Mixtures Of CF4 Research Articles

Reactivity of Callovo-Oxfordian Claystone and its Clay Fraction With Metallic Iron: Role of Non-Clay Minerals in the Interaction Mechanism

AbstractIn order to better understand the possible interactions between steel canisters and a claystone host rock, in this case the Callovo-Oxfordian rock (COx), the present study investigated in detail, under conditions relevant to high-level radioactive waste repositories (anoxic conditions, temperature of 90°C), the reactions between metallic iron and: (1) COx; (2) the clay fraction extracted from COx (CF); and (3) mixtures of CF with quartz, calcite, or pyrite. Batch experiments were then carried out in the presence of NaCl-CaCl2 background electrolyte, for durations of 1, 3, and 9 months. Solid and liquid end-products were characterized by a combination of techniques including liquid analyses, transmission and scanning electron microscopies, X-ray diffraction, N2 adsorption at 77 K, and Mössbauer spectroscopy. The interaction between CF and metallic iron appeared to proceed by means of pathways similar to those illustrated in previous studies on interactions between metallic iron and purified clays. In spite of the many similarities with previous studies, significant differences were observed between the behavior of COx and CF, particularly in terms of pH and Eh evolution, iron consumption, chemical composition of the neoformed particles, and textural evolution. Such differences demonstrate the important role played by non-clay minerals in reaction pathways. The addition of carbonates or pyrite to CF did not lead to significant change in reactivity. In contrast, under the conditions used in the present study, i.e. for relatively low iron:clay ratios, the presence of quartz strongly influenced reaction pathways. In the presence of quartz, magnetite was observed only in trace abundances whereas the amounts of magnetite were significant in experiments without quartz. Furthermore, filamentous serpentine particles with a small Al:Si ratio appeared which could develop from an FeSiAl gel that only forms in the presence of quartz. Considering that most clay rocks currently being considered for radioactive waste disposal contain significant amounts of quartz, the results obtained in the present study may be of significant interest for predicting the long-term behavior of clay barriers in such sites.

Characterization of fluorinated silica thin films with ultra-low refractive index deposited at low temperature

Structural and optical properties of low refractive index fluorinated silica (SiOxCyFz) films were investigated. The films were deposited on p-type silicon and polycarbonate substrates by radio frequency plasma enhanced chemical vapor deposition method at low temperatures. A mixture of tetraethoxysilane vapor, oxygen, and CF4 was used for deposition of the films. The influence of oxygen flow rate on the elemental compositions, chemical bonding states and surface roughness of the films was studied using energy dispersive X-ray analyzer, Fourier transform infrared spectroscopy in reflectance mode and atomic force microscopy, respectively. Effects of chemical bonds of the film matrix on optical properties and chemical stability were discussed. Energy dispersive spectroscopy showed high fluorine content in the SiOxCyFz film matrix which is in the range of 7.6–11.3%. It was concluded that in fluorine content lower than a certain limit, chemical stability of the film enhances, while higher contents of fluorine heighten moisture absorption followed by increasing refractive index. All of the deposited films were highly transparent. Finally, it was found that the refractive index of the SiOxCyFz film was continuously decreased with the increase of the O2 flow rate down to the minimum value of 1.16±0.01 (at 632.8nm) having the most ordered and nano-void structure and the least organic impurities. This sample also had the most chemical stability against moisture absorption.

Characterization and optimization to improve uneven surface on MEMS bridge fabrication

This paper presents an optimized fabrication method for developing a freestanding bridge for RF MEMS switches. In this method, the sacrificial layer is patterned and hard baked a 220°C for 3min, after filling the gap between the slots of the coplanar waveguide. Measurement results by AFM and SEM demonstrate that this technique significantly improves the planarity of the sacrificial layer, reducing the uneven surface to less than 20nm, and the homogeneity of the Aluminum thickness across the bridge. Moreover, a mixture of O2, Ar and CF4 was used and optimized for dry releasing of the bridge. A large membrane (200×100μm2) was released without any surface bending. Therefore, this method not only simplifies the fabrication process, but also improves the surface flatness and edge smoothness of the bridge. This fabrication method is fully compatible with standard silicon IC technology.

