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.     

Study of well adherent DLC film deposited on piezoelectric LiTaO3 substrate

A well adherent diamond-like carbon (DLC) film was deposited on piezoelectric LiTaO₃ substrate using PECVD by inserting SiO₂ interlayer. DLC film was characterized using Raman spectroscopy and AFM. Physical and mechanical properties were measured using XRR, ellipsometry, scratch test and nano-indentation. The DLC film exhibits the characteristics of hydrogenated amorphous carbon and a very smooth surface with a 0.25 nm RMS. Scratch test shows that critical load (L_c) is 18 N, which is good enough for applying DLC film to SAW device. The measured mass density, refractive index, hardness and Young’s modulus of DLC film deposited on LiTaO₃ are comparable to the reported values for hydrogenated amorphous carbon film, irrespective of substrates on which the films were deposited.     

Evaluation of bacterial adhesion on Si-doped diamond-like carbon films

Diamond-like carbon (DLC) films as biomaterial for medical devices have been attracting great interest due to their excellent properties such as hardness, low friction and chemical inertness. It has been demonstrated that the properties of DLC films can be further improved by the addition of silicon into DLC films, such as thermal stability, compressive stress, etc. However no research work on anti-bacterial properties of silicon-doped diamond-like carbon films has been reported. In this paper the surface physical and chemical properties of Si-doped diamond-like carbon films with various Si contents on 316 stainless steel substrate prepared by a magnetron sputtering technique were investigated, including surface topography, surface chemistry, the sp³/sp² ratio, contact angle, surface free energy, etc. Bacterial adhesion to Si-doped DLC films was evaluated with Pseudomonas aeruginosa, Staphylococcus epidermidis and Staphylococcus aureus which frequently cause medical device-associated infections. The experimental results showed that bacterial adhesion decreased with increasing the silicon content in the films. All the Si-doped DLC films performed much better than stainless steel 316L on reducing bacterial attachment.     

CH4或CH4+Ar介质阻挡放电中的离子能量和类金刚石膜制备

实验上，利用纯CH₄及CH₄+Ar在几百帕量级气压下的介质阻挡放电 制备类金刚石膜，研究了气压p与放电间隙d乘积(pd值)以及Ar的体积百分比R_Ar 对膜硬度的影响.理论上，从离子与气体分子的双体碰撞出发，利用较高折合电场强度E/n( 电场强度与粒子数密度之比)下离子及中性粒子速度分布的双温模型、离子在其他气体中运 动时遵守的朗之万方程及离子在混合气体中运动时遵守的布兰克法则，对CH⁺4和Ar⁺离子能量进行了分析.结果表明：1)CH₄介质阻挡 放电中，pd值由1.862×10³Pa mm降低至2.66×10²Pa mm时，CH+₄能量由5.4eV增加到163eV，类金刚石膜硬度由2.1GPa提高到17.6GPa ; 2) 保持总气压p=100Pa,放电间距d=5mm不变，在CH₄中加入Ar气，当R_Ar 由20％增加至83%时，CH⁺₄的能量由69eV增加到92eV,而Ar＋能量由93eV降低至72eV.虽然CH⁺₄能量增加有助于提高 沉积膜硬度，但当R_Ar大于67%，高强度Ar⁺轰击会导致膜表面石墨 化，膜硬度降低.为了验证离子能量理论模型的正确性，实验测量了H₂介质阻挡 放电中离子能量，测量结果与理论计算之间最大相对误差为16%. 关键词： 离子能量 介质阻挡放电 类金刚石膜     

Effects of the ion-beam voltage on the properties of the diamond-like carbon thin film prepared by ion-beam sputtering deposition

Diamond-like carbon(DLC) thin film is one of the most widely used optical thin films.The fraction of chemical bondings has a great influence on the properties of the DLC film.In this work,DLC thin films are prepared by ion-beam sputtering deposition in Ar and CH4 mixtures with graphite as the target.The influences of the ion-beam voltage on the surface morphology,chemical structure,mechanical and infrared optical properties of the DLC films are investigated by atomic force microscopy(AFM),Raman spectroscopy,nanoindentation,and Fourier transform infrared(FTIR) spectroscopy,respectively.The results show that the surface of the film is uniform and smooth.The film contains sp2 and sp3hybridized carbon bondings.The film prepared by lower ion beam voltage has a higher sp3 bonding content.It is found that the hardness of DLC films increases with reducing ion-beam voltage,which can be attributed to an increase in the fraction of sp3 carbon bondings in the DLC film.The optical constants can be obtained by the whole infrared optical spectrum fitting with the transmittance spectrum.The refractive index increases with the decrease of the ion-beam voltage,while the extinction coefficient decreases.     

