Formation Of Amorphous Carbon Films Research Articles

Interfacial effects on anticorrosive and tribological properties of electrodeposited amorphous carbon film on AA2024-T3 aluminum alloys using ethanol as carbon source

Amorphous carbon (a-C) films were prepared by electrodeposition technique on AA2024-T3 and proposed as an anticorrosive film. Ethanol (CH2CH2OH) was used as carbon source and the electrodeposition was carried under constant voltage of 1200 V or 800 V for 3, 8 and 24 h using a graphite bar as anode and an AA2024-T3 aluminum alloy as substrate.The morphology, structure and chemical properties of a-C films was investigated using Raman spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Raman spectra of 1200 V 24 h electrodeposited film showed the presence of characteristic peaks for a-C films, typical D and G bands at 1373 cm−1 and 1574 cm−1, which proves the formation of amorphous carbon film. Electrochemical measurements was carried in order to evaluate the anticorrosive behavior of a-C film over AA2024-T3 alloy. The interfacial effect (AA2024-T3 alloy /a-C film / Electrolyte) on electrochemical behavior shows a character of pores blockage of amorphous carbon film, which shows a pseudo resistance due to corrosion products into microcracks of film.

Influence of Cu impurities and surface temperature to the formation of thin a-C:H(Me) film

The aim of this experimental work is identify most important physical and chemical processes on the surface during amorphous carbon films formation on the silicon surface with copper nanoclusters (Cu). Duration of films deposition on n type silicon (100) surface by using different substrate temperatures (25 °C, 100 oC and 250 °C) was 45s. Velocity of film growth from C2H2 gas plasma depended on surface temperature and was variable (0.2-0.5 nm/s). Data of null ellipsometry, Raman spectroscopy and element analysis showed that formation of amorphous carbon film is in the early stage and mixture of Si-C, Si-COH and GLC fragments is dominant on the surface. The experimental RS curves were fitted by few Gaussian-shape lines in the spectral range from 500 cm-1 to 700 cm-1, from 700 cm-1 to 900 cm-1, from 900 cm-1 to 1100 cm-1 and from 1100 cm-1 to 1900 cm-1 and analysis of the additional peaks in all ranges confirmed complexes of different carbons structures in the film. Carbon films with more ordered C-C bonds grows during film formation at higher temperatures (>100o C) on the silicon surface with Cu particles, because atoms of copper penetrate into the deeper layers of silicon. The substrate temperature influenced the surface amorphisation because of active oxygen and hydrogen diffusion into deeper layers and formation of hydrogenated silicon carbon with fragments of amorphous carbon films becomes not significant.

In-situ tribochemical formation of self-lubricating diamond-like carbon films

Diamond-like carbon (DLC) films were tribochemically formed from ambient hydrocarbons on the surface of a highly stable nanocrystalline Pt-Au alloy. A sliding contact between an alumina sphere and Pt-Au coated steel exhibited friction coefficients as low as μ = 0.01 after dry sliding in environments containing trace (ppb) organics. Ex situ analysis indicated that the change in friction coefficient was due to the formation of amorphous carbon films, and Raman spectroscopy and elastic recoil analysis showed that these films consist of sp2/sp3 amorphous carbon with as much as 20% hydrogen. Transmission electron microscopy indicated these films had thicknesses exceeding 100 nm, and were enhanced by the incorporation of worn Pt-Au nanoparticles. The result was highly wear-resistant, low-friction DLC/Pt-Au nanocomposites. Atomistic simulations of hydrocarbons under shear between rigid Pt slabs using a reactive force field showed stress-induced changes in bonding through chain scission, a likely route towards the formation of these coatings. This novel demonstration of in situ tribochemical formation of self-lubricating films has significant impact potential in a wide range of engineering applications.

Synthesis of nanostructured amorphous carbon-copper composite films by plasma-enhanced chemical vapour deposition

Nanostructured amorphous carbon-copper composite films were formed by plasma-enhanced chemical vapour deposition. The formation was done on copper-silicon substrates at 25°C, 300°C, 520°C, and 700°C temperatures using an acetylene gas at 40–70Pa pressure. The heating of the CuSi substrate induced formation of Cu nanospheres with 50–500nm size depending on the substrate temperature. The microstructure and composition of nanostructured carbon-copper composite films were investigated. The SEM views showed formation of amorphous carbon films with the randomly distributed nanostructures. The oxygen concentration in the composite films decreased with the increased heating temperature. The surface roughness measurements indicated that the surface roughness values increased with the increase of the temperature. The increase of the substrate temperature stimulated to the graphitization, enhanced the fraction of sp2 CC sites and lead to the formation of the nanocrystaline graphite clusters in composite films. The nanohardness values of the formed nanostructured amorphous carbon-Cu films varied in the range of 0.2–3GPa.

