Wettability and antibacterial activity of modified diamond-like carbon films

Diamond-like carbon (DLC) films can be used in a numerous industrial applications, including biomedical coatings with bactericidal properties. It has been demonstrated that DLC surface can be modified with oxygen plasma treatment. The purpose of this paper is to study the wettability and bactericidal activity of oxygen plasma-treated DLC films produced by plasma enhanced chemical vapor deposition technique. The sp³/sp² ratio increased after the treatment due to the increase in the generation of the unstable carbon bonds caused by the energetic ions, especially O-H group. The treated DLC surface becomes superhydrophilic and rougher, although the roughness values are still lower. DLC antibacterial activity did not increased with plasma treatment. Therefore, oxygen plasma treatment can be used to make superhydrophilic DLC but not to increase its bactericidal properties.     

Nanoindentation measurements on modified diamond-like carbon thin films

In the present study, we explored the effect of metallic interlayers (Cu and Ti) and indentation loads (5-20 mN) on the mechanical properties of plasma produced diamond-like carbon (DLC) thin films. Also a comparison has been made for mechanical properties of these films with pure DLC and nitrogen incorporated DLC films. Introduction of N in DLC led to a drastic decrease in residual stress (S) from 1.8 to 0.7 GPa, but with expenses of hardness (H) and other mechanical properties. In contrast, addition of Cu and Ti interlayers between substrate Si and DLC, results in significant decrease in S with little enhancement of hardness and other mechanical properties. Among various DLC films, maximum hardness 30.8 GPa is observed in Ti-DLC film. Besides hardness and elastic modulus, various other mechanical parameters have also been estimated using load versus displacement curves.     

椭偏光散射分析类金刚石薄膜的散射特性

 基于光学薄膜反射椭偏法的测量原理,对光学薄膜散射椭偏特性进行了研究。给出了光学薄膜散射逆问题的解决方法,并对不同脉冲频率下采用脉冲真空电弧离子镀技术沉积的类金刚石薄膜的散射特性进行了研究。分析了光学薄膜界面的相关特性以及膜层中局部缺陷对散射光椭偏特性的影响。结果表明:随着脉冲频率的增加,所沉积的类金刚石薄膜的相关性变差,且薄膜中的局部缺陷引起的体散射越明显。     

Effect of deposition voltage on the field emission properties of electrodeposited diamond-like carbon films

Diamond-like carbon (DLC) films were deposited on Al substrates by electrodeposition technique under various voltages. The surface morphology and compositions of synthesized films were characterized by scanning electron microscopy and Raman spectroscopy. With the increase of deposition voltage, the sp² phase concentration decreased and the surface morphology changed dramatically. The influence of deposition voltage on the field electron emission (FEE) properties of DLC films was not monotonic due to two adverse effects of deposition voltage on the surface morphology and compositions. The DLC film deposited under 1200 V exhibited optimum FEE property, including a lowest threshold field of 13 V/μm and a largest emission current density of 904.8 μA/cm² at 23.5 V/μm.     

Gas barrier properties of diamond-like carbon films coated on PTFE

Diamond-like carbon (DLC) films were deposited on polytetrafluoroethylene (PTFE) using radio frequency (RF) plasma-enhanced chemical vapour deposition (PE-CVD). Before the DLC coating, the PTFE substrate was modified with a N₂ plasma pre-treatment to enhance the adhesive strength of the DLC to the substrate. The influences of the N₂ plasma pre-treatment and process pressure on the gas permeation properties of these DLC-coated PTFE samples were investigated. In the Raman spectra, the G peak position shifted to a lower wave number with increasing process pressure. With scanning electron microscopy (SEM), a network of microcracks was observed on the surface of the DLC film without N₂ plasma pre-treatment. The density of these cracks decreased with increasing process pressure. In the film subjected to a N₂ plasma pre-treatment, no cracks were observed at any process pressure. In the gas barrier test, the gas permeation decreased drastically with increasing film thickness and saturated at a thickness of 0.2 μm. The DLC-coated PTFE with the N₂ plasma pre-treatment exhibited a greater reduction in gas permeation than did the samples without pre-treatment. For both sample types, gas permeation decreased with increasing process pressure.     

Characterization of diamond-like carbon films by SEM, XRD and Raman spectroscopy

Diamond-like carbon films were deposited by electrolysis of a water-ethanol solution on Cu at low voltages (60-100 V) at 2 mm interelectrode separation. The films were characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and Raman spectroscopy. The films were found to be continuous and compact with uniform grain distribution. Raman spectroscopy analysis revealed two broad bands at ∼1350 and ∼1580 cm⁻¹. The downshift of the G band of graphite is indicative of the presence of DLC. For XRD analysis, the three strong peaks located at 2θ values of 43.2°, 74.06° and 89.9° can be identified with reflections form (1 1 1), (2 2 0) and (3 1 1) plane of diamond.     

