Diamond synthesis from CO-H2 mixed gas plasma

Particulate or film-like diamond was prepared on silicon substrates from CO-H₂ mixed gas using a microwave plasma technique. The growth rate of diamond without graphite and amorphous carbon, as measured by Raman spectroscopy, was 9m h^–1 for particles and 4mh^–1 for flims. These values were larger than those in other source gas systems, such as CH₄-H₂, CH₄-H₂-H₂O and CH₃OH-H₂. The good formation rate and high quality of diamond in the CO-H₂ system was attributed to acceleration of methyl radical formation by the reaction of excited CO and H₂ molecules and removal of by-product graphite by OH radicals in the plasma.     

Pressure-pulsed chemical vapour infiltration of SiC to porous carbon from a gas system SiCl4-CH4-H2

SiC matrix was deposited into porous carbon from a gas system SiCl₄-CH₄-H₂ in the temperature range 900–1200 °C using pressure-pulsed chemical vapour infiltration (PCVI) process. At 1000 °C, silicon single phase, a mixed phase of (Si + SiC), and SiC single phase, were detected by X-ray diffractions for specimens obtained with the reaction time per pulse of 1, 2–3, and 5 s, respectively. At 1100 °C, SiC single phase was obtained with a reaction time of only 0.3s. Between 1050 and 1075 °C, deposition rate accelerated suddenly. The increase of SiCl₄ concentration increased the deposition rate linearly up to 4%–6%. The residual porosity decreased from 29% to 6% after 2×10⁴ pulses of CVI at 1100 °C, and the flexural strength was 110 MPa.     

Pressure pulsed chemical vapour infiltration of SiC to two-dimensional-Tyranno/SiC-C preforms

Preforms of two-dimensional Tyranno fibre (SiC base) of 7×20×1.3 mm³ were chemically vapour infiltrated with SiC at 850–1050 °C from a gas mixture of CH₃SiCl₃ (6%)-H₂ using pressure pulses between below 0.3 kPa and 0.1 MPa. Above 900 °C, films grew on the macrosurface dominantly. At 850 °C, residual porosity decreased to about 10% after 10⁵ pulses, and three point flexural strength reached about 200 MPa. X-ray diffractograms (XRDs) on the surface showed the deposits to be -SiC only.     

The relation of hardness to toughness and retained austenite content in N2-H2-CH4 sintered T6, T15 and T42 high-speed steels

The increase of toughness, 10 to 35 MPam^1/2, with decreasing hardness,V _H 950 to 500, is reported for sintered T6, T15 and T42 high-speed steels. This range of properties resulted from combinations of sintering temperatures (in N₂-H₂-CH₄), HIPping and tempering treatments of steels processed from water-atomized powders. Toughness is related to the properties of the matrix, but more specifically to the retained austenite content, varying between 5% (HV10 950,K _lc 10 MPam^1/2) and 70% (HV10 500,K _lc 35 MPam^1/2). Austenite retention is caused by the stabilizing affect of nitrogen (0.3 to 0.7%), picked up from the sintering atmosphere. Fractographic examination revealed that, although failure proceeded by complex modes that could be described mainly as quasi-cleavage, microplasticity was observed in the high austenite materials, as opposed to the flatter fracture surfaces, with much less plasticity apparent, for the lower retained austenite-containing materials.     

Deposition characteristics and properties of iron nitride films by CVD using organometallic compound

Iron nitride films were prepared by chemical vapour deposition from the gas mixture of Fe(C₅H₅)₂-NH₃-H₂-CO₂. The effects of deposition parameters on the deposition characteristics were investigated. Iron nitride films were deposited above 500 ° C and the films of -Fe₄N single phase were deposited above 700 ° C. At 700 ° C and under the total gas flow rate from 1 to 8 l min^–1, the deposition rate of the film may be controlled by the transport of Fe(C₅H₅)₂ molecules to the surface of the deposits. At 700 °C and under the total gas flow rate of 4 l min^–1, the phases and nitrogen contents of the films were determined bypNH₃/pH₂ ^3/2, the controlling factor of the nitrogen contents of the films. Decreasing of the total gas flow rate and increasingpCO₂ increased the nitrogen contents of the films and phases with higher nitrogen were deposited. On the other hand, increasingpFe(C₅H₅)₂ and the absence ofpCO₂ increases the carbon contents of the films, and the phase with a greater solubility in carbon, i.e. -Fe₂N, was codeposited with -Fe₄N. The saturation magnetization of the films deposited at 700 ° C was in good agreement with that reported for the bulk iron nitride, which depended not on the deposition conditions but on the nitrogen contents of the films.     

