Secondary Electron Emission Yield Research Articles

Secondary electron emission measurements from imidazolium-based ionic liquids

Abstract The electron-induced secondary electron emission (SEE) yields of imidazolium-based ionic liquids are presented for primary electron beam energies between 30 and 1000 eV. These results are important for understanding plasma synthesis of nanoparticles in plasma discharges with an ionic liquid electrode. Due to their low vapor pressure and high conductivity, ionic liquids can produce metal nanoparticles in low-pressure plasmas through reduction of dissolved metal salts. In this work, the low vapor pressure of ionic liquids is exploited to directly measure SEE yields by bombarding the liquid with electrons and measuring the resulting currents. The ionic liquids studied are [BMIM][Ac], [EMIM][Ac], and [BMIM][BF4]. The SEE yields vary significantly over the energy range, with maximum yields of around 2 at 200 eV for [BMIM][Ac] and [EMIM][Ac], and 1.8 at 250 eV for [BMIM][BF4]. Molecular orbital calculations indicate that the acetate anion is the likely electron donor for [BMIM][Ac] and [EMIM][Ac], while in [BMIM][BF4], the electrons likely originate from the [BMIM]+ cation. The differences in SEE yields are attributed to varying ionization potentials and molecular structures of the ionic liquids. These findings are essential for accurate modeling of plasma discharges and understanding SEE mechanisms in ionic liquids.

New experimental methodology for determining the second crossover energy in insulators under stationary e-irradiation in a SEM

A new experimental methodology is proposed which uses the electrostatic influence method (EIM) in scanning electron microscope (SEM) in order to estimate the second crossover energy EC2 for uncharged insulators. This experimental methodology based on simultaneous time measurement of the displacement and leakage currents, is approached to the short pulse irradiation technique but under stationary e-irradiation and allows determining the intrinsic secondary electron emission yield, σ0 (σ0 is the value of the total secondary electron yield just at the beginning of the irradiation before significant charge accumulation or before the formation of a surface potential). The obtained value of EC2 for soda-lime glass is confirmed by two additional experiments based on secondary electron imaging. This value is in good agreement with those previously obtained by other studies based on the surface potential measurement or the pulsed irradiation technique.

Mechanism exploration of ion-implanted epoxy on surface trap distribution: An approach to augment the vacuum flashover voltages

Abstract The augmentation of the epoxy (EP) resin surface to advance flashover performance has become a pivotal point of global interest. This research introduces a novel surface modification method and its mechanism for insulation materials. The research follows an electron cyclotron resonance ion implantation system to subject the surface of EP insulation to ion beams with diverse energies, i.e., 6, 10, 20, 40, 50, and 60 keV for a consistent time of 300 s at an angle of 90°. The experimental phase includes the DC flashover examination under negative polarity. Besides, the simulation phase includes the Monte Carlo model constructed using SRIM software to examine the range and distribution of bombarded ions in the targeted insulation. Results reveal that the flashover properties are affected by the surface potential, surface conductivity, trap distribution, water contact angle, and elemental composition. Likewise, based on the outcomes and theoretical point of view, it is revealed that the bombardment of energetic ions enhances the trap depth, assisting in a reduction in surface conductivity, confining the surface charge movements, and extensively suppressing the secondary electron emission yield. Also, the enhanced trap depth induces homo-charge formation near triple junctions. Synergistically, the factors contribute to high flashover voltages.

Secondary Ion Emissions of Tm and Tb Targets Under Bombardment With Cluster Ions

ABSTRACTIn this work, the features of secondary emission phenomena were investigated under cluster bombardment. The emission of ion‐photons, secondary ions, and electrons associated with the thermal peak regime were experimentally carried out. The experiments were conducted using modernized a static magnetic mass spectrometer. The integral yield of secondary ion and electron emission was measured by bombarding Tb and Tm targets with cluster ions Aum− (m = 1–9) and Bim− (m = 1–7) within the energy range of 1–21 keV for the bombarding ions. Additionally, the integral yield of ion‐photon emission was measured by bombarding a Tm target with cluster ions Bim− (m = 1–5) within the same energy range. The experimental results showed that an increase in the yield of ion‐photon emission, secondary ion, and ion‐electron emission was observed with an increase in the number of atoms bombarded by cluster ions. This can be explained the formation of thermal peaks under dense collision cascades.