Influences of ultraviolet irradiation on structure and tribological properties of diamond-like carbon films

Two types of diamond-like carbon (DLC) films with different bonding configurations were produced by pulse-assisted and DC-assisted plasma chemical vapor deposition. The chemical composition, surface morphology, microstructure, internal stress and tribological properties of the two films before and after the ultraviolet (UV) irradiation were investigated and compared. It was found that the UV irradiation had little effects on the chemical composition and surface morphology of both the films, but greatly influenced their tribological properties in the opposite trends. This result was attributed to the different changing outcomes of the bonding configuration induced by the UV actions of primary photo-dissociation and secondary recombination, wherein the inherent bonding configuration and internal stress played important roles.     

Effects of CPII implantation on the characteristics of diamond-like carbon films

A diamond-like carbon film (DLC) was successfully synthesized using a hybrid PVD process, involving a filter arc deposition source (FAD) and a carbon plasma ion implanter (CPII). A quarter-torus plasma duct filter markedly reduced the density of the macro-particles. Graphite targets were used in FAD. Large electron and ion energies generated from the plasma duct facilitate the activation of carbon plasma and the deposition of high-quality DLC films. M2 tool steel was pre-implanted with 45 kV carbon ions before the DLC was deposited to enhance the adhesive and surface properties of the film. The ion mixing effect, the induction of residual stress and the phase transformation at the interface were significantly improved. The hardness of the DLC increased to 47.7 GPa and 56.5 GPa, and the wear life was prolonged to over 70 km with implantation fluences of 1 × 10¹⁷ ions/cm² and 2 × 10¹⁷ ions/cm², respectively.     

Understanding the friction behavior of sulfur-terminated diamond-like carbon films under high vacuum by first-principles calculations

Generally, the repulsive force was a key factor account for superlow friction of H or F doped diamond-like carbon (DLC) films under high vacuum. As we known, H or F doped DLC usually exhibited superlow friction under high vacuum. However, the superlow friction of S doped DLC under high vacuum was not found so far. This phenomenon was desirable to be well investigated. In this work, S-terminated diamond interfaces also exhibited strong repulsive force, however, the estimated friction coefficient was variable for S-terminated diamond interfaces. The lowest and largest friction coefficient was about 0.003 and 0.4 respectively, which indicated that the superlow friction of S doped DLC could achieve in theory. In order to well probe the unusual friction behavior of S doped DLC under high vacuum, using first-principles method, the repulsive interaction between sliding surfaces was well investigated in order to understand the unusual friction behavior of S doped DLC films.     

Atomic oxygen resistant behaviors of Mo/diamond-like carbon nanocomposite lubricating films

Mo doped diamond-like carbon (Mo/DLC) films were deposited on Si substrates via unbalanced magnetron sputtering of molybdenum combined with plasma chemical vapor deposition of CH₄/Ar. The microstructure of the films, characterized by transmission electron microscopy and selected area electron diffraction, was considered as a nanocomposite with nano-sized MoC particles uniformly embedded in the amorphous carbon matrix. The structure, morphology, surface composition and tribological properties of the Mo/DLC films before and after the atomic oxygen (AO) irradiation were investigated and a comparison made with the DLC films. The Mo/DLC films exhibited more excellent degradation resistant behaviors in AO environment than the DLC films, and the MoC nanoparticles were proved to play a critical role of preventing the incursion of AO and maintaining the intrinsic structure and excellent tribological properties of DLC films.     

Femtosecond pulsed laser deposition of diamond-like carbon films: The effect of double laser pulses

The bonding structure of carbon films prepared by pulsed laser deposition is determined by the plasma properties especially the change of the kinetic energy. Using double laser pulses the ablation process and the characteristics of the generated plasma can be controlled by the setting of the delay between the pulses. In our experiments, amorphous carbon films have been deposited in vacuum onto Si substrates by double pulses from a Ti:sapphire laser (180 fs, λ = 800 nm, at 1 kHz) and a KrF laser system (500 fs, λ = 248 nm, at 5 Hz). The intensities have been varied in the range of 3.4 × 10¹² to 2 × 10¹³ W/cm². The morphology and the main properties of the thin layers were investigated as a function of the time delay between the two ablating pulses (0-116.8 ps) and as a function of the irradiated area on the target surface. Atomic force microscopy, spectroscopic ellipsometry and Raman-spectroscopy were used to characterize the films. It was demonstrated that the change of the delay and the spot size results in the modification of the thickness distribution of the layers, and the carbon sp²/sp³ bonding ratio.     

