CF4 Gas Research Articles

Mode transition in CF4 + Ar inductively coupled plasma

The E to H mode transitions are studied by a hairpin probe and optical emission spectroscopy in inductively coupled CF4 + Ar plasmas. Electron density, optical emission intensity of Ar, and the voltage and current are measured during the E to H mode transitions. It is found that the electron density and plasma emission intensity increase continuously at low pressure during the E to H mode transition, while they jump up discontinuously at high pressure. Meanwhile, the transition threshold power and △P (the power interval between E and H mode) increase by increasing the pressure. When the ratio of CF4 increases, the E to H mode transition happens at higher applied power, and meanwhile, the △P also significantly increases. Besides, the effects of CF4 gas ratio on the plasma properties and the circuit electrical properties in both pure E and H modes were also investigated. The electron density and plasma emission intensity both decrease upon increasing the ratio of CF4 at the two modes, due to the stronger electrons loss scheme. The applied voltages at E and H modes both increase as increasing the CF4 gas ratio, however the applied current at two modes behave just oppositely with the gas ratio.

Hydrophobic, mechanical, and tribological properties of fluorine incorporated hydrogenated fullerene-like carbon films

Abstract Fluorine-incorporated hydrogenated fullerene-like nanostructure amorphous carbon films (F-FLC) were synthesized by employing the direct current plasma enhanced chemical vapor deposition (dc-PECVD) technique using a mixture of methane (CH4), tetra-fluoromethane (CF4), and hydrogen (H2) as the working gases. The effect of the fluorine content on the bonding structure, surface roughness, hydrophobic, mechanical, and tribological properties of the films was systematically investigated using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Raman analysis, atomic force microscope (AFM), contact angle goniometer, nano-indenter, and reciprocating ball-on-disc tester, respectively. The fluorine content in the films increased from 0 to 2.1 at.% as the CF4 gas flow ratio increased from 0 to 3 sccm, and incorporated fluorine atoms existed in the form of C-F X (X = 1, 2, 3) bonds in the film. The fullerene nanostructure embedded in the hydrogenated amorphous carbon films was confirmed by Raman analysis. The water contact angle was significantly increased because of fluorine doping, which indicates that the hydrophobicity of the carbon films could be adjusted to some extent by the fluorine doping. The hardness and elastic modulus of the films remained relatively high (22 GPa) as the fluorine content increased. Furthermore, the friction coefficient of the carbon films was significantly reduced and the wear resistance was enhanced by fluorine doping.

A study of Ar + C2H4 and Xe + CF4 gas mixtures

Mixtures of Ar + 40 ppm C2H4 and 50% Xe + 50%CF4 have been investigated. The spatial distributions of photoelectron clouds produced by primary scintillations on α- and β-particle tracks, as well as the distributions of photoelectron clouds due to photons from avalanches at the pin anode, have been measured for the first time. For a mixture of 50% Xe + 50%CF4, it has been shown for the first time that CF4 is a photosensitive dopant in a mixture with Xe. For a mixture of Xe + CF4 (1: 1), the maximum electron multiplication factors at the pin anode are K(β)max = 3 × 104 and K(α)max = 3 × 103 at a pressure of 1 atm (abs.) and K(β)max = 104 and K(α)max = 4 × 103 at a pressure of 10 atm (abs.)

Low Energy Investigations at Kamioka Observatory

At Kamioka Observatory many activities for low energy rare event search are ongoing. Super-Kamiokande(SK), the largest water Cherenkov neutrino detector, currently continues data taking as the fourth phase of the experiment (SK-IV). In SK-IV, we have upgraded the water purification system and tuned water flow in the SK tank. Consequently the background level was lowered significantly. This allowed SK-IV to derive solar neutrino results down to 3.5 MeV energy region. With these data, neutrino oscillation parameters are updated from global fit; Δm212 = 7.44+0.2−0.19 × 10−5eV2, sin2 θ12 = 0.304 ± 0.013, sin2 θ13 = 0.0301+0.017−0.015. NEWAGE, the directional sensitive dark matter search experiment, is currently operated as "NEWAGE-0.3a" which is a 0.20 × 0.25 × 0.31 m3 micro-TPC filled with CF4 gas at 152 Torr. Recently we have developed "NEWAGE-0.3b". It was succeeded to lower the operation pressure down to 76 Torr and the threshold down to 50 keV (F recoils). XMASS experiment is looking for scintillation signals from dark matter interaction in 1 ton of liquid xenon. It was designed utilizing its self-shielding capability with fiducial volume confinement. However, we could lower the analysis threshold down to 0.3 keVee using whole volume of the detector. In February 2012, low threshold and very large exposure data (5591 kg·days) were collected. With these data, we have excluded some part of the parameter spaces claimed by DAMA/LIBRA and CoGeNT experiments.

