In nanoscale science and technology, the ability to measure an object’s dimensions with nanometer accuracy is of paramount importance. The most precise tool for determining the lateral dimensions of patterns on a surface is scanning probe microscopy. Along the vertical coordinate, dimensions can be inferred using the fact that an incoming electron beam is attenuated depending on a material’s thickness (Fig. 1). For the past 50 years, researchers have thought that a universal law could be used to convert electron-attenuation factors into thicknesses for a broad range of electron energies (see note in Ref. [1]). The law, however, has barely been tested for low energies (1–50 eV)—a range of increasing scientific and technological importance. Now Daniël Geelen at Leiden University in the Netherlands and co-workers have characterized the propagation of electrons through multilayer graphene at these energies, showing clear deviations from the expected universal behavior [2]. Their analysis indicates that electron-beam attenuation is significantly affected by the band structure of the solid and is thus material dependent. The result will benefit the quantitative understanding of many techniques employing low-energy electron beams, including photoemission, microscopy, diffraction, and electron-beam lithography.

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