Mean Electron Energy Research Articles

SU‐C‐201‐07: Towards Clinical Cherenkov Emission Dosimetry: Stopping Power‐To‐Cherenkov Power Ratios and Beam Quality Specification of Clinical Electron Beams

Purpose:We propose a Cherenkov emission (CE)‐based reference dosimetry method, which in contrast to ionization chamber‐based dosimetry, employs spectrum‐averaged electron restricted mass collision stopping power‐to‐Cherenkov power ratios (SCRs), and we examine Monte Carlo‐calculated SCRs and beam quality specification of clinical electron beams.Methods:The EGSnrc user code SPRRZnrc was modified to compute SCRs instead of stopping‐power ratios (single medium: water; cut‐off: CE threshold (observing Spencer‐Attix conditions); CE power: Frank‐Tamm). SCRs are calculated with BEAMnrc for realistic electron beams with nominal energies of 6–22 MeV from three Varian accelerators (TrueBeam Clinac 21EX, Clinac 2100C/D) and for mono‐energetic beams of energies equal to the mean electron energy at the water surface. Sources of deviation between clinical and mono‐energetic SCRs are analyzed quantitatively. A universal fit for the beam‐quality index R50 in terms of the depth of 50% CE C50 is carried out.Results:SCRs at reference depth are overestimated by mono‐energetic values by up to 0.2% for a 6‐MeV beam and underestimated by up to 2.3% for a 22‐MeV beam. The variation is mainly due to the clinical beam spectrum and photon contamination. Beam angular spread has a small effect across all depths and energies. The influence of the electron spectrum becomes increasingly significant at large depths, while at shallow depths and high beam energies photon contamination is predominant (up to 2.0%). The universal data fit reveals a strong linear correlation between R50 and C50 (ρ > 0.99999).Conclusion:CE is inherent to radiotherapy beams and can be detected outside the beam with available optical technologies, which makes it an ideal candidate for out‐of‐beam high‐resolution 3D dosimetry. Successful clinical implementation of CE dosimetry hinges on the development of robust protocols for converting measured CE to radiation dose. Our findings constitute a key step towards clinical CE dosimetry.

Model of a small surface wave discharge at atmospheric pressure

Self-consistent model of a small microwave plasma source based on a surface wave sustained discharge at 2.45 GHz is presented in this study. The model includes dispersion relation of azimuthally symmetric surface waves, sustaining the discharge in a high permittivity ceramic tube (εd = 9.3) and the radial distribution of the field components at curtain values of the electron density are obtained. The electron Boltzmann equation under the local approximation is solved together with the heavy particle balance equations. A detailed collisional-radiative model for argon discharge at atmospheric pressure is implemented in the model. The changes in the EEDF shape and the mean electron energy with the value of the electron density are investigated. Results show that the EEDF is close to Maxwellian at our experimental conditions for the plasma density above 2.1020 (m-3).

Nonthermal Plasma System for Marine Diesel Engine Emission Control

A nonthermal plasma reactor (NTPR) using two 2.45-GHz microwave (MW) generators for the abatement of nitrogen oxides ( ${\text {NO}}_{\text {x}}$ ) and sulfur ( ${\text {SO}}_{\text {x}}$ ) contained in the exhaust gas of a 200-kW marine diesel engine was built and tested. Numerical analysis based on a nonthermal plasma kinetics model for the abatement of ${\text {NO}}_{\text{x}}$ and ${\text{SO}}_{\text{x}}$ from marine diesel engine exhaust gas was performed. A generic kinetic model that implements electron collisions and plasma chemistry has been developed for applications involving low-temperature (50–100 K) nonthermal plasma. Abatement efficiencies of ${\text {NO}}_{\text{x}}$ and ${\text {SO}}_{\text{x}}$ were investigated for a range of mean electron energies, which directly impact on the rate constants of electron collisions. The simulation was conducted using the expected composition of exhaust gas from a typical two-stroke, slow-speed marine diesel engine. The simulation results predict that mean electron energy of 0.25–3.2 eV gives abatement efficiency of 99% for ${\text {NO}}_{\text{x}}$ and ${\text {SO}}_{\text{x}}$ . The minimum residence time required was found to be 80 ns for the mean electron energy of 1 eV. Multimode cavity was designed using COMSOL multiphysics. The NTPR performance in terms of ${\text {NO}}_{\text{x}}$ and ${\text {SO}}_{\text{x}}$ removal was experimentally tested using the exhaust from a 2-kW lab scale, two-stroke diesel engine. The experimental results also show that the complete removal of NO is possible with the MW plasma (yellow color) generated. However, it was found that generating required MW plasma is a challenging task and requires further investigation.

