Secondary Electron Emission Materials for Transmission Dynodes in Novel Photomultipliers: A Review

Secondary electron emission materials are reviewed with the aim of providing guidelines for the future development of novel transmission dynodes. Materials with reflection secondary electron yield higher than three and transmission secondary electron yield higher than one are tabulated for easy reference. Generations of transmission dynodes are listed in the order of the invention time with a special focus on the most recent atomic-layer-deposition synthesized transmission dynodes. Based on the knowledge gained from the survey of secondary election emission materials with high secondary electron yield, an outlook of possible improvements upon the state-of-the-art transmission dynodes is provided.

Mapping Conductance and Switching Behavior of Graphene Devices In Situ

Graphene is proposed for use in various nanodevice designs, many of which harness emergent quantum properties for device functionality. However, visualization, measurement, and manipulation become nontrivial at nanometer and atomic scales, representing a significant challenge for device fabrication, characterization, and optimization at length scales where quantum effects emerge. Here, proof of principle results at the crossroads between 2D nanoelectronic devices, e-beam-induced modulation, and imaging with secondary electron e-beam induced currents (SEEBIC) is presented. A device platform compatible with scanning transmission electron microscopy investigations is introduced. Then how the SEEBIC imaging technique can be used to visualize conductance and connectivity in single layer graphene nanodevices, even while supported on a thicker substrate (conditions under which conventional imaging fails) is shown. Finally, it is shown that the SEEBIC imaging technique can detect subtle differences in charge transport through time in nonohmic graphene nanoconstrictions indicating the potential to reveal dynamic electronic processes.

The Role of Molecular Structure in Monte Carlo Simulations of the Secondary Electron Yield and Backscattering Coefficient from Methacrylic Acid

In this paper, we show the influence of the chemical structure of four different conformers on the secondary electron emission and backscattering of an electron beam from a gel of methacrylic acid. The conformers have different permanent dipole moments, which determines the cross sections for elastic collisions with electrons. The cross sections are used in Monte Carlo simulations of an electron beam, which enters the gel of methacrylic acid. The secondary electron yield and the backscattering coefficient are computed as a function of the beam energy.

Study of TiO2 on the Voltage Holdoff Capacity of Cr/Mn-Doped Al2O3 Ceramic in Vacuum

With the development of vacuum electronic devices toward high power, high frequency, and miniaturization, the voltage holdoff capacity of the insulation materials in devices has also been raised to a higher demand. Cr/Mn/Ti-doped Al₂O₃ ceramics were prepared, and the bulk density, micromorphology, phase composition, resistivity, secondary electron emission coefficient, and surface flashover threshold in the vacuum of the Al₂O₃ were characterized. The results show that the addition of TiO₂ to the Al₂O₃ ceramic can promote the sintering of the ceramic. The Cr/Mn/Ti-doped Al₂O₃ ceramic with a homogeneous microstructure can be obtained by an appropriate amount of TiO₂ addition. In the process of the heat treatment, the TiO₂ in the ceramics was reduced to a certain degree, which had an impact on the microstructure of the Al₂O₃ ceramic. Adding a small amount of TiO₂ can improve the voltage holdoff performance in the vacuum. The value of the surface flashover threshold in the vacuum of the Cr/Mn/Ti-doped Al₂O₃ ceramic containing 1 wt.% TiO₂ reached a value of 33 kV, which is 32% higher than that of the basic Al₂O₃ ceramic. The preparation of Al₂O₃ ceramics with a high voltage holdoff capacity in a vacuum provides fundamental technical support for the development of vacuum electronic devices.

Imaging Secondary Electron Emission from a Single Atomic Layer

Graphene-based devices hold promise for a wide range of technological applications. Yet characterizing the structure and the electrical properties of a material that is only one atomic layer thick still poses technical challenges. Recent investigations indicate that secondary-electron electron-beam-induced current (SE-EBIC) imaging can reveal subtle details regarding electrical conductivity and electron transport with high spatial resolution. Here, it is shown that the SEEBIC imaging mode can be used to detect suspended single layers of graphene and distinguish between different numbers of layers. Pristine and contaminated areas of graphene are also compared to show that pristine graphene exhibits a substantially lower SE yield than contaminated regions. This SEEBIC imaging mode may provide valuable information for the engineering of surface coatings where SE yield is a priority.

Ferrites with a Minimized Secondary Electron Yield

Ferrites are an essential material in modern industry due to their exceptional magnetic properties and high resistivity. Many applications of ferrites necessitate exposure to high energy electrons, particularly space science and particle accelerators, where charging, multipacting, and electron clouds (ECs) are major issues. ECs are of particular concern around the Ni/Zn soft ferrite kicker magnets as the large hadron collider (LHC) undergoes its high luminosity upgrade. Here, laser engineered surface structures (LESS) are used to reduce the secondary electron yield (SEY) of Ni/Zn ferrites from 2.1 to its experimentally determined minimum of 0.81, eliminating the ferrites ability to contribute to the formation of ECs. This demonstrates the applicability of LESS outside of metals and its broader applicability to reducing the SEY of technical materials.