High Secondary Electron Emission Yield Research Articles

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.

Effects of secondary electron emission yield properties on gain and timing performance of ALD-coated MCP

The technology of atomic layer deposition has been used to improve the lifetime of the microchannel plate-photomultiplier tube (MCP-PMT) effectively and makes MCP possible to choose to coat different potential emissive materials on the internal surface of the MCP channels in the future. However, it is still an open question to what extent the secondary electron emission (SEE) yield properties of the emissive materials influence the behavior of the ALD-coated MCP. In this work, the dependences of the gain and timing performance on the SEE yield properties were assessed by using the Monte Carlo and particle-in-cell methods. We established the three-dimensional MCP single channel model in Computer Simulation Technology (CST) Particle Studio. Three important secondary electron emissions, the backscattered, rediffused and true SEEs, were discussed numerically based on the probabilistic model. The secondary electron cascade processes in the MCP single channel were simulated. The simulation results indicate that the opportunities for improving the gain of the ALD-coated MCP by improving the SEE yields corresponding to the incident energies of 0 eV–100 eV. The backscattered and rediffused electrons are found to have strong effects on the gain and timing performance of the MCP. Although the higher the SEE yield the higher the MCP gain, the drawback is the extremely high SEE yield will make the MCP saturated prematurely and degrade the time resolution. The simulation results will be used to guide the design and selection of emissive material for ALD-coated MCP development.

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).

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.

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.

Picosecond Breakdown in High-Voltage Open Pulse Discharge With Enhanced Secondary Electron Emission

A 300-ps breakdown was registered in the experiments in the high-voltage open discharge with counter-propagating electron-beams with applying voltage pulses with rise times in 10–20 ns range. Discharge operates between two cathodes and grid-anode in the midplane at 10–35 Torr in helium at voltage 5–13 kV. It is shown in Particle-in-cell Monte Carlo collision (PIC MCC) simulations that the contributions of electrons, ions and energetic atoms in ionization and excitation processes are important for current development. The influence of different emissive cathode materials (titanium, silicon carbide, and CuAlMg-alloy) on evolution of discharge current is studied in the experiment and in kinetic PIC MCC simulations. The secondary electron emission from the cathodes is found to be a dominant process at the final stage of the breakdown. The current growth rate is larger (up to 700 A/cm2ns) for the cathode with a higher secondary electron emission yield. By choosing the cathode material, applied voltage amplitude and gas pressure, the characteristic time of the gas breakdown can be reduced.

Shape control of magnesium oxysulfate granules using an ethanolamine chelate.

Shape control of inorganic nanomaterials during hydrothermal syntheses is crucial for fine-tuning the function of these materials, which are widely utilized in semiconductors, ceramics, and optical devices. In particular, magnesium compounds possess many desirable physical properties such as high thermal stability, wide band gap and high secondary electron emission yield, which allow their application as polymeric resins, cements, reinforcements, and fillers. However, conventional synthetic methods often require extreme reaction conditions such as high temperatures, high pressures, or prolonged reaction times. Additionally, various shape control methods are typically quite complicated and time consuming under conventional parameters. In this work, magnesium oxysulfate (5Mg(OH)2 x MgSO4 x 3H2O) granules of various shapes were fabricated by introducing ethanolamine chelate during hydrothermal reaction at a relatively low temperature and pressure. The strong interaction between ethanolamine and Mg2+ produced 5Mg(OH)2 x MgSO4 x 3H2O granules in the form of flakes, flowers, or whiskers through self-assembly this formation is dependent on concentration, reaction time, and temperature. The physicochemical properties of the samples were investigated using X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis.

Defect states of transition metal-doped MgO for secondary electron emission of plasma display panel

High secondary electron emission (SEE) yield is one of the important properties of MgO for industrial applications such as alternating-current plasma display panel (AC-PDP), which reduces the firing voltage for discharge. SEE induced by low-energy Ne and Xe ions can be described by potential emission mechanism of Auger neutralization. Defect states in MgO can play an important role in enhancing the SEE. The electronic density of states of Ti-, Cr-, Fe-, Ni-, Zn-doped and undoped MgO was calculated using CASTEP. The occupied defect levels of the Ti-, Cr-, Fe-, Ni- and Zn-doped MgO are at 5.23, 3.90, 2.76, 1.22 and 0.06 eV above the valence band, respectively. Higher defect level appears to be advantageous for getting larger SEE yield. Considering the fact that Ti-doped MgO reveals n-type conductivity, Cr seems to be the proper dopant among the studied elements for the purpose of high SEE yield in AC-PDP.

Synthesis and electron emission properties of MgO nanowires

Magnesium oxide film has high secondary electron emission yield and is found as applications in flat panel display widely. In this work, MgO nanowire electron emission properties, including both secondary and field emissions, are reported. MgO nanowire thin films have been synthesized on stainless steel substrate by thermal vapor deposition. The turn-on field of 9 MV/m for the field emission is measured with the MgO nanowire thin film, and the maximum secondary electron emission (SEE) yield of 8.3 is obtained. In addition, the good stability of SEE yield is also observed under long-time electron bombardment.