Electrical Characteristics of an Argon Glow Discharge in the Presence of Metastable Atom Density

The paper deals with numerical modelling studies of DC glow discharge in argon with metastable atom density. The values of pressure is between 133.32 Pa and 330 Pa, and voltage ranges from 250 to 400 V in the case of input data taken from the Boltzmann equation in multi term approximation. In the frameworks, an analysis of glow discharge characteristics is carried out in the case of input data obtained from BOLISG+ code. As conclusion of these different input data in the same gas the output results are different and they appear in the cathode region. The spatio-temporal distributions of electron and ion densities, the potential and electric field, the mean electron energy and the metastable atom density are shown. A 1D fluid model is used to solve self-consistently the first three moments of the Boltzmann equation coupled with the Poisson's equation. The results are validated with those obtained by recent papers.

Fluid model of a single striated filament in an RF plasma jet at atmospheric pressure

The filaments occurring in an RF argon atmospheric-pressure plasma jet are investigated by means of numerical modelling. The special setup of the jet leads to the establishment of filaments in very regular modes under certain conditions. Such a single filament generated in the active volume between the powered and grounded electrode is described by a time-dependent, spatially two-dimensional fluid model. This self-consistent model includes those mechanisms which can lead to constriction and stratification such as the heat balance equation and the dependence of electron collision rate coefficients on the ionization degree. A curved filament with a contracted radial profile of particle densities and very pronounced striations along its trace has been obtained by the model calculation for a typical discharge parameter condition of the plasma jet. The resulting calculated electron density and mean energy in the filament as well as the period length of the striations agree qualitatively with recent experimental observations. The analysis of the ionization budget makes clear that the constriction and stratification is mainly caused by the different nonlinear dependences of ionization and recombination rates on the electron density.

(Invited) Numerical Simulation of a CAP Needle and Its Prospective Therapeutical Applications

