Abstract
We report the first thermal study of a triple band plasmonic nanoantenna strongly coupled to a molecular mode at mid IR wavelength (MW IR). The hybrid plasmonic structure supports three spatially and spectrally variant resonances of which two are magnetic and one is dipolar in nature. A hybridized mode is excited by coupling the structure’s plasmonic mode with the vibrational mode of PMMA at 5.79 μm. Qualitative agreement between the spectral changes in simulation and experiment clearly indicates that resistive heating is the dominant mechanisms behind the intensity changes of the dipolar and magnetic peaks. The study also unveils the thermal insensitivity of the coupled mode intensity as the temperature is increased. We propose a mechanism to reduce the relative intensity change of the coupled mode at elevated temperature by mode detuning and surface current engineering and demonstrate less than 9% intensity variation. Later, we perform a temperature cycling test and investigate into the degradation of the Au-PMMA composite device. The failure condition is identified to be primarily associated with the surface chemistry of the material interface rather than the deformation of the nanopatterns. The study reveals the robustness of the strongly coupled hybridized mode even under multiple cycling.
Highlights
Potentially feasible for integration of real time plasmonic detection with microfluidics due to their enhanced integral response[15]
The PMMA surface is typically thiolated before the gold deposition[19] there has not been any study on the thermal degradation of viscoelastic PMMA thin film directly spin cast on the gold patterns for photonic applications demanding large resonance contrast with asymmetric profile
This work studies the reliability of the Au-PMMA composite device over multiple thermal cycles within a moderate temperature range (25–125 deg.) and links the failure condition with the Au-PMMA and SiO2-PMMA surface chemistry rather than any structural deformation of the nanopatterns
Summary
Dihan Hasan[1,2,3,4], Chong Pei Ho1,2,4, Prakash Pitchappa[1,2,4], Bin Yang[3], Chunsheng Yang3 & Chengkuo Lee[1,2,4]. This work studies the reliability of the Au-PMMA composite device over multiple thermal cycles within a moderate temperature range (25–125 deg.) and links the failure condition with the Au-PMMA and SiO2-PMMA surface chemistry rather than any structural deformation of the nanopatterns. The modification includes etching plasmonic voids following the algorithm of a 2nd order Sierpiński gasket[22] in order to pursue three specific objectives: (i) to lessen the intrinsic damping effect on the quality factor by reducing metal surface area (ii) to excite both dipolar and magnetic resonance on the same platform and (iii) to reduce the impact of thermal expansion coefficient (TEC) mismatch between the pattern and the substrate and to increase the spatial field coupling between the pattern and the overlayer (superstrate). Only reflection signal can be captured while the heating stage is incorporated (Figure S1, supplementary information)
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