Abstract Nanostructured hematite films are promising for photoactive materials applications. One of the main challenges in this matter is to improve the understanding about the behavior of the optical properties affected by the nanostructure. This work presents a robust ellipsometric analysis (supported by AFM, XRD, and XPS characterization) of the optical response of nanostructured hematite films synthesized by an alternative methodology based on chemical bath deposition. The good match between the measured and calculated Δ and Ψ angles after the fitting processes is an evidence of the reliability of the ellipsometric model constructed here and leads to a well-agreement between the thicknesses obtained from ellipsometry and those from AFM and profilometry. The analysis of the fitted model parameters made possible to determine the existence of two types of porosity in the films. On a microscopic scale, cracks or gross porosity were quantified directly from the v% of air in an effective medium layer of the model. A fine porosity with nanometric size persisting among the solid-phase that constitutes the nanostructured hematite films, was inferred from their lower refractive index with respect to bulk hematite. The extinction coefficient reveled a strong electronic transition centered at ~550 nm associated with the optical bandgap of the films, determined in approx. 2 eV (620 nm), which correspond with bulk hematite. All results shown here reveal a complex relationship between the morphology and the optical response, which introduce relevant aspects about the nanostructured hematite films, like density and porosity, that could be used to propose performance improvements in their potential applications as photoactive material.

中文翻译：

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形态、成分和结构对纳米结构赤铁矿薄膜光学响应的​​作用

摘要 纳米结构的赤铁矿薄膜在光敏材料应用中很有前景。这方面的主要挑战之一是提高对受纳米结构影响的光学特性行为的理解。这项工作对通过基于化学浴沉积的替代方法合成的纳米结构赤铁矿薄膜的光学响应进行了强大的椭偏分析（由 AFM、XRD 和 XPS 表征支持）。拟合过程后测量和计算的 Δ 和 Ψ 角之间的良好匹配证明了此处构建的椭偏模型的可靠性，并导致从椭偏测量获得的厚度与从 AFM 和轮廓测量获得的厚度之间的良好一致性。拟合模型参数的分析使得确定薄膜中存在两种类型的孔隙成为可能。在微观尺度上，裂缝或总孔隙率直接从模型有效介质层中空气的 v% 量化。从构成纳米结构赤铁矿薄膜的固相中持续存在纳米尺寸的细孔是从它们相对于块状赤铁矿的较低折射率推断出来的。消光系数揭示了与薄膜的光学带隙相关的以~550 nm 为中心的强电子跃迁，大约在 2 eV (620 nm)，对应于块状赤铁矿。这里显示的所有结果揭示了形态和光学响应之间的复杂关系，它介绍了纳米结构赤铁矿薄膜的相关方面，