Chemistry studies of SF6/CF4, SF6/O2 and CF4/O2 gas phase during hollow cathode reactive ion etching plasma

In this work, mass spectrometry and optical emission spectroscopy techniques were used to monitor the molecular and atomic neutral species during SF6/CF4, SF6/O2 and CF4/O2 plasmas generated in a radio-frequency Hollow Cathode Reactive Ion Etching (HCRIE) reactor keeping constant the following operational conditions: total gas flow rate, gas pressure, and discharge power. The investigations were aimed to understand the chemistry behavior of plasmas generated with SF6 and CF4 mixtures or mixed separately with O2. The neutral mass spectrometry analysis showed a high concentration of gas species namely SF5+ (parent specie = SF6), SF3+ (SF4), CF3+ (CF4) and HF+ (HF) in SF6/CF4 plasmas, SF5+, SF3+, O2+ (O2), F+ (F) and HF+ in SF6/O2 plasmas and CF3+, O2+, CO2+ (CO2) and HF+ in CF4/O2 plasmas. The presence of other species was observed in quantities lower than 1% of total gas pressure. It was used the actinometry method to monitor the atomic fluorine (F) concentration during discharge operation. Higher density of F was observed in all experiments, varying from (2.8–9.5) × 1019 m−3 in SF6/CF4 plasmas, (0.2–1.7) × 1020 m−3 in SF6/O2 plasmas and (0.06–1.17) × 1020 m−3 in CF4/O2 plasmas. The addition of CF4 in SF6 plasma reduces monotonically the F concentration when compared with the SF6/O2 and CF4/O2 plasmas that promotes an increase of F for low O2 concentrations. This effect shows the importance of oxygen species in the dissociative processes of the fluorine-based plasma also for this type of plasma reactor. Moreover, it is highlighted the higher concentrations of HF in gas phase that promotes reactions paths that decrease the F species in gas/plasma phase.

Determination of the Rate Constant for the OH(X2Π) + OH(X2Π) → H2O + O(3P) Reaction Over the Temperature Range 295 to 701 K

The rate constant for the radical-radical reaction OH(X(2)Π) + OH(X(2)Π) → H2O + O((3)P) has been measured over the temperature and pressure ranges 295-701 K and 2-12 Torr, respectively, in mixtures of CF4, N2O, and H2O. The OH radical was produced by the 193 nm laser photolysis of N2O. The resulting O((1)D) atoms reacted rapidly with H2O to produce the OH radical. The OH radical was detected by high-resolution time-resolved infrared absorption spectroscopy using a single Λ-doublet component of the OH(1,0) P1e/f(4.5) fundamental vibrational transition. A detailed kinetic model was used to determine the reaction rate constant as a function of temperature. These experiments were conducted in a new temperature controlled reaction chamber. The values of the measured rate constants are quite similar to the previous measurements from this laboratory of Bahng and Macdonald (J. Phys. Chem. A 2007 , 111 , 3850 - 3861); however, they cover a much larger temperature range. The results of the present work do not agree with recent measurements of Sangwan and Krasnoperov (J. Phys. Chem. A 2012 , 116 , 11817 - 11822). At 295 K the rate constant of the title reaction was found to be (2.52 ± 0.63) × 10(-12) cm(3) molecule(-1) s(-1), where the uncertainty includes both experimental scatter and an estimate of systematic errors at the 95% confidence limit. Over the temperature range of the experiments, the rate constant can be represented by k1a = 4.79 × 10(-18)T(1.79) exp(879.0/T) cm(3) molecule(-1) s(-1) with a uncertainty of ±24% at the 2σ level, including experimental scatter and systematic error.

Low-pressure plasma-etching of bulk polymer materials using gas mixture of CF4 and O2

In this study, we have proposed a low-pressure reactive ion etching of bulk polymer materials with a gas mixture of CF4 and O2, and have achieved precise fabrication of poly(methyl methacrylate) (PMMA) and perfluoroalkoxy (PFA) bulk polymer plates with high-aspect-ratio and narrow gap array structures, such as, pillar, frustum, or cone, on a nano/micro scale. The effects of the etching conditions on the shape and size of each pillar were evaluated by changing etching duration and the size/material of etching mask. The fabricated PMMA array structures indicate possibilities of optical waveguide and nanofiber array. PFA cone array structures showed super-hydrophobicity without any chemical treatments. Also, polystyrene-coated silica spheres were used as an etching mask for the pillar array structure formation to control the gap between pillars.

