Characteristics of high deposition rate PIN diodes from pure SiH4 and 10% dilution of SiH4 in H2

In this paper, we present the results of the electrical characterization of PIN diodes up to 18 μm thick fabricated on high deposition rates a-Si:H layers obtained from pure SiH₄ and from a 10% dilution of SiH₄ in H₂, using a 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) with geometrical modifications in the plasma reactor. I-V and I-T curves were investigated, concluding that the changes introduced in the deposition reactor to increase the deposition rate did not affect the characteristics of the fabricated diodes. Results are compared with characteristics, reported for diodes obtained by standard and other high deposition rate methods     

Surface modification of SUS304 stainless steel by atmospheric pressure Ar/N2/O2 plasma

The surface characteristics of SUS304 stainless steel are investigated before and after surface modification by Ar/N₂/O₂ plasma under atmospheric pressure conditions. It was found that plasma treatment of a stainless steel plate has a significant effect on the wettability, contact angle, and free energy of the SUS304 surface. The contact angle and surface free energy were analyzed. The optimal surface modification parameters are a power of 1000 W, a torch-to-sample distance of 80 mm, a treatment time of 300 s, and an oxygen content of 1.5 wt%. Under these processing conditions, a contact angle of just 1.60° was obtained. The surface morphology, surface element composition, and surface roughness of the treated SUS304 specimens were examined using scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively. The results show that the optimal surface modification conditions lead to the formation of fine, uniformly distributed crystallites in the SUS304 microstructure. Moreover, compared to the untreated surface, the treated surface had a significantly lower carbon content and a more uniform distribution of surface peaks.     

CO2和O2地浸铀矿原液中SO2-4的快速测定

为改良现有硫酸钡比浊法测定含铀浸出液中SO^2-₄不能长时间稳定均匀地形成硫酸钡悬浊液的缺点,采用吸光比浊法研究不同波长、酸度、稳定剂、无水乙醇用量对硫酸钡分散体系稳定性的影响以提高测量准确度。实验结果表明,改良比浊法测定SO^2-₄浓度体系中的最佳实验条件为1.0 mL HCl（3 mol/L）、5.0 mL聚乙烯醇溶液(含w=10%BaCl₂•2H₂O)、3.0 mL 无水乙醇。在最佳波长440 nm处,SO^2-₄质量浓度在0.2~1.5 g/L范围内符合比尔定律。该方法的检出限为 0.003 6 mg/L,定量限为 0.012 0 mg/L（n=20）。该方法样品测量回收率为99.0%~99.8%,加标相对标准偏差为 0.63%~2.44%(n=2)。与 GB/T 5750.5-2006 国标法比较,该方法操作简便、快捷,结果准确度高,在CO₂和O₂地浸采铀浸出原液SO^2-₄浓度的测定中有广阔的应用前景。     

Hybrid Simulation of Duty Cycle Influences on Pulse Modulated RF SiH4/Ar Discharge

A one-dimensional fluid/Monte-Carlo(MC)hybrid model is developed to describe capacitively coupled SiH_4/Ar discharge,in which the lower electrode is applied by a RF source and pulse modulated by a square-wave,to investigate the modulation effects of the pulse duty cycle on the discharge mechanism.An electron Monte Carlo simulation is used to calculate the electron energy distribution as a function of position and time phase.Rate coefficients in chemical reactions can then be obtained and transferred to the fluid model for the calculation of electron temperature and densities of different species,such as electrons,ions,and radicals.The simulation results show that,the electron energy distribution f(ε)is modulated evidently within a pulse cycle,with its tail extending to higher energies during the power-on period,while shrinking back promptly in the afterglow period.Thus,the rate coefficients could be controlled during the discharge,resulting in modulation of the species composition on the substrate compared with continuous excitation.Meanwhile,more negative ions,like Si H_3~-and Si H_2~-,may escape to the electrodes owing to the collapse of ambipolar electric fields,which is beneficial to films deposition.Pulse modulation is thus expected to provide additional methods to customize the plasma densities and components.     

Photoionization and photoabsorption cross sections of He, O,N2 and O2 for aeronomic calculations

A compilation of experimental and theoretical photoionization and photoabsorption cross sections is presented for He, O, N₂, and O₂ for use in studies of ion and photoelectron production in the terrestrial ionosphere. In wavelength regions where rapid variations occur in the cross sections, averaged cross sections are calculated. When necessary the cross sections have been extrapolated to shorter wavelengths. The cross sections are tabulated at the wavelengths of the solar lines and continua given in the solar reference spectrum of Hinteregger from ～1030 to ～34 Å. For the molecules N₂ and O₂, branching ratios are given for ionization into the ground and electronic states of the molecular ions and for dissociative ionization.     

