This article presents a study performed with a dedicated scanning electron microscope on the electrical property evolution of monoclinic ZrO2 (m-ZrO2) and yttria-stabilized zirconia (YSZ). The charging behavior is studied during the charge injection process at 1 keV, by measuring the secondary electron emission σ. The physical properties of zirconia change are shown under the dopant effect. In fact, for YSZ, the substituting cation Y3+ has a lower valence than that of the initial cation Zr4+, so oxygen vacancies are created to maintain the neutrality. These vacancies promote the relaxation of created charges within YSZ. For this reason, we distinguish between the conductive behavior of YSZ and trapping behavior of m‑ZrO2. The new conductive behavior of YSZ is clearly visible in the variation of the charge generated as a function of the injected dose. Indeed, for m‑ZrO2, the generated charge tends towards a constant, independent of the dose, while for YSZ, it varies linearly as a function of it. This proves that the probability of charges, successive jumps from one oxygen vacancy to another, increases and, subsequently, the mobility becomes sufficiently high to generate a current within YSZ and an expansion of the injected charge.

This article presents a detailed study of the variation of secondary electron emission as a function of the primary energy. This study is performed with a dedicated scanning electron microscope on the electrical property evolution of the magnesium oxide (100) single crystal. It is shown that the crystalline orientation has a significant influence on the intrinsic secondary electron emission at low energies below 7 keV, but for high energies, the loss function of the secondary energy extending more deeply, disperses before its release. As the incidence angle of the primary beam energy differs from the normal and takes important values, the secondary electron yield increases. The increase in the incidence angle has a similar and complementary effect on the current density growth.

In this article we have studied, using the Scanning Electron Microscopy SEM LEO 440, the surface electrical properties of MgO (111) irradiated with 30 keV electrons. The study of the evolution of the secondary electronic emission of MgO (111) shows that lnσ increases and reaches a value lower than zero. After an injection of 5000 pC, we observe a pseudo mirror, which is due to a very negative surface potential. Finally, we have shown the very high stability of charges within MgO (111) thanks to the use of Atomic Force Microscopy coupled with Scanning Electron Microscope. We can then conclude that MgO (111) is a good trapping insulator.

This study is performed with a dedicated scanning electron microscope (SEM) which allows the injection of few electrons doses in a large domain of energies and the measures of the secondary electron emission and the induced current created in the sample holder by the charges generated in the sample. In this paper, we present a detailed calcul of the precision measure on the intrinsic Secondary Electron Emission yield σ 0 and the stationary electron emission σ st of magnesium oxide (MgO) single crystals of different crystalline orientation (100), (110) and (111) . We notice that the precision measure becomes more and more excellent with increasing n ( n is the number of equal time intervals Δ t in which the measure of the induced and secondary currents is carried). The results shown that the crystalline orientation has a significant influence on intrinsic secondary electron emission σ 0 at low energies below 7 keV, but for high energies, the loss function of energy extending more deeply, the secondaries are dispersed before their release.

Charging phenomena of insulating materials were studied thanks to a scanning electron microscope (SEM) which allows the injection of few electrons doses in a large domain of energies and the measurements of the secondary electron emission. The results shown that the secondary electron emission yield (SEE) is a very sensitive parameter to characterise the charging state of an insulator. It is well known that the presence of space charge in an insulator is correlated with an electric breakdown. In this work we investigate the charging effect of (110) magnesium oxide single crystal irradiated with 5 and 30 KeV. The results show the effect of the electric field generated by the trapping of charges within the material. At 5 keV the material reaches an " aging regime " characterized by a positive surface charge, when a negative charge was expected, that is due to the brutal detrapping of accumulated electrons in depth by Poole-Frenkel effect. At 30 keV, we notice that the consequences of the electric field increase are very violent because of the brutal detrapping of the charges accumulated near the surface. In fact the trapped charges create electric fields close to the rupture dielectric field of the material, therefore the irreversible degradation regime is reached in MgO (110).

Charging phenomena of insulating materials were studied thanks to a scanning electron microscope SEM LEO 440 which allows the injection of electrons doses in a large domain of energies and the measurements of the secondary electron emission and the induced current created in the sample holder by the charges generated in the sample. The results show that the secondary electron emission yield is a very sensitive parameter to characterise the charging state of an insulator.

