The Transport Properties of Hot Electrons in a Xenon/Methane Mixture

The results are given of numerical solution of the Boltzmann equation in a binomial approximation in view of elastic and inelastic electron collisions in Xe+CH₄ mixtures and in pure methane. The electron energy distribution functions obtained are used to calculate the electron transport coefficients for E/N values of up to several Townsends, i.e., the drift velocity, mobility, average and characteristic energies, diffusion coefficient. The results of calculation for pure methane fit the available experimental data. A similarity rule is found for the electron transport coefficients in a Xe+CH₄ mixture with different concentrations of methane molecules, which enables one to determine the values of transport coefficients in a mixture with a minor (less than 30 percents) methane content.     

Dry etching of TaN thin film using CH4/Ar inductively coupled plasma

In this research, we investigated the TaN etch rate and selectivity with under layer (HfO₂) and mask material (SiO₂) in inductively coupled CH₄/Ar plasma. As the CH₄ content increased from 0% to 80% in CH₄/Ar plasma, the TaN etch rate was increased from 11.9 to 22.8 nm/min. From optical emission spectroscopy (OES), the intensities for CH [431 nm] and H [434 nm] were increased with the increasing CH₄ content from 0% to 100% in CH₄/Ar plasma. The results of x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) showed no accumulation of etch by-products from the etched surface of TaN thin film. As a result of OES, AES and XPS analysis, we observed the etch by-products from the surfaces, such as Ta–N–CH and N–CH bonds. Based on the experimental results, the TaN etch was dominated by the chemical etching with the assistance of Ar sputtering in reactive ion etching mechanism.     

Dry etching of TaN thin film using CH4/Ar inductively coupled plasma

In this research, we investigated the TaN etch rate and selectivity with under layer (HfO₂) and mask material (SiO₂) in inductively coupled CH₄/Ar plasma. As the CH₄ content increased from 0% to 80% in CH₄/Ar plasma, the TaN etch rate was increased from 11.9 to 22.8 nm/min. From optical emission spectroscopy (OES), the intensities for CH [431 nm] and H [434 nm] were increased with the increasing CH₄ content from 0% to 100% in CH₄/Ar plasma. The results of x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) showed no accumulation of etch by-products from the etched surface of TaN thin film. As a result of OES, AES and XPS analysis, we observed the etch by-products from the surfaces, such as Ta-N-CH and N-CH bonds. Based on the experimental results, the TaN etch was dominated by the chemical etching with the assistance of Ar sputtering in reactive ion etching mechanism.     

Study of the law of corresponding states of viscous properties of classical liquids

The law of corresponding states is studied for the coefficients of shear η* _S and volume η* _V viscosities of classical liquids (Ar, Kr, Xe, O₂, N₂, CH₄); the analytical expressions are derived on the basis of kinetic equations for one- and two-particle distribution functions. The reduced iso-frequency coefficients Φ(|r|) and g(|r|) for liquid Ar, Kr, Xe, O₂, N₂, and CH₄ are numerically calculated in a wide range of variations at the reduced temperatures T* and densities ρ*, which satisfy the law of corresponding states, at a definite choice of the intermolecular interaction potential η _S * and radial distribution function η _V *.     

Potential energy of adsorption in A-type zeolites and adsorption thermodynamic characteristics of noble gases and methane

Simple models of the NaA and CaNaA lattice were developed and applied to the computation of the potential energy of interaction of Ar, Kr, Xe and CH₄ molecules with the zeolite lattice at many points in the large cavity. The corresponding potential reliefs have been constructed and are illustrated in this Paper. The spatial distribution of potential energy was used in molecular statistical computations of Henry constants and isosteric heats of adsorption in the low coverage region. Agreement between calculated and observed thermodynamic characteristics was achieved via selection of the most appropriate formula to calculate the constants of dispersion attraction.     

Mechanism of production of ultra-fine silicon carbide powder by arc plasma irradiation of silicon bulk in methane-based atmospheres

The mechanism of production of ultra-fine SiC powder from a silicon bulk by arc plasma irradiation in either an Ar + CH₄ + H₂ or an Ar + CH₄ atmosphere was studied. Layer and island phases were newly formed in the silicon bulk upon irradiation, and it was revealed from scanning electron and Auger electron spectroscopy that these phases were composed of SiC. The intensity of the X-ray diffraction peaks due to the SiC phase increased with irradiation time almost in parallel to the carbon content involved in the silicon bulk. It is proposed that CH₄ is dissociated in the arc plasma and dissolved in the molten silicon bulk to produce the SiC phase, the sublimation of which is mostly responsible for the production of ultra-fine SiC powder.     

