Department of Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
Nano Lett. 2013 Apr 10;13(4):1743-50. doi: 10.1021/nl400328x. Epub 2013 Mar 19.
The occurrence of plasmon resonances in thin (~20 nm) Al and Au films, perforated with nanoholes, was studied. In both metals, two plasmon resonances were observed: (i) A surface plasmon polariton mode associated with a maximum in extinction and (ii) a localized resonance in the nanohole associated with a minimum in extinction. By varying the diameter of the nanoholes, the scaling of the peak positions of the plasmon resonances was determined as a function of hole diameter. In the large nanohole limit, the plasmon peak positions depend only on the nanohole diameter being independent of the material. On the other hand, for small nanoholes the plasmon peak positions are material and size dependent. In contrast to Al films where the localized plasmons can be excited from the near-IR to the UV, no plasmon resonances were observed for Au at energies above the interband threshold (2.4 eV). The interaction between a distinct interband transition in Al at 1.5 eV and the localized plasmon resonance is considered in detail. We observe for the first time experimentally a noncrossing behavior of the interband transition and the localized plasmon resonance. The energy (size) dependence of surface plasmon peak width, being a measure for the decay/damping of the latter, is very different for the two metals. This can be explained by considering the different decay mechanisms active in the two metals. Apart from these basic plasmonics results, we test the potential of using the shifts of the plasmon resonances in perforated Al films to follow the atmospheric oxidation/corrosion kinetics of Al. The results are quantified by model calculations. The obtained kinetic law for the oxide growth is in good agreement with a previous XPS study on plain Al films. This suggests that the nanohole-induced plasmon resonances can be a sensitive and simple measure for Al corrosion and metal corrosion in general.
研究了具有纳米孔的约 20nm 厚的 Al 和 Au 薄膜中的等离子体激元共振的发生。在这两种金属中，观察到了两种等离子体激元共振：（i）与消光最大值相关的表面等离子体极化激元模式，以及（ii）与消光最小值相关的纳米孔中的局域共振。通过改变纳米孔的直径，确定了等离子体共振峰值位置随孔直径的变化。在大纳米孔极限下，等离子体共振峰位置仅取决于纳米孔直径，与材料无关。另一方面，对于小孔，等离子体共振峰位置取决于材料和尺寸。与 Al 薄膜不同，Al 薄膜中的局域等离子体可以从近红外激发到紫外，而 Au 在能带隙以上的能量（2.4eV）没有观察到等离子体共振。详细考虑了 Al 中的一个独特的带间跃迁与局域等离子体共振之间的相互作用。我们首次实验观察到带间跃迁和局域等离子体共振的非交叉行为。表面等离子体峰值宽度的能量（尺寸）依赖性，作为后者衰减/阻尼的度量，对于两种金属非常不同。这可以通过考虑两种金属中不同的衰减机制来解释。除了这些基本的等离子体学结果外，我们还测试了利用穿孔 Al 薄膜中等离子体共振的位移来跟踪 Al 的大气氧化/腐蚀动力学的潜力。结果通过模型计算进行量化。获得的氧化物生长动力学规律与之前对纯 Al 薄膜的 XPS 研究非常吻合。这表明纳米孔诱导的等离子体共振可以作为 Al 腐蚀和一般金属腐蚀的敏感和简单的测量方法。