Revelation of the high surface insulation performance of the electron-delocalized group through molecule self-assembly on alumina insulator

Surface modification of vacuum insulators is a promising way to improve their surface insulation performance but commonly used surface modification technologies in surface insulation area such as fluorination and plasmas treatment are unable to control the surface chemical components at the molecular level, which makes it hard to explore molecular groups with high surface insulation performance. In this paper, molecule self-assembly is introduced to control the surface molecular structure precisely and vacuum surface insulation performance of a special molecular structure electron-delocalized group is studied. Hexagonal phenyl group containing delocalized electrons and cyclohexyl group with the same hexagonal molecular structure but without delocalized electrons are grafted onto the surface of alumina insulators through molecule self-assembly. Secondary electron emission yield test shows that phenyl group endows alumina insulators lower SEY than cyclohexyl group. Correspondingly, phenyl group grafted alumina insulators show higher surface insulation performance than cyclohexyl group. The results indicate that group containing delocalized electrons can endow insulators higher surface insulation characteristics.

Enhancing vacuum surface flashover voltage of alumina insulator by self-assembly of fluorine-containing molecule

In this study, a fluorocarbon chain was grafted on the surface of the alumina insulator through the molecule self-assembly of perfluorododecyl trichlorosilane to enhance the vacuum surface flashover voltage. A hydrocarbon chain with the same molecular structure, devoid of fluorine element, was also grafted through the self-assembly of dodecyl trichlorosilane to enable comparison. The surface state examination of the self-assembled alumina insulators shows that both the molecules are attached to the alumina surface. The arrangement of the molecules on the surface is regular. Surface property tests reveal that the fluorocarbon chain endows the surface of alumina with a lower secondary electron emission yield and a lower gas adsorption volume than the hydrocarbon chain. Correspondingly, the surface flashover voltage of the fluorocarbon chain grafted insulator is higher than that of the hydrocarbon chain. This implies that the surface flashover voltage can be improved through surface fluorination, which converts hydrocarbon bonds to fluorocarbon bonds. The study demonstrates this possibility at the molecule level.

Enhanced secondary electron emission properties of sputter-deposited MgO–Au composite film via Cr doping

High and stable secondary electron emission yield (SEY) is essential for thin film materials used for electrical signal amplification in electronic devices. To enhance the secondary electron emission (SEE) capability of MgO–Au composite film, Cr-doped MgO–Au film was prepared by magnetron sputtering and the effect of Cr doping on the SEE properties of MgO–Au film was intensively investigated. It was confirmed that the doped Cr element is distributed through the whole composite film in a form of Cr2O3. Compared to the conventional MgO–Au film, the Cr-doped MgO–Au film with a Cr/(Cr + Mg) atomic ratio of 0.71 % achieves a SEY of 7.1 with a 4.4 % rise at the primary electron energy (Ep) of 300 eV and a maximum SEY of 10.9 with a 10.1 % increase at the Ep of 800 eV, and it also has a reduction of 49.2 % in SEE decay rate under continuous electron bombardment. For this novel composite film, the SEY ascension mainly attributes to the MgO grain enlargement and chemical stability enhancement, and the decreased SEE decay rate is associated with the improvements of resistance to electron bombardment and electric conductivity induced by Cr doping.

Secondary electron emission yield in thick dielectric materials: a comparison between Kelvin probe and capacitive methods

The recent high demand of secondary electron emission yield (SEY) measurements in dielectric materials from space industry has driven SEY laboratories to improve their facilities and measurement techniques. SEY determination by the common capacitive method, also known as pulsed method, is well accepted and has given satisfactory results in most cases. Nevertheless, the samples under study must be prepared according to the experimental limitations of the technique, i.e. they should be manufactured separated from the devices representing faithfully the surface state of the own device and be as thin as possible. A method based on the Kelvin probe (KP) is proposed here to obtain the SEY characteristics of electrically floating Platinum, Kapton and Teflon placed over dielectric spacers with thicknesses ranging from 1.6 to 12.1 mm. The results are compared with those of the capacitive method and indicate that KP SEY curves are less sensitive to spacer thickness. An explanation based on the literature is also given. In all, we have established that KP is better suited for the analysis of dielectric samples thicker than 3 mm.

