Secondary ion emission from Si under nitrogen ion bombardment

The yield and energy distribution of positive secondary ions emitted from Si under N₂⁺ ion bombardment were measured. The obtained mass peaks correspond to three types of secondary ion species, that is, physically sputtered ions (Si⁺, Si₂⁺), chemically sputtered ions (SiN⁺ Si₂N⁺) and doubly charged ions (Si²⁺). The dependence of secondary ion emission on the primary ion energy was studied in a range of 2.0–20.0 keV. The yields of physically and chemically sputtered ions were almost independent of the primary ion energy. The yield of the doubly charged ion strongly depended on the primary ion energy. The energy distribution of secondary ions of the three types showed the same dependence on the primary ion energy. The most probable energy of the distribution increased with the primary ion energy. On the other hand, for the energy distribution curves of sputtered ions, the tail factors N in E^?N were constant and showed a m/e dependence.     

Registration of accelerated multiply charged ions from the cathode jet of a vacuum discharge

The parameters of Cuⁿ⁺ and Taⁿ⁺ ions from the plasma of a vacuum spark with a voltage up to 2.5 kV and a current rise rate up to 2 × 10¹⁰ A/s are studied using the time-of-flight method. At the initial stage of the discharge, bursts of beams of accelerated multiply charged ions from the cathode flame have been detected. It is established that the charge state distribution and energy of a beam are controlled by the initial voltage U ₀ of the capacitor. Upon an increase in this voltage, the average charge of copper ions attains the value +9, and the average charge of tantalum ions can be as high as +20, while the energy attains values of 150 and 350 keV, respectively. It is found that the average energy of ions with charge Z increases in proportion to the charge and is close to the energy eZU ₀ which would have been acquired by ions accelerated in the electric field of the discharge gap.     

氮气辉光放电阴极鞘层重粒子输运过程研究

采用蒙特卡罗模拟对氮气辉光放电等离子体阴极鞘层内离子(N₂⁺,N⁺)和快中性分子(N_2f)的输运过程进行了研究,计算了阴极鞘层中离子(N₂⁺,N⁺)和快中性分子的能量及角分布的空间变化,较好地解释了实验结果.得到了氮气辉光放电等离子体阴极附近主要存在着能量较低的荷能分子、密度较低的高能原子离子及密度和能量居中的分子离子.诸粒子状态随放电条件而变化.模拟结 关键词：     

Statistical mechanism of the formation of the energy spectra of sputtered molecular clusters

The energy spectra of Si _n O _m ^? clusters sputtered from Si targets by Xe⁺ ions with O₂ pumping onto a bombarded surface, as well as by O ₂ ⁺ ions, are studied. It is shown that the form of the Si _n O _2n+1 ^? energy distributions does not depend on the experimental conditions. Significant differences in the energy spectra of O and Si monomers as compared to Si _n O _2n+1 ^? clusters are revealed. The mentioned features of the energy distribution of Si _n O _m ^? clusters are explained within the framework of the statistical recombination mechanism of their formation in combinatorial synthesis processes.     

Die Energieaufnahme der Ionen in einem sehr schnellen Theta-Pinch

In a theta pinch with an extremely fast rising magnetic field (dB/dt 10¹¹ G/sec), a strong compression wave is produced in an initially fieldless low-density deuterium plasma. Assuming simple plasma models, a high-energy gain of the ions is expected already during the implosion of the plasma. In agreement with these calculations for a filling pressure of 20 μ D₂, a mean ion energy of 1–2 keV is determined from the first neutron emission at the end of the implosion, only 150 nsec after ignition. Decreasing the initial pressure to 10 μ D₂ does not cause any further increase of the achieved ion energy. This limitation of the ion heating is explained by a strong broadening of the current carrying layer at low densities which is observed by magnetic probe measurements. In the adiabatic compression, the mean ion energy attains values of several keV. During the first part of this phase, the energy distribution function of the ions is found to be essentially anisotropic, and monoenergetic rather than Maxwellian.     

