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High-gradient insulators (HGIs) are materials created by alternating layers of insulating and conducting materials, which can result in a higher holdoff voltage than a monolithic insulator of the same length. We model the HGIs periodic electric field and use both a particle-in-cell direct simulation Monte Carlo code and a test particle approach to parameterize the growth of the secondary electron emission avalanches (SEEAs). To determine the effect of various HGI design parameters on secondary electron trajectories and SEEA growth, the following factors are investigated: layer width, edge layer materials, secondary electron yield, cell coupling, and surface defects as an electron source. We propose an alternative mechanism for initiating surface flashover, which considers surface defects on the downstream side of insulating layers, which differs from the current theory of cell coupling between adjacent insulating layers. Our results indicate surface conditioning is necessary because surface defects are a significant electron source in many cases. Our results reinforce the theory that thin layer widths are better at minimizing the growth of a surface avalanche, even though they will be more susceptible to cell coupling. If an HGI will not be conditioned prior to use, then thin layers are essential because of the significant avalanche growth capable along thicker layers. Finally, a metal layer adjacent to the cathode and an insulating layer adjacent the anode seems the optimal configuration to minimize the probability of flashover.

As a secondary electron emission layer, an Al2O3/MgO double-layer structure is fabricated by atomic layer deposition (ALD) technology. The thickness range from 1 nm to 4 nm of the top Al2O3 layer deposited on 20 nm MgO creates a double-layer. The morphology of the cross section, element distribution, surface roughness, X-ray diffraction, and secondary electron yield (SEY) values were measured by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM) and secondary electron emission (SEE) measurement systems. The SEE characteristics of the MgO single layer, Al2O3 single layer and MgO/Al2O3 double-layer were measured. The maximum SEY of a single MgO layer reached 6.2@600 eV, and the maximum SEY of a single Al2O3 layer reached 3.92@400 eV. The SEY of the Al2O3/MgO double-layer decreased when the Al2O3 thickness ranged from 1 nm to 4 nm, and the SEY reduction value of the double-layer decreased as the Al2O3 thickness increased. Finally, Dionne's semiempirical SEE model was employed to explain the SEE yield of the prepared composite film structures. These results are useful for depositing a secondary electron emission layer in the channel of microchannel plates.

PTDC/NAN-MAT/30565/2017 D01-284/2019 (INFRAMAT) IBB BASE 2020-2023 UID/FIS/00068/2019. The ability to change the secondary electron emission properties of nitrogen-doped graphene (N-graphene) has been demonstrated. To this end, a novel microwave plasma-enabled scalable route for continuous and controllable fabrication of free-standing N-graphene sheets was developed. High-quality N-graphene with prescribed structural qualities was produced at a rate of 0.5 mg/min by tailoring the high energy density plasma environment. Up to 8% of nitrogen doping levels were achieved while keeping the oxygen content at residual amounts ( 1%). The synthesis is accomplished via a single step, at atmospheric conditions, using ethanol/methane and ammonia/methylamine as carbon and nitrogen precursors. The type and level of doping is affected by the position where the N-precursor is injected in the plasma environment and by the type of precursors used. Importantly, N atoms incorporated predominantly in pyridinic/pyrrolic functional groups alter the performance of the collective electronic oscillations, i.e. plasmons, of graphene. For the first time it has been demonstrated that the synergistic effect between the electronic structure changes and the reduction of graphene $-plasmons caused by N doping, along with the peculiar “crumpled” morphology, leads to sub-unitary (textless 1) secondary electron yields. N-graphene can be considered as a prospective low secondary electron emission and plasmonic material. publishersversion published

While the properties of surfaces and interfaces are crucial to modern devices, they are commonly difficult to explore since the signal from the bulk often masks the surface contribution. Here we introduce a methodology based on scanning electron microscopy (SEM) coupled with a pulsed laser source, which offers the capability to sense the topmost layer of materials, to study the surface photovoltage (SPV) related effects. This method relies on a pulsed optical laser to transiently induce an SPV and a continuous primary electron beam to produce secondary electron (SE) emission and monitor the change of the SE yield under laser illumination. We observe contrasting behaviors of the SPV-induced SE yield change on n-type and p-type semiconductors. We further study the dependence of the SPV-induced SE yield on the primary electron beam energy, the optical fluence, and the modulation frequency of the optical excitation, which reveal the details of the dynamics of the photocarriers in the presence of the surface built-in potential. This fast, contactless, and bias-free technique offers a convenient and robust platform to probe surface electronic phenomena, with great promise to probe nanoscale effects with a high spatial resolution. Our result further provides a basis to understand the contrast mechanisms of emerging time-resolved electron microscopic techniques, such as the scanning ultrafast electron microscopy.

It is shown that a film consisting of the Mo–O, Mo–Ba–O, and Ba–O compounds is formed in the ion-implanted layer upon implantation of MoO3 with the Ba+ ions. Such a process leads to a sharp variation in the density of state of valence electrons, a decrease in work function eφ to 2.7 eV, a decrease in band gap Eg by a factor of about 1.5, and an increase in maximum coefficient of the secondary electron emission σm by a factor of 1.5. It is shown that the emission efficiency of the secondary electrons of the near-surface layer of pure Mo is significantly higher than the emission efficiency of the ion-implanted Mo layers. Thus, an increase in coefficient σm after the ion implantation is predominantly due to a decrease in surface work function eφ. Heating of the ion-implanted MoO3 to 900 K leads to a decrease in work function eφ to 2 eV, and coefficient σm increases when temperature increases to 1000 K.

Atomic layer deposition (ALD) is utilized to prepare thin MgO coatings 1–50 nm on Si substrate. In addition, secondary electron emission (SEE) coefficient of MgO/Si double-layered structure is evaluated as a function of coating thickness and primary electron (PE) energy. After neutralizing the surface of test specimen, we have accurately analyzed the relationship between secondary electron yield (SEY) of MgO coating and PE energy. Meanwhile, SEE characteristics of MgO/Si double-layered structure have been systematically analyzed. A maximum SEY value of 6.15 has been achieved at coating thickness of 30 nm and PE energy of 550 eV. Furthermore, theoretical model is established by using Dionne's SEE model to analyze experimentally measured SEY data, demonstrating consistency between experimentally measured and theoretically calculated results. This work demonstrates that SEE level of MgO coating can be optimized by tuning coating thickness and presents novel insights into SEE characteristics of composite materials. Those results can serve as a baseline for further design and fabrication of a wide array of electronic devices.

