Thin oxide degradation after high-energy ion irradiation

We have investigated the degradation induced by I- and Si-ions on 10- and 3-nm-thick oxide MOS capacitors. Ten-nanometer oxides were biased at low electric field (⩽3.3 MV/cm) during irradiation up to 100 Mrad(Si). DC radiation induced leakage current (RILC) has been observed after irradiation, and the differences of RILC characteristics between 10-nm and thinner oxides are discussed. In 10-nm oxides, RILC is attributed to multitrap assisted tunneling, which is reduced by subsequent Fowler-Nordheim electron injection. The density of the radiation-induced positive charged defect, the positive charge recombination by Fowler-Nordheim electron injection, and the negative charge trapping in radiation-induced neutral electron traps have been also addressed. On the other side, radiation-induced soft breakdown (RSB) is triggered by I-ions in 3-nm oxides at low doses (<1 krad(Si)) for moderate applied electric fields (4.4 MV/cm). Silicon ion irradiation is unable to produce RSB and RILC in 10-nm oxides, but it can generate a peculiar RILC in 3-nm oxides     

Preparation of Massive Plutonium Metal Directly from Its Oxides

This report details a technique for the rapid production of massive Pu metal directly from its oxides. Salient features of this single unit process are as follows: the reduction of plutonium oxides with Ca metal; the extraction, by dissolution, of the calcium oxide reaction product with molten calcium chloride; and a quantitative separation of the two immiscible molten metal phases by the immiscible salt solution.

Reduction, separation and massive metal yield efficiencies are in excess of 99.96%. The purity of the metal produced is equal to that of the initial feed material. The batch cycle time is 15 min. The single waste product is far below recovery level and is discardable as a small volume solid waste.     

Nanoscale metal-silicide films prepared by surfactant sputtering and analyzed by RBS

Surfactant sputtering has been applied to modify the surface structure of Si substrates and to produce ultrathin metal-silicide films with nickel and platinum surfactants, utilizing the steady state coverage of a Si-substrate surface with surfactant atoms simultaneously during sputter erosion by combined ion irradiation and surfactant atom deposition. Si (1 0 0) substrates were eroded using 5 keV Xe-ions and 10–30 keV Ar ions at incident angles of 65° and 70° with fluences of up to 2 × 10¹⁸/cm² under continuous sputter deposition of platinum and nickel from targets irradiated simultaneously by the same ion beam. These surfactant atoms form metal-silicides in the surface near region and strongly modify the substrate sputter yield and the surface nanostructure. Atomic force microscopy and scanning electron microscopy were carried out to observe a transition of surface topography from ripple to relief patterns, granular patterns or smooth surfaces. The Si and metal sputter yield as function of the steady state metal coverage were determined by combination of Rutherford-backscattering spectroscopy (RBS) and profilometry. The composition and the depth distributions of metal-silicide films were analyzed via high-resolution RBS and transmission electron microscopy. We show that RBS results in comparison with SRIM and TRIDYN sputter yield simulations allows us to identify the silicide surface structure on the nanometer scale.     

Liquid Metal Extraction for Removal of Molybdenum from Molten Glass Containing Simulated Nuclear Waste Elements