Study of the dielectric breakdown properties of hot SF6–CF4 mixtures at 0.01–1.6 MPa

The dielectric breakdown properties of SF6–CF4 mixtures were investigated at different ratios of SF6, 0.01–1.6 MPa, and gas temperatures up to 3000 K. Initially, the equilibrium compositions of SF6–CF4 mixtures were calculated by minimizing the Gibbs free energy under the assumptions of local thermodynamic and chemical equilibrium. Then the electron energy distribution function was obtained based on those data by solving the Boltzmann equation under the zero-dimensional two-term spherical harmonic approximation. Finally, the critical reduced electric field strength (E/N)cr of SF6–CF4 mixtures, which is defined as the value for which total ionization reaction is equal to total attachment reaction, were determined and analyzed. The results confirm the superior breakdown properties of pure SF6 at relatively low gas temperatures. However, for higher gas temperatures (i.e., T > 2200 K at 0.4 MPa), the (E/N)cr in SF6–CF4 mixtures are obviously higher than that in pure SF6 and the values of (E/N)cr increase with the reduction of the ratio of SF6.

Simulations and Experiments on O Density and Distribution in Ashing Process Using Surface Plasma Excited by Microwave

Simulation methods for the density and spatial distribution of O atoms have been developed to analyze high-density plasma (1011 cm-3) excited by two microwave sources. The density of O atoms, that react with photoresist, was calculated in a gas mixture of CF4 and O2, and the density has a maximum value at 10% CF4 partial pressure. For the distribution simulation, the rate of reaction between O atoms and photoresist was measured in a small cell, and the sticking coefficient was estimated to be 0.002. The O atom distribution on a glass substrate was calculated by the simulator, where the sticking coefficient was input, focusing on the density under a beam that connected the microwave sources and had no plasma source. The results of both the simulations are in good agreement with the experimental results. The simulations were applied to optimize the chamber configuration and process conditions. As a result, a high ashing rate of over 1430 nm with a uniformity of ±9.3% was obtained.

Thermal stability and mechanical properties of fluorinated diamond-like carbon coatings

Diamond-like carbon (DLC) coatings with variable fluorine content were produced by a plasma assisted chemical vapour deposition (PACVD) technique, based on a remote plasma configuration. The feed gas consisted of mixtures of C2H2 and CF4 and the fluorine percentage in the coatings was in the range of 0–36at.%. Competition between fluorine and hydrogen in defining the coating composition is discussed. Microindentation experiments were performed to evaluate hardness and elastic modulus, which were found to decrease as the fluorine content increases. A similar trend was shown by the internal stress of the coatings. Adhesion to the substrate was assessed by scratch tests and high critical load was achieved with moderate fluorine content (12at.%). The counteracting effects of internal stress and interface toughness may explain this behaviour.The thermal stability of the coatings was investigated by performing annealing treatments in a vacuum furnace at 500°C for variable times. All tested samples maintained their integrity at the end of the heat treatments, but the fluorine content and hardness decreased as the annealing time increased. Coatings with low fluorine content retained good hardness after being annealed for 57.6ks (16h).

Primary scintillation characteristics of Ar+CF4 gas mixtures excited by proton and alpha particles

In this paper, we report how the concentration of carbon-tetrafluoride (CF4) affects the primary scintillation from Ar+CF4 gas mixtures excited by proton and alpha particles. The single photon counting method was used to measure the time spectra of the primary scintillation from Ar, CF4 and their mixtures at atmospheric pressure. Pure Ar exhibits a fast decay time constant, which is approximately 6ns, and a slow decay time tail. Initially, increases in the concentration of CF4 increase the decay time of the Ar+CF4 gas mixture. However, when the concentration of CF4 exceeds a certain threshold, the decay time decreases to that of pure CF4, approximately 8–9ns. We also report the photon emission spectra of Ar+CF4 mixtures excited by protons. The emission spectrum of the primary scintillation from Ar is improved by CF4 in both the ultraviolet region and the visible to near-infrared region.

