High Secondary Electron Emission Research Articles

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.

Enhancing plasma discharge dynamics through analysis of secondary electron emission: A numerical modeling approach for improved thin film deposition

This research examines the impact of the coefficient of secondary electron emission (SEE) on various discharge features of plasma to improve the performance of deposited thin films. Unlike previous studies, we employed two-dimensional numerical modeling (2D) of an ICP reactor at a radiofrequency of 13.56 MHz and a low pressure of 1 Torr, using a finite element approach. This detailed investigation into parameters such as ionization rate, electric field, electron temperature, and electron density provides new insights into plasma interactions. Our findings reveal a significant correlation between the SEE coefficient and key plasma attributes. Notably, increased secondary electrons lead to a substantial rise in electron density and a reduction in sheath thickness, indicating an impactful change in the spatial distribution of plasma particles. Additionally, electron temperature increases exclusively in sheath regions, a novel observation not reported in earlier studies. Furthermore, higher SEE coefficients correlate with increased ionization rates within each sheath, suggesting a crucial role in maintaining discharge processes. This comprehensive analysis uncovers complex interdependencies within the plasma discharge system, offering valuable advancements for thin film deposition techniques.

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.

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.

A novel double dielectric barrier discharge reactor with high field emission and secondary electron emission for toluene abatement

Dielectric barrier discharge (DBD) has been extensively investigated in the fields of environment and energy, whereas its practical implementation is still limited due to its unsatisfactory energy efficiency. In order to improve the energy efficiency of DBD, a novel double dielectric barrier discharge (NDDBD) reactor with high field emission and secondary electron emission was developed and compared with traditional DDBD (TDDBD) configuration. Firstly, the discharge characteristics of the two DDBD reactors were analyzed. Compared to TDDBD, the NDDBD reactor exhibited much stronger discharge intensity, higher transferred charge, dissipated power and gas temperature due to the effective utilization of cathode field emission and secondary electron emission. Subsequently, toluene abatement performance of the two reactors was evaluated. The toluene decomposition efficiency and mineralization rate of NDDBD were much higher than that of TDDBD, which were 86.44%–100% versus 28.17%–80.48% and 17.16%–43.42% versus 7.17%–16.44% at 2.17–15.12 W and 1.24–4.90 W respectively. NDDBD also exhibited higher energy yield than TDDBD, whereas the overall energy constant of the two reactors were similar. Finally, plausible toluene decomposition pathway in TDDBD and NDDBD was suggested based on organic intermediates that generated from toluene degradation. The finding of this study is expected to provide reference for the design and optimization of DBD reactor for volatile organic compounds control and other applications.

An investigation of secondary electron emission from ZnO based nanomaterials for future applications in radiation detectors

This paper discusses the use of nanomaterials for the improved performance of time-of-flight particle detectors based on secondary electron emission (SEE). The purpose of the research presented in this paper is to find a nanomaterial that has a higher SEE than gold. In this article, we present a measurement of the SEE properties from 1D (one-dimensional) nanostructures of ZnO and ZnO/GaN (ZnO with GaN coating) composed of a mostly regular pattern of nanotubes grown on a thin Si3N4 substrate. The study was performed with 4.77 meV/u Au beam. We observed an average increase of 2.5 in the SEE properties from the 1D ZnO nanotubes compared to gold.

Fabrication and Study of the Electronic Structure of МоO3/Мо Nanofilms

The composition, the surface morphology, and the crystalline and electronic structure of МоО3 nanofilms are studied using a set of methods, namely, scanning electron spectroscopy and high energy electron diffraction, photoelectron spectroscopy, and secondary electron emission. These nanofilms are obtained by implanting $${\text{O}}_{{\text{2}}}^{{\text{ + }}}$$ ions into a Mo single crystal heated to Т = 850 K. Films with different thicknesses (~30, 60, and 90 A) are obtained at an ion energy of 1–5 keV and a dose of D = (4–8) × 1017 cm–2. It is shown that a continuous and homogeneous polycrystalline МоО3 film with a surface roughness of at most 1.5 nm is formed. The band gaps of these films are ~3.4 eV, and the widths of the conduction bands are 4.5 eV. It is discovered that there are four maxima of the density of electronic states in the valence band; probably, they are due to hybridization of the N5, N45, N4 energy levels of Mo with the L2, L23, and L3 energy levels of oxygen.