Gas Storage in Fullerenes

Abstract

Fullerenes and in particular C₆₀ have been shown to store effectively a wide range of gases from simple monatomic rare gases to diatomics and polyatomics. A review of the research in this area conducted at ANSTO is given. The trapping of Ar, Kr, Xe, and CO₂ are discussed in detail whilst preliminary results pertaining to N₂O, CH₄, CF₄, C₂H₆ and SF₆ are also reported. A range of techniques have been used to elucidate both the structure of the new fullerene intercalated solid and the trapped gas itself. The preponderant techniques used, include infra-red absorption spectroscopy (IR), X-ray powder diffraction a (XRD), neutron powder diffraction (NRD), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA).     

Equations for the second virial coefficients from the barker bobetic potential

The Barker Bobetic potential has been shown to be an accurate approximation to the interatomic potential of argon. In this paper it is shown how, using this potential, series expansions can be obtained which accurately represent the expression for the second virial coefficient, B. These equations were used to calculate the values of B required in obtaining force constants for the BB potential using the method of least squares with experimental data for B. Values for the force constants for the BB potential of Ne, Ar, Kr, Xe, CH₄, CF₄, SF₆, C (CH₃)₄, N₂, O₂, CO, N₂O, C₃H₈, C₂H₄, and CO₂ are tabulated. Some difficulties with the BB potential are also discussed.     

Kinetics of Carbon Multi‐wall Nanotube Synthesis by Catalytic Pyrolysis of Methane

Abstract

By method of isothermal gravimetry at 600–700°C, CH₄ concentration 32–100% in Ar and 91–100% in H₂ under atmospheric pressure the kinetics of CH₄ pyrolysis under Ni/La₂O₃ catalysts is studied. Estimated apparent activation energy of reaction is 73 kJ/mol for fresh catalyst and 71 kJ/mol for aged one. The reaction order on CH₄ changes from 1.05 at 600°C to 1.3 at 700°C. The influence of H₂ concentration on the reaction rate is more complicated. On the basis of kinetics measurements continuously working laboratory‐scale reactor with gas and catalyst counter‐flow is constructed and tested.     

Chemical bonding of a-Ge1−xCx:H films grown by RF reactive sputtering

Amorphous hydrogenated germanium-carbon (a-Ge_1−xC_x:H) films were deposited by RF reactive sputtering pure Ge (1 1 1) target at different flow rate ratios of CH₄/(CH₄+Ar) in a discharge Ar/CH₄, and their composition and chemical bonding were investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). XPS and FTIR results showed the content of germanium in the films decreased with the increase of the flow rate ratio CH₄/(Ar+CH₄), and the Ge-C, Ge-H, C-H bonds were formed in the films. The fraction of Ge-C, Ge-H, and C-H bonds was strongly dependent on the flow rate ratio. Raman results indicated that the films also contain both Ge-Ge and C-C bonding. Based on the change of the chemical bonding of a-Ge_1−xC_x:H films with the flow rate ratio CH₄/(CH₄+Ar), an optimal experimental condition for the application of infrared windows was obtained.     

The influence of CH4 addition on composition, structure and optical characteristics of SiCN thin films deposited in a CH4/N2/Ar/hexamethyldisilazane microwave plasma

Amorphous silicon carbonitride (a-SiCN) thin films were synthesized in a microwave plasma assisted chemical vapor deposition system using N₂, Ar, CH₄ and hexamethyldisilazane vapor (HMDSN). Composition, morphology and optical constants of the layers have been studied as a function of CH₄ rate in the range 0 to 9%. It was found that films are mainly composed of silicon nitride like compound whatever the CH₄ rate. However, CH₄ addition leads to less hydrogenated and denser films. In addition, a refractive index augmentation from 1.7 to 2.0 and a Tauc gap decrease from 5.2 eV to 4.8 eV is measured with CH₄ rate increase. It is believed that the refractive index augmentation is due to higher thin film density whereas hydrogen bonds decrease is assumed to contribute to the band gap narrowing. Besides, CH₄ addition to the gaseous mixture increases thin film oxidation resistance. These results show the ability of varying composition, structure and optical constants of a-SiCN films by modifying CH₄ rate in a N₂/Ar/HMDSN plasma.     