The influence of microgeometries on the Secondary Electron Yield (SEY) of surfaces is investigated. Laser written structures of different aspect ratio (height to width) on a copper surface tuned the SEY of the surface and reduced its value to less than unity. The aspect ratio of microstructures was methodically controlled by varying the laser parameters. The results obtained corroborate a recent theoretical model of SEY reduction as a function of the aspect ratio of microstructures. Nanostructures - which are formed inside the microstructures during the interaction with the laser beam - provided further reduction in SEY comparable to that obtained in the simulation of structures which were coated with an absorptive layer suppressing secondary electron emission.

The electron multipliers gain is closely related to the secondary electron emission coefficient (SEE) of the emission layer materials. The SEE is closely related to the thickness of the emission layer. If the emission layer is thin, the low SEE causes the low gain of electron multipliers. If the emission layer is thick, the conductive layer can't timely supplement charge to the emission layer, the electronic amplifier gain is low too. The electron multipliers usually choose Al2O3 and MgO film as the emission layer because of the high SEE level. MgO easy deliquescence into Mg(OH)2 Mg2(OH)2CO3 and MgCO3 resulting in the lower SEE level. The SEE level of Al2O3 is lower than MgO, but Al2O3 is stable. We designed a spherical system for testing the SEE level of materials, and proposed to use low-energy secondary electrons instead of low-energy electron beam for neutralization to measuring the SEE level of Al2O3, MgO, MgO/Al2O3, Al2O3/MgO, and precisely control the film thickness by using atomic layer deposition. We propose to compare the SEE under the adjacent incident electrons energy to partition the SEE value of the material, and obtain four empirical formulas for the relationship between SEE and thickness. Since the main materials that cause the decrease in SEE are Mg2(OH)2CO3 and MgCO3, we use the C element atomic concentration measured by XPS to study the deliquescent depth of the material. We propose to use the concept of transition layer for SEE interpretation of multilayer materials. Through experiments and calculations, we put forward a new emission layer for electron multipliers, including 2–3 nm Al2O3 buffer layer, 5–9 nm MgO main-body layer, 1 nm Al2O3 protective layer or 0.3 nm Al2O3 enhancement layer. We prepared this emission layer to microchannel plate (MCP), which significantly improved the gain of MCP. We can also apply this new emission layer to channel electron multiplier and separate electron multiplier.

International audience; The multipactor is a phenomenon that plays a determining role in the design and development of high-power microwave components in satellite payloads. It relates to a resonant RF electron discharge in which electron multiplication takes place due to the secondary electron re-emission process 1. The discharge is mainly encountered in RF accelerating structures where the combination of RF fields and surfaces of high secondary yield metals (e.g., copper or aluminum) will increase the number of electrons at each impact. For the estimation of the multipactor and for sensing the maximum power that can be handled by a microwave component without the occurrence of a breakdown event, we typically consider the two following conditions: i) the synchronization of electron movement with the RF fields and ii) the electron multiplication via secondary electron emission. The latter is normally addressed relying on semi-empirical models of the Total Electron Emission Yield (TEEY) (Vaughan, Furman) or curves derived from measurement of an equivalent surface. © 2021 IEEE.

Vacuum electronic devices that are exposed to oscillating electric fields can undergo multipactor discharges. During multipactor, radiofrequency electric fields accelerate free electrons into surfaces, causing them to undergo secondary electron emission [1] . These secondary electrons continue this process of acceleration and secondary emission, causing the electron population to multiply exponentially. The resultant electron cloud can cause a number of deleterious effects. Multipactor causes signal attenuation, cavity loading, and reduces the signal quality [2] . The repeated electron impacts can even cause localized heating, potentially leading to catastrophic damage to the device.

The universal formulae for λ(χreal, Eg, T) and λ(χreal, Eg, T)p of insulator having less impurities are experimentally proved, where λ(χreal, Eg, T) is the mean escape depth at Kelvin temperature T of secondary electrons emitted from insulators with band gap Eg and efficient electron affinity χreal, λ(χreal, Eg, T)p is the λ(χreal, Eg, T) due to electron-lattice interaction. Based on the mechanism of electron-insulator interaction, experimental data, existing formulae, ESTAR program and formulae for λ(χreal, Eg, T) and λ(χreal, Eg, T)p of insulator having less impurities, the methods of obtaining λ(χreal, Eg, T)e-e, λ(χreal, Eg, T)e-defect and λ(χreal, Eg, T)i are presented, where λ(χreal, Eg, T)e-e is the λ(χreal, Eg, T) due to electron–electron interaction, λ(χreal, Eg, T)e-defect is the λ(χreal, Eg, T) due to electron–defect interaction, λ(χreal, Eg, T)i is the λ(χreal, Eg, T) due to electron-impurity interaction. The λ(χreal, Eg, T)p, λ(χreal, Eg, T)e-e, λ(χreal, Eg, T)e-defect and λ(χreal, Eg, T)i can provide corresponding information regarding electron-insulator interaction. Thus, it can be concluded that the method of investigating electron-insulator interaction by secondary electron emission SEE is successfully presented in this work. According to experimental data, formula for λ(χreal, Eg, T), ESTAR program, calculated parameters of primary range and existing formulae for SEE, the method of calculating the ẟ at different T and in the range of 1.0 keV ≤ Epo ≤ 100.0 keV from insulator having less impurities is successfully presented, where ẟ is secondary electron yield, Epo is incident energy of primary electron.

MAST-SEY is an open-source Monte Carlo code capable of calculating secondary electron emission using input data generated entirely from first principle (density functional theory) calculations. It utilizes the complex dielectric function and Penn’s theory for inelastic scattering processes, and relativistic Schrodinger theory by means of a partial-wave expansion method to govern elastic scattering. It allows the user to include explicitly calculated momentum dependence of the dielectric function, as well as to utilize first-principle density of states in secondary electron generation, which provides a more complete description of the underlying physics. In this paper we thoroughly describe the theoretical aspects of the modeling, as used in the code, and present sample results obtained for copper and aluminum.

