Z variations in yields of multicharged ions scattered and recoiled from a silicon surface

The doubly charged and triply charged ion yields from keV ion-silicon surface scattering are found to have a strong dependence on the atomic number Z₁ of the incident ion. For Z₁ < Z₂ the yield of scattered multicharged ions increases with Z₁, so that these ions dominate the recoiling Si²⁺ and Si³⁺ ions by Z₁ = 9. In contrast, when Z₁ > Z₂, there are large yields of Si²⁺ and Si³⁺ ions, and the multicharged scattered ion yields are too small to detect. The interaction radius at which shell vacancies are produced is also found to change, suggesting that electron promotion occurs at a different level crossing on either side of Z₁ = Z₂.     

Material dependence of total electron emission yields following slow highly charged ion impact

The total electron emission yields following the interaction of “Slow (2 keV/a.u.) Highly Charged Ions” (SHCI) (O³⁺⁷⁺, Xe¹²⁺⁵²⁺, Au⁵⁴⁺⁶⁹⁺) with different target surfaces (highly-oriented pyrolytic graphite (HOPG), Au and SiO2) have been measured. The emission yields increase with charge state, and is found to be highest for carbon, the HOPG target, and lowest for the SiO₂ target. An empirical formula for the electron emission is including recent results from investigations of plasmon excitation following SHCI impact are used to interpret the results.     

Electron emission induced by H and H incident on thin carbon foils: influence of charge changing processes

The forward and backward electron emission yields γ_F and γ_B have been calculated by Monte Carlo simulation for protons (H⁺) and hydrogen atoms (H⁰) (with energies between 25 keV and 5 MeV) incident on thin amorphous carbon foils. Direct electron excitations by the incident projectiles as well as electron excitations resulting from charge exchange processes undergone by H⁺ or H⁰ have been taken into account. For the latter, Auger and Shell processes have been considered. Subsequent electron transport has been considered in order to calculate the forward and backward electron emission yields γ_F and γ_B.     

Measurements of the erosion of stainless steel, carbon, and SiC by hydrogen bombardment in the energy range of 0.5 – 7.5 keV

Total erosion yields by sputtering and blistering for 1 to 15 keV H₂⁺ bombardment at normal incidence have been measured by weight loss of 304 stainless steel, pyrolytic graphite, carbon fibres, glassy carbon and SiC. The erosion yields are in the range of 3 × 10⁻³ to 2.6 × 10⁻² atoms per incident hydrogen atom. Observation in the scanning electron microscope shows that blisters occur in stainless steel and SiC at doses of 5 × 10¹⁸ particles/cm², but disappear at doses of 5 × 10 particles/cm² . The surface roughening observed depends largely on grain orientation. On carbon no blistering could be found. After bombardment the carbon surfaces are generally more smooth than before.     

Effect of Auger neutralization on yields of He ions backscattered and alkali ions sputtered from the surface of alkali halides by keV He ion impact

The yields of ions and neutrals backscattered and alkali ions sputtered from LiF crystals by keV He⁺ ion impact have been measured by means of the coaxial impact collision ion scattering spectroscopy in time of flight analysis mode using the charging-up effect. It is found that as the charging-up potential increases due to continuous irradiation of the pulsed ion beam, the time of flight of the He⁺ ions backscattered shifts toward the shorter time, while that of the neutrals backscattered shifts toward the longer, and that of Li ions sputtered also shifts much more clearly toward the shorter. The charging-up potential has been estimated as a function of irradiation time of the pulsed ion beam from the time of flight data and the ion to neutral ratio in the backscattering yields is estimated to be about 0.15. The mechanisms for ionization on He and sputtering of alkali ions are discussed in terms of charging-up and trion (bihole and electron) produced by Auger neutralization of keV He⁺ ions at the target surface.     

Investigation on the characteristics of an atmospheric-pressure microplasma plume confined inside a long capillary tube

An atmospheric-pressure microplasma plume of diameter 10 μm is generated inside a long tube. The length of the microplasma plume reaches as much as 2 cm. First, with the assistance of an air dielectric barrier discharge (DBD), the ignition voltage of the microplasma decreases from 40 kV to 23.6 kV. Second, although the current density reaches as high as (1.2−7.6)×10⁴ A cm ⁻² , comparable to the current density in transient spark discharge, the microplasma plume is non- thermal. Third, it is interesting to observe that the amplitude of the discharge current in a positive cycle of applied voltage is much lower than that in a negative cycle of applied voltage. Fourth, the electron density measured by the Stark broadening of Ar spectral line 696.5nm reaches as high as 3×10¹⁶ cm⁻³ , which yields a conductivity of the microplasma column of around 48 S m⁻¹ . In addition, the propagation velocity of the microplasma plume, obtained from light signals at different axial positions, ranges from 1×10⁵ m s ⁻¹ to 5×10 ⁵ m s⁻¹ . A detailed analysis reveals that the surface charges deposited on the inner wall exert significant influence on the discharge behavior of the microplasma.     