Vacancy defects induced in sintered polished UO2 disks by helium implantation

Vacancy defects have been investigated in sintered polished and annealed uranium oxide disks. Slow positron beam coupled with Doppler broadening spectrometer was used to probe the track region of 1 MeV ³He ions implanted in uranium dioxide (UO₂) disks. The low and high momentum annihilation fractions, S and W, respectively, were measured in the first micrometer near surface region of the disks as a function of positron energy. The S and W values indicate that the 1 MeV He ions induce vacancy defects in the track region of their range. The vacancy defect depth distribution is heterogeneous. The positron trapping at these vacancy defects increases with the depth and with the implantation fluence indicating an increase of the vacancy defect concentration. The nature of the induced vacancy defects does not change with the fluence.     

Trapping ions at high temperatures: thermal decay of C60 +

An ensemble of trapped C₆₀ ⁺ ions has been heated with a continuous CO₂ laser to a stationary state where, in time average, the same energy is emitted as absorbed. With 10 W laser power, equilibria have been reached, which correspond to temperatures between 1800 and 2000 K. The ions are confined in a radio frequency quadrupole field created by a set of ring electrodes (split ring electrode trap). The number of stored ions can be determined in two ways, on one side by extracting and counting them with a Daly detector, on the other side via imaging their thermal emission onto an intensified CCD camera. Single photon sensitivity and a spatial resolution of a few μm provide precise information on the geometrical distribution and the total number of the trapped C₆₀ ⁺ ions. The spectral distribution of the emitted photons or their total number provides information on the internal energy of the ions. Trapping times of many minutes make it possible to follow very slow thermal loss of C₂ from hot C₆₀ ⁺ resulting in fragmentation rates between 10^?1 and 10^?3 s^?1. Correlating them to the internal temperature leads to a curved Arrhenius plot. The resulting parameters are smaller than the values derived from nonequilibrium ensembles.     

The peculiarities of the low-energy ion scattering by polycrystal targets

In the present work, experimental and computer simulation studies of low-energy (E₀ = 80-500 eV) Cs⁺ ions scattering on Ta, W, Re target surfaces and K⁺ ions scattering on Ti, V, Cr target surfaces have been performed for more accurate definition of mechanism of scattering, with a purpose of evaluation of an opportunity of use of slow ions scattering as a tool of surface layers analysis. The choice of the targets was based on the fact that the ratios of atomic masses of target atoms and ions μ = m₂/m₁ were almost the same for all cases considered and greater than 1 (direct mass ratio) however, the difference of binding energies of target atoms in the cases of Cs⁺ and K⁺ scattering was almost twice as much. It has been noticed that the dependencies of the relative energy retained by scattering ions at the maximum of energy distribution versus the initial energy E_m/E₀ (E₀) have a similar shape in all cases. The relative energy retained by scattering ions increases while the initial energy of incidence ions decreases. The curves are placed above each other relative to the binding energies of target atoms, to show what this says about the influence of binding energy on a process of scattering of low-energy ions. The correlation between value of energy change maintained by an ion for different values of E₀ in the case of scattering by targets with different masses of atoms and its binding energies is experimentally established. The contrary behavior of the E_m/E₀ (E₀) dependencies concerning the target atom binding energy quantity E_b for cases with direct (μ > 1) and inverse (μ < 1) mass ratio of colliding particles is established. The comparison of experimental energy distributions with calculated histograms shows that the binary collision approximation cannot elucidate the abnormally great shift in the maxima of relative energy distributions towards greater energy retained by scattering ions.     

Variations of ionic binding energies and the distribution of charge carriers in orthorhombic La2−x Sr x CuO4

The significance of heterovalent, substitutional disorder for the distribution of charge carriers in La_2?x Sr _x CuO₄ has been investigated. Disorder is shown to cause strong variations of binding energies of the ions ranging to some eV for Sr contentsx=0.1. Balancing the energy for a hole transport, Cu³⁺+O^2?→Cu²⁺+O^?, and taking binding energy variations into account, the process is realized to become possible without consuming energy for a subset Θ for allx Cu³⁺ in one formula unit of La_2?x Sr _x CuO₄. The functions Θ(x) are presented for hole transports to apex and in-plane oxygens, respectively. The delocalization of charge carriers is interpreted to be caused by valency disorder on metal lattice sites.     