Laboratory-scale experiments for removing Mo and MoO3 from molten borosilicate glass were performed using liquid Cu as an extractant. Removal of Mo from the simulated HLW glass containing oxides of Nd, Fe, Zr, Mo, Sn, Ni, Sr, Cd, Ru, and Se was also performed, and the fractions of these elements transferred into Cu were examined. Mixtures of Cu anda ternary SiO₂-B₂O₃-Na₂O glass containing metallic Mo or MoO₃ were heated in an alumina crucible at 1,673K in an Ar environment. The amounts of Mo and MoO₃ added to 10 g of the ternary glass were fixed at 0.1 and 0.15 g, respectively. As for the glass containing metallic Mo, more than 90% of Mo was extracted into liquid Cu. Spherical Cu metal buttons containing Mo formed on the bottom of the crucible when Cu was added at more than 10 times that of Mo on a mass basis. Removal of Mo from the glass containing MoO3 was also achieved by the addition of Si as a reducing agent for the reduction from MoO₃ to Mo. The fraction of Mo extracted into liquid Cu depended on the molar ratio of Si to Cu added to the glass. The fraction increased up to 84% with an increase in the molar ratio of Si/Cu. However, the excess addition of Si may enhance the chemical interaction between the metal phase and the glass phase, and some of the metal phase containing Mo remained in the glass phase without forming a metal button. The optimum molar ratio of Si/Cu that produces the highest removal fraction was found to be approximately 0.5. Almost the same removal fraction of 88% was obtained from the simulated HLW glass under the condition of Si/Cu = 0.5. Nearly 100% of Ru was extracted into Cu with Mo, while Sr, Zr, and Nd were hardly extracted and remained in the glass.     

金属Ce表面氧化物的真空稳定性

为探讨金属铈在超高真空条件下作为钚模拟材料的可行性，采用X射线光电子能谱（XPS）分析技术研究了超高真空条件下金属Ce表面氧化物在不同温度时的真空稳定性。实验结果表明，不同温度和超高真空条件下，金属Ce表面氧化物的真空稳定性各不相同。在室温、超高真空条件下没有观察到金属Ce表面氧化物发生变化；但在873 K、超高真空条件时，金属Ce表面氧化物发生还原反应，样品表面生成Ce₂O₃。根据热力学计算，推断了高温、超高真空条件下发生还原反应的过程，金属Ce表面氧化物的真空特性与金属Pu存在一定差异。     

Hole Transport and Recovery Characteristics of SiO2 Gate Insulators

The transient response, or flat-band voltage recovery, in a number of pedigreed SiO2 gate insulator MOS capacitors following exposure to a pulsed 13-MeV electron beam was studied as a function of time, temperature, and applied bias. A quantitative comparison of the response characteristics of the different oxides is made. It is found generally that the response consists of two stages. The first (early time) stage in most cases encompasses most of the recovery and is dominated by hole transport through the insulator film to the interface. This hole transport recovery stage in all the oxides studied is well described by the stochastic model of hopping transport based on a continuous time random walk used previously in the analysis of hole transport in SiO2. It is further shown that all the main features of the hole transport are consistent with a model of the holes moving via polaron hopping between localized sites in the SiO2. The second or long-term stage of recovery commences after cessation of the hole transport in the oxide and is found to vary significantly in its importance and time of onset among the various oxides. This stage involves a radiation-induced buildup of interface states and possibly, in some cases, an annealing of a trapped-hole distribution near the SiO2/Si interface.     

Effect of the Concentration of Metal Ions on their Adsorption on Various Hydrous Iron and Aluminum Oxides

The adsorption of Eu(III) and Co(II) on laboratory-prepared amorphous hydrous iron and aluminum oxides, goethite and gibbsite, was studied as a function of pH over a wide range of metal ion concentrations, in order to see the effect of the change in the degree of site occupation by metal ions. When the metal ion concentrations were low, a simple Langmuir equation with a single adsorption constant was able to describe adsorption on these hydrous oxides. At high metal ion concentrations, adsorption on goethite and gibbsite exhibited clear saturation maxima expected from a simple one-to-one interaction between the metal ion and the adsorption site, while adsorption on laboratory-prepared hydrous oxides continued to increase gradually even at high metal ion concentrations.     

