Infrared Thin Film Detectors Based on Thermoresponsive Microgels with Linear Shrinkage Behavior and Gold Nanorods

To overcome the drawbacks of existing infrared detectors, infrared thin film detectors based on microgels and gold nanorods (Au NRs) are investigated. The microgels with a linear shrinkage of the hydrodynamic diameter between 10 and 55 degrees C are copolymerized by monomers di(ethylene glycol) methyl ether methacrylate, oligo(ethylene glycol) methyl ether methacrylate, and acrylic acid with a molar ratio of 1:1:1. Homogenous thin films are obtained by spin coating from an aqueous solution on silicon substrates. Upon heating in a water vapor atmosphere, the film thickness of the hybrid films linearly decreases. Heat generation from a plasmon resonance enhanced absorption of the infrared radiation by the Au NRs triggers a linear shrinkage in the hybrid microgel-Au NR films as well. A linear correlation between the film thickness and the applied infrared power density is observed. The sensitivity is enhanced by a slight increase in the amount of Au NRs in the films. Infrared detectors are constructed from the hybrid microgel-Au NR films by adding two electrodes via deposition of two silver layers at the film ends. By monitoring the ohmic resistance, the intensity of the incident infrared light can be obtained. The detectors not only possess a good reversibility and fast response rate but also show a high stability after the resistance measurements. Compared with the traditional infrared detectors, the infrared thin film detectors based on microgels are sensitivity adjustable. Thus, they can be promising candidates for replacing expensive inorganic infrared detectors in areas of daily life applications.