Secondary electron emission reduction from boron nitride composite ceramic surfaces by the artificial microstructures and functional coating

Boron nitride-silicon dioxide (BN–SiO2) composite ceramic is a typical Hall thruster wall material, and its secondary electron emission (SEE) property dominates the sheath characteristics inside the thrusters. Lowering the SEE yield (SEY) of the wall surface can remarkably improve the sheath stability of Hall thrusters. To accomplish the SEY reduction for BN–SiO2, artificial surface microstructure and surface coating technologies are employed. The morphology analysis demonstrated the shape and feature sizes of the microstructure could be largely controlled by adjusting the laser etching parameters. Then we realized an increasingly significant SEY reduction for BN–SiO2 as the average aspect ratio of the microhole increases. The microstructures showed a remarkable SEY reduction when the laser power was 10 W and the scanning cycle was 50. In this case, the SEY peak values (δ m) of the two BN–SiO2 samples with mass ratios of 7:3 and 6:4 decrease from 2.62 and 2.38 to 1.55 and 1.46 respectively. For a further SEY reduction, a sputtering process was employed to deposit TiN film on the microstructures. The results showed that the TiN coating of 246 nm thickness reduced the δ m values of the two samples from 1.55 and 1.46 to 0.82 and 0.76, which achieved a notable SEY reduction compared to the original surface. Via simulation work, the SEY reduction achieved by microstructures was theoretically interpreted. Besides, by considering the effect of surface charging, the results of SEY converged to 1 with the irradiation pulse increasing presented. The research demonstrated a remarkable SEY reduction for BN–SiO2 ceramic by constructing surface microstructure and depositing TiN coating, which has application sense for low SEY engineering in specific working scenarios.

Effective improvement of the micro-discharge threshold and environmental stability in microwave devices based on carbon/silver/titanium composite films

The micro-discharge effect limits the development of high-frequency microwave power components to miniaturization and integration. Therefore, it has become a focus of research to effectively suppress the micro-discharge effect, increase the micro-discharge threshold, and strengthen the environmental stability of high-frequency microwave devices. In this study, different elemental ratios of carbon (C)/silver (Ag)/titanium (Ti) composite films were obtained by multi-target magnetron co-sputtering technology and then systematically analyzed for micro-discharge effects. When the doping ratio of C/Ag/Ti was 3.538/1/0.013, the corresponding maximum secondary electron emission coefficient (δmax) decreased to 1.01 owing to the suppression of secondary electron emission by the increase in the content of sp2 hybrid bond. The micro-discharge threshold of Ku band waveguide filters coated with moderate C/Ag/Ti composite films showed an optimal performance of 10 000−12 500 W, which was increased by approximately 20 times. Moreover, the microstructure of the composite films exhibited higher density and flatness with a tiny increase in the titanium doping ratio, representing good environmental stability. Thus, the effective suppression of the secondary electron emission yield, significant improvement in the micro-discharge threshold, and enhancement of the environment stability of microwave components could be realized simultaneously by reasonably controlling the content of titanium in silver and titanium co-doped carbon-based composite films.

Modelling the Impact of Graphene Coating of Different Thicknesses on Polyimide Substrate on the Secondary Electron Yield

Polyimide material is widely used in the aerospace field, but its secondary electron emission yield is high. In this study, a graphene coating was used to suppress its secondary electron emission, and the secondary electron emission yield of graphene-coated materials with different thicknesses was calculated using the GEANT4 numerical simulation method. The suppression effect of different thicknesses of graphene coatings on the secondary electron emission was analyzed. The simulation results showed that the optimal graphene coating thicknesses for the lowest secondary electron yield of polyimide materials were 1 nm and 5 nm, which reduced the secondary electron emission yield by 13% in terms of simulation. The 5 nm graphene coating reduced the secondary electron emission yield by 6% compared to the polyimide material from an experimental perspective. The 5 nm coating showed better results at higher energies and was experimentally verified by preparing five layers of graphene coating, which showed good agreement between the simulation and experiment. Meanwhile, with the increase in graphene coating thickness, the surface secondary electron emission displacement range decreased, and the secondary electrons produced at the surface were of low energy. The results of this study can provide technical reference for polyimide in aerospace applications and secondary electron emission simulation.

