Hardware Development

Aberration-corrected Imaging

In collaboration with Nigel Browning, UCD and LLNL, and Angus Kirkland, Oxford, UK, we evaluated the usability of aberration corrected TEM imaging for biological samples, a work that resulted in direct images of Si [110] at 1.1 Å, and of Paraffin at 1.6 Å, all under cryo-low dose conditions (Evans et al., Ultramic., in press). While aberration corrected TEM imaging is not interesting in the general case for biological samples, our work paves the path to aberration corrected imaging TEM in combination with a phase plate for optimal contrast of biological specimens.

One of the main bottlenecks in biological electron microscopy is caused by the beam-induced resolution loss when imaging tilted cryo-EM samples. This affects all types of cryo-EM that have to tilt the sample. In collaboration with Browning, we now have collected data that prove that STEM imaging of tilted frozen hydrated cryo-EM samples is not affected from that resolution loss. The problem with conventional STEM, however, is the absence of phase contrast and a high electron dose or dose-rate. We have developed the theory and computer simulations, and are in the process of implementing high-resolution low-dose phase-contrast STEM of tilted biological cryo-EM samples (James Buban). This development involves aberration corrected illumination, multi-channel multi-ring bright-field and dark-field detectors, while ultrafast beam and instrument control for dynamic focusing on tilted sample planes allow recording of the data. We have data that show that the simultaneous collection of the BF and HAADF signals from an aberration corrected STEM allows access to the phase-contrast signal at good signal-to-noise ratio per beam-damage.