Improving the conductivity of diamond-like carbon films with zinc doping and its material properties

Zinc doped diamond-like carbon (DLC) nanocomposite thin films are fabricated by KrF pulsed laser deposition. Carbon targets containing 3.0, 5.0 and 10.0 atomic percentages of zinc are used as the source for the laser system. Investigation of electrical properties by the four-point probe shows that doping zinc into DLC can lower the electrical sheet resistivity. Microstructural analysis by Raman spectroscopy and XPS show a lower sp³ content but a higher SiC content with an increasing amount of zinc incorporation. The increase of SiC leads to an increase in adhesion strength. Surface roughness of the films also increases while the coefficients of friction for the films do not change.     

衬底温度对类金刚石薄膜力学性能的影响

 采用脉冲激光沉积方法在不同衬底温度下制备了最高硬度与弹性模量分别达45 GPa和290 GPa,且表面十分光滑的类金刚石薄膜。在相对湿度为80%的条件下,薄膜最低的摩擦系数与磨损率分别为0.045与5.74×10^-10 mm³·N^-1·m^-1。实验结果表明,硬度与弹性模量随衬底温度升高而降低,摩擦系数与磨损率随衬底温度升高而增大。拉曼光谱表明:在室温下制备的薄膜为典型类金刚石结构,sp³含量高达76.8%,而随温度升高,薄膜结构逐渐经无定形碳结构向纳米晶石墨结构方向发展,sp³含量也随之降低,力学性能变差。     

Surface modification of diamond-like carbon films with perfluorooctyl functionalities and their surface properties

Photolysis of perfluoroazooctane with diamond-like carbon (DLC) films led to the surface modification to introduce perfluorooctyl functional groups, confirmed by means of FT-IR, XPS, Raman and TOF-SIMS measurements. The DLC films modified with fluorine moieties showed reduction of the surface energy evaluated by contact angle to water, as compared with pristine DLC film. The contact angle of chemically modified DLC film is 105°, comparable to that of polytetrafluoroethylene (PTFE). By monitoring with XPS, we found that the results on the value of fluorine/carbon ratio of fluorinated DLC films depending on irradiation time are consistent with those of contact angle. Chemical modification of DLC films with perfluorooctyl functionalities also led to improvement of their frictional properties. The friction coefficient of the modified film is 0.05 under vacuum condition, whereas that of the pristine film shows very high value (>1).     

Deodorisation effect of diamond-like carbon/titanium dioxide multilayer thin films deposited onto polypropylene

Many types of plastic containers have been used for the storage of food. In the present study, diamond-like carbon (DLC)/titanium oxide (TiO₂) multilayer thin films were deposited on polypropylene (PP) to prevent flavour retention and to remove flavour in plastic containers.For the flavour removal test, two types of multilayer films were prepared, DLC/TiO₂ films and DLC/TiO₂/DLC films. The residual gas concentration of acetaldehyde, ethylene, and turmeric compounds in bottle including the DLC/TiO₂-coated and the DLC/TiO₂/DLC-coated PP plates were measured after UV radiation, and the amount of adsorbed compounds to the plates was determined. The percentages of residual gas for acetaldehyde, ethylene, and turmeric with the DLC/TiO₂ coated plates were 0.8%, 65.2% and 75.0% after 40 h of UV radiation, respectively. For the DLC/TiO₂/DLC film, the percentages of residual gas for acetaldehyde, ethylene and turmeric decreased to 34.9%, 76.0% and 85.3% after 40 h of UV radiation, respectively. The DLC/TiO₂/DLC film had a photocatalytic effect even though the TiO₂ film was covered with the DLC film.     

Influence of crystalline diamond nanoparticles on diamond-like carbon friction behavior

Crystalline diamond (CD) particles have been incorporated in diamond-like carbon (DLC) film structure in order to improve DLC electrochemical corrosion resistance. This paper shows the investigation of CD-DLC friction behavior according to the CD average sizes and concentration. The films were growth over 304 stainless steel using plasma enhanced chemical vapor deposition. The response surface methodology was used to develop a mathematical modeling of friction for these films, using the experimental results, in order to identify parameters that control friction and construct tribological maps according to the CD average sizes. The presence of bigger CD particles (250 and 500 nm) increased the film roughness. Films with CD particles of 4 nm presented the most homogeneous friction map, with minor variation in friction coefficient with the increase/decrease of load and sliding speed even when the CD concentration increase. This result suggests that in CD-DLC films containing CD particles of 4 nm average size, the nanoparticles are better incorporated in DLC structure due to its average size (4 nm) that is near than DLC grain size and could occupy the nanospaces between DLC grains.     

