Unveiling the orbital angular momentum and acceleration of electron beams

New forms of electron beams have been intensively investigated recently, including vortex beams carrying orbital angular momentum, as well as Airy beams propagating along a parabolic trajectory. Their traits may be harnessed for applications in materials science, electron microscopy and interferometry, and so it is important to measure their properties with ease. Here we show how one may immediately quantify these beams' parameters without need for additional fabrication or non-standard microscopic tools. Our experimental results are backed by numerical simulations and analytic derivation.Comment: 2 figures in text, 2 in supplementar

Spectral and spatial shaping of Smith Purcell Radiation

The Smith Purcell effect, observed when an electron beam passes in the vicinity of a periodic structure, is a promising platform for the generation of electromagnetic radiation in previously-unreachable spectral ranges. However, most of the studies of this radiation were performed on simple periodic gratings, whose radiation spectrum exhibits a single peak and its higher harmonics predicted by a well-established dispersion relation. Here, we propose a method to shape the spatial and spectral far-field distribution of the radiation using complex periodic and aperiodic gratings. We show, theoretically and experimentally, that engineering multiple peak spectra with controlled widths located at desired wavelengths is achievable using Smith-Purcell radiation. Our method opens the way to free-electron driven sources with tailored angular and spectral response, and gives rise to focusing functionality for spectral ranges where lenses are unavailable or inefficient

Spherical aberration correction in a scanning transmission electron microscope using a sculpted foil

Nearly twenty years ago, following a sixty year struggle, scientists succeeded in correcting the bane of electron lenses, spherical aberration, using electromagnetic aberration correction. However, such correctors necessitate re-engineering of the electron column, additional space, a power supply, water cooling, and other requirements. Here, we show how modern nanofabrication techniques can be used to surpass the resolution of an uncorrected scanning transmission electron microscope more simply by sculpting a foil of material into a refractive corrector that negates spherical aberration. This corrector can be fabricated at low cost using a simple process and installed on existing electron microscopes without changing their hardware, thereby providing an immediate upgrade to spatial resolution. Using our corrector, we reveal features of Si and Cu samples that cannot be resolved in the uncorrected microscope.Comment: Roy Shiloh, Roei Remez, and Peng-Han Lu equally contributed to this wor

Molecular Control of Structural Dynamics and Conductance Switching in Bismuth Nanoparticles

Bismuth nanoparticles, protected by two types of capping ligands, 1-dodecanethiol and ethylene diamine tetra-acetate, were probed by TEM and STM at 80 and 300 K. Both types of nanoparticles show temperature-dependent structural fluctuations leading to pronounced changes in their anisotropic conductance properties. We show that the different capping ligands dramatically alter the structural dynamics in these particles. This finding suggests that molecular control of structural and consequently electronic switching in anisotropic nanosystems is feasible

Molecular Control of Structural Dynamics and Conductance Switching in Bismuth Nanoparticles

Bismuth nanoparticles, protected by two types of capping ligands, 1-dodecanethiol and ethylene diamine tetra-acetate, were probed by TEM and STM at 80 and 300 K. Both types of nanoparticles show temperature-dependent structural fluctuations leading to pronounced changes in their anisotropic conductance properties. We show that the different capping ligands dramatically alter the structural dynamics in these particles. This finding suggests that molecular control of structural and consequently electronic switching in anisotropic nanosystems is feasible

Large Anisotropic Conductance and Band Gap Fluctuations in Nearly Round-Shape Bismuth Nanoparticles

Unlike their bulk counterpart, nanoparticles often show spontaneous fluctuations in their crystal structure at constant temperature [Iijima, S.; Ichihashi T. <i>Phys. Rev. Lett.</i> <b>1985</b>, <i>56</i>, 616; Ajayan, P. M.; Marks L. D. <i>Phys. Rev. Lett.</i> <b>1988</b>, <i>60</i>, 585; Ben-David, T.; Lereah, Y.; Deutscher, G.; Penisson, J. M.; Bourret, A.; Korman, R.; Cheyssac, P. <i>Phys. Rev. Lett.</i> <b>1997</b>, <i>78</i>, 2585]. This phenomenon takes place whenever the net gain in the surface energy of the particles outweighs the energy cost of internal strain. The configurational space is then densely populated due to shallow free-energy barriers between structural local minima. Here we report that in the case of bismuth (Bi) nanoparticles (BiNPs), given the high anisotropy of the mass tensor of their charge carriers, structural fluctuations result in substantial dynamic changes in their electronic and conductance properties. Transmission electron microscopy is used to probe the stochastic dynamic structural fluctuations of selected BiNPs. The related fluctuations in the electronic band structure and conductance properties are studied by scanning tunneling spectroscopy and are shown to be temperature dependent. Continuous probing of the conductance of individual BiNPs reveals corresponding dynamic fluctuations (as high as 1 eV) in their apparent band gap. At 80 K, upon freezing of structural fluctuations, conductance anisotropy in BiNPs is detected as band gap variations as a function of tip position above individual particles. BiNPs offer a unique system to explore anisotropy in zero-dimension conductors as well as the dynamic nature of nanoparticles