Metal–Organic Vapor Phase Epitaxy Growth of Embedded Gallium Nitride Nanocolumn for Reduction in Dislocation Density

The use of nanocolumn crystals is thought to be effective in producing a low-dislocation-density GaN layers. In this paper, we propose a metal–organic vapor phase epitaxial (MOVPE) growth method for producing uniform GaN nanocolumns using deep through-holes in a thick SiO2 selective growth mask. A SiO2 film with a thickness of 500 nm was deposited by sputtering on an AlN buffer layer/SiC substrate. A nanoimprinting technique was applied to produce dot openings. Then, dry etching with CF4 gas was carried out to form deep through-holes in the SiO2 film. In the second MOVPE growth, individual GaN nanocolumns coalesced into a planarized GaN layer, after thinning the SiO2 mask to 100 nm. A cathode-luminescence image of the GaN layer on a GaN nanocolumn template shows a low dislocation density of 1.3×108 cm-2, while that of a GaN layer directly grown on an AlN buffer layer shows a dislocation density of 9.4×108 cm-2.

Evaluation of the Reliability of Insulating Gases for the Bushing in Cryogenic Environment

Conventional high-voltage bushings, which adopt SF6 gas as an insulation media, cannot be directly applied in cryogenic environment due to the liquefaction of SF6 gas. In our previous study, it was shown that SF6 gas could not be used as an insulation gas in cryogenic environment, but instead, CF4 gas has shown excellent insulation properties with little liquefaction phenomena, and have a possibility to be applied for the insulation gas for high-voltage bushings in cryogenic environment. However, in order to apply CF4 gas for cryogenic bushing, it should be determined whether CF4 gas can maintain its insulation characteristics in long-term operation. In order to reveal the long-term insulation properties of various gases, which have a possibility to be applied in high-voltage bushings in cryogenic environment, the long-term breakdown characteristics of CF4 gas, SF6 gas, N2 gas, and dry-air were compared over time in a cryogenic environment. For an experiment, a high-vacuum cryostat and a cryo-cooler were prepared to prevent the evaporation of liquid nitrogen for long-term duration. An fiberglass reinforced plastics bushing was installed on the cryostat to apply high voltage up to 60 kV. A rod to plane electrode was set in a cryostat to determine the breakdown voltage of insulating gases. The lightning impulse and ac overvoltage tests have been performed and the test results were analyzed. From the test, the reduction of breakdown voltage of CF4 gas were observed as time passed by, and it was more severe in SF6 . However, stable breakdown characteristic have been shown with N2 gas. Therefore, increasing the pressure of N2 would be a viable option for increasing the breakdown voltage in a cryogenic environment.

High precision measurements of carbon disulfide negative ion mobility and diffusion

High precision measurements were made of reduced mobility, lateral and longitudinal diffusion of CS2(-) ions in 40 Torr CS2 and a 30-10 Torr CS2-CF4 gas mixture. The reduced mobility was found to be 0.4645 ± 0.0006 cm(2) atm/s V in CS2 and 0.523 ± 0.001 cm(2) atm/s V in the CS2-CF4 gas mixture at STP. The lateral diffusion temperatures for these two gases (295 ± 15 K and 297 ± 6 K) were found to be in good agreement with room temperature. By contrast longitudinal diffusion temperature was found to be slightly elevated (319 ± 10 (stat) ± 8 (sys) K and 310 ± 20 (stat) ± 6 (sys) K) though given the errors, room temperature diffusion cannot be ruled out. For lateral diffusion, significant capture distances (0.21 ± 0.07 mm and 0.15 ± 0.03 mm) were measured while for longitudinal diffusion the results were not conclusive.

Fabrication of Flux Qubit with a Mechanical Degree of Freedom

We report on the fabrication and characterization of superconducting flux qubit coupled to nanomechanical resonator vibration modes. Anisotropic and isotropic etching processes parameters of plasma created by a reactive ion etching of a CF4 gas, were optimized to suspend one arm of the qubit. One of the beams was characterized using a magnetomotive detection scheme in the transmission regime. And suspended beams with different length coupled to a superconducting flux qubits were characterized at base temperature by performing spectroscopy measurements.