Application of a chronoamperometric measurement to the on-line monitoring of a lithium metal reduction for uranium oxide

Both a potentiometric and a chronoamperometric electrochemical technique have been applied in an attempt to develop an efficient method for an on-line monitoring of a lithium metal reduction process of uranium oxides at a high-temperature in a molten salt medium. As a result of this study, it was concluded that the chronoamperometric method provided a simple and effective way for a direct on-line monitoring measurement of a lithium metal reduction process of uranium oxides at 650 °C by the measuring electrical currents dependency on a variation of the reduction time for the reaction. A potentiometric method, by adopting a homemade oxide ion selective electrode made of ZrO₂ stabilized by a Y₂O₃ doping, however, was found to be inappropriate for an on-line monitoring of the reduction reaction of uranium oxide in the presence of lithium metal due to an abnormal behavior of the adopted electrodes. The observed experimental results were discussed in detail by comparing them with previously published experimental data.     

Regulation characteristics of oxide generation and formaldehyde removal by using volume DBD reactor

Discharge plasmas in air can be accompanied by ultraviolet(UV) radiation and electron impact,which can produce large numbers of reactive species such as hydroxyl radical(OH·),oxygen radical(O·),ozone(O3),and nitrogen oxides(NOx),etc.The composition and dosage of reactive species usually play an important role in the case of volatile organic compounds(VOCs) treatment with the discharge plasmas.In this paper,we propose a volume discharge setup used to purify formaldehyde in air,which is configured by a plate-to-plate dielectric barrier discharge(DBD) channel and excited by an AC high voltage source.The results show that the relative spectral-intensity from DBD cell without formaldehyde is stronger than the case with formaldehyde.The energy efficiency ratios(EERs) of both oxides yield and formaldehyde removal can be regulated by the gas flow velocity in DBD channel,and the most desirable processing effect is the gas flow velocity within the range from2.50 to 3.33 m s-1.Moreover,the EERs of both the generated dosages of oxides(O3 and NO2) and the amount of removed formaldehyde can also be regulated by both of the applied voltage and power density loaded on the DBD cell.Additionally,the EERs of both oxides generation and formaldehyde removal present as a function of normal distribution with increasing the applied power density,and the peak of the function is appeared in the range from 273.5 to 400.0 W l-1.This work clearly demonstrates the regulation characteristic of both the formaldehyde removal and oxides yield by using volume DBD,and it is helpful in the applications of VOCs removal by using discharge plasma.     

Stopping power of 11B in Si and TiO2 measured with a bulk sample method and Bayesian inference data analysis

The popular stopping power interpolative schemes require experimental data to be developed. Where the data bases are sparse, with few experiments available, interpolations can be more inaccurate. This is the case for the stopping of heavy ions, where even for important targets such as Si there is a need for more measurements. For compounds, the situation is even worse with very few measurements available. In particular, the stopping in oxides and nitrides often deviates significantly from what would be expected using the Bragg’s rule. We apply a method that uses bulk or thick film samples to determine the stopping power of ¹¹B in Si and TiO₂. The method, which relies on Bayesian inference analysis of RBS spectra obtained at different energies, has been previously validated by verifying the results obtained in the well-known system ⁴He in Si.     

Determination of stoichiometry in silicon carbide materials using elastic backscattering spectrometry

Elastic backscattering spectrometry (EBS) was performed on SiC materials, using ⁴He particles at energies ranging from 2 to 4 MeV, in order to establish the energy values that lead to an accurate measurement of the Si/C ratio. Analysis of the random yield of “bulk” SiC single crystals indicates that energy values of 3.25 and 3.75 MeV are the most suitable for chemical composition determination; backscattering yield of carbon is enhanced compared to the yield measured at 2 MeV, while the excitation of strong resonances above 3.75 MeV are suppressed. Random backscattering yield measurements were then carried out at an energy of 3.25 MeV on unhydrogenated SiC thin films grown on Si(1 0 0), by pulsed laser deposition, at different substrate temperatures. The Si and C atomic concentrations in the films were determined with an uncertainty of 1% and little interference from the underlying substrate. The films were found to be stoichiometric with a Si/C ratio of 1.03 ± 0.05, independent of deposition temperature, which indicates that the films were grown under congruent ablation conditions. The analysis proved to be applicable to both amorphous and crystalline SiC layers, as confirmed by the results obtained for films deposited at 400 and 950 °C, respectively.     

