Electron flow enhancement with a diamond membrane

Secondary electron emission from 2.5-to 5.0-μm thick diamond films (membranes) is considered. The process is studied in the reflection regime, where secondary electrons leave the front surface of the membrane exposed to primary electrons, and in the transmission regime, where primary electrons cause secondary emission from the opposite surface. The secondary emission coefficient is determined based on the behavior of 0.1-to 30-keV electrons in the solid. In the reflection regime, the secondary emission coefficient may be higher than 100 for electron energies of about 3 keV; in the transmission regime, it is no more than 5 even for 30-keV electrons. The emissivity of the membranes in the transmission regime can be improved, specifically, by using porous membranes, which allow one to obtain characteristics similar to those in the reflection regime. Experimental data obtained agree with calculations. The production of diamond films, including porous membranes, is described.     

Secondary electron emission from solid HD and a solid H2-D2 mixture

Secondary electron emission from solid HD and a solid 0.6 H₂ + 0.4 D₂ mixture has been studied for electron and hydrogen ion bombardment at primary energies from 0.5 to 3 keV and 2 to 10 keV/amu, respectively. The yield for solid HD is well explained by a simple stoichiometric model of the low-energy stopping power for the internal secondaries. The secondary electron yield from the mixture is somewhat larger than the expected value, but lies between the values for pure solid H₂ and D₂. The secondary electron emission coefficient for solid tritium may be determined from a linear extrapolation of the present data.     

Neutron yield when fast deuterium ions collide with strongly charged tritium-saturated dust particles

The ultrahigh charging of dust particles in a plasma under exposure to an electron beam with an energy up to 25 keV and the formation of a flux of fast ions coming from the plasma and accelerating in the strong field of negatively charged particles are considered. Particles containing tritium or deuterium atoms are considered as targets. The calculated rates of thermonuclear fusion reactions in strongly charged particles under exposure to accelerated plasma ions are presented. The neutron generation rate in reactions with accelerated deuterium and tritium ions has been calculated for these targets. The neutron yield has been calculated when varying the plasma-forming gas pressure, the plasma density, the target diameter, and the beam electron current density. Deuterium and tritium-containing particles are shown to be the most promising plasmaforming gas–target material pair for the creation of a compact gas-discharge neutron source based on the ultrahigh charging of dust particles by beam electrons with an energy up to 25 keV.     

Two-dimensional hydrogen behaviors on solid surfaces studied by hydrogen microscope

Recently, much work has been done to study hydrogen behavior on solid surfaces for applications in fuel cells, semiconductor devices, and diamond-like carbon films. We have developed a hydrogen microscope making use of electron stimulated desorption (ESD) spectroscopy. A thermal-field emission type electron gun set to a low-energy range (<1 keV) is used to obtain a beam size less than 100 nm in diameter. A pulsed beam has been used to measure the time-of-flight (TOF) to detect desorbed ions from specimen surfaces. Scanning the pulsed beams across solid surfaces, a two-dimensional distribution image of hydrogen atoms can be obtained. This paper reviews some capabilities of the hydrogen microscope and a chemical state analysis for H and O adsorbed by different elements on a surface.     

Elektronenausbeute bei Lithium-Ionenbeschuß von Bildwandlerflächen

The electron yield in the case of bombardment of a V2A type stainless steel plate by Li⁺ ions with energies between 20 and 80 keV was measured. The yield is increasing from 2·5 electrons per ion for 20keV to 4 for 70 keV. The electron yield in case of transmission by Li⁺ ions (number of electrons emitted on the back side of the foil per incident ion) of thin carbon foils with a layer of evaporated silver was measured. For this purpose the electrons emitted on the foil back side are accelerated in an immersion objective lens, and the resulting crossover of the beam is focussed into a Faraday cage by a projector lens. The electron yield depends on the ion energy and the foil thickness. Its value lies between 1 for a 1050 AU thick silver foil and 40 keV and 4 for a 380 AU thick silver foil and 80 keV. The range of Li⁺ ions in silver can be estimated by extrapolation of the yield curves. It is increasing from 600 AU for 10 keV to 2300 AU for 80 keV. The electron yield may not be characteristic for the target material since in a vacuum of 10^?4Torr the formation of a thin layer of polymerized hydrocarbon on the surface must be expected.     