Plasma medicine is an emerging field where plasma physics is used for therapeutical applications. Plasmas seem to have healing effects on different skin diseases, and are also promising on cancer treatment.One of their capabilities is the increase of antimicrobial activity without damaging surrounding tissue, combined with a controlled stimulation of tissue regeneration. A plasma discharge can be applied directly on biological tissues. The so-called cold atmospheric plasmas or CAPs are used for these purposes. They can be generated by different sources, namely, barrier discharges (BDs), plasma jets, and corona discharges. In order to characterize the plasma chemistry, some experimental methods, such as mass spectrometry, can be used. However, these methods suffer from inaccuracies and it is difficult to obtain a complete understanding of the plasmas by just using them. Therefore, mathematical modeling and numerical simulations are essential tools that can be used for an improved interpretation of experimental diagnostics and better understanding of these plasma processes and their optimization. In our group at the TU Dresden, we are currently working on finite-element simulations of CAPs. We are performing simulations of two main devices: plasma jets and plasma needles. Both of them are well known and they are starting to be widely used in the discipline of plasma medicine. These devices are able to operate with different gases, being the most common argon and helium. In order to simplify simulations, literature generally starts with more simplified plasma chemistries. We also did, however, extended this to more complex chemistries also. The plasma discharge is simulated using a fluid model. Drift-diffusion equations are used in order to calculate electron densities, electron energies and heavy particles transport. Poisson´s equation is used for calculating the electric potential. Boltzmann equation has also been investigated in order to calculate the electron energy distribution function eedf (depending on the electron mean energy) and the electron transport coefficients. Temperature is an important factor to take into account for the applications of plasma to biological systems. During the treatment of a tissue, its temperature could increase to critical values. The model developed by our group to simulate the plasma needle is capable of predicting skin temperature during a treatment with a radio frequency driven plasma needle, as it was shown in [1], assuming helium to be the gas which is forming the plasma discharge. The results provide maximum application times for different power depositions in order to avoid reaching critical skin temperatures. To achieve this, a discharge model was coupled to a heat transfer and fluid flow model. The detailed procedure, it´s advantages and disadvantages will be discussed in the presentation. Moreover, some simulations using this plasma needle have been performed considering argon plasma chemistry. The results show very low power depositions in comparison with experimental results. Including a more complex argon chemistry does not change this fact. One of the possible reasons is that, in actual devices, argon is mixed with other species. Therefore the plasma power deposition may change significantly in comparison with pure argon plasma discharges. We built a 1D plasma discharge model with a complex chemistry of argon and oxygen which proved that the presence of oxygen increases importantly the power deposition. This could be the explanation for our “low” power depositions when using just argon in a plasma needle. Further results will be discussed in detail as for instance simulated plasma jets and complete loops of plasma discharge, heat transfer and fluid flow to the plasma jet. All model simulations will be evaluated with respect to literature data and possible applications in medical treatment. [1] M. Schröder, A. Ochoa Brezmes und C. Breitkopf, „Numerical simulation of an atmospheric pressure RF-driven plasma needle and heat transfer to adjacent human skin using COMSOL,“ Biointerphases, Nr. 10, p. 029508, 2015.

Chemical kinetics and relaxation of non-equilibrium air plasma generated by energetic photon and electron beams

The comprehension of electromagnetic perturbations of electronic devices, due to air plasma-induced electromagnetic field, requires a thorough study on air plasma. In the aim to understand the phenomena at the origin of the formation of non-equilibrium air plasma, we simulate, using a volume average chemical kinetics model (0D model), the time evolution of a non-equilibrium air plasma generated by an energetic X-ray flash. The simulation is undertaken in synthetic air (80% N2 and 20% O2) at ambient temperature and atmospheric pressure. When the X-ray flash crosses the gas, non-relativistic Compton electrons (low energy) and a relativistic Compton electron beam (high energy) are simultaneously generated and interact with the gas. The considered chemical kinetics scheme involves 26 influent species (electrons, positive ions, negative ions, and neutral atoms and molecules in their ground or metastable excited states) reacting following 164 selected reactions. The kinetics model describing the plasma chemistry was coupled to the conservation equation of the electron mean energy, in order to calculate at each time step of the non-equilibrium plasma evolution, the coefficients of reactions involving electrons while the energy of the heavy species (positive and negative ions and neutral atoms and molecules) is assumed remaining close to ambient temperature. It has been shown that it is the relativistic Compton electron beam directly created by the X-ray flash which is mainly responsible for the non-equilibrium plasma formation. Indeed, the low energy electrons (i.e., the non-relativistic ones) directly ejected from molecules by Compton collisions contribute to less than 1% on the creation of electrons in the plasma. In our simulation conditions, a non-equilibrium plasma with a low electron mean energy close to 1 eV and a concentration of charged species close to 1013 cm−3 is formed a few nanoseconds after the peak of X-ray flash intensity. 200 ns after the flash application, the electrons are thermalized and their concentration has decreased from about 1013 cm−3 down to about 1012 cm−3 leaving positive and negative ionised species and atomic radicals whose recombination characteristic times are much longer.

Propagation distance-resolved characteristics of filament-induced copper plasma.

Copper plasma generated at different filament-copper interaction points was characterized by spectroscopic, acoustic, and imaging measurements. The longitudinal variation of the filament intensity was qualitatively determined by acoustic measurements in air. The maximum plasma temperature was measured at the location of peak filament intensity, corresponding to the maximum mean electron energy during plasma formation. The highest copper plasma density was measured past the location of the maximum electron density in the filament, where spectral broadening of the filament leads to enhanced ionization. Acoustic measurements in air and on solid target were correlated to reconstructed plasma properties. Optimal line emission is measured near the geometric focus of the lens used to produce the filament.

