Microstructure and mechanical properties of Mo/DLC nanocomposite films

Mo-doped diamond-like carbon (Mo/DLC) films were deposited on stainless steel and Si wafer substrates via unbalanced magnetron sputtering of molybdenum combined with inductively coupled radio frequency (RF) plasma chemical vapor deposition of CH₄/Ar. The effects of Mo doping and sputtering current on the microstructure and mechanical properties of the as-deposited films were investigated by means of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, atomic force microscopy (AFM), and nano-indentation. It was found that Mo doping led to increase in the content of sp² carbon, and hence decreased the hardness and elastic modulus of Mo/DLC films as compared with that of DLC films. The content of Mo in the films increased with the increasing sputtering current, and most of Mo reacted with C atoms to form MoC nanocrystallites at a higher sputtering current. Moreover, the Mo-doped DLC films had greatly decreased internal stress and increased adhesion to the substrate than the DLC film, which could be closely related to the unique nanocomposite structure of the Mo-doped films. Namely, the Mo/DLC film was composed of MoC nanoparticles embedded in the cross-linked amorphous carbon matrix, and such a kind of nanostructure was beneficial to retaining the loss of hardness and elastic modulus.     

Electro-deposition of adherent films of H2-free quality diamond-like carbon materials on SS-304 substrates using nanocrystalline SnO2 interlayer

H₂-free diamond-like carbon (DLC) films are deposited on bare as well as nanocrystalline SnO₂-coated stainless steel (SS) 304 substrates. SnO₂ films are deposited by electrolysis of 10 mM SnCl₂ solution in nitric acid medium and then subsequently heating the sample in oxygen-ambient condition. The carbon films, on the other hand, are prepared by dissociative cleavage of methanol under high DC potential of 1 kV. Deposition conditions are optimised to get the best quality films, which are characterized by Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). It has been observed that films grown on SnO₂ interlayer are much more adherent when compared to those deposited on bare SS. Moreover, the quality of films on coated substrates is found to be much superior to those grown on bare SS. It is believed that the SnO₂ layer acts both as protective barrier against carbon diffusion into the SS substrate and also promotes nucleation due to anchorage of CH₃ and H⁺ radicals (necessary for growth of DLC film) onto its oxygen deficient sites.     

Effect of carbonitriding temperature process on the adhesion properties of diamond like-carbon coatings deposited by PECVD on austenitic stainless steel

The deposition of adherent coatings such as diamond-like carbon (DLC) on substrates of iron-based materials is difficult to obtain for two reasons: high residual compressive stress occurs in the inner film formation, and the mismatch of thermal expansion coefficient between steel and DLC film generates delamination effects. In order to determine the carbonitriding temperature prior to film deposition, the steel substrate and the DLC films were analyzed for their microstructure and mechanical properties of adhesion as a function of temperature. The technique used to deposit the coating was DC-pulsed plasma enhanced chemical vapor deposition. The delamination distances and the critical load of the film were obtained by scratch testing. The surface analysis by X-ray diffraction indicated the formation of nitride phases on the steel. Raman spectroscopy showed the fraction of sp³ carbon bonds in DLC films. Hardness profiling was used to verify the extent of the interface modified by carbonitriding along the cross section. For this, the steel sample with the appropriate surface modification to have high adhesion of the DLC film was used.     

Study on the diamond-like carbon multilayer films for tribological application

In this paper, DLC multilayer films consisting of alternating layers of soft and hard carbon films were deposited on Si wafer by a plasma CVD deposition system. Different DLC multilayer films were prepared by varying the sub-layer thickness (from 1000 to 25 nm) and the ratio of hard to soft sub-layer (H/S) thickness (from 1:1 to 4:1). By using a ball-on-disk tribo-tester, the friction and wear properties of the DLC multilayer films were measured in vacuum, O₂ and dry-air environments respectively. By comparing with single-layer DLC film, the change of the multilayer structure has little influence on friction coefficient of the multilayer films. However, the wear rate of the DLC multilayer films is restricted effectively by constructed the multilayer structure in the film. The wear rate of the multilayer films is lower than that of the single film in reactive (O₂ and dry-air) environments. An DLC multilayer film with excellent wear resistance, approximately in the level of 10⁻⁸ mm³/Nm in different environments (dry-air, O₂ and vacuum), is obtained as the DLC multilayer film at a certain sub-layer thickness and ratio.     

