Erfan Mafakheri

Highly efficient electron vortex beams generated by nanofabricated phase holograms

We propose an improved type of holographic-plate suitable for the shaping of electron beams. The plate is fabricated by a focused ion beam on a silicon nitride membrane and introduces a controllable phase shift to the electron wavefunction. We adopted the optimal blazed-profile design for the phase hologram, which results in the generation of highly efficient (25%) electron vortex beams. This approach paves the route towards applications in nano-scale imaging and materials science.

Holographic Generation of Highly Twisted Electron Beams

Free electrons can possess an intrinsic orbital angular momentum, similar to those in an electron cloud, upon free-space propagation. The wave front corresponding to the electrons wave function forms a helical structure with a number of twists given by the angular speed. Beams with a high number of twists are of particular interest because they carry a high magnetic moment about the propagation axis. Among several different techniques, electron holography seems to be a promising approach to shape a conventional electron beam into a helical form with large values of angular momentum. Here, we propose and manufacture a nanofabricated phase hologram for generating a beam of this kind with an orbital angular momentum up to 200ℏ. Based on a novel technique the value of orbital angular momentum of the generated beam is measured and then compared with simulations. Our work, apart from the technological achievements, may lead to a way of generating electron beams with a high quanta of magnetic moment along the propagation direction and, thus, may be used in the study of the magnetic properties of materials and for manipulating nanoparticles.

Realization of electron vortices with large orbital angular momentum using miniature holograms fabricated by electron beam lithography

Free electron beams that carry high values of orbital angular momentum (OAM) possess large magnetic moments along the propagation direction. This makes them an ideal probe for measuring the electronic and magnetic properties of materials, and for fundamental experiments in magnetism. However, their generation requires the use of complex diffractive elements, which usually take the form of nano-fabricated holograms. Here, we show how the limitations of focused ion beam milling in the fabrication of such holograms can be overcome by using electron beam lithography. We demonstrate experimentally the realization of an electron vortex beam with the largest OAM value that has yet been reported (L = 1000h\bar), paving the way for even more demanding demonstrations and applications of electron beam shaping.

Generation and application of bessel beams in electron microscopy

We report a systematic treatment of the holographic generation of electron Bessel beams, with a view to applications in electron microscopy. We describe in detail the theory underlying hologram patterning, as well as the actual electron-optical configuration used experimentally. We show that by optimizing our nanofabrication recipe, electron Bessel beams can be generated with relative efficiencies reaching 37±3%. We also demonstrate by tuning various hologram parameters that electron Bessel beams can be produced with many visible rings, making them ideal for interferometric applications, or in more highly localized forms with fewer rings, more suitable for imaging. We describe the settings required to tune beam localization in this way, and explore beam and hologram configurations that allow the convergences and topological charges of electron Bessel beams to be controlled. We also characterize the phase structure of the Bessel beams generated with our technique, using a simulation procedure that accounts for imperfections in the hologram manufacturing process.

Measuring the orbital angular momentum spectrum of an electron beam

Electron waves that carry orbital angular momentum (OAM) are characterized by a quantized and unbounded magnetic dipole moment parallel to their propagation direction. When interacting with magnetic materials, the wavefunctions of such electrons are inherently modified. Such variations therefore motivate the need to analyse electron wavefunctions, especially their wavefronts, to obtain information regarding the materials structure. Here, we propose, design and demonstrate the performance of a device based on nanoscale holograms for measuring an electrons OAM components by spatially separating them. We sort pure and superposed OAM states of electrons with OAM values of between −10 and 10. We employ the device to analyse the OAM spectrum of electrons that have been affected by a micron-scale magnetic dipole, thus establishing that our sorter can be an instrument for nanoscale magnetic spectroscopy.

Holograms for the Generation of Vortex States with L=500h Fabricated by Electron Beam Lithography

1. Dipartimento FIM, Università di Modena e Reggio Emilia, Via G. Campi 213/a, I-41125 Modena, Italy 2. CNR-Istituto Nanoscienze, Centro S3, Via G. Campi 213/a, I-41125 Modena, Italy 3. CNR-IMEM Parco Area delle Scienze 37/A, I-43124 Parma, Italy 4. CNR-IMM, Via P. Gobetti 101, I-40129 Bologna, Italy 5. Department of Physics, University of Ottawa, 25 Templeton, Ottawa, Ontario, K1N 6N5 Canada 6. Institute of Optics, University of Rochester, Rochester, New York 14627, USA

Structured Electron Beam Illumination: A New Control Over the Electron Probe Weird Probes and New Experiments

1. CNR-Istituto Nanoscienze, Centro S3, Via G. Campi 213/a, I-41125 Modena, Italy 2. CNR-IMEM Parco Area delle Scienze 37/A, I-43124 Parma, Italy 3. Department of Physics, University of Oregon, Eugene, 97403-1274 Oregon, USA 4. Department of Physics, University of Ottawa, 25 Templeton, Ottawa, Ontario, K1N 6N5 Canada 5. CNR-IMM Bologna, Via P. Gobetti 101, 40129 Bologna, Italy 6. Dipartimento FIM, Universitá di Modena e Reggio Emilia, Via G. Campi 213/a, I-41125 Modena, Italy 7. Institute of Optics, University of Rochester, Rochester, New York 14627, USA

Experiments and Potentialities for the use of Bessel Beam in Superresolution STEM

1. CNR-Istituto Nanoscienze, Centro S3, Via G Campi 213/a, I-41125 Modena, Italy 2. CNR-IMEM, Parco delle Scienze 37a, I-43100 Parma, Italy. 3. Department of Physics, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada 4. CNR-IMM Bologna, Via P. Gobetti 101, 40129 Bologna, Italy 5. Dipartimento FIM, Universitá di Modena e Reggio Emilia, Via G. Campi 213/a, 41125 Modena, Italy 6. Institute of Optics, University of Rochester, Rochester, New York 14627, USA

Innovative Phase Plates for Beam Shaping

1. CNR-Istituto Nanoscienze, Centro S3, Via G Campi 213/a, I-41125 Modena, Italy 2. CNR-IMEM, Parco delle Scienze 37a, I-43100 Parma, Italy 3. Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario K1N 6N5, Canada 4. CNR-IMM Bologna, Via P. Gobetti 101, 40129 Bologna, Italy 5. Dipartimento FIM, Universita di Modena e Reggio Emilia, Via G. Campi 213/a, 41125 Modena, Italy 6. Institute of Optics, University of Rochester, Rochester, New York 14627, USA