Deuterium depth profiling in polymers using heavy ion elastic recoil detection

We have used ²⁰Ne and ⁴⁰Ar beams with energies between 3 and 8 MeV for elastic recoil detection (ERD) analysis of hydrogen isotopes in polymer samples and have also studied the depth resolution and the radiation damage. For the investigation of polymer mixtures it was possible to improve the depth resolution of ERD down to 8 nm FWHM with-out changing the experimental setup of conventional ERD, due to the higher energy loss factor of heavier ions and a reduced stopper foil thickness. For an improved surface depth resolution heavier ions are suitable, whereas lighter elements have a larger profiling depth. We found a ²⁰Ne beam with an energy between 4 and 6 MeV to have a maximum analysing depth of 380 nm with a near surface depth resolution of 9 nm; however, for high resolution ⁴⁰Ar-ERD measurements this maximum profiling depth is reduced to 90 nm. Due to the larger Rutherford scattering cross-section of heavier ions the measuring time decreases with increasing ion mass. We have investigated the ion beam radiation damage in polymer samples and introduced beam current density limits related to polystyrene samples. These results are supported by model calculations which give approximated values of the radiation damage.     

A magnetically insulated negative ion source for neutral beam heating

A new, magnetically insulated negative ion source has recently been discovered which can produce pulsed negative ion beams (H^?, Li^?, and C^?) with intensities of of 100–300 A/cm² at 1–4 MeV. This source may provide the basis for a high energy neutral beam system for heating large tokamaks.     

3D visualization of heavy ion beam energy deposition in two different target shapes

Heavy ion beams have favorable energy deposition behavior because they can penetrate and deposit their energy well inside the target. Ion beams have potential uses in fields including heavy ion beam fusion, high-energy density physics and material processing. Intense heavy ion beams can generate high-energy density matter in the laboratory under extreme density and pressure conditions. Additionally, in heavy ion fusion, a stringent requirement for successful fuel ignition and sufficient fusion energy release is that the ion energy deposition profiles are calculated precisely in the energy absorber layer. In this work, the OK2 code was used to simulate the heavy ion beam energy deposition in various target materials, and a computer program was written to provide 3D visualization of the results. The heavy ion beams used in this work were composed of lead, uranium, and cesium ions with energies of 8 GeV and carbon ions with energies of 5 MeV. The targets included two shapes: a monolayer sphere that can be used in direct-driven fusion and a cylindrical shape that is common in indirectly driven heavy ion fusion.     

Synthesis of carbon-nitride films using a fast-switched dual-source low energy ion beam deposition system

Thin C_xN_y films were deposited in UHV using alternating low energy ion beams of C⁺ and N⁺ or N₂⁺ in the energy range of 5 to 100 eV. The ion beam deposition system is equipped with two Freeman ion sources, mass analysis and fast automated beam switching, allowing perpendicular bombardment of the target with a single ion beam at a time. The composition and density of the films were studied by ARS (in situ), XPS and RBS. The dependence of the film properties and growth mechanisms on ion energy, beam switching rate, and C-to-N arrival ratio have been investigated. The influence of the deposition parameters on the film stoichiometry is discussed. Exposure of the film to atmosphere leads to oxygen incorporation, resulting in a lowered surface concentration of nitrogen. The XPS N 1s and C Is binding energies vary in a relatively broad range indicating that several bond states may be present. The influence of the substrate material on film growth has also been studied. On Si{100}, film growth commences with the formation of an interfacial silicon nitride. No film growth was observed on gold, however deposition was possible on tantalum and molybdenum.     

Taper angle dependence of the focusing effect of high energy heavy ion beams by glass capillaries

The 6.4 MeV ¹⁵N²⁺ ion beams are focused using glass capillary optics. The transmitted beam includes ions which have suffered slight energy loss. The areal density of the transmitted beam is enhanced by approximately 10 times, and the enhancement factor does not depend on the incident beam current. The NRA spectrum intensity decreases with the increase of the capillary taper angle. These results all together suggest that the nuclear forward scattering is more significant in the focusing mechanism than the low energy ions case.     

