This study is the first attempt of applying thermal stress cleavage to a single-crystal round sapphire bar having a morphologically continuous circumference surface. Previously, thermal stress cleavage was only applied to brittle material substrates or wafers owing to the crack propagation behaviour induced by thermal stress distribution. To overcome this issue, a V-shaped groove was prepared on the circumference as an initial point for crack propagation, and a continuous-wave carbon dioxide (CO₂) laser was used as the heat source. The thermal stress behaviour was simulated via finite element analysis, and the effect of the initial crack morphology on the thermal stress behaviour was evaluated. In addition, the crack propagation was monitored using an acoustic emission sensor, and the separation mechanism of the round sapphire bar was investigated. Results indicated that the thermal stress cleavage using the CO₂ laser beam allowed the complete separation of the round sapphire bar with the V-shaped groove without any final edge remaining. The crack propagation behaviour was determined from the relationship between the thermal stress distribution and morphology change during crack propagation. The fabricated sharp V-shaped groove improved the quality of the cleaved surface, and the high aspect ratio of the groove enabled a high-quality cleavage. The initial crack propagation immediately after the start of laser beam irradiation was affected by the tip of the V-shaped groove, and the crack propagation direction could be controlled through the tip morphology of the V-shaped groove.

这项研究是首次尝试将热应力解理应用于具有形态连续圆周表面的单晶圆形蓝宝石棒。以前，由于热应力分布引起的裂纹扩展行为，热应力解理仅适用于脆性材料基板或晶片。为了克服这个问题，在圆周上准备了一个 V 形凹槽作为裂纹扩展的起点，连续波二氧化碳 (CO ₂）激光被用作热源。通过有限元分析模拟热应力行为，并评估初始裂纹形态对热应力行为的影响。此外，使用声发射传感器监测裂纹扩展，并研究圆形蓝宝石棒的分离机制。结果表明，使用 CO ₂的热应力裂解激光束使圆形蓝宝石棒与 V 形凹槽完全分离，没有任何最终边缘。裂纹扩展行为由裂纹扩展过程中热应力分布与形貌变化之间的关系确定。制造的尖锐V形凹槽提高了解理面的质量，凹槽的高纵横比实现了高质量的解理。激光束照射开始后的初始裂纹扩展受V形槽尖端的影响，裂纹扩展方向可以通过V形槽的尖端形貌来控制。