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The global trends of urbanization and industrialization have given rise to critical environmental and air pollution issues that often receive insufficient attention. Among the myriad pollution sources, volatile organic compounds (VOCs) stand out as a primary cluster, posing a significant threat to human society. Addressing VOCs emissions requires an effective mitigation action plan, placing technological development, especially in detection, at the forefront. Photonic sensing technologies rooted in the infrared (IR) light and matter interaction mechanism offer nondestructive, fast-response, sensitive, and selective chemical measurements, making them a promising solution for VOC detection. Recent strides in nanofabrication processes have facilitated the development of miniaturized photonic devices and thus sparked growing interest in the creation of low-cost, highly selective, sensitive, and fast-response IR optical sensors for VOC detection. This review work thus serves a timely need to provide the community a comprehensive understanding of the state of the art in this field and illuminate the path forward in addressing the pressing issue of VOC pollution. 

This research studies the impact of the charging effect on the RIE-etched profile of narrow-slot Lead- Selenide (PbSe) gratings. By decreasing the slot width from 4 to 2 𝜇𝑚, we observed the increased irregularity and RIE-lag in etched profiles.We suggest that the charging effect is the main responsible mechanism for this phenomenon. The accumulated charge on the non-conductive photoresist plays a crucial role in forming this effect. Therefore, introducing a conductive layer can neutralize the accumulated charge and significantly improves the profile. To prove this theory, we introduced a thin layer of copper on the gratings. While without any conductive coating, we failed to etch gratings with a slot width of less than 1 𝜇𝑚, by introducing a copper layer, we succeeded etching gratings with 0.7 𝜇𝑚 slot width with the improved sidewall profiles. Hence, this technique enables us to fabricate sub-micron PbSe gratings with applications of mid-infrared (MIR) devices. 

Designing a metasurface with appropriate phase correlation between light's linear and circular polarization states is challenging. The focus here is obtaining the geometric phases from different geometric shapes for optimum dielectric metasurface design.