Tunable NIR nano-absorber based on photothermal response and thermoplasmonic modulation of Au@GSST core-shell nanoparticle

Abstract

Phase change materials (PCMs) are attractive candidates for tunable devices due to their unique properties, such as high degree of scalability, thermal control, low power consumption, wide waveband operation, and the ability to switch between different optical phases. These properties can be enhanced by integrating PCMs with other materials, such as plasmonic nanoparticles. In this work, a core-shell nanostructure (Au@GSST) is proposed comprising a gold nanoparticle (AuNP) core coated with Ge₂Sb₂Se₄Te₁ (GSST), a PCM with high optical contrast, embedded in an aqueous medium. We demonstrate how the phase transition of GSST can be actively controlled by the light energy absorption of the Au@GSST. The integration of the Au core facilitates the phase change process of GSST due to its plasmonic effect, which leads to lower heat capacity and higher heat conductivity of the AuNP. These characteristics accelerate the GSST phase change process at a lower continuous wave (CW) laser intensity compared to a bare GSST nanoparticle. An induced photothermal process that includes heat transfer, the crystalline fraction, and the electric field enhancement of the Au@GSST, as functions of the laser wavelength and intensity is investigated. Our results show that through this process, the GSST shell can be tuned between fully amorphous, intermediate, and fully crystalline states. This phase transition leads to a substantial modification of the optical responses of the Au@GSST. The absorption, scattering and extinction cross-sections of the structure over a wide range of wavelengths before and after the GSST phase transition is studied. We focus on two specific wavelengths, 778 nm and 919 nm, which exhibit higher light absorption contrast in both the amorphous and crystalline phases of GSST. Such active tunning of Au@GSST without morphological variation can be utilized in reconfigurable nanophotonic devices, such as switches, modulators, and sensors.