Dynamic secondary electron emission in rough composite materials

Properties of TiN and TiZrV thin film as a remedy against electron cloud

Secondary electrom emission yield (δ) and the surface work function values (φ) were measured for lead zirconium titanate (PZT) doped with lanthanum, strontium, and niobium. The single pulse method was used in LEED/Auger geometry for measuring the secondary electron emission yield δ while the retarding potential technique was employed for measuring the work function. In view of the application of ceramics as continuous dynodes in electron multipliers, the secondary electron emission and electical conductivity data is analysed for reduced PLZT ceramics. Maximum δ of 2.7 was found to remain unchanged after reduction of PLZT. Dionne's equation was used as a basis for analysis of secondary electron emission measurements to estimate escape depth and emission probability.

Secondary emission from dust grains with a surface layer: comparison between experimental and model results

We provide a detailed description of a model and its computational algorithm for the secondary electron emission process. The model is based on a broad phenomenological fit to data for the secondary emission yield (SEY) and the emitted-energy spectrum. We provide two sets of values for the parameters by fitting our model to two particular data sets, one for copper and the other one for stainless steel. We also present details of the electron-cloud simulation code POSINST that are relevant to the secondary emission process. This note expands on our previously published article.

Secondary electron (SE) emission (SEE) from material surfaces is a frequent phenomenon in space and vacuum environments. SEE modulation is important since it governs the performance of some devices such as electronic multipliers or induces some detrimental effects such as multipactors. Surface coating has been reported to modulate SEE effectively, whereas SEE behaviors of coating structures are not clearly understood yet, and the appropriate theory to describe SEE characteristics quantitatively for coating structures is less developed so far. Here, we have prepared four alumina coatings possessing various thicknesses to research the SEE characteristics of coating structures and have shown how the coating thickness affects the SEE behaviors. Besides, by considering coating/substrate as an ideal double-layer structure, we have derived several equations to describe the producing, transmitting, and escaping processes of excited inner SEs and finally constructed a unidimensional SEE model for double-layer structures. The model is applicable to reveal the dependence of true SE yield (TSEY) on the top and bottom layers’ physical properties and estimate TSEY proportions contributed by the top and bottom layers at random energy points. By employing the concept, SEE characteristics of Al2O3/Si, MgO/Si, and TiO2/Si double-layer structures have been quantitatively interpreted. Moreover, the abnormal SEY curve with a double-hump shape, which is induced by the peak position distinction of SiO2/Si structures, can also be explained. This work is of great significance to comprehend TSEY modulating regularities of various double-layer structures applied in surface engineering.

Studies on the pressed yttrium oxide-tungsten matrix as a possible dispenser cathode material

A new method for the determination of the secondary emission yield of dielectrics is discussed. Results are given for Teflon® , Aclar, Kapton® , and Mylar® . Surfaces of dielectrics irradiated with electrons of energies above 2 keV become negatively charged. For lower energies the number of backscattered primaries plus backward emitted secondaries eventually exceeds that of the incoming primaries. Then the surface can be positively charged. It was recognized that this effect might lead to a simple method for the determination of the total backscatter plus secondary emission yield. This effect is used to determine the total emission yield curve in one run with a single beam energy.

Secondary photon emission studies of ion bombarded beryllium

Secondary electron emission and surface potential of SiO 2 film surface by negative ion bombardment

