical properties of graphene? This is particularly important to assess if graphene is suitable as component for electronic and mechanical devices. Additionally, it should be investigated if the nanomechanical properties of defects change with time due to aging in certain environments.