Growth Of Diamond-like Carbon Films Research Articles

Targeting Biomechanical Endurance of Dental-Implant Abutments Using a Diamond-Like Carbon Coating.

Abutment components (i.e., fixtures associated with oral implants) are essentially made of titanium (Ti), which is continuously exposed to the hash oral environment, resulting in scratching. Thus, such components need to be protected, and surface treatments are viable methods for overcoming long-term damage. Diamond-like carbon (DLC), an excellent protective material, is an alternative surface-treatment material for Ti abutments. Here, we demonstrate that a silicon interlayer for DLC film growth and the pulsed-direct current plasma-enhanced chemical vapor deposition (DC-PECVD) method enables the deposition of an enhanced protective DLC film. As a result, the DLC film demonstrated a smooth topography with a compact surface. Furthermore, the DLC film enhanced the mechanical (load-displacement, hardness, and elastic modulus) and tribological properties of Ti as well as increased its corrosion resistance (16-fold), which surpassed that of a bare Ti substrate. The biofilm formed (Streptococcus sanguinis) after 24 h exhibited an equal bacterial load (∼7 Log colony-forming units) for both the groups (Ti and DLC). In addition, the DLC film exhibited good cytocompatibility, owing to its noncytotoxicity toward human gingival fibroblast cells. Therefore, DLC deposition via DC-PECVD can be considered to be a promising protective and cytocompatible alternative for developing implant abutments with enhanced mechanical, tribological, and electrochemical properties.

Experimental Study of Diamond-like Carbon Film on Aermet100 Steel and First-Principles Calculation of Interfacial Adhesion.

Three different types of surface-modified layers of N, C, and N+C are successfully prepared on AerMet100 steel by plasma-assisted thermochemical treatment, and diamond-like carbon (DLC) films are formed on the top surfaces of the latter two. The results show that the DLC films produced by prenitriding and then carburizing (N+C) exhibit a smoother and finer morphology and higher sp3 content than that without prenitriding (C). In addition, the wear resistance of the N+C specimen with a high hardness nitrided layer as the support for the outermost DLC films is superior to that of the C specimen. In view of the catalytic effect of the Fe3C phase on the growth of DLC films, the interfacial properties of Fe3C(001)/diamond(111) are investigated using first-principles calculations. On the basis of the most preferred Fe-terminated HCP site model, the effects of alloyed cementite (Fe2MC) on interfacial adhesion of Fe2MC(001)/diamond(111) are also investigated. Furthermore, the mechanisms of interfacial adhesion for two representative dopings (Zr weakened and V enhanced) are revealed in detail. These results are expected to provide a potential promising means for future experimental works on the preparation of high-performance DLC films on alloy steel surfaces by plasma carburizing.

Growth of diamond-like carbon films with significant nanocrystalline phases in a low-pressure high-density CH4 plasma in ICP-CVD: Effect of negative dc substrate bias

Working at relatively low-temperature and low-pressure, the development and optimization of diamond-like carbon (DLC) films with significant nanodiamond components on inexpensive glass substrates, without conventional pre-treatment by diamond powders, is the main objective of the present work. Using the most familiar CH4-precursors diluted by Ar in a high-density plasma triggered at high rf power (900 W) in a planar inductively-coupled plasma chemical vapour deposition (ICP-CVD) system, DLC thin-films are prepared via optimization in the flow rate of the precursor gas at 30 mTorr (∼4 Pa) pressure and 450 °C substrate temperature and, further by applying negative dc-bias to the substrates. The optimized samples obtained with negative substrate-bias possess good crystalline properties. From Raman results, the most crystalline sample is obtained with characteristic minimum ID/IG ratio reduced from 0.75 to 0.61, maximum IDia/ID enhanced from 0.94 to 1.09, and the sp3 hybridized CC bonds increased from 44% to ∼64% at a substrate-bias of –40 V. The residual stress, and the optical band gap were calculated from Raman analysis. The optimized DLC film exhibits a high optical band gap (3.71 eV) as calculated from Tauc’s plot analysis of the UV–Vis data. The well-identified 〈111〉 crystallographic planes in the TEM micrograph demonstrate a significant fraction of nanocrystalline diamond component in the optimum DLC film.

