图8. 实验样品的扫描电子显微镜照片: (a) 单级结构表面(标尺为200 $\mu$m); (b) 底面刻蚀有封闭式次级结构的多级结构表面(标尺为200 $\mu$m); 其中, 左插图: 封闭式篝火堆状纳米级柱状结构(标尺为2 $\mu$m); 右插图: 一簇"篝火堆"的细节照片, (标尺为 500 nm); (c) 底面刻蚀有开放式次级结构的多级结构表面(标尺为200 $\mu$m); 其中插图为微结构底面纳米直立柱的细节照片(标尺为300 nm)

Fig. 8. Scanning electron microscopic (SEM) images of samples:(a) single level surface (scale bar: 200 $\mu$m); (b) hierarchically structured surface with "closed" sublevel structures etched on the bottom (scale bar: 200 $\mu$m); left inset: bonfire-like "closed" sublevel structures (scale bar: 2 $\mu$m); right inset: detailed photo of the bonfire-like "closed" sublevel structures (scale bar: 500 nm); (c) "open" sublevel structures etched on the bottom (scale bar: 200 $\mu$m); inset: detailed photo of the upright nano-columns on the bottom (scale bar : 300 nm)