Cross-section for D(p,p)D elastic scattering from 1.8 to 3.2 MeV at the laboratory angles of 155° and 165°

The D(p,p)D cross-sections for elastic scattering of proton on deuterium over incident proton energy range from 1.8 to 3.2 MeV at both laboratory angles of 155° and 165° were measured. A thin solid state target Ni/TiD_x/Ta/Al used for cross-section measurement was fabricated by firstly depositing layers of Ta, Ti and Ni film on the Al foil substrate of about 7 μm in turn using magnetron sputtering and then deuterating under the deuterium atmosphere. The areal density of metal element in each layer of film was measured with RBS analysis by using a 4.0 MeV ⁴He ion beam, while the areal density of the deuterium absorbed in the Ti film was measured with ERD analysis by using a 6.0 MeV ¹⁶O ion beam. The results show that the cross-sections of p-D scattering under this experimental circumstance were much enhanced over the Rutherford cross-section value. It was found that the enhancement increases linearly as the energy of the incident beam increases. The total uncertainty in the measurements was less than 7.5%.     

Production of highly-charged recoil-ion beams at very low energy

An apparatus for production of an intense, charge-state separated, recoil-ion beam of very low energy and good collimation has been constructed. In a test experiment, in which 30 MeV C1⁵⁺ projectiles were used to produce recoil ions, the feasibility of the method was demonstrated. The mass to charge ratio of the beam is selected by means of a Wien-filter, and the beam energy can be varied between 2qeV and 1q keV with a constant charge-state resolution. Presently, the angular definition of the beam is 2.5°, but it can be impoved by at least a factor of 2. Very low energy Ar-ion beams, of intensities usable for secondary slow collision experiments, can be created for charge states ranging from one to nine. For example, beams of Ar⁴⁺ and Ar⁶⁺ of intensities 2.5 × 10⁴ and 5 × 10³ s⁻¹, respectively, can be furnished at energies of 10 q eV, while the corresponding numbers for 2 q eV beams ar approximately five times lower.     

Studies on the high electronic energy deposition in polyaniline thin films

We report here the physico-chemical changes brought about by high electronic energy deposition of gold ions in HCl doped polyaniline (PANI) thin films. PANI thin films were synthesized by in situ polymerization technique. The as-synthesized PANI thin films of thickness 160 nm were irradiated using Au⁷⁺ ion of 100 MeV energy at different fluences, namely, 5 × 10¹¹ ions/cm² and 5 × 10¹² ions/cm², respectively. A significant change was seen after irradiation in electrical and photo conductivity, which may be related to increased carrier concentration, and structural modifications in the polymer film. In addition, the high electronic energy deposition showed other effects like cross-linking of polymer chains, bond breaking and creation of defect sites. AFM observations revealed mountainous type features in all (before and after irradiation) PANI samples. The average size (diameter) and density of such mountainous clusters were found to be related with the ion fluence. The AFM profiles also showed change in the surface roughness of the films with respect to irradiation, which is one of the peculiarity of the high electronic energy deposition technique.     

Properties of Ion Beams Generated by Nitrogen Plasma Focus

Numerical experiments have been systematically carried out using the modified Lee model code on various plasma focus devices operated with nitrogen gas. The ion beam properties (ion beam energy, ion beam flux, ion beam fluence, beam ion number, ion beam current, power flow density, and damage factor) of the plasma focus have been studied versus gas pressure for each plasma focus device. The results show that, for these studied plasma focus devices, the mean ion energies decrease with increasing gas pressure, while the beam ion number increases with higher pressure. The fluence, flux, ion current, power flow density and damage factor have maximum values at the optimum pressure. It is shown that, the maximum power flow densities range from 10¹² to 10¹⁴ W m^?2 and the damage factor values reach almost 10⁹–10¹¹ W m^?2 s^0.5. The obtained results provide much needed benchmark reference values and scaling trends for ion beams of a plasma focus operated in nitrogen gas. These results could be used as an indicator for ion properties emitted from nitrogen plasma focus for various applications including material processing.     