This article presents a study performed with a dedicated scanning electron microscope (SEM) on the electrical property evolution of magnesium oxide (1 1 0) single crystal during 15 and 30 keV irradiation. First, the charging behavior is studied during the charge injection process at low current density J(0), by measuring the logarithm of the secondary electron emission yield (In sigma). Next, we have investigated the dependence on the current density of the charge-trapping phenomena in MgO (1 1 0). The results shown that beyond the crossover energy E-2, the observed effects varies depending on whether the energy of the primary electrons is lower or higher than an energy called critical energy E-c = 20 keV (in the case of MgO (1 10)). When irradiating the material at E-0 < E-c and at low J(0), self regulated regime is obtained, if J(0) is sufficiently intense an aging regime is reached. This latter regime is characterized by a positive surface charge, when a negative charge was expected. At E-0 > E-c, and for low J(0), the detailed monitoring of the charge kinetic of MgO (1 1 0) at high primary energy E-0 = 30 keV, permit to show that the combined effect of the increased negative surface potential during irradiation and extractor field below the surface of MgO fact that In sigma undergoes a strong slope failure at the beginning of the injection and stabilizes at a value much less than zero leading to the formation of an electrostatic mirror. At high J(0), the consequences of the charge accumulation are violent and a breakdown phenomenon is observed. (C) 2014 Elsevier B.V. All rights reserved.

It is well known that the presence of space charge in an insulator is correlated with an electric breakdown. Many studies have been carried out on the experimental characterization of space charges. In our previous work, we have studied the difference in the charging kinetics between “trapper” insulator (pure spinel) and “conductive” one (Yttria Stabilized Zirconia (YSZ)) at low current density J0 of primary beam. This difference is attributed to the difference in conductivities. The main objective of this paper is to first review the charging effects occurring when a “conductive” material YSZ is subjected to electron irradiation at low J0, using a Scanning Electron Microscopy (SEM), and next to study the dependence of the charge-trapping phenomena in YSZ on the current density. The results show the existence of permanent current in the conductive material which is characterized by a steady state yield σ∞ which fixes the maximum value of J0 being withstood by a “conductive” material without charge accumulation beneath its surface.

Insulators are currently used in high technological devices. They are chosen because of their electrical properties of insulation and their thermal properties. It is well known that the presence of space charge in an insulator is correlated with an electric breakdown. Charging phenomena of insulator were studied thanks to a scanning electron microscope (SEM) which allows the injection of few electrons doses in a large domain of energies. SEM permits also the measurements of the secondary electron emission and the induced current created in the sample holder by the charges generated in the sample. The results showed that the secondary electron emission yield (SEE) σ is a very sensitive parameter to characterize the charging state of an insulator. In this work we investigate the charging effect of insulator surfaces like pur spinel (MgAl2O4) during 1.1, 5 and 15keV. The results showed that the fundamental parameter controlling the charging kinetic is the current density J0. At low energies 1.1 and 5keV, two different kinds of self-regulated regime (σ=1) were observed as a function of current density. At 15keV energy, the electron emission appears to be stimulated by the current density, due to the Poole–Frenkel effect.

Spinel and zirconia were studied by measuring the total secondary electron emission (SEE) yield σ in a dedicated scanning electron microscope (SEM) especially equipped to study the fundamental aspects of the charge trapping in insulating materials during a 1.1keV electron irradiation at room temperature. The variation of the total SEE yield with the injected dose for both spinel and zirconia is different. In spinel the coefficient σ starts from its intrinsic value σ0=4 and reaches a plateau at σ=1 at the end of irradiation, which corresponds to the self-regulated regime. The continuity of the curves, shot after shot, proves that the trapped charges are stable and does not spread out in the material as injection proceeds. In this case spinel is called “trapper insulator”. In contrast with the spinel, σ in zirconia, never reaches unity while the injected charge increases: it evolves from its intrinsic yield σ0=2.3 to a steady value a few percent above 1. The curve shows the relaxation of the positive generated charge. In this case zirconia is called “conductive insulator”. The difference in the charging kinetics of the two materials is attributed to the difference in conductivities.

The charge dynamics of insulating or weakly conductive materials can be studied by the secondary electronic emission (SEE) method. Those two types of compounds behave differently to irradiation: charge trappers such as PMMA or SiO2 can have a charge excess after irradiation, so that they can be trapped for a long time, and can even cause 'microbreakdowns' to dielectric breakdowns, while in contrast, conductive materials have a kind of charge flow. SEE yield can also be affected by changing the current density. When the current density increases, the SEE intrinsic yield sigma(0) and the SEE stationary yield sigma(st) decrease. Unexpected behaviour of negative charging is observed showing that there must be competition between diffusion and accumulation effects.

