Secondary Electron Emission Yield Measurements Research Articles

Modelling the impact on the secondary electron yield of carbon layers of various thicknesses on copper substrate

This work presents comparisons between numerical simulations and secondary electron emission yield measurements. The impact on the secondary electron emission yield of a growing graphite layer deposited on copper substrates is analyzed. The numerical simulations confirm experimental observations showing that a very thin coating deposit, with a thickness of few nm, can affect significantly the emission yield of an irradiated material. Beyond 5 nm thickness, the surface material alone drives the secondary emission.

Secondary electron emission yield measurements of dielectrics based on a novel collector-only method

The total electron-induced Secondary Electron Yield (SEY) of alkali-free glass has been determined by a novel technique which is solely based on the use of a collector electrode and of two interchangeable dielectric samples. The current from a charge-saturated sample provides a direct measure of the primary beam current. The SEY from the (uncharged) sample under investigation can then be determined simply as the ratio between the collector currents measured at the same electron energy from both samples. We further apply a low-current, short-pulse procedure to limit sample charging, needed to mitigate distortion of the SEY by charging effects. The potential build-up during the experiment could be reconstructed based on the primary electron currents and the measured SEY. This strategy permitted us to measure a 6-point SEY curve, without the need for intermediate discharging of the sample, as the total induced surface potential rise could be kept below +2.55 V.

In-situ analysis of ion-induced physicochemical change of Si surface by secondary electron yield detection

We report the variation of secondary electron yield with ion fluence during 10 keV N+1 and Ar+1 ions bombardment on a Si (1 0 0) surface at normal and oblique incidence. The initial high secondary electron yield from Si surface is observed due to the native oxide layer on Si for both nitrogen and argon ion bombardment. The secondary electron yield is expected to decrease and stabilize for continue ion bombardment, which is observed for the argon ion irradiation. However, a significant variation of the electron yield with continuing nitrogen ion bombardment is observed. Ex situ measurement of ion bombarded surfaces by Atomic Force Microscope shows that the variation of secondary electron yield is correlated with the surface topography development due to ion bombardment. Also, the reaction of the projectile with target atom alters the secondary electron emission in case of N+ ion bombardment. The mean free path length of the secondary electron is estimated using the Parilis-Kishinevsky theory and the variation is presented. Real-time physicochemical changes of Si surface due to low energy ion bombardment have been probed in-situ by monitoring the secondary electron emission yield measurements.

Modeling Facility Effects on Secondary Electron Emission Experiment

Secondary electron emission is one of the most fundamental problems in spacecraft charging. An accurate prediction of secondary electron yield at low-energy electron impingement has long been a challenging problem due to both the complexity of the process and the difficulty in carrying out accurate measurements in a vacuum chamber. This paper discusses a correlated modeling and experimental study to investigate the facility effects on secondary electron emission yield measurement in a vacuum chamber.

Secondary electron emission and charging mechanisms in Auger Electron Spectroscopy and related e-beam techniques

Mechanisms of charging in AES are reconsidered to the light of recent developments concerning the leading role of secondary electron emission (SEE) in the self-regulation processes taking place in insulating materials irradiated with keV-electrons. A specific attention is paid to SE angular distribution and to distortion of SE trajectories by the electric field build-up into the vacuum when the surface potential is negative. These external mechanisms are associated to internal mechanisms resulting from the effect of low potential barrier or of low hollow in the SE generation region. From these investigations the main parameters governing the time dependence of charging have been identified and the fact that the critical energy (between positive and negative charging region at steady state), E 2 C , is less than the convention critical energy E° 2 (where the total SEE yield is unity) has been re-confirmed for AES. Common points and differences between AES and other electron beam techniques (such as those based on external collector positively biased in SEE yield measurements) are also discussed in detail and possible experimental artefacts are also pointed out (such as those resulting from the incorrect use of the shift of Duane-Hunt limit with a X-ray detector in a SEM). Some practical consequences to minimize charging effects (specimen preparation, operating conditions and use of additional irradiations) have been deduced.

Secondary Electron Emission Measurement of Insulating Materials for Spacecraft

We studied how to measure the secondary electron emission (SEE) of metal and insulating materials used for satellite thermal insulation or other such purposes. SEE yield measurement is very important for analyzing charge accumulation on the satellite surfaces due to the space environment because electron emission due to irradiated electrons influences the amount of surface charge. Therefore, we tried to measure the SEE yield. To measure SEE, we used an improved SEM system for SEE measurement that has a beam blanking unit and a Faraday cup. From this system, we can obtain the characteristics of the SEE yield from insulation materials irradiated by an electron beam with an energy of 600eV to 5keV. In this report, we introduce the SEE yield measurement results of reference materials (Au, Ag and Quartz glass) and insulating materials. From those results, we discuss the characteristics of SEE that depend on each material. Furthermore, we also propose a future plan of SEE measurement for satellite materials.

