Research to better ‘shape’ the electron beam, particularly to overcome lens aberrations, has been active since the beginnings of electron microscopy [8]. Modern electron microscope aberration correctors are the culmination of extensive work, relying upon high tolerance multipole magnetic and/or electrostatic lenses and electronics, coupled with computational controls [9]. Alternatives to using these multipole lenses include mirror correctors and placing partially transmissive objects in the beam path[12-14]. The latter approaches, where the beam no longer traverses purely through vacuum before reaching the sample, or before reaching the detectors has seen particular appeal in recent years, owing to the relative ease with which nm level accuracy can now be achieved on microfabricated components.

This is exemplified in experiments that placed holographic gratings into electron microscopes to produce vortex beams [16], where the resulting orbital angular momentum offers a new means to explore magnetic properties, for example [17, 18]. Since this work, a wide variety of beam profiles have been produced, see e.g. [15, 19]. It was also found that shaped or ‘phase sculpted’ beams, produced by phase-plates or gratings placed in the beam, offer advantages for ptychographic methods and 4D-STEM by either improved robustness in the reconstruction [20] or promoting stronger or more linear contrast [21]. Phase plates are also used in conventional TEM to improve phase contrast[22]. Indeed, recent developments of hole-free Zernike type plates [23, 24] have dramatically increased their use, and they are now becoming more commonplace in cryo-EM biological molecule structure determination[25], through offering superior phase contrast transfer characteristics.

Such elements are being microfabricated at UVic to shape the electron beam, which combined with our dual aberration corrected TEM equipped with multiple bi-prisms, allows the creation of unique electron beam profiles. These are being researched for enhanced information transfer from ‘phase-objects’ such as biological samples, and for investigation of magnetic phases and plasmonic behaviour of advanced materials at the ultimate resolution.

Electron beam induced changes in the sample, either temporary or permanent, often become the ultimate limit of the usefulness of the information provided by the electron microscope[26]. Changes induced include atomic displacement, e-beam sputtering, structural damage, mass loss, specimen heating, and material deposition, and electrostatic charging. These processes typically occur on timescales < 1 sec, and in proteins, for example, changes significant enough to result in incorrect structure determination can occur with electron doses above 10 e^–/Ų, at typical beam energies[27]. Techniques to investigate and mitigate this generally involve some degree of electron dose fractionation, so that in effect time resolved imaging is employed, which can for example be drift corrected[28]. Alternatively or in combination with this it appears that carefully controlling the timing of electrons arriving on the sample can be used to mitigate damage mechanisms [29]. Using our pixelated direct electron detector, with its unique high-speed triggering and exposure capabilities, these effects are being investigated.