Fig. 4: Spatially resolved magnon EELS measurements across a NiO thin film.

a, High-angle annular-dark-field image of a 30-nm NiO thin film grown on a YSZ substrate. b, Experimental diffraction pattern along the NiO \([\bar{1}10]\) zone axis at a 31 mrad semi-convergence angle, with the monochromating slit inserted, showing the off-axis displacement of the round EELS collection aperture along the [002] direction (marked by the black arrow). c, Asymmetric (displaced) annular-dark-field image acquired during EELS measurements. d, Integrated intensity map of the magnon peak over the energy window indicated by a shaded area, after background subtraction, as illustrated in e with the signal integrated over the whole NiO film area (the background-subtracted version is presented, pink curve, inset). Scale bars, 15 nm (a); 7.7 Å⁻¹, 60 mrad (b); 5 nm (c,d).