It is well known that carbon present in scanning electron microscopes (SEM), Focused ion beam (FIB) systems and FIB-SEMs, causes imaging artefacts and influences the quality of TEM lamellae or structures fabricated in FIB-SEMs. The severity of such effects depends not only on the quantity of carbon present but also on its bonding state. Despite this, the presence of carbon and its bonding state is not regularly monitored in FIB-SEMs. Here we demonstrated that Secondary Electron Hyperspectral Imaging (SEHI) can be implemented in different FIB-SEMs (ThermoFisher Helios G4-CXe PFIB and Helios Nanolab G3 UC) and used to observe carbon built up/removal and bonding changes resulting from electron/ion beam exposure. As well as the ability to monitor, this study also showed the capability of Plasma FIB Xe exposure to remove carbon contamination from the surface of a Ti6246 alloy without the requirement of chemical surface treatments.

The formulas for δms(χ, Eg), Epoms(χ, Eg), B (χ, Eg), and λ(χ, Eg)s of monocrystalline semiconductors and insulators (MSI) with χ ≥ 0.6 eV and Eg ≥ 0.6 eV were deduced and proved to be correct, where δms(χ, Eg) is the maximum secondary electron yield of MSI with original electron affinity χ and the width of forbidden band Eg, Epoms(χ, Eg) is primary incident energy Epo corresponding to δms(χ, Eg), B(χ, Eg) is the probability that an internal secondary electron escapes into vacuum upon reaching the surface of MSI with Eg and χ, and λ (χ, Eg)s is the mean escape depth of secondary electrons emitted from MSI with χ and Eg. The method that uses the deduced formula for δms(χ, Eg) to calculate χ and the one that uses the deduced formula for Epoms(χ, Eg) to calculate χ were presented. It can be concluded that the χ of MSI with χ ≥ 0.6 eV and Eg ≥ 0.6 eV calculated with the two methods are correct. The χ and λ (χ, Eg)s of both MSI MgO and NaBr calculated in this study are also correct. It can be concluded that the method presented in this study of calculating χ of MgO and NaBr can be extended to calculate χ of MSI with 0.5 eV ≥ χ ≥ 0.6 eV and Eg ≥ 0.6 eV. The method using the deduced formulas to study quantitative influence of vacuum degree on χreal and parameters of secondary electron emission (SEE) is a common method to characterize surface state of MSI, where χreal is real electron affinity; the results obtained by the method are applicable in studying quantitative influence of vacuum degree on SEE induced by ion and those induced by X-ray. It is concluded that the method of studying quantitative influence of vacuum degree on χreal and parameters of SEE from MSI is significant.

We introduce laser-assisted Time-Resolved SEM (TR-SEM), joining Scanning Electron Microscopy and laser light excitation, to probe the long-term temporal evolution of optically excited charge distributions at the surface of Metal Ammonium Lead Triiodide (MAPbI3) hybrid perovskite thin films. Laser-assisted TR-SEM relies on the optically induced local modification of Secondary Electron (SE) detection yield to provide mapping of photoexcited potentials and charge dynamics at surfaces, and qualifies as a complementary approach to near-field probe microscopies and nonlinear photoemission spectroscopies for photovoltage measurements. Real-time imaging of evolving field patterns are provided on timescales compatible with SEM scanning rates, so that temporal resolution in the millisecond range can be ultimately envisaged. MAPbI3 is an outstanding light-sensitive material candidate for applications in solar light harvesting and photovoltaics, also appealing as an active system for light generation. In this work, the real time temporal evolution of optically induced SE contrast patterns in MAPbI3 is experimentally recorded, both under illumination by a 405 nm blue laser and after light removal, showing the occurrence of modifications related to photoinduced positive charge fields at surface. The long term evolution of these surface fields are tentatively attributed to ion migration within the film, under the action of the illumination gradient and the hole collecting substrate. This optical excitation is fully reversible in MAPbI3 over timescales of hours and a complete recovery of the system occurs within days. Permanent irradiation damage of the material is avoided by operating the SEM at 5 keV of energy and 1–10 pA of primary current. Optical excitation is provided by intense above-bandgap illumination (up to 50 W/cm2). TR-SEM patterns show a strong dependence on the geometry of SE collection. Measurements are taken at different axial orientations of the sample with respect to the entrance of the in-column detection system of the SEM and compared with numerical modeling of the SE detection process. This enables to single out the information regarding the local potential distribution. Results are interpreted by combining data about the spectral distribution of emitted SEs with the configuration of the electric and magnetic fields in the specimen chamber. The present modeling sets a robust basis for the understanding of photoinduced SE electron contrast.

An improved corona discharge ignited by oxide cathodes (MgO/NiO/Ni cathode and NiO/Ni cathode) with high secondary electron emission is proposed for toluene degradation. The overall aim of this investigation is to explore the discharge characteristics and toluene degradation performance with oxide cathodes. Current-voltage characteristics results show that discharge currents with MgO/NiO/Ni cathode and NiO/Ni cathode are 2.6–17.4 times (applied voltage of 10.5–13.0 kV) and 1.2–13.5 times (applied voltage of 11.5–14.0 kV) larger, respectively, than the one with Ni cathode. Besides, from the discharge images and optical analysis, the ionization and excitation processes also take place around the oxide cathodes surface, except for the normal corona discharge around the discharge electrode (wires). Moreover, discharges with oxide cathodes exhibit remarkably better toluene degradation, mineralization, and energy performance than the one with Ni cathode. The toluene degradation efficiency, CO2 selectivity, and energy yield in the discharge with MgO/NiO/Ni cathode (P = 5.2 W) are 36.2%, 15.3%, 0.39 g·kWh−1 higher, respectively, than with Ni cathode (P = 6.2 W), and they are 19.4%, 7.9%, 0.15 g·kWh−1 higher, respectively, with NiO/Ni cathode (P = 5.5 W). It is believed that abundant secondary electrons emitted from oxide cathodes, which are induced by the intense electric field within the oxide layers caused by positive charges accumulated on the oxide layer surface, resulting the remarkable increase of discharge current. Besides, the emitted electrons cause extra gas discharge on the oxide layer surface, increasing the number and spatial distribution of electrons/reactive species in the whole discharge gap for good toluene degradation performance.

