Ion beam analysis and microscopic characterization of natural topaz stones

Rutherford backscattering spectroscopy (RBS) and elastic recoil detection (ERD) techniques were used to determine the presence of metallic as well as nonmetallic (also hydrogen) components in two kinds of natural topaz stones originating from Sri Lanka and Nigeria. A computer simulation program was applied in order to compare the theoretical and experimental results of the RBS analysis. The changes in surface morphology induced by irradiation with high energy analysing ion beams were monitored using optical microscopy. RBS analysis proved the presence of trace amount of metallic admixtures in the stones — potassium, zinc, nickel or cobalt, lead (and/or bismuth) were detected mainly in the surface region of the samples. ERD analysis allowed to determine the total content and depth distribution of hydrogen; the depth distribution of hydrogen was proved to be almost uniform. Microscopic investigation indicated the existance of damage and precipitates on the polished surfaces, whereas radiation damage, probably connected with helium-blistering, was observed after the ERD analysis.     

贮氢金属中氢同位素的离子束分析方法评估

文章介绍用离子束方法分析贮氢金属中氢同位素含量与分布的实验条件与设计，并分析各自的优、缺点。通过实验测量与分析表明，用离子束分析方法可获得氢同位素含量与分布的丰富信息和精确数值。用6.0MeV的O离子束进行ERD分析的优点是截面为卢瑟福截面，所用的Mylar膜薄，能使H、D、T明显分开，测量精确，缺点则是对样品制备要求高，分析深度小；用7.4MeV的⁴He离子束进行ERD分析能得到H、D、T的分布信息，对Ti的分析深度可达到3.0μm，缺点则是三者的谱图相互重叠，模拟解谱的误差较大；用3.0MeV的质子进行PBS分析，只能获得D、T的分布信息，但分析深度更深。      

High resolution elastic recoil detection analysis of polystyrene depth profiles using carbon ions

The resolution of conventional elastic recoil detection (ERD) is enhanced by using ions which are efficiently stopped by matter. We describe an ERD experiment using a 2.4 MeV carbon ion beam which has a surface resolution of 80 Å FWHM in polystyrene. The maximum analysable depth for this geometry is 1000 Å. We show that by cumulating spectra with a low enough dose on different points of the same sample it is possible to avoid a substantial beam-induced modification of the true depth profile. The technique is demonstrated with experiments showing the decrease in the surface segregation of deuterated polystyrene (dPS) as a function of its molecular weight (Mw) in films of blends of deuterated and protonated polystyrene.     

An ERD/RBS/PIXE apparatus for surface analysis and channeling

A system for surface analysis, lattice localisation of impurities, defect studies in crystalline solids and routine ERD (elastic recoil detection) is described. The apparatus features a high vacuum chamber, a computer controlled precision goniometer and an energy plus time-of-flight mass discrimination system. First results of channeling/ERD experiments using 15–30 MeV ³⁵Cl beams on silicon crystals implanted with B⁺ and BF₂⁺ are presented, as well as data on the effect of beam induced damage on the boron distribution.     

钛膜中氘氚浓度的弹性反冲法测量

研究采用弹性反冲探测(ERD)方法测量钛膜中氘、氚的浓度。实验所用Ti膜用磁控溅射法制备，膜厚小于100nm，以石英玻璃（SiO₂）为底衬，Ti膜加镀了1层Ni保护膜，以防Ti膜氧化和增强Ti膜吸氢。以6.0MeVO粒子作为入射粒子，在30°方向上探测反冲粒子，在此实验条件下，O粒子对D、T的碰撞截面为卢瑟福截面。对两个样品用ERD方法测量钛膜中的D、T含量，获得了D、T的面密度。测量结果表明，采用如上方法测量Ti膜中D、T浓度的误差小于7％。     

3D hydrogen profiling by elastic recoil detection analysis in transmission geometry

An analytical procedure and a simulation-optimization algorithm are described for hydrogen determination based on elastic recoil detection induced by low-energy ⁴He ions ( 3 MeV) using transmission geometry. Hydrogen concentration depth profiles can be derived from the experimental recoil spectra for a depth range of up to 6 μm with a resolution better than 40 nm at the surface. The method is applied to thin polyimide films irradiated by high-energy heavy ions. The 3D hydrogen distribution is determined with a ⁴He⁺ mubeam. A high-hydrogen-concentration zone below the surface is shown. The hydrogen distribution is seen to evolve during the ⁴He⁺ irradiation.     

