Application Of Micro-Raman Spectroscopy In Study On Mechanical Properties Of Nanomaterials

With the rapid evolution of micro/nano science and technology, there is a pressingneed for the investigations on the new micro/nano mechanical testing technique andthe multi-scale association analysis method of experimental mechanics. Micro-Ramanspectroscopy (MRS) is a new method of experimental mechanics in micro-scale. It isthe essential requirement to develop the fundamental theory, and the analysis methodsas well, of the Raman-mechanical measurement before its general application. Thisthesis presented the study on the Raman-mechanical measurement theory and themulti-scale experimental analysis methodology for two kinds of nanocompositesincluding carbon nanotube (CNT) fibers/films and wafer-based nano porous silicon(PS) films.Firstly, a multi-scale measurement system is constructed by combining themacroscopic tension test, the microscopic morphology observation and themicro-spectroscopy detection technology for the experimental study on themulti-scale mechanical behavior of CNT materials. In this system, the mechanicalresponse of the lattice structure of materials is detected by MRS at the microscale, themesostructure deformation is observed by SEM at the mesoscale, and the stress/strainof materials are measured at the macroscale. Associating the experiment at differentscales by in-situ test, this system can realize the multi-scale experimental study on themechanical properties of CNT materials with hierarchical structure.By using the multi-scale measurement system above, the mechanical propertiesand their control mechanisms of CNT fiber and film materials are studied. Themechanical behaviors of CNT fibers during the tension until fracture and the cyclicloading are measured, and the load response of structures at all levels, that is,“fiber–bundle&thread–CNT” are analyzed. Base on the experiment analysis, aconstitutive equation is developed to characterize the macroscopic mechanicalproperties of the CNT fibers. This work not only provides an initial insight into theunderlying mechanism of the strength and toughness of CNT materials, but also guideto improve the manufacturing technology for the macroscopic materials as well asoptimize and enhance their mechanical performance. Moreover, the mechanicalproperties of CNT film materials with anisotropy are studied by measuring the deformation response of the CNT films under uniaxial loading in three differentdirections. A CNT bundle adhesive basic unit network model of the CNT film isproposed, and the deformation and fracture mechanisms of the films under tensionalong the different directions are analyzed based on this model.Besides, a Raman mechanical measurement theory for wafer-based nano poroussilicon films is presented to measure the residual stress in PS films by MRS. Theanalytic relationship of the Raman shift to the stress components of PS films isdeduced by analyzing the transversely isotropic characteristics of PS films.Meanwhile, the nanoindentation technique and digital speckle correlation method areintroduced to detect the elastic moduli and Poisson’s ratio of PS films, respectively.Based on the analytic model and material parameters determined in the experiment,the Raman-shift to stress coefficients of PS films are determined. Using themeasurement theory studied, the distribution of residual stress along the thicknessdirection in the PS-film/silicon-substrate structure is measured and analyzed.