Diamond-like Carbon Thin Films Research Articles

PECVD process parameter optimization: towards increased hardness of diamond-like carbon thin films

ABSTRACTDiamond-like carbon thin film coatings are extensively used in manufacturing, medical and aerospace industries due to their excellent tribological, mechanical, optical and biological properties. Due to the non-linear relationship of each process parameter in the deposition process, it is difficult to determine the response results without conducting large numbers of experiments. To counter this, a carefully designed experimentation scheme along with two nature-inspired metaheuristic algorithms are used in the current study. Hydrogen flow rate, Argon-C2H2 flow rate and deposition temperature are used as the design variables for maximizing the thin film hardness.

Deposition of Diamond-like Carbon and Carbyne Thin Film by Cathodic Plasma Electrolysis Process

Deposition of Diamond-like Carbon and Carbyne Thin Film by Cathodic Plasma Electrolysis Process

Diamond-like carbon-deposited films: a new class of biocorrosion protective coatings

A series of diamond-like carbon thin films was applied on AISI 316L stainless steel substrates through a pulsed-direct current plasma-enhanced chemical vapor deposition technique to study the effects of working parameters (bias voltage and deposition pressure) on the microstructure and biocorrosion resistance of films. Raman spectra indicated that under low bias voltage and higher deposition pressure, the films possess a higher amount of sp2structure, lower internal stress and an improved biocorrosion resistance due to a smooth and defect-free morphology. The lamellar sp2structure blocked a penetration of corrosive entities. The oxygen content of locally corroded areas (∼11·9 wt.%) was much higher than that of non-corroded areas (2·6 wt.%) corroborating galvanic corrosion between carbide and nitride phases. Moreover, by increasing the deposition pressure from 20 to 40 Pa, the internal stress decreased from 1·03 to 0·82 GPa. The results confirmed that it is possible to tailor the properties of the coatings such as structural composition and particularly biocorrosion resistance by the control over the working parameters. Such anticorrosive diamond-like coatings could benefit biomedical implants used for tissue regeneration.

Investigation of Fe3Al-based PVD/HVOF duplex coatings to protect stainless steel from sliding wear against alumina

In this work, the sliding wear properties of several duplex (thin-on-thick) coating systems used to protect stainless steels were evaluated under different loading conditions. The coating systems consisted of a 304-stainless steel (SS304) substrate or the same steel previously coated with a layer of iron aluminide (Fe3Al) based material using the high velocity oxy-fuel (HVOF) technique, onto which a thin film of CrN or DLC (diamond-like carbon) was deposited using the physical vapor deposition (PVD). The mechanical properties of coatings were investigated by indentation, and their wear properties were evaluated using a pin-on-disc tribo-system with alumina as counterpart material in ambient conditions under applied loads between 5 N and 15 N. Wear mechanisms of coatings were assessed by examining the morphology of top surfaces and cross-sections of wear tracks, and by analyzing the counterpart material using scanning electron microscopy, energy dispersive and Raman spectroscopies. Results show that the addition of a top coat significantly enhances the wear resistance of the SS304 substrate and of the HVOF coatings due to the excellent tribological properties of DLC and CrN films. Moreover, the PVD/HVOF/SS304 coating systems exhibit excellent wear properties when compared to PVD/SS304 coatings alone due to the high load bearing capacity of the HVOF layers. The wear resistance of such systems increases with the hardness of the HVOF layer. The DLC/HVOF/SS304 duplex coatings show the best tribo-mechanical performance due to their very low coefficients of friction and good bond strengths between layers. On the contrary, the relatively poor tribological performance of the CrN/HVOF/SS304 duplex coatings can be attributed to the brittle nature of the CrN film. The main degradation mechanisms for the DLC-based duplex coatings were adhesive wear and plastic deformation, while in the case of the CrN-based duplex system, brittle fractures and oxidation wear were predominant. In both coating systems, abrasive wear has also contributed to the material loss.

