Formation Of Carbon Films Research Articles

Amorphous hydrogenated carbon film formation from benzene by electron cyclotron resonance chemical vapor deposition

Amorphous hydrogenated carbon thin films have been deposited from benzene vapor in an electron cyclotron resonance plasma-enhanced chemical vapor deposition reactor. The effects of gas flow rate, pressure, and microwave power on deposition rates, chemical structure and composition, and on film density were investigated. Plasma enhanced dissociation and ionization reactions were monitored by mass spectrometry and by optical emission spectroscopy. Dissociation products included a variety of unsaturated hydrocarbon species (primarily ethylene) and hydrogen. Deposited films were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, and fluorescence spectroscopy. Films displayed a condensed, aromatic, hydrocarbon-like structure, albeit without extensive conjugation. Possible reaction sequences leading to the observed film structures have been proposed.

On the Kinetics of Heterogeneous Acetylene Pyrolysis

The independent experimental data on the variation of the rate of carbon film formation on the hot cylinder surface in an acetylene–argon flow are theoretically analyzed. The quantitative model uses the detailed mechanism of the gas-phase pyrolysis of acetylene and takes into account both thermal conductivity and diffusion of the gaseous components in the boundary layer. An increase in the rate of the heterogeneous thermal decomposition of acetylene experimentally observed at high temperatures cannot be described within the framework of the pyrocarbon formation mechanism that accounts for the contribution of the products of the partial gas-phase pyrolysis of acetylene. The experimental data are quantitatively described using the model developed earlier for the growth of soot particles. The quantitative macrokinetics of the heterogeneous growth of the carbon film is determined assuming that the above description correctly reflects an experimental increase in the rate of the heterogeneous reaction.

Formation of crystalline diamond by ion beam deposition

Direct ion beam deposition was used to study the effect of ion bombardment on the formation of carbon films. Amorphous carbon films were deposited on mirror-polished (0 0 1) silicon substrates by means of a low-energy ion beam of Ar/H 2/CH 4. High-resolution transmission electron microscopy, field emission scanning electron microscopy and micro-Raman microscopy were used to determine some of the properties of the samples. We found that the amorphous carbon film condensed to form clusters and the surface roughness of the film increased with increasing the ion dose. At ion doses ∼10 19/cm 2, crystalline diamond particles with sizes of 15–30 nm were formed in the matrix of amorphous carbon films. The formation of crystalline diamond particles may be due to the ion bombardment induced stress and energy fluctuation.

Characterization and enhanced properties of plasma immersion ion processed diamond-like carbon films

The formation and properties of diamond-like carbon (DLC) films prepared on silicon substrates at room temperature, using C2H2–Ar plasma immersion ion processing, are investigated with respect to film deposition parameters. Decreases in the reactive gas-flow ratios of C2H2 to Ar(FC2H2/FAr) or the gas pressure were found to decrease the hydrogen content, increase the density and hardness, and improve the surface finish of the DLC films, all of which led to enhanced tribological properties. Decreasing the friction coefficient requires increasing the hardness of the film and smoothing its surface, whereas increasing the wear resistance correlates with reducing both the hydrogen content and residual stress in DLC films. High hardness and optimum tribological properties were reached as the growth of DLC films was subjected to low-energy ion impingement, which was induced by a −150 V pulsed bias from the C2H2–Ar plasma produced at low reactive gas pressures with low FC2H2/FAr ratios.

Formation and characteristics of undoped and doped tetrahedral amorphous carbon films

Abstract Synthesis of undoped and doped tetrahedral amorphous carbon (ta-C) films has been achieved using magnetic field filtered plasma stream system in an ambient gas of pure Ar and Ar with N 2 , respectively. The optical and electrical properties of these films as a function of the substrate bias voltages ( V b ) or nitrogen partial pressures ( P N ) have been studied using UV-visible optical absorption spectroscopy, Fourier-transform infra-red spectroscopy (FTIR) and measurements of electrical conductivity. The results show that ta-C films with a high sp 3 fraction were formed when the V b was in the range of −10 to −50 V. The optical band gap of such ta-C films was found to be larger than 3 eV. The incorporation of nitrogen into the ta-C films deposited at low P N ( P N

High rate deposition of diamond-like carbon films by sheet-like plasma chemical vapor deposition

A high deposition rate of 0.69 μm/min was achieved in the formation of diamond-like carbon (DLC) film with sufficient hardness and flatness under a high density, widely spread sheet-like plasma at room temperature. The argon plasma was generated by a dc arc plasma gun under a magnetic field and it decomposed the toluene gas which was fed into the deposition chamber. During the deposition, the substrate was negatively biased by radio frequency (rf) in order to improve the hardness of the films. The DLC films were characterized by Raman and infrared absorption spectrometers. An optical emission spectrometer and a quadrupole mass spectrometer were used to identify the radicals in the plasma. The influence of the discharge current on the film properties is discussed.

