Thermal and blackbody radiations are tightly entangled with the material’s quantum properties for any finite temperature above 0 K. Such radiation is incoherent, both spatially and temporally. However, this characteristic change abruptly in the optical near-field region where it is related to the local density of photonic states (LDOS) [1]. Near-field thermal emission experiences huge amplification close to the epsilon-near-zero (ENZ) spectral region, i.e. at those specific LDOS phonon resonances where the material’s complex dielectric permittivity ε approaches zero. It may lead to narrow-band emission, directionality and coherence properties. Here, we investigate the near-field of anisotropic two-dimensional ENZ materials (Hexagonal boron nitride and α-Molybdenum Trioxide) with Synchrotron Infrared Nano-Spectroscopy and s-SNOM imaging using quantum cascade lasers. Theoretical and numerical investigations confirm the observed enhanced oscillating behaviour of the LDOS around the ENZ frequency. Tuning of the emission properties of 2D ENZ material via external control of the temperature is also demonstrated using a setup for nano-imaging at low temperature.
Phyllosilicate minerals are an emerging class of naturally occurring layered insulators with large bandgap energy that have gained considerable attention from the scientific community. This class of lamellar materials has been recently explored at the ultrathin two-dimensional level due to their specific mechanical and optoelectronic properties, which are crucial for engineering novel devices (including heterostructures). Due to these properties, phyllosilicate minerals can be considered promising low-cost nanomaterials for future electronics, photonics, and optoelectronics applications. Here, we will provide an overview of nano-optics and local chemistry of various 2D natural phyllosilicates by IR s-SNOM. Also, the relevant features of these layered materials for their use in potential optoelectronic applications will be presented.
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