Formation of a diamond-like phase under conditions of preferential deposition of nondiamond carbon in a microwave gas discharge plasma with electron cyclotron resonance

Films with crystallite sizes up to approximately 0.5 μm were obtained. Results of complex investigations of these films are presented. Pis’ma Zh. Tekh. Fiz. 24, 25–31 (February 26, 1998)     

PECVD of diamond-like carbon (a-C:H) from the decomposition of methane in a high-density inductively coupled discharge

The paper describes an experimental investigation of the diamond-like carbon deposition process from methane precursor with an innovative high-density inductively coupled plasma source. It appears that a high plasma density allows a fast growth of diamond-like carbon coatings exhibiting a high hardness. In contrast to what is usually found in the literature, it seems that the ion species participate significantly to the growth of the carbon film when exposed to a high ion flux.     

Coating of diamond-like carbon nanofilm on alumina by microwave plasma enhanced chemical vapor deposition process

Diamond-like carbon (DLC) nanofilms with thickness varied from under one hundred to a few hundred nanometers have been successfully deposited on alumina substrates by microwave plasma enhanced chemical vapor deposition (MW-PECVD) process. To obtain dense continuous DLC nanofilm coating over the entire sample surface, alumina substrates were pre-treated to enhance the nucleation density. Raman spectra of DLC films on samples showed distinct diamond peak at around 1332 cm(-1), and the broad band of amorphous carbon phase at around 1550 cm(-1). Full width at half maximum height (FWHM) values indicated good formation of diamond phase in all films. The result of nano-indentation test show that the hardness of alumina samples increase from 7.3 +/- 2.0 GPa in uncoated samples to 15.8 +/- 4.5-52.2 +/- 2.1 GPa in samples coated with DLC depending on the process conditions. It is observed that the hardness values are still in good range although the thickness of the films is less than a hundred nanometer.     

The kinetics of a diamond-like film growth in a microwave gas discharge plasma

Spontaneous variations of the microstructure and properties of carbon films during deposition in a microwave gas discharge plasma were studied. The ion current component of the gas discharge plasma favors the selective growth of a diamond-like phase with a thickness exceeding that achieved in the case of a pyrolytic deposition process.     

Modeling of the carbon nanotube chemical vapor deposition process using methane and acetylene precursor gases

Chemical vapor deposition of carbon nanotubes (CNTs) in a horizontal tube-flow reactor has been investigated with a fully coupled reactor-scale computational model. The model combined conservation of mass, momentum, and energy equations with gas-phase and surface chemical reactions to describe the evolution of a hydrogen and hydrocarbon feed-stream as it underwent heating and reactions throughout the reactor. Investigation was directed toward steady state deposition onto iron nanoparticles via methane and hydrogen as well as feed-streams consisting of acetylene and hydrogen. The model determines gas-phase velocity, temperature, and concentration profiles as well as surface concentrations of adsorbed species and CNT growth rate along the entire length of the reactor. The results of this work determine deposition limiting regimes for growth via methane and acetylene, demonstrate the need to tune reactor wall temperature to specific inlet molar ratios to achieve optimal CNT growth, and demonstrate the large effect that active site specification can have on calculated growth rate.     

Appearance of molecular hydrogen in the ultraviolet spectra of diamond-like carbon

Ultraviolet Raman scattering is used to study the state of hydrogen in diamond-like α-C:H. Scattering lines are observed corresponding to transitions between the rotational states of the hydrogen molecule. The interaction with the α-C:H matrix increases the internuclear distance and perturbs the electronic-vibrational terms of the H₂ molecule, so that resonance Raman scattering can be observed, excited by 10.04 eV photons. Pis’ma Zh. Tekh. Fiz. 23, 19–24 (June 26, 1997)     

电沉析条件对钛合金表面液相沉积类金刚石薄膜的影响

在钛合金表面沉积类金刚石膜能改进钛合金的生物相容性，拓展其在人体植入材料中的应用。探讨了用液相电解沉积法在钛合金表面制备类金刚石薄膜的新方法。讨论了不同沉积条件对膜的影响。在1650和1850V时可以得到坚固的棕色膜。沉积36h后，膜厚基本不变。沉积膜的Raman谱图表明，在1650和1850V沉积得到的是类金刚石薄膜，而在2000V时无法得到类金刚石薄膜。对膜的XPS分析表明，其主要成份是碳。XPS谱还表明在1650V时得到的膜可以将钛合金表面完全覆盖，而在1850V时则不能。以SEM分析表明在1650和1850V时得到的膜是由粒径约为400nm的小颗粒组成，而在2000V时得到只是疏松结构。并对类金刚石膜及钛合金的血液相容性进行了比较。     

Effect of hydrogen dilution in preparation of carbon nanowall by hot-wire CVD

Carbon nanowall films prepared on the stainless steel substrates by hot-wire chemical vapor deposition using CH₄ with different hydrogen dilution ratios and structure variation in the CNWs against hydrogen dilution have been studied. In the scanning electron microscope images, the wall height and width in the samples prepared with the hydrogen dilution ratio, H₂/(CH₄ + H₂), between 10% and 25% were larger than that prepared without hydrogen dilution. In the Raman spectra for the samples prepared with the H₂/(CH₄ + H₂) below 25%, the intensity ratio of the G peak to the D peak, I_G/I_D, increased with increasing the H₂/(CH₄ + H₂). In the samples prepared with the H₂/(CH₄ + H₂) over 25%, the wall size and the I_G/I_D decreased.     

