  Transmission electron microscopy at very low energy is a promising way to
avoid damaging delicate biological samples with the incident electrons, a known
problem in conventional transmission electron microscopy. For imaging in the
0-30 eV range, we added a second electron source to a low energy electron
microscopy (LEEM) setup, enabling imaging in both transmission and reflection
mode at nanometer (nm) resolution. The latter is experimentally demonstrated
for free-standing graphene. Exemplary eV-TEM micrographs of gold nanoparticles
suspended on graphene and of DNA origami rectangles on graphene oxide further
establish the capabilities of the technique. The long and short axes of the DNA
origami rectangles are discernable even after an hour of illumination with low
energy electrons. In combination with recent developments in 2D membranes,
allowing for versatile sample preparation, eV-TEM is paving the way to
damage-free imaging of biological samples at nm resolution.
