Study by EELS of helium bubbles in a martensitic steel

This work presents measurements of the helium density and pressure in small bubbles in a martensitic steel, which is a vital first step towards identifying their role in the microstructural mechanisms determining the macroscopic properties of the material. Electron Energy-Loss Spectroscopy in the Scanning Transmission Electron Microscope has been used to analyse individual bubbles. The energy shift of the 1s → 2p transition and the helium density have been measured for each bubble analysed. The pressure inside the bubbles has been calculated from the helium density using an equation of state. In these bubbles, the values for the helium pressure seem to be smaller than the equilibrium pressure, and agree in trend with the findings of previous studies, although our results extend to smaller radii and higher pressures.     

Irradiation effects in helium implanted silicon carbide measured by X-ray absorption spectrometry

Silicon carbide (SiC) is investigated as a possible structural material for future nuclear power plants. It is utilized as fibre and/or as matrix in ceramic composite materials. The fibre reinforcement is necessary to provide the required ductility. In this work, the behaviour of pure SiC under irradiation by He implantation is studied. Samples are investigated by means of the extended X-ray absorption fine structure (EXAFS) spectroscopy, performed at the Si K-edge. The Fourier transforms of the EXAFS data indicate a decrease of the Si-Si bond related shells around the absorbing Si. The possible damage features are discussed and the three most probable ones for the irradiation conditions are selected for future modelling work.     

Nanoscratch study of ZnO thin films deposited using radio frequency magnetron sputtering

In this study, a radio frequency magnetron sputtering system was used to deposit zinc oxide (ZnO) thin films onto langasite substrates. The thickness of the ZnO film increased from 0.3 to 1.2 μm upon increasing the deposition power from 100 to 200 W. The predominant growth orientation was along the c-axis (0 0 2); the intensities of the signals in the X-ray diffraction spectrum increased significantly upon increasing the film thickness. Scanning electron microscopy images revealed columnar structures in the ZnO films and the morphology of ZnO grains is found to be continuous and dense. It is attributed that oxygen chemisorbs on the target and cases a surface layer of adsorbed oxygen. We suggest that the more neutral ion bombardment on the growing film which induces the higher sputtering rate of the growing film. From in situ imaging of scratched tracks, measurement of the coefficient of friction was an effective means of detecting the occurrence of structural defects in the microstructures. We also found that the chemical compositions of ZnO films prepared under various deposition powers could be investigated using X-ray photoelectron spectroscopy.     

Study of atomic clusters in neutron irradiated reactor pressure vessel surveillance samples by extended X-ray absorption fine structure spectroscopy

Copper and nickel impurities in nuclear reactor pressure vessel (RPV) steel can form nano-clusters, which have a strong impact on the ductile-brittle transition temperature of the material. Thus, for control purposes and simulation of long irradiation times, surveillance samples are submitted to enhanced neutron irradiation. In this work, surveillance samples from a Swiss nuclear power plant were investigated by extended X-ray absorption fine structure spectroscopy (EXAFS). The density of Cu and Ni atoms determined in the first and second shells around the absorber is affected by the irradiation and temperature. The comparison of the EXAFS data at Cu and Ni K-edges shows that these elements reside in arrangements similar to bcc Fe. However, the EXAFS analysis reveals local irradiation damage in the form of vacancy fractions, which can be determined with a precision of ∼5%. There are indications that the formation of Cu and Ni clusters differs significantly.     

Preparation and characterization of Ag-coated cenospheres by magnetron sputtering method

In this paper, we show the feasibility of the magnetron sputtering deposition technique to grow 10-100-nm thick, uniform, continuous and well adhesive silver films on cenosphere particles so that the properties of the core particles can be suitably modified. Experiments were conducted with a magnetron sputtering deposition system in which a newly designed sample stage equipped with an ultrasonic vibration generator was used for the tumbling of cenosphere particles. The cenosphere particles are characterized by X-ray diffraction (XRD) analysis, field emission scanning electron microscope (FE-SEM) and inductively coupled plasma-atom emission spectrometer (ICP-AES) before and after the coating process. All results show the metal film has been successfully coated onto cenosphere particles. Under the given conditions, up to 3.0 wt.% silver was deposited on cenosphere particles measured by ICP-AES. The FE-SEM results indicate that at the micro-scale the relatively uniform, compact and well adhesive silver films with about 51 nm thickness were successfully deposited on cenosphere particles. The XRD analytic result indicates that the nanometer metal film has a face-centered cubic structure.     

