In an effort to scale-up nanomaterial growth over large surface areas, we aim to effectively study the structural non-homogeneities within the arrays of zinc oxide nanowires (ZnO-NWs). The assessment of the lateral gradient of the nanowires' characteristics is presented including their height and surface density. To this end, spectroscopic ellipsometry and the rather recently reported technique of spectral domain attenuated reflectometry are used as two fast, simple and non-invasive characterization methods with further capabilities of scanning over the sample surface. Simple models are proposed by considering ZnO-NWs as the equivalent of thin stratified layers based on the effective medium approach. The methodology not only reveals the presence of gradients, but also enables quantitative analysis for all the samples grown using the hydrothermal method with different growth times ranging from 0.5 h up to 4 h. The gradients are confirmed using scanning electron microscopy (SEM) observations taken as a reference. The results also suggest that the sample orientation during the growth influences the NW growth besides the other parameters already known to affect the growth mechanisms.

中文翻译：

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对纳米材料同质性的快速评估揭示了氧化锌纳米线阵列中的横向结构梯度。

为了扩大纳米材料在大表面积上的生长，我们旨在有效研究氧化锌纳米线（ZnO-NWs）阵列中的结构非均质性。提出了对纳米线特性的横向梯度的评估，包括其高度和表面密度。为此，光谱椭圆偏振法和较新近报道的光谱域衰减反射法技术被用作两种快速，简单且非侵入性的表征方法，并具有在样品表面上进行扫描的进一步能力。通过基于有效介质方法，将ZnO-NWs视为等效于薄分层的层，提出了一种简单的模型。该方法不仅揭示了梯度的存在，而且还可以对使用水热法生长的所有样品进行定量分析，其生长时间从0.5小时到4小时不等。使用作为参考的扫描电子显微镜（SEM）观察结果确认梯度。结果还表明，除了已知的其他影响生长机理的参数外，生长过程中样品的取向还会影响NW的生长。