This study reviews a host of issues related to international migration in Sub-Saharan Africa and presents an overview of the state of the art of research and knowl-edge. Its aim is to identify policies and research areas that will improve understanding and management of migration in Sub-Sahara Africa and help maximize the potential benefits of migration, especially for poor people, while minimizing its risks and costs. The study covers a broad range of issues in the migration literature, but is not exhaustive. This report first provides a historical overview of migration in Sub-Saharan Af-rica and then examines the scale and regional trends of migration. It explores the intersec-tions between migration and labor market and the links between migration and develop-ment. It also looks at institutions and policies and investigates issues related to politics, ethics, and migration before exploring implications for further investigation.

A study performed with a dedicated scanning electron microscope (SEM) on the surface electrical properties of (100)-oriented yttria-stabilized zirconia (YSZ) single crystals irradiated with 1MeV electrons is presented. When compared with virgin YSZ, the 1MeV-irradiated YSZ shows a decrease of the intrinsic total electron emission coefficient σ0 and an increase of the time constant τ associated with the charging kinetics of the material at room temperature. These measurements performed with the SEM beam at 10keV indicate that the defects induced by the 1MeV-electron irradiation generate a positive electric field of the order of 0.5×106V/m at a depth of about 1μm that prevents electrons to escape. When the SEM beam with a 1.1keV energy is used, a smaller field (∼0.5×103V/m) is detected closer to the surface (∼20nm). The fading of these fields during the thermal annealing in the 400–1000K temperature range provides information on the nature of defects induced by the 1MeV-electron irradiation.

This paper reports a study of the high-temperature stability of ion-implanted yttria-stabilized zirconia and magnesium aluminate spinel, which are foreseen as matrices for the transmutation of nuclear waste. Stable analogs of radiotoxic fission products (Cs) were implanted into both materials and the stability of the implanted systems was studied upon annealing at a high temperature. Rutherford backscattering spectrometry experiments with a macro- and a micro-ion-beam, scanning electron microscopy, and atomic force microscopy observations show that the annealing behavior strongly depends on the material. In zirconia Cs begins to desorb out of the crystal at 550°C in samples which remain homogeneous. On the contrary, the desorption of Cs is observed at 850°C in spinel by the exfoliation of the surface of the samples.

The secondary electron emission contrast between poled and unpoled regions in thermally poled Ge-doped silica films were measured according to different annealing temperatures and electron doses with electron acceleration energy of 5keV. It is used for measuring the change on annealing of poling induced electric field and other insulating properties like electron traps population and conductivity in high field. Concerning the change of the contrast at low dose arising from the poling electric field, we show that this field begins to disappear at around 450°C and is erased completely at 650°C. Using a larger dose allows measuring the change in conductivity contrast. We find a stability similar to the electric field with a disappearance around 450∼650°C. On the contrary, for intermediate dose, the contrast remains for larger annealing temperature. It allows measuring properties of the electron traps. Their number appears to be modified in the poling process.

It is well known that the presence of space charge in an insulator is correlated with an electric breakdown. Many studies have been carried out on the experimental characterization of space charges. In this paper, we outline the dependence on the current density of the charge-trapping phenomenon in magnesium oxide. Our study was performed with a dedicated scanning electron microscope (SEM) on the electrical property evolution of surface of magnesium oxide (100) (MgO) single crystal, during a 1.1, 5 and 30keV electron irradiation. The types of charges trapped on the irradiated areas and the charging kinetics are determined by measuring the total secondary electron emission (SEE) σ during the injection process by means of two complementary detectors. At low energies 1.1 and 5keV, two different kinds of self-regulated regime (σ=1) were observed as a function of current density. At 30keV energy, the electron emission appears to be stimulated by the current density, due to the Poole–Frenkel effect.

Amorphous N- or Ge-doped H:SiO 2 films deposited on silica by the matrix distributed electron cyclotron resonance-PECVD method were irradiated by an electron-beam with different doses in order to pole the material and induce second harmonic generation (SHG). SHG was measured using the Maker-fringe method. When irradiated at an acceleration voltage of 25 kV, an incident current of 5 nA during 480 s, the N-doped H:SiO 2 films exhibited a maximum second harmonic signal in the order of 0.003 pm/V, but when irradiated with an acceleration voltage of 30 kV, at 5 nA during 240 s, the films exhibited a maximum second harmonic signal of 0.006 pm/V. With a smaller current of 0.5 nA during 25 s and 25 kV acceleration voltage, the Ge-doped H:SiO 2 films (3.8 at. % Ge) showed a maximum second-order nonlinearity of 0.0005 pm/V. But an H:SiO 2 films with a smaller Ge content (1.0 at. % Ge), showed a large SHG: d 33 =0.09 pm/V when irradiated at 25 kV, 0.5 nA during 15 s.