Characteristics of nano-crystalline diamond films prepared in Ar/H2/CH4 microwave plasma

Characteristics of nano-crystalline diamond (NCD) thin films prepared with microwave plasma chemical vapor deposition (CVD) were studied in Ar/H₂/CH₄ gas mixture with a CH₄ gas ratio of 1-10% and H₂ gas ratio of 0-15%. From the Raman measurements, a pair of peaks at 1140 cm^− 1 and 1473 cm^− 1 related to the trans-polyacetylene components peculiar to nano-crystalline diamond films was clearly observed when the H₂ gas ratio of 5% was added in Ar/H₂/CH₄ mixture. With an increase of H₂ gas content up to 15%, their peaks decreased, while a G-peak at roughly 1556 cm^− 1 significantly increased. The degradation of NCD film quality strongly correlates with the decrease of C₂ optical emission intensity with the increase of hydrogen gas contents. From the surface analysis with atomic force microscopy (AFM), it was found that grain sizes of NCD films were typically of 10-100 nm in case of 5% H₂ gas addition.     

On the chemical vapour deposition of Ti3SiC2 from TiCl4-SiCl4-CH4-H2 gas mixtures

In the ternary system Ti-Si-C, the ternary compound Ti₃SiC₂ seems to exhibit promising thermal and mechanical properties. Its synthesis as a thin film from the vapour phase is very difficult owing to the complexity of the system. A contribution to the knowledge of the CVD of Ti₃SiC₂ from a TiCl₄-SiCl₄-CH₄-H₂ gas mixture is proposed on the basis of a thermodynamic approach. This approach is based on a reliable estimation of Ti₃SiC₂ thermodynamic data in good accordance with recent experimental results on its thermal stability. A first equilibrium calculation for the deposition on an inert substrate shows the influence of the experimental parameters on the composition of both the deposit and the gas phase. As a result, the deposition of Ti₃SiC₂ can be favoured by an excess of TiCl₄ ( 45%), a rather low pressure (10–20 kPa), high temperature ( 1273 K) and low H₂ dilution ratio. On the basis of equilibrium calculations for various reactive substrates, complex mechanisms of Ti₃SiC₂ deposition are pointed out, with intermediate steps of substrate consumption, e.g. the formation of TiC from a carbon substrate or TiSi₂ from a silicon substrate.     

Growth and structure of TiC coatings chemically vapour deposited on graphite substrates

TiC coatings were grown on graphite substrates by the chemical vapour deposition technique, using gas mixtures of CH₄-TiCl₄-H₂ at a total pressure of 10.7 kPa and at temperatures of 1400 and 1425 K. The growth rate and structure of the TiC coatings were investigated as a function of CH₄ and H₂ concentrations. The deposition rate of TiC increased with increasing CH₄ flow rate, but did not change with H₂ flow rate. This behaviour was explained by a mass transport theory. Thermodynamic analyses based on minimization of Gibbs' free energy predicted carbon codeposition with TiC. X-ray diffraction and Auger electron spectroscopy (AES) studies and microstructural observations, however, suggested that free carbon did not form. Textural analyses indicated that the growth of TiC coatings was initiated as randomly oriented crystallites, and as the thickness of the coatings increased, preferentially oriented columnar grains developed. The textures of TiC coatings with the same thickness changed from the 110 orientation to the 100 orientation with decreasing H₂ flow rate for a constant CH₄ flow rate. The CH₄ concentration also greatly influenced the preferred orientation of the coatings.     

Effects of applied power on hydrogenated amorphous carbon (a-C:H) film deposition by low frequency (60 Hz) plasma-enhanced chemical vapor deposition (PECVD)

Hydrogenated amorphous carbon (a-C:H) films were deposited onto glass substrates using low frequency (60 Hz) plasma-enhanced chemical vapor deposition and the effects of the applied power on a-C:H films deposition were investigated. During deposition, the electron temperature and the density of CH₄-H₂ plasma were 2.4-3.1 eV and about 10⁸ cm⁻³, respectively. The main optical emission peak of the carbon species observed in the CH₄-H₂ plasma is shown to be excited carbon CH* at 431 nm. The sp³/sp² ratio, band gap, hydrogen content, and refractive index of a-C:H films gradually increased up to a power of 25 W and then saturated at higher power. This tendency is similar to the variation of plasma parameters with varying applied power, thereby indicating that a strong relationship exists between the properties of the films and the plasma discharge.     

