Fabrication, optical characterization, and simulation of subwavelength TiO₂ hole arrays exhibiting geometry-tunable, omnidirectional color response across the visible spectrum is described. Partially suspended TiO₂ grating “membranes” (hole arrays supported by a high void-fraction, low-index underlayer) with quasiperiodic hexagonal order were created on an Si substrate using colloidal lithography, metal mask, plasma-based pattern transfer, and XeF₂ etching. Optical measurements under specular and diffuse reflection conditions, along with finite-difference time-domain simulations, indicated that the omnidirectional color response of the hole arrays emerges from a broad distribution of Fano resonance states formed by coupling between guided and internal Fabry–Pérot (FP) cavity modes of the TiO₂ layer. Higher-order FP resonances from the external cavity formed between the TiO₂ layer and substrate control the apparent color when devices are viewed in direct light. The simulated modal behavior of arrays was found to be very sensitive to the degree of Si removal from the underlayer, in agreement with experimental observations. The fabrication methodology presented herein is substrate-agnostic and can be employed to fabricate suspended, subwavelength hole arrays in many material systems, with potential application to optical filters and reflectors, photocatalytic electrodes, photovoltaics, and sensors.

中文翻译：

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具有可调谐，全向颜色响应的准有序亚波长TiO2孔阵列

描述了在可见光谱范围内表现出几何形状可调的全向颜色响应的亚波长TiO ₂孔阵列的制造，光学表征和仿真。使用胶体光刻，金属掩模，基于等离子体的图案转移和XeF ₂在Si基板上创建了具有准六方六边形顺序的部分悬浮的TiO ₂光栅“膜”（由高空隙率，低折射率底层支撑的孔阵列）。蚀刻。在镜面反射和漫反射条件下的光学测量，以及时域有限差分模拟表明，孔阵列的全向颜色响应来自法诺共振态的宽分布，该分布是由引导和内部法布里-珀罗（FP）之间的耦合形成的TiO ₂层的腔模。来自TiO ₂之间形成的外腔的高阶FP共振当在直射光下观看设备时，层和基板控制外观颜色。与实验观察结果一致，发现阵列的模拟模态行为对从底层去除硅的程度非常敏感。本文介绍的制造方法学与衬底无关，可用于制造许多材料系统中的悬浮亚波长孔阵列，并有可能应用于光学滤波器和反射器，光催化电极，光伏和传感器。