Violation of the additivity rule for the ion energy loss in hydrocarbons

Based on the experimental data, the rule of additivity of energy losses in hydrocarbon compounds is shown to be violated at low ion energies. This indicates the necessity of taking into account the chemical bonds in molecular targets. Deviation from the additivity rule increases with increasing nuclear charge of incident ions and decreases with increasing ion energy. The additivity rule is most strongly violated in the molecular targets with double and triple carbon-carbon bonds.     

Energies of carbon plasma beams in the deposition of diamond-like coatings with the pulsed-arc-discharge method

The carbon plasma ion energies produced by the pulsed filtered arc-discharge method have been measured as a function of the anode-cathode voltage. The energies were determined by using the electro-optical time-of-flight method. The highest anode-cathode voltage was 5 kV and yielded the energy of 140 eV for the plasma ions. In addition, it was demonstrated that a rather slight change of the parameters in the arc-discharge method has a strong effect on the plasma ion energies and the properties of the diamond-like coatings prepared.     

Energy spectra of 6–32 keV neutral and ionized Ar and He scattered from Au targets; ionized fractions as functions of energy

The neutralization of ions is an important aspect of low energy ion scattering for surface analysis. Electrostatic energy analyzers (ESA) have been used almost exclusively in such work, and information on charge neutralization efficiencies is needed for quantitative interpretation of ESA data. In the past, the occurrence in low energy ion spectra of surface peaks and low backgrounds due to scattering from inside the solid has been attributed to preferential neutralization of ions which penetrate beyond the surface. In the work to be described, a time-of-flight technique was used to measure energy spectra of both neutral and ionized Ar and He scattered at 90° from a polycrystalline gold target. Incident energies of 6–32 keV were used. The energy spectra of neutral Ar scattered from polycrystalline gold exhibit sharp surface peaks, and double scattering shoulders, over this entire energy range. For He there is a gradual downward slope toward lower energy rather than a sharp surface peak. The behavior in both cases is attributed to large scattering cross-sections which cause a loss of beam particles during penetration. A calculation using a $\text{1}\text{r}{}^2$ potential illustrates this effect as a function of energy for helium. In the present experiments we find that the ion fraction of scattered argon does indeed depend on depth of penetration. This is in contrast to the behavior of He and H at higher energies, e.g. 100 keV, in which cases the charge state depends on emergent velocity but not on depth of penetration. The characteristic shapes of ion scattering spectra in this energy range appear to result from both neutralization and beam attenuation inside the target.     

乙胺分子的多光子电离过程质谱研究

报道了乙胺分子在４４０～４７５ｎｍ波长范围内多光子电离（ＭＰＩ）质谱（ＭＳ）研究结果。碎片离子主要由母体离子碎裂模式产生。母体离子ＣＨ３ＣＨ２Ｎ＋·Ｈ２由经３ｓ里德堡态的（２＋２）共振多光子电离产生后，大部分发生β键断裂，形成ＣＨ２＝Ｎ＋Ｈ２离子，还有一部分再吸收一个光子，通过Ｃ－Ｈ（ＣＨ２）键的断裂产生了ＣＨ３ＣＨ＝Ｎ＋Ｈ２离子。ＣＨ３ＣＨ＝Ｎ＋Ｈ２和ＣＨ２＝Ｎ＋Ｈ２离子最容易发生的碎裂过程是脱去氢分子，分别产生Ｃ２Ｈ４Ｎ＋（分子式）离子和ＣＨ≡Ｎ＋Ｈ离子。     

北京大学1.7MV串列静电加速器的离子注入/辐照实验系统

北京大学1.7 MV串列静电加速器运行至今已有三十多年.该加速器配备有高频电荷交换负离子源和铯溅射负离子源,能够引出从H到Au之间的大部分元素的离子.离子能量可被加速至几百keV到若干MeV,主要开展离子注入/辐照实验和卢瑟福背散射(RBS)和沟道分析等离子束分析工作.基于辐照实验需求,建立了高温辐照系统,温度最高可达...     

