Enhanced spontaneous emission of 2D materials on epsilon-near-zero substrates

Photoluminescence enhancement of MoS2 monolayers on TiN thin films grown on sapphire by molecular-beam-epitaxy (MBE) is observed. The PL spectra of MoS2 flakes on MBE-grown 58-nm-thick TiN crystalline film and on reference sapphire substrate are obtained at room temperature using a confocal laser scanning microscope with 405, 445, 488 and 561 nm excitation wavelengths. The maximum PL enhancement for B-exciton (6-fold) and A- trion (15-fold) is obtained at the excitation wavelength 488 nm that matches most closely to the epsilon-near-zero wavelength, 473 nm, of TiN film. A good agreement is observed between measured and calculated enhancements. The enhancement is attributed to increased light absorption when excitation wavelength matches the epsilon-near-zero wavelength of TiN film.