Recently, there has been much interest in applying the color changes of nano-patterned structures to sensor technology. However, the lithographic nano-patterning process is not environmentally friendly, and it is difficult to fabricate large areas of color due to limitations associated with this approach. In this study, we realized a highly tunable structural coloration based on a Fabry–Perot interferometer design that does not require nano-patterning processes. To increase the reflected color change according to the angle, a color element using an asymmetric metal–insulator–metal structure was applied, fabricated using silver–silicon dioxide–tin (Sn), respectively. Using the optical properties of Sn, we maximized the change in reflection color and realized three primary colors of subtractive color of cyan, magenta and yellow according to the angle of designed MIM structure. Theoretical and experimental results revealed that the color and intensity of the reflectance depended strongly on the angle of the reflective surfaces. The manufacturing process is simple and yields large surfaces of high quality. Based on this premise, we fabricated a soft robot capable of color camouflage, and an angle-detecting color sensor for inspecting the three-dimensional shape quality of curved glass with a high sensitivity of 1.8 nm/degree. In addition, we propose a shape evaluation method by color, spectrometry, and monochromatic light.
Remarkable advances in nanomaterials and nanotechnology have led researchers in various fields. The scale effects imparted by nanomaterials are associated with unexpected macroscale phenomena and properties that find many applications. However, multi-functionalization may be accompanied by physical and commercial limitations. Therefore, research must proceed in several different directions. Here, we define multi-functionalization and the electrical applications thereof in terms of increasing performance, addition of new and valuable properties, and multi-physics in play. We deal with sensors, actuators, energy harvesters, and solar cells and explore research that seeks to increase sensitivity, append “stretchability”, and facilitate untethered communication. Furthermore, we analyze research trends in materials use and manufacturing, and highlight useful fabrication methods. With the aim of predicting future research trends, our review presents a roadmap that will aid research on sensing and multi-functional applications.
Light‐driven shape memory alloy (SMA)‐based microscale actuators show great promise for artificial muscle and biomedical applications, as they are actuated remotely and have a fast response speed. However, ultraviolet (UV) light is required for device actuation; thus, the operating environment has been limited. Here, an infrared (IR) light‐driven SMA actuator is proposed, in which the plasmonic effect is used to enhance IR light absorptance. A sub‐micrometer pattern is used to create an optical meta‐surface capable of tuning the light absorptance. Conical nanohole arrays are fabricated with a focused ion beam. The absorptance tuning effect is evaluated in terms of the optical characteristics and performance of the actuator. The nanopatterned surface increases the narrow‐band IR light absorption by up to 55%. Optics simulations are conducted to verify the experimental results. A pattern design method is proposed, based on the light wavelength of the stimulating source. Combining heterogeneous surfaces, both UV and IR light achieve decoupled microscale actuation. These actuators show a response similar to that of the iris muscle, which is responsible for the eye's pupillary reflex. It is expected that these actuators will broaden SMA applications in clinical devices and soft robotics.
High-performance gas sensors with low operating temperatures are of emerging research interest. They do not require heaters, thus guaranteeing cost-effectiveness and low power consumption. This is a study to demonstrate the possibility of fabricating a high-performance sensor through a simplified mechanism based on the surface property changes of a Fabry–Perot cavity. Here, the upper metal reacts independently, allowing accurate analyses to be performed while minimizing errors due to external factors. The proposed sensor rapidly responds to corrosive gases; it shifts the absorption wavelength by over 45 nm, that is, from 552 to 597 nm within 15 min at room temperature, significantly changes the color from purple to blue, and can be fabricated in bulk using conventional electron-beam physical vapor deposition. NO2 gas experiments verify the sensor’s superior performance and productivity potential, demonstrating its applicability in urban areas and factories.
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