Momentum-Resolved Dielectric Response of Free-Standing Mono-, Bi-, and Trilayer Black Phosphorus

Abstract

Black phosphorus (BP), a 2D semiconducting material of interest in electronics and photonics, exhibits physical properties characterized by strong anisotropy and band gap energy that scales with reducing layer number. However, the investigation of its intrinsic properties is challenging because thin layer BP are photo oxidized in ambient conditions and the energy of their electronic states shift in different dielectric environment. We prepared free-standing samples of few layer BP in glovebox conditions and probed the dielectric response in vacuum using Scanning Transmission Electron Microscopy and Electron Energy Loss Spectroscopy (STEM-EELS). Thresholds of the excitation energy are measured at 1.9 eV, 1.4 eV and 1.1 eV for the mono-bi-and tri-layer BP, respectively and these values are used to estimate the corresponding optical band gaps.A comparison of our results with electronic structure calculations indicates that the variation of the quasi-particle gap is larger than that of the exciton binding energy. The dispersion of the plasmons versus momentum for 1-3 layer BP and bulk BP highlights a deviation from parabolic to linear dispersion and strong anisotropic fingerprints. Summary 1-Exfoliation and TEM grid preparation. 2-Layer number determination based on HAADF Z-contrast. 3-Computational details (gap and binding energy)1-Exfoliation and TEM grid preparation.

Systematic competition between strain and electric field stimuli in tuning EELS of phosphorene

“…On the other hand, the high-energy interband transitions correspond to the ZZ direction, while the low-energy ones belong to the AC direction. These all are in an excellent agreement with recent measurements [72][73][74] .…”

Isotropic or anisotropic screening in black phosphorous: Can doping tip the balance?

“…As shown in Fig. 2(c)-(d), the frequency-dependent dielectric function curves at q = 1.1 Å −1 show more obvious anisotropy than that at the long-wavelength limit, which is in agreement with previous results about the anisotropic dispersion of the plasmons versus momentum for BP [35]. The dielectric curves of single-layer BP in Fig.…”

“…At ω = 0 eV, real parts of dielectric function under longwavelength limit for two directions are slightly different, which is consist with the results in Table Ⅰ. The imaginary part of the permittivity describes the dissipation of energy, with −Im[1 ɛ (ω) ⁄ ] proportional to the electron energy loss spectroscopy (EELS) loss function [35]. The peak for imaginary part of dielectric function is closely related to the dispersion of the plasmons versus momentum.…”

Directional effects in plasmon excitation and transition radiation from an anisotropic 2D material induced by a fast charged particle

“…Moreover, ab initio calculations of the optical conductivity of phosphorene were performed in ref. 27–30 for a broad range of frequencies, from the THz to the vacuum ultraviolet (VUV). Incidentally, such a phenomenon has significant implications for functional photonic applications that require active tuning of directional light propagation, i.e.…”