Enhancement of electron–ion recombination rates at low energy range in the heavy ion storage ring CSRm

Recombination of Ar¹⁴⁺, Ar¹⁵⁺, Ca¹⁶⁺, and Ni¹⁹⁺ ions with electrons has been investigated at low energy range based on the merged-beam method at the main cooler storage ring CSRm in the Institute of Modern Physics, Lanzhou,China. For each ion, the absolute recombination rate coefficients have been measured with electron–ion collision energies from 0 meV to 1000 meV which include the radiative recombination(RR) and also dielectronic recombination(DR)processes. In order to interpret the measured results, RR cross sections were obtained from a modified version of the semiclassical Bethe and Salpeter formula for hydrogenic ions. DR cross sections were calculated by a relativistic configuration interaction method using the flexible atomic code(FAC) and AUTOSTRUCTURE code in this energy range. The calculated RR + DR rate coefficients show a good agreement with the measured value at the collision energy above 100 meV.However, large discrepancies have been found at low energy range especially below 10 meV, and the experimental results show a strong enhancement relative to the theoretical RR rate coefficients. For the electron–ion collision energy below 1 meV, it was found that the experimentally observed recombination rates are higher than the theoretically predicted and fitted rates by a factor of 1.5 to 3.9. The strong dependence of RR rate coefficient enhancement on the charge state of the ions has been found with the scaling rule of q^3.0, reproducing the low-energy recombination enhancement effects found in other previous experiments.     

Internal energy content of n-butylbenzene, bromobenzene, iodobenzene and aniline molecular ions generated by two-photon ionization at 266 nm. A photodissociation study

A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd.     

Electron loss of heavy many-electron ions in relativistic collisions with neutral atoms

Electron-loss processes arising in collisions of heavy many-electron ions (like U²⁸⁺) with neutral atoms (H, N, Ar) are considered over a wide energy range including relativistic energies. Various computer codes (LOSS, LOSS-R, HERION, and RICODE), created for calculation of the electron-loss cross sections, and their capability are described. Recommended data on the electron-loss cross sections of U²⁸⁺ ions colliding with H, N, Ar targets and predicted lifetimes of U²⁸⁺ ion beams in accelerator are given. Calculated electronloss cross sections are compared with available experimental data and other calculations.     

Molecular dynamic simulation of secondary ion emission from an Al sample bombarded with MeV heavy ions

Spluttering yields and kinetic energy distributions (KED) of Al atomic ions ejected from a pure aluminium sample under MeV silicon ion bombardment were simulated with the molecular dynamic method.Since the electronic energy loss Se is much higher than the nuclear energy loss Sn when the incident ion energy is as high as several MeV,the Se effect was also taken into consideration in the simulation.It was found that the simulated sputtering yield fits well with the experimental data and the electronic energy loss has a slight effect at incident ion energies higher than 4MeV.The simulated secondary ion KED spectrum is a little lower in the peak energy and narrower in the peak width than that in the experiment.     

Inelastic effect in low energy ion-surface collisions: He+Au,Ag

Energy distributions of He⁺ ions scattered by Au and Ag surfaces are measured by an ISS system with high energy resolution, at a scattering angle of 90° and at incident ion energies ranging from 277 to 977 eV. It is found that the observed peak energies deviate toward the low energy side by several electron-volts with respect to the calculated elastic single collision energies. Both the deviation Q' and the inelastic loss energy Q are plotted as a function of incident ion energy for the Au surface.     