Isothermal Re-Emission of Hydrogen Implanted into Isotropic Graphite

Isothermal re-emission of hydrogen from graphite implanted with 5 keV H₂ ⁺ ion beam up to saturation (3×10¹⁸/cm²) at room temperature has been studied by means of the elastic recoil detection (ERD) technique at temperatures of 450, 500, 550 and 600°C. It is found that the concentration of retained hydrogen decreases rapidly in the beginning and then decreases very gradually as the annealing time increases.

The re-emission profiles have been analyzed taking into account local molecular recombination between activated hydrogen atoms and that between an activated hydrogen atom and a trapped one together with retrapping of the activated hydrogen atom. It is shown that the re-emission of hydrogen by isothermal annealing occurs mainly due to the former type of local molecular recombination and that the activation energy of the thermally activated detrapping rate constant is 0.50±0.04eV. Moreover, it is shown that an analytical expression for the re-emission profile reproduces reasonably well the observed thermal desorption spectra.     

Analysis of diffusion and dissolution of two-component hydrogen (H + D) in lead lithium

A lead–lithium eutectic alloy (Pb–Li) is one of the most promising candidate materials for the liquid blanket of an advanced fusion reactor. We have experimentally determined mass-transfer properties by an unsteady permeation method, which data are necessary to design a system to recover tritium (T) from a Pb–Li blanket. An experiment of simultaneous H and D permeation through Li₁₇Pb₈₃ is performed to clarify interactions between atoms in the two-component permeation process. The experimental results are analyzed by a model of one-dimensional or two-dimensional permeation through Li₁₇Pb₈₃. The major permeation proceeds in the longitudinal direction of the present system, and the ratio of hydrogen leak in the radial direction is evaluated using the simulation. As a result, it was found that H and D atoms permeate independently regardless of the H/D component ratio within the present experimental conditions. The permeability and diffusivity of H are 1.4 times higher than that of D. The solubility of H is close to that of D. The isotope effect in diffusivity is in proportion to the square root of the mass ratio of D to H. When these data can be extended to the case of T, T permeability and diffusivity is predicted as 1/1.7 times lower than that of H in the temperature range from 773 K to 973 K.     

Characterisation of ferromagnetic magnetic storage media surfaces by complementary particle induced X-ray analysis and time of flight-energy dispersive elastic recoil detection analysis

Thin (10 nm–1 μm) films of ferromagnetic material constitute an important class of materials that are difficult to analyse by conventional ion beam analytical (IBA) techniques because they are based on the ferromagnetic elements (Co, Fe, Mn, Ni, and Cr). The similar or overlapping isotope masses makes it difficult to separate the elemental signals using time of flight and energy dispersive elastic recoil detection (ToF-E ERD). In this exploratory study we have investigated the use of Particle Induced X-ray Emission (PIXE) measurements to refine the mass dispersive depth profile information from ToF-E ERD. The surfaces of two commercial magnetic media were investigated. One sample was a double density diskette with a coating of ferrite particles in an organic binder. The other sample was a complex C/Co/Cr/Ni–P/Al multilayer structure taken from a standard hard disc. The Lund nuclear microprobe with a 2.55 MeV proton beam was used for PIXE analysis. ToF-ERD measurements were carried out using a 55 MeV ¹²⁷I¹⁰⁺ ion beam incident at 67.5° to the surface normal. The time of flight and kinetic energy of recoils ejected at 45° to the ion beam direction was measured in a detector telescope. The findings demonstrate that by detailed analysis of the PIXE spectra it is possible to remove the ambiguities in mass assignment of the ToF-ERD data associated with the ferromagnetic elements.     

Measurement of carbon distribution in nuclear fuel pin cladding specimens by means of a secondary ion mass spectrometer

Cladding carburization during irradiation of advanced mixed uranium plutonium carbide fast breeder reactor fuel is possibly a life limiting fuel pin factor. The quantitative assessment of such clad carbon embrittlement is difficult to perform by electron microprobe analysis because of sample surface contamination, and due to the very low energy of the carbon K_α X-ray transition.The work presented here describes a method developed at the Swiss Federal Institute for Reactor Research (EIR) to use shielded secondary ion mass spectrometry (SIMS) as an accurate tool to determine radial distribution profiles of carbon in radioactive stainless steel fuel pin cladding. Compared with nuclear microprobe analysis (NMA) [1], which is also an accurate method for carbon analysis, the SIMS method distinguishes itself by its versatility for simultaneous determination of additional impurities.     