An outlook of heavy ion driven plasma research at IMP-Lanzhou

Since the successful completion of the cooling storage ring (CSR) project in China at the end of 2007, high qualitative heavy ion beams with energy ranging from keV to GeV/u have been available at the Heavy Ion Research Facility at Lanzhou (HIRFL). More than 10⁹ 1 GeV/u C⁶⁺ particles or 10⁸ 235 MeV/u Xe particles can be stored in the CSR main-ring and extracted within hundred nano-seconds during the test running, the beam parameters will be improved in the coming years so that high energy density (HED) conditions could be achieved and investigated there. Recent scientific results from the experiments relevant to plasma research on HIRFL are summarized. Dense plasma research with intense heavy ion beams of CSR is proposed here.     

Development of a time-of-flight spectrometer at the Ruder Boškovi? Institute in Zagreb

A new TOF telescope has been constructed for thin film and surface analysis. The timing system consists of two electrostatic mirror type detectors of Busch design. The detection efficiency of timing stations for very light ions was significantly improved using DLC (diamond like carbon) foils coated with LiF instead of the conventionally used carbon foils. Ion energy is measured by a 300 mm² ULTRA ion-implanted silicon detector. For the ERDA measurements with heavy and energetic ion beams, a time-of-flight (TOF) spectrometer is positioned at 37.5°. Spectrometer can be easily moved to 120° backward angle for time-of-flight RBS analysis with low energy beam of light ions. Positioning and fine adjustments of sample orientation are performed with a motorized sample stage. The same spectrometer can be also installed at the ion microprobe scattering chamber for 3D elemental imaging.     

Measurement of beam power and profile for DNB on HT-7 tokamak

In normal experimental operation, a diagnostic neutral beam (DNB) can produce 6 A of extracted beam current in hydrogen at an energy of 49 keV with a pulse length of 100 ms. Hydrogen and deuterium beams can be produced as well. The diagnostic neutral beam has been added to the diagnostic set so that charge-exchange recombination spectroscopy (CXRS) can be used to acquire ion temperature and rotation. The beam power and beam profile distribution of the DNB injection can be obtained with a thermocouple probe measurement system on the HT-7 superconducting tokamak. The thermocouple probe measurement system with 13 thermocouples crossly distributed on the probe plate was used to measure the temperature rise of each coppery target, so the profile distribution of the ion/neutral beam was obtained by calculation. In this paper, the structure of the probe plate on the DNB for HT-7 tokamak and some measurement results are presented.     

脉冲离子束轰击靶的热效应数值模拟

分析了脉冲离子轰击靶膜和衬底的热效应,在能量较低的情形下,离子轰击处理为靶膜表面热流输入。采用有限元程序,对能量为600keV、束流为12mA的不同束斑半径的脉冲离子流轰击Cu基Ti靶的热传导进行了数值计算,得到了热传导清晰物理图象。     

Effect of MeV beams on the interface structure of metal(adlayer)-silicon (crystal substrate) systems

The influence of MeV ion beams on the measured intensity of the surface peak (SP) in channeling studies has been examined for Ag and/or Au covered Si(111), and Pd covered Si(111) systems with film thicknesses up to several monolayers. A simple phenomenological model is introduced to analyse the observed increase in atomic displacements induced by probing He ions of 1 MeV. For the Ag and Pd cases, effects attributable to the deposited metal was small while for Au an appreciable enhancement of the beam sensitivity was observed which increases with increasing Au thickness for beam doses of ? 3.1 × 10¹⁶ ions/cm². The observe differences cannot be explained by the difference in mass and atomic number of the overlayer atoms. The model suggests that the chemical nature of atomic bonds near the interface affects the damage threshold energy.     