Lipon thin films grown by plasma-enhanced metalorganic chemical vapor deposition in a N2-H2-Ar gas mixture

Lithium phosphorus oxynitride (Lipon) thin films have been deposited by a plasma-enhanced metalorganic chemical vapor deposition method. Lipon thin films were deposited on approximately 0.2 μm thick Au-coated alumina substrates in a N₂-H₂-Ar plasma at 13.56 MHz, a power of 150 W, and at 180 °C using triethyl phosphate [(CH₂CH₃)₃PO₄] and lithium tert-butoxide [(LiOC(CH₃)₃] precursors. Lipon growth rates ranged from 10 to 42 nm/min and thicknesses varied from 1 to 2.5 μm. X-ray powder diffraction showed that the films were amorphous, and X-ray photoelectron spectroscopy (XPS) revealed approximately 4 at.% N in the films. The ionic conductivity of Lipon was measured by electrochemical impedance spectroscopy to be approximately 1.02 μS/cm, which is consistent with the ionic conductivity of Lipon deposited by radio frequency magnetron sputtering of Li₃PO₄ targets in either mixed Ar-N₂ or pure N₂ atmosphere. Attempts to deposit Lipon in a N₂-O₂-Ar plasma resulted in the growth of Li₃PO₄ thin films. The XPS analysis shows no C and N atom peaks. Due to the high impedance of these films, reliable conductivity measurements could not be obtained for films grown in N₂-O₂-Ar plasma.     

Preparation of silicon carbide powders by chemical vapour deposition of the SiH4-CH4-H2 system

Chemical vapour deposition (CVD) of the SiH₄ + CH₄ + H₂ system was applied to synthesize-silicon carbide powders in the temperature range 1523 to 1673 K. The powders obtained at 1673 K were single-phase-SiC containing neither free silicon nor free carbon. The powders obtained below 1623 K were composite powders containing free silicon. The carburization ratio (SiC/(SiC + Si)) increased with increasing reaction temperature and total gas flow rate, and with decreasing reactant concentration. The average particle sizes measured by TEM ranged from 46 to 114nm, The particle size increased with the reaction temperature and gas concentration but decreased with gas flow rate. The-SiC particles obtained below 1623 K consisted of a silicon core and a-SiC shell, as opposed to the-SiC particles obtained at 1673 K which were hollow. Infrared absorption peaks were observed at 940 and 810 cm^–1 for particles containing a silicon core; whereas a single peak at about 830 cm^–1 with a shoulder at about 930 cm^–1 was observed for the-SiC hollow particles. The lattice parameter of-SiC having a carburization ratio lower than 70 wt%, was larger than that of bulk-SiC and decreased with the increasing carburization ratio. However, when the carburization ratio exceeded 70 wt%, the lattice parameter became approximately equal to that of bulk-SiC.     

Formation of mixed TiC/Al2O3 layers and αa- and κ-Al2O3 on cemented carbides by chemical vapour deposition

Al₂O₃ and Ti(C, O) were codeposited as a mixed chemical vapour deposition (CVD) layer from AlCl₃-TiCl₄-CH₄-CO₂-H₂ gas mixtures on cemented carbides and pure alumina substrates. A thermodynamical approach of this CVD system is presented. The coatings were described by SEM and X-ray diffraction analysis. They consist of large facetted-Al₂O₃ crystals containing some titanium and surrounded by a fine grained Ti(C, O) matrix. Carbon diffusing from the cemented carbide substrate can considerably influence the morphology and the composition of the mixed coating.Methane in a AlCl₃-CO₂-H₂ environment stabilizes the-Al₂O₃ phase which can be deposited as a compact layer without whisker formation on a WC-Co substrate even without a TiC underlayer.     

Hysteresis,structural and composition characteristics of deposited thin films by reactively sputtered titanium target in Ar/CH4/N2 gas mixture

Abstract

Hysteresis, crystal structure and chemical composition of thin films deposited through reactive sputtering of titanium metal target in Ar/CH₄/N₂ gas mixture have been investigated. The transition from metallic to compound sputtering mode was clearly seen as the reactive gases (CH₄ and N₂) flowrate concentration first increased and subsequently decreased. Abrupt cathode current drop from 273 mA to reach a minimum value of 195 mA was observed upon addition of nitrogen gas from 0 to 10% flowrate concentration to the Ar/CH₄ gas mixture. This was also accompanied by an abrupt change in reactive gas partial pressure. Exploration of the deposition rate and film thickness showed that it decreased from 4·5 to 1·5 nm min^?1 and from 140 to 40 nm as the N₂ flowrate concentration increased from 1·5 to 7·5% at 5·5%CH₄ flowrate concentration respectively. X-ray diffraction and X-ray photoelectron spectroscopy analyses of the deposited films confirmed the formation of titanium carbide and carbonitride phases as the methane and nitrogen gas concentrations in the sputtering gas were increased.     

Preparation of silicon carbide powders by chemical vapour deposition of the (CH3)2SiCl2-H2 system

Silicon carbide (SiC) powders were prepared by chemical vapour deposition (CVD) using (CH₃)₂SiCl₂ and H₂ as source gases at temperatures of 1273 to 1673 K. Various kinds of SiC powders such as amorphous powder, -type single-phase powder and composite powder were obtained. The composite powders contained free silicon and/or free carbon phases of about a few nanometres in diameter. All the particles observed were spherical in shape and uniform in size. The particle size increased from 45 to 130 nm with decreasing reaction temperature and gas flow rate, as well as with increasing reactant concentration. The lattice parameter of the -SiC particles decreased with increasing reaction temperature. All the lattice parameters were larger than those of bulk -SiC.     