C2F6 /O2 /Ar Plasma Chemistry of 60 MHz/2 MHz Dual-Frequency Discharge and Its Effect on Etching of SiCOH Low-k Films

This work investigated C2F6/O2 /Ar plasma chemistry and its effect on the etching characteristics of SiCOH low-k dielectrics in 60 MHz/2 MHz dual-frequency capacitively coupled discharge. For the C2F6/Ar plasma, the increase in the low-frequency (LF) power led to an increased ion impact, prompting the dissociation of C2F6 with higher reaction energy. As a result, fluorocarbon radicals with a high F/C ratio decreased. The increase in the discharge pressure led to a decrease in the electron temperature, resulting in the decrease of C2F6 dissociation. For the C2F6/O2 /Ar plasma, the increase in the LF power prompted the reaction between O2 and C2F6 , resulting in the elimination of CF3 and CF2 radicals, and the production of an F-rich plasma environment. The F-rich plasma improved the etching characteristics of SiCOH low-k films, leading to a high etching rate and a smooth etched surface.     

Properties of lenticular pores in UO2, (U,Pu) O2 and PuO2

Lenticular pore migration rates in oxide muclear fuels were experimentally measured in out-of-pile heating experiments. It is deduced that those pores which are in part responsible for the formation of columnar grains, are only produced in the absence of relevant amounts of filling gas. Specimens containing important concentrations of He, produced by Pu alpha decay, show columnar grain restructuring by grain boundary migration. Some consequences are drawn concerning the possible role played by lenticular pores in the mechanisms of fission gas release from nuclear fuels.     

O NMR study in (Pu0.91Am0.09)O2

In order to investigate the magnetic properties of Am⁴⁺ ions in the cubic fluorite structure, we have performed ¹⁷O NMR measurements on (Pu_0.91Am_0.09)O₂. We have observed a temperature-dependent ¹⁷O NMR line broadening induced by classical dipolar hyperfine fields from the Am 5f moments. From NMR line simulations, the effective moment of the Am moments has been estimated to be μ_eff=1.38μ_B/Am. This value is comparable with μ_eff=1.32 or 1.53μ_B/Am reported for AmO₂. We have also carried out nuclear relaxation measurements for ¹⁷O nuclei. The magnetization recovery has been found to exhibit a nonexponential time dependence with an exponent β∼0.5. This result is well understood in terms of the nuclear relaxation mechanism induced by the Am 5f moment fluctuations via dipolar hyperfine fields.     

Abnormal Enhancement of N2+ Emission Induced by Lower Frequency in N2 Dual-Frequency Capacitively Coupled Plasmas

Nitrogen dual-frequency capacitively coupled plasmas(DF-CCPs) with different frequency configurations,i.e.,60/2 MHz and 60/13.56 MHz,are investigated by means of optical emission spectroscopy(OES) and a floating double probe.The excited nitrogen molecule ion N + 2(B) is monitored by measuring the emission intensity of the(0,0) bandhead of the first negative system(FNS) at 391.44 nm.It is shown that in the discharge with 60/13.56 MHz,the N + 2 emission intensity decreases with the increase in pressure.In the discharge with 60/2 MHz,however,an abnormal enhancement of N + 2 emission at higher pressure is observed when a higher power of 2 MHz is added.Variation in the ion density shows a similar dependence on the gas pressure.This indicates that in the discharge with 60/2 MHz there is a mode transition from the alpha to gamma type when a higher power of 2 MHz is added at high pressures.Combining the measurements using OES and double probe,the influence of low frequency on the discharge is investigated and the excitation route of the N + 2(B) state in the discharge of 60/2 MHz is also discussed.     