Theoretical study of pre-ionization by inductive field in tokamaks

A one-dimensional fluid model is developed for a numerical study of pre-ionization in a tokamak device under a given external inductive field. The calculation space is a magnetic field line connecting the bottom and the top limiters, and the spatial profiles of ion and electron densities and their time evolutions are calculated, assuming density growth by the Townsend avalanche. It was found that at a low initial density, electrons are evacuated and exponential growth can be stopped (i.e. stagnation phase), and at a high density, formation of an ambipolar diffusion state may suppress further avalanche by compensating the external inductive field. The numerical study revealed that these two obstacles for pre-ionization can be avoided or mitigated under a certain condition. A high ion impact secondary electron emission efficiency at the limiter, a long field line length and a large Townsend’s coefficient are preferable to avoid the stagnation phase or to resume growth from the stagnation phase. The ambipolar diffusion state can be mitigated or avoided using the following four mechanisms: drift induced diffusion, and curvature drifts, a high ion impact secondary electron emission efficiency and AC inductive field. Among them, only the first is practically useful in weak inductive field large devices. Various analytical expressions describing these behaviors and the conditions for a successful pre-ionization are obtained.

Synthesis and Characterization of Physical Properties of MgO Thin Films by Various Concentrations

Abstract In this work, magnesium oxide was elaborated on a glass substrate at 450°C by a pneumatic spray technique. The structural, optical, and electrical properties were studied at different MgO concentrations (.05, .10, .15, and .2 mol L−1). Poly-crystalline MgO films with a cubic structure with a strong (002) preferred orientation were observed at all sprayed films, with a maximum crystallite size of 21.4 nm attained by the sprayed film at .2 mol L−1. Good transmission was found in the deposited MgO thin films with lowest molarity. The transmission of MgO thin films decreases rapidly as the wavelength increases in the range of 300–400 nm and then increases slowly at higher wavelengths. The bandgap of MgO thin films decreases as the molarity increases, and the band gap values range between 4.8 and 4.3 eV. The Urbach energy values range between 375 and 519 meV. The electrical resistance of our films is on the order of 2 × 107Ω. The prepared MgO thin films were suitable for electronic packaging; they are capable to provide very stable and high secondary electron emission combined with low bandgap energy and low electrical resistance.

Self-Oscillating Mode of a Probe with Increased Secondary Emission for Nonequilibrium Plasma Diagnostics

A method of ion saturation current measurement in a nonequilibrium plasma by a self-oscillating voltage sweep on the probe is described. The generation of voltage pulses is possible if a high secondary electron emission from the probe surface is ensured, significantly exceeding unity at a moderate negative potential. The theoretical basis of the self-oscillating probe method has been considered, which made it possible to describe the ways for controlling the repetition rate and pulse amplitude and the effect of plasma parameters on the shape of current and voltage signals. It is shown that the features of the phase trajectory of the signal from the probe on the (U, I) plane allow one to determine the reference points of instantaneous probe characteristic, in particular, the ion saturation current. The results of experiments on testing the self-oscillating probe technique, which were carried out using the PR-2 plasma-beam facility, are presented.

Effect of hydrogen plasma treatment on secondary electron emission properties of polycrystalline diamond films

The polycrystalline diamond films were prepared by microwave plasma chemical vapor deposition (MPCVD), and the prepared diamond films were treated with hydrogen plasma for different times. The secondary electron emission (SEE) performance of these films were studied. The film treated with plasma for 10 min has the highest SEE yield. It was found that when the films are exposed to the hydrogen plasma, the film surfaces are etched with the hydrogen plasma and the surface content of C–H components are increased with the exposure time, conversely, the oxygen content of the surfaces are gradually reduced, which leads to the higher SEE yield. When the film is continuously irradiated by the incident electron beam, the SEE yield will decrease with time, this is because the electron beam bombardment destroys the hydrogen-termination and decreases the film's surface negative electron affinity (NEA).