Model of a surface-wave discharge at atmospheric pressure with a fixed profile of the gas temperature

We present a 3D model of a surface-wave-sustained discharge at 2.45 GHz at atmospheric pressure. A small plasma source creates a plasma column in a dielectric tube and a plasma torch is observed above the top. The plasma parameters and the axial profile of the gas temperature are significantly changed in the presence of the substrate above the plasma torch. The Boltzmann equation for electrons under the local approximation is solved, together with the heavy particle balance equations at a fixed axial profile of the gas temperature. The model of this finite length plasma column includes also the dispersion relation of azimuthally-symmetric surface waves. A detailed collisional-radiative model is also implemented for argon discharge at atmospheric pressure, which includes 21 rate balance equations for excited Ar atoms [(Ar(1s5-1s2), Ar(2p10-2p1), Ar(2s3d), Ar(3p)], for positive Ar+ and Ar2+ ions and for excited molecules. The changes in the EEDF shape and the mean electron energy along the plasma column are investigated and the axial structures of the discharge and plasma parameters are obtained.

A hybrid model for low pressure inductively coupled plasmas combining a fluid model for electrons with a plasma-potential-dependent energy distribution and a fluid-Monte Carlo model for ions

A hybrid plasma model is utilized for the simulation of inductively coupled plasmas (ICPs). It consists of a plasma fluid model coupling fluid with Maxwell’s equations and a Monte Carlo (MC) particle tracing model utilized for the calculation of the ion mobility in high electrostatic fields (sheaths). The model is applied to low pressure Argon plasma in the gaseous electronics conference (GEC) reference cell. Following measurements of electron energy distribution function (EEDF) in low pressure ICPs, a three-temperature EEDF is considered; it is formulated with a generalized equation and depends on the local plasma potential. The use of a predefined formula for the EEDF entails a low computational cost: All parameters affected by the EEDF are calculated as functions of the plasma potential and the mean electron energy once and before the solution of the model. The model results are validated by a comparison with spatially resolved (on axial and radial distance) measurements of electron density, electron temperature, and plasma potential. Both the calculation of the ion mobility by the MC model and the consideration of the three-temperature EEDF are critical for the accuracy of the model results. The very good agreement of the model results with the measurements and the low computational cost in combination with the flexibility of the code utilized for the numerical solution manifest the potential of the hybrid plasma model for the simulation of low pressure ICPs.

The hollow cathode effect in a radio-frequency driven microhollow cathode discharge in nitrogen

A two-dimensional particle-in-cell Monte-Carlo code has been developed to study the physical mechanism of the hollow cathode effect (HCE) in an rf microhollow cathode discharge (rf-MHCD). Under the simulated conditions, the HCE in the rf-MHCD is the result of sheath-superposition, and both α ionization and γ ionization play a role. However, α ionization mode is predominant. Electrons undergo a pendular motion during the negative portion of the rf cycle. When the rf hollow electrode has a positive voltage, the majority of the electrons move toward the rf electrode, and the mean electron energy near the rf electrode is higher than that in a dc hollow cathode discharge, resulting in a large number of energetic electrons bombarding the hollow cathode wall, an important characteristic of the rf-MHCD. When the hollow cathode aperture is sufficiently small, many electrons strike the hollow electrode and are removed from the discharge space, so that the plasma density decreases. The average energy of the ions in the quasi-neutral plasma region near the axis is greater than the thermal energy in a molecular gas. Therefore, high density, high energy, and high chemical activity are characteristic advantages of rf-MHCD plasma sources.