Study on metal-doped diamond-like carbon films synthesized by cathodic arc evaporation

In this study, we developed a novel method of synthesizing metal-doped diamond-like carbon films (DLC) using the cathodic arc evaporation (CAE) process. Intense Cr plasma energy activated the decomposition of hydrocarbon source gas C₂H₂ to form a metal-doped amorphous carbon film on steel substrates. We deposited a Cr interlayer to prevent interdiffusion between DLC and the steel substrates. When the C₂H₂ partial pressure is higher than 1.3 Pa, the deposition reaction switched from Cr₃C₂ to DLC formation. The result is a hydrogenated DLC thin film possessing excellent microhardness as high as 3824 Hv(25g), and for which the incorporation of a Cr interface and Cr doping in the DLC matrix ensure film ductility and sufficient film adhesion. We employed Raman spectroscopy to evaluate the influences of reactive gas flow and substrate bias on the DLC composition; we carried out the microstructure and mechanical property measurements by scanning electron microscopy (SEM), X-ray diffraction (XRD), glow discharge optical spectroscopy (GDS) and wear tests.     

Duplex DLC coatings fabricated on the inner surface of a tube using plasma immersion ion implantation and deposition

A duplex plasma immersion ion implantation and deposition (PIIID) process, involving carbon ion implantation and diamond-like carbon (DLC) deposition, is proposed to modify the inner surface of a tube. In the research, samples of GCr15 bearing steel were placed inside a tube in the vacuum chamber. After the vacuum chamber was evacuated to a base pressure of 6 × 10^− 3 Pa, C₂H₂ gas was introduced into the chamber, and the tube was biased by a negative pulsed bias. Since a pulsed glow discharge (PGD) plasma can be formed by the bias, carbon ion implantation and DLC film deposition process can be obtained by biasing the tube with a high and low bias, respectively. To synthesize different DLC films, single PIIID processes employing a low voltage (several kV) PGD method and duplex PIIID processes combining the high (several tens kV) and low voltage PGD techniques were carried out. The as-synthesized films were characterized by Raman spectrum, nano-indentation, scratch, tribological and electrochemical tests. Raman results show that duplex DLC films were synthesized by this duplex PIIID process. In addition, compared with the single DLC film synthesized by the low voltage PGD process, the duplex DLC films can obtain a high wear and corrosion resistances. Furthermore, using this duplex PIIID method, batch treatment of outer-rings of the bearing was realized.     

Mechanical properties of DLC films prepared in acetylene and methane plasmas using electron cyclotron resonance microwave plasma chemical vapor deposition

Diamond-like carbon (DLC) films were deposited on silicon using methane and acetylene plasma induced by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-MPCVD). The mechanical properties of DLC films were characterized by micro-Raman system, atomic force microscope, tribometer, nano-indenter used for both hardness and nano-scratch test measurements. The mechanical properties of both DLC films, prepared in methane and acetylene plasmas, respectively, strongly depended on the kinetic energy of impinging particles. The deposition at −120 V substrate bias gave rise to DLC films with the best mechanical properties for both methane and acetylene plasmas. The hardness measurements with variable indentation depth showed the characteristic changes in hardness values implying elastic deformations of supporting substrates. The maximum hardness value of DLC^M films was 20 GPa while that of DLC^A films was 28 GPa. However, the hardness dropped when DLC films were prepared at substrate biases more negative than −120 V due to the thermal graphitization. The improvement in DLC properties usually provided the films with smaller hydrogen content and higher density of sp³ bondings. These parameters were engineered through controlling the deposition parameters. Particularly, the bombardment of growing DLC films by energetic ions showed to be extremely important to yield films with lower internal stress.     