CF4, CH4, Ar 혼합기체의 전리와 부착계수

Ionization and Attachment Coefficients in pure CH<SUB>4</SUB>, CF<SUB>4</SUB> and mixtures of CF<SUB>4</SUB> and Ar, have been analyzed over a range of the reduced electric field strength between 0.1 and 350[Td] by the two-term approximation of the Boltzmann equation (BEq.) method and the Monte Carlo simulation (MCS). The calculations of electron swarm parameters require the knowledge of several collision cross-sections of electron beam. Thus, published momentum transfer, ionization, vibration, attachment, electronic excitation, and dissociation cross-sections of electrons for CH<SUB>4</SUB>, CF<SUB>4</SUB> and Ar, were used. The results of the Boltzmann equation and the Monte Carlo simulation have been compared with the data presented by several workers. The deduced transport coefficients for electrons agree reasonably well with the experimental and simulation data obtained by Nakamura and Hayashi. The energy distribution function of electrons in CF<SUB>4</SUB>-Ar mixtures shows the Maxwellian distribution for energy. That is, f(ε) has the symmetrical shape whose axis of symmetry is a most probably energy. The proposed theoretical simulation techniques in this work will be useful to predict the fundamental process of charged particles and the breakdown properties of gas mixtures.BR

Abatement of CF4 and CHF3 byproducts using low-pressure plasmas generated by annular-shaped electrodes

Three different driving schemes are tested for a plasma reactor designed to abate the greenhouse gases emitted by the semiconductor industry. The reactor and electrodes all have a concentric annular shape, which allows them to be easily connected to pre-existing pipelines without any disturbance to the exhaust stream. The destruction and removal efficiencies are measured for CF4 by varying the O2/CF4 ratio and pressure. The influences of adding O2 and H2O to the byproducts of the CHF3 abatement process are investigated by analyzing the spectra resulting from Fourier transform infrared spectroscopy measurements. Based on the experimental results we suggest an appropriate combination of driving scheme and reactant gas species for efficient and economical abatement of a mixture of CHF3 and CF4. Then, the optimal flow rate of the reactant gas is presented. Finally, the reduction rates for global warming emissions are estimated to demonstrate the feasibility of using our device for abatement of greenhouse gases emitted by the semiconductor industry.

The Discrimination Capabilities of Micromegas Detectors at Low Energy

The latest generation of Micromegas detectors show a good energy resolution, spatial resolution and low threshold, which make them idoneous in low energy applications. Two micromegas detectors have been built for dark matter experiments: CAST, which uses a dipole magnet to convert axion into detectable x-ray photons, and MIMAC, which aims to reconstruct the tracks of low energy nuclear recoils in a mixture of CF4 and CHF3. These readouts have been respectively built with the microbulk and bulk techniques, which show different gain, electron transmission and energy resolutions. The detectors and the operation conditions will be described in detail as well as their discrimination capabilities for low energy photons will be discussed. c � 2011 Elsevier BV. Selection and/or peer-review under responsibility of the organizing committee for TIPP 2011.

The DRIFT Directional Dark Matter Experiments

The current status of the DRIFT (Directional Recoil Identification From Tracks) experiment at Boulby Mine is presented, including the latest limits on the WIMP spin-dependent cross-section from 1.5 kg days of running with a mixture of CS2 and CF4 . Planned upgrades to DRIFT IId are detailed, along with ongoing work towards DRIFT III, which aims to be the world’s first 10 m3 -scale directional Dark Matter detector.

Simulation program for multiwire-type two-dimensional neutron detector with individual readout

We are currently developing a multiwire-type two-dimensional neutron detector system for use at the Materials and Life Science Experimental Facility at J-PARC. This system can attain a high response time and a high spatial resolution using the individual line readout method, and the performance parameters of the system strongly depend on a gas composition and pressure of a fill gas that is a gas mixture of He-3 and CF4. A simulation program for our system was developed to determine this gas condition. In addition, a small detector prototype was fabricated to evaluate the simulation program. The program involves the following calculations for each gas condition: the probability of a reaction between a neutron and He-3, the ranges of secondary particles generated by the nuclear reaction, the ejection angle of the particles, the wall effect caused by the conversion gap, and the pitch of the multiwire element. The simulation results agreed well with the experimental results obtained using the small detector prototype. Thus, it was confirmed that the simulation program can be effectively used to determine the gas composition and pressure when the required spatial resolution and detection efficiency are known.

