Optimizing Contrast in Automated 4D STEM Cryotomography.

4D STEM is an emerging approach to electron microscopy. While it was developed principally for high-resolution studies in materials science, the possibility to collect the entire transmitted flux makes it attractive for cryomicroscopy in application to life science and radiation-sensitive materials where dose efficiency is of utmost importance. We present a workflow to acquire tomographic tilt series of 4D STEM data sets using a segmented diode and an ultrafast pixelated detector, demonstrating the methods using a specimen of a T4 bacteriophage.

Quantitative atomic cross section analysis by 4D-STEM and EELS.

We demonstrate the use of a 4-dimensional scanning transmission electron microscope (4D-STEM) to extract atomic cross section information in amorphous materials. We measure the scattering amplitudes of 200 keV electrons in several representative specimens: amorphous carbon, silica, amorphous ice of pure water, and vitrified phosphate buffer solution. Diffraction patterns are recorded by 4D-STEM with or without energy filter at the zero-loss peak.

Synchronization of scanning probe and pixelated sensor for image-guided diffraction microscopy.

A 4-dimensional modality of a scanning transmission electron microscope (4D-STEM) acquires diffraction images formed by a coherent and focused electron beam scanning the specimen. Newly developed ultrafast detectors offer a possibility to acquire high throughput diffraction patterns at each pixel of the scan, enabling rapid tilt series acquisition for 4D-STEM tomography. Here we present a solution to the problem of synchronizing the electron probe scan with the diffraction image acquisition, and demonstrate on a fast hybrid-pixel detector camera (ARINA, DECTRIS).

Sampling theory perspective on tomographic tilt increment schemes.

Given a limited radiation exposure to be distributed over a discrete number of tilted projections in tomography, the optimal collection of information depends on the tilt increment scheme. Relying on principles of sampling theory, several tilt increment schemes can be compared and quantified. Following reasoning of Saxton, a revised scheme is offered in which the tilt angle increments Δθ are proportional to 1/cosθ.

ClusterAlign: A fiducial tracking and tilt series alignment tool for thick sample tomography.

Thick specimens, as encountered in cryo-scanning transmission electron tomography, offer special challenges to conventional reconstruction workflows. The visibility of features, including gold nanoparticles introduced as fiducial markers, varies strongly through the tilt series. As a result, tedious manual refinement may be required in order to produce a successful alignment.