The effect of CO2 addition to the (C2H2 + H2) gas system on the low-temperature growth of diamond-like carbon (DLC) with prominent nano-diamond phase

Diamond-like carbon (DLC) films were grown on untreated glass substrates by MW-PECVD system utilizing a (C2H2/H2/CO2) gas combination at low temperature (∼300 °C). Regulating the flow of CO2, we investigate the relevant influence on the sp3 and sp2 hybridized carbon components, optical transmittance, and surface morphology of the DLC films, using Raman spectroscopy, UV–Vis absorption spectroscopy, and field emission scanning electron microscopy, respectively. The results demonstrated a superior quality of the nano-diamond phase in the DLC film, having the most significant magnitude of IDia/IG ratio ∼ 1.13, the corresponding minimum magnitude of ID/IG ratio ∼ 0.90, and the narrowest width of the diamond peak at ∼ 1332 cm−1 when an optimized flow of CO2 gas at 3 sccm was added to the (C2H2 + H2) gas mixture. The optimum DLC film demonstrated the maximum optical transmittance of ∼ 89%, and the corresponding FE-SEM image revealed a uniform surface microstructure. It has been established that in addition to atomic-H, atomic-O played a key role in chemically reacting with the a-C and other non-diamond graphitic phases and etching out those components to facilitate the growth of DLC films, preserving the sp3 hybridized superior nano-diamond component within the network.

Mechanism of high growth rate for diamond-like carbon films synthesized by helicon wave plasma chemical vapor deposition

A high growth rate fabrication of diamond-like carbon (DLC) films at room temperature was achieved by helicon wave plasma chemical vapor deposition (HWP-CVD) using Ar/CH4 gas mixtures. The microstructure and morphology of the films were characterized by Raman spectroscopy and scanning electron microscopy. The diagnosis of plasma excited by a helicon wave was measured by optical emission spectroscopy and a Langmuir probe. The mechanism of high growth rate fabrication for DLC films by HWP-CVD has been discussed. The growth rate of the DLC films reaches a maximum value of 54 μm h−1 at the CH4 flow rate of 85 sccm, which is attributed to the higher plasma density during the helicon wave plasma discharge. The CH and Hα radicals play an important role in the growth of DLC films. The results show that the Hα radicals are beneficial to the formation and stabilization of C=C bond from sp2 to sp3.

Synthesis of flat sticky hydrophobic carbon diamond-like films using atmospheric pressure Ar/CH4 dielectric barrier discharge

An Ar/CH4 atmospheric pressure dielectric barrier discharge (AP-DBD) was used to synthesize sticky hydrophobic diamond-like carbon (DLC) films on glass surface. The film is formed with plasma treatment duration shorter than 30 s, and water contact angles larger than 90° together with contact angle hysteresis larger than 10° can be achieved. According to Fourier transform infrared spectroscopy and atomic force microscopy analysis, hydrocarbon functional groups are created on the glass substrate, producing coatings with low surface energy (∼35 mJ m−2) with no modification of the surface roughness. To infer the plasma processes leading to the formation of low energy DLC surfaces, optical emission spectroscopy was used. From the results, a direct relationship between the CH species present in the plasma and the carbon concentration in the hydrophobic layer was found, which suggests that the CH species are the precursors of DLC film growth. Additionally, the plasma gas temperature was measured to be below 350 K which highlights the suitability of using AP-DBD to treat thermo-sensitive surfaces.

Morphological and Chemical Evolution of Gradually Deposited Diamond-Like Carbon Films on Polyethylene Terephthalate: From Subplantation Processes to Structural Reorganization by Intrinsic Stress Release Phenomena.

