Optical performance of surface plasmon resonance critically depends on the material loss of the metals, which deteriorates the quality factor of the resonance. In addition to intrinsic loss that comes from interband electric transitions, the metal possesses extrinsic loss due to crystal imperfections, such as grain boundaries and point and line defects. Thermal annealing is a useful method to reduce these imperfections via recrystallization. However, the annealing treatment has to reconcile with the deformation of the shape of nanostructures at high temperatures, which limits recrystallization. Here, we boosted the annealing effect notably for silver (Ag) nanoparticle arrays by increasing the temperature higher than the melting point of Ag (=962 °C). To prevent the change of the shape and damage to the nanoparticles during the annealing, we coated the nanoparticles with a conformal layer of aluminum oxide (10 nm) by atomic layer deposition. The heat treatment at 1000 °C for 30 s in a lamp furnace successfully reduces the material loss while retaining the shape. Consequently, the quality factor of the optical resonance of the sample increases. This work opens the way to increase the performance of the plasmonic structures up to the material limit by reducing the extrinsic loss sources of crystalline imperfections.

中文翻译：

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通过原子层沉积涂层和高于熔点的退火来改善银纳米颗粒阵列的等离子体响应。

表面等离子体激元共振的光学性能主要取决于金属的材料损失，这会降低共振的品质因数。除了由于带间电跃迁产生的固有损耗外，由于晶体缺陷（例如晶界和点和线缺陷），金属还具有非本征损耗。热退火是一种通过重结晶减少这些缺陷的有用方法。然而，退火处理必须与高温下纳米结构形状的变形相协调，这限制了再结晶。在这里，我们通过提高高于Ag熔点（= 962°C）的温度来显着提高银（Ag）纳米颗粒阵列的退火效果。为了防止退火期间形状变化和对纳米颗粒的损坏，我们通过原子层沉积法在纳米颗粒上涂覆了一层氧化铝保形层（10 nm）。在灯炉中于1000°C进行30 s的热处理可以成功地减少材料损失，同时保持形状。因此，样品的光共振的品质因数增加。这项工作通过减少晶体缺陷的非本征损耗源，开辟了将等离激元结构的性能提高到材料极限的途径。