Effect of Radio-Frequency and Low-Frequency Bias Voltage on the Formation of Amorphous Carbon Films Deposited by Plasma Enhanced Chemical Vapor Deposition

The effect of radio-frequency (RF) or low-frequency (LF) bias voltage on the formation of amorphous hydrogenated carbon (a-C:H) films was studied on silicon substrates with a low methane (CH4) concentration (2–10 vol.%) in CH4+Ar mixtures. The bias substrate was applied either by RF (13.56 MHz) or by LF (150 kHz) power supply. The highest hardness values (∼18–22 GPa) with lower hydrogen content in the films (∼20 at.%) deposited at 10 vol.% CH4, was achieved by using the RF bias. However, the films deposited using the LF bias, under similar RF plasma generation power and CH4 concentration (50 W and 10 vol.%, respectively), displayed lower hardness (∼6–12 GPa) with high hydrogen content (∼40 at.%). The structures analyzed by Fourier Transform Infrared (FTIR) and Raman scattering measurements provide an indication of trans-polyacetylene structure formation. However, its excessive formation in the films deposited by the LF bias method is consistent with its higher bonded hydrogen concentration and low level of hardness, as compared to the film prepared by the RF bias method. It was found that the effect of RF bias on the film structure and properties is stronger than the effect of the low-frequency (LF) bias under identical radio-frequency (RF) powered electrode and identical PECVD (plasma enhanced chemical vapor deposition) system configuration.

Evaluation of the scavenging effect by low temperature laboratory plasmas driven with radiofrequency

Proposed materials for ITER are beryllium for first wall and tungsten tiles (plus carbon fibre composites) for the divertor. The use of carbon materials at the divertor plates of ITER can be problematic due to the formation of tritium-containing co-deposits coming from the products of chemical erosion and physical sputtering. Scavenging effect in the hidden regions of the divertor has been proposed as a possible technique to eliminate the formation of amorphous carbon films. Nitrogen gas has been proposed as a good scavenger. Although a complete suppression of the formation of amorphous carbon films by nitrogen was achieved in laboratory experiments (in a low temperature plasma), only a moderate reduction (<30–40%) was seen at JET in type-III ELM discharges (Tabares et al 2005 J. Nucl. Mater. 337–339 867–71). This justifies further analyses for an understanding of physicochemical processes for the deposition/inhibition of carbon films. In this work, experiments in RF plasma discharges at low pressures of CH4/N2 admixtures were carried out. The formation of amorphous carbon films was investigated under different physical conditions, with high and low energetic ions on powered and floating electrodes, respectively. Optical emission spectroscopy of ion and neutral species was employed as the main diagnostic.

Formation of amorphous carbon films in plasma of hydrogen and hydrocarbon mixtures

Deposition of amorphous hydrogenated carbon (a-C:H) films in CF4, hexane (C6H14), or acetylene (C2H2) precursors and their mixtures with hydrogen (H2) is reported. The films were characterized by Raman spectroscopy (RS) and X-ray spectroscopy (XPS). RS indicates increase of the sp/sp bonding ratio and disorder in graphite clusters with increasing hydrogen content (from 0 to 50% for the acetylene precursor) in the deposition gas mixture. The opposite trend is observed when the hydrogen concentration exceeds 50% (for acetylene) or additional hydrogen is used (for hexane). Formation of polymer-like films in fluorine-containing gas plasma is observed with additional low quantity of hydrogen (∼5%). Composition of these films depends on treatment duration and conditions of irradiation.

Effect of chamber pressure and atmosphere on the microstructure and nanomechanical properties of amorphous carbon films prepared by pulsed laser deposition

We have investigated the effect of chamber pressure and atmosphere on the microstructure and nanomechanical properties of amorphous carbon thin films prepared by pulsed laser deposition. The amorphous carbon films were deposited in various atmospheres such as nitrogen and argon at different chamber pressures. We used Raman spectroscopy to study the bonding characteristics of the deposited amorphous carbon films. Atomic force microscopy and optical microscopy were utilized to observe the surface conditions and the microstructures of the deposited films. Nanoindentation measurements were carried out on various samples prepared under different conditions to study the effect of chamber pressure and atmosphere on the elastic modulus and nanohardness of the films. It was found that reduced vacuum leads to formation of amorphous carbon films with reduced elastic modulus and nanohardness. Amorphous carbon films prepared under higher chamber pressures exhibit an increased density of particulates and significantly roughened surface. The results were understood in combination with the optical emission and electrostatic measurements of the laser plasma plume. It was found that the presence of atmosphere decreases the leading edge ionic energies of the species in the laser plasma plume and increases the thermalization of the laser plasma due to an increased possibility of collision.

Effect of mixing oxygen or diborane on the formation of amorphous carbon films from methane by r.f. plasma chemical vapour deposition

Amorphous carbon films were investigated for X-ray mask substrate applications. The films were deposited by r.f. plasma chemical vapour deposition from a methane-hydrogen mixture. It was found that oxygen (up to 10% of the total flow) improved the optical transparency and doubled the deposition rate. An increase in the deposition rate by a factor of 5 was observed in the case of diborane. The film stress and adhesion with reference to silicon substrate backetching are presented. A sandwich structure consisting of a central BCN compound film with top and bottom amorphous carbon films as stress absorption and protective layers against wet etching and synchrotron radiation damage is reported on.