New Theory of Superconductivity. Does the London Equation Have the Proper Solution? No, It Does Not. Self-Generated and External Magnetic Fields in Superconductors

Hereby it studied the fundamental theory created by the London brothers for interpretation of the magnetic field reduction in superconductors. As demonstrated, this theory is not correct. The author of this work has developed the new theory of superconductivity. The equation describing the electron distribution function under the effect of magnetic field explains existence of the Meissner-Ochsenfeld effect. It is shown that the critical field equation matches the width of a potential well in the kinetic energy dependence of mean electron energy. As a result, the supercurrent density formula has been derived. Existence of magnetic fields is explained by two steady-state Maxwell equations. There are magnetic fields that are found to be created in individually shaped metals. Penetration of the external magnetic field in a superconductor has been explained.

Secondary Electron Emission from Cylindrical Particles

The secondary electron emission (SEE) caused by high energy electrons, incident obliquely on a cylindrical particle has been derived by considering appropriate paths traversed by the primary electron in the particle into account. Expressions for the SEE efficiency corresponding to mono-energetic as well as Maxwellian energy distribution of primary electrons have been derived. Further the dependence of this efficiency on the penetration depth (xm), angle of incidence (λ), particle radius (a) and the mean energy (kTe) of the incident primary electrons has been analyzed and graphically illustrated. The analysis reflects that the SEE is dominant for small cylindrical particles and high energy primary electrons. The yield is more pronounced in the case of spherical particles than that in the case of cylindrical particles of the same radius. The study is of relevance to space and laboratory dusty plasmas where cylindrical particles are frequent.

Experimental and simulation study of a capacitively coupled oxygen discharge driven by tailored voltage waveforms

We report experimental and particle-based kinetic simulation studies of low-pressure capacitively coupled oxygen plasmas driven by tailored voltage waveforms that consist of up to four harmonics of base frequency 13.56 MHz. Experimentally determined values of DC self-bias and electrical power deposition, as well as flux density and flux-energy distribution of the positive ions at the grounded electrode are compared with simulation data for a wide range of operating conditions. Very good agreement is found for self-bias and flux-energy distribution of the positive ions at the electrodes, while a fair agreement is reached for discharge power and ion flux data. The simulated spatial and temporal behaviour of the electric field, electron density, electron power absorption, ionization rate and mean electron energy shows a transition between sheath expansion heating and drift-ambipolar discharge modes, induced by changing either the number of harmonics comprising the excitation waveform or the gas pressure. The simulations indicate that under our experimental conditions the plasma operates at high electronegativity, and also reveal the crucial role of singlet metastable molecules in establishing discharge behavior via the fast destruction of negative ions within the bulk plasma.

Evaluation of backscatter dose from internal lead shielding in clinical electron beams using EGSnrc Monte Carlo simulations

Internal lead shielding is utilized during superficial electron beam treatments of the head and neck, such as lip carcinoma. Methods for predicting backscattered dose include the use of empirical equations or performing physical measurements. The accuracy of these empirical equations required verification for the local electron beams. In this study, a Monte Carlo model of a Siemens Artiste linac was developed for 6, 9, 12, and 15 MeV electron beams using the EGSnrc MC package. The model was verified against physical measurements to an accuracy of better than 2% and 2 mm. Multiple MC simulations of lead interfaces at different depths, corresponding to mean electron energies in the range of 0.2–14 MeV at the interfaces, were performed to calculate electron backscatter values. The simulated electron backscatter was compared with current empirical equations to ascertain their accuracy. The major finding was that the current set of backscatter equations does not accurately predict electron backscatter, particularly in the lower energies region. A new equation was derived which enables estimation of electron backscatter factor at any depth upstream from the interface for the local treatment machines. The derived equation agreed to within 1.5% of the MC simulated electron backscatter at the lead interface and upstream positions. Verification of the equation was performed by comparing to measurements of the electron backscatter factor using Gafchromic EBT2 film. These results show a mean value of 0.997±0.022 to 1σ of the predicted values of electron backscatter. The new empirical equation presented can accurately estimate electron backscatter factor from lead shielding in the range of 0.2 to 14 MeV for the local linacs.PACS numbers: 87.53.Bn, 87.55.K‐, 87.56.bd