Electron field emission from filtered arc deposited diamond-like carbon films using Au and Ti layers

In this work, tetrahedral diamond-like carbon (DLC) films are deposited on Si, Ti/Si and Au/Si substrates by a new plasma deposition technique — filtered arc deposition (FAD). Their electron field emission characteristics and fluorescent displays of the films are tested using a diode structure. It is shown that the substrate can markedly influence the emission behavior of DLC films. An emission current of 0.1 μA is detected at electric field E_DLC/Si=5.6 V/μm, E_DLC/Au/Si=14.3 V/μm, and E_DLC/Ti/Si=5.2 V/μm, respectively. At 14.3 V/μm, an emission current density J_DLC/Si=15.2 μA/cm², J_DLC/Au/Si=0.4 μA/cm², and J_DLC/Ti/Si=175 μA/cm² is achieved, respectively. It is believed that a thin TiC transition layer exists in the interface between the DLC film and Ti/Si substrate.     

Tribological properties of DLC films with different hydrogen contents in water environment

Diamond-like carbon (DLC) films were deposited on silicon wafers by thermal electron excited chemical vapor deposition (CVD). To change the hydrogen content in film, we used three types of carbon source gas (C₇H₈, CH₄, and a CH₄+H₂) and two substrate bias voltages. The hydrogen content in DLC films was analyzed using elastic recoil detection analysis (ERDA). Tribological tests were conducted using a ball-on-plate reciprocating friction tester. The friction surface morphology of DLC films and mating balls was observed using optical microscopy and laser Raman spectroscopy.Hydrogen content in DLC films ranged from 25 to 45 at.%. In a water environment, the friction coefficient and specific wear rate of DLC films were 0.07 and in the range of 10⁻⁸–10⁻⁹ mm³/Nm, respectively. The friction coefficient and specific wear rate of DLC film in water were hardly affected by hydrogen content. The specific wear rate of DLC film with higher hardness was lower than that of film with low hardness. Mating ball wear was negligible and the friction surface features on the mating ball differed clearly between water and air environments, i.e., the friction surface on mating balls in water was covered with more transferred material than that in air.     

Synthesis of nitrogen incorporated diamond-like carbon thin films using microwave surface-wave plasma CVD

Nitrogenated diamond-like (DLC:N) carbon thin films have been deposited by microwave surface wave plasma chemical vapor deposition on silicon and quartz substrates, using argon gas, camphor dissolved in ethyl alcohol composition and nitrogen as plasma source. The deposited DLC:N films were characterized for their chemical, optical, structural and electrical properties through X-ray photoelectron spectroscopy, UV/VIS/NIR spectroscopy, Raman spectroscopy, atomic force microscope and current–voltage characteristics. Optical band gap decreased (2.7 to 2.4 eV) with increasing Ar gas flow rate. The photovoltaic measurements of DLC:N / p-Si structure show that the open-circuit voltage (V_oc) of 168.8 mV and a short-circuit current density (J_sc) of 8.4 μA/cm² under light illumination (AM 1.5 100 mW/cm²). The energy conversion efficiency and fill factor were found to be 3.4 × 10^{− 4}% and 0.238 respectively.     

Preparation of diamond like carbon thin films above room temperature and their properties

Diamond like carbon (DLC) thin films were deposited on p-type silicon (p-Si), quartz and ITO substrates by microwave (MW) surface-wave plasma (SWP) chemical vapor deposition (CVD) at different substrate temperatures (RT ∼ 300 °C). Argon (Ar: 200 sccm) was used as carrier gas while acetylene (C₂H₂: 20 sccm) and nitrogen (N: 5 sccm) were used as plasma source. Analytical methods such as X-ray photoelectron spectroscopy (XPS), FT-IR and UV–visible spectroscopy were employed to investigate the structural and optical properties of the DLC thin films respectively. FT-IR spectra show the structural modification of the DLC thin films with substrate temperatures showing the distinct peak around 3350 cm^− 1 wave number; which may corresponds to the sp² C–H bond. Tauc optical gap and film thickness both decreased with increasing substrate temperature. The peaks of XPS core level C 1 s spectra of the DLC thin films shifted towards lower binding energy with substrate temperature. We also got the small photoconductivity action of the film deposited at 300 °C on ITO substrate.     