Vibrational and electronic spectra of alkali halides doped with CrO42− ions

The i.r. spectra of alkali halides doped with FrO₄^2? ions are very sensitive to the concentration of background divalent impurities. Highly pure crystals containing CrO₄^2? ions show a 5 line i.r. spectrum in the v₃ stretch frequency region. One of these lines is attributed to CrO₄^2? ions in perfect crystal surroundings having T_d symmetry and the other 4 lines are attributed to C_s symmetry produced by a charge compensating anion vacancy in the nearest neighbour position. If the crystal contains a concentration of divalent cation impurity which is equal to or more than that of CrO₄^2? ions, a different spectrum characteristic of C_2x symmetry as well as the line corresponding to T_d symmetry are obtained. The crystals of ordinary purity contain all the three (C_s, C_2x and T_d symmetry) species and show eight line spectra. The changes in force constants calculated from the observed splitting of the energy levels agree with those evaluated from the known polarizability of the chromate ions.At 600°C, the vibration spectra of the highly pure crystals doped with CrO₄^2? ions show an increase in intensity of the line characteristic of T_d symmetry and the other lines practically disappear, because the anion vacancies move away from the neighbourhood of the CrO₄^2? ions at high temperatures. The energy of association of the vacancy with CrO₄^2? ions and the energy of migration of the vacancy are derived from the spectra obtained at different temperatures and with different heat treatments.The electronic spectra of the crystals show 3 bands (at 345, 270 and 240 nm for KCI). The lowest energy band has a fine structure with a spacing of about 800 cm^?1 at LAT. Since the transition involved is from a non-bonding to an antibonding state, the Condon parabola is shifted in the excited state and therefore the fine structure is attributed to a vibrational progression involving a totally symmetric frequency 800 cm^?1 in the excited state.     

Quasielastic and inelastic neutron scattering from AgPO3-AgI glass

A quasielastic neutron scattering experiment was performed on the fast ionic conductor AgPO₃-Agl, which is a vitreous electrolyte. This experiment was performed on the time-of-flight spectrometer IN 6 of the Institut Laue-Langevin in Grenoble, with the following parameters: λ=5.1 Å; 1.25 Å;^-1<Q<2.04^-1; instrumental resolution— FWHM=0.070 meV; sample thickness: 1.5 mm, 299 K <T< 368 K. The spectra generally show a quasielastic broadening of the elastic peak and a long tail up to 10 meV which is due to an inelastic distribution. In order to obtain the quasi-elastic contribution, the profile of the central peak was fitted within ± 0.6 meV for nine different spectra and for five temperatures. The elastic incoherent structure factor (EISF) was constant at 85%. The profile of the quasielastic contribution was found to be Lorentzian. When plotting the energy width ΔE times S(Q), the coherent structure factor, versus Q², a straight line is obtained for all temperatures. This means that the mechanism of the conductivity is certainly a translational diffusion with a coefficient of self-diffusion of the silver ions D=1.32x10^-5exp(-2080⧸RT) (activation energy being in calories). The value of the activation energy is very close to that of α-AgI measured by electric conductivity. The value of EISF: 0.85 indicates that the observed quasielastic scattering is due to half of the silver ions. These two results seem to confirm our hypothesis on the structure of these glasses: small “clusters” of AgI with tetrahedral coordination are dispersed in the AgPO₃ host glass. The two peaks observed in the inelastic frequency distribution function can be related to vibrations of the AgPO₃ host glass and of AgI₄ structural units respectively.     

Relativistic doppler effect in199Hg+ stored ions atomic frequency standard

RF traps are widely used nowadays in high resolution hyperfine spectroscopy. The spectrum of the microwave hyperfine transition at 40.5 GHz of the fundamental level² S _1/2 of¹⁹⁹Hg⁺ is phase modulated at the secular frequency of the stored ions and it consists of a narrow central line and lateral bands broadened by the ion trajectory and velocity distribution. The central line itself is shifted by the second-order Doppler effect which is the most important systematic error of stored ions frequency standards. In this paper the relativistic Doppler effect in the case of¹⁹⁹Hg⁺ stored ions is deduced applying a mathematical formalism and using physical parameters that we have measured experimentally.     

63Cu nuclear magnetic resonance study of RbCu4I2−xCl3+x

The nuclear magnetic resonance of ⁶³Cu has been investigated in RbCu₄I_2?xCl_3+x for 0?x?0.25. The fast motion of the Cu ions is thermally activated with energies ranging from 0.094 eV to 0.125 eV; no indication of a discontinuous change of the activation energy could be detected. The amount of unreacted CuI and/or CuCl for x=0, 0.125 and 0.25 is 2, 1, and less than 0.1 wt%.     