Measurements of secondary electron emission effects in the Hall thruster discharge

The dependence of the maximum electron temperature on the discharge voltage is studied for two Hall thruster configurations, in which a collisionless plasma is bounded by channel walls made of materials with different secondary electron emission (SEE) properties. The linear growth of the temperature with the discharge voltage, observed in the channel with a low SEE yield, suggests that SEE is responsible for the electron temperature saturation in the thruster configuration with the channel walls having a higher SEE yield. The fact that the values of the electron temperature at saturation are rather high may indirectly support the recently predicted kinetic regime of the space charge saturation of the near-wall sheath in the thruster discharge. A correlation between the effects of the channel wall material on the electron temperature and the electron cross-field current was also observed.

CsI: a high effective gamma coating for plasma display panels

Reduction of the breakdown voltage in plasma panel discharge cells calls for electrode coatings with a high secondary-electron emission yield. MgO is most widely used in this field because of its high secondary-electron yield, which is primarily governed by ion-induced emission processes. To overcome the limits of ion-induced emission, opening an additional channel via photon-induced emission is a possible option. The present study shows that this is indeed feasible, with a photosensitive material showing a substantially higher effective secondary-electron emission coefficient γeff when compared to state-of-the-art MgO electrode films.

LaF3/MgO Protective Layer in AC-Plasma Display Panels

A LaF3/MgO layer was studied in AC-plasma display panels (PDPs) as a new protective layer in order to obtain a higher secondary electron emission yield than that obtained with the conventional MgO layer. The material characteristics of this protective layer were examined by varying the deposition conditions. It is demonstrated that this LaF3/MgO is effective in enhancing the secondary electron emission yields of PDPs and also in lowering the discharge voltages of the panel.

MgO/Carbon Nanotubes Protective Layer in AC-Plasma Display Panels

A new protective layer, incorporating carbon nanotubes (CNTs) under the conventional MgO protecting layer, was proposed and a prototype of an AC-plasma display panel (PDP) was fabricated using this protective layer. The discharge characteristics were obtained for these prototypes and explained in terms of the high secondary electron emission yield of the MgO/CNT layer. Thus, this MgO/CNT layer can be considered as a potential protective layer for use in AC-PDPs.

Luminous efficiency and secondary electron emission characteristics of alternating current plasma display panels with MgO–SrO–CaO protective layers

Development of protective layers with a higher secondary electron emission yield than that of the conventional MgO is necessary to attain both a lower driving voltage and a higher luminous efficiency in alternating current plasma display panels. Alkaline earth metal oxides, such as SrO and CaO were added to the pure MgO in order to improve the electrical characteristics of the conventional MgO protective layer. With addition of SrO and CaO to MgO, the intensity of the (111) peak remained unchanged but the (311) peak newly appeared in the x-ray diffraction results. The secondary electron emission yield of Mg1−x−ySrxCayO films was found to be larger than that of the MgO film and in particular, the Mg0.7Sr0.2Ca0.1O films showed the largest secondary electron emission yield among the prepared films of the Mg–Sr–Ca–O system in this work. The luminous efficiency of the panel with the Mg0.7Sr0.2Ca0.1O protective layer was also much higher than that of the panel with the MgO protective layer probably due to its lower discharging voltage. The increase in the luminous efficiency and the decrease in the driving voltage were in good agreement with the results of the secondary electron emission yield as expected.

The absolute detection efficiency of vacuum electron multipliers, to keV protons and Ar + ions

The single-ion detection efficiency of two types of electron multipliers is provided for incident energies reaching 10 keV. Absolute efficiencies above 90% were measured for a discrete dynode electron multiplier (DDEM), in response to Ar + ions and protons, above an energy of 5 keV. The efficiency to detect protons is consistently higher than that of Ar + ions, due to a higher secondary electron emission yield. For a channel electron multiplier we have measured a similar maximal detection efficiency for Ar + ions; though strongly varying across the detector surface.

An amorphous silicon imaging tube using high-velocity beam scanning

An imaging tube using hydrogenated amorphous silicon as the photoconductive target with a blocking-type structure and a high secondary electron emission yield surface is successfully operated using a high-velocity electron-beam scanning mode. The internal electric field in the photoconductor is the opposite of those used in conventional tubes in that the secondary electron current is obtained as a video signal. This imaging tube overcomes a lot of the disadvantages of conventional imagers, especially very small decay lag at both high- and low-illumination levels, a high uniform resolution of more than 700 TV lines, and no burning or blooming.

Polymer film‐type channel electron multipliers: Their characteristics and comparison with bulk‐type flexible multipliers

AbstractPolymer film‐type channel electron multipliers (CEMs) were developed and their characteristics investigated in comparison with bulk‐type flexible CEM. As film‐type CEMs, a paint‐coating‐type CEM and a solvent‐etching‐type CEM were fabricated. The paint‐coating‐type CEM is made by coating a “paint” which is prepared by dissolving in a solvent an electronically conductive polymeric composition having a high secondary electron emission yield. Up to the present study the mean gain of the film‐type CEM, in spite of the lower resistivity of the dynode, seems to be slightly more dependent on the count rate than that of the bulk‐type CEM made of the same material. However, the convenience of fabricating the dynode film by coating the dynode‐forming paint on the internal surface of any shaped tube or a flexible polymer tube would overcome the slight disadvantage mentioned above.