Effects of internal bremsstrahlung of tritium β-decay and surface roughness in the BIXS method

We have studied the effects of the internal bremsstrahlung of tritium β-decay, sample surface roughness and tritium content as well on the tritium β-decay induced X-ray spectroscopy (BIXS) for tritium measurements based on Monte Carlo simulations. The Knipp-Uhlenbeck-Bloch theoretical model was adopted for the internal bremsstrahlung. It is found that the contributions of internal bremsstrahlung of tritium β-decays are approximately 30%, 10%, 4% and 2% of the corresponding external bremsstrahlung for C, Ti, Mo and W materials, respectively, and the sample surface roughness may cause an error of several percent in the BIXS method if the surface roughness of a sample is in a reasonable range. Moreover, the effect of tritium content should be taken into account when a sample contains a large amount of tritium, otherwise, the tritium contents measured by the BIXS method will be underestimated, for example, by up to ∼15% for Ti metal.     

Precise nitrogen depth profiling by high-resolution RBS in combination with angle-resolved XPS

Nitrogen depth profiling in a high-k gate stack structure, SiON/HfO₂/SiON/Si(0 0 1) was performed by high-resolution Rutherford backscattering spectroscopy (HRBS) in combination with angle-resolved X-ray photoelectron spectroscopy (AR-XPS). The nitrogen depth profile is determined so that both the HRBS spectrum and the angular dependence of the XPS yield are reproduced. The obtained nitrogen profile is compared with the result of high-resolution elastic recoil detection (ERD) which is the most reliable technique for depth profiling of light elements. The agreement between the result of the present combination analysis and that of high-resolution ERD is fairly good, showing that the present combination analysis is a promising method for the analysis of light elements.     

Energy Dependence of MeV He+ Ion-Induced Re-Emission of Hydrogen Isotopes Implanted into Graphite

The energy dependence of MeV He⁺ ion-induced re-emission of hydrogen isotopes (H and D) implanted into graphite has been measured by means of the elastic recoil detection (ERD) technique in order to clarify the collision process for the ion-induced detrapping. The experimental re-emission profiles have been analyzed by solving the mass balance equations, in which the ion-induced detrapping cross section σ _d and the rate constants of the retrapping Σ ^T and local molecular recombination K between an activated hydrogen atom and a trapped one are taken into account. The values of σ _d and K/Σ _T have been determined from the best-fit analytical solution to the experimental re-emission profiles. It has been found that the average values of σ _d and K/Σ _T for H are twice as large as those for D, which is the so-called isotope effect.

It has been shown that the experimental values of σ _d and their energy dependence agree well with the theoretical ones, which are calculated using the power-law approximations for Thomas-Fermi potential, on the assumption that the ion-induced detrapping of hydrogen isotopes takes place due to elastic displacement collisions with energetic carbon recoils produced by incident MeV He⁺ ions.     

用弹性反冲分析法测定吸附剂中氢的含量

本文介绍用弹性反冲分析技术分析了对二甲苯吸附剂中的氢含量。首先测定已知氢含量的Mylar膜的原子比,实验结果与预期值一致。实验中用Kapton膜作为标样,测定了各种工艺条件的吸附剂中的氢含量,为实际使用提供了依据。 本方法在E_0=2MeV下,可探测深度范围为0.5μm左右,深度分辨率约为700A,灵敏度为0.1％原子数。     

Vacuum plasma etching of 1 wt% La2O3 dispersed tungsten

Vacuum plasma etching of 1 wt% La₂O₃ doped tungsten alloy surfaces were carried out to refine the surface morphology for enhancing its bonding characteristics with copper for fusion reactor components. Three different gas compositions containing argon with zero, 14.3 and 25 vol% hydrogen were used to carry out the plasma etching from 30 to 120 s on the given samples. Mitutoyo surface roughness (R_a) measurement, FORM TALYSURF and scanning electron microscopy (SEM) were employed to measure the changes in the surface roughness. Plasma etching with 14.3 vol% hydrogen mixture was found to be the best in micro-roughening the alloy surface. The maximum increase of 44% in R_a value was obtained with this gas mixture, when etched for 90 s.     

Depth profiling of hydrogen by detection of recoiled protons

The elastic recoil detection technique (ERD) using a 2.5 MeV ⁴He beam for depth profiling of hydrogen in the near-surface regions of solids is described. The optimization of the experimental conditions such as scattering geometry and analyzing beam energy is discussed. The factors limiting the depth resolution of the method have been evaluated showing that a depth resolution of the order of 20 nm can be obtained. Also presented are typical applications for hydrogen profiling in a silicon matrix.     

