The cold emission of particles from surfaces under intense electric fields is a process which underpins a variety of applications including atom probe tomography (APT), an analytical microscopy technique with near-atomic spatial resolution. Increasingly relying on fast laser pulsing to trigger the emission, APT experiments often incorporate the detection of molecular ions emitted from the specimen, in particular from covalently or ionically bonded materials. Notably, it has been proposed that neutral molecules can also be emitted during this process. However, this remains a contentious issue. To investigate the validity of this hypothesis, a careful review of the literature is combined with the development of new methods to treat experimental APT data, the modeling of ion trajectories, and the application of density-functional theory simulations to derive molecular ion energetics. It is shown that the direct thermal emission of neutral molecules is extremely unlikely. However, neutrals can still be formed in the course of an APT experiment by dissociation of metastable molecular ions. charged molecules (molecular ions) are regularly detected [30][31][32]. As detailed in thorough review articles by Mathur [33, 34], molecular ions have been the subject of intense studies in the field of mass spectrometry as they can form due to the impact of other charged particles or photons. Molecular ions are metastable and usually dissociate into smaller fragments. Beyond its fundamental interest, the dissociation of molecular ions is also a commonly encountered problem in mass spectrometry of (e.g.) organic compounds, and computational methods have often been used to interpret experimental observations [35]. In addition, molecular ions are known to be very reactive [36] and the dissociative recombination [37] of molecular ions is known to play a role in atmospheric and spatial chemical processes [38].The rate of publication of pulsed-laser APT data has surged in recent years [39,40]. In stark contrast, progress in understanding the fundamental physics of laser-assisted field evaporation, particularly for non-metals, has failed to keep pace. For metals, it is accepted that field evaporation is caused by a sharp increase in the specimen temperature due to the absorption of the light from each laser pulse, which is then quenched as the heat is transported inwards and then along the length of the shank [41] in a transient process that is often referred to as a thermal pulse [42,43]. The least conservative estimates for the case of a metal specimen predict temperature increases of up to a maximum of 600 K in tungsten [41] when the standing electric field is 75% of the intensity required to field evaporate the specimen without laser illumination. However, these are conditions that are not expected to yield good APT performance [44] and are usually avoided.Recent research indicated that the field evaporation mechanisms for semiconductors may differ to that of metals with high and fast phonon excitation that could result in very high ...

Electron microscopy touches on nearly every aspect of modern life, underpinning materials development for quantum computing, energy and medicine. We discuss the open, highly integrated and data-driven microscopy architecture needed to realize transformative discoveries in the coming decade.

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