Raman and XPS characterization of fuel-cladding interactions using miniature specimens

A combination of laser Raman spectroscopy and X-ray photoelectron spectroscopy was applied in a study of fuel-cladding chemical interactions on miniature oxide-coated HT-9 disks at elevated temperature. The experiments were intended as a preliminary step toward the development of a quick-screening technique for candidate alloys for cladding materials and actinide-based mixed oxide fuel mixtures. The results indicated that laser Raman spectroscopy was capable of determining the major oxides on HT-9 and how they changed in composition due to heating. However, X-ray photoelectron spectroscopy was necessary to identify the role of the metallic phases and provide depth resolution. Using the two techniques the kinetics of chromia growth were shown to be affected by the presence of an applied oxide coating. A single replacement reaction involving residual reduced metal within the coating was also identified.     

γ射线辐照改性聚碳硅烷提高热解陶瓷产率

在N2气中用γ射线对聚碳硅烷(Polycarbosilane,PCS)进行辐照,利用傅里叶红外光谱分析、凝胶渗透色谱分析和热重分析等手段研究了不同吸收剂量下PCS的化学结构、分子量和热分解特性。结果显示,经γ射线辐照处理后的PCS轻微失重,分子量和软化点随着吸收剂量的增加而增加,说明PCS经辐照后发生了分子间的交联反应。红外分析表明,PCS的交联主要是通过Si-H键和C-H键的断裂产生新的Si-C-Si结构实现的。热重分析表明,PCS热解为碳化硅的陶瓷产率随吸收剂量的增加显著升高,剂量达到1.5 MGy后PCS样品的陶瓷产率基本提高到稳定值,此时,陶瓷产率从改性前的61.9%提高到80.0%。     

Measurement of Anisotropy of Diffusion Coefficient in Plate Cell

Ion-exchange property and thermal stability were studied on four synthetic hydrous metal oxides from the viewpoint of applicability for the processing of liquid radioactive waste. Hydrous titanium (IV) oxide and hydrous niobium (V) oxide, consisting of metal ions having larger ionic potential, possessed large cation-exchange capacities, and showed high affinity for both the transition metal ions and the representative element ions. Hydrous tin (IV) oxide and hydrous zirconium (IV) oxide, consisting of metal ions having smaller ionic potential, were amphoteric ion exchangers possessing large anion-exchange capacities, and showed much higher affinity for the transition metal ions than for the representative element ions. The selectivity series are understood in terms of the formation of a bond partially covalent in character for the transition metals, and the purely electrostatic interaction between anionic exchange sites and unhydrated or hydrated cations for the representative elements. An examination of the effects of heat treatment in air on the ion-exchange properties indicated that the hydrous niobium (V) oxide was the most stable among the four hydrous metal oxides. Even this material, however, was not stable enough to be used under hydrothermal conditions.     

Synthesis of simulated cruds for development of decontaminating agents

The Chalk River Unidentified Deposit (cruds) were classified into Types 1 and 2 based on the analyses of actual cruds from target objects such as steam generator (SG) of Korea and Japan Pressurized Water Reactor (PWR). A metal oxide or metal hydroxide was used to synthesize simulated cruds having chemical compositions and crystalline structure similar to the actual one by 12 different methods. CRUD 4 (metal oxides in the autoclave vessel) and CRUD 10 (metal oxides in a crucible after hydrazine pretreatment) were chosen as the best method for Types 1 and 2, respectively. These simulated cruds showed reasonable dissolubilities by dissolution tests using well-known decontaminating agents. As these cruds can be synthesized easily without using any specialized equipment or reagents in a short time and in large quantities, they are expected to stimulate the development of decontaminating agents and processes.     

