Secondary Emission Characteristics Research Articles

Influence of external impact on secondary emission characteristics of anti-multipactor nanocarbon

This work demonstrates that a thin nanocarbon film applied to a metal surface is capable of decreasing the coefficient of secondary emission down to the value of 1 ÷ 1.5. Thereby, eliminating the possibility of a multipactor discharge. In this paper we describe a method of making an anti-multipactor coating from a colloid solution of nanocarbon. The colloid solution of nanocarbon is made by creating a multi-spark high voltage pulse discharge in ethanol where argon is injected into the inter electrode space. Thermal, climate and tear-off tests have shown that emission properties of the surface are retained.

Measurement and modeling of electron cloud in a field free environment using retarding field analyzers

As part of the CesrTA program at Cornell, diagnostic devices to measure and quantify the electron cloud effect have been installed throughout the CESR ring. One such device is the retarding field analyzer, which provides information on the local electron cloud density and energy distribution. In a magnetic field free environment, retarding field analyzer measurements can be directly compared with simulation to study the growth and dynamics of the cloud on a quantitative level. In particular, the photoemission and secondary emission characteristics of the instrumented chambers can be determined simultaneously.

Simulation of the sputtering of Si nanoclusters with diameters of (2–8) nm under bombardment with monatomic and cluster ions using the method of classical molecular dynamics

The sputtering of Si nanoclusters with diameters of (2–8) nm under bombardment with Si1 ions and Si12 clusters with energies of 1 to 12 keV has been studied using the method of classical molecular dynamics. It is shown that the total sputtering yield is higher under the bombardment of nanoclusters with monatomic ions than in the case of the crystal plane surface mainly due to an increase in the contribution of the cluster component of the secondary-emission spectrum. In this case, in practice there is nonoccurrence of any correlation between the secondary-emission characteristics and the particle-projectile impact parameter. In the case of cluster bombardment, the cluster component of the spectrum of sputtered particles is dominant for large impact parameters (i.e., for glancing impact) and the sputtering yield and the probability of the ejection of large fragments (containing half of the initial-nanocluster atoms or more) increase significantly (as compared with similar values obtained under bombardment with monatomic particles). It is established that the main mechanism for the emission of large fragments is the co-called “recoil effect”, where the impinging particle-projectile causes the secondary emission of nanocluster-target atoms predominantly toward the substrate; as a result, the cluster-target acquires momentum in the opposite direction. It is shown that this “recoil effect” can lead to the desorption of the nanocluster, deposited onto a plane Si(111) substrate.

Classical molecular dynamic simulation of (111) Si and Al surface sputtering under bombardment by polyatomic clusters

The self-sputtering processes of (111) Si and Al surfaces under bombardment by SiN and AlN ions and clusters (N = 1−60) with the same energy per particle-projectile atom (1 keV/atom) are studied in this paper. The nonlinear effects produced in the target during the development stage of an atomic-collision cascade and during the postcascade stage are analyzed, and a correlation between these effects and secondary emission characteristics is found. The study has been carried out in the framework of classical molecular dynamics. As a result, a number of features of (111) Si and Al surface sputtering and erosion have been revealed. Thus, it has been established that the sputtering yield increases nonadditively as the size N of the implanted cluster increases at N > 10, which is related to the appearance of nonlinear cascades and the postcascade heat spike, and is accompanied by microcrater formation. It is shown that the implantation of clusters into the Si target leads to the formation of amorphous regions.

Numerical Calculation and Research of the Effects of Secondary Emission Characteristics on Surface Charging

表面充电是最早被人们发现的空间环境效应, 是由空间环境引起的航天器异常和故障的主要诱因之一. 采用较精确的金属二次电子发射公式和局部电流平衡模型, 在无光照的情况下, 对不同表面材料及不同几何形体的航天器表面充电电位进行计算, 并绘制了表面材料的充电电位与最大二次电子发射系数之间的关系曲线. 根据数值计算结果及次级电子发射系数和曲线图得知, 航天器阴面充电电位与表面材料的原子序数、最大二次电子发射系数和入射离子引起的次级发射系数均有关. 该计算对航天器表面材料的选取和设计工艺有一定的参考价值.