Early stages of carbon film growth: carbide interface formation on molybdenum

In this study we present an investigation of the carbide formation and early stages of carbon film growth using a low energy carbon beam to supply the growth species. Carbon is supplied through electron beam evaporation of graphite and between 0.1 and 40 ML are deposited on a molybdenum substrate (substrate temperature 400 °C). Photoelectron spectroscopy in the ultraviolet and X-ray regime was employed to characterize the surface and observe the carbide and carbon film formation. Two regimes, with respect to the surface composition, can be identified: firstly, the carbide formation, and, secondly the growth of a pure carbon overlayer. A carbide interface with Mo 2 C stoichiometry is created, and the formation of a pure amorphous carbon layer is observed for carbon coverages exceeding about 3.4 ML. But even after the onset of carbon film growth, the carbide interface growth is not terminated, and the extension of the carbide region into the bulk continues to increase. Diffusion through the carbide interface is still present and a dynamic rather than static interfacial layer exists. The diffusion of carbon through the metal carbide dominates the interface formation, which is also evidenced by a delayed onset of carbon film formation at 600 °C. Apart from the observation of interface formation, this experiment also enabled us to observe the valence band spectrum of molybdenum carbide (Mo 2 C) for the first time. The sequential deposition of carbon was shown to be a suitable method to produce clean carbide surfaces.

Effect of oxygen on ion-beam induced synthesis of SiC in silicon

The properties of Si-structures with a buried silicon carbide (SiC) layer created by high-dose carbon implantation into Cz–Si or Fz–Si wafers followed by high-temperature annealing were studied by Raman and infrared spectroscopy. The effect of additional oxygen implantation on the peculiarities of SiC layer formation was also studied. It was shown that under the same implantation and post-implantation annealing conditions the buried SiC layer is more effectively formed in Cz–Si or in Si (Cz-or Fz-) subjected to additional oxygen implantation. So we can conclude that oxygen in silicon promotes the SiC layer formation due to SiO x precipitate creation and accommodation of the crystal volume in the region where SiC phase is formed. Carbon segregation and amorphous carbon film formation on SiC grain boundaries were revealed.

Solid Solubility of Nitrogen in Amorphous Carbon Films Deposited in Electron Cyclotron Resonance Plasma

Electron cyclotron resonance plasma is used in the formation of nitrogen-containing carbon films with a CH4+N2 gas mixture. To accelerate cations from the plasma room, rf-induced negative dc bias voltage is applied to the Si substrate. An increase in negative bias is effective for implantation of nitrogen, however, the nitrogen fraction saturates at [N]/([N]+[C])=0.09 at 300 V. The results of X-ray photoelectron spectroscopy suggests that the films have the C–N–C bond or nitrogen terminates the carbon dangling bond. In addition, ion acceleration causes a G-band and a D-band to appear on IR spectrum, which would normally appear on the Raman spectrum obtained from typical diamond-like carbon films. Furthermore, the hardness and maximum Young's modulus of nitrogen-containing carbon films are comparable to those of most diamond-like carbon films.

Dynamic behavior of carbon ultrathin film formation

We present here investigations of the initial steps in the formation of ultrathin carbon films on a carbon highly oriented pyrolytic graphite substrate by the deposition of low energy carbon ions at temperatures from ambient to 300 °C. We used an ultrahigh vacuum scanning tunneling microscopy to observe the growth of these films. At a nanometer scale, we revealed a roughening transition of the island’s growth, from lateral to tridimensional growth. Also, here we introduce the scaling analysis of roughness to describe the evolution of the morphology of the interface during growth. The ultrathin film formation mechanisms are studied as a function of ion density and annealing.