Diamond-like carbon (DLC) films on polyethylene terephthalate (PET) are nowadays intensively studied composites due to their excellent gas barrier properties and biocompatibility. Despite their applicative features being highly explored, the interface properties and structural film evolution of DLC coatings on PET during deposition processes are still sparsely investigated. In this study two different types of DLC films were gradually deposited on PET by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) using acetylene plasma. The surface morphology of the deposited samples has been analyzed by atomic force microscopy (AFM). Their chemical composition was investigated by diffusive reflectance infrared Fourier transform (DRIFT) and Raman spectroscopy analysis and the surface wettability by contact angle measurements. Subplantation processes and interface effects are revealed through the morphological and chemical analysis of both types. During plasma deposition processes the increasing carbon load causes the rise of intrinsic film stress. It is proven that stress release phenomena cause the transition between polymer-like to a more cross-linked DLC network by folding dehydrogenated chains into closed 6-fold rings. These findings significantly lead to an enhanced understanding in DLC film growth mechanism by RF-PECVD processes.

High surface area diamond-like carbon electrodes grown on vertically aligned carbon nanotubes

Electrochemically active diamond-like carbon (DLC) electrodes featuring high specific surface area have been prepared by plasma-enhanced chemical vapour deposition (CVD) onto densely packed forests of vertically aligned multiwall carbon nanotubes (VACNTs). The DLC:VACNT composite film exhibits a complex topography with web like features and ridges generated by partial coalescence of the DLC over the CNT arrays. DLC:VACNT electrodes exhibit low background responses over a large potential window, low uncompensated resistance, as well as low charge-transfer impedance in the presence of ferrocyanide as a redox probe. The interfacial capacitance associated with the DLC:VACNT electrode is in the range of 0.6mFcm−2, a value two orders of magnitude larger than in conventional flat carbon electrodes. DLC films grown onto single-crystal Si(100) under identical conditions resulted in essentially insulating layers. Conducting-atomic force microscopy studies reveal that the film electro-activity does not arise from specific topographic features in the highly corrugated film. The ensemble of experimental results suggests that the enhanced electrochemical responses are not connected to areas in which the CNT support is exposed to the electrolyte solution. This is remarkable behaviour considering that no dopants have been included during the DLC film growth.

Structural properties and growth evolution of diamond-like carbon films with different incident energies: A molecular dynamics study

Structural properties and growth evolution of diamond-like carbon (DLC) films with different incident energies were investigated systematically by the molecular dynamics simulation using a Tersoff interatomic potential for carbon-carbon interaction. The results revealed that the density, sp3 fraction and residual compressive stress as a function of incident energy increased firstly and then decreased; when the incident energy was 70eV/atom, the density could reach to 3.0g/cm3 with the maximal compressive stress of 15.5GPa. Structure analysis indicated that the deviation of both bond angles and lengths from the equilibrium position led to the generation of a large residual stress, while the high compressive stress mainly attributed to the decrease of both bond angles and lengths among carbon atoms. The growth of DLC films underwent a formation process of “Line-Net” structure accompanied with the interaction of many atomic motion mechanisms, and the “Point” stage was only found for DLC films with low incident energy.

X-ray reflectivity study of bias graded diamond like carbon film synthesized by ECR plasma

Diamond like carbon (DLC) coatings were deposited on silicon substrates by microwave electron cyclotron resonance (ECR) plasma CVD process using plasma of Ar and CH 4 gases under the influence of negative d.c. self bias generated on the substrates by application of RF (13·56 MHz) power. The negative bias voltage was varied from −60 V to −150 V during deposition of DLC films on Si substrate. Detailed X-ray reflectivity (XRR) study was carried out to find out film properties like surface roughness, thickness and density of the films as a function of variation of negative bias voltage. The study shows that the DLC films constituted of composite layer i.e. the upper sub surface layer followed by denser bottom layer representing the bulk of the film. The upper layer is relatively thinner as compared to the bottom layer. The XRR study was an attempt to substantiate the sub-plantation model for DLC film growth.