Fabrication of DLC nanoparticle clusters by μ-wave oven based plasma reactor with acetylene diluted in air precursor

This work developed a microwave oven based plasma reactor operated under vacuum pressure. This microwave plasma deposition system used to deposit diamond-like carbon (DLC) thin film on silicon substrate. System is custom-made and economically provides a very inexpensive way to conduct film deposition experiments by using a household microwave oven as a microwave source to get plasma discharge. DLC thin films were successfully deposited on silicon substrates by pure acetylene (C2H2) plasma. Plasma species composed of; CN, N2, CO, C2, and H are presented revealed by Optical Emission Spectroscopy. Energy Dispersive X-ray analysis indicated that the deposited film composed of carbon atoms 46.25% and silicon atoms 53.75%. Raman analysis showed D-band, G-band and nanocrystalline diamond band with sp3-hybridization contained in the films in the range of 48.75–64.08% that composed of chemical bonding; CC, CO, CN, CN, CO, CNH, NO, OH and HOH, analyzed by XPS technique. XRD indicated that the grown films are cubic diamond (1 1 1) crystallography and formed in coral-like clusters from nanoparticles of a mixture between sp2 and sp3 hybridization with high porosity in surface texture that introducing the hydrophobic property on the grown DLC surface by changing the hydrophilic property of smooth silicon substrate surface.

Micro-wear and friction of carbon film with molecularly thin PFPE lubricants

When a surface protective diamond-like-carbon (DLC) film experiences high speed contact, it can be degraded and damaged by mechanical stress and frictional temperature rise. In this study, the thermomechanical contact behavior of thin DLC film on a magnetic recording disk was systematically investigated with respect to the contact speed (1.2 m/s ~ 36.1 m/s) using a newly-developed experiment technique. For comparison, experiments were performed on the DLC film samples with and without molecularly thin perfluoropolyether (PFPE) lubricants on the surface. Using the post experiment samples, atomic force microscopy (AFM) and micro Raman measurements were carried out to examine the mechanisms of surface wear and material degradation. It was observed that the higher contact speed (12.0 m/s & 36.1 m/s) caused earlier failure and wider wear track on the surface than the lower contact speed (i.e., 1.2 m/s). When a monolayer thick PFPE lubricant is applied onto the surface, it significantly improved the friction and wear performance of the DLC film. Based on the Raman analysis, it could be found that the DLC on the contact area showed a clear evidence of thermal degradation, i.e., graphitization process, by frictional heat generation.

Nanometric thin films of non-doped diamond-like carbon grown on n-type (P-doped) silicon substrates as electrochemical electrodes

The electrochemical response of thin non-doped diamond-like carbon films grown by pulsed laser deposition onto n-type (P-doped) silicon substrates was studied using different redox-active couples. The experiments were conducted as a function of the film thickness which can be controlled by the deposition time. It could be demonstrated that the film thickness greatly influences the electrochemical response and the electron transference rate at the surface, thus reaching an optimal response for films with a thickness of around 35 nm. This holds true for all redox couples studied. Those films show rather similar properties compared to boron-doped diamond electrodes, thus becoming an interesting coating to be studied as electrochemical electrode.

The influence of gas flow rate on the structural, mechanical, optical and wettability of diamond-like carbon thin films