Synthesis and mechanical properties of carbon nanotube/diamond-like carbon composite films

Diamond-like carbon (DLC) coatings were successfully deposited on carbon nanotube (CNT) films with CNT densities of 1 × 10⁹/cm², 3 × 10⁹/cm², and 7 × 10⁹/cm² by a radio frequency plasma-enhanced chemical vapor deposition (CVD). The new composite films consisting of CNT/DLC were synthesized to improve the mechanical properties of DLC coatings especially for toughness. To compare those of the CNT/DLC composite films, the deposition of a DLC coating on a silicon oxide substrate was also carried out. A dynamic ultra micro hardness tester and a ball-on-disk type friction tester were used to investigate the mechanical properties of the CNT/DLC composite films. A scanning electron microscopic (SEM) image of the indentation region of the CNT/DLC composite film showed a triangle shape of the indenter, however, chippings of the DLC coating were observed in the indentation region. This result suggests the improvement of the toughness of the CNT/DLC composite films. The elastic modulus and dynamic hardness of the CNT/DLC composite films decreased linearly with the increase of their CNT density. Friction coefficients of all the CNT/DLC composite films were close to that of the DLC coating.     

Formation and characterization of DLC:Cr:Cu multi-layers coating using cathodic arc evaporation

Chromium and copper-doped diamond-like carbon (DLC:Cr:Cu) films were deposited on SKH 51 tool steel. We have prepared multilayers of DLC:Cr and DLC:Cu by cathodic arc evaporation process using chromium (Cr) and copper (Cu) target arc sources to provide Cr and Cu in the DLC. Acetylene reactive gases were also activated at a pressure of 5 mTorr to 25 mTorr and a temperature fixed at 180 °C to provide the DLC. The resulting DLC:Cr:Cu film contained Cr_xCu_y as well as Cr_xC_y nanoparticles vital for the film mechanical properties. The crystal structure was investigated using X-ray diffraction (XRD) and transmission electron microscopy, while the surface morphology and chemical composition were studied by field emission scanning electron microscopy and X-ray photoelectron spectroscopy. The process parameters were compared by studying the various mechanical properties of the films such as microhardness and residual stress. The result of this process enhanced the DLC:Cr:Cu composite coatings for high toughness and lower friction coefficient (0.08). The profiles of sp³/sp² (XPS) ratios corresponded to the change of microhardness profile by varying the pressure of the hydrocarbon gases (C₂H₂).     

Corrosion and tribological properties of ultra-thin DLC films with different nitrogen contents in magnetic recording media

The corrosion spot density and contact–start–stop tribological properties that correlate to mechanical properties, electrical resistivity and lubricant bonded ratio of DLC overcoats on different disks of various surface roughness were investigated. DLC overcoats of hydrogenated carbon (CH) and nitrogenated carbon (CN) films were deposited by ion beam deposition (IBD) and sputter, respectively. Results show that the intensity ratio I(D)/I(G) increases with decreasing IBD-CH film thickness and increasing N₂ concentration of sputtered-CN layer, which implies that the films prepared at higher N₂ concentration contain a relatively lower sp³ bonded carbon. The composite hardness and Young's modulus of DLC films decrease with decreasing IBD-CH thickness and increasing N₂ concentration of sputtered-CN layers. Compared to disk overcoats deposited with only IBD-CH of comparable thickness, the lubricant bonded ratio is dramatically increased from 12 to 30% when the 0.5 nm CN is deposited on IBD-CH film. By increasing the N₂ concentration in the CN layer from 10 to 50 at.%, the electrical resistivity decreased from 3.6 to 0.8 kΩ and the lubricant bonded ratio increased from 30 to 46%. The corrosion spots density of sputtered-CN film surface decreases with increasing N₂ concentration. It is concluded that the dual layer of 1.5 nm IBD-CH/0.5 nm sputtered-CN with 30% N₂ deposition has the best integrated performance of corrosion resistance and CSS tribological properties.     