Energy distributions of atomic and molecular ions sputtered by C60 projectiles

In the process of investigating the interaction of fullerene projectiles with adsorbed organic layers, we measured the kinetic energy distributions (KEDs) of fragment and parent ions sputtered from an overlayer of polystyrene (PS) oligomers cast on silver under 15 keV C₆₀⁺ bombardment. These measurements have been conducted using our TRIFT™ spectrometer, recently equipped with the C₆₀⁺ source developed by Ionoptika, Ltd. For atomic ions, the intensity corresponding to the high energy tail decreases in the following order: C⁺(E^−0.4) > H⁺(E^−1.5) > Ag⁺(E^−3.5). In particular, the distribution of Ag⁺ is not broader than those of Ag₂⁺ and Ag₃⁺ clusters, in sharp contrast with 15 keV Ga⁺ bombardment. On the other hand, molecular ions (fragments and parent-like species) exhibit a significantly wider distribution using C₆₀⁺ instead of Ga⁺ as primary ions. For instance, the KED of Ag-cationized PS oligomers resembles that of Ag⁺ and Ag_n⁺ clusters. A specific feature of fullerene projectiles is that they induce the direct desorption of positively charged oligomers, without the need of a cationizing metal atom. The energy spectrum of these PS⁺ ions is significantly narrower then that of Ag-cationized oligomers. For characteristic fragments of PS, such as C₇H₇⁺ and C₁₅H₁₃⁺ and polycyclic fragments, such as C₉H₇⁺ and C₁₄H₁₀⁺, the high energy decay is steep (E⁻⁴ − E⁻⁸). In addition, reorganized ions generally show more pronounced high energy tails than characteristic ions, similar to the case of monoatomic ion bombardment. This observation is consistent with the higher excitation energy needed for their formation. Finally, the fraction of hydrocarbon ions formed in the gas phase via unimolecular dissociation of larger species is slightly larger with gallium than with fullerene projectiles.     

Regularities of energy transfer in aqueous solutions of Ln(III) ions upon formation of their bridged complexes via the CO 3 2− and OH− anions

The influence of the solvent pH and of the presence of carbonic acid anions on the energy transfer from the Eu(III) and Tb(III) ions to a large namber of Ln(III) ions, as well as on the concentration quenching of the Dy(III) ions, is studied. It is shown that, when the anions are present in solution at a concentration by 2–4 orders of magnitude lower than that of the lanthanide ions, the energy transfer rates increase by 2–4 orders of magnitude, but the luminescence decay remains exponential. It is established that the rate constant for energy transfer (k _t ) via the hydroxyl bridge increases with decreasing concentration of lanthanide ions in solution. In an alkalinized solution, (k _t ) depends weakly on the initial water pH, because the concentration of hydroxo groups is governed by hydrolysis of water under the action of the lanthanide ions introduced into it. It is found that, at the 10^?2 M concentration of lanthanide ions in solution, the values of (k _t ) change by almost two orders of magnitude depending on the choice of an ion pair; however, these changes in no way correlate with the overlap integrals of spectra, calculated by adopting the Forster mechanism, and the inclusion of an interaction of higher multipoles does not improve the agreement with the experimental data. It is shown that, when the energy is transferred via the OH^? bridge in solutions with a total concentration of Ln(III) ions of 10^?4 M, the value of (k _t ) increases up to 10⁷ M^?1 s^?1 and becomes independent of the choice of pairs of Ln(III) ions. The dependence of (k _t ) on the ratio of the dissociation constant for a binuclear complex and the probability of energy transfer between the ions within this complex are discussed. It is concluded that the change in this ratio explains the disappearance of the dependence of (k _t ) on the choice of ions as their concentration in solution decreases, but does not explain all the observed changes in (k _t ) if only the dipole-dipole mechanism of energy transfer between the ions in bridged complexes is considered.     

Cluster projectile ions used for the SIMS analysis of silicon

Comparative studies of the emission of Si _n ⁺ (n = 1–11) cluster ions and impurity-containing polyatomic ions under bombardment of B-doped single crystal silicon with A _m ^? (m = 1–5) cluster ions with an energy of E ₀ = 6–18 keV are carried out. The peculiarities of sputtering an adsorbed-particle layer with cluster ions are revealed. The possibility of determining the depth distribution of adsorbed particles by analyzing the yield of sputtered heteroatomic molecular ions upon bombardment is demonstrated.     