掠入射X射线散射法研究超光滑镜面粗糙度

在Xiaomin Tong等的理论上发展了一个二维理论模型,建立散射光强分布与超光滑表面功率谱密度(PSD)的关系。在上海同步辐射光源小角散射实验站上,用不同粗糙度的210 mm和320 mm长的超光滑反射镜进行掠入射X射线散射法(GIXRS)实验,测量散射分布并进行处理,计算出两块反射镜的表面均方根粗糙度(RMS)。与白光干涉法测量结果的比对结果表明,根据这种理论进行数据处理得到的RMS值,与白光干涉法的测量结果非常符合。     

Structural changes in helium implanted Zr0.8Y0.2O1.9 single crystals characterized by atomic force microscopy and EXAFS spectroscopy

The present work is devoted to investigate the local atomic environment (of Zr, Y and O) as well as surface modifications associated with excess helium in the cubic phase of (1 0 0)-oriented Zr_0.8Y_0.2O_1.9 single crystal substrates. Commercially available oxide crystals have been implanted at various fluences in the range 0.15-2.0 × 10¹⁶ He-atoms/cm² using a 2.74 MeV He⁺ ion beam passing through a 8.0 μm Al foil. The microstructure and surface morphology of the irradiated surface are examined using atomic force microscopy (AFM). The local atomic environments of Zr, Y and O in the implanted layer are studied using synchrotron radiation and by extended X-ray absorption fine structure (EXAFS) measured at glancing angles to probe the implanted layer. From AFM studies it was observed that the surface roughness increases as fluence increases and above a critical fluence stage, small blister-like structures originating from helium bubbles are scattered on the irradiated surface. The radial distribution functions (RDFs), derived from EXAFS data at the Zr K-edge, have been found to evolve continuously as a function of ion fluence describing the atomic scale structural modifications in YSZ by helium implantation. From the pristine data, long range order (beyond the first- and second-shell) is apparent in the RDF spectrum. It shows several nearest neighbour peaks at about 2.1, 3.6, 4.3 and 5.4 Å. In the implanted specimens, all these peaks are greatly reduced in magnitude and their average positions are changed, typical of damaged material. A simple model taking into account only the existence of lattice vacancies has been used for the interpretation of measured EXAFS spectra.     

Hydrolysis kinetics of lead silicate glass in acid solution

Hydrolysis kinetics of the lead silicate glass (LSG) with 40 mol% PbO in 0.5 N HNO₃ aqueous acid solution was investigated. The surface morphology and the gel layer thickness were studied by scanning electron microscopy (SEM) micrographs. Energy dispersive X-ray spectroscopy (EDS) and inductively coupled plasma spectroscopy (ICP) were used to determine the composition of the gel layer and the aqueous solution, respectively. The silicon content of the dissolution products was determined by using weight-loss data and compositions of the gel layer and the solution. The kinetic parameters were determined using the shrinking-core-model (SCM) for rate controlling step. The activation energy obtained for hydrolysis reaction was Q_che = 56.07 kJ/mole. The diffusion coefficient of the Pb ions from the gel layer was determined by using its concentration in solution and in LSG. The shrinkage of the sample and the gel layer thickness during dissolution process were determined.     

Localised modifications of anatase TiO2 thin films by a Focused Ion Beam

A Focused Ion Beam (FIB) has been used to implant micrometer-sized areas of polycrystalline anatase TiO₂ thin films with Ga⁺ ions using fluencies from 10¹⁵ to 10¹⁷ ions/cm². The evolution of the surface morphology was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). In addition, the chemical modifications of the surface were followed by X-ray photoelectron spectroscopy (XPS). The implanted areas show a noticeable change in surface morphology as compared to the as-deposited surface. The surface loses its grainy morphology to gradually become a smooth surface with a RMS roughness of less than 1 nm for the highest ion fluence used. The surface recession or depth of the irradiated area increases with ion fluence, but the rate with which the depth increases changes at around 5 × 10¹⁶ ions/cm². Comparison with implantation of a pre-irradiated surface indicates that the initial surface morphology may have a large effect on the surface recession rate. Detailed analysis of the XPS spectra shows that the oxidation state of Ti and O apparently does not change, whereas the implanted gallium exists in an oxidation state related to Ga₂O₃.