Diamond-like carbon films synthesized under atmospheric pressure synthesized on PET substrates

Diamond-like carbon films were synthesized under atmospheric pressure (AP-DLC) and their gas barrier properties and hardness were measured. The AP-DLC films were uniformly obtained by RF-plasma CVD method at room temperature with a size of 450 mm². The growth rate increased as a function of C₂H₂ concentration and the average growth rate was around 12 μm/min. The maximum deposition rate was ~ 1 μm/s, which is approximately 2000 times larger than that by low-pressure plasma CVD of 1–2 μm/h. The gas barrier properties of AP-DLC films, ~ 1 μm thick, were 5–10 times larger than those of uncoated PET substrates. The microhardness of AP-DLC films was around 3 GPa, measured by the nano-indentation method. The issue lies in the removal of macro-particles of the films to improve the microhardness and the surface roughness.In this paper, we report the physical properties of DLC films synthesized under atmospheric pressure by the radio-frequency CVD method. We also summarize a brief history of PET bottle coating by vacuum-DLC films, as well as that of the development of atmospheric pressure technology and related DLC films, focused on gas barrier properties and micro-hardness.     

Effects of iodine doping on optoelectronic properties of diamond-like carbon thin films deposited by microwave surface wave plasma CVD

We report the effects of iodine (I) doping on the electrical and optical properties of diamond-like carbon (DLC) thin films grown on silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition at low temperature (<100 °C). For film deposition, we used argon gas with methane or camphor dissolved with ethyl alcohol composition as plasma source. The optical gap and photoconductivity measurements of the samples were carried out before and after the iodine doping. The results show that optical gap dropped from 3.4 to 0.9 eV corresponding to nondoping to iodine-doping conditions, respectively. The photovoltaic measurements show that the open-circuit voltage (V_oc) and short-circuit current density (J_sc) of I-doped DLC film deposited on n-type silicon substrate under light illumination (AM1.5, 100 mW/cm²) were approximately 177 mV and 1.15 μA, respectively, and the fill factor was found to be 0.217.     

Diamond-like carbon thin films by microwave surface-wave plasma CVD aimed for the application of photovoltaic solar cells

The nitrogen doped diamond-like carbon (DLC) thin films were deposited on quartz and silicon substrates by a newly developed microwave surface-wave plasma chemical vapor deposition, aiming the application of the films for photovoltaic solar cells. For film deposition, we used argon as carrier gas, nitrogen as dopant and hydrocarbon source gases, such as camphor (C₁₀H₁₆O) dissolved with ethyl alcohol (C₂H₅OH), methane (CH₄), ethylene (C₂H₄) and acetylene (C₂H₂). The optical and electrical properties of the films were studied using X-ray photoelectron spectroscopy, Nanopics 2100/NPX200 surface profiler, UV/VIS/NIR spectroscopy, atomic force microscope, electrical conductivity and solar simulator measurements. The optical band gap of the films has been lowered from 3.1 to 2.4 eV by nitrogen doping, and from 2.65 to 1.9 eV by experimenting with different hydrocarbon source gases. The nitrogen doped (flow rate: 5 sccm; atomic fraction: 5.16%) film shows semiconducting properties in dark (i.e. 8.1 × 10^{− 4} Ω^{− 1} cm^{− 1}) and under the light illumination (i.e. 9.9 × 10^{− 4} Ω^{− 1} cm^{− 1}). The surface morphology of the both undoped and nitrogen doped films are found to be very smooth (RMS roughness ≤ 0.5 nm). The preliminary investigation on photovoltaic properties of DLC (nitrogen doped)/p-Si structure show that open-circuit voltage of 223 mV and short-circuit current density of 8.3 × 10^{− 3} mA/cm². The power conversion efficiency and fill factor of this structure were found to be 3.6 × 10^{− 4}% and 17.9%, respectively. The use of DLC in photovoltaic solar cells is still in its infancy due to the complicated microstructure of carbon bondings, high defect density, low photoconductivity and difficulties in controlling conduction type. Our research work is in progress to realize cheap, reasonably high efficiency and environmental friendly DLC-based photovoltaic solar cells in the future.     

