The generation of atmospheric pressure microplasmas using microwave resonators is promising for many applications due to the possibility of high electron densities and low electrode degradation. In particular, such plasmas may help enable reconfigurable metamaterials operating from GHz to THz. Since plasma metamaterials may require the generation of tens to hundreds of plasmas, it is important to find ways to reduce the power required for plasma breakdown. Here, we study gold and silver microwave split-ring resonators (SRRs) with a variety of materials near the interelectrode gap (Cu, CuO nanowires, aluminum oxide). We focus on those fabricated using a traditional thick film technique, screen-printing, and using fs- and ns-laser ablation. The use of laser ablation allows us to explore small interelectrode gap sizes (7-100um) and the use of different lasers and laser parameters enables us to produce a variety of microstructures. We utilize Weibull statistics to examine breakdown in atmospheric pressure Ar with and without deep ultraviolet illumination of SRRs. Fabrication methods and materials are shown to influence both Q-factor of the SRRs and breakdown voltage independently. It is found that superior performance in terms of breakdown voltage and consistency in breakdown is related to Weibull modulus. The power requirement for breakdown varied as widely as an order of magnitude depending on fabrication method and material used for the SRRs. Furthermore, we consider the performance differences seen between various resonators and relate this to microstructure/material which suggests that field-emission may play a role in providing the seed electrons required for breakdown. This need for seed electrons appears to be especially important for gap sizes of 40um and smaller.

中文翻译：

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微波裂环谐振器中大气压等离子体产生的威布尔分析和场发射证据

由于高电子密度和低电极退化的可能性，使用微波谐振器产生大气压微等离子体在许多应用中具有前景。特别是，这种等离子体可能有助于实现可重构超材料，工作频率从 GHz 到 THz。由于等离子体超材料可能需要产生数十到数百个等离子体，因此找到降低等离子体击穿所需功率的方法很重要。在这里，我们研究了在电极间间隙附近具有各种材料（Cu、CuO 纳米线、氧化铝）的金和银微波裂环谐振器 (SRR)。我们专注于使用传统厚膜技术、丝网印刷以及使用 fs 和 ns 激光烧蚀制造的那些。激光烧蚀的使用使我们能够探索小电极间间隙尺寸（7-100um），并且使用不同的激光和激光参数使我们能够生产各种微结构。我们利用威布尔统计来检查大气压 Ar 在有和没有 SRR 的深紫外线照射的情况下的分解。制造方法和材料显示独立影响 SRR 的 Q 因子和击穿电压。发现在击穿电压和击穿一致性方面的优越性能与威布尔模量有关。击穿所需的功率因 SRR 所用的制造方法和材料而异，变化幅度大到一个数量级。此外，我们考虑了各种谐振器之间的性能差异，并将其与微观结构/材料联系起来，这表明场发射可能在提供击穿所需的种子电子方面发挥作用。对于 40um 或更小的间隙尺寸，这种对种子电子的需求似乎特别重要。