Adhesion Studies of Diamond-Like Carbon Films Deposited on Ti6Al4V Alloy after Carbonitriding

Diamond-like Carbon (DLC) coatings have attracted significant attention due to their low friction coefficient, high degree of hardness, chemical inertness, and high wear resistance as well as and their many possible uses in metallurgical, aeronautical, and biomedical applications. However, DLC has low adhesion strength to metallic substrates. Carbonitriding was performed before DLC deposition to improve this adherence. Different concentration of nitrogen in the gas mixture was used during the carbonitriding of Ti6Al4V alloy. DLC films were subsequently grown from methane using plasma enhanced chemical vapor deposition. The samples were characterized with Raman scattering spectroscopy, nanoindentation, and tribological tests. Films from 80.0% N2 had the best friction coefficient (0.07) and a critical load of ~22 N. In the scratching test, these films had adhesive failure and they completely detached from the substrate only in the end of the tests. SEM images show carbonitring promoted a significant increase in the surface defects (homogeneously distributed) but without the presence of microcracks. EDX analysis indicated that nitrogen element was diffused throughout the thickness of the samples. Hydrogen and carbon atoms from carbonitriding formed a diffusion-barrier layer that can be used as the first step for DLC deposition. This carbonitriding can also provide a carbide layer, which serves as the precursor for the nucleation and growth of DLC films.

Atomistic simulations of diamond-like carbon growth

Diamond-like carbon (DLC) films are composed of carbon bonds with different hybridizations, including sp2, sp3 and even sp1. Understanding the atomic bonding structure is essential to understanding the properties and optimizing the process parameters of the films. Because of the limited analytical tools for characterizing the atomic bonding structure in amorphous materials, computational research at the atomistic scale could provide significant insight into the structure–property relationships in diamond-like carbon films and has been applied to understanding the various phenomena occurring during DLC film growth. The contributions of the atomistic simulations and electronic structure calculations pertain mainly to three important issues: (i) the sp3 bond formation and stress generation mechanisms, (ii) the stress reduction mechanism by metal incorporation, and (iii) the impact angle-dependent surface smoothening/roughening mechanisms.

Exploring the potential of high power impulse magnetron sputtering for growth of diamond-like carbon films

Amorphous carbon films are deposited employing high power impulse magnetron sputtering (HiPIMS) at pulsing frequencies of 250Hz and 1kHz. Films are also deposited by direct current magnetron sputtering (dcMS), for reference. In both HiPIMS and dcMS cases, unipolar pulsed negative bias voltages up to 150V are applied to the substrate to tune the energy of the positively charged ions that bombard the growing film. Plasma analysis reveals that HiPIMS leads to generation of a larger number of ions with larger average energies, as compared to dcMS. At the same time, the plasma composition is not affected, with Ar+ ions being the dominant ionized species at all deposition conditions. Analysis of the film properties shows that HiPIMS allows for growth of amorphous carbon films with sp3 bond fraction up to 45% and density up to 2.2gcm−3. The corresponding values achieved by dcMS are 30% and 2.05gcm−3, respectively. The larger fraction of sp3 bonds and mass density found in films grown by HiPIMS are explained in light of the more intense ion irradiation provided by the HiPIMS discharge as compared to the dcMS one.

Buffered internal stresses in diamond-like carbon films reinforced with single-walled carbon nanotubes

Diamond-like carbon (DLC) films reinforced with single-walled carbon nanotubes (SWCNTs) were fabricated by sputter-deposition of DLC onto a few monolayers of spray-coated SWCNTs on glass substrates. The thickness-averaged internal stress was reduced by 1.5 GPa by incorporation of SWCNTs into 10-nm-thick DLC films. Stress analysis indicates that the internal stress is reduced by 1.8 GPa at the SWCNT-DLC nanocomposite layer and decreases exponentially as a function of film thickness. Microscopy reveals significant cracking and delamination in 150-nm-thick DLC films, while the SWCNT-reinforced films remain essentially intact. The results demonstrate that SWCNTs in DLC films influence the early stage of DLC film growth and act as an effective stress-buffering layer near the boundary between the film and substrate.

Growth and properties of the ion beam deposited SiO x containing DLC films

In the present study SiO x containing diamond-like carbon (DLC) films were synthesized by the closed drift ion source from hexamethyldisiloxane vapor. Kinetics of the growth of DLC films was investigated using optical emission spectroscopy (OES). Structure, chemical composition, electrical and optical properties of the synthesized films were studied. The effects of ion beam energy were investigated. The main atomic hydrogen Balmer series lines and the intense broad CH group related peak were detected in the OES spectra registered in-situ during SiO x containing diamond-like carbon film synthesis. The intensity ratio of H-β/CH peaks increased with the increase of applied ion beam energy. It was explained by activation of the dissociation of the hexamethyldisiloxane molecules. Changes of the structure of the diamond-like carbon films were observed for the films deposited under intense dissociation conditions.