Antibacterial activity of DLC and Ag–DLC films produced by PECVD technique

Diamond-like carbon (DLC) films have been the focus of extensive research in recent years due to its potential application as surface coatings on biomedical devices. Doped carbon films are also useful as biomaterials. As silver (Ag) is known to be a potent antibacterial agent, Ag–DLC films have been suggested to be potentially useful in biomedical applications. In this paper, DLC films were growth on 316L stainless steel substrates by using Plasma Enhanced Chemical Vapour Deposition (PECVD) technique with a thin amorphous silicon interlayer. Silver colloidal solution was produced by eletrodeposition of silver electrodes in distilled water and during the deposition process it was sprayed among each 25 nm thickness layer DLC film. The antibacterial activity of DLC, Ag–DLC and silver colloidal solution were evaluated by bacterial eradication tests with Escherichia coli (E. coli) at different incubation times. With the increase of silver nanoparticle layers in Ag–DLC, the total compressive stress decreased significantly. Raman spectra showed the film structure did not suffer any substantial change due to the incorporation of silver. The only alteration suffered was a slightly reduction in hardness. DLC and Ag–DLC films demonstrated good results against E. coli, meaning that DLC and Ag–DLC can be useful to produce coatings with antibacterial properties for biomedical industry.     

Carbon nanotube deposits and CNT/SiO2 composite coatings by electrophoretic deposition

Abstract

Multiwalled carbon nanotube (CNT) films have been successfully fabricated by electrophoretic deposition (EPD) on stainless steel substrates. Electrophoretic deposition was performed using optimised aqueous suspensions under constant voltage conditions. Triton X-100 was used as a surfactant to disperse CNT bundles, and iodine was added as a particle charger. CNT/SiO₂ composite coatings were prepared by electrophoretic co-deposition. Experimental results show that the CNTs were efficiently mixed with SiO₂ nanoparticles to form a network structure. Layered CNT/SiO₂ porous composites were obtained by sequential EPD experiments alternating the deposition of CNT and SiO₂ nanoparticles. The structure of all films deposited was studied in detail by scanning electron microscopy. Possible applications of CNT and CNT/SiO₂ films are as porous coatings in the biomedical field, thermal management devices, biomedical sensors and other functional applications where the properties of CNTs are required.     

Electrochemical behavior of diamond-like-carbon coatings deposited on AlTiC (Al2O3 + TiC) ceramic composite substrate in HCl solution

The electrochemical characterization/corrosion behavior of diamond-like carbon thin films is worthwhile to study and needed in the field (as there has been limited comprehensive evaluation of this across all types of DLC in the literature). In this paper, newly developed tetrahedral amorphous carbon (ta-C) and hydrogenated amorphous carbon (a-C:H) films, prepared by filtered cathodic arc deposition (FCVA) and plasma enhanced chemical vapor deposition (PECVD) respectively were deposited over AlTiC (Al₂O₃ + TiC) ceramic composite substrate. Electrochemical impedance spectroscopy (EIS) and polarization measurements have been used to evaluate the coating performance in 2 M HCl solution. This ceramic substrate is used widely for the hard disk drives and read and write heads in computer. The memory of the hard disks can be increased by improving the surface quality and decreasing the pinholes. The DLC coatings were modified under different preparation conditions by changing the nitrogen-doping ratios as an attempt for improving the surface distribution and minimizing the surface coating defects.