Secondary electron emission enhancement of MgO/Au composite film by adopting a gold buffer layer

An electron-induced secondary electron emission (SEE) enhancement strategy of depositing a gold buffer layer for MgO/Au composite film was proposed. The influence of the gold buffer layer thickness on the microstructure, electrical conductivity and SEE properties of MgO/Au film was investigated. To deposit a gold buffer layer between the substrate and MgO/Au composite film markedly promotes the subsequent MgO grain growth, which leads to an increase in the SEE coefficient. Additionally, the improved electrical conductivity of this composite film caused by the gold buffer layer can effectively suppress the surface charging, which makes the MgO/Au film maintain a higher SEE coefficient for a longer time under continuous electron bombardment. An MgO/Au composite film with a 20-nm-thick gold buffer layer has a SEE coefficient of 5.1 at a primary electron energy of 200 eV with an increase of 13.3% compared with the one without a gold buffer layer.

DC discharge with high secondary electron emission oxide cathode: Effects of gas pressure and oxide cathode structure

In present study, DC discharge with high secondary electron emission (SEE) oxide cathodes (NiO/Ni and MgO/NiO/Ni cathode) is characterized with a significant increase in discharge current compared to the one with normal Ni cathode at different gas pressures from 400 to 700 torr. The increase multiple value of the discharge current decreases as the gas pressure increases, which can be related to a relative weakened ion-induced SEE process at high gas pressure. The NiO intermediate layer plays an important role in a sandwich MgO/NiO/Ni cathode for DC discharge, which may be due to the fact that its high resistance favors field-enhanced SEE process. Regardless of the gas pressure, the structural characteristics (thickness and roughness) of oxide layer have an effect on the enhancement of the discharge current, which can be attributed to field-enhanced SEE process. Additionally, the increase in the number of needle electrodes is conducive to the increase of discharge current with oxide cathode, which is related to an increase in the discharge area on the cathode surface according to the discharge images.

A novel bowl-shaped microchannel plate with high electron collection efficiency and good time performance

Abstract Owing to the severe loss of photoelectrons striking at the input electrode of conventional microchannel plate (MCP), photoelectron collection efficiency (CE) of devices based on traditional MCP fluctuates around the MCP open area ratio and cannot make a breakthrough. Photoelectron backscattering from the MCP surface also causes late pulses smearing timing and spatial performance. In this work, a novel bowl-shaped MCP with an open area ratio higher than 90% whose input electrode is coated by a thin film with high secondary electron emission yield (SEY) is proposed as an effective approach to improve CE and suppress late pulses. A three-dimensional MCP-PMT model is developed in CST Studio Suite to evaluate CE and time performance of the bowl-shaped MCP, and compared with the traditional one. Results show that CE of the PMT based on the bowl-shaped MCP is nearly 100% and the delayed pulse is less than 2%. This indicates that good temporal and spatial resolution can be achieved with the bowl-shaped MCP.

An improved corona discharge ignited by oxide cathodes with high secondary electron emission for toluene degradation

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.

Characteristics of a corona discharge ignited by a MgO/NiO/Ni sandwich cathode with high secondary electron emission for VOC degradation

In this paper, an improved corona discharge in air at atmospheric pressure is ignited by a MgO/NiO/Ni sandwich cathode with high secondary electron emission and is then employed for volatile organic compound degradation. Current–voltage characteristics, discharge images, and spectroscopic investigations are compared for two corona discharges with a MgO/NiO/Ni cathode and a Ni cathode, respectively. The discharge current with the MgO/NiO/Ni cathode is about 2.5–3.3 times larger than the one with the Ni cathode at various applied voltages from 12 to 19 kV. Besides, discharge images show that, as well as the expected glow discharge around the needle tips, luminous points also occur on the surface of the MgO/NiO/Ni cathode simultaneously, indicating that ionization and excitation processes take place around the cathode surface. This is attributed to the fact that an internal field within the oxide layer calculated by the measured surface potential, which is induced by positive charges accumulated on the oxide layers, is sufficient to induce field emission and further cause the improved corona discharge generation. Such improved corona discharge with the MgO/NiO/Ni cathode is then applied to toluene degradation, and the toluene degradation efficiency and energy yield are much higher than those with the Ni cathode, respectively.

