Intensity analysis of boron and nitrogen K-edge spectra for hexagonal boron nitride by EELS

Boron and nitrogen K-edge spectra for hexagonal boron nitride (h-BN) were measured by electron energy loss spectroscopy (EELS) at orientations of a momentum transfer q parallel and perpendicular to the c-axis in order to investigate anisotropic unoccupied states π* and σ*, separately. Differences between intensity profiles for B_K and N_K spectra are attributed to different transition probabilities at B_K and N_K edges from Is states to the π* and σ* states. The intensity of the first peak at q ∥ c in the B_K spectrum, which is ascribed to the transition from B-1s to the Q^—₂ state in the π* band, is 10 times as large as that in the N_K spectrum. Quantitative calculation of transition probabilities for B_K and N_K spectra at q ∥ c shows that the contribution of B-2p_z orbital to the Q^—₂ state is 1–7 times as large as that of N-2p_z. This value suggests that the enhanced peak in the B_K spectrum is explained by means of single electron excitations, disregarding the electron-electron interactions for the exciton reported by several workers. The contributions of 2p_x and 2p_y orbitals of B and N atoms to σ* states are also estimated by intensity analysis of B_K and N_K spectra at q⊥c .