Investigations of Droplet‐Plasma Interaction using Multi‐Dimensional Coupled Model

AbstractRecently developed multi‐dimensional coupled fluid‐droplet model is used to investigate the behavior of complex interaction between the liquid precursor droplets and atmospheric pressure plasma (APP). The significance of this droplet‐plasma interaction is not well understood under diverse realm of working conditions in two‐phase flow. In this study, we explain the implication of vaporization of liquid droplets in APP which are subsequently responsible to control major characteristics of surface coating depositions. Coalescence of water droplets is more dominant than Hexamethyldisiloxane (HMDSO) droplets because of its sluggish rate of evaporation. A disparity in the performance of evaporation is identified in two independent mediums, such as gas mixture and discharge plasma using HMDSO precursor. The length of evaporation of droplets is amplified by an increment of gas flow rate indicating with a reduction in the gas temperature and electron mean energy. In particular, the spatio‐temporal density distributions of charged particles show a clear pattern in which the typical nitrogen impurity ions are primarily effective as compared to other helium ionic species along the pulse of droplets in APP. Finally, we contrast the behavior of discharge species in the pure helium and He‐N2 gas mixtures revealing the importance of stepwise and Penning ionization processes. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Impact of weak interactions of free nucleons on the r-process in dynamical ejecta from neutron star mergers

We investigate beta-interactions of free nucleons and their impact on the electron fraction (Y_e) and r-process nucleosynthesis in ejecta characteristic of binary neutron star mergers (BNSMs). For that we employ trajectories from a relativistic BNSM model to represent the density-temperature evolutions in our parametric study. In the high-density environment, positron captures decrease the neutron richness at the high temperatures predicted by the hydrodynamic simulation. Circumventing the complexities of modelling three-dimensional neutrino transport, (anti)neutrino captures are parameterized in terms of prescribed neutrino luminosities and mean energies, guided by published results and assumed as constant in time. Depending sensitively on the adopted neutrino-antineutrino luminosity ratio, neutrino processes increase Y_e to values between 0.25 and 0.40, still allowing for a successful r-process compatible with the observed solar abundance distribution and a significant fraction of the ejecta consisting of r-process nuclei. If the electron neutrino luminosities and mean energies are relatively large compared to the antineutrino properties, the mean Y_e might reach values >0.40 so that neutrino captures seriously compromise the success of the r-process. In this case, the r-abundances remain compatible with the solar distribution, but the total amount of ejected r-material is reduced to a few percent, because the production of iron-peak elements is favored. Proper neutrino physics, in particular also neutrino absorption, have to be included in BNSM simulations before final conclusions can be drawn concerning r-processing in this environment and concerning observational consequences like kilonovae, whose peak brightness and color temperature are sensitive to the composition-dependent opacity of the ejecta.

Design of magnetic field configuration for controlled discharge properties in highly ionized plasma

In the present article, the effect of magnetic field design on electron and ion properties in both a metallic Ti/Ar and a reactive Ti/Ar + O2 high power impulse magnetron sputtering (HiPIMS) discharges is investigated. For the purpose, a variable magnetron with defined imbalance and geometrical coefficients K and , respectively, was utilized. The electron density, the mean electron energy, the plasma potential, and the floating potential were determined by employing time-resolved Langmuir probe measurements, for four specified magnetic field configurations. Mass spectroscopy was used in order to determine the energy distribution function of metal (Ti+ , Ti2+) and gaseous (Ar+ , Ar2+ , O+ , O) ions. Analysis of the measured data shows that the magnetic field design dramatically affects the charged particles energy- and spatial-distribution, causing a change in the plasma properties. It is concluded that a well-determined configuration of the magnetic field is necessary in order to insure discharge stability and reproducibility.