The formation of diamond-like carbon films due to molecular impacts on graphite

Abstract Molecular dynamics simulation is used to investigate the formation of diamond-like carbon films due to energetic impacts of large molecules such as fullerene C 60 , bucky tubes C 100 and C 200 and polyethylene on a graphite surface. The local densification around the impact site and the consequent change in the bonding of both the constituent atoms of the striking molecule and the struck graphite target surface are analysed as a function of the energy per particle of the incoming molecule. Simulation data are presented in the relative probability of forming sp 3 - and sp 1 -bonded carbon from the energetic collision of these molecules with the surface. It is found that the ratio of sp 3 and sp 1 bonds create peaks at around 100 eV per atom.

Formation of silicon carbide and amorphous carbon films by pulse biasing silicon to a high voltage in a methane electron cyclotron resonance microwave plasma

Silicon was pulse biased to −45 kV in a methane plasma generated by microwave excitation in the electron cyclotron resonance (ECR) mode. Hydrocarbon ions were accelerated in the electrical field and implanted into the silicon. Rutherford backscattering (RBS) measurements showed that it is possible to incorporate a concentration of up to 95 at.% C into the Si. Cross-section transmission microscopy (XTEM) showed that the resulting surface layer was amorphous. Annealing at 1250 °C resulted in the formation of 10 to 60 nm thick, crystalline SiC layers.

The interaction of carbon with the diamond surface: An in-situ photoelectron spectroscopy investigation

Abstract An investigation of the interaction of carbon with the diamond surface serves as a model experiment to study different aspects of diamond growth. The electronic structure of the surface, which is closely linked to the geometric arrangement of the atoms, is probed by photoelectron spectroscopy in the ultraviolet (UPS) and X-ray (XPS) regime. The carbon was supplied by electron beam evaporation of graphite and was deposited on polycrystalline diamond films. Carbon films with a thickness between 0.2 and 15 monolayers (ML) are deposited on the diamond surface at two different substrate temperatures (ambient and 700°C). Even at elevated substrate temperatures, diamond growth cannot be continued. In the course of carbon film formation we observe in the gradual emergence of the p - π band (ambient temperature), connected to the formation of an amorphous carbon film, or graphitic features (700°C) in the valence band (VB) spectra, which is accompanied by the disappearance of typical diamond features. The differences in film structure for the two temperatures are already apparent after the deposition of only one monolayer of carbon. The Cls core level peak reflects the changes in surface band bending and thereby formation of a reconstructed surface and/or a Schottky barrier. A comparison with the ion-irradiated diamond surfaces is made. The results are discussed with respect to diamond growth mechanisms and the applicability of this method to introduce sp 2 structures at the diamond surface.

Carbon nucleation on Si(100) using a negative carbon ion beam

The initial nucleation stages of carbon film on Si(100) substrates were investigated by low energy electron diffraction (LEED) and Auger electron spectroscopy. In the initial stages, energetic carbon ions lead to a phase transformation from a two domain p(2×1) to a (1×1) LEED structure pattern after about 6×1015 carbon ion/cm2 dose (3 atomic layers). At room temperature, the energetic carbon ions are deposited as silicon carbide (SiC) up to a thickness of about 10 atomic layers. As the deposition temperature increases to 300 °C, the thickness of the SiC interlayer increases to 30 atomic layers. An increased carbon ion dose leads to the formation of sp3 or sp2 rich carbon film depending on the carbon ion energy and the deposition temperature. Higher energy (150 eV) C− ion beams and lower deposition temperatures (room temperature) produce sp3 rich carbon films. At 150 eV ion energy, the transition temperature from sp3 to sp2 rich carbon film during deposition is about 150 °C. Lower energy (<50 eV) C− ion beams at room temperature produce sp2 rich carbon films. During postdeposition annealing, the sp3 rich carbon film deposited at room temperature was converted to an sp2 rich carbon film above 740 °C.

Investigation of impurity deposition on plasma facing component using electron beam technique

In experiments in PISCES-B facility we have observed carbon film formation on beryllium substrates after hydrogen plasma exposure. The sources of the carbon are gaseous impurities in the vacuum system, which also exist in a fusion reactor such as the International thermonuclear experimental reactor (ITER). Thin film formation, resulting from electron-impurity interactions, is studied using a focused electron beam. Initial results show that carbon films are readily formed on beryllium surface in a range of power densities from two kilowatts to over one megawatt per square meter. Electron beam experiments on silicon and tungsten substrates, under the same conditions, do not result in carbon film formation. Microanalyses using scanning electron microscopy, Energy Dispersive X-ray spectroscopy and Raman are presented.

