Measurement of Local Stress Components in Single Crystal Alumina by Using Raman Microspectroscopy with Sub-Micro Spatial Resolution

Recently, it is very important to grasp the stress states in sub-micro scale area. In this study, components of stresses/strains in a single crystal sapphire are determined by Raman microspectroscopy with sub-micro spatial resolution. The sapphire belongs to a D3d point group with two A1g and five Eg vibration mode Raman lines. First, the relationships between the change of Raman shift and strain components for A1g and Eg modes are theoretically derived based on energy change under mechanical loading. In these equations, 20 unknown parameters are included. Second, these parameters are experimentally determined. In A1g and Eg modes, the relationships between Raman shift and applied strain indicate the linearity. Third, components of strains are determined by Raman microspectroscopy, and stresses are calculated by using Hook's law. Last, stress measurements around the notch root in the single crystal sapphire are conducted. The measured stresses are good agreement with the FEM results. Therefore, the applicability of Raman microspectroscopy to stresses/strains measurement in micro scale area is confirmed.