Properties of stannic oxide thin films produced from the SnCl4-H2O and SnCl4-H2O2 reaction systems

Transparent and conductive stannic oxide films were produced at the relatively low temperature of 250°C from the SnCl₄-H₂O and SnCl₄-H₂O₂ reaction systems by a chemical vapour deposition method. The films were not doped with impurities. Films formed from the first system are superior to those formed from the second with respect to electrical properties although they have a lower deposition rate at the same deposition temperature. The former system gives rise to films with resistivities in the range 10–10^-3 Ω cm between 250 and 400°C. The latter system produces films with resistivities in the range 10²–10^-2 Ω cm between 250 and 450°C. The electrical properties depend on the absorption of hydrogen peroxide as well as on the grain size, which depends on the deposition temperature and the reaction system. The spectral transmissivity for films 0.36–1.1 μm thick varies over the range 80–95% in the regions between 400 and 650 nm for both systems. Different reaction mechanisms take place in different temperature regions for both systems since there are two activation energies in the plot of deposition rate as a function of temperature.     

The effect of input gas ratio on the growth behavior of chemical vapor deposited SiC films

In an effort to protect a RBSC (reaction-bonded silicon carbide) reaction tube, SiC films were chemically vapor deposited on RBSC substrates. SiC films were prepared to investigate the effect of the input gas ratios (dilute ratio, = P _H2/P _MTS = Q _H2/Q _MTS) on the growth behavior using MTS (metyltrichlorosilane, CH₃SiCly₃) as a source in hydrogen atmosphere. The growth rate of SiC films increased and then decreased with the decrease of the input gas ratio at the deposition temperature of 1250°C. The microstructure and preferred orientation of SiC films were changed with the input gas ratio; Granular type grain structure exhibited the preferred orientation of (111) plane in the high input gas ratio region ( = 3–10). Faceted columnar grain structure showed the preferred orientation of (220) plane at the low input gas ratios ( = 1–2). The growth behavior of CVD SiC films with the input gas ratio was correlated with the change of the deposition mechanism from surface kinetics to mass transfer.     

Plasma enhanced chemical vapor deposition of nanocrystalline silicon films from SiF4-H2-He at low temperature

A high degree of crystallinity is obtained in nc-Si:H films deposited by r.f. PECVD, produced from SiF₄-H₂-He mixtures. The amorphous-to-nanocrystalline transition is favored because of the presence of F atoms, which preferentially etch the amorphous phase. The addition of He to the SiF₄-H₂ gas mixture gives an increase of F and H atoms in the plasma, thus inducing higher crystallinity. A further improvement in the nc-Si:H film structure and properties is obtained by adjusting the r.f. power and the deposition temperature. Under optimized plasma conditions, substrate temperatures as low as 120°C can be reached for the deposition of nc-Si:H having 100% of crystallinity.     

Chemical vapour growth of HfC whiskers and their morphology

HfC whiskers were prepared from a gas mixture of HfCl₄ + CH₄ + H₂ + Ar in the presence of metal impurities, and the growth conditions and morphology were examined. The HfC whiskers preferentially grew at an H/Cl ratio of above 8, an HfCl₄ gas flow rate of 10–20 standard cm³ min^–1, a CH₄ flow rate of 10–20 standard cm³ min^–1, and at temperatures above 1050 °C. HfC whiskers, 60–170 m long, with a ball-like tip and periodically varying diameters, were obtained at 1250 °C using a cobalt impurity.     

The dissolution of Na2O-MgO-CaO-SiO2 glass in aqueous HF solutions

The dissolution (or etching) of a multicomponent (Na₂O-MgO-CaO-SiO₂) silicate glass in aqueous HF solutions is studied. The solutions were chosen in the systems HF-HNO₃-H₂O, HF-HCl-H₂O and HF-H₂SO₄-H₂O, and the temperatures varied from 25 to 60° C. SEM micrographs of the glass surface after etching show an orange peel surface structure which develops during etching and which originates from surface flaws. The dissolution rate of the glass was found to increase with higher HF concentration, higher strong-acid concentrations and higher temperatures. The dissolution rate is determined by the reaction of HF molecules and HF₂ ions with the Si-O-Si grouping surrounding the SiO₄ tetrahedron. In the multicomponent glass some of these bonds are non-bridging due to the presence of Na₂O, CaO and MgO, increasing the dissolution rate significantly. H⁺ ions introduced by adding strong acids to the etch solution adsorb on the surface and catalyse the dissolution reaction. Several models used to describe the relation between the dissolution rate and the H⁺ concentration are discussed.