Effects of gas flow rate on the etch characteristics of a low-k sicoh film with an amorphous carbon mask in dual-frequency CF4/C4F8/Ar capacitively-coupled plasmas

Highly selective nanoscale etching of a low-dielectric constant (low-k) organosilicate (SiCOH) layer using a mask pattern of chemical-vapor-deposited (CVD) amorphous carbon layer (ACL) was carried out in CF4/C4F8/Ar dual-frequency superimposed capacitively-coupled plasmas. The etching characteristics of the SiCOH layers, such as the etch rate, etch selectivity, critical dimension (CD), and line edge roughness (LER) during the plasma etching, were investigated by varying the C4F8 flow rate. The C4F8 gas flow rate primarily was found to control the degree of polymerization and to cause variations in the selectivity, CD and LER of the patterned SiCOH layer. Process windows for ultra-high etch selectivity of the SiCOH layer to the CVD ACL are formed due to the disproportionate degrees of polymerization on the SiCOH and the ACL surfaces.

Applicability of molecular simulations for modelling the adsorption of the greenhouse gas CF4 on carbons

Tetrafluoromethane, CF4, is a powerful greenhouse gas, and the possibility of storing it in microporous carbon has been widely studied. In this paper we show, for the first time, that the results of molecular simulations can be very helpful in the study of CF4 adsorption. Moreover, experimental data fit to the results collected from simulations. We explain the meaning of the empirical parameters of the supercritical Dubinin–Astakhov model proposed by Ozawa and finally the meaning of the parameter k of the empirical relation proposed by Amankwah and Schwarz.

Using an 80% CF4+20% CO2 gas mixture to recover aged anode wires in proportional chambers

A technique to recover a gas proportional counter with an aged anode wire using a glow discharge in an 80%CF4+20%CO2 gas mixture, has been developed and tested. Studies of aging effects were carried out under sustained irradiation by an intense 90Sr β-source of straw proportional counters operated with a 60%Ar+30%CO2+10%CF4 gas mixture. Special attention was paid to the aging mechanism of the anode wires. Our experience showed that using a given gas mixture the swelling of the anode wires is a typical mode of aging that leads to degradation of the gas gain. The proposed method restores the gas gain and the signal amplitude in the damaged zone of the wire. SEM/XEM analysis confirmed that the tungsten oxide deposits have been removed.

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.

Microstructure, mechanical properties and wetting behavior of F: Si–C–N films as bio-mechanical coating grown by DC unbalanced magnetron sputtering

A systematic structure and properties investigation on the deposition of fluorinated silicon–carbon–nitride (Si–C–N) films under varying CF4 flows was carried out by direct current unbalanced magnetron sputtering techniques. Significant role of fluorine and carbon-doped on growth characteristics and mechanical properties in the film was observed. The chemical bonding configurations, surface topography and mechanical properties were characterized by means of X-ray photoelectron spectroscopy (XPS), Raman and infrared spectroscopies, atomic force microscopy (AFM) and nano-indentation technique and CSM pin-on-disk tribometer. It was found that the as-deposited F: Si–C–N films are amphipathic nature, and large variations took place these films’ deposition rate, composition, microstructure and mechanical properties when CF4 flows varied from 0 to 9sccm. At CF4 gas flow rate 9sccm, the F: Si–C–N coatings demonstrated a fluorine content of 5.95at.% and a moderate friction coefficient of 0.03. It is obvious from the hardness results that the F: Si–C–N coating enhances the hardness of the Co–Cr–Mo alloy to approximately 16.3GPa on a smoother surface. The tribological characterization of Co–Cr–Mo alloy with F: Si–C–N coating sliding against ultrahigh molecular weight polyethylene (UHMWPE) counter-surface in fetal bovine serum, shows that the wear resistance of the F: Si–C–N coated Co–Cr–Mo alloy/UHMWPE sliding pair show much obviously improvement over that of uncoated Co–Cr–Mo alloy/UHMWPE sliding pair. The F: Si–C–N and Si–N films have potential properties for joint surface modification applications.

Characteristic Variations of Graphene Field-Effect Transistors Induced by CF4Gas

The influence of tetrafluoromethane (CF4) gas on the electrical characteristics of monolithic graphene field-effect transistors (FETs) is reported. Compared with the results in nitrogen ambient, FETs in CF4 ambient exhibit a positive shift in the Dirac point voltage and an increase in drain current. These changes are ascribed to the electronegative nature of the fluorine atoms in CF4 gas, which is found to induce p-type doping and excess charge carriers in graphene. The electrical response to CF4 gas exposure demonstrates the feasibility of using monolithic graphene FETs as chemical sensors.