Vacuum Surface Flashover Characteristics and Secondary Electron Emission Characteristics of Epoxy Resin and FRP Insulator

Neutral beam injectors (NBI) used for JT-60 are required to generate negative ions of 500 keV energies. To produce such high-energy ions, the electrostatic accelerators consisting of 3-stage of electrodes and three insulator rings are applied. The insulators are made of Fiberglass Reinforced Plastic (FRP) which is composed of epoxy resin and glass fibers. The surface discharges along the insulators are one of the most serious problems in the development of NBI. To increase the hold-off voltage against surface flashover events, it is necessary to investigate the FRP and epoxy resin insulator properties related to surface discharges in vacuum. This paper describes surface flashover characteristics for epoxy resin, FRP and Alumina samples under vacuum condition. In addition, the measurements of secondary electron emission (SEE) characteristics are also reported. These are important parameters to analyze surface discharge characteristics of insulators in vacuum.

Investigation of the secondary emission characteristics of CVD diamond films for electron amplification

Chemical vapour deposition (CVD) diamond offers great potential as a low-cost, high-yield, easily manufactured secondary electron emitter for electron multiplication in devices such as photomultiplier tubes. Its potential for high secondary electron yield offers several significant benefits for these devices including higher time resolution, faster signal rise time, reduced pulse height distribution, low noise, and chemical stability. We describe an experiment to characterize the secondary emission yield of CVD diamond manufactured using different processes and process parameters and discuss the degradation of secondary electron yield and experimental difficulties encountered due to unwanted electron beam-induced contamination. We describe techniques utilized to overcome these difficulties, and present measurements of secondary yield from CVD diamond dynodes in reflection mode. We discuss the application of CVD diamond dynode technology, both in reflection and transmission mode, to advanced high-speed imaging and photon-counting detectors and describe future plans in this area.

Mathematical simulation of phototransfer of the proton of a hydrogen bond under irradiation of a molecule by two light pulses

The time-dependences of the populations of molecular states are determined by the numerical solution of a set of equations for the matrix elements of a density operator for the five-level model of a molecule with different values of parameters of two nonoverlapping in time irradiation pulses and of the constants governing the rates of induced radiative transitions of the molecule, as well as the radiative and nonradiative decays of molecular states. It is proposed to use the results obtained as reference points in interpreting experimental data on the spectro-temporal characteristics of secondary emission upon photoisomerization of molecules with an intramolecular hydrogen bond under irradiation by two light pulses and in determining the mechanism of phototransfer of the hydrogen-bond proton occurring in this process.

Analysis of the composition and structure of aqueous media under excitation by lasers and light emitting diodes

We developed a method for detecting traces of foreign components in water and analyzing the microstructure of water. The method is based on studies of the characteristics of secondary emission arising in aqueous media under excitation by radiation of ultraviolet lasers and light emitting diodes. A new type of cuvette (capillary cuvettes) for studying the secondary emission in molecular media was elaborated. The cuvettes enable the study of aqueous solutions at small concentrations of the components; they enable one to recognize the type of molecular compound present in aqueous media, in view of the photoluminescence spectra.

Determination of Characteristics of Secondary Emission of the Field of an Electromagnetic Wave of Mirror Antennas Used in Multichannel Radio Communication Facilities

The problem of ensuring electromagnetic compatibility of RES is one of main problems of the contemporary stage of development of telecommunication systems, including multichannel radio communication facilities. The article presents methods of calculation and results of modeling the processes of secondary emission of the field of an electromagnetic wave of the mirror antenna in the far zone.

