Georges Hamaoui | Searcharxiv

arXiv2026

Enhancement of far-field thermal emission via polaritonic cavity modes

Controlling thermal emission is crucial for applications involving thermophotovoltaics, thermal sensing, imaging, and camouflage. While prior studies focused on the emission of thermally excited guided modes (TEGMs) inside cavities, their contribution to the far-field radiation outside cavities has remained unexplored. Here, we demonstrate a tunable far-field thermal channel enabled by TEGMs arising from the coupling of surface phonon-polaritons and cavity resonances. By combining infrared emissivity experiments with fluctuational electrodynamics simulations, we identify distinct spectral features marking the conversion of two-dimensionally confined polaritonic modes into three-dimensional radiative channels. We find that silicon cavities covered with SiO2 enhance the emissivity by up to 200% near the polaritonic spectral resonance, whereas bare silicon cavities yield only broadband enhancement. These findings provide experimental evidence of TEGMs and establish a simple cavity architecture as an effective and scalable platform for tailoring thermal radiation without complex nanofabrication.

cond-mat.mes-hall↗

arXiv2022

Wideband Mid Infrared Absorber using surface Doped Black Silicon

Black silicon (BSi) is a synthetic nanomaterial with high aspect ratio nano protrusions inducing several interesting properties such as a very large absorptivity of incident radiation. We have recently shown that heavily doping the BSi in volume enables to significantly enhance its mid infrared absorptivity and tune its spectral range of interest up to 20 micrometer. In the present letter, we explore the effect of surface doping on BSi radiative properties and it absorptance, in particular since surface doping enables reaching even larger dopant concentrations than volume doping but at more limited penetration depths. We considered 12 different wafers of BSi, fabricated with cryogenic plasma etching on n and p-type silicon wafers and doped using ion-implantation with different dopant types, dosages and ion beam energies leading to different dopant concentrations and profiles. The different wafers radiative properties, reflectance, transmittance and absorptance, are measured using Fourier transform infrared spectroscopy. We show that doping an n-type BSi wafer with Phosphorous with a dose of 10^17 atm/cm2 and an energy of 100 keV increases its absorptivity up to of 98% in the spectral range of 1-5 micrometer. We propose a simple phenomenological explanation of the observed results based on the dopant concentration profiles and the corresponding incident radiation penetration depth. Obtained results provide simple design rules and pave the way for using ion-implanted BSi for various applications such as solar energy harvesting, thermo-photovoltaics and infrared radiation sensing where both high absorptance and variable dopant concentration profiles are required.

cond-mat.mes-hall↗