Nanoscale dry etching of germanium by using inductively coupled CF4 plasma

The nanoscale dry etching of germanium was investigated by using inductively coupled CF4 plasma and electron-beam lithography. The optimal dose of PMMA as E-beam lithography resist was ∼200 mC/cm2. When ICP Power was 200W, CF4 gas flow rate was 40 sccm, and process pressure was 20 mTorr, it had a smooth surface and good etch rate. The etching selectivity of Ge wafer to PMMA resist was as low as ∼1.5. Various sub-100 nm dry-etching patterns have been obtained. SEM pictures showed good profile qualities with a smooth etching sidewall and ultrasmall etching features.

Application of nanosphere lithography to charge trap flash memories with patterned Si3N4 trap layers

Graphical abstractDisplay Omitted Highlight? Nanosphere lithography is applied to the charge trap flash memories. ? A 500-nm-diameter polystyrene bead array was used as a mask to make patterns. ? The pattern depth measured by atomic force microscope was about 4 nm. ? The patterned MANOS capacitor shows a good memory characteristics. In this paper, nanosphere lithography (NSL) is applied to the surface of the Si3N4 trap layer in the charge trap flash device to improve its memory characteristics. A 500-nm-diameter polystyrene bead array was used as a mask to make patterns on the surface of the Si3N4 trap layer during etching processes using CF4 gases. The pattern depth measured by atomic force microscope was about 4nm. The metal-aluminum oxide-nitride-oxide-silicon capacitor that has a patterned surface shows a larger capacitance-voltage memory window of 5V, higher tunneling current at bias voltages higher than 10V, and faster program speeds of 50ms, as compared to those measured from the capacitor with the flat surface. These results are thought to be due to abundant memory traps available at the interface between the nitride and top oxide formed by NSL.

Characteristic Variations of Graphene Field-Effect Transistors Induced by CF4 Gas

The influence of tetrafluoromethane (CF4) gas on the electrical characteristics of monolithic graphene field-effect transistors (FETs) is reported. Compared with the results in nitrogen ambient, FETs in CF4 ambient exhibit a positive shift in the Dirac point voltage and an increase in drain current. These changes are ascribed to the electronegative nature of the fluorine atoms in CF4 gas, which is found to induce p-type doping and excess charge carriers in graphene. The electrical response to CF4 gas exposure demonstrates the feasibility of using monolithic graphene FETs as chemical sensors.

Neutron beam tests for Micro Pixel Chamber (μ-PIC)

We have tested the Micro Pixel Chamber (μ- PIC) with a fast neutron source which is a candidate to replace the forward muon trigger system of the ATLAS experiment in the luminosity upgrade. We performed the test of the behavior of μ-PIC under a high neutron background environment, as is expected in ATLAS, using a 7 MeV neutron beam at Kobe University. In order to find the gas mixture with less sparks, spark rates were measured for several gas mixtures; Ar+C2H6, Ne+C2H6, and Ne+C2H6+CF4 gases. Using tungsten and nickel for the drift mesh, the effects of sparks from detector materials were also studied. In this paper, we concentrate on the setup for the neutron tests. The details of the experimental results can be found in [1].

A prototype detector for directional measurement of the cosmogenic neutron flux

This paper describes a novel directional neutron detector. The low pressure time projection chamber uses a mix of helium and CF4 gases. The detector reconstructs the energy and angular distribution of fast neutron recoils. This paper reports results of energy calibration using an α source and angular reconstruction studies using a collimated neutron source. The best performance is obtained with a 12.5% CF4–87.5% He gas mixture. At low energies the target for fast neutrons transitions is primarily helium, while at higher energies, the fluorine contributes as a target. The reconstruction efficiency is both energy and target dependent. For neutrons with energies less than 20MeV, the reconstruction efficiency is ∼40% for fluorine recoils and ∼60% for helium recoils.

Dark Matter Time Projection Chamber : Recent R&D Results

The Dark Matter Time Projection Chamber collaboration recently reported a dark matter limit obtained with a 10 liter time projection chamber filled with CF4 gas. The 10 liter detector was capable of 2D tracking (perpendicular to the drift direction) and 2D fiducialization, and only used information from two CCD cameras when identifying tracks and rejecting backgrounds. Since that time, the collaboration has explored the potential benefits of photomultiplier tube and electronic charge readout to achieve 3D tracking, and particle identification for background rejection. The latest results of this effort is described here.