Modeling of breakdown behavior in radio-frequency argon discharges with improved secondary emission model

This work represents the investigation of the dependence of the breakdown voltage on the gas pressure and on the frequency in radio-frequency argon discharges. Calculations were performed by using a one-dimensional particle-in-cell/Monte Carlo code with three velocity components with a new secondary emission model. The obtained results show that the multivalued nature of the left-hand branch of the breakdown curve can be achieved only by taking into account energy dependence of the yield per ion. The multivalued nature of the left-hand branch of the breakdown curve is attributed to the influence of the secondary emission characteristics of the electrodes on the breakdown voltage. Simulation results show a good agreement with the available experimental data. Disagreements between simulation results and theoretical predictions based on the phenomenological method indicate that a more accurate determination of molecular constants is needed. As a result of the satisfactory agreement between simulation and experimental data for dependence of the breakdown voltage on the frequency, a frequency scaling law is proposed.

Multiple secondary ion emission from keV massive gold projectile impacts

We present the first experimental data on secondary ion emission characteristics from the impact of 26 keV Au 3 + and 74.6–114.6 keV Au 400 4+. In particular we show secondary ion yield distributions and secondary ion and coincidental ion yields of molecular cluster ions from single impact events. The target consisted of an amorphous (HfO 2) 0.6(SiO 2) 0.4 layer deposited on a Si wafer. Large increases in higher order emission events and both secondary ion and coincidental ion yields within these events were observed for bombardment with Au 400 4+ even though the energy per atom of this projectile is more than an order of magnitude less than Au 3 +.

The radiofrequency breakdown in low pressure argon

The Monte Carlo simulation technique, previously used by the author (1996 Nuovo Cimento D 18 919) for computing, in the case of an ideal gas and plane-parallel electrodes, the threshold radiofrequency (rf) voltage for breakdown versus the gas pressure in the transition region from diffusion to multipacting controlled conditions, has been applied to the case of a real gas, argon. For this purpose the Monte Carlo algorithm has been modified to include the elastic and inelastic argon cross sections for electron collisions, the finite size of the electrodes and also a surface reflection coefficient for the primary electrons impinging on the electrodes. Furthermore, the so-called null-collision method has been introduced in order to handle the velocity dependency of the electron-atom collision frequency and, for a better description of the secondary emission characteristics of the electrodes, Vaughan's empirical formula has been preferred to the previously used Dionne's formula. The modified algorithm has been used for determining the threshold breakdown voltages for the experimental set-up conditions of Hoehn et al (1997 Phys. Plasmas 4 940). With the agreement with the experimental data being satisfactory, breakdown voltage values have also been determined for low-pressure conditions of practical interest in the case of argon rf capacitive reactors. In particular, indicative limits for the existence of the discharge at very low pressures are given and the behaviours of the pressure-dependent curves, providing the breakdown voltage versus the ratio of gap width over wavelength, are discussed.

Ion Pairing of Hydrophilic Analytes with Surfactants to Enhance FABMS Spectra

Abstract Recently the use of ion-pairing of inorganic and organic ions to ionic surfactants has been exploited in Fast Atom Bombardment Mass Spectrometry (FAB-MS) in order to increase secondary ion emission. Hydrophilic organic ions, such as 6-aminopenicillanic acid (6-APA), can be selectively ‘bound’ to the surface of a hydrophilic FAB matrix such as glycerol via interaction with an ionic surfactant of opposite charge. Thus, ion-pairing of analyte to surfactant allows for utilization of the surface specificity of FAB. In order to assess the utility and limitations of ion-pairing in FAB, we studied the secondary ion emission characteristics of a cation exchange model system consisting of the quaternary ammonium salt choline chloride (CC), the surfactant octyl sodium sulfate (OSS), and glycerol. Large, weakly solvated ions such as the tetramethylammonium ion of choline readily exchange sodium from sulfonate based cation exchange resins. Cation affinity for sulfate in increasing order is Li+< H+< Na+< NH4 +...

