This study explores the impact of crystalline fraction on the mechanical losses of amorphous tantalum oxide (tantala, Ta₂O₅) thin films intended for gravitational wave detectors. We use ion beam sputtering technique to prepare a series of samples, which are then subjected to controlled thermal annealing to achieve varying degrees of crystallized fraction. The microscopic structure of the annealed samples is characterized by combining different analytical techniques. Our investigation reveals that the amorphous films comprise randomly distributed crystalline grains, whose density and average size depends on the duration of thermal treatment. To assess mechanical losses of the coatings, a gentle nodal suspension system is applied. Remarkably, a substantial reduction of approximately 20% in the coating’s mechanical loss angle with respect to annealed amorphous coatings is observed for samples exhibiting a crystalline fraction of around 5%. This improvement may lead to the definition of alternative thermal treatments to improve the mechanical performances of coatings for gravitational wave detectors or other highly sensitive optical experiments. However the reduction in mechanical losses comes at the expense of an increase in optical scattering. The possibility of reducing the optical losses to the level required by gravitational interferometers by modifying the grain size distribution via appropriate annealing treatments is discussed.

中文翻译：

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通过部分结晶减少离子束溅射氧化钽薄膜的机械损失

本研究探讨了结晶分数对用于引力波探测器的非晶氧化钽（tantala，Ta ₂ O ₅ ）薄膜的机械损耗的影响。我们使用离子束溅射技术制备一系列样品，然后对其进行受控热退火以获得不同程度的结晶分数。通过结合不同的分析技术来表征退火样品的微观结构。我们的研究表明，非晶薄膜包含随机分布的晶粒，其密度和平均尺寸取决于热处理的持续时间。为了评估涂层的机械损失，采用了温和的节点悬挂系统。值得注意的是，对于结晶分数约为 5% 的样品，观察到与退火非晶涂层相比，涂层的机械损耗角显着降低了约 20%。这种改进可能会导致替代热处理的定义，以提高引力波探测器或其他高灵敏度光学实验涂层的机械性能。然而，机械损失的减少是以光学散射增加为代价的。讨论了通过适当的退火处理改变晶粒尺寸分布，将光学损耗降低到重力干涉仪所需水平的可能性。