Electron-emission materials: Advances, applications, and models

Abstract

Electron emission represents the key mechanism enabling the development of devices that have revolutionized modern science and technology. Today, science still relies on advanced electron-emission devices for imaging, electronics, sensing, and high-energy physics. New generations of emission devices are continuously being improved based on innovative materials and the introduction of novel physical concepts. Recent advances are highlighted by emerging low-work-function and low-dimensional materials with unusual electronic and thermal properties. Nanotubes, nanowires, graphene, and electron-emission models are discussed in this issue, as well as original mechanisms, such as the thermoelectronic effect, thermionic emission, and heat trap processes. Advances in electron-emission materials and physics are driving a renaissance in the fi eld, both opening up new applications, such as energy conversion and ultrafast electronics, as well as improving traditional applications in electron imaging and high-energy science. ELECTRON-EMISSION MATERIALS: ADVANCES, APPLICATIONS, AND MODELS 489MRS BULLETIN • VOLUME 42 • JULY 2017 • www.mrs.org/bulletin thermionic, and fi eld electron emission, or combinations of one or more of these. Each particular physical stimulus necessitates cathode materials with physical properties specifi cally engineered for optimal performance. This section will present an overview of the latest results on the development of advanced materials and related applications, categorized by the specifi c type of electron emission. Photoemission and secondary electron emissionPhotomultipliers remain the lowest noise, highest sensitivity, and fastest imaging systems. Used, for instance, in fl uorescence and laser scanning confocal microcopy, they exploit electron emission from a photocathode and, successively, secondary emissions from electron multiplying stages. Photons to be detected induce the emission of electrons from a material, usually a thin layer in transmission mode. The emitted electron can be accelerated in a vacuum tube by an electric fi eld toward an electron multiplier stage composed of a set of dynodes, which are basic components that emit several low-energy electrons (secondary electrons) when one high-energy electron (primary electron) impinges on their surfaces. Figure 2 shows two common photomultiplier confi gurations. The sensitivity of photocathodes depends on the energy of impinging photons. Consequently, it is not possible to defi ne the best possible photoemission material for a wide range of optical wavelengths.III-V semiconductors with a bandgap engineered according to the corresponding photon energy band are the preferred solution for detecting visible and infrared (IR) radiation; these are also characterized by ultrafast response.4 Cesium-coated GaAs operates at wavelengths up to 930 nm, whereas InGaAs extends the IR range up to 1700 nm. Ag-O-Cs materials are also used for visible-IR detection, with a preferred use in the near-IR region due to a higher sensitivity.5 Multi-alkali-b...

Electron Emission Devices for Energy‐Efficient Systems

“…At a fundamental level, the number of emitted electrons is related to the electrode–vacuum interface barrier height and is important to understand how electrons cross the barrier to reach vacuum level from electrode surface. Multiple stimuli are used to achieve the electron emission, such as thermal‐energy (thermionic emission), photon (photoemission), ion‐electron bombardment (secondary emission), and electric field (field emission) . Diverse theories and formulae have been defined to calculate the electron emission under different conditions and a wide range of material are available in this domain.…”

Field Emission Cathodes to Form an Electron Beam Prepared from Carbon Nanotube Suspensions

“…Various electron sources can be used to emit electrons. In the literature, we can find electron emission sources based on thermal energy [18], field emission (FE) [19], Schottky emission [20], photoemission, and secondary emission [21]. Murphy and Good [19] identified that either one of the primary conditions (temperature or electric field strength) governs electron emission or that an intermediate region exists, where the temperature and electric field both contribute to the electron emission.…”

Work function and negative electron affinity of ultrathin barium fluoride films

“…In the last years, following the increasing interest on electron‐emission‐based devices, 1 a hybrid thermionic‐photovoltaic (TIPV) converter was proposed and developed in the frame of European H2020 project AMADEUS for the conversion of stored thermal energy 2 . A TIPV device is constituted of a hot thermionic cathode, able to emit electrons and photons at an operating temperature in the range of 1700–2000 K, and a cooled thermionic anode coupled with a thermo‐photovoltaic (TPV) cell.…”