Properties and coating rates of diamond-like carbon films produced by R.F. glow discharge of hydrocarbon gases

We studied the properties of films produced by cracking various hydrocarbon gases in an r.f. glow discharge. Mass spectrometry studies and optical spectroscopy of the glow discharge were performed during the experiments.We found that the production rates for the films increased with the molecular weight for gases having the same structural form, e.g.C₄H₁₀ had a higher coating rate than CH₄ under the same plasma conditions. Also the sputter-etch rate of the films depended on both the substrate material and the hydrocarbon gas used.Films several microns thick were manufactured onto steel substrates and showed a microhardness of more than 3000 kgf mm^-2.     

辅助气体组成对类金刚石薄膜结构和性能的影响

分别以氩气-甲烷、氩气-乙炔为辅助气体,高纯石墨为靶材,利用中频脉冲非平衡磁控溅射技术制备了类金刚石薄膜.采用Raman光谱、X射线光电子能谱、纳米压痕测试仪、原子力显微镜对所制备类金刚石薄膜的键结构、机械性能、表面形貌进行了分析.Raman光谱和X射线光电子能谱测试结果表明,以氩气-甲烷为辅助气体制备的类金刚石薄膜中sp3杂化键的含量比以氩气-乙炔为辅助气体制备的类金刚石薄膜的高.纳米压痕测试结果表明,以氩气-甲烷为辅助气体制备的类金刚石薄膜的纳米硬度比以氩气-乙炔为辅助气体的高.原子力显微镜测试结果表明,以氩气-甲烷为辅助气体制备的类金刚石薄膜的RMS表面粗糙度比以氩气-乙炔为辅助气体的低.以上结果说明辅助气体组成对类金刚石薄膜的键结构、机械性能、表面形貌有较大的影响.     

Intrinsic stress in diamond-like carbon films and its dependence on deposition parameters

The compressive stresses and the hydrogen content inside diamond-like carbon films were measured for various deposition conditions. Four methods of film deposition were tested: primary beam containing CH₄; primary beam containing CH₄ with simultaneous bombardment of second beam of energetic argon ions; primary beam containing C₄H₁₀, and sputter deposition of graphite with the addition of hydrogen gas. The compressive stresses in the films were attributed mainly to the bombarding energy of the ion beam. An additional contribution to the compressive stresses probably came from the complex species in the discharge. The contribution of the hydrogen to the stresses in the films did not seem to be obvious.     

Influence of a DC field on the near-electrode zone of nonuniform microwave discharge in hydrogen

We investigate, by the emission spectroscopy, the influence of the DC electric field on the nearsur-face plasma of the electrode microwave hydrogen discharge (EMD) at pressures of 1 to 5 Torr. We obtain the DC current-voltage characteristics of the EMD, the strength values of the microwave field, and its spatial distributions in the EMD near-electrode zone. Under a positive voltage on the electrode as against the chamber, the variation in the discharge structure are minor, and, at the particular voltages depending on the pressure and the microwave power, the spatial charge layer breakdown takes place near the discharge chamber surface. Under a negative voltage on the electrode (the plasma cathode microwave mode), the discharge structure and dimensions vary and, at high currents, the discharge cancels.     

Preparation of diamond-like carbon films by cathodic micro-arc discharge in aqueous solutions

Diamond-like carbon films (DLC) and silicon doped diamond-like carbon films were deposited on Ni substrate by cathodic micro-arc discharge at room temperature in aqueous solutions. The deposit potential was 130 V. The structure of the films was characterized by a scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Raman spectra and XPS analysis demonstrated that the films were diamond-like carbon clearly. SEM observation showed that the DLC films were uniform and the thickness was about 200 nm. Potentiodynamic polarization curve indicated the corrosion resistance of the Ni substrate was markedly improved by DLC films.     