Tuning Effect of N2 on Atmospheric-Pressure Cold Plasma CVD of TiO2 Photocatalytic Films

To deposit TiO2 films through plasma CVD, the partial pressure ratio of O2 to TiCl4 should be greater than the stoichiometric ratio (pO2 /pTiCl4>1). However, this may lead to the formation of powder instead of film on the substrate when using volume dielectric barrier discharge (volume-DBD) at atmospheric pressure. In this study, by adding N2 into the working gas Ar, TiO2 photocatalytic films were successfully fabricated in the presence of excess O2 (pO2 /pTiCl4=2.6) by using a wire-to-plate atmospheric-pressure volume-DBD. The tuning effect of N2 on the deposition of TiO2 film was studied in detail. The results showed that by increasing the N2 content, the deposition rate and particle size of the TiO2 film were reduced, and its photocatalytic activity was enhanced. The tuning mechanism of N2 is further discussed.     

Reactivity of hydrogen peroxide towards Fe3O4, Fe2CoO4 and Fe2NiO4

The kinetics of CRUD oxidation by H₂O₂ has been studied using aqueous suspensions of metal oxide powder. Fe₃O₄, Fe₂CoO₄ and Fe₂NiO₄ were used as model compounds for CRUD. In addition, the activation energies for the reaction between H₂O₂ and the three CRUD models were determined. The rate constants at room temperature were determined to 6.6 (±0.4) × 10⁻⁹, 3.4 (±0.4) × 10⁻⁸ and 1.6 × 10⁻¹⁰ m min⁻¹ for Fe₃O₄, Fe₂CoO₄ and Fe₂NiO₄, respectively. The corresponding activation energies are 52 ± 4, 44 ± 5 and 57 ± 7 kJ mol⁻¹, respectively. The mechanism of the reaction is briefly discussed indicating that the final solid product in all three cases is Fe₂O₃. In addition to the experimental studies, the theoretical grounds for kinetics of reactions in particle suspensions are discussed. The theoretical discussion is also used to explain the somewhat unexpected trends in reactivity observed experimentally.     

Study of Formation and Propagation of Streamers in SF6 and Its Gas Mixtures with Low Content of SF6 Using a One-Dimensional Fluid Model

Using a hybrid Monte Carlo Collision/Fluid model,the formation and propagation of streamers in SF 6 and its gas mixtures are simulated.The simulation is based on an accurate numerical solution of Poisson’s equation in conjunction with the continuity fluid equation for electrons,negative ions,and positive ions.The factors that influence the formation and propagation of streamers are investigated.The electron density,positive and negative ion density,and electric field in the discharge channel are also presented,which are very important in understanding the phenomena of streamers and in assessing the insulation strength of the gas mixture.     

Graphitization of free carbon precipitating through the reaction of UC or UC2 with N2

It has been found by X-ray diffraction that free carbon produced from reaction of UC or UC₂ with nitrogen gas is not graphite but an amorphous carbon. The degree of graphitization increases with increasing temperature and with decreasing pressure of nitrogen gas. Thermodynamic treatment of these amorphous carbons is discussed in terms of the degree of graphitization. The free energies of the amorphous carbons are calculated to be higher by about 500 cal/mol than that of graphite. Furthermore, the influence of the crystal structure of UC or UC₂ on the degree of graphitization is considered qualitatively.     

Thermophysical properties of (U,Y)O2

We prepared polycrystalline pellets of (U,Y)O₂, containing YO_1.5 up to 11 mol.%. We performed indentation tests on the pellets, and evaluated the Young’s modulus and hardness. We measured the heat capacity and the thermal diffusivity, and evaluated the thermal conductivity. We succeeded in evaluating the effect of Y content on the thermophysical properties of (U,Y)O₂. We revealed that the Young’s modulus, hardness, and thermal conductivity of (U,Y)O₂ decreased with increasing the Y content.     

CO2+O2地浸采铀饱和树脂酸化技术与应用

介绍了CO₂+O₂地浸采铀和酸法地浸采铀的水冶回收工艺,依据新疆某地浸铀矿山的铀矿水冶工艺现状,提出将CO₂+O₂地浸采铀工艺下饱和树脂纳入酸法地浸水冶回收系统进行处理的酸化工艺。分析了CO₂+O₂浸出工艺下碳酸铀酰型饱和树脂的酸化转化机理,开展了以酸法水冶系统中淋洗剂、转型剂、洗涤合格液为酸化剂的搅拌浸泡试验。结果表明,酸法水冶系统中的洗涤合格液是符合工艺要求的酸化剂,可充分利用洗涤合格液中的剩余酸度对碳酸铀酰型饱和树脂进行转化,并将转化后树脂对铀的吸附容量由74.71 g/L提高至76.73 g/L,实现了与酸法水冶系统再饱和树脂的共同淋洗和转型。     

