A detailed spectroscopic and structural characterization of ultrathin cobalt oxide films grown by O-assisted molecular-beam epitaxy on $\ensuremath{\alpha}\ensuremath{-}{\text{Al}}_{2}{\text{O}}_{3}(0001)$ single crystals is reported. The experimental results show that the cobalt oxide films become progressively more disordered with increasing thickness, starting from the early stages of deposition. Low-energy electron-diffraction patterns suggest that the unit cell remains similar to that of $\ensuremath{\alpha}{\text{-Al}}_{2}{\text{O}}_{3}(0001)$ up to a thickness of $17\text{ }\text{\AA{}}$, while at larger thicknesses a pattern identified with that of ${\text{Co}}_{3}{\text{O}}_{4}(111)$ becomes visible. X-ray photoelectron spectroscopy reveals sudden changes in the shape of the $\text{Co}\text{ }2p$ lines from 3.4 to $17\text{ }\text{\AA{}}$ cobalt oxide thickness, indicating the transition from an interfacial cobalt oxide layer toward [111]-oriented ${\text{Co}}_{3}{\text{O}}_{4}$. In particular, the absence of characteristic satellite peaks in the $\text{Co}\text{ }2p$ lines indicates the formation of a trivalent, octahedrally coordinated, interfacial cobalt oxide layer during the early stages of growth, identified as the ${\text{Co}}_{2}{\text{O}}_{3}$ corundum phase.

Experimental study of the interfacial cobalt oxide in Co 3 O 4 / α − Al 2 O 3 ( 0001 ) epitaxial films

Based on a more realistic description of the in-depth secondary electron generation than that of standard (constant loss) model, a new model for the e-induced secondary electron emission yield, δ = f(E0), is applied to account for the observed mean atomic number dependence of the reduced yield curves (RYC), δ / δ max = f ( E 0 / E max 0 ) of a wide variety of inorganic insulators. It is next used to extract and to discuss physical information on secondary electron escape probability and attenuation length of a number of oxides and alkali halides and to deduce their X-ray-induced secondary electron emission yield, δX = f(hν). Extrapolation of experimental data above the few keV energy range including the estimate of the nominal critical energy E 2 0 is also illustrated. Correlation between time dependence of charging and of secondary electron emission is next analyzed and various charging effects such as the observed negative charging when a positive charging was expected or the possible change of sign of the specimen current, are explained by the difference between E 2 0 and E 2 C (critical energy obtained under permanent irradiation). Strategies to identify charging effects via their influence on the distortion of the yield curve and to reduce them are finally suggested.

e-Induced secondary electron emission yield of insulators and charging effects

Heat transfer—A review of 2005 literature

The fabrication of nanopores in thin silicon nitride and aluminum oxide membranes by water vapor assisted, low-energy (0.2?20?kV) electron beam machining using a scanning electron microscope (SEM) is described. Using this technique, pores with diameters ranging in size from < 5 to 20?nm are easily formed. The nanopores are characterized by SEM, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The mechanism of etching is briefly discussed.

http://iopscience.iop.org/article/10.1088/0957-4484/21/37/375301/pdf

Nanopore formation by low-energy focused electron beam machining.

The accumulation of space charge in the XLPE insulation of a power cable sample under dc stress was investigated. Conditioning the sample at 82°C removed preexisting space charge. When an external dc field was applied after conditioning at 82°C and atmospheric pressure, space charge accumulated considerably faster than before conditioning. However the rate of accumulation following conditioning at 82°C under reduced pressure was much slower than before conditioning. The faster rate could be recovered by reconditioning the sample at atmospheric pressure. Inversion of the equilibrium space charge profile, following reversal of the applied field, was observed. A model incorporating electron injection/extraction at the electrodes, and an inhomogeneous distribution of dipole molecules in the bulk, is proposed. Water is the most likely molecular dipole, but complexes incorporating molecular oxygen loosely bonded to the polymer matrix might also be involved.