Deposition of polycrystalline Si thin films on glass substrates by direct negative Si ion beam deposition

Polycrystalline Si (Poly-Si) thin films were deposited on a glass substrate by direct negative Si (Si⁻) ion beam deposition. The glass substrate temperature was kept constant at 500 °C for all depositions. Prior to deposition, the ion energy spread and ion-to-atom arrival ratio were evaluated as a function of the ion beam energy.The Si⁻ ion energy spread was less than 10% regardless of the ion energy, while the ion-to-atom arrival ratio increased proportionally from 1.3 to 1.6 according to the ion beam energy.Atomic force microscopy images showed that a relatively rough surface was obtained at 50 eV of Si⁻ ion energy and it is also concluded that the Si⁻ ion beam irradiation at 50 eV is effective to deposit Si thin film with small grains as shown in Fig. 3.     

Radiation-induced grafting of dimethylaminoethylmethacrylate onto PE/PP nonwoven fabric

A new adsorbent was prepared by radiation-induced graft polymerization of dimethylaminoethylmethacrylate (DMAEMA) onto polyethylene/polypropylene (PE/PP) nonwoven fabric. The trunk polymer was irradiated by electron beam at a voltage of 2 MeV and a current of 3 mA in nitrogen atmosphere at dry-ice temperature to different doses. The degree of grafting was determined as a function of irradiation dose, monomer concentration, temperature and reaction time. Grafting conditions were optimized and about 150% grafted samples were used for further experiments. DMAEMA grafted polymer was later protonated in acid solution to prepare specialty adsorbent for the removal of phosphate. Adsorption experiments were performed in column mode for removal of phosphate. It was shown that 2000 bed volumes of phosphate-free water can be produced from 100 ppb phosphate (as P) solution at high space velocity.     

New Method of Large-Area DC Ion Beam Formation with Multiple Electron Beams, (II)

A new method to form a small divergence dc ion beam using a large-area single-hole electrode instead of a multiaperture electrode is described. A distinctive feature of this method is to make use of multiple electron beams in an ion source to control the spatial ion density distribution at the region of ion beam formation; the electron beams play a role to aid formation of the concave plasma boundary, which is required to extract a convergent ion beam from gaseous plasma according to the experimental facts described in Part (I). In this experiment, it was verified with three slab-like electron beams that formation of the concave boundary was possible in a stable and steady state. This electrode system can be applied to some types of the present high current ion sources to obtain large-area dc ion beams.     

Infrared analysis of ion beam irradiated polymers

Irradiation with heavy ions can produce several modifications in the chain structure of polymers. These modifications can be related to scissioning and cross-linking of chemical bonds, which depend on the ion fluence and the density of energy deposited in the material. Stacked thin film Makrofol-KG^® samples were irradiated with 350 MeV Au²⁶⁺ ions and FTIR absorption spectroscopy was used to determine the bond changes in the samples. Data on the absorption bands as a function of the fluence indicated a higher probability for simple-bonds scissioning than for double-bonds scissioning and no dependence on the number of double bonds breaking with ion fluence. Since sample irradiation was done in a non-track-overlapping regime, a novel process for double bonds formation is suggested: the excitation of a site in the material by only one incident ion followed by a double bond formation during the de-excitation process.     

Effect of different ion beam energy on properties of amorphous carbon film fabricated by ion beam sputtering deposition (IBSD)

Amorphous carbon (a-C) films were fabricated by ion beam sputtering technique. The influence of sputtering ion beam energy on bonding structure, morphologic, mechanical properties, tribological properties and corrosion resistance of a-C films are investigated systematically. Morphology study shows that lowest surface roughness exists for mid-ion beam energy. Improved adhesion is observed for the films that are prepared under high ion beam energy, attributed to film graphitization, low residual stress and mixed interface. Relatively, a-C films prepared with ion beam energy of 2 keV exhibits optimum sp³ bond content, mechanical properties and corrosion resistance. It is found that the wear rate of DLC films decrease with increased ion beam energy in general, consistent with the varied trend of the H/E value which has been regarded as a suitable parameter for predicting wear resistance of the coatings. The correlation of the sp³ bond fraction in the films estimated from Raman spectroscopy with residual stress, nanohardness and corrosion resistance has been established.