Accurate measurement of Secondary Electron Emission (SEE) in scientific experiments provides better insight and understanding of field emission and multipacting properties in accelerator cavities. SEE properties of Niobium (Nb) are of significant importance to the performance and operation of accelerator cavities. Additionally, accurate Secondary Electron Yield (SEY) measurements from primary electrons generated from samples measured under different incident angles represent a technical challenge. For that purpose, the sample positioning system presented in this article is a design that allows for precise sample orientation and handling during single pump-down of the vacuum system in the experimental setup. Measurement techniques supported by a mechatronic system provide the means for acquisition of large quantities of data and at the same time reduce the experimental errors related to sample positioning. The authors describe a sample manipulation system and method for controlling the position of samples used for the measurement of SEY.

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.

Multipactor growth in rectangular waveguides is probed based on a kinetic approach. Unlike most studies relying on the Vaughan model, a probabilitic approach for random multiple secondary particle emissions is used. Spread in electron emission velocities, the angular dependence of secondary emission yields, and an external radio frequency (RF) driving field due to a TE10 mode, were all built in. The calculations predict the secondary emission yield for copper, probe the population growth dynamics, and obtain the susceptibility diagram. Despite a maximum field at the waveguide center from the RF excitation, maximum electron densities are predicted at locations symmetrically displaced from the center. The secondary electron yield (SEY) characteristics, its local maxima, and the role of oblique incident angles, collectively lead to multipactor finding its place at off-center locations.

This paper suggests the mechanism of the discharge phenomenon that leads to tracking progress. For this purpose, a polyvinyl-chloride-sheathed flat cord (PVCSFC), which is widely used as a distribution cord, was employed and an artificial crack was intentionally made on the surface. Tracking was progressed using electrolyte droplets. The mechanism of the discharge phenomenon was suggested from the measurement and analysis of the current waveform. As carbonization progressed during the tracking progress, the frequency of scintillation discharge also significantly increased. The mechanism for scintillation discharge during the tracking progress was based on the change in the electric field of the dry band, initial electron, electron avalanche, photoionization, secondary electron generation (electron detachment, photoemission, and secondary electron emission avalanche), space charge due to positive ions, and formation of conductive channels. This discharge mechanism could explain the physical phenomenon and change in the current waveform that occurs during the tracking progress.

An MgO/Au composite film with a 1.8 at% Zn-doped MgO surface layer prepared by reactive magnetron sputtering exhibited a superior electron-induced secondary electron emission (SEE) performance, and it had a SEE coefficient of 5.4 with an increase of 9.3% and a similar SEE degradation rate in comparison with an undoped composite film under primary electron bombardment of 200 eV. The mechanism for this SEE coefficient increase is tightly related to the reduced work function of Zn-doped MgO crystal analyzed by first-principles calculations and the enlarged MgO grains as well as the decreased surface roughness of Zn-doped MgO/Au film observed by morphological characterizations. In addition, for the Zn-doped MgO/Au film its improved electrical conductivity induced by Zn doping results in a similar SEE degradation rate even though it emits secondary electrons with the higher coefficient all the time under continuous electron bombardment compared with the undoped film.

Secondary electron emission (SEE) of the oxygen-free high-conductivity copper (OFHC) target surface in neutron generators limits the stability and improvement of the neutron yield. A novel-type target of titanium–palladium films coated on laser-treated OFHC target substrate was proposed and explored in this work to obtain low secondary electron yield (SEY) without introducing any components. The combination of Ti–Pd films and laser-treated OFHC substrate can effectively suppress secondary electron emission and enhance the adsorption ability to hydrogen isotopes with the existence of Pd film. The surface morphologies, surface chemical states, and SEYs of Ti–Pd films with laser-treated OFHC substrate were studied systematically for the first time. The XPS results showed that the laser-treated OFHC substrate surface was basically covered by Pd film. However, the Pd film surface was partially oxidized, with percentages of 21.31 and 10.02% for PdO and PdO2, respectively. The SEYs of Ti–Pd films with laser-treated OFHC substrate were all below 1 within the investigated primary energy range of 100–3000 eV, which would be sufficient for application in neutron generators. Specifically, the maximum SEY (δmax) of laser-treated OFHC substrate coated by Ti–Pd films was 0.87 with corresponding incident electron energy of 400 eV.

Understanding the effects that sterilization methods have on the surface of a biomaterial is a prerequisite for clinical deployment. Sterilization causes alterations in a material's surface chemistry and surface structures that can result in significant changes to its cellular response. Here we compare surfaces resulting from the application of the industry standard autoclave sterilisation to that of surfaces resulting from the use of low‐pressure Argon glow discharge within a novel gas permeable packaging method in order to explore a potential new biomaterial sterilisation method. Material surfaces are assessed by applying secondary electron hyperspectral imaging (SEHI). SEHI is a novel low‐voltage scanning electron microscopy based characterization technique that, in addition to capturing topographical images, also provides nanoscale resolution chemical maps by utilizing the energy distribution of emitted secondary electrons. Here, SEHI maps are exploited to assess the lateral distributions of diverse functional groups that are effected by the sterilization treatments. This information combined with a range of conventional surface analysis techniques and a cellular metabolic activity assay reveals persuasive reasons as to why low‐pressure argon glow discharge should be considered for further optimization as a potential terminal sterilization method for PGS‐M, a functionalized form of poly(glycerol sebacate) (PGS)., A novel technique built upon secondary electron spectroscopy (SES) provides a detailed investigation into the effects argon plasma treatment has on a biomaterial's surface structures. This unique approach allows for key insights into a samples emission properties and in turn their chemical functional groups, which results in high resolution chemical imaging.