Autoionising state excitation in collisions of inert gas projectiles with an Al surface and effects of initial stages of oxidation

Results of an angle resolved electron spectroscopy study of low keV He⁺, Ne and Ne⁺ collisions with an Al surface are presented. Production of projectile autoionising states is demonstrated to exist not only for the previously known Ne⁺ case but also for Ne and He⁺. The characteristics of autoionising peak line shapes suggest differences in angular distributions of the different Ne^** states. Initial stages of the oxidation of Al are studied. Saturation coverages of oxygen are reached for exposures greater than 100 L. An initial decrease in the work function is observed amounting to 160 meV for a 30 L exposure. Exposure to oxygen results in a strong decrease of autoionising state production. State-selective attenuation is observed and reflects changes in electron transfer rates.     

Kinetic electron emission in the interactions of slow ions with MgO surfaces

We report experimental energy distributions and yields of electrons emitted from MgO surfaces under the impact of slow noble gas and sodium singly charged ions at varying incident energies.

At impact energies below 1 keV, electron spectra are nearly independent of ion type and energy. A tail of high-energy electrons is observed to grow at higher impact energies.

The results are explained in terms of promotion of oxygen-2p electrons during binary projectile-oxygen collisions populating continuum and excitonic states. Excitons can significantly contribute to electron emission due to the negative electron affinity of the surface.     

Light emission from oxygen covered Al and Cu surfaces

Ion beam induced light emission is used to investigate the sputtering yield, S_O, of oxygen atoms on the surfaces of a polycrystalline copper and an Al(1 1 1) target. Under Ar⁺ and Ne⁺ ion bombardment of Al(1 1 1) and polycrystalline copper targets, spectral lines of Cu I and Al I emitting from sputtered excited atoms are measured as a function of the oxygen partial pressure, wavelength and beam energy. The light emission for two Al I lines (3082 and 3962 Å) and Cu I lines (3247 and 3274 Å) are proportional to the oxygen partial pressure (1×10⁻⁴ Torr). Above 2×10⁻⁴ Torr, the light intensities start to decrease which is consistent with other measurements. From saturated-oxygen covered target surfaces, light intensities of Al I and Cu I lines are measured as a function of time and oxygen partial pressures. The sputtering yields could be determined from the curves of spectral lines directly. For 10 and 20 keV Ar⁺ ions bombarding the copper surface, the oxygen sputtering yields are 0.34 and 0.22 (atoms/ion), respectively. The same copper target was bombarded by Ne⁺ ions at 5 and 10 keV, the oxygen sputtering yields are 0.87 and 0.59, respectively. For 10, 15, and 20 keV Ar⁺ bombarding an Al(1 1 1) target, the obtained sputtering yields are 0.44, 0.31, and 0.2 (atoms/ion), respectively.     

Electron microscopy and Rutherford backscattering spectrometry characterisation of 6H SiC samples implanted with He

6H SiC single crystals were implanted at room temperature with 1 MeV He⁺ up to a fluence of 2 × 10¹⁷ at./cm². RBS-channeling analysis with a 2 MeV He⁺ beam indicated the formation of extended defects or the generation of point defects at a constant concentration over a depth of about 1 μm. Electron microscopy characterisation revealed the presence of two amorphous buried layers at depths of about 1.75 and 4.8 μm. They are due to the implantation and to the analysing RBS beam, respectively. No extended planar or linear faults were found in the region between the surface and the first amorphous layer. However, at the surface, a 50 nm thick amorphous layer was observed in which crystalline inclusions were embedded. Electron diffraction and HREM data of the inclusions were typical for diamond. These inclusions were even found in the crystalline SiC material below this layer, however at a reduced density.     