Comparison of Lorentz–Berthelot and Tang–Toennies Mixing Rules Using an Isotropic Temperature-Dependent Potential Applied to the Thermophysical Properties of Binary Gas Mixtures of CH4, CF4, SF6, and C(CH3)4 with Ar, Kr, and Xe

In this paper the isotropic temperature-dependent potential (ITDP) approach and the concepts introduced in our previous papers have been used to calculate equilibrium and transport properties of low-density gas mixtures. The twelve binary mixtures considered here are: Ar–CH₄, Ar–CF₄, Ar–SF₆, Ar–C(CH₃)₄, Kr–CH₄, Kr–CF₄, Kr–SF₆, Kr–C(CH₃)₄, Xe–CH₄, Xe–CF₄, Xe–SF₆ and Xe–C(CH₃)₄. The (n–6) Lennard–Jones potential parameters n (repulsive parameter), R_m (equilibrium distance), and (potential well depth) of the pure noble gases Ar, Kr, and Xe are obtained by a minimization of the sum of squared deviations between experimental and calculated viscosity (), and second pVT (B) and acoustic () virial coefficients normalized to their relative experimental error a_exp. The number of included experimental points for B, , was N = 305, 210, and 167 for Ar, Kr, and Xe, respectively. For the pure globular gases the potential parameters were taken from previous publications. The calculations of B, , and D₁₂ of binary mixtures were compared with experimental data by using two different mixing rules (Lorentz–Berthelot and Tang–Toennies). Recommended sets and fitting formulae for the potential parameters that can be used for the calculation of low-pressure thermophysical properties of these mixtures are provided.     

Reactive ion etching of ZnS films for thin-film electroluminescent devices

Reactive ion etching (RIE), employing CH₄/H₂/Ar plasmas, of ZnS films grown by metalorganic chemical vapor deposition (MOCVD) is reported. The etching rates are investigated as functions of the plasma parameters: pressure, RF power and relative composition of reactive gases. It is found that the amount of CH₄ in a CH₄/H₂/Ar gas discharge will decide whether the polymer will be produced. The optimum composition of the mixed gas is 1CH₄/7H₂/4Ar, when the pressure, RF power and total flow rate are 30 mTorr, 245 W and 30 sccm, respectively. The etching mechanism is also proposed. The quality of the etched surfaces under these conditions is examined by X-ray photoelectron spectroscopy. It is found that the amount of overt damage is small under these etching conditions. A dot-matrix thin-film electroluminescent device employing a ZnS:Mn phosphor layer is also fabricated by this etching process.     

Effect of argon and substrate bias on diamond thin film surface morphology

Nanocrystalline materials are of high interest, because mechanical and physical properties of such materials are different from those or coarse-grained type. Continuous and smooth nanocrystalline diamond (NCD) thin films were successfully grown on mirror polished silicon substrates, using double bias plasma-enhanced hot filament chemical vapour deposition technique. A gas mixture of Ar:CH₄:H₂ and CH₄:H₂ was used as the precursor gas. The effect of the gas composition, flow rate and substrate bias during deposition on diamond crystallite size was investigated. Changing the growth parameters facilitates control of grain size of polycrystalline diamond thin films from microcrystalline to nanocrystalline. The structure of fine-grained NCD films has been studied with scanning electron microscopy and Raman spectroscopy.     

Carbon occupancy of interstitial sites in vanadium carbide films deposited by direct current reactive magnetron sputtering

Vanadium carbide thin films were deposited on Si substrates by direct current reactive magnetron sputtering from a V target in Ar/CH₄ plasma, varying the Ar/CH₄ partial pressure ratio and substrate temperature. The films were characterized by glancing angle X-ray diffraction and Rutherford backscattering spectrometry. Well defined crystalline structures were obtained for CH₄ content higher than 13%. The increase of substrate temperature during deposition diminishes the film thickness slightly while diminishing substantially the C/V atomic ratio. The intensity ratio of the Bragg peaks (111)/(200) decreases for increasing substrate temperature. This result is discussed in terms of a proposed mechanism for interstitial diffusion of carbon atoms in vanadium carbide thin films with fcc-like crystalline structure and the temperature dependence of carbon occupancy of tetrahedral or octahedral interstitial sites.     