In this research, diamond-like carbon (DLC) thin films were deposited on silicon substrates by radio-frequency plasma enhanced chemical vapor deposition method using gas mixture of CH4 and Ar. The effect of different CH4/Ar gas ratio on the structure, refractive index, transmission and hardness of the DLC thin films were investigated by means of Raman spectroscopy, ellipsometry, Fourier transform Infrared Spectroscopy and nano-indentation methods, respectively. Nuclear resonant reaction analysis was used to measure the amount of hydrogen and carbon in the thin films. Furthermore, wettability of the thin films was achieved by measuring of water contact angle (WCA). The results indicated that the structural properties of the diamond-like carbon thin films are strongly dependent on the composition of gas mixture. Based on ellipsometry results, refractive index of the thin films varied in the range of 1.89–2.06 at 550 nm. FTIR results determined that deposition of DLC thin films on silicon substrate led to an increase of the light transmission in IR region and these films have the potential to be used in silicon optics as the antireflective coatings in this region. Nano-indentation analysis showed that the thin films hardness changed in the range of 7.5–11 GPa. On the other hand hydrogen content and fraction of C‒H bonds in the samples increased by an increase in the gas ratio of CH4/Ar. Also, WCA measurements indicated that WCA for thin films with gas ratio of 3/7 is the most and equal to 79°.

Substrate-independent stress–strain behavior of diamond-like carbon thin films by nanoindentation with a spherical tip

Abstract

A study for anticorrosion and tribological behaviors of thin/thick diamond-like carbon films in seawater

The thin and thick diamond-like carbon (DLC) films were prepared by unbalanced magnetron sputtering technique on 304L stainless steels and (100) silicon wafers. Microstructure, mechanical, corrosion and tribological properties were systematically investigated by SEM, Raman, nanoindenter, scratch tester, modulab electrochemical workstation and R-tec multifunctional tribological tester. Results showed that the adhesion force presented a descending trend with the growth in soaking time. The adhesion force of the thin DLC film with high residual compressive stress (−3.72 GPa) was higher than that of the thick DLC film (−2.96 GPa). During the corrosion test, the thick DLC film showed a higher impendence and a lower corrosion current density than the thin DLC film, which is attributed to the barrier action of large thickness. Compared to bare 304L substrate, the friction coefficients and wear rates of DLC films in seawater were obviously decreased. Meanwhile, the thin DLC film with ideal residual compressive stress, super adhesion force and good plastic deformation resistance revealed an excellent anti-wear ability in seawater.

Diamond-like carbon thin films prepared by pulsed-DC PE-CVD for biomedical applications

In the present research, diamond-like carbon (DLC) thin films were applied on steel substrates by means of pulsed-direct current (DC) plasma-enhanced chemical vapor deposition (PE-CVD). The effects of bias voltage and deposition pressure on the films’ structure and properties were investigated. The Raman spectra of the films revealed features typical of G and D bands, indicating the formation of a DLC phase. The results demonstrate that the sp3 carbon fraction or the so-called diamond-like character of the DLC films increased with increasing bias voltage. Moreover, an increase in the bias voltage resulted in a decrease in the film thickness from 800 to 200 nm. Also, the DLC films prepared at a higher deposition pressure showed a higher fraction of sp2-bonded carbon – that is, graphitic domains. Furthermore, it was found that the variation in the bias voltage and deposition pressure also affected the internal stress values of the DLC films in a way that they increased from 1 to 11 GPa when the bias voltage was increased from 475 to 675 V. The effectiveness of DLC films formed on the steel substrates can pave the way for developing a new class of advanced materials to enhance the performance of stainless steel for biomedical applications.

Structural Evolution of Q-Carbon and Nanodiamonds

This article provides insights pertaining to the first-order phase transformation involved in the growth of densely packed Q-carbon and nanodiamonds by nanosecond laser melting and quenching of diamond-like carbon (DLC) thin films. DLC films with different sp3 content were melted rapidly in a controlled way in super-undercooled state and quenched, leading to formation of distinct nanostructures, i.e., nanodiamonds, Q-carbon, and Q-carbon nanocomposites. This analysis provides direct evidence of the dependence of the super-undercooling on the structural evolution of Q-carbon. Finite element heat flow calculations showed that the super-undercooling varies monotonically with the sp3 content. The phenomenon of solid–liquid interfacial instability during directional solidification from the melt state is studied in detail. The resulting lateral segregation leads to formation of cellular filamentary Q-carbon nanostructures. The dependence of the cell size and wavelength at the onset of instability on the sp3 content of DLC thin films was modeled based on perturbation theory.