Suppression of Secondary Electron Emissions on the Graphene-Coated Polyimide Materials Prepared by Chemical Vapor Deposition

Polyimide thin-film materials are widely used in aerospace and particle gas pedals, etc., but the phenomenon of secondary electron emission occurred under vacuum conditions. The graphene-coated polyimide materials were prepared for this phenomenon to suppress secondary electron emissions. The graphene coating was prepared on the polyimide surface through chemical vapor deposition (CVD). Scanning electron microscope images (SEM), X-ray photoelectron spectrometer images (XPS), Raman spectroscopy, atomic force microscopy (AFM), and other analytical methods were used to characterize the properties of the prepared materials. The C1s XPS fine spectra and Raman curve analyses showed that the material has an abundant sp2 hybridized structure, and the sp2 structure can reduce secondary electron emissions. The C, O, and N contents in the tested samples were 65.85, 20.47, and 13.68 at.%, respectively. It was examined that the graphene coating had an inhibitory effect on the secondary electron emissions of polyimide materials, and the secondary electron emission yield (SEY) was significantly reduced. The results of secondary electron tests showed that the maximum SEY (δmax) of the polyimide material decreased from 1.72 to 1.52 after the preparation of the graphene coating. The mechanism of using a graphene coating to reduce the SEY of polyimide was analyzed from experimental and theoretical perspectives. The results of this study can provide research ideas for polyimide thin film materials in aerospace, particle gas pedals, and other applications.

Measurements of secondary electron emission yield in the linear plasma simulator BPD-PSI

The secondary emission properties of the surface play one of the key roles in its interaction with plasma. This paper presents the first study of electron-induced electron emission yield performed in the linear plasma simulator BPD-PSI. To verify the applicability of the measurement technique used, a series of experiments was conducted to investigate the total secondary electron yield as a function of the energy of primary electrons for several pure elements, such as carbon, copper, and tungsten. Particular attention was paid to the latter as one of the essential plasma-facing materials, due to its ability to withstand moderate plasma loads. The change in the total secondary electron yield of tungsten was studied in-vacuo after each subsequent change in its surface morphology as a result of: annealing at 2770 K, exposure to pure helium plasma at 1250 K and annealing of plasma-modified tungsten surface at 2770 K. The growth of nanoscale structures, known as fuzz, on its surface caused a reduction in the total yield of secondary electrons by 10–18% compared to the clean surface. A non-monotonic relationship between total secondary electron yield and primary electron energy was observed. The interpretation of this phenomenon is given in the present work.

A search for chiral asymmetry in secondary electron emission from cysteine induced by longitudinally polarized electrons.

We performed experiments searching for chirality-dependent secondary electron emission for a 141eV longitudinally spin-polarized electron beam incident on a thick solid cysteine target. We determined the secondary electron yield by measuring the positive current produced when the cysteine target was negatively biased. No spin-dependent effects to a level of 10-3 were found for the secondary electron emission yield.

Temperature effects on electric charge transport processes and electron emission in PBS–clay nanocomposites submitted to electron bombardment

The effects of isothermal conditions on the charge transport processes and electron emission properties of polybutylene succinate (PBS) nanocomposites with different nanoclay content are investigated. The temperature range used (20 °C–80 °C) is close to the working conditions of materials used in many applications (insulation, sensors). These effects are highlighted using an appropriate device placed in a scanning electron microscope, allowing measurement of induced current in an electron-irradiated specimen. The experimental results show that the rise in temperature involves a decrease in the charging ability and an increase in the conductivity of PBS nanocomposites. The mobility of charge carriers and its thermal dependency deduced during the discharge step were found to be lower for the nanocomposites. A qualitative analysis, expressed to understand these observations, is based on the determination of the electron trap energy distribution (i.e. density of occupied states). Secondary electron emission yield decreased with increasing temperature. The results help us envision a new class of insulators with improved electrical performance. The operating thermal stress, combined with the absence of trapped charges, allows a reduction of electrical and thermal aging and consequently ensures the long-term reliability of the insulators (for instance under High Voltage).

Development of hybrid resistive plate chambers

Resistive Plate Chambers (RPCs) are essential active media of large-scale experiments as part of the muon systems and (semi-)digital hadron calorimeters. Among the several outstanding issues associated with the RPCs, the loss of efficiency for the detection of particles when subjected to high particle fluxes, and the limitations associated with the common RPC gases can be listed. In order to address the latter issue, we developed novel RPC designs with special anode plates coated with high secondary electron emission yield materials such as Al2O3 and TiO2. The proof of principle was obtained for various designs and is in progress for the rest. The idea was initiated following the achievements on the development of the novel 1-glass RPCs.Here we report on the construction of various different RPC designs, and their performance measurements in laboratory tests and with particle beams; and discuss the future test plans.