中频磁控溅射制备AlN薄膜

设计了一套阳极层离子源辅助中频磁控溅射装置,并在Si(111)衬底上沉积AlN薄膜。用X射线衍射、原子力显微镜和扫描电镜分析了AlN薄膜的结构、形貌和成分。在优化的实验条件下制备的AlN薄膜具有较强的(002)衍射峰,其半高宽为612–648弧秒。气体流量、衬底偏压、离子源等对薄膜结构有明显影响。     

中频磁控溅射制备AIN薄膜

设计了-套阳极层离子源辅助中频磁控溅射装置,并在Si(111)衬底上沉积AIN薄膜.用X射线衍射、原子力显微镜和扫描电镜分析了AIN薄膜的结构、形貌和成分.在优化的实验条件下制备的AIN薄膜具有较强的(002)衍射峰,其半高宽为612-648弧秒.气体流量、衬底偏压、离子源等对薄膜结构有明显影响.     

CrN films deposited by ion source-assisted magnetron sputtering

CrN coatings were deposited on Si(100) and piston rings by ion source assisted 40 kHz magnetron sputtering.Structure and composition of the coatings were characterized by X-ray diffraction,atomic force microscopy,scanning electron microscopy and transmission electron microscopy.Mechanical and tribological properties were assessed by microhardness and pin-on-disc testing.The ion source-assisted system has a deposition rate of 3.88 μm/h,against 2.2 μm/h without ion-source assistance.The CrN coatings prepared with ion source assistance exhibited an increase in microhardness(up to 16.3 GPa) and decrease in friction coefficient(down to 0.48) at the optimized cathode source-to-substrate distance.Under optimized conditions,CrN coatings were deposited on piston rings,with a thickness of 25 μm and hardness of 17.85 GPa.     

直流磁控溅射法制备含氦铝膜

采用氦氩混合气氛下直流磁控溅射沉积方法制备含有氦原子的金属铝膜。经碳原子弹性前冲散射分析（C-ERDA），薄膜中氦原子浓度可达约7％，且分布均匀。实验研究了薄膜中的氦含量与溅射真空室气氛中氦的相对含量、基底偏压及沉积温度间的关系。薄膜的X射线衍射分析结果显示：膜中的氦含量变化并未引起明显的峰位移，只是随氦含量增加谱峰宽化。热释放实验证实，氦在薄膜中稳定存在，约500℃以上时方出现氦的释放。     

Structural analysis of DC magnetron sputtered and spin coated thin films using RBS, TEM and X-ray reflectivity methods

Metallic thin films such as Au, Cr, Ag, etc., on silicon substrate have many technologically important applications as contact layers in microelectronic industry, as reflecting mirrors in synchrotron radiation research, etc. The native oxide layer on crystalline silicon surface inhibits wetting of few nm thick Au or Ag on native oxide/silicon systems. To obtain continuous thin metallic films (a few nm thick), a Cr layer was first deposited as a adhesion layer on the Si substrate. In this paper, Rutherford backscattering analysis (RBS) of Si/Cr/SiO₂/Si, Si/Au/SiO₂/Si, Si/Au/Cr/SiO₂/Si and Polystyrene (PS) polymer coated on some of these bi- or tri-layer structures has been reported. The X-ray reflectometry and transmission electron microscopy studies were carried out to complement the RBS measurements. The thickness, surface and interface roughness, and crystalline quality have been determined.     

Proton sputtering from polycrystalline Al surface interacting with highly charged ions at grazing incidence angle

Sputtering processes of protons from a polycrystalline Al surface interacting with Ar^q+ (q = 3-14) ions at a grazing incidence angle (∼0.5°) were investigated. The intensity of protons (I_H) detected in coincidence with scattered Ar atoms was measured as a function of q. I_H saturated at q ? 10, although it increased rapidly with q at 3 ? q ? 8. The angular distribution of protons with low kinetic energy (?2 eV) began to deviate from the cosine distribution and assumed a rather flat equidistribution as q increased. To analyze the sputtering processes of protons at the grazing incidence angle, a modified model of the “above-surface potential sputtering model” was proposed by considering image acceleration of projectile ions.     