Optoelectronic and mechanical properties of PVD diamond-like carbon films

The role of sp3and sp2 bonding and hydrogen content on the optical, electronic and elastic properties of diamond-like carbon (DLC) thin films is investigated. The films were prepared using a graphite target and CH4/Ar ambient by RF and DC reactive magnetron sputtering at 4.41W/cm2. Raman spectroscopy and transmission infrared spectroscopy were used to estimate the sp3/sp2 ratio and hydrogen content. The density, thickness and the surface roughness dependence on the sp3/sp2 fraction was studied by X-ray reflectivity (XRR). Surface Brillouin scattering on diamond-like carbon thin films / (001)Si establish the correlation between elastic constants and the sp3/sp2 bond ratio.

Diamond-like carbon prepared by pulsed laser deposition with ion bombardment: physical properties

Diamond-like carbon (DLC) and titanium-doped DLC thin films were prepared by unique hybrid system consisting of pulsed laser deposition, ion source (bombardment) and magnetron sputtering. The influence of deposition parameters (ion energies, deposition pressures and magnetron power) on composition and physical properties was studied. Composition and sp3/sp2 ratio were determined by XPS. sp3/sp2 ratio was in the range from 1.4 to 2.2 for undoped DLC and from 3.4 to 4.8 for Ti-DLC. AFM showed that the layers were smooth, but with small amounts of random droplets. The measurements of the contact angle and determination of surface free energy were made for water, diiodomethane and ethylene glycol. Hardness and reduced Young’s modulus varied from 20 to 31 GPa and from 182 to 276 GPa, respectively. Film adhesion was determined by scratch test; LC3 reached 23 N for DLC and 27 N for TiDLC. Optimization of sp3/sp2 ratio, hardness and adhesion to biomedical alloys will advance the DLC coatings usability in the field of implantology.

Nano-diamond and Diamond-like Carbon Thin Films for Anti-Reflecting Coating Application on Silicon Solar Cells

Highly transparent nano-diamond (NCD) and diamond-like carbon (DLC) films are produced by Micro-Wave PECVD and Radio-Frequency magnetron sputtering, respectively for comparative study on application perspective, as antireflection coating (ARC) for silicon solar cells. Considering application of ARC on the already fabricated top electrode of solar cells, the typical synthesis techniques are selected on the basis of their advantages of being the low temperature processes. Optical band-gap (Eg), transmittance, reflectance, ID/IG ratio in Raman spectra and sp3-fraction of the films have been estimated and the magnitude of refractive index has been optimized between that of air (n= 1) and Si (n= 3.4), satisfying the basic requirement. Economic development of commercially viable ARC-grade NCD and DLC films are developed for Si solar cells without any external heating of the substrates.

Fabrication and electrochemistry characteristics of nickel-doped diamond-like carbon film toward applications in non-enzymatic glucose detection

This research work focused on the fabrication of nickel-doped diamond-like carbon (DLC) films and their characteristics including of surface morphology, microstructure, and electrochemical aiming at applications in non-enzymatic glucose detection. Novel nanodiamond target was employed in unbalanced magnetron radio-frequency co-sputtering process to prepared high quality Ni-doped DLC thin film at room temperature. TEM analysis reveals a highly uniform distribution of Ni crystallites in amorphous carbon matrix with fraction ranged from 3 to 11.5 at.% which is considered as active sites for the glucose detection. Our cyclic voltammetry measurements using 0.1 M H2SO4 solution demonstrated that the as-prepared Ni-doped DLC films possess large electrochemical potential window of 2.12 V, and this was also observed to be significantly reduced at high Ni doping level owing to lower sp3 fraction. The non-enzymatic glucose detection investigation indicates that the Ni-doped DLC thin film electrode prepared under 7 W of DC sputtering power on Ni target possesses good detecting performance, high stability, and high sensitivity to glucose concentration up to 10 mM, even with the existence of uric acid and ascorbic acid. The peak current was observed to be proportional to glucose concentration and scanning rate, demonstrating highly reversibility redox process of the film electrode and glucose.

