Sub-angstrom low-voltage performance of a monochromated, aberration-corrected transmission electron microscope.

Lowering the electron energy in the transmission electron microscope allows for a significant improvement in contrast of light elements and reduces knock-on damage for most materials. If low-voltage electron microscopes are defined as those with accelerating voltages below 100 kV, the introduction of aberration correctors and monochromators to the electron microscope column enables Angstrom-level resolution, which was previously reserved for higher voltage instruments. Decreasing electron energy has three important advantages: (1) knock-on damage is lower, which is critically important for sensitive materials such as graphene and carbon nanotubes; (2) cross sections for electron-energy-loss spectroscopy increase, improving signal-to-noise for chemical analysis; (3) elastic scattering cross sections increase, improving contrast in high-resolution, zero-loss images. The results presented indicate that decreasing the acceleration voltage from 200 kV to 80 kV in a monochromated, aberration-corrected microscope enhances the contrast while retaining sub-Angstrom resolution. These improvements in low-voltage performance are expected to produce many new results and enable a wealth of new experiments in materials science.