Energy distribution of ions produced by excimer-laser ablation of solid and molten targets

2 . The measurements reveal components with different charge-to-mass ratio and distinct components with the same charge/mass ratio. The most probable kinetic energy has values of several tens of eV for singly charged ions, and is larger by a factor exceeding 2 for doubly charged ions. The role of target material and state, solid or liquid, laser photon energy and fluence has been investigated and is discussed in comparison to the findings of previous investigations. An estimate of the electrostatic plasma potential in PLA, based on electron loss rate arguments, is presented to account for the high ion energies observed. Received: 9 March 1998 / Accepted: 27 November 1998 / Published online: 24 February 1999     

Apparent velocity threshold in the electronic stopping of slow hydrogen ions in LiF

The electronic energy loss of hydrogen ions (protons and deuterons) in thin supported films of LiF has been studied in backscattering geometry for specific energies from 700 eV/u to 700 keV/u, using Rutherford backscattering spectroscopy and time-of-flight low-energy ion scattering spectroscopy. For specific energies below 8 keV/u, our data confirm velocity proportionality for the stopping cross section epsilon (like in a metal) down to 3.8 keV/u, as observed previously for protons and antiprotons despite the large band gap (14 eV) of LiF. Below 3.8 keV/u, the present results indicate an apparent velocity threshold at about 0.1 a.u. for the onset of electronic stopping.     

The Effect of Symmetrical Energy and Shell Correction on the Cluster Formation in QMD

Based on the QMD model, in addition to the Skyrrne-type, Yukawa and Coulomb interactions,a cluster's N, Z dependent macroscopic potential, which consists of the symmetrical energy of liquid drop model and shell, pairing correction energies, has been taken into account.It improved the structure of the clusters formed in heavy ion reactions at intermediate energy.     

Ion storage at eV energies in an octopole ring

To store ions for times up to several seconds with energies in the 10 eV/amu range a tabletop storage ring with a circumference of about 1 m will be constructed. The ions will be confined and guided by RF-multipoles. The first objective is the production of pure ground state beams of (multiply charged) ions. This will allow for elucidating the unknown rule of metastable ions in electron capture studies, which will be performed in a crossed beam experiment after extraction of the ion beam from the storage ring. In order to test the technique of ion storage by means of RF-multipoles a linear RF-octopole beam guide has been constructed. First results of highly charged ion injection and subsequent electron capture studies in the RF-octopole beam guide are presented for C⁴⁺ ions.     

Neutralization of helium ions backscattered from tungsten

Measurements and computer simulations of the energy spectra of helium ions backscattered from clean, polycrystalline tungsten at 138° have been combined to obtain estimates of the probability of survival against neutralization. For incident ion energies of 300, 1180 and 2600 eV, the estimated survival probabilities for ions backscattered near the surface are 0.05%, 0.2% and 1%, respectively. The estimated survival probability for subsurface backscattered ions has been found to range from a value of 1% at 2600 eV, comparable to that of near-surface backscattered ions, down to near zero at 300 eV incident ion energy. Evidence is presented that the final charge state of ions which backscatter from beneath the surface is not controlled by their emergence speed but by their previous history in the solid.     

On the energy spectra of secondary ions emitted from silicon and graphite single crystals

Secondary ion emission from silicon and graphite single crystals bombarded by argon ions with energies E ₀ varied from 1 to 10 keV at various angles of incidence α has been studied. The evolution of the energy spectra of C⁺ and Si⁺ secondary ions has been traced in which the positions of maxima (E _max) shift toward higher secondary-ion energies E ₁ with increasing polar emission angle θ (measured from the normal to the sample surface). The opposite trend has been observed for ions emitted from single crystals heated to several hundred degrees Centigrade; the E _max values initially remain unchanged and then shift toward lower energies E ₁ with increasing angle θ. It is established that the magnitude and position of a peak in the energy spectrum of secondary C⁺ ions is virtually independent of E ₀, angle α, and the surface relief of the sample (in the E ₀ and α intervals studied). Unusual oscillating energy distributions are discussed, which have been observed for secondary ions emitted from silicon (111) and layered graphite (0001) faces. Numerical simulations of secondary ion sputtering and charge exchange have been performed. A comparison of the measured and calculated data for graphite crystals has shown that C⁺ ions are formed as a result of charge exchange between secondary ions and bombarding Ar⁺ ions, which takes place both outside and inside the target. This substantially differs from the ion sputtering process in metals and must be taken into account when analyzing secondary ion emission mechanisms and in practical applications of secondary-ion mass spectrometry.     