V4+ brownian motion in splat cooled amorphous V2O5 after water vapor adsorption

Splat cooling of molten V₂O₅ yields an amorphous oxide consisting of strongly entangled polymeric vanadium-oxygen chains. Upon hydration of this powder, a swelling process takes place and a Brownian motion of the fibres occurs. Vanadium pentoxide is usually non-stoichiometric and contains vanadium ions in a reduced oxidation state, namely V₄₊. These paramagnetic ions, which are part of the fibres constituents, can be used as spin probes to study the Brownian motion. X and Q band ESR spectra appear to be drastically modified when water is adsorbed on the powder at a given temperature. They have been analysed according to Kivelson's theory in the fast tumbling region between 293 and 373 K. An apparent activation energy of 3.8 kcal mole^-1 and a correlation time of about 10^?10 sec are observed. These results agree with the polymeric model proposed to explain the solubility of amorphous V₂O₅.     

Ionization and dissociative ionization of methane molecules

A technique for mass-spectrometric investigation of the yield of positive ions produced by direct and electron-impact dissociative ionization of methane molecules is described, and respective experimental data are presented. Doubly charged C ₂ ⁺ , CH ₃ ²⁺ , and CH ₄ ²⁺ ions, as well as singly charged D ₂ ⁺ , CD ₃ ⁺ , and CD ₄ ⁺ ions, are detected in the mass spectrum of a methane molecule at electron energy U _e = 90 eV for the first time. From ionization efficiency curves, the ionization energy of the parent molecule and the appearance energy of fragment ions are determined. The ionization energy of the CH₄ molecule is found to be 12.62 ± 0.20 eV. Electron-molecular reactions that may take place when a low-energy electron beam interacts with a methane molecule are analyzed. The ionization process and the formation of methane molecule fragments are studied.     

On the energy dependence of the yield of doubly charged negative ions during the capture of free electrons by C60(CF3)12 trifluoromethylfullerene molecules

Peaks of C₆₀(CF₃) _n ^2? doubly charged negative ions (n = 6–12) have been observed in the mass spectra of the resonance electron capture by trifluoromethylfullerene C₆₀(CF₃)₁₂ molecules. It has been established that these ions are formed owing to the attachment of two free isoenergetic electrons. The autodetachment of an extra electron has been detected for the doubly charged molecular ions (n = 12). It has been established from the observation of the delayed fragmentation of the most abundant ions with n = 8 and 10 that the doubly charged negative ions, like their singly charged analogs, are metastable with respect to the separation of the CF₃ fragment(s). The yield of doubly charged negative ions has been obtained as a function of the electron energy. By comparing them with the analogous dependences for the singly charged ions, the specific features have been revealed which were associated with the presence of the repulsive Coulomb barrier and the regular effect of the doubled energy of two additional electrons on the energy dependence of the dissociative decay of the doubly charged negative ions. The absolute cross section for the formation of the C₆₀(CF₃) ₁₀ ^2? ions has been measured. At the energy of their yield maximum near the 5 eV, it is ～1 × 10^?19 cm².     

The generation of fast particles in plasmas created by laser pulses with different wavelengths

By means of spatially resolved high-resolution X-ray spectroscopy, we have investigated the generation of fast ions at various laser installations with different flux densities and laser wavelengths. It is demonstrated that the fast ion generation in laser-produced plasma can be achieved for a very low level of the averaged laser intensity on the target. The time-of-flight mass spectrometry ion diagnostics and X-ray spectrographs give very close results for the energy distribution of the thermal ion component. For higher energies, however, we found significant differences: the spatially resolved high-resolution spectrographs expose the presence of suprathermal ions, while the time-of-flight method does not. Suprathermal ion energies E _ion plotted as a function of the qλ² parameter show a large scatter far above the experimental errors. The cause of these large scatters is attributed to a strong nonuniformity of the laser intensity distribution in the focal spot. The analysis by means of hydrodynamics and spectral simulations show that the X-ray emission spectrum is a complex convolution from different parts of the plasma with strongly different electron density and temperature. It is shown that the highly resolved Li-like satellite spectrum near Heαcontains significant distortions even for very low hot electron fractions. Non-Maxwellian spectroscopy allows determination of both the hot electron fraction and the bulk electron temperature.