Fig. 1
From: Probing low-energy hyperbolic polaritons in van der Waals crystals with an electron microscope
STEM-EELS map of a hexagonal boron nitride flake. a STEM HAADF image of the h-BN flake on a TEM membrane. Brighter areas correspond to a larger h-BN thickness, black is the supporting TEM membrane. Scale bar, 500 nm. White dashed lines are guides marking steps on the flake surface, dash-dotted line marks the flake edge. Blue, red, and green rectangles mark the area from which the spectra in Fig. 4d were collected. Orange line shows where the data for Fig. 6c were taken from. b Typical spectra acquired on h-BN (open circles) and on an empty TEM membrane (magenta); the corresponding locations are marked, respectively, by magenta and blue crosses in a. Each spectrum is normalized to its ZLP maximum. Inset shows the 3D sketch of the sample topography from a. c Close-up view of the same spectrum as in b (open circles); the thick magenta curve shows the ZLP averaged along the horizontal magenta line in a. Closed circles show the spectrum after ZLP subtraction and the red curve shows a Gaussian fit. d Map of the peak position ω 0. Black color marks regions of insufficient signal level (below 2.5x10−4 threshold) and of otherwise irregular fits (see Methods for details). Black dashed and dash-dotted lines are the same eye guides as marked in a
