Low-loss EELS of 2D boron nitride

Electron energy loss spectroscopy provides a probe of the dielectric function of a material which can be affected by the size and morphology of a sample. In this paper, the effect on the loss function when hexagonal boron nitride is reduced to a single layer is investigated. The previously predicted red-shift of the spectrum is seen in experiment and reproduced by modelling using density functional theory. The dielectric function shows that, for a single layer, the lack of screening causes the real part of the dielectric function to tend to 1 so that the loss function resembles the imaginary part of the dielectric function.