Sputter-induced photon emission study at various doses of implanted ions

A novel experimental method for the investigation of secondary emission processes during ion bombardment of a solid surface is proposed. This method gives a unique possibility to measure secondary emission characteristics at various fixed surface concentrations, n v, of implanted ions. Some fixed n v values in the interval 0.01 n ∞⩽ n v⩽ n ∞ ( n ∞ is the equil implanted particles) may be obtained by choosing the surface renewal velocity V. Using this method, we investigated the sputter-induced photon emission from a Ta surface bombarded by a Dy + ion beam. It was observed that the photon yield and spectrum shape were substantially dependent on the n v value. The main results of our research are the following: (1) the continuum radiation source is the excited molecule of metal-oxygen type (DyO, TaO, etc.), and (2) this method allows us to detect the excited adsorbed particles from submonolayer surface coverage.

Multi-electron secondary emission from solid surface bombarded by fast atomic particles

This article reviews the most recent experimental approaches to the study of, and the results of investigations of multi-electron secondary emission resulting from the bombardment of the surface of a solid by atomic particles with energies of 1–103 keV. The results of measurements of the differential characteristics of secondary electron emission (emission statistics, energy and angular distributions) are discussed. Theoretical approaches to a quantitative description of the principal characteristics of multi-electron secondary emission are considered, and the results of a Monte Carlo modeling, reproducing the principal observed MUSE effects are discussed.

Analysis of surface and bulk composition of amorphous metallic alloys

Surface and bulk composition of amorphous metallic alloys (AMA) has been analyzed by AES and SIMS. Original surface segregation and its variation has been studied in detail under the effect of different treatment techniques. Secondary ion energy distributions were measured for different structural states and primary ions. Data obtained can be used in practical SIMS analysis. Kinetical characteristics of secondary ion emission (SIE) are shown to be useful for surface characterization. Structure-sensitive SIE is changed greatly and irreversibly during transition from the amorphous to the crystalline state.

Transformation of resonant Raman scattering into luminescence in Cd xZn 1−xTe mixed crystals: Time-resolved spectroscopy

We report an experimental study of time characteristics of secondary emission in Cd xZn 1-xTe mixed crystals ( x = 0.32) under resonant excitation with a picosecond dye laser. When the incident laser frequency is tuned on to the luminescence maximum of localized excitons, the decay curve of the intensity of “Raman-like” lines exhibits a single exponential decay. Off resonance, however, a short-lived component corresponding to Raman scattering appears in addition to the long-lived component. The intensity of the Raman component relative to that of the luminescence component increases with increase of the off-resonance frequency. From these temporal behaviors, we have found, for the first time, the transformation of resonant Raman scattering into luminescence in mixed crystals as a function of incident frequencies.

Electron reflection and secondary emission characteristics of sputter-textured pyrolytic graphite surfaces

Low secondary and reflected primary electron emissions from the collector electrode surfaces are important for optimum collector efficiency and hence for high overall efficiency of microwave amplifier tubes used in communication satellites and in military systems. Ion sputter texturing effectively suppresses electron emission from the surface of pyrolytic graphite, a promising collector electrode material. In this paper we present secondary and reflected primary electron emission characteristics of sputter-textured pyrolytic graphite surfaces with microstructures of various sizes and densities. The microstructure with the lowest electron emission levels, which were less than those of soot, consisted of a dense array of tall thin spires.

Effects of bulk and surface conductivity on the potential developed by dielectrics exposed to electron beams

The charging and discharging of a dielectric material which has bulk and surface conductivities is discussed. Two model problems are solved. In the first problem, a semi-infinite dielectric plane, attached to an infinite grounded conducting substrate and exposed to a monoenergetic electron beam, is analyzed. Bulk and surface conductivities and secondary emission characteristics are taken into account as parameters. In the second problem the dielectric is charged but the electron beam is shut off so only the bulk and surface conductivities enter the calculation. The principal result of the latter calculation is to show that steep tangential gradients develop in the presence of a surface conductivity during decay, and that for asymptotic times the temporal behavior, for a fixed position, is proportional to t1/2 rather than exponential, as expected in the presence of a bulk conductivity.