Tailoring Tamm Plasmon Resonances in Dielectric Nanoporous Photonic Crystals

The fields of plasmonics and photonic crystals (PCs) have been combined to generate model light-confining Tamm plasmon (TMM) cavities. This approach effectively overcomes the intrinsic limit of diffraction faced by dielectric cavities and mitigates losses associated with the inherent properties of plasmonic materials. In this study, nanoporous anodic alumina PCs, produced by two-step sinusoidal pulse anodization, are used as a model dielectric platform to establish the methodology for tailoring light confinement through TMM resonances. These model dielectric mirrors feature highly organized nanopores and narrow bandwidth photonic stopbands (PSBs) across different positions of the spectrum. Different types of metallic films (gold, silver, and aluminum) were coated on the top of these model dielectric mirrors. By structuring the features of the plasmonic and photonic components of these hybrid structures, the characteristics of TMM resonances were studied to elucidate effective approaches to optimize the light-confining capability of this hybrid TMM model system. Our findings indicate that the coupling of photonic and plasmonic modes is maximized when the PSB of the model dielectric mirror is broad and located within the midvisible region. It was also found that thicker metal films enhance the quality of the confined light. Gas sensing experiments were performed on optimized TMM systems, and their sensitivity was assessed in real time to demonstrate their applicability. Ag films provide superior performance in achieving the highest sensitivity (S = 0.038 ± 0.001 nm ppm-1) based on specific binding interactions between thiol-containing molecules and metal films.

Impact of Different Metals on the Performance of Slab Tamm Plasmon Resonators

We investigate the concept of slab Tamm plasmons (STP) in regard to their properties as resonant absorber or emitter structures in the mid-infrared spectral region. In particular, we compare the selective absorption characteristics resulting from different choices of absorbing material, namely Ag, W, Mo or highly doped Si. We devised a simplified optimization procedure using finite element simulations for the calculation of the absorption together with the application of micro-genetic algorithm (GA) optimization. As characteristic for plasmonic structures, the specific choice of the metallic absorber material strongly determines the achievable quality factor (Q). We show that STP absorbers are able to mitigate the degradation of Q for less reflective metals or even non-metals such as doped silicon as plasmonic absorber material. Moreover, our results strongly indicate that the maximum achievable plasmon-enhanced absorption does not depend on the choice of the plasmonic material presuming an optimized configuration is obtained via the GA process. As a result, absorptances in the order of 50-80% could be achieved for any absorber material depending on the slab thickness (up to 1.1 µm) and a target resonance wavelength of 4.26 µm (CO₂ absorption line). The proposed structures are compatible with modern semiconductor mass fabrication processes. At the same time, the optimization procedure allows us to choose the best plasmonic material for the corresponding application of the STP structure. Therefore, we believe that our results represent crucial advances towards corresponding integrated resonant absorber and thermal emitter components.

Effect of metal film thickness on Tamm plasmon-coupled emission

Tamm plasmons (TPs) are the result of trapping optical energy at the interface between a metal film and a one-dimensional photonic crystal. In contrast to surface plasmons, TPs display unique properties such as the ability to undergo direct optical excitation without the aid of prisms or gratings, being populated using both S- and P-polarized light, and importantly, they can be created with incident light normal to the surface. This latter property has recently been used to obtain Tamm plasmon-coupled emission (TPCE), which beams along a path directly perpendicular to the surface. In this paper the effects of metal film thickness on the TPCE are investigated using back focal plane (BFP) imaging and spectral resolutions. The observed experimental results are in agreement with the numerical simulations. The present work provides the basic understanding needed to design structures for TPCE, which in turn has potential applications in the fabrication of active materials for light emitting devices, fluorescence-based sensing, using microarrays, and imaging.