Влияние энергии электронного пучка на характеристики зарядки полимерных композитов с включением углеродных нанотрубок

The possibility of using polymer composite materials based on epoxy resins with the inclusion of carbon nanotubes as coatings with a low coefficient of secondary electron emission has been studied. Four types of samples were obtained: epoxy polymer, polymer composites with fillers (non-oriented and oriented carbon nanotubes, carbon soot). It is shown that the secondary electron emission yield depends on the structure of the introduced carbon filler, and polymer composites with oriented nanotubes exhibit antidynatron properties.

Modeling electron transport and multiplication in photomultiplier tubes using COMSOL Multiphysics®

Combining stochastic and finite element methods, a modeling approach was executed that will inform new photomultiplier tube and scintillation detector designs. Time-dependent signal formation within a commercially available photomultiplier tube was modeled including the release and transport of electrons from the photocathode through the dynode stages. An ET Enterprises 9214B photomultiplier tube was digitally reproduced using Computed Tomography, X-ray radiography, and SolidWorks solid-modeling software. Simulations were executed with COMSOL Multiphysics® finite element solving package. Stochastic models of electron emission from the photocathode and dynodes were integrated within the COMSOL framework. Photoelectron emission energy was modeled by combining NaI(Tl) spectral emission characteristics and K2CsSb photocathode quantum efficiency. Secondary electron emission yields were produced to follow nominal photomultiplier gain, while secondary electron energies were sampled from the Chung-Everhart distribution. Electron emission trajectories were sampled according to Lambert's cosine law. Coupling stochastic and finite element models, simulation reproduced signal formation for the commercial photomultiplier tube including timing characteristics within 9.5% and gain within 3% over a voltage range of 900–1250 V.

Effects of hot-rolling on secondary electron yield properties of Cu-2.7Be alloy

The effects of hot-rolling on the secondary electron property evolution of activated Cu-2.7Be sheets were investigated in this study. The microstructures of both pristine and activated Cu-2.7Be alloys subjected to different hot-rolling temperatures were characterized. Their phase compositions were found to comprise an α matrix and eutectoid phases ( α + γ ). Using electron back-scattered diffraction, the initial average grain size ( d 0 ) was found to vary from 6.45 μ m to 15.63 μ m as the hot-rolling temperature increased from 680 °C to 830 °C. Scanning electron microscopy and X-ray photoelectron spectroscopy studies of the activated Cu-2.7Be sheets revealed that the amount of BeO increased with a decrease in the average grain size, resulting in the enhancement of the peak secondary electron emission yield. Scanning Kelvin probe force microscopy measurements confirmed that the main contributor to the BeO enhancement was the α matrix, while transmission electron microscopy analysis showed that BeO formed preferentially from sub-grain boundaries, indicating the importance of grain boundaries for BeO formation. Moreover, the peak secondary electron yield ( δ m ) exhibited a linear relationship with d 0 −0.5 similar to the Hall-Petch relation. The results in this study will be important for enhancing the secondary electron yield of Cu-Be dynodes used in photomultiplier tubes and electron multipliers. • The peak secondary electron yield (SEY)of Cu-2.7Be alloys after activation are inversely proportional to the rolling temperature. • The lower the deformation temperature is, the more BeO content is after activation. • The matrix contributes more to the increase of SEY than eutectoid structure.

Development of Novel Designs of Resistive Plate Chambers

Resistive Plate Chambers (RPCs) are a key active media of the muon systems of current and future collider experiments as well as the CALICE (semi-)digital hadron calorimeter. The outstanding issues with RPCs can be listed as the loss of efficiency for the detection of particles when subjected to high particle fluxes and the limitations associated with the common RPC gases. We developed novel RPC designs with: low resistivity glass plates; a single resistive plate; and a single resistive plate and a special anode plate coated with high secondary electron emission yield material. The cosmic and beam tests confirmed the viability of these new approaches for calorimetric applications. The chambers also have improved single-particle response, such as a pad multiplicity close to unity. Here, we report on the construction of various different glass RPC designs and their performance measurements in laboratory tests and with particle beams. We also discuss future test plans, which include the long-term performance tests of the newly developed RPCs, investigation of minimal gas flow chambers, and feasibility study for the large-size chambers.