OES Diagnostics of HMDSO/O&lt;sub&gt;2&lt;/sub&gt;/CF&lt;sub&gt;4&lt;/sub&gt; Microwave Plasma for SiOC&lt;sub&gt;x&lt;/sub&gt;F&lt;sub&gt;y&lt;/sub&gt; Films Deposition

SiOF like films have been elaborated in microwave excited DECR plasma reactor (Distributed Electron Cyclotron Resonance) from a mixture of oxygen-hexamethyldisiloxane (HMDSO/O2) and CF4. The fluorine contents in the precursor mixture were adjusted by varying the CF4 gas flow ratio in the range of 10% - 70%. Optical emission spectroscopy (OES) and Fourier transform infrared (FTIR) have been used for the plasma diagnostic and the deposited films structure analysis, respectively. Actinometric technique was used to find trends in the concentrations of species present in the plasma. A large number of species have been detected, such as F, Si, O, C and H. Depending on the gas mixture composition, FTIR spectra revealed the presence of several chemical bonds such as Si-F and Si-O.

Plasma Etching for Failure Analysis of Integrated Circuit Packages

Plastic integrated circuit packages with copper wire bonds are decapsulated by a Microwave Induced Plasma system. Improvements on microwave coupling of the system are achieved by frequency tuning and antenna modification. Plasmas with a mixture of O2 and CF4 showed a high etching rate around 2 mm3/min. The role of O2 and CF4 in etching molding compound is described. Plastic package with 38 um Cu bond wires and a 2 mm * 3.5 mm die inside is fully decapsulated in 20 minutes. Cu wires remain undamaged after decapsulation proving the efficiency of this method.

Hydrophobic treatment of organics against glass employing nonequilibrium atmospheric pressure pulsed plasmas with a mixture of CF4 and N2 gases

A hydrophobic organics surface selectively against glass was realized by employing nonequilibrium atmospheric-pressure pulsed plasmas with a mixture of CF4 and N2 gases. The organic surface was drastically altered to have a high hydrophobicity, while the glass surface itself remained hydrophilic after the plasma treatment with the addition of a small amount of CF4 to the N2 gas. After 100 CF4/N2 plasma treatments, no thin film deposition was observed on the organic material. To investigate the characteristics of the CF4/N2 plasma, the exhaust gas from the plasma was measured by using ion attachment mass spectroscopy (IAMS). The IAMS spectrum indicated that the amounts of CF3 and F radicals were increased drastically with increasing addition of CF4. A mechanism of the selective surface modification was clarified on a result of surface chemical bonding with the gas phase.

Plasma etching of polydimethylsiloxane: Effects from process gas composition and dc self-bias voltage

Films made of polydimethylsiloxane elastomers have been etched using reactive ion etching. The elastomers are etched using different mixtures of CF4, SF6, and O2 as process gases. The etch rate and profile of the etched area are measured as function of the process pressure for different process gas compositions. At low pressure the highest etch rate is achieved in SF6+O2 plasma. At high pressure the highest etch rate is achieved in CF4+SF6+O2 plasma. The profile of the etched surface is strongly dependent on the process gas composition and the dc bias voltage in the plasma.

Electron transport coefficients in mixtures of CF4 and CF2 radicals

Electron kinetics determines the rate of production of chemically active species in processing plasmas. Precise transport coefficients are needed to describe conditions such as those found in plasma assisted technologies for semiconductor production, but these are affected by the density of free radicals, which in themselves depend on the chemical kinetics. We present transport coefficients for electrons in mixtures of CF4 with CF2 (and we also show similar results for other radicals) for ratios of the electric field to the gas number density E/N from 1 to 1000 Td (1 Td = 10−21 V m2). Our analysis of non-conservative collisions revealed a range of E/N where electron attachment to radicals significantly changes the electron kinetics compared with pure CF4 gas. The results are obtained using simple solutions for Boltzmann's equation and exact Monte Carlo simulations.