Electronic properties of black phosphorus using monochromated low-loss EELS

Highlights: • Monochromated EELS experiments on black phosphorus flakes are thoroughly investigated. • Excitonic binding energy of black phosphorus was determined. • Low bandgap and excitonic features of black phosphorus were detected by EELS. • Electronic properties of black phosphorus are found in accord with DFT properties. In the present study, monochromated low-loss electron energy-loss spectroscopy in a scanning transmission electron microscope, confronted with ab-initio calculations, is used to investigate the bandgap and excitons energies of black phosphorus flakes in the near infrared region. Due to the monochromation of the electron beam and to a spectrometer with an energy resolution of 20 meV, a direct measurement of the narrow bandgap energy, E₀, of about 0.33 eV was successful, along with an intraband electronic transition E₁ at around 0.75 eV. Interestingly, additional transitions, excitonic in nature, are identified at 0.42 eV and 0.55 eV, the intensity of which increases with decreasing thickness. All these findings demonstrate the ability of monochromated low-loss electron energy loss spectroscopy to reveal unprecedented electronic and excitonic transitions in very narrow bandgap semiconductors.