S.1. Depth and Energy Response
The microscope used has a residual chromatic aberration of 1.2 mm in the confocal
trajectory providing an energy selection in EFSCEM with an energy resolution of 2.3 eV for
a point like pinhole.26 In order to increase signal counts, in this work, the size of the collector
aperture was increased to 0.32 nm in diameter, which however, deteriorates both energy and
depth response.
Fig. S1 shows the theoretical EFSCEM z-response as a function of sample height, z, and
energy deviation,  , for the experimental condition used with a collector aperture 0.32 nm in
diameter. This 2-D plot was generated by convolution of the ideal 2D response for a pointlike collector aperture (Fig. 4 in Ref 26) with the broadening functions introduced by the 0.32
nm collector aperture, along both z and  directions. To further examine the depth and energy
response, the two-dimensional plot shown in Fig. S1 has been projected to form both a zresponse (-o-), integrated over all possible electron losses and an energy filtering response (□-), integrated over all possible heights in a scattering plane. This provides an estimate for
the FWHM of the z-response of ca. 46 nm, and for the energy-response of ca. 7.8 eV. This
energy-response was smaller than the experimentally used energy selecting window of 20 eV
and therefore, the effective energy selecting window (ESW) was taken to be 7.8 eV, full
width half maximum.
Figure S1. Calculated effective energy selecting window imposed by a physical collector aperture
0.32 nm in diameter.