Generation and analysis of electron beams are of great use still today to elucidate electronic and microscopic features of solid materials. Some interesting methods, in terms of visualization of physical property at the sub-micrometer-scale structures, are addressed from researchers’ view point in the fields of material science and technology. Readers will conceive something new in the introduced articles that appear in this special issue of the journal.
Recent progress of the microfabricated field emitter array (FEA) and the planar type electron source is overviewed. The volcano-structured double-gate FEA is promising for obtaining matrix driven and focused electron beams. The beam half angle less than one degree was achieved by using this structure. High current density of more than 25 A/cm2 is also achieved by using nickel-based alloy as an emitter material. A major breakthrough in the field of planar type electron sources is a using graphene as a top electrode in Metal/Oxide/Semiconductor type emitter, which is owing to the development of the direct deposition technique of graphene on insulating material. The emission efficiency of more than 30% is achieved. The graphene/oxide/semiconductor type electron source can emit electrons not only in poor vacuum but also in liquid. This unique feature enables new application, such as hydrogen production using non-electrolyte aqueous solution by injecting low energy electrons.
Over the last half century an experimental method has been developed for measuring momentum density distributions of each electron bound in a molecule or looking at spatial patterns of individual molecular orbitals in momentum space. The method, called electron momentum spectroscopy, is based on the electron-impact ionizing reaction by Compton scattering that occurs near the Bethe ridge at incident electron energies of the order of 1 keV or higher. This account reviews frontiers of the field, as well as another application of electron Compton scattering, that is, direct observation of intramolecular motions of each constituting atom.
In this review, our recent study on spin-polarized field electron emitter using Cr(001) surface and Heusler alloy Co2MnGa is described. To obtain a stable and highly spin-polarized electron beam by the field emission, the surface structure of emitters was well-characterized by field ion microscopy (FIM). The atomically clean surface of Cr/W(001) and ⟨100⟩-oriented Co2MnGa emitter realized values of spin polarization of 50% and 60%, respectively, which consistent with spin polarization at the Fermi level predicted theoretically. Especially, the maximum spin polarization of 75% obtained from the Co2MnGa(100) surface is higher than that from other transition metals reported previously. Additionally, it is important for the highly spin-polarized field emitter to keep the clean surface. Our results will promise to equip the spin-polarized field emitters to instruments for spin-resolved analysis.
Field-emission electron source and Shottky-emission electron source are used for higher-resolution scanning electron microscope (SEM). The resolution is limited by reduced brightness and electron energy distribution of electron source. The development of the electron source with higher reduced brightness and lower electron distribution is expected for future SEM.