The electron-cloud phenomenon is one cause of beam instabilities in high intensity positive particle accelerators. Among the proposed techniques to mitigate or control this detrimental effect, micro-/nano-geometrical modifications of vacuum chamber surfaces are promising to reduce the number of emitted secondary electrons. Femtosecond laser surface structuring readily allows the fabrication of Laser Induced Periodic Surface Structures (LIPSS) and is utilized in several fields, but has not yet been tested for secondary electron emission reduction. In this study, such treatment is carried out on copper samples using linearly and circularly polarized femtosecond laser pulses. The influence of the formed surface textures on the secondary electron yield (SEY) is studied. We investigate the morphological properties as well as the chemical composition by means of SEM, AFM, Raman and XPS analyses. Surface modification with linearly polarized light is more effective than using circularly polarized light, leading to a significant SEY reduction. Even though the SEY maximum is only reduced to a value of ~1.7 compared to standard laser-induced surface roughening approaches, the femtosecond-LIPSS process enables to limit material ablation as well as the production of undesired dust, and drastically reduces the number of redeposited nanoparticles at the surface, which are detrimental for applications in particle accelerators. Moreover, conditioning tests reveal that LIPSS processed Cu can reach SEY values below unity at electron irradiation doses above 10−3 C/mm2.

Based on expression of primary range R and the R at Epo ≥ 10.0 keV and L at Epo ≥ 1.0 keV calculated by ESTAR program [1] , the method of obtaining formula for R at Epo ≥ 1.0 keV is presented; where Epo is incident energy of primary electron, and L is the energy loss of primary electron per unit path length at the incident surface of the materials. Based on the obtained formula for R, experimental δ, relationships among parameters of δ and the processes and characteristics of secondary electron emission SEE, the universal formula for δ is deduced and the method of calculating δ at Epo ≥ 1.0 keV of insulators and negative electron affinity NEA semiconductors is presented and experimentally proved, where δ is secondary electron yield. The methods of calculating mean escape depth of secondary electrons 1/α and B of insulators and NEA semiconductors are presented, respectively; where B is the probability that an internal secondary electron escapes into vacuum upon reaching the surface of emitter. From the relationships among parameters of SEE and the comparison between the values of 1/α and B obtained in this study and those obtained in former work, it concludes that the methods of calculating 1/α and B are correct.

Electrical double layers play a key role in a variety of electrochemical systems. The mean free path of secondary electrons in aqueous solutions is on the order of a nanometer, making them suitable for probing ultrathin electrical double layers at solid-liquid electrolyte interfaces. Employing graphene as an electron-transparent electrode in a two-electrode electrochemical system, we show that the secondary electron yield of the graphene-liquid interface depends on the ionic strength and concentration of the electrolyte and the applied bias at the remote counter electrode. These observations have been related to polarization-induced changes in the potential distribution within the electrical double layer and demonstrate the feasibility of using scanning electron microscopy to examine and map electrified liquid-solid interfaces.

Surface modification of different materials exposed to an environment typical for hot cathode ionisation vacuum gauges was investigated. Such environment has been generated in a specially designed setup which simulates conditions in a Bayard-Alpert ionisation vacuum gauge. Characterisations by means of X-ray photoelectron spectroscopy and work function study have been performed before and after the sample exposure to Ar and H2 gas discharges. The majority of studied materials, such as molybdenum, gold or stainless steel, are considered to be of interest as ion collectors. In addition, experiments with copper and graphite revealed the major processes that are taking place during the exposure to an ionisation vacuum gauge environment. Since the stability of ionisation vacuum gauges can be affected by the change of secondary electron emission properties of ion collectors during the operation, the corresponding electron yield induced by bombardment of low energy Ar+ ions was measured. Results show that exposure to ionisation vacuum gauge environment contributes to development of hydrocarbon layers, independently from the collector material or the dominant species in the gas discharge. Therefore, ion induced secondary electron yield of clean materials will be changing during the gauge operation and eventually reach saturation regardless of the collector material. The results also show that the hydrocarbon layer cannot be desorbed by standard vacuum baking procedures, whilst ion bombardment will even increase the rate of the hydrocarbon layer formation., accepted to Vacuum on 7th of November 2020

In order to clarify the mechanism on electron multiplication of MCP, it is necessary to study the secondary electron emission properties of inner wall surface. The secondary electron emission is not completely required by materials or devices, and sometimes it can bring bad effects such as noise. In addition to the secondary electron produced by electron colliding with the inner wall, there are additional secondary electrons produced by the ionized cation colliding with the inner wall, which is the key to control the noise of MCP. In this paper, the secondary electron emission produced by the ionized cation colliding with the inner wall of MCP was analyzed after the materials were acid and alkaline treated and hydrogen reduced at high temperature. Time of Flying (ToF) was used to detect secondary electron emission yield (SEEY) of lead silicate glass surface. By comparative analyses, the influence trend of surface treatment process on the secondary electron emission yield of glass surface was acquired. It is expected to provide data supports for parameters optimization of MCP manufacture and preparation of MCP with high signal to noise ratio (SNR).

Despite the discovery of secondary electron emission over a century ago, repeatability in secondary electron emission measurements remains challenging. This work discusses the transient effects associated with sensing low-level currents during SEY measurements. Operations in the low-level range are shown to be prone to long settling times, transmission line effects, and capacitive coupling between isolated circuits. By programming our measurement system to avoid transients, our system was able to perform SEY measurements with currents as low as 140 fA.

To better characterize the lifetime and performance of electrospray thrusters, electron emission due to electrode impingement by the propellant cation 1-ethyl-3-methylimidazolium (EMI+) has been evaluated with semi-empirical modeling techniques. Results demonstrate that electron emission due to grid impingement by EMI+ cations becomes significant once EMI+ attains a threshold velocity of &sim, 9e5cm/s. The mean secondary electron yield, &gamma, &macr, exhibits strong linearity with respect to EMI+ velocity for typical electrospray operating regimes, and we present a simple linear fit equation corresponding to thruster potentials greater than 1kV. The model chosen for our analysis was shown to be the most appropriate for molecular ion bombardments and is a useful tool in estimating IIEE yields in electrospray devices for molecular ion masses less than &sim, scientific&minus, notation=false1000u and velocities greater than &sim, e6cm/s. Droplet-induced electron emission (DIEE) in electrospray thrusters was considered by treating a droplet as a macro-ion, with low charge-to-mass ratio, impacting a solid surface. This approach appears to oversimplify back-spray phenomena, meaning a more complex analysis is required. While semi-empirical models of IIEE, and the decades of solid state theory they are based upon, represent an invaluable advance in understanding secondary electron emission in electrospray devices, further progress would be gained by investigating the complex surfaces the electrodes acquire over their lifetimes and considering other possible emission processes.

