Peculiar rotation of electron vortex beams

International audienceStandard electron optics predicts Larmor image rotation in the magnetic lens field of a TEM. Introducing the possibility to produce electron vortex beams with quantized orbital angular momentum brought up the question of their rotational dynamics in the presence of a magnetic field. Recently, it has been shown that electron vortex beams can be prepared as free electron Landau states showing peculiar rotational dynamics, including no and cyclotron (double-Larmor) rotation. Additionally very fast Gouy rotation of electron vortex beams has been observed. In this work a model is developed which reveals that the rotational dynamics of electron vortices are a combination of slow Larmor and fast Cony rotations and that the Landau states naturally occur in the transition region in between the two regimes. This more general picture is confirmed by experimental data showing an extended set of peculiar rotations, including no, cyclotron. Larmor and rapid Cony rotations all present in one single convergent electron vortex beam. (C) 2015 Elsevier B.V. All rights reserved

Nanoparticles as a support: CaO deposits on MgO cubes

International audienceMgO nanocubes with an average particle size of 8 nm were used to support thermally stable CaO deposits. Energy-filtered transmission electron microscopy (EFTEM) reveals their unprecedented high dispersion with sizes significantly below 4 nm. CaO-specific photoluminescence emission results from the photoexcitation of oxygen anions in edges and oxygen-terminated corners that, for the first time, are available at a sufficiently high concentration to be detected by ensemble averaging techniques. The presented approach can be easily extended to a variety of other thermally labile oxides that find important applications in optics, sensing, and catalysis and, on this base, can be incisively characterized

Threshold and efficiency for perforation of 1nm thick carbon nanomembranes with slow highly charged ions

Wilhelm RA, Gruber E, Ritter R, et al. Threshold and efficiency for perforation of 1nm thick carbon nanomembranes with slow highly charged ions. 2D Materials. 2015;2(3): 035009.Cross-linking of a self-assembled monolayer of 1,1'-biphenyl-4-thiol by low energy electron irradiation leads to the formation of a carbon nanomembrane, that is only 1 nm thick. Here we study the perforation of these freestanding membranes by slow highly charged ion irradiation with respect to the pore formation yield. It is found that a threshold in potential energy of the highly charged ions of about 10 keV must be exceeded in order to form round pores with tunable diameters in the range of 5-15 nm. Above this energy threshold, the efficiency for a single ion to form a pore increases from 70% to nearly 100% with increasing charge. These findings are verified by two independent methods, namely the analysis of individual membranes stacked together during irradiation and the detailed analysis of exit charge state spectra utilizing an electrostatic analyzer