Highly charged ion interactions with thin insulating films

The electrical conductance of magnetic tunnel junction (MTJ) devices whose ultra-thin aluminum oxide tunnel barriers were irradiated by highly charged ions (HCIs) increases linearly with the fluence of HCIs, while retaining a current-voltage relationship indicative of a tunnel junction. The slope of the MTJ conductance σ_c as a function of fluence varies with different tunnel barrier thicknesses d, levels of oxidation (stoichiometry) and charge state q. Since the MTJ conductance after HCI irradiation is due to tunneling, the increased conductance can result from thinning the barrier, reducing the effective tunnel barrier height φ, or both. Measurements of the current-voltage profile provide sufficient degrees of freedom to substantially constrain d and φ provided the reduction of the barrier remains within the assumptions of the commonly used WKB (Wentzel-Kramers-Brillouin) tunneling formalism. For the Xe³²⁺ ions discussed here the perturbation of the tunnel barrier is much weaker than in our previously reported measurements of Xe⁴⁴⁺ and application of WKB is still reasonable. This analysis reveals a trend of decreasing d while φ changes little.     

中频磁控溅射制备GaN薄膜

采用中频磁控溅射技术,以金属Ga为靶材料,在si(111)衬底上形成了GaN薄膜,研究了溅射压强、衬底温度等对GaN薄膜结构和成分的影响.发现沉积气压为0.4～1.0 Pa时,薄膜呈GaN(002)取向,气压大于1.0 Pa和小于0.4 Pa时,用X射线衍射方法难以观察到GaN(002)的衍射峰.X射线能谱分析表明在最佳实验条件下制备的GaN薄膜的元素比Ga∶N为1∶1.     

Microprobe analysis of neutron irradiated and autoclaved zirconium niobium claddings using synchrotron-based hard X-ray imaging and spectroscopy

Two zirconium alloys (Zr-2.5%Nb) - one oxidized in a pressurized water reactor, the other oxidized in autoclave and used as reference - are analyzed by combining synchrotron-based scanning transmission and fluorescence X-ray microscopy and micro-X-ray absorption spectroscopy (micro-XAS). Two-dimensional zirconium distribution maps recorded on the neutron irradiated and the non-irradiated autoclaved Zr-2.5%Nb alloys clearly allow the localization of the oxide and the metal parts of the interface with a micrometer spatial resolution. Micro-XAS investigations make possible the determination of the speciation of zirconium and niobium both in the oxide and the metal parts of the interface for the irradiated and non-irradiated samples. The coordination environment and/or the valency of zirconium and niobium in the metal and the oxide parts of the interface have been determined for both materials, and interpreted on the basis of comparison with metal and oxide reference compounds.     

Fracture behavior of austenitic stainless steels irradiated in PWR

Fracture behavior of cold-worked 316 stainless steels irradiated up to 73 dpa in a pressurized water reactor was investigated by impact testing at −196, 30 and 150 °C, and by conventional tensile and slow tensile testing at 30 and 320 °C. In impact tests, brittle IG mode was dominant at −196 °C at doses higher than 11 dpa accompanying significant decrease in absorbed energy. The mixed IG mode, which was characterized by isolated grain facets in ductile dimples, appeared at 30 and 150 °C whereas the fracture occurred macroscopically in a ductile manner. The sensitivity to IG or mixed IG mode was more pronounced for higher dose and lower test temperature. In uniaxial tensile tests, IG mode at a slow strain rate appeared only at 320 °C whereas mixed IG mode appeared at both 30 and 320 °C at a fast strain rate. A compilation of the results and literature data suggested that IG fracture exists in two different conditions, low-temperature high-strain-rate (LTHR) and high-temperature low-strain-rate (HTLR) conditions. These two conditions for IG fracture likely correspond to two different deformation modes, twining and channeling.     

Research on deposition rate of TiZrV/Pd film by DC magnetron sputtering method

An accelerator storage ring needs clean ultrahigh vacuum.A TiZrV non-evaporable getter (NEG) film deposited on interior walls of the chamber can realize distributed pumping,effective vacuum improvement and reduced longitudinal pressure gradient.But accumulation of pollutants such as N2 and O2 will decrease the adsorption ability of the NEG,leading to a reduction of NEG lifetime.Therefore,an NEG thin film coated with a layer of Pd,which has high diffusion rate and absorption ability for H2,can extend the service life of NEG and improve the pumping rate of H2 as well.In this paper,with argon as discharge gas,a magnetron sputtering method is adopted to prepare TiZrV-Pd films in a long straight pipe.By SEM measurement,deposition rates of TiZrV-Pd films are analyzed under different deposition parameters,such as magnetic field strength,gas flow rate,discharge current,discharge voltage and working pressure.By comparing the experimental results with the simulation results based on Sigmund's theory,the Pd deposition rate C can be estimated by the sputtered depth.     