The effect of argon dilution on deposition of microcrystalline silicon by microwave plasma enhanced chemical vapor deposition

Microwave plasma-enhanced chemical vapor deposition (PECVD) is a very promising method for industrial scale fabrication of microcrystalline silicon solar cells since the technique is well applicable for large areas, and high deposition rates can be obtained. We have investigated the effect of Ar dilution on the growth process and the material properties of microcrystalline silicon. The major benefit of Ar addition in the MWPECVD process, using H₂ and SiH₄ as reactant gases, is an improved stabilization of the plasma, in particular at low pressure and MW power. We show, however, that material properties of the microcrystalline silicon layers deteriorate if we partly substitute H₂ by Ar during the deposition. The density of the layers - as expressed by the refractive index - decreases, and the defect density (measured by Fourier transform photocurrent spectroscopy) increases with increasing Ar flow. Investigation of the plasma by optical emission study shows that Ar atoms play a very active role in the dissociation processes of H₂ and SiH₄. Substitution of H₂ by Ar decreases the SiH^? emission and increases the Si^? emission. On the other hand, the H_α/H_β ratio increases upon substitution of H₂ by Ar. The latter effect shows that Ar addition does not lead to higher electron temperatures and we conclude that the changes of SiH^? and Si^? emissions are due to dissociation of SiH₄ by Ar^? (quenching reactions). The precise role of Ar in MWPECVD of microcrystalline silicon needs further investigation, but we conclude that the usage of this gas should be minimized in order to maximize the quality of the silicon layers.     

Effect of substrate pretreatment on diamond deposition in a microwave plasma

The evolution of substrate surface at an early stage of diamond formation in a microwave plasma was studied with a high-resolution scanning electron microscope. Changes in the shape, size and population of diamond particles at the same points were observed at prescribed time intervals. The substrate used was a mirror-polished Si (100) plate which was ultrasonically pretreated with diamond, c-BN or -Al₂O₃ powders prior to the deposition. The pretreatment introduced fragments of the abrasives as well as many scratches on the substrate surface. When the diamond and c-BN abrasive were used, diamond was formed on the surface of abrasive residues. With -Al₂O₃ abrasive powder, on the other hand, residues vanished in the plasma and no deposition was observed. These results suggest that the deposition site of diamond from the vapour phase is dependent on the type of abrasive powder used for substrate pretreatment.     

Fabrication of diamond-like carbon film on rubber by T-shape filtered-arc-deposition under the influence of various ambient gases

Diamond-like carbon (DLC) films were prepared on rubber substrates using T-shape filtered-arc-deposition (T-FAD), which effectively removes the macrodroplets emitted from the graphite cathode spot from the processing plasma. In the present study, the influence of ambient gas (no gas, Ar, H₂, C₂H₂, C₂H₄, CH₄) was investigated. The DLC films adhered well to the rubber substrate. When the substrate was stretched, the small DLC islands were separated and clefs were opened. The deposition rate on rubber was approximately twice higher than that on a Si substrate. When hydrocarbon gas was introduced as an ambient gas, the deposition rate became higher than that for no gas and H₂ gas. In the cases of C₂H₄ and CH₄ gases, the DLC film was considered to contain a considerable amount of hydrogen. When C₂H₂ gas was used, the highest deposition rate with less surface roughness was achieved.     

Application of Ni:SiO2 nanocomposite to control the carbon deposition on the carbon dioxide reforming of methane

Stable Ni nanoparticles embedded in a mesoporous silica material were used as catalysts for the conversion of methane into synthesis gas. This catalyst has the singular properties of controlling the carbon deposition and deactivation of active sites. A comparative study of our nanocomposites with conventional catalysts showed that impregnation material presented a preferential encapsulation and growth of carbon nanotubes on the metal surface. The impregnated catalyst showed a higher tendency for carbon nanotube and whiskers formation.     

Advances of microwave plasma-enhanced chemical vapor deposition in fabrication of carbon nanotubes: a review

Journal of Materials Science - Microwave plasma chemical vapor deposition (MPCVD) has received tremendous research interest in fabrication of carbon nanotubes (CNTs) due to its unique advantages of...     

Formation of carbon nanostructures in the decomposition of methane in the plasma of a high-voltage atmospheric-pressure discharge

Results of experimental investigations of the conditions of formation of carbon nanomaterials in the decomposition of methane in the plasma of a high-voltage atmospheric-pressure discharge have been presented. The influence of the temperature gradient, the cathode material, and the deposition-surface material on the process of formation of carbon nanostructures has been investigated. It has been established that the processes of catalytic decomposition of methane occur, with a large degree of probability, on the metallic deposition surface in the presence of the temperature gradient between the gas flow and the surface. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 4, pp. 617–620, July–August, 2008.     

Aroused problems in the deposition of diamond-like carbon films by using the liquid phase electrodeposition technique

Hydrogenated diamond-like carbon (DLC) films were prepared by using liquid phase electrodeposition technique. The effects of the applied potential and the carbon sources on the deposition process and film structures were studied. It has been found that the organic liquids with high dielectric constants, small viscosities and the methyl group bonding to the polar group are appropriate carbon sources. The increasing of potential improves the formation of sp³ carbon during the deposition process. In a high electric field, organic molecules are polarized and reacted on the surface of the electrode, turning out DLC and other products. It is believed that the reaction follows a polarization-reaction mechanism.