晶态合金Fe_(79)Si_7B_(14)、Fe_(83)Si_4B_(10)C_3结构弛豫的穆斯堡尔效应研究

本文应用示差热分析和穆斯堡尔谱学方法,对非晶态合金Fe_(79)Si_7B_(14)和Fe_(83)Si_4B_(10)C_3的结构弛豫过程进行了实验研究,认为其结构弛豫过程包括拓扑短程序弛豫、化学短程序弛豫和基体金属相形核长大三种形式的结构变化。     

Luminescence properties of zirconium oxide films

Various luminescence techniques have been applied in the characterisation of the zirconium oxide film formed on the metal matrix. Our investigation shows that some alloying elements in the zirconium alloys show characteristic emissions which could be used to study their distribution in the zirconium oxide. While the origin and detailed mechanism of luminescence in the zirconium oxide system is not well established, cathodoluminescence (CL) and thermoluminescence results from this study support the theory that oxygen vacancies in complexes with impurities are responsible for the intrinsic luminescence in the oxide system. The specific oxygen vacancy and impurity complex is reported in literature as the T-defect, having an energy of 2.2 eV. To aid in interpretation of the CL data, optical transmission properties of the oxides were also measured. The latter investigation showed the thickness of the oxide illuminated by the CL technique is greatly dependent on the optical transmission properties of the oxide, and it ranges from 20 μm for pure zirconium or low-alloyed zirconium oxides to less than 3 μm for oxides of alloys with more absorbing, or higher alloying element concentrations. The 20 μm depth of illumination is significantly deeper than the electron penetration depth, which suggests a secondary source of excitation, possibly characteristic X-rays emitted by the specimen. These combined properties of the oxide and technique can result in CL images showing structural contrast not easily seen during SEM or optical microscopy of oxidised surfaces.     

焊接接头非均匀力学性能对J积分和失效评定曲线的影响

由于焊缝填充金属的不同和焊接热循环的作用,焊接接头不同区域有着不同的力学性能。本文将焊接接头模化为由两种材料组成,即母材金属和焊缝金属,用弹塑性有限元分析法计算了焊接接头强度组配对Ｊ积分和失效评定曲线的影响。结果表明,焊接接头不均匀强度组配对裂纹驱动力－Ｊ积分和失效评定曲线的形状与位置有很大影响。对于一个特定的焊接接头,如果接头为低组配或等组配,则以母材金属的极限载荷作为无因次载荷而建立的安全评定     

Analysis of Si crystal irradiated by highly-charged Ar ions using RBS-channeling technique

An ion-beam is one of the powerful tools applied in nanotechnology and nanoscience. It is expected that the application of highly-charged ion (HCI) beams, which have a higher reactivity in materials, would yield further developments in these fields. For effective applications of HCI beams, it is important to investigate any modifications of irradiated materials from a microscopic point of view. For this purpose, an irradiation-induced defect in a single crystal was analyzed by means of Rutherford backscattering-channeling (RBS) technique. In order to induce defects, Ar⁶⁺ and Ar⁹⁺ beams with an energy of 100 keV were irradiated onto a single crystal of Si. By means of a simple analysis, the depth distribution of disordered Si atoms induced by the irradiation was extracted from the observed RBS-C spectra. The present result implies that the productivity of defects in a Si crystal is enhanced for Ar⁹⁺ ions compared with Ar⁶⁺ ions in a limited region of the surface.     

硅胶表面季铵功能化接枝过程的29SiCP/MSNMR和XPS法研究

本工作采用29SiCP/MSNMR和XPS测试方法对硅胶表面接枝季铵功能基团的过程和机理进行了分析。XPS光谱分析结果表明，硅基季铵化产品的XPS谱中含有Si、O、C、N元素，并出现了以R4N+形式存在的401.26eV结合能峰，表明硅胶表面已被季铵化。TGA-DTA分析其接枝率为 0.46mmol/g，同时，本工作采用29SiCP/MSNMR法对接枝机理进行探索研究，得出了接枝的可能反应途径和产品分子结构。