Charge transfer in grazing scattering on clean and oxygen covered Cu(1 1 0) surfaces: velocity effects

We have measured negative (F⁻) and positive (Na⁺, Li⁺) charge fractions produced by grazing scattering from the corrugated metallic Cu(1 1 0) surface. A wide range of incident energies and scattered angles were explored in order to analyse the effects of the parallel and perpendicular velocities of the projectiles on the charge transfer process. The obtained dependences of F⁻ formation and of Na⁺ and Li⁺ neutralization with the parallel velocity are in good agreement with previous experimental and theoretical studies, which incorporate parallel velocity effects via the “shifted Fermi sphere” model. The surface structure is then modified by adsorption of oxygen. The dependence of charge fractions with oxygen adsorption and the effects of velocity in the case of the Cu–O surface are analysed.     

新型铯选择性吸附剂的合成及性能

在金属镍粉表面原位合成了与金属基体紧密结合的亚铁氰化镍钾(KNiFC/Ni)吸附剂。经分析,其表面为面心立方晶系的亚铁氰化镍钾(KNiFC),厚度约为40~80nm,晶格参数为0.996 0nm,化学组成可表示为K1.4Ni1.3Fe(CN)6。结果表明:该吸附剂不水解,对137 Cs具有较高的吸附容量,非常快的吸附速率,很高的选择性,Cs的吸附分配系数(Kd)可达105 mL/g,即使在1.0mol/L NaNO3溶液中,Kd值也大于103 mL/g;该吸附剂吸附137 Cs为典型的离子交换机制,NH+4由于具有和Cs+相近的离子半径所以竞争最为强烈。本吸附剂有望用于含铯废液的处理及137 Cs的分离或提取。     

W fuzz layers: very high resistance to sputtering under fusion-relevant He+ irradiations

In this study, we have modeled the sputtering process of energetic He⁺ ions colliding with W nano-fuzz materials, based on the physical processes, such as the collision and diffusion of energetic particles, sputtering and redeposition. Our modeling shows that the fuzzy nanomaterials with a large surface-to-volume ratio exhibit very high resistance to sputtering under fusion-relevant He⁺ irradiations, and their sputtering yields are mainly determined by the thickness of fuzzy nano-materials, the reflection coefficients and mean free paths of energetic particles, surface sputtering yields of a flat base material, and the geometry of nano-fuzz. Our measurements have confirmed that the surface sputtering yield of a W nano-fuzz layer with the columnar geometry of nano-fuzz in cross-section is about one magnitude of order lower than the one of smooth W substrates. This work provides a complete model for energetic particles colliding with the nano-fuzz layer and clarifies the fundamental sputtering process occurring in the nano-fuzz layer.     

A large-grain-size thick-film polycrystalline diamond detector for x-ray detection

A diamond film with a size of 6 × 6 × 0.5 mm³ is fabricated by electron-assisted chemical vapor deposition. Raman spectrum analysis, x-ray diffraction and scanning electron microscope images confirm the high purity and large grain size, which is larger than 300 μm. Its resistivity is higher than ${10}^{12}\,{\rm{\Omega }}\cdot {\rm{cm}}.$ Interlaced-finger electrodes are imprinted onto the diamond film to develop an x-ray detector. Ohmic contact is confirmed by checking the linearity of its current–voltage curve. The dark current is lower than 0.1 nA under an electric field of 30 kV cm⁻¹. The time response is 220 ps. The sensitivity is about 125 mA W⁻¹ under a biasing voltage of 100 V. A good linear radiation dose rate is also confirmed. This diamond detector is used to measure x-ray on a Z-pinch, which has a double-layer 'nested tungsten wire array'. The pronounced peaks in the measured waveform clearly characterize the x-ray bursts, which proves the performance of this diamond detector.     

Surface modifications and erosion yields of silicon and titanium doped graphites due to low energy D bombardment

Influences of low energy D⁺ ion bombardment and target temperature on surface topography, surface concentration and erosion yield of carbon based binary compounds were investigated. The samples contained 10 at.% Si and 10 at.% Ti, respectively. The surface concentration was determined in situ by Auger electron spectroscopy and the topography ex situ by scanning electron microscopy. During low energy D⁺ bombardment a pronounced conelike surface developed with silicon respective titanium rich ‘caps’ protecting the underlaying carbon rich shafts from erosion. The average dopant surface concentration was up to 7 × the bulk concentration. The erosion mechanism was determined by surface concentration and chemical state of the surface: At high temperatures carbidic bindings dominated, while at room temperature a mixture of graphite and carbide covered the surface.     

