Complementary LEEM and eV-TEM for imaging and spectroscopy

TL;DR

This paper introduces a combined low energy electron microscopy and eV-TEM technique that enables damage-free imaging and spectroscopy of delicate biological samples at nanometer resolution, demonstrated on graphene, gold nanoparticles, and DNA origami.

Contribution

The paper presents a novel setup combining LEEM and eV-TEM for imaging in the 0-30 eV range, enabling damage-free, high-resolution imaging of biological samples.

Findings

Successful imaging of graphene in transmission and reflection modes.

Clear micrographs of gold nanoparticles and DNA origami on graphene.

DNA structures remain stable under low energy electron illumination.

Abstract

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.