Stress Characterization of Crystal Junction of a Mosaic Diamond Substrate (an Approximately 4 cm ² ) Using Near‐Field Optical Raman Microscopy

We measured the Raman spectra of a commercially available mosaic diamond substrate using both far‐field (confocal) and near‐field Raman microscopy (SNOM). Although the mosaic diamond substrate is optically transparent, it contains a junction approximately 40 μm wide. Raman measurements revealed the presence of strong compressive and tensile stresses on the order of GPa within the junction region. Analysis of the Raman linewidth indicates that the junction comprises three distinct layers: melting, adhesive, and melting layers. The compressive and tensile stresses measured by SNOM were at least twice as large as those obtained with far‐field Raman microscopy near the junction. This discrepancy is attributed to the different probing depths and spatial resolutions of the two techniques. Based on a simple edge‐force model, we explain the large compressive and tensile stress distributions observed in the vicinity of the junction. Our results indicate that stresses are distributed inhomogeneously not only within the junction of the mosaic diamond crystal but also throughout the thickness of the crystal, from the substrate bottom to the surface.