Energy-resolved secondary electron spectroscopy has been performed on air-exposed standard Cu samples and modified Cu surfaces that are tested and possibly applied to efficiently suppress electron cloud formation in the high-luminosity upgrade of the Large Hadron Collider at CERN. The Cu samples comprise pristine oxygen-free, carbon-coated and laser-structured surfaces, which were characterized prior to and after electron irradiation and rare-gas ion bombardment. Secondary-electron and reflected-electron yields measured with low charge dose of the samples exhibit a universal dependence on the energy of the primary impinging electrons. State-of-the-art models can successfully be used to describe the spectroscopic data. The supplied spectral dependence of electron emission and integrated electron yield as well as the derived parametrization can serve as a basis for forthcoming simulations of electron cloud formation and multipacting.

Megawatt-class gyrotrons are designed to distribute the residual electron beam energy across a large collecting surface, to keep power densities low enough to be dissipated without threatening long-term vacuum integrity. Because the incident beam is very narrow, various techniques are used to lower the instantaneous and time-averaged power densities on the collector surface, while keeping the size of the collector within the limits of current fabrication capabilities. Gyrotron collector design typically focuses on optimizing the power deposition of the incident (“primary”) beam. It is often assumed that the effects of secondary electron emission from the collector surface (whether due to reflection of primaries, or true secondary emission) will tend to further spread the power density profile. Such additional spreading can be beneficial if it lowers peak power densities, but can be detrimental if it deposits power in undesired locations or sends particles back toward the gyrotron’s interaction region. Here, we simulate the effects of secondary/reflected electrons in the VGT-8115, a 110 GHz, 1.2 MW, 10-second gyrotron used for electron cyclotron heating and current drive in the DIII-D tokamak. We examine the ramifications of secondary emission under various operating conditions, such as variations in collector sweeping parameters and collector depression voltage, comparing power densities and particle trajectories with and without secondaries.

Secondary electron yield of a material is a crucial factor in designing many electronic devices, from electron multipliers to high-power radio frequency devices used in the aerospace industry. In the latter, it is key in mitigating the highly destructive multipactor, where a low value of secondary electron yield is desired. In this work we present results for select elemental metals obtained using a newly developed, state-of-the-art, Monte Carlo code for modeling secondary electron emission with entirely first principle input. The results are compared with the available experimental data.

Secondary electron emission (SEE) inhibition and vacuum instability are two important issues in accelerators that may induce multiple effects in accelerators, such as power loss and beam lifetime reduction. In order to mitigate SEE and maintain high vacuum simultaneously, open-cell copper metal foam (OCMF) substrates with Ti-Zr-V-Hf non-evaporable getter (NEG) coatings are first proposed, and the properties of surface morphology, surface chemistry and secondary electron yield (SEY) were analyzed for the first time. According to the experimental results tested at 25 &deg, C, the maximum SEY (&delta, max) of OCMF before and after Ti-Zr-V-Hf NEG film deposition were 1.25 and 1.22, respectively. The XPS spectra indicated chemical state changes of the metal elements (Ti, Zr, V and Hf) of the Ti-Zr-V-Hf NEG films after heating, suggesting that the NEG films can be activated after heating and used as getter pumps.

When a spacecraft is operating in space orbit, the phenomenon of secondary electron emission will occur under the influence of charged particles in space, causing the surface of the spacecraft to charge, and long-term accumulation will cause damage to the spacecraft and its instruments. In response to the needs of spacecraft live protection and life evaluation, this paper has researched the secondary electron emission yield spectrum test technology of space materials and completed the development of the test system. Firstly, we use an electron gun with an energy range of 0-2000eV, a beam current of 1nA-10μA, and a minimum beam spot diameter of 0.5mm to achieve stable electron beam current in the secondary electron emission coefficient measurement system in this paper. Secondly, the vacuum system uses mechanical pumps, molecular pumps, and sputtering ion pump, so that it can reach a vacuum of 1×10-6pa. Thirdly, the measurement scheme of vacuum secondary electron collecting ball and grid structure is proposed for the first time, which can realize the distinguished collection and measurement of true secondary electrons and backscattered secondary electrons. Finally, the measurement of the secondary electron yield spectrum of metal materials was studied, and the efficient measurement of the secondary electron emission yield spectrum of oxygen-free copper and gold materials was completed. The test results have reached that the secondary electron emission yield spectrum data of Cu and Au samples under 0-2000eV incident electrons is consistent with the literature, which verifies the reliability of the test system.

In the study of secondary electron emission, this paper first uses the Furman model to classify secondary electrons into three types of electrons and model them separately. Second, the Monte Carlo simulation process of the model is realized. In the process of establishing Monte Carlo simulation, a single particle model is used, and the energy spectrum distribution of the entire model is presented based on the superposition of a large number of single-particle distributions. Thirdly, several sets of experiments on the corresponding energy spectrum distribution data obtained under different incident energies of one electron and different incident angles were carried out. Then, discuss the relationship between the secondary electron yield and the incident angle and energy of the primary electron, and quantitatively analyze the relationship between the secondary electron yield and the incident electron angle and incident energy. Finally, the relationship between the incident electron energy and incident angle and the secondary electron emission yield was compared and verified.

Secondary electron (SE) emission is a superficial physical phenomenon. The range of SEs excited in materials which are finally emitted from the surface is generally within a few tens of nanometers. SE emission from materials by electron irradiation has great dependence on surface quality, such as gas adsorption, oxidation, contamination, and morphology. In this paper, the influence of surface adsorption of N2, O2, Ar and air on SE yield (SEY) and the SE spectrum (SES) of copper was investigated by experiment. The measured SEY and SES were compared before and after the copper surface was sputtered by Ar ions. The results show that gas adsorption could increase SEY, and air adsorption lead to the maximum increase, Ar adsorption the minimum. Meanwhile, the relationship between the SES and the SEY was deduced and validated by the experiment. It was also found in the experiment that the Ar ion sputtering or heating alone can effectively reduce the SEY, while heating the sample after Ar ion sputtering increases SEY. The reasons for the variation of the SEYs with gas adsorption, sputtering and heating are preliminarily explained with the help of in-situ XPS. Accordingly, the research helps to further reveal the mechanism of SEE influenced by complex superficial factors.