Space charge accumulation in power cable XLPE insulation

The purpose of this paper is to give some aspects of charging effects on dielectric materials submitted to continuous electron beam irradiation in a scanning electron microscope (SEM). When the dielectric is irradiated continuously, the so-called total yield approach (TYA) used to predict the sign of the charge appeared on electron irradiated insulators fails because the charge accumulated in the dielectric interferes with the electrons emission processes. Based on previous experimental and theoretical works found in the literature, an analysis of the evolution of the electron yield curves σ  =  f ( E 0 ) of insulators during irradiation is given. The aim of this work is firstly to determine experimentally the second crossover energy E 2C under continuous electron irradiation (charging conditions) and secondly to demonstrate that the charge balance occurs at this beam energy and not at E 2 the energy deduced from non-charging conditions (pulse primary electron beam experiments) as commonly asserted. It is however possible to apply the TYA by substituting the critical energy E 2 for E 2C . The experimental procedure is based on simultaneous time dependent measurements of surface potential, leakage current and displacement current. The study underlines the difference between the landing energy of primary electrons E L at the steady state and the second crossover energy, E 2C , for charged samples. Some preliminary results are also obtained concerning the influence of the incident beam density on the energy E 2C . The samples used for this study are PMMA, polycrystalline silicone dioxide (p-SiO 2 ), polycrystalline alumina (p-Al 2 O 3 ) and soda lime glass (SLG).

Second crossover energy of insulating materials using stationary electron beam under normal incidence

Ultraviolet radiation aging impact on physicochemical properties of crosslinked polyethylene cable insulation

This paper presents a comparative study of electrical charging and discharging behavior of different glasses submitted to electron beam irradiation in scanning electron microscope. Charge storage and charge spreading in these glasses have been examined with help of a time resolved current method. Our interest concerns more particularly the dynamic behavior and the amount of the space charge build-up during and after electron irradiation under different experimental conditions of primary beam energy and current density. The precise contributions of different possible self regulation processes (leakage current and secondary electron emission) for charge accumulation are analyzed. Moreover, to characterize the ability of glasses to store charges in a stable way we introduce a relevant parameter that expresses quantitatively the variation in the released charge. The primary beam energy and the current density effects on the evolution of secondary electron emission yield during irradiation are also examined. As expected, the charge storage and spreading processes appear to be extremely dependent on the incident beam energy, current density and on the chemical composition of the studied glasses.

Analysis of electrical charging and discharging kinetics of different glasses under electron irradiation in a scanning electron microscope

This paper deals with charge trapping and charge transport of polyethylene terephthalate (PET) polymer subjected to electron irradiation in a scanning electron microscope (SEM). Measurement of displacement current and leakage current using an arrangement adapted to the SEM allows the amount of trapped charge during and after electron irradiation to be determined and the charge mechanisms regulation to be studied. These mechanisms involve several parameters related to the electronic injection, the characteristics of insulator and the effects of the trapped charge itself. The dynamic trapping properties of PET samples are investigated and the time constants of charging are evaluated for various conditions of irradiation. The determination of the trapping cross section for electrons is possible by using the trapping rate at the onset of irradiation. Many physical processes are involved in the charging and discharging mechanisms; among them surface conduction is outlined. Through the control of irradiation conditions, various types of surface discharging (flashover phenomenon) behaviour are also observed. The strength of the electric field initiating surface discharge is estimated.

https://iopscience.iop.org/article/10.1088/0022-3727/41/24/245504/pdf

Charging effects of PET under electron beam irradiation in a SEM

The goal of this article is first to review the charging effects occurring when an insulating material is subjected to electron irradiation in a scanning electron microscope (SEM) and next their consequences from both scanning electron microscopy and electron probe microanalysis (EPMA) points of view. When bare insulators are observed, the so-called pseudo mirror effect leads to an anomalous contrast and also to an erroneous surface potential, V(S), measurement when a Duane-Hunt limit (DHL) method is used. An alternative possibility is to use an electron toroidal spectrometer (ETS), specially adapted to a SEM, which directly gives the V(S) value. In the case of a bulk specimen coated with a grounded layer, although the layer prevents external effects of the trapped charge, the electric field beneath the coating is reinforced and leads to loss of ionizations that reduces the number of generated X-ray photons. To take into account both effects mentioned above, whether the studied insulator is coated or not, a method is proposed to deduce the trapped charge inside the insulator and the corresponding internal or external electric field.

S. Rondot

Papers

Second crossover energy of insulating materials using stationary electron beam under normal incidence

Ultraviolet radiation aging impact on physicochemical properties of crosslinked polyethylene cable insulation

Analysis of electrical charging and discharging kinetics of different glasses under electron irradiation in a scanning electron microscope

Charging effects of PET under electron beam irradiation in a SEM

Charge Implantation Measurement on Electron-Irradiated Insulating Materials by Means of a SEM Technique