The secondary electron emission yield of muscovite mica: Charging kinetics and current density effects

Abstract

Using a dedicated Scanning Electron Microscope (SEM), operating in the spot mode, the charging properties of muscovite mica have been studied in the energy range 100-8000 eV. The intrinsic yield curve σ 0 (E), representing the variation of the yield of the uncharged material with the energy E, has been established: the maximum value of the yield is 3.92 at E = 300 eV and the two crossovers corresponding to σ 0 (E) = 1 are respectively at energies E I < 100 eV and E II = 4850 eV. At a given energy and under a low current density J ≤ 100 nA/cm 2 , the yield varies with the electron fluence from its intrinsic value σ 0 up to the value corresponding to the Self Regulated Regime (SRR) for which σ = 1. This variation is independent of J. The fluence dependence of the yield σ(D) is due to the internal field produced by the accumulation of charges that blocks the emission when the charging is positive and enhances it when it is negative. At room temperature, the relaxation time of stored charges is estimated to be of the order of 250 sec for holes and 150 sec for electrons. Three current density effects have been observed when J ≥ 400 nA/cm 2. (i) The variation of σ(D) with the fluence D depends on J. (ii) Negative charging is obtained at high current density in the energy range (E I ,E II) where the material is normally positively charged at low current density. (iii) Electron exo emission (bursts of electrons) is produced at low energy when the net stored charge is positive. The interpretation of the current density effect on σ(D) is based on the high rate of charging, the effect relative to negative charging is due to the expansion of the electron distribution, while the exoemission effect is due to the collective relaxation process of electrons.

Electron-emission yield under electron impact of ceramics used as channel materials in Hall-effect thrusters

“…This is achieved by alternating short electron pulses where r < 1 when the sample is positively charged and where r > 1 when the sample is negatively charged. [17][18][19] Note that the "as received" ceramics are usually charged before being exposed to electron beams and may in some cases exhibit a surface potential of tens to hundreds of volts (positive or negative). For instance, a positive surface potential of 67 V was measured on the BN-SiO 2 sample, whereas a negative surface potential of À49 V was measured on Al 2 O 3 .…”

Study of discharge after electron irradiation in sapphires and polycrystalline alumina

“…4,5 In essence and in the case of oxides, it has been shown that breakdown could be delayed by introducing impurities, whose nature and concentrations meet specific requirements, or by achieving a microstructure that favors to some degree the spreading of charges. [6][7][8][9][10][11][12] Indeed, it contributes to the improvement of component reliability of industrial devices, for instance in thin insulating systems as those used in plasma display panels, 13 spacecraft insulating, 14 alumina rf-window, 15 power electronic capacitors, 16 high-k materials of metal-oxidesemiconductor structures, 17 and field emission display spacers. [6][7][8][9][10][11][12] Indeed, it contributes to the improvement of component reliability of industrial devices, for instance in thin insulating systems as those used in plasma display panels, 13 spacecraft insulating, 14 alumina rf-window, 15 power electronic capacitors, 16 high-k materials of metal-oxidesemiconductor structures, 17 and field emission display spacers.…”

“…[6][7][8] Therefore, the ability of insulators to keep the charges trapped ͑or conversely to spread them͒ controls their dielectric properties. 18 Experiments using electron irradiation [8][9][10][11][12][13][14][15][16][18][19][20][21] and simulation studies [21][22][23] have provided a coherent framework for comprehensive description of the evolution of the generated charges ͑i.e., the injected electrons and the charge carriers ͑electrons and holes͒ that have been produced during the slowing down process of the primary electrons within the irradiated zone͒. 18 Experiments using electron irradiation [8][9][10][11][12][13][14][15][16][18][19][20][21] and simulation studies [21][22][23] have provided a coherent framework for comprehensive description of the evolution of the generated charges ͑i.e., the injected electrons and the charge carriers ͑electrons and holes͒ that have been produced during the slowing down process of the primary electrons within the irradiated zone͒.…”

“…[13][14][15][16][17][18] The choice of the experimental conditions, mainly very low current beam density ͑4 ϫ 10 4 pA/ cm 2 ͒ and defocused electron beam ͑over a diameter of about 500 m͒, was dictated by the need to avoid undesirable perturbations and to probe a representative volume.…”

Effects of the Microstructure Induced by Sintering on the Dielectric Properties of Alumina

“…This decrease has been associated with a progressive accumulation of positive charges that are distributed over a depth of about the escape length of secondary electrons λ. As suggested, this could be assigned to recombination of electrons with holes (in this zone), which should be otherwise emitted (Cazaux, 1986) or to field effect (Blaise et al, 2009). The other important feature is indeed that during injection, a negative charge distribution develops in the vicinity of the penetration depth of primary electrons R p .…”