Chemical routes to two-dimensional photonic crystal sensors equipped with nano/microcavities

开发简单、小巧、高灵敏度的有害物质检测传感器是当前学术研究和商业应用的热点之一。在这种背景下，基于纳米/微结构硅的光学传感器引起了人们的极大兴趣，人们已经研究了不同的结构，如马赫-曾德尔干涉仪、光栅、光波导和光子晶体器件。如果这些传感器的几何布局设计得当，并采用特定的光学读出方法，就可以显示出非凡的传感性能。最有希望实现极高灵敏度的是基于二维光子晶体平板的光学传感器。传感器通常是通过在薄硅片上形成周期性的空穴阵列来实现的，该空穴阵列可以显示光子带隙(阻带)，其特征是阻止光在一定频率范围内传播。因此，它们的光谱中实现了窄共振线宽，这使它们成为传感器应用的理想候选者。此外，通过在周期性的空穴晶格中引入点或线缺陷，形成了光学纳米/微腔，从而促进了光的强烈限制。尽管对这些传感器的需求很高，但二维光子晶片几乎完全是通过自上而下的方法制造的，例如光刻和电子束光刻。这些方法可以精确定义纳米结构的几何尺寸，包括它们的大小和形态，但需要复杂的设备。相比之下，自下而上的方法提供了使用自组装过程构建大片区域的简单和成本效益高的方法。尤其是在胶体光刻方面，人们在实现高度有序和层次化的纳米结构方面取得了巨大的进展。然而，到目前为止，利用胶体光刻技术制备微纳米尺度上具有位置选择性变化的纳米材料的研究还很少，尽管人们非常希望获得简单、快速和低成本的此类材料的制备方法。该项目旨在利用胶体光刻技术和金属辅助刻蚀技术在硅基衬底上制作具有纳米/微腔结构的二维光子晶体传感器。为此，将利用刺激响应型水凝胶微凝胶的特殊性质来提供对沉积在衬底表面上的水凝胶微凝胶的二维阵列中的晶格常数和胶体直径的独立控制。所得胶体掩模将用于制备金纳米盘阵列，随后将用于金属辅助刻蚀硅基衬底。因此，利用纳米/微腔的二维光子晶体传感器将以一种简单而经济的方式在大面积上实现。

The development of simple, small, and highly sensitive sensors for detecting hazardous substances is one of the hot topics in both academic research and commercial applications. In this context, optical sensors based on nano/microstructured silicon are highly interesting and different configurations such as Mach-Zehnder interferometers, gratings, waveguides and photonic crystal devices have been investigated. These sensors can show extraordinary sensing performance if their geometrical lay-out is well designed and specific optical read-out methods are applied. Most promising for achieving extremely high sensitivities are optical sensors based on two-dimensional photonic crystal slabs. The sensors are often realized by creating a periodic array of holes in a thin silicon slab which can exhibit a photonic band gap (stop band) characterized by the prevention of light propagation at a range of frequencies. Thereby, narrow resonance linewidths in their optical spectra are achieved making them ideal candidates for sensor applications. Furthermore, by introducing point or line defects into the periodic lattice of holes optical nano/microcavities are formed facilitating a strong confinement of light. Despite the high demand for these sensors, two-dimensional photonic crystal slabs are almost exclusively fabricated by top-down methods, e.g. photo- and e-beam lithography. These methods allow for a precise definition of the geometric dimensions of nanostructures, including their size and morphology, but require sophisticated equipment. In contrast, bottom-up approaches provide simple and cost-efficient methods for structuring large areas using self-assembly processes. Especially in colloidal lithography tremendous progress was made towards the realization of highly ordered and hierarchical nanostructures. However, until now the fabrication of nanomaterials with site-selective variations in their dimensions on the micro/nanoscale by colloidal lithography was barely investigated even though simple, fast and cost-efficient production methods for these kinds of materials are highly desirable. This project aims at the fabrication of 2D photonic crystal sensors equipped with nano/microcavities using a combination of colloidal lithography and metal-assisted etching of silicon-based substrates. For this purpose, the exceptional properties of stimuli-responsive hydrogel microgels will be exploited in order to provide independent control over lattice constants and colloid diameters in two-dimensional arrays of hydrogel microgels deposited on the substrate surface. Resulting colloidal masks will be used for preparing gold nanodisc arrays which will subsequently be employed for metal-assisted etching of the silicon-based substrate. Thereby, 2D photonic crystal sensors equipped with nano/microcavities will be realized in a simple and cost-efficient way on large areas.