X-ray reflectivity studies on DLC films deposited by microwave ECR CVD: Effect of substrate bias

Diamond like carbon (DLC) films were deposited at room temperature on Si (111) substrates by microwave electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) process using plasma of methane diluted with argon gas. During deposition, dc self bias (− 25 V to − 200 V) on substrate was varied by application of RF power to the substrate. The influence of substrate bias on density of the deposited films was studied by X-ray reflectivity (XRR). The results from these measurements are further correlated with the results from UV and visible Raman spectroscopy. DLC film is modeled as a structure having three different layers such as low density surface, bulk and interface with the substrate. This three-layer model is used to fit the measured XRR data to evaluate the surface, interface and interlayer roughness, thickness and density of these films. The surface roughness obtained from XRR is correlated with the results from Atomic Force Microscopy (AFM) measurements. The observed results are explained based on the subplantation model for DLC film growth.

Growth of diamond-like carbon films using low energy ion beam sputter - bombardment deposition with Ar ions

An alternative to a widely used ion assisted deposition method has been developed where a single beam of low energy Ar ions is used to simultaneously sputter a graphite target and to bombard a growing film. By placing the substrate at low incident angles to the axis of the ion beam and therefore subjecting the growing film to the additional ion energy we aimed to promote the formation of sp3 bonding. Sp2 rich amorphous carbon (a-C) and diamond-like carbon (DLC) films with significant fractions of sp3 bonding were formed by sputtering from a Kaufmann - type ion source. Experimental results revealed that when the substrate was placed at grazing angles to the incoming ions no DLC, but only polymeric a-C films were produced as a result of a secondary resputtering process. For DLC synthesis the optimal angles of the target and the substrate to the ion flux were found to be 30° and 0° respectively and the ion energies of 0.8 – 1.0 keV.

Role of atomic transverse migration in growth of diamond-like carbon films

The growth of diamond-like carbon (DLC) films is studied using molecular dynamics simulations. The effect of impact angle on film structure is carefully studied, which shows that the transverse migration of the incident atoms is the main channel of film relaxation. A transverse-migration-induced film relaxation model is presented to elucidate the process of film relaxation which advances the original model of subplantation. The process of DLC film growth on a rough surface is also investigated, as well as the evolution of microstructure and surface morphology of the film. A preferential-to-homogeneous growth mode and a smoothing of the film are observed, which are due to the transverse migration of the incident atoms.

Rapid Growth of Diamond-like Carbon Films by Nanopulse Magnetron Chemical Vapor Deposition

In this paper, we describe the development of a rapid deposition method for diamond-like carbon (DLC) films. The deposition rate of DLC films is investigated using magnetic field enhanced nanopulse plasma chemical vapor deposition (CVD). The maximum deposition rate of DLC films produced by this magnetron CVD is approximately fifty times larger than that of the same films produced by conventional plasma CVD. The area of DLC films having a high deposition rate corresponds to the region of the magnetic field distribution where the field is parallel to the substrate at heights of 15–20 mm.

Substrate Effect on the Diamond-Like Carbon Films Synthesized by RF Plasma Enhanced Chemical Vapor Deposition

Diamond-like carbon (DLC) films were synthesized by RF plasma enhanced chemical vapor deposition using methane as carbon source. Effect of substrate on the growth of DLC films was investigated by using four different substrate materials, silicon wafer (100), glass, flat-polished and mirror-polished alumina. The carbon films were deposited at four different self-bias voltages (-157 V, -403 V, -500 V and -590 V) by changing the plasma power under fixed flow rate and working pressure. Raman analyses indicated that DLC films were deposited on silicon and glass substrates at the self-bias -403 V ~ -590 V, and polymer-like carbon films were obtained at -157 V. For the alumina substrates, different Raman results were observed for flat-polished and mirror-polished alumina substrates. The hardness of DLC films, deposited on silicon and glass substrates at the self-bias -403 V ~ -590 V, was within 16~20 GPa using nanoindentation technique.