Structural and optical properties of Ni-embedded hydrogenated diamond-like carbon (Ni-DLC) prepared by co-deposition of RF-Sputtering and RF-PECVD method

The composite nickel incorporated diamond-like carbon (Ni-DLC) thin films were produced by using RF-Sputtering and RF-Plasma enhanced chemical vapor deposition(RF-PECVD) from acetylene gas and nickel target in various RF powers. The structural and optical properties of thin films with increasing nickel content were investigated. X-Ray Diffraction (XRD) study shows completely an amorphous structure. The presence of Ni and carbon content were confirmed by Energy dispersive X-ray (EDX) Spectra. The optical band gap energy decreases from 4.58 to 3.66eV with increasing applied power. The Urbach energy displays a decreasing trend from 0.472 to 0.189eV. It is shown that the Ni content and the size of nanoparticles could be controlled by adjusting RF applied power.

Cu incorporated amorphous diamond like carbon (DLC) composites: An efficient electron field emitter over a wide range of temperature

The effect of temperature on the electron field emission properties of copper incorporated amorphous diamond like carbon (a-Cu:DLC) thin films have been reported. The a-Cu:DLC thin films have been deposited on indium tin oxide (ITO) coated glass and silicon substrate by the radio frequency sputtering process. The chemical composition of the films was investigated using X-ray photoelectron spectroscopy and the micro structure was established using high resolution transmission electron microscopy. The sp2 and sp3 bonding ratio in the a-Cu:DLC have been analyzed by the Fourier transformed infrared spectroscopy studies. The material showed excellent electron field emission properties; which was optimized by varying the copper atomic percentage and temperature of the films. It was found that the threshold field and effective emission barrier were reduced significantly by copper incorporation as well as temperature and a detailed explanation towards emission mechanism has been provided.

Adhesion enhancement of DLC on CoCrMo alloy by diamond and nitrogen incorporation for wear resistant applications

Diamond like carbon (DLC) coating is promising to increase the service lifetime of hip joints made of CoCrMo alloy. However, the weak adhesion of DLC on the alloy presents problems for this application. This work aims to improve the adhesion of DLC on CoCrMo alloy with nitrogen doping and diamond incorporation. Microcrystalline diamond particles were synthesized on CoCrMo alloy sheets by Microwave Plasma Enhanced Chemical Vapor Deposition and nitrogen doped DLC thin films were then deposited on them by Inductively Coupled Plasma assisted Chemical Vapor Deposition. The effect of nitrogen doping and diamond incorporation on the film adhesion was investigated by Rockwell C indentation. The results show that nitrogen doping and diamond incorporation can improve the film adhesion significantly. Ball-on-disc friction and wear testing results reveal that the friction coefficient and wear rate between polyethylene balls and DLC (doped with nitrogen) coated CoCrMo decreases with the increase of nitrogen content in the coatings. Those results have demonstrated that the modified DLC films are promising for total hip joint replacement application.

On the influence of PDMS (polydimethylsiloxane) substrate surface energy in wrinkling of DLC (diamond-like carbon) thin films

We have explored the influence of surface energy of the PDMS (polydimethylsiloxane) substrate on the wrinkling of diamond-like carbon thin films. The surface energy of PDMS can be tuned by exposure to oxygen plasma or by shallow-implantation of gold. The result is an increase in the wrinkling wavelength and amplitude. By means of a tri-layer wrinkling model, we discuss whether the major contribution to the wavelength variation is via the surface energy of the substrate or via the mechanical properties of the interface layer resulting from the surface treatment. We conclude that the surface energy of the substrate is an important property that must be considered in order to provide a complete description of wrinkling phenomena.