(Invited) Electronic and Acoustic Applications of Anodized Nano-Crystalline Silicon

Electrochemically anodized nano-crystalline Si (nc-Si) behaves as a functional material with a confined structure. In the electron transport through a chain of nc-Si dots, phonon scattering losses are minimized due to discrete energy levels in the conduction band, and then ballistic electrons are generated at the early stage of injection [1]. This induces efficient ballistic hot electron emission from an nc-Si diode. It is possible to use this emitter not only in vacuum, but also in atmospheric-pressure gases and solutions [2]. Extremely lowered thermal conductivity and heat capacity of the nc-Si layer [3], on the other hand, significantly enhances thermo-acoustic effect. In contrast to the conventional piezoelectric transducer, the thermally induced acoustic emission exhibits no resonant peaks in the frequency response. Here we discuss topics in the studies on these subjects. The nc-Si emitter is a kind of MIS diode consisting of a thin film surface electrode, an nc-Si layer (~1 μm thick), a crystalline silicon wafer substrate, and a back contact. The nc-Si layer includes chains of nc-Si dots (~3 nm in mean diameter) interconnected with tunnel oxides. When a positive voltage is applied to the surface electrode, electrons are accelerated in the nc-Si layer toward the outer surface, and then some of them are emitted through the surface electrode as ballistic hot electrons with a small angle dispersion (±10°with respect to the normal). At applied voltages of 12-20 V, the mean energy of output electrons reaches 3-7 eV [2]. One possible application of the nc-Si emitter is the use as an exposure source of multibeam parallel lithography. The emitter array is fabricated on a Si substrate by planar processes. Each emitter with an active area of 10 μm☐ is connected to an active matrix driving circuit through a TSV technique. The evaluation was performed with the 1:1 exposure test system, in which an EB-resist coated target wafer was placed at about 4 mm distance from the emitter surface. The wafer was grounded, and emitter surface was set at -5 kV for accelerating the electron. It has been demonstrated that the selected emitter patterns is delineated well corresponding to the activated emitters [4]. The integrated nc-Si emitter array is compatible with the active-matrix drive for multi-beam massive parallel lithography. Another application is thin film deposition using the reducing activity of ballistic hot electrons. When the emitter is driven in metal-salt solutions such as CuSO4, CuCl2, NiCl2, SiCl4, and GeCl4, injected electrons directly reduce Cu2+, Si4+ and Ge4+ ions, and then thin Cu films [5] and amorphous Si and Ge films [6,7] are grown on the emitting area with neither contaminations nor byproducts. Based on this observation, a printing scheme has been employed, in which a target substrate is separately located in close proximity to the emitter. A gap between the nc-Si emitter and the target substrate is controlled by a piezoelectric actuator depending the ambient (N2 gas) pressure. Emitted electrons hit metal-salt solutions on the substrate leading to the reducing reaction. The first printing experiment was sought for deposition of thin metal film, where an extremely small amount of CuSO4 or CuCl2 solution was coated on a single-crystalline Si wafer and used as a target substrate. It has been observed that thin Cu films are deposited on the irradiated area. The broad-band flat emissivity of the nc-Si thermo-acoustic device is useful for developing low-distortion digital speaker [8] and reproducing complicated ultrasonic communication calls between mice [9].

Numerical Simulation of the Characteristics of Electrons in Bar-plate DC Negative Corona Discharge Based on a Plasma Chemical Model

In order to explore the characteristics of electrons in DC negative corona discharge, an improved plasma chemical model is presented for the simulation of bar-plate DC corona discharge in dry air. The model is based on plasma hydrodynamics and chemical models in which 12 species are considered. In addition, the photoionization and secondary electron emission effect are also incorporated within the model as well. Based on this model, electron mean energy distribution (EMED), electron density distribution (EDD), generation and dissipation rates of electron at 6 typical time points during a pulse are discussed emphatically. The obtained results show that, the maximum of electron mean energy (EME) appears in field ionization layer which moves towards the anode as time progresses, and its value decreases gradually. Within a pulse process, the electron density (ED) in cathode sheath almost keeps 0, and the maximum of ED appears in the outer layer of the cathode sheath. Among all reactions, R1 and R2 are regarded as the main process of electron proliferation, and R22 plays a dominant role in the dissipation process of electron. The obtained results will provide valuable insights to the physical mechanism of negative corona discharge in air.