Effects of secondary electron emission on plasma density and electron excitation dynamics in dual-frequency asymmetric capacitively coupled argon plasmas

Effects of secondary electron emission (SEE) on the plasma density and electron excitation dynamics in dual-frequency (2 MHz and 14 MHz) capacitively coupled Ar plasmas are investigated. The plasma density np is measured with a hairpin probe, and the spatio-temporal distribution of electron excitation rate (ground state into Ar 2p1 state) is determined by phase resolved optical emission spectroscopy. It is generally found that as the low-frequency (LF) voltage ϕL increases, np first decreases at low ϕL, due to compressed the plasma bulk length by the LF source, and then increases slightly with ϕL, suggesting that the plasma is dominated by the α mode. When ϕL exceeds some critical value, np increases dramatically with ϕL, due to significantly enhanced ionization by secondary electrons, indicating a α–γ mode transition. An excitation pattern caused by SEE at the edge of the completely expanded LF sheath is observed at relatively high ϕL. Under various conditions, including the high-frequency voltage ϕH, the pressure p, the electrode gap L, and the electrode material, different dependences of np on ϕL are also discussed. It is found that the discharge turns into the γ mode at a lower ϕL when ϕH is higher. As p increases, the density peak moves axially towards the powered electrode, due to reduced sheath thickness, while its distance to the powered electrode is almost independent of other external conditions (ϕH, L, electrode material, etc). A higher p or higher L is favorable for the enhancement of np in γ mode, because secondary electrons can contribute more to the ionization. Due to the higher SEE coefficient of the aluminum electrode, a more significant increase in np in the γ mode can be seen than that with a stainless steel or copper electrode. Meanwhile, the spatio-temporal distributions of the electron excitation rate under the same conditions are analyzed to further understand the SEE effects.

Theoretical Study and Monte Carlo Simulation on the Dynamic Process of a Novel Multipacting Cathode for High-Current Diode

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.

Dynamic determination of secondary electron emission using a calorimetric probe in a plasma immersion ion implantation experiment

A passive thermal probe has been used to detect dynamic changes in the secondary electron emission (SEE). Oxidized and nitrided materials have been studied during argon ion sputtering in a plasma immersion ion implantation process. Identical measurements have been performed for the metallic state with high voltage pulses accelerating nitrogen ions towards the surface, supposedly forming a nitride layer. Energy flux data were combined with scanning electron microscopy images of the surface to obtain information about the actual surface composition as well as trends and changes during the process. Within the measurements, a direct comparison of the SEE within both employed ion species (argon and nitrogen) is possible while an absolute quantification is still open. Additionally, the nominal composition of the investigated oxide and nitride layers does not always correspond to stoichiometric compounds. Nevertheless, the oxides showed a remarkably higher SEE compared to the pure metals, while an indistinct behavior was observed for the nitrides: some higher, some lower than the clean metal surfaces. For the aluminum alloy AlMg3 a complex time dependent evolution was observed with consecutive oxidation/sputtering cycles leading to a very rough surface with a diminished oxide layer, leading to an almost black surface of the metal and non-reproducible changes in the SEE. The presented method is a versatile technique for measuring dynamic changes of the surface for materials commonly used in PVD processes with a time resolution of about 1 min, e.g. magnetron sputtering or HiPIMS, where changes in the target or electrode composition are occurring but cannot be measured directly.

Effect of Aluminum Nitride on Discharge Mode Transition in Atmospheric Pressure He/O2 DBD

In this paper, the effects of aluminum nitride and alumina ceramics on the discharge mode of He/O2 mixed gas are studied and compared. It is found that when the O2 volume fraction is in the range of 0.2%–1%, dielectric barrier discharge (DBD) with Al2O3 is always in the unstable filamentary mode, and homogeneous and filamentary modes are observed in DBD with AlN. Under the homogeneous discharge mode, there is only one current pulse each half-voltage cycle, and the intensified charge-coupled device discharge image shows that it is glow discharge. The relative permittivity and surface charge decay characteristics of AlN and Al2O3 are measured. The experimental results show that the relative permittivity of AlN is lower than that of Al2O3, but its surface charge decay is obviously slower than that of Al2O3. The derived electron trap density from the surface charge decay of AlN ceramic is higher than that of Al2O3, which shows AlN has a strong charge capacity and can emit more electrons in the second half cycle of the discharge. The higher secondary electron emission coefficient can make the discharge ignition voltage lower and the formation of stable homogeneous discharge easier. This paper provides a new control method for expanding homogeneous discharge in He/O2 mixed gas.