Electron beam induced structural changes in Bi 2 Sr 2 CaCu 2 O 8+x studied by cathodoluminescence microscopy and secondary electron emission

Sr2CaCu2O8+x superconducting ceramics have been irradiated in the scanning electron microscope (SEM), and the irradiation-induced effects investigated by cathodoluminescence (CL), secondary electron emission (SEE) and X-ray microanalysis. Electron beam irradiation causes a slight Bi depletion and an inhomogeneous Ca distribution. A higher CL intensity emission is found in the irradiated areas, where besides an enhancement of the oxygen content related 2. 4 eV band, another CL bands probably related to new non-superconducting phases induced by irradiation can be observed. SEE yield measurements allow to detect an oxygen depleted region surrounding the irradiated areas. X-ray microanalysis shows that this intermediate region retains the cationic composition of the unaffected material. CL spectra from bright zones inside the same area also show a dominant 2. 4 eV emission band, which supports its relation with oxygen deficiency or rearrangement in high-\(\) superconductors.

Cathodoluminescence Microscopy and Secondary Electron Emission in Mechanically Polished and Electron Irradiated YBa2Cu3O7−x Ceramics

Cathodoluminescence (CL) and secondary electron emission (SEE) in the scanning electron microscope have been used to study the effects of mechanical polishing and electron irradiation on YBa2Cu3O7-x ceramics. CL spectra from the mechanically polished superconductors show an enhanced 2.4 eV luminescence band, which is related to oxygen content redistribution or depletion. Electron irradiation induces strong morphological and compositional changes which are proposed to be connected with melting-resolidification processes and surface phase segregation. SEE yield measurements allow to detect an oxygen depleted area with stoichiometric cationic composition surrounding the irradiated region. CL spectra recorded from this oxygen-deficient area also show an enhanced 2.3 to 2.4 eV emission band in comparison with the spectra recorded from the non-irradiated material. Strongly luminescent non-superconducting phases appear in the irradiated regions, showing intense 3.1 and 0·78 to 0·81 eV emission bands.

Oxide overlayers and the superconducting rf properties of yttrium-processed high purity Nb

Superconducting rf surface resistance measurements were made on oxidized Nb cavities that had been warmed for a few minutes to temperatures between 250 and 300° C. Warmed oxide layers were further studied using X-ray photoelectron spectroscopy, Auger electron spectroscopy and secondary electron emission yield measurements. Warming usually reduced the temperature-dependent (BCS) part of the surface resistance by 10–20% while, for warming temperatures near 300° C, the low-temperature residual surface resistance increased by as much as 70 nΩ. Surface spectroscopy measurements showed that, at temperatures between 200 and 250° C, the oxide layer was chemically altered but remained surface-segregated; between 250 and 300° C, however, surface oxygen dissolved into the Nb bulk. Changes in the BCS resistance were consistent with a model based on a shortening of the electron mean free path by oxygen that had diffused into the Nb metal and based on the theoretical dependence of BCS resistance on electron mean free path. No specific cause for the increased residual resistance could be positively identified, although oxygen-induced surface roughening is a possibility.

Surface properties of Cr2O3

Thin (<5 nm) air-oxidized Cr layers are deposited on the alumina output windows of radio-frequency klystron tubes to prevent electron multipactor by reducing the secondary electron emission yield of the alumina surface. The top several nanometers of these layers appear to be Cr2O3. To compare the measured surface properties of these layers with those of clean stoichiometric Cr2O3, quasibulk Cr2O3 layers were produced by wet-H2-firing magnetron-deposited Cr films on Cu substrates and characterized by x-ray photoelectron-, Auger electron-, and electron energy loss spectra and secondary electron emission yield measurements. Other properties measured were x-ray diffraction structure, sheet resistance, and optical reflectivity. In particular, the peak of the secondary electron yield was found to be ∼1.7, which is considerably higher than the <1 yield value reported earlier in the literature. The Cr2O3 Cr 2p x-ray photoelectron core level spectrum was curve-fit using Doniach–Sunjic line shapes and statistical fitting methods. It is shown that each 2p level is composed of three multiplet-split peaks 1.1 eV apart. In addition, the three 2p1/2 peaks are folded with a 2p3/2 3d satellite.