Effects of lubricants on friction and wear of [formula omitted] steel sliding pairs

The friction and wear properties of Ti(CN) 1045 steel rubbing pairs were investigated under dry and lubricated conditions by using a pin-on-disk tribometer. The selected speed range was 0.8 to 3.2 m/s and the load range was 58.8 to 235.2 N. Distilled water and a mineral oil (no additives) were used for lubrication, respectively. The wear of Ti(CN) ceramic under dry conditions was caused mainly by adhesion between the rubbing surfaces and the microfracture of Ti(CN). With the load and speed increasing, the adhesion and diffusion between rubbing surfaces increased and resulted in wear increasement of Ti(CN). Because of the brittleness of ceramics, the microfracture wear of Ti(CN) increased rapidly when the load was raised to some high values. The lubricating and cooling effects of the lubricants could improve the frict on and wear. Compared with water, oil was much better in improving the tribological properties. The analysis results obtained from XPS and AES examinations showed that ferrous oxide was produced on the wear scars, which could reduce the adhesion between the rubbing surfaces to some extent. The lubricating effects of the oil under boundary lubrication conditions were attributed to the formation of carbon films on the rubbing surfaces.

A theory for the formation of tetrahedral amorphous carbon including deposition rate effects

A theoretical model is presented to describe the effect of ion beam bombardment rate on the formation of tetrahedral amorphous carbon (ta-C) films. The critical ion energy, E c, corresponding to a 50% sp 3 content in the films, is found to be dependent on both the effective thermal resistance and the ion beam bombardment rate. In the model, the ‘window’ width in the ion energy scale for the formation of ta-C material increases with decreasing deposition rate and with a reduction in the effective thermal resistance, until limited by lower and upper boundary thresholds. Experimental data are reproduced by the model. The plasmon energy, which correlates with sp 3 fraction, is found experimentally of be higher for lower deposition rate and smaller effective thermal resistance. Data points for high sp 3 content ta-C films deposited on silicon substrates at room temperature occupy a region in the ion energy-deposition rate ( E- r) diagram similar to that predicated from the theory.

Effects of surrounding atmosphere on the formation of carbon films at 450°C

AbstractThe object of the present work is to present the results of research into the effects of surrounding atmosphere on the formation of carbon films by lubricating oil cracking at 450°C. The following six kinds of surrounding atmospheres were used: O2(5%), O2(95%), O2(70%), O2(50%), O2(20%) (with the remainders N) and air. Cr2O3 and Mo alloy coatings were selected as friction pair materials and a synthetic ester oil as lubricant. The experimental results on a SRV test machine showed that solid carbon films could be generated only in the atmosphere with a certain O2 content. No valid carbon films were generated in surrounding atmospheres rich in nitrogen and oxygen. Surface analyses with SEM, WDS, XPS and X‐ray diffraction indicated that graphite films with excellent solid lubricating effect resulted from the catalytic cracking of the hydrocarbon components in the lubricating oil at high temperature in the air atmosphere after the failure of fluid lubrication.

Ions as a useful tool for carbon film deposition and modification

This work demonstrates the potential of inert ions as a useful tool for carbon film deposition and modification. At first, the possibility of using a computer controlled ion assisted evaporation (IAE) system for a systematic investigation of carbon film formation will be discussed. For a better understanding of growth mechanisms the particle fluxes to the substrate were studied with ion probes and quadrupole mass spectroscopy. The effect of the additional ion bombardment on the resulting films (surface topography, microstructure and microhardness) is shown. The results will be discussed in the light of possible ion-solid interactions affecting the growth. Furthermore, the ion-based modification of the surface topography, bulk and surface structure is shown. An example demonstrates the potential of ion induced patterning of diamond resulting in an enhanced cold field emission current.

Capabilities of plasma beam discharge for the formation of diamond-like carbon films

Abstract In this paper we describe the system developed on the basis of plasma beam discharge producing high density plasma (10 10 –10 13 cm −3 ). The system allows the formation of charged-particle flows (10–100 mA cm −2 ) at an energy of 60–200 eV onto a treated surface. We have presented results obtained for the diamond-like carbon films produced by this system. It was shown that the film resistivity increased from 10 8 to 10 12 Ω cm, and the optical band gap from 2.4 to 3.2 eV, depending on the type of charged particles (ions or electrons) incident on the grown layer surface. The addition of oxygen (up to 20%) to the original working gas permits the deposition of hard transparent diamond-like carbon films with a band gap of 3.5 eV.