Measurement and calculation of high-energy neutron spectra behind shielding at the CERF 120 GeV/c hadron beam facility

Neutron energy spectra were measured behind the lateral shield of the CERF (CERN-EU High Energy Reference Field) facility at CERN with a 120 GeV/c positive hadron beam (a mixture of mainly protons and pions) on a cylindrical copper target (7-cm diameter by 50-cm long). An NE213 organic liquid scintillator (12.7-cm diameter by 12.7-cm long) was located at various longitudinal positions behind shields of 80- and 160-cm thick concrete and 40-cm thick iron. The measurement locations cover an angular range with respect to the beam axis between 13 and 133°. Neutron energy spectra in the energy range between 32 MeV and 380 MeV were obtained by unfolding the measured pulse height spectra with the detector response functions which have been verified in the neutron energy range up to 380 MeV in separate experiments. Since the source term and experimental geometry in this experiment are well characterized and simple and results are given in the form of energy spectra, these experimental results are very useful as benchmark data to check the accuracies of simulation codes and nuclear data.Monte Carlo simulations of the experimental set up were performed with the FLUKA, MARS and PHITS codes. Simulated spectra for the 80-cm thick concrete often agree within the experimental uncertainties. On the other hand, for the 160-cm thick concrete and iron shield differences are generally larger than the experimental uncertainties, yet within a factor of 2. Based on source term simulations, observed discrepancies among simulations of spectra outside the shield can be partially explained by differences in the high-energy hadron production in the copper target.     

ZnO thin films deposited by capillaritron ion beam sputtering deposition

ZnO thin films were deposited by capillaritron ion beam sputtering deposition. The crystalline quality, stoichiometry and photoluminescence properties of as-deposited and annealed ZnO thin films were studied. The as-deposited ZnO films show no preferred crystallographic orientations while annealed films exhibit a strong single ZnO (0 0 2) diffraction peak at 34.50°. The stoichiometry of ZnO films were found to be dependent on both beam energy and annealing conditions that the atomic percent ratio of Zn/O can be controlled between 0.95 and 1.10. ZnO films deposited with 4 keV ion beam and annealed at 800 °C in oxygen shows the lowest defect related deep level visible emission, while 80% of oxygen atoms are still located in fully oxidized stoichiometric ZnO matrixes.     

Oxidation behavior of Incoloy 800 under simulated supercritical water conditions

For a correct design of supercritical water-cooled reactor (SCWR) components, data regarding the behavior of candidate materials in supercritical water are necessary. Corrosion has been identified as a critical problem because the high temperature and the oxidative nature of supercritical water may accelerate the corrosion kinetics. The goal of this paper is to investigate the oxidation behavior of Incoloy 800 exposed in autoclaves under supercritical water conditions for up to 1440 h. The exposure conditions (thermal deaerated water, temperatures of 723, 773, 823 and 873 K and a pressure of 25 MPa) have been selected as relevant for a supercritical power plant concept. To investigate the structural changes of the oxide films, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and electrochemical impedance spectroscopy (EIS) analyses were used. Results show changes in the oxides chemical composition, microstructure and thickness versus testing conditions (pressure, temperature and time). The oxide films are composed of two layers: an outer layer enriched in Fe oxide and an inner layer enriched in Cr and Ni oxides corresponding to small cavities supposedly due to internal oxidation.     

Control of growth and structure of Ag films by the driving frequency of magnetron sputtering

The growth and structural properties of Ag films prepared by radio-frequency (2,13.56 and 27.12 MHz) and very-high-frequency (40.68 and 60 MHz) magnetron sputtering were investigated.Using 2 MHz sputtering,the Ag film has a high deposition rate,a uniform and smooth surface and a good fcc structure.Using 13.56 and 27.12 MHz sputtering,the Ag films still have a high deposition rate and a good fcc structure,but a non-uniform and coarse surface.Using 40.68 MHz sputtering,the Ag film has a moderate deposition rate and a good fcc structure,but a less smooth surface.Using 60 MHz sputtering,the Ag film has a uniform and smooth surface,but a low deposition rate and a poor fcc structure.The growth and structural properties of Ag films are related to the ions' energy and flux density.Therefore,changing the driving frequency is a good way to control the growth and structure of the Ag films.