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Novel spectroscopic experiments through probe shaping in the TEM - Johan Verbeeck

Pays-Bas - (Bât T-18 – Parc Club Orsay)


Transmission electron microscopy (TEM) has provided an wealth of information about the microscopic world around us. Compared to light microscopy, it offers the benefit of atomic spatial resolution even though the wave optical concepts it is based on are often mimicking earlier technological developments in light microscopy. This is mostly due to the difficulty of designing arbitrary shaped lenses for TEM leading to the perhaps surprising fact that electron microscopy in its current state is still very far from being limited by the ultimate wavelength barrier. Indeed, a modern state of the art aberration corrected TEM delivers a numerical aperture of a mere NA 0.02, compared to light microscopy where even a modest instrument can deliver diffraction limited imaging at NA>1. In this presentation we take a close look at a development in optical microscopy that has dramatically expanded the capabilities of optical microscopy over the last decades : the ability to arbitrarily adapt the phase of light waves in optical instruments. Several examples of breakthrough achievements with this technology will be shown leading to the natural question : would this also be possible for electron waves ? We will treat this question from both the hypothetical assumption that a programmable phase manipulating device would exist for electrons, focusing on the possibilities it would open. On a more realistic note, we will explore novel experimental realisations of setups where phase manipulation already leads to improved detection of sample features. Examples include the use of electron vortex beams to bring out magnetic information as well as a measurement of crystal chirality and their potential to act as quantum edge enhancement filters for weak phase objects. We explore the class of pi-beams showing their potential to mimic the effect of polarisation in light optics for the excitation of surface plasmon polaritons in nanoparticles. Also so-called nondiffracting beams are experimentally realised and their possible uses are discussed. All these experimental realisations show that TEM might well be on the verge of yet another breakthrough where adaptive optics and versatile phase manipulation can expand the capabilities of TEM as a materials characterisation tool even further.

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