Feature Profile Evolution During Etching of SiO2 in Radio-Frequency or Direct-Current Plasmas

We have developed a plasma etching simulator to investigate the evolution of pattern profiles in SiO2 material under different plasma conditions. This model focuses on energy and angular dependent etching yield (physical sputtering in this paper), neutral and ion angular distributions, and reflection of ions or neutrals on the surface of a photoresist or SiO2 . The effect of positive charge accumulation on the surface of insulated mask or SiO2 is studied and the charge accumulation contributes to a deflection of ion trajectory. The wafer profile evolution has been simulated using a cellular-automata-like method under radio-frequency (RF) bias and direct-current (DC) bias, respectively. On the basis of the critical role of angular distribution of ions or neutrals, the wafer profile evolution has been simulated for different variances of angles. Observed microtrenching has been well reproduced in the simulator. The ratio of neutrals to ions has been considered and the result shows that because the neutrals are not accelerated by an electric field, their energy is much lower compared with ions, so they are easily reflected on the surface of SiO2 , which makes the trench shallower.     

Thermal expansion studies on UMoO5, UMoO6, Na2U(MoO4)3 and Na4U(MoO4)4

In the present work, thermal expansion behavior of lower valent sodium uranium molybdates, i.e., Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ were studied under vacuum in the temperature range of 298-873 K using high temperature X-ray diffractometry (HTXRD). Expansion behaviors of UMoO₅ and UMoO₆ were also studied in vacuum from 298 to 873 K and 773 K, respectively. UMoO₅ was synthesized by reacting UO₂ with MoO₃ in equi-molar proportion in evacuated sealed quartz ampoule at 1173 K for 14 h. Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ were prepared by reacting UMoO₅ and MoO₃ with 1 and 2 moles of Na₂MoO₄, respectively, at 873 K in evacuated sealed quartz ampoule. XRD data of UMoO₅ and UMoO₆ were indexed on orthorhombic and monoclinic systems, respectively, whereas, the data of Na₂U(MoO₄)₃ and Na₄U(MoO₄)₄ were indexed on tetragonal system. The lattice parameters and cell volume of all the four compounds, fit into polynomial expression with respect to temperature, showed positive thermal expansion (PTE) up to 873 K.     

NHO3氧化去除Np—Pu反萃液中的H2C2O4

研究了用ＮＨＯ３氧化去除ＴＲＰＯ流程反萃Ｎｐ－Ｐｕ的Ｈ２Ｃ２Ｏ４反萃液中Ｈ２Ｃ２Ｏ４的条件。７．５ｍｏｌ．Ｌ＾－１ＨＮＯ３－０．３ｍｏｌ．Ｌ＾－１Ｈ２Ｃ２Ｏ４混合液于９０℃下蒸发１３０ｈ和１００℃下蒸馏回流６ｈ,Ｈ２Ｃ２Ｏ４可完全分解去除;混合液中添加适量催化剂ＭｎＣＯ３,于１００℃下蒸发或蒸馏回流,Ｈ２Ｃ２Ｏ４分解加速,１－１．５ｈ内Ｈ２Ｃ２Ｏ４完全分解。蒸发或蒸馏回流过程中产生的ＨＮＯ２把Ｎｐ     

Thermal conductivities of irradiated UO2 and (U, Gd)O2 pellets

Thermal diffusivities of UO₂ and (U, Gd)O₂ pellets irradiated in a commercial reactor (maximum burnups: 60 GWd/t for UO₂ and 50 GWd/t for (U, Gd)O₂) were measured up to about 2000 K by using a laser flash method. The thermal diffusivities of irradiated UO₂ and (U, Gd)O₂ pellets showed hysteresis phenomena: the thermal diffusivities of irradiated pellets began to recover above 750 K and almost completely recovered after annealing above 1400 K. The thermal diffusivities after recovery were close to those of simulated soluble fission products (FPs)-doped UO₂ and (U, Gd)O₂ pellets, which corresponded with the recovery behaviors of irradiation defects for UO₂ and (U, Gd)O₂ pellets. The thermal conductivities for irradiated UO₂ and (U, Gd)O₂ pellets were evaluated from measured thermal diffusivities, specific heat capacities of unirradiated UO₂ pellets and measured sample densities. The difference in relative thermal conductivities between irradiated UO₂ and (U, Gd)O₂ pellets tended to become insignificant with increasing burnups of samples.