Ion secondary electron emission from Al2O3 and MgO films

Coefficients of ion induced secondary electron emission (ISEE) γ from thin films of Al₂O₃ and MgO have been measured for argon ions in the energy range between 0–3 keV. Dionne's equation for secondary electron emission, which consists of production and emission terms has been modified to explain the kinetic emission of ISEE. The production term for ion induced secondary electrons has been separately formulated, taking account of the energy loss of primary ions, while the process of emission is considered to remain the same as in SEE. The escape depth λ_S and emission probability B were obtained from the SEE data and were used, along the range value of incident ions, to calculate the emission term in ISEE. The modified form of the equation was used to evaluate theoretically expected ISEE yield energy curves. Fairly good correlation is observed in theoretical and experimental curves which supports the validity of the proposed theoretical model.     

A new observation method of ion-electron emission

The energy spectra of secondary electrons emitted from a molybdenum target in the shape of a wire upon bombardment with 5 keV He⁺ ions is examined. It is shown that for the grazing angleof ion incidence the structure of the energy spectrum is most sensitive to the target treatment. At such a geometry the ion-electron emission can be used for analysis of the solid surface covered by adsorbed or contaminant particles.     

Angular and energy distribution of electrons produced by 200–500 keV protons in gases

The cross beam method was used to measure double differential ionization cross sections for electron production by 200–500 keV protons incident on a molecular beam. The ejected secondary electrons were detected by an electron multiplier and an electrostatic 90 °-spectrometer which was movable in the scattering chamber from 18 °–155 ° with respect to the incident proton direction. After the elimination of disturbing electric and magnetic fields, electrons were measured at energies down to 1 eV. The absorption of the very slow electrons along their path through the spectrometer could be minimized by using a relatively low gas pressure in the scattering chamber of a few 10^?5 Torr. The efficiency of the electron detector was determined with an electron source whose emission rate per solid angle was known. Absolute cross sections and their angular dependence were obtained by measuring the slow electrons—ejected with a relatively high rate—without the molecular beam; these data being used to normalize the electron spectra acquired with the molecular beam. Ionization cross sections with 300 keV protons incident on helium are discussed and except for the very slow electrons, a good agreement is found with results of Ruddet al.     

No enhanced electron emission from high-density atomic collision cascades in metals

Ion-induced secondary electron emission was studied for vanadium and niobium cluster ions at incident energies between 12.5 and 25 keV. The number of electrons ejected per incident atomic particle was found to be solely a function of the velocity, being independent of the number of atoms in the cluster. In spite of the extremely high energy densities created by cluster ion impact, there is no enhanced electron emission from collision spikes. This is discussed in terms of energy coupling between the system of lattice atoms and that of the electrons in the solid.     

The influence of ion bombardment on emission properties of small dust grains

Dust grains that are present in many plasma and vacuum systems and in the space usually carry a non-negligible charge. Their charging significantly depends on surface properties of the grain material. In cold plasma, charging is mainly given by electron attachment, nevertheless, when plasma becomes hot, other processes (secondary electron emission, field emission, etc.) take place. Emission properties of the grain surface could be modified by grain baking or by ion bombardment. Our study is carried out at the dust charging experiment dealing with a single dust grain electro-dynamically levitated in a 3D quadrupole trap. The grain can be exposed to the ion beam in the energy range of 100 eV–5 keV and to the electron beam in the energy range of 100 eV–10 keV. We have chosen He⁺ and Ar⁺ ions for the surface treatment and the observed influence on the surface properties is discussed in terms of secondary emission. A non-negligible shift of the secondary electron emission yield, as well as a change of energy distribution of secondary electrons, were measured after Ar⁺ bombardment. A preliminary study suggests that the effects of He⁺ and Ar⁺ are comparable.     