Secondary electron emission of Y 2O 3–Mo cermet cathode

Summary form only given. Secondary electron emission (SEE) can potentially lead to beam instabilities, material degradation and r.f. breakdown. The past SEE studies have deduced secondary electron yield by invoking a conservation of charge without the need to experimentally account for all measurables. In the spatial distribution studies of SEE, one may not invoke conservation of charge without some knowledge leading to wall loss effects. An electron gun in the SEE test stand at UNLV directs the primary electron beam through a beam drift tube piercing the center of a particle position detector with controlling grid towards the sample under test. Secondary electrons emitted by the sample either drift freely or are drawn by a grid potential to the particle position detector. The location and number of electrons impinging on the detector records the number of electrons and the locations of electron impact. Low primary beam currents are necessary in order to perform these measurements within the resolution of the detector. Because the detector surface is flat and finite in dimension, some loss to the chamber walls will result. Consequential SEE loss to the walls is not measurable in a noise environment even if the experimental apparatus (the SEE test stand) is isolated from the earth ground. To monitor the primary beam current, a C shaped ferromagnetic core coil fitted to the beam drift tube was designed to divert the primary beam to the beam drift tube for measurement with minimal SEE loss from the tube. Assuming successive shots are similar, the total number of incident charge can be deduced statistically. The coil current is then changed to partially null the Earth's magnetic field when experiments are performed. Beam drift tube, grid, and sample currents are monitored and integrated to yield the number of charges collected by each component over time. Along with time resolved, spatially distributed, SEE count from the detector, wall loss may be deduced by invoking conservation of charge. Spatial distributions of secondary electron yield and secondary' electron emission wall loss counts will be reported. Such distributions offer insights in determining the initial conditions on the emitted secondary electrons.

Secondary electron yields of (110) copper surfaces, covered with either carbon, nitrogen, or their dioxides, have been studied by employing combined first principles methods for the material properties and Monte Carlo simulations for electron transport. Furthermore, by studying electron transport inside the Cu system and modeling the power loss taking account of the inelastic electron scattering within the material, changes in the thermal energy of the system have been modeled. The physical reasons behind the increase and decrease of the yield for each system from an electronic perspective are discussed. In agreement with results observed in studies of secondary electron emission, it is shown that the formation of C2 and N2 monolayers reduce the secondary electron yields, while CO2 and NO2 increase the yield significantly. It is demonstrated that in the case of C2 and N2 formation, changes in the surface electronic barrier reduce the probability of electron escape from the Cu surface, resulting in lower secondary electron emission. Formation of CO2 and NO2, on the other hand, reduce the electronic barrier effects. In addition, due to weak bonding of the CO2 layer with the Cu host, the surface provides an additional source of secondary electrons resulting in higher electronic emission yield. Moreover, the NO2 adsorbate creates a surface electric field that changes the surface electron energy and increases the electron escape probability. Additionally, it is verified that thermal change in the system is negligible and so during secondary electron emission measurements, negligible (if any) surface adsorption or desorption could occur.

The plasma-wall interaction in the presence of strong secondary electron or thermionic emission has been studied theoretically and experimentally both as a basic phenomenon and in relation to numerous plasma applications such as, for example, fusion devices and plasma propulsion. For Hall thrusters, existing fluid models predict that secondary electron emission (SEE) is strong enough to enhance electron energy losses at the walls. According to the kinetic simulations, the electron velocity distribution function in a collisionless thruster plasma is non-Maxwellian, anisotropic, and features beams of secondary electrons emitted from the walls. Under such conditions, the effects of SEE on the plasma can be substantially weaker than predicted by the fluid models. This talk will review previous and recent experimental results, including probe measurements in the Hall thruster with various wall materials, which support the predictions of the kinetic studies. It is also shown that the wall material properties affect the electron cross-field transport in the thruster discharge. We will also discuss how these results can help in implementation of highly efficient and stable plasma regimes of the Hall thrusters.

Secondary emission yield by extreme relativistic particles

Secondary electron emission (SEE) critically limits the performance of high-power microwave components and particle accelerators. Amorphous carbon (a-C) films featuring a low secondary electron yield (SEY) and surface grooves offer promising applications for suppressing the SEE effects. However, the efficiency of SEE suppression and the underlying microscopic mechanisms remain subjects of debate. This paper employs the Monte Carlo method to develop a novel electron scattering and an SEE model for copper surfaces coated with a-C films and patterned with rectangular grooves. The model accurately simulates electron transport within the film and substrate, explicitly accounting for the influences of the film/substrate interface energy barrier and the groove walls on electron scattering trajectories. Results demonstrate that increasing the a-C film thickness from 0 to 5 nm reduces the maximum SEY from 1.18 to 0.82. The SEE suppression effect is significantly enhanced on grooved a-C surfaces. Specifically, with a groove depth of 30 nm and a film thickness of 5 nm, the maximum SEY reaches a minimum value of 0.47. These findings provide important insights into the mechanism by which grooves and a-C films suppress SEE and offer practical guidance for designing high-performance, low-SEY surfaces for the next generation of high-power devices.