Abstract A Monte Carlo calculation of the secondary electron emission from a SiO2 macro-capillary in the backward direction induced by electron irradiation is presented with the aim to understand transmission guiding of a scanning electron beam through a borosilicate glass macro-capillary. The theoretical modeling of electron transport in SiO2 capillary incorporates the elastic, inelastic and phonon scatterings, resulting, respectively, from the interactions with nucleus, electrons and phonons. The influence on electron inelastic scattering by the insulator bandgap is also considered. In this work a simplified approach has been employed to deal with the charging of the internal wall of the capillary and it is found that at a glancing incident angle, the secondary electrons are mostly originated from the top surface. Graphical abstract

The Monte Carlo (MC) method is used for evaluating the many physical quantities necessary to the study of the interactions of particle-beams with solid targets. Studies of backscattered and secondary electrons are of great interest for many analytical techniques. A better comprehension of the processes which occur before the emission of backscattered and secondary electrons would allow a more comprehensive understanding of surface physics.

The (secondary) electron emission from multilayered Al$_2$O$_3$/TiN membranes has been investigated with a hemispherical collector system in a scanning electron microscope for electrons with energies between 0.3 and 10 keV. These ultra-thin membranes are designed to function as transmission dynodes in novel vacuum electron multipliers. Two different types, a bi-layer and a tri-layer, have been manufactured by means of atomic-layer deposition (ALD) of aluminum oxide and sputtering of titanium nitride. The reflection and transmission electron yield ($\sigma_R$, $\sigma_T$) have been measured for both types of membranes. In comparison, the tri-layer membranes outperformed the bi-layer membranes in terms of transmission electron yield for films with the same effective thickness. The highest transmission electron yield was measured on an Al$_2$O$_3$/TiN/Al$_2$O$_3$ film with layer thicknesses of 5/2.5/5 nm, which had a maximum transmission electron yield $\sigma_\text{T}^\text{max}(E_0)$ of 3.1 (1.55 keV). Furthermore, the bi-layer membranes have been investigated more in-depth by performing an additional measurement using a positive sample bias to separate the transmitted fraction $\eta_T$ and the transmission secondary electron yield $\delta_T$. The transmitted fraction was used to determine the transmission parameter $p$, which characterizes the interaction of primary electrons (PEs) in thin films. The transmission secondary electron yield was used to compare the energy transfer of PEs in films with different thicknesses.

We performed a combined secondary electron yield and X-ray photoelectron spectroscopy study on a prototypical system formed by increasing coverages of amorphous carbon (a-C) deposited on atomically clean Cu. A remarkably thin a-C layer, of about 6-8 nm, is surprisingly enough to lower below 1 the secondary emission yield of the whole system. This feature qualifies such low thickness coatings as a optimal multipacting suppressor that will not significantly affect impedance issues. The concomitant reduction of surface conductivity observed after antimultipacting coating is, in fact, a major drawback, reducing its applicability in many research fields. The consequences of this observation are discussed mainly for a-C coating applications to mitigate detrimental multipacting effects in radio-frequency devices and accelerators, but are expected to be of interest for other research fields and to hold for other conductive substrates and overlayers.

Based on processes and characteristics of secondary electron emission (SEE), experimental data and the relations among parameters of secondary electron yield from semiconductors δ, the formula for δ in the range of 20 eV ≤ Epo ≤ 800 eV of semiconductors with Epom ≤ 800 eV as a function of Epo, Epom, atomic number Z and maximum δ (δm) was deduced and proved experimentally, where Epo and Epom are incident energy of primary electron and the Epo of δm, respectively. From the existing formula and the relation among Z, mean escape depth of secondary electrons emitted from semiconductors and primary range R at Epom deduced in this study, the formula for R in the range of 150 eV ≤ Epo ≤ 800 eV in monocrystalline semiconductors with Epom ≤ 800 eV, χ ≥ 0.6 eV and Eg ≥ 0.6 eV was successfully deduced, where χ is original electron affinity, Eg is the width of forbidden band. The method of calculating B(χreal, Eg) of semiconductor with Epom ≤ 800 eV, χreal ≥ 0.5 eV and Eg ≥ 0.6 eV and that of calculating B of semiconductor with Epom ≤ 800 eV were presented, respectively; Where B is the probability that an internal secondary electron escapes into vacuum upon reaching the surface of semiconductor, and the B(χreal, Eg) is the B relative to semiconductor with Eg and real electron affinity χreal. It can be concluded that the two methods are correct. From the analysis of calculated B, experimental Epom and relations among parameters of SEE, it can be concluded that this paper can research the surface state of semiconductor with Epom ≤ 800 eV by SEE. Keywords: Secondary electron yield, Semiconductors, Primary range, The probability, Surface state

In view of the multipactor effect caused by the resonant multiplication of secondary electrons in space high-power microwave components, this paper proposes an intra-expansion trap surface to strongly suppress the emission of secondary electrons, and analyzes the suppression characteristics on multipactor via numerical simulation. We track each electrons' trajectory inside the trap to obtain secondary electron emission, and compare with a traditional straight hole trap to present its suppression effects. In addition, the influence of the structure parameters on the secondary electron emission characteristics and the power threshold of multipactor was studied. Results show that comparing with the traditional straight hole trap surface, the proposed intra-expansion trap surface performs 13% more remarkable suppression effect on secondary electron emission, and the power threshold of multipactor can be improved from 8969W to 15437W. A deeper intra-expansion trap surface can enhance the multipactor power threshold further.