Neutron-, ion-, and electron-energy spectra in a 1 kJ plasma focus

The neutron energy spectrum (4 Torr deuterium) was determined from 30 m flight histograms.—An average energy of approximately 100±20 keV of the neutron producing deuterons within an assumed cone angle of approximately 40 degrees along thez-axis was calculated by means of the target beam model.—Shadow bar techniques reveal that only 10% of the neutrons are produced in the ≈1 cm long focus.—Experimental time of flight analysis confirms that the ion spectrum extends from less than 70 to greater than 400 keV. The electron spectrum in 8 Torr hydrogen follows a ≈3 keV Boltzmann distribution, but demonstrates the presence of nonthermal >100 keV electrons.     

Formation of Ti and TiN ultra-thin films on Si by ion beam sputter deposition

Ultra-thin titanium and titanium nitride films on silicon substrate were obtained by ion beam sputtering of titanium target in vacuum and nitrogen atmosphere, using argon ions with energy of 5 keV and 15 μA target current. Elemental composition and chemical state of obtained films were investigated by X-ray photoelectron spectroscopy with using Mg-Kα X-ray radiation (photon energy 1253.6 eV). It was shown that it is possible to form both ultra-thin titanium films (sputtering in vacuum) and ultra-thin titanium nitride films (sputtering in nitrogen atmosphere) in the same temperature conditions. Photoelectron spectra of samples surface, obtained in different steps of films synthesis, detailed spectra of photoelectron emission from Si 2p, Ti 2p, N 1s core levels and also X-ray photoelectron spectra of Auger electrons emission are presented.     

二次电子对离子束流品质影响的动态研究

基于粒子云网格的计算方法,建立了具有外电路的加速系统模型,模拟了氘离子束轰击靶面产生二次电子的过程,动态地分析了二次电子的产生对离子加速电压的影响以及对氘离子束束流品质和氘离子束轰击靶面能量的影响。结果表明,当有0.06 A的二次电子电流产生时,离子加速电压将会下降45%,从而导致氘离子束束流品质下降,参与氘氚反应的氘离子数减少,相应的氘离子束轰击靶面的能量下降43.8%。     

Nuclear Reactions under Irradiation of Deuterated Structures by X Rays

Measurements of emission from nuclear reaction products (neutrons and protons) have been carried out appearing in the deuterated structures of textured CVD diamond, palladium, titanium, and zirconium under irradiation with a beam of X rays using independent methods (neutron detector based on He-3 counters, Si surface-barrier semiconductor detectors and CR-39 track detector). The possibility of enhancement of both DD reaction and multi-particle deuterium fusion by the beam of X rays with energy ranging 20–30 keV in solid deuterated targets has been established. Analysis of X-ray fluorescence spectra of the target bombarded by beams of ions has revealed “additional” peaks, the occurrence of which cannot be related to any of the known elements, and requires separate study.

     

One-dimensional solution to the stable, space-charge-limited emission of secondary electrons from plasma-wall interactions

Numerical solutions to the stable, space-charge-limited emission of secondary electrons from plasma-wall interaction are found based on one-dimensional plasma moment equations that assume cold ions, Maxwellian electrons and cold secondary electrons. The numerical method finds a range of plasma parameters that permit stable emission of secondary electrons in the absence of normal electric fields to the wall. These solutions were not obtained with previous method that solves only for the marginally stable plasma sheath. Range of the ion Mach number at the sheath edge, the floating wall potential relative to the plasmas, and secondary electron emission coefficients corresponding to the vanishing normal electric fields are found for hydrogen, argon and xenon plasmas. The results show that a relatively small range of secondary electron emission coefficient exists to allow stable sheaths structures along with larger ranges of ion injection speed at the sheath edge and floating potential of the emitting wall.     