含氮类金刚石薄膜的紫外辐照研究

 用射频等离子体方法在玻璃基底上制备的类金刚石（DLC）薄膜，采用离子注入法掺氮，并对掺氮DLC薄膜紫外（UV）辐照前后的性能变化进行了研究。研究结果表明：随氮离子注入剂量及UV辐照时间的增加，位于2 930cm^-1附近的SP ³C-H吸收峰明显变小，而位于1 580cm^-1附近的SP2C-H吸收峰则明显增强，薄膜的电阻率明显呈下降趋势；随UV辐照时间的增加，位于1 078cm^-1附近的Si-O-Si键数量及位于786cm^-1附近的Si-C键数量明显增加。即氮离子注入和UV辐照明显改变了DLC薄膜的结构与特性。     

Influence of sulfidation treatment on the structure and tribological properties of nitrogen-doped diamond-like carbon films

The nitrogen-doped diamond-like carbon (DLC) films were deposited on high speed steel (HSS) substrates in the direct current unbalanced magnetron sputtering system. Sulphurized layer was formed on the surface of DLC films by means of liquid sulfidation in the intermixture of urea and thiourea solution in order to improve the tribological properties of DLC films. The influence of sulfidation treatment on the structure and tribological properties of DLC films was investigated in this work. The structure and wear surface morphology of DLC films were analyzed by Raman spectroscopy, XPS and SEM, respectively. It reveals that the treated films are smooth and uniform; and sulfur atoms are bonded chemically. The treated films have broader distribution of Raman spectra in the range of 1000-1800 cm⁻¹ and higher I_D/I_G ratio than the untreated films as a result of the appearance of the crystalline graphite structure after the sulfidation treatment. It is showed that the sp² relative content increase in the treated films from the XPS measurement. The Raman results are consistent with the XPS results. The tribological properties of DLC films were investigated using a ball-on-disk rotating friction and wear tester under dry friction conditions. It is found that the sulfidation concentration plays an important part in the tribological properties of the treated DLC films. The results showed the treated films with low sulfidation concentration have a lower friction coefficient (0.1) than the treated films with high sulfidation concentration (0.26) and the untreated films (0.27) under the same friction testing conditions, which can be attributed to both the presence of sulfur-containing materials and the forming of the mechanical alloyed layer on the wear surface. Adding the dry nitrogen to the sliding surface in the testing system helps the friction coefficient of the treated films with low sulfidation concentration to decrease to 0.04 further in this work. On the basis of the experimental results, it is indicated that the liquid sulfidation technique, which is low-cost, non-polluting and convenience, would be an appropriate method for the surface treatment of DLC films.     

Influence of high temperature annealing on the structure, hardness and tribological properties of diamond-like carbon and TiAlSiCN nanocomposite coatings

Diamond-like carbon (DLC) and TiAlSiCN nanocomposite coatings were synthesized and annealed at different temperatures in a vacuum environment. The microstructure, hardness and tribological properties of as-deposited and annealed DLC-TiAlSiCN nanocomposite coatings were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Raman spectroscopy, nano-indentation and friction tests. The TEM results reveal that the as-deposited DLC-TiAlSiCN coating has a unique nanocomposite structure consisting of TiCN nanocrystals embedded in an amorphous matrix consisting of a-Si₃N₄, a-SiC, a-CN and DLC, and the structure changed little after annealing at 800 °C. However, XPS and Raman results show that an obvious graphitization of the DLC phase occurred during the annealing process and it worsened with annealing temperature. Because of the graphitization, the hardness of the DLC-TiAlSiCN coating after annealing at 800 °C decreased from 45 to 36 GPa. In addition, the DLC-TiAlSiCN coating after annealing at 800 °C has a similar friction coefficient to the as-deposited coating.     

Quantification of oxygenated species on a diamond-like carbon (DLC) surface

This paper discusses the use of chemical derivatization methods for surface chemical composition analysis of diamond-like carbon (DLC) films synthesized through plasma-enhanced chemical vapor deposition with X-ray photoelectron spectroscopy (XPS). The main challenge in applying chemical derivatization reactions for titration of organic functional groups on the DLC surface is that sub-surface oxygenated species are not accessible to the derivatizing agent. As a simple approximation, a functional group that can be quantified unambiguously with XPS can be used as an internal reference to estimate the accessible-to-inaccessible ratio, and this information can be used to estimate the total amount of other functional groups from the chemical-derivatization-assisted XPS analysis. The use of this principle to obtain the surface composition of hydroxyl, ether, carbonyl, and carboxyl groups in the oxidized surface region of the DLC film was demonstrated.