Atomic near-infrared noble gas scintillations I: Optical spectra

Particle beam excited emission spectra from Ne, Ar, Kr and Xe in the wavelength range 350–930 nm and in the pressure range 20–200 kPa are studied. Ar, Kr and Xe show dominant emission from neutral atoms in the near-infrared region. For Ne this emission extends from the visible to the near-infrared region.To study the emission spectra of electrostatic field enhanced scintillations a wire was inserted into the chamber and spectra from Ne, Ar, Kr and Xe were recorded with positive and negative wire potentials. The same dominant emission from neutral atoms is present in these spectra. Due to contamination of N₂ in the Ne gas strong emission of N₂ bands are seen in the electrostatic field enhanced scintillation Ne spectra.     

Getter pumping to allow economical sputtering with xenon

Increases in sputter rate, under equivalent commercial operating conditions, can often be achieved by using inert gases heavier than Ar. High atomic weight targets and high sputter voltages result in Kr and Xe having higher sputter yields than Ar. The larger ionization cross sections of Kr and Xe also result in a plasma enhancement. The high consumption rate of sputter gas has previously prevented the economical utilization of Kr and Xe. A d.c.-powered Ti sputter target was added to an r.f. planar diode sputtering system. The sputtered titanium was deposited directly on the vacuum chamber walls to form a large room temperature getter pumping surface. Calculations showed an increase of two orders of magnitude in the pumping speeds of O₂, N₂, H₂O and H₂ over that of a conventional throttled 10 cm diffusion pump. This pumping speed allowed improved sputter cleaning of substrates and the deposition of higher purity films. Operating the Ti getter pump with the diffusion pump closed allowed sputtering with very little inert gas consumption. R.f. sputtering of a Ti target with 750 W at 8 mTorr gas pressure resulted in a sputter gas consumption rate of 3 × 10^-3 cm³ min^-1 for both Ar and Xe. This consumption rate corresponds to a Xe cost of less than 1 ¢ h^-1.     

Vapour-liquid equilibrium of the CH4Ar,CH4CO,and ARCO systems at elevated pressures

High pressure vapour-liquid equilibrium data for the CH₄Ar, CH₄CO, and ArCO systems are presented in this work. The data are obtained isothermally and for each data point T, P, x_i, and y_i are measured. When possible, the measurements are compared to other published data, and good agreement is found with previous investigations.Each isotherm is subjected to a thermodynamic analysis, and activity coefficients are calculated. When both components are condensable, the ordinary symmetrical convention for normalization of activity coefficients is used, and when one component is supercritical, the unsymmetrical convention is used.The activity coefficients are adjusted to a constant pressure via the Poynting correction factor, and these pressure adjusted activity coefficients are subjected to a thermodynamic consistency test based on the isothermal-isobasic form of the Gibbs-Duhem equation. It is found that the maximum inconsistency for the data presented in this work is 10%.     

Nano-crystalline CVD diamond films deposited on cemented carbide using high current extended DC arc plasma process

Nano-crystalline diamond (NCD) films have been grown on cemented carbide substrates by high current extended DC arc plasma process using Ar/H₂/CH₄ gas mixture at low gas pressure. The plain view and cross section of films are characterized with scanning electron microscopy. A uniform and smooth surface morphology of NCD thin films is observed. Raman spectroscopy has been used to investigate purity of the NCD films. Experimental results on the synthesis and characterization of the NCD films on cemented carbide substrates are discussed in this article.     

Etch characteristics of CoFeB magnetic thin films using high density plasma of a H2O/CH4/Ar gas mixture

Etch characteristics of CoFeB magnetic thin films patterned with TiN hard masks were investigated using inductively coupled plasma reactive ion etching in H₂O/Ar and H₂O/CH₄ gas mixes. As the H₂O concentration in the H₂O/Ar gas increased, the etch rates of CoFeB and TiN films decreased simultaneously, while the etch selectivity increased and etch profiles improved slightly without any redeposition. The addition of CH₄ to the H₂O gas resulted in an increase in etch selectivity and a higher degree of anisotropy in the etch profile. X-ray photoelectron spectroscopy was performed to understand the etch mechanism in H₂O/CH₄ plasma. A good pattern transfer of CoFeB films masked with TiN films was successfully achieved using the H₂O/CH₄ gas mix.