Contribution of backscattered electrons to the total electron yield produced in collisions of 8–28 keV electrons with tungsten

It is shown experimentally that under energetic electron bombardment the backscattered electrons from solid targets contribute significantly (∼80%) to the observed total electron yield, even for targets of high backscattering coefficients. It is further found that for tungsten (Z = 74) with a backscattering coefficient of about 0.50, about 20% of the total electron yield is contributed by the total secondary electrons for impact energies in the range of 8–28 keV. The yield of true backscattered electrons at normal incidence (η ₀), total secondary electrons (δ) and the total electron yield (δ _tot) produced in collisions of 8–28 keV electrons with W have been measured and compared with predictions of available theories. The present results indicate that the constant-loss of primary electrons in the target plays a significant role in producing the secondary electrons and that it yields a better fit to the experiment compared to the power-law.      

SIMS,EID and flash-filament investigation of O2, H2, (O2 + H2) and H2O interaction with vanadium

Comparative investigations of secondary ion emission, electron induced ion emission and flash filament signals from polycrystalline vanadium surfaces exposed to well-defined O₂, H₂, H₂O and (O₂ + H₂) doses (<500 L) have been carried out. The vanadium target could be heated and bombarded by either electrons (300 eV) or ions (3 keV) under ultra high vacuum conditions (<10^?10 Torr). The investigations were carried out with a computer controlled ultra high vacuum mass spectrometer. The experimental results establish exact reproducible spectra of well defined surface layers. They give detailed insight into the reactions between H₂, O₂ H₂O and vanadium, and some interactions between these species. They further indicate the importance of bulk and surface diffusion as well as the influence of the probing ion and electron bombardment. A clear distinction between bulk oxygen, surface oxides, and adsorbed oxygen for the vanadium-oxygen interaction at room temperature could be established. For the interaction of hydrogen with clean and oxygen covered vanadium surfaces the formation of adsorbed hydrogen, bulk solution of hydrogen, and the formation of OH groups and H₂O could be demonstrated. A detection limit below 10^?5 of one single monolayer for metal bonded hydrogen could be established.     

Determination of the thickness of a gold layer deposited onto silicon via reflected electron spectroscopy

The energy spectra of electrons reflected from a gold layer deposited onto a silicon substrate have been measured when the energy losses are comparable with the energy of a probe electron beam (5 keV) and the elastic energy losses correspond to an electron-beam energy of 14 keV. A subsequent theory for calculating the energy spectra of electrons and light ions reflected from a multilayer target, which is used to interpret the energy spectra measured in the wide range of energy losses, has been developed. It is found that the elastic scattering processes in the gold layer (the thickness of which is tens of monolayers) substantially affect formation of the energy spectra. The Au layer thicknesses calculated by means of the developed theory are compared with those determined from the spectra of elastically reflected electrons. The errors of the Au layer thickness measurements via the proposed method are discussed.     

Anomalous asymmetry of carbon nanopillar growth on both sides of a thin substrate irradiated with a focused electron beam

The dynamics of carbon nanopillar growth on both surfaces of amorphous carbon films 40–180 nm thick irradiated with a focused electron beam with an energy of 20 keV is studied. Prolonged irradiation causes the retardation and even complete termination of nanopillar growth on the upper side of the substrate while growth on the lower side continues. This unexpected result is explained by the dissociation of precursor molecules diffusing along the substrate by secondary electrons emitted from the conical nanopillar tip. The substrate acts as a filter allowing primary electrons to easily pass, but intercepting low energy secondary electrons. The lower efficiency of secondary electrons emitted in the lower half-space may be due to a decrease in the current density within the expanding beam of scattered electrons.     

Experiments with energetic μd and μt emitted from solid hydrogen

A set of experiments is reviewed which makes use of the emission of muonic deuterium from the surface of a layer of solid hydrogen. The behaviour of muons in a solid target system has been studied via detection of muon decay electrons, muonic X-rays, and fusion products (neutrons and charged particles). The emission of muonic deuterium is understood to result from the Ramsauer-Townsend scattering minimum. The energy distribution of the emitted atoms ranges from tenths of eV to about 10 eV, and can be controlled to some extent. A proposal is described to use muonic tritium emission to measure the energy dependence of muonic molecular formation.