Mechanisms of subthreshold atomic emission from solid surfaces

Computer simulation of the dynamics of ions and atoms on the surfaces of solids has been carried out. The Coulomb, Pauli, exchange and Van der Waals potentials have been taken into account. The semi-empirical quantum-chemical method has been used also. In the case of alkali halide surfaces it is shown that if recharge of an anion (X⁻ →X⁺) occurs in two surface layers, it may initiate the ejection of positive metal ions (M⁺) and, assisted by the capture of an electron by a departing M⁺ of metal atoms M⁰. Besides the Coulomb repulsion the Pauli shock is shown to play an essential role in the driving of the ejection process. This mechanism of desorption has large efficiency when the excitation of a core electron occurs in case of alkali halide crystals and has a strong dependence on the crystal ionicity. We obtained the energy distribution of ejected particles for different mechanisms of electron-ion emission.     

Development of a helicon-wave excited plasma facility with high magnetic field for plasma-wall interactions studies

The high magnetic field helicon experiment system is a helicon wave plasma(HWP)source device in a high axial magnetic field(B_0)developed for plasma–wall interactions studies for fusion reactors.This HWP was realized at low pressure(5?×?10~(-3)?-?10 Pa)and a RF(radio frequency,13.56 MHz)power(maximum power of 2 k W)using an internal right helical antenna(5 cm in diameter by 18 cm long)with a maximum B_0of 6300 G.Ar HWP with electron density~10~(18)–10~(20)m~(-3)and electron temperature~4–7 e V was produced at high B_0 of 5100 G,with an RF power of 1500 W.Maximum Ar~+ion flux of 7.8?×?10~(23)m~(-2)s~(-1)with a bright blue core plasma was obtained at a high B_0 of 2700 G and an RF power of 1500 W without bias.Plasma energy and mass spectrometer studies indicate that Ar~+ion-beams of 40.1 eV are formed,which are supersonic(~3.1c_s).The effect of Ar HWP discharge cleaning on the wall conditioning are investigated by using the mass spectrometry.And the consequent plasma parameters will result in favorable wall conditioning with a removal rate of 1.1?×?10~(24)N_2/m~2 h.     

模拟高盐溶液中硫酸钛水解对Sr的去除研究

研究了硫酸钛在模拟高盐溶液中的水解反应对Sr²⁺的吸附能力并对其水解产物进行了分析。首先,通过电感耦合等离子体质谱（ICP-MS）对硫酸钛水解过程中对Sr²⁺的吸附能力进行了研究;其次,通过扫描电子显微镜（SEM）和X射线衍射（XRD）对硫酸钛水解产物的形貌及结构进行了表征;最后,对该工艺进行了放射性工程热试验验证,验证试验以100 L/h的废液处理规模,连续运行105 h。研究结果表明,随着溶液pH值的升高,硫酸钛水解对Sr²⁺的吸附能力逐渐增强。当pH=13时,吸附能力达到最大值,此时对Sr²⁺的吸附率达99.4%,对Sr²⁺的吸附量为1.67 mmol/g。另外,研究还证明,该吸附过程是短时间内完成的,反应时间对吸附率基本无影响。放射性工程热试验验证了工艺的可行性,试验中⁹⁰Sr的去污因子（DF）达215。     

Structure and kinetic studies of U(VI)-benzamidoxime complex in non-aqueous solutions by H- and C-NMR

The structural and kinetic studies of U(VI) complex with benzamidoxime(Hba) as ligand in CD₃COCD₃ have been studied by means of ¹H and ¹³C NMR. The Hba molecule was found to coordinate to UO₂²⁺ in the form of anionic benzamidoximate (ba), and the number of ba coordinated to UO₂²⁺ was determined to be 3 by analyzing the chemical shift of ¹³C NMR signal for Hba in the presence of UO₂²⁺. The exchange rate constants(k_ex) of ba in [UO₂(ba)₃] were determined by the NMR line-broadening method. The kinetic parameters were obtained as follows: k_ex(25°C) = 3.1 × 10³s⁻¹, ΔH^≠ = 35.8 ± 3.5 KJ mol⁻¹, and ΔS^≠ = −65 ± 13.7 J K⁻¹ mol⁻¹. The UV-visible absorption spectra of solutions containing UO₂²⁺ and Hba were also measured. The molar extinction coefficient of the complex was found to be extremely large compared with those of UO₂(L)₅²⁺ (L = unidentate oxygen donor ligands) complexes. This is due to the strong electron withdrawing of UO₂²⁺ from Hba and suggests that an interaction between UO₂²⁺ and Hba is very strong. Such a high affinity of monomeric amidoxime to UO₂²⁺ reasonably explains the high adsorptibility of amidoxime resin to U(VI) species, and is considered to result in the high recovery of U(VI) species from sea water using amidoxime resin.