A simple post-accelerator foil stripper assembly for atomic collision experiments

A multiple foil holder for use in ultra high vacuum (UHV) environment as a post accelerator ion stripper has been designed and fabricated. It is used to produce beams of an ion in different charge states at a given energy from a 14 MV pelletron accelerator. These ions are required in several types of atomic collision experiments. The assembly is tested with³²S ions at various energies.     

In-depth modifications of implanted amorphous carbon films

Amorphous carbon films (a-C:H) and nitrogen incorporated carbon films [a-C:H(N)] deposited by a self-bias glow discharge have been implanted with 70 keV nitrogen ions at fluences of 0.6, 1 and 2×10¹⁷ N/cm². The in-depth modifications caused by ion implantation were determined by means of nuclear techniques, such as Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection Analysis (ERDA), as well as by Auger Electron Spectroscopy (AES) and Raman scattering. ERDA profiles show that nitrogen implantation causes hydrogen depletion, the amount of which depends on the film composition and on the ion fluence. In a-C:H(N) films nitrogen loss was also measured. The induced structural modifications in both a-C:H and a-C:H(N) films were followed by both AES, using factor analysis, and microprobe Raman spectroscopy. They turn out to be related to the energy deposited by the incident ions. Our results indicate that the ion-beam bombardment causes in both a-C:H and a-C:H(N) films an increase of either the degree of disorder or the ratio between sp²/sp³ bonds across the hydrogen-depleted layer, which depends on the ion fluence.     

Progress and upgrading of the Heidelberg high current injector

A specialized rf-accelerator system HSI consisting of two RFQ’s and 8 rf seven-gap cavities was built for injection of high intensities of singly charged heavy ions into the Heidelberg heavy ion storage ring TSR. With different ion sources, this system now is used to deliver positive or negative, atomic and molecular ion beams with energies between 150 keV/a.m.u. and 5.3 MeV/a.m.u. final energy. For a future replacement of the MP-tandem-postaccelerator-system the new HSI-accelerator is to be equipped with an ECR source for high intensities of highly charged ions. An advanced commercial ECR source with a 18 GHz rf klystron and an adjustable extraction system for adaption of a wide range of injection energies has been commissioned at the manufacturer and is delivered. Test bench operation presently is in preparation at Heidelberg. A stripper section with an achromatic charge state selector is under construction between injector and postaccelerator. Other ion sources, e.g., for ultra cold H ₃ ⁺ molecular ion beams are under development.     

Applicability of the polyimide films as an SSNTD material

Track registration properties in polyimide films, KAPTON, for heavy ions have been examined by means of FT-IR spectrometry and the chemical etching in sodium hypochlorite solution. The effective track core size for the loss of CO and C–N–C composing imide bonds, and diphenyl ethers of C–O–C have been evaluated under the irradiations by Ne, Fe and Xe ions at energies less than 6 MeV/n. On the other hand, the etching property of the polyimide films has been examined in the sodium hypochlorite solution at temperature of 55 °C. Before the etchings, the films were exposed to H, C, Ne, Fe and Xe ions, at incident energies below 6 MeV/n. The etch pits are found only on the films exposed to Fe and Xe ions, indicating significant difference on the etch pit size between them. This implies that the polyimide film has charge or energy resolution for these relatively heavy ions. The threshold level of the etchable track registration is inferred to be around 2500 keV/μm. The effective track core radius at this stopping power for the loss of diphenyl ether is 1.6 nm, which is equivalent to the length between the adjacent diphenyl ether bonds in the polyimide chains. Breakings at two adjacent diphenyl ethers in radial direction of latent tracks may produce etchable tracks in KAPTON.