We propose a new model to calculate the proton-induced secondary electron yield (SEY) from elemental solids. The model combines the stopping power formula generated by Lindhard dielectric response function and a modified version of Bethe formula for electron stopping. The former works well at low energies while the latter at high energies. The present work further modifies the Bethe formula to adapt it to the proton stopping to complement the stopping formula generated by the dielectric theory. The combination of the stopping power formulae of the dielectric and Bethe theories are connected with the SEY formula of Batrakin et al. [Sov. Phys. JETP 62(3) (1985) 633–634] to frame the present new model. The proposed model is applied to calculate the SEY values of 18 elements with atomic numbers Zt = 3–83 over a broad energy domain 1 keV–1000 MeV. The present results show a reasonable agreement with the available experimental data and other calculations. Universal curves of the normalized SEY values against the reduced energy is drawn to verify the validity of our calculations. Keywords: Secondary electron emission, Stopping cross-sections, Dielectric theory, Bethe formula

Power supplies have played crucial role to improve and extend plasma applications. Several dc, pulsed, and radio frequency (RF) stabilized power supplies have been developed over a wide range of frequencies and voltage waveforms. However, the influence of voltage waveform on the plasma densification, mainly due to the secondary electrons emission from the electrodes, has not been quite explored. This paper proposes an asymmetric pulsed bipolar power supply, adjustable in frequency, amplitude, pulsewidth, and number of pulses for generation of cold plasmas. Short period positive pulses, between longer negative pulses, increase greatly the secondary electron emission from the electrodes and, consequently, the plasma ionization rate. Short pulses (ns) are obtained by the phase shift between each carrier, and the high-intensity pulses are obtained by cascading the cell submodules in a half-bridge cascade topology, using a modular half-bridge converter configuration. The intensity of the positive and negative pulses can be varied independently. There is no unintended dc voltage level between the electrodes, which appear in RF plasmas. The plasma generated in this way is free of electric arc and can be kept stable within a broader range of operating parameters, mainly the voltage and the working gas pressure.

We present calculations of secondary electron emission (SEE) yields in tungsten as a function of primary electron energies between 100 eV and 1 keV and incidence angles between 0 and 90 ° . We conduct a review of the established Monte Carlo methods to simulate multiple electron scattering in solids and select the best suited to study SEE in high-Z metals. We generate secondary electron yield and emission energy functions of the incident energy and angle and fit them to bivariate fitting functions using symbolic regression. We compare the numerical results with experimental data, with good agreement found. Our calculations are the first step towards studying SEE in nanoarchitected surfaces for electric propulsion chamber walls.

Secondary electron emission from thin silicon nitride films of different thicknesses on silicon excited by helium ions with energies from 15 to 35 keV was investigated in the helium ion microscope. Secondary electron yield measured with Everhart-Thornley detector decreased with the irradiation time because of the charging of insulating films tending to zero or reaching a non-zero value for relatively thick or thin films, respectively. The finiteness of secondary electron yield value, which was found to be proportional to electronic energy losses of the helium ion in silicon substrate, can be explained by the electron emission excited from the substrate by the helium ions. The method of measurement of secondary electron energy distribution from insulators was suggested, and secondary electron energy distribution from silicon nitride was obtained.

The prototype and configuration design of a novel multipacting cathode producing a ring-like electron beam for high-current diode are presented. The whole dynamic process of the moving secondary electron on the multipacting cathode surface is theoretically investigated and numerically simulated using the Monte Carlo method. The results indicate that the prototype of the novel multipacting cathode for high-current diode is feasible. Under the interactions of the applied electric field (~MV/m) in axial and radial directions and the guiding magnetic field (~T) in axial direction, the seed electrons from the triple junctions move with spiral advancing trajectories along axial direction. Electron number can be effectively increased by each impact on the coating surface with high secondary electron emission yield coefficient. This phenomenon will achieve electron current amplification with the ring-like electron beam output till multipacting enters into saturation. The simulated characteristic parameters of the secondary electron and the working range of the multipacting cathode agree with the theoretical results. Under the typical condition, the moving distance of the secondary electron is on the order of submillimeters, the fight time is on the order of picoseconds, and the spread speed is on the order of 106 to 107 m/s. In addition, the multipacting saturation mechanism is analyzed, and the emission current density is roughly estimated to ~kA/cm2. Enhancing the magnitude of applied electric field in radial direction can effectively improve the emission current density.

Magnesium oxide (MgO) and MgO/Al2O3 composite thin films were prepared on silver substrates by DC magnetron sputtering technique and their secondary electron yields (δ) and working durability under constant electron bombardment were investigated. X-ray photoelectron spectroscopy and Auger electron spectroscopy analyses reveal that uniform MgO/Al2O3 composite films were developed and residual Al exists in the films after sputtering of the Mg-Al alloy in an Ar-O2 mixed atmosphere on silver substrates heated at 400°C. The MgO/Al2O3 composite films show superior δ as high as 11.6 and much better resistance to electron bombardment than that of pure MgO films. Good secondary electron emission (SEE) properties of the MgO/Al2O3 film are probably due to the presence of alumina in the film, which has higher bond dissociation energy than MgO, as well as the presence of residual Al in the film, which contributes to effective electron transport in the film and diminished surface charging during SEE. With superior SEE performance, MgO/Al2O3 films have potential for practical electron multipliers in various vacuum electron devices.

In this paper we have investigated the effect of ion nonthermality on nonlinear dust acoustic wave propagation in a complex plasma in presence of weak secondary electron emission from dust grains. Equilibrium dust charge in this case is negative. Dusty plasma under our consideration consists of inertialess nonthermal ions, Boltzman distributed primary and secondary electrons and negatively charged inertial dust grains. Both adiabatic and nonadiabatic dust charge variations have been taken into account. Our analysis shows that in case of adiabatic dust charge variation, at a fixed non-zero ion nonthermality increasing secondary electron emission decreases amplitude and increases width of the rarefied dust acoustic soliton whereas for a fixed secondary electron yield increasing ion nonthermality increases amplitude and decreases width of such rarefied dust acoustic soliton. Thus shape of the soliton may be retained if strength of both the secondary electron yield and the ion nonthermality are increased. Nonadiabatic dust charge variation shows that, at fixed non-zero ion nonthermality, increasing secondary electron emission suppresses oscillation of oscillatory dust acoustic shock at weak nonadiabaticity and pronounces monotonicity of monotonic dust acoustic shock at strong nonadiabaticity. On the other hand at a fixed value of the secondary electron yield, increasing ion nonthermality enhances oscillation of oscillatory dust acoustic shock at weak nonadiabaticity and reduces monotonicity of monotonic dust acoustic shock at strong nonadiabaticity. Thus nature of dust acoustic shock may also remain unchanged if both secondary electron yield and ion nonthermality are increased.