Electrical conditioning of diamond-like carbon films for the formation of coated field emission cathodes

Diamond-like carbon (DLC) films deposited on different substrates by plasma enhanced chemical vapour deposition were investigated. Bonding states and film quality were characterized by FT-IR spectroscopy. The influence of the power of plasma and the deposition time on the sp²/sp³ ratio as well as the concentration of CH_n bonds was studied. The influence of sp²/sp³ ratio on the formation process of conducting channels in diamond-like carbon films as a result of electrical breakdown was determined. Reproducible increase of diamond-like carbon film conductivity, with initial sp²/sp³ ratio larger than 0.16, was observed after electrical breakdown.     

A magnetron sputtering technique to prepare a-C:H films: Effect of substrate bias

Amorphous hydrogenated carbon (a-C:H) films were deposited by magnetron sputtering with a mixture gas of Ar and CH₄. The a-C:H films deposited by this method have relatively low internal stress (<1 GPa) compared to some films deposited by conventional deposition process. The effects of substrate bias voltage on microstructure, surface morphology and mechanical properties of the films were investigated by various techniques. It has been found that the polymer-like structure is dominated at low bias voltage (−100 V), while the diamond-like structure with the highest hardness and internal stress is the main feature of the a-C:H films deposited under high bias voltage (−300 V). With increasing the bias voltage further, the feature of diamond-like structure decreases associating with the increase of graphitization. The frictional test shows that the friction coefficient and wear rate of the a-C:H films are depended strongly on structure and mechanical properties, which were ultimately influenced by the deposition method and bias voltage.     

类金刚石薄膜及其进展

为了使研究者能更详细地了解类金刚石（DLC）薄膜的研究现状,综述了类金刚石薄膜的特性及应用,分析对比了目前常用的一些类金刚石薄膜的制备方法,包括物理气相沉积法（PVD）和化学气相沉积法（CVD）,并对类金刚石薄膜的抗强激光损伤特性以及提高其激光损伤阈值的方法进行了论述。结果发现,利用PVD法制备的DLC膜的硬度可以达到40 GPa~80 GPa,且薄膜的残余应力可以达到0.9 GPa~2.2 GPa之间,而CVD法则由于反应气体的充入导致类DLC薄膜的沉积速率大大降低,故使用率不高。同时,优化膜系的电场强度设计,采用合理的制备工艺,进行激光辐照后处理,施加外界电场干预均可有效地提高DLC薄膜的抗激光损伤能力, 且目前的DLC薄膜的激光损伤阈值可达到2.4 J/cm2。     

乙炔气体流量对纳米TiC类金刚石复合膜的化学结构及力学性能影响

采用离子注入与反应磁控溅射相结合的方法在钛合金及硅片基体表面上制备了纳米TiC类金刚石(DLC)复合膜.通过纳米压痕技术检测了薄膜的纳米硬度，显微划痕试验评估了薄膜的结合力.通过X射线光电子能谱及X射线衍射表征了薄膜的化学结构.结果表明，通过改变C₂H₂气体流量，可以达到控制薄膜中钛原子含量的目的，合适的C₂H₂气体流量可以在DLC膜中形成较多的纳米TiC晶粒，形成DLC包覆TiC晶粒的复合结构，使DLC膜力学性能得到明显提高.另外，划痕试验表明掺钛、先注入后沉积工艺都使薄膜的结合力得到了较大提高. 关键词： 纳米TiC类金刚石复合膜 类金刚石膜 力学性能     

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。     

Fabrication and characterization of freestanding ultrathin diamond-like carbon targets for high-intensity laser applications

Here, we report the fabrication of diamond-like carbon (DLC) thin films using pulsed laser deposition (PLD). PLD is a well-established technique for deposition of high-quality DLC thin films. Carbon tape target was ablated using a KrF (248 nm, 25 ns, 20 Hz) excimer laser to deposit DLC films on soap-coated substrates. A laser fluence between 8.5 and 14 J/cm² and a target to substrate distance of 10 cm was used. These films were then released from substrates to obtain freestanding DLC thin foils. Foil thicknesses from 20 to 200 nm were deposited using this technique to obtain freestanding targets of up to 1-inch square area. Typically, 100-nm-thick freestanding DLC films were characterized using different techniques such as AFM, XPS, and nano-indentation. AFM was used to obtain the film surface roughness of 9 nm rms of the released film. XPS was utilized to obtain 74 % sp², 23 % sp³, and 3 % C–O bond components. Nano-indentation was used to characterize the film hardness of 10 GPa and Young’s modulus of 110 GPa. Damage threshold properties of the DLC foils were studied (1,064 nm, 6 ns) and found to be 7 × 10¹⁰ W/cm² peak intensity for our best ultrathin DLC foils.     

离子束反应溅射沉积SiO2薄膜的光学特性

 主要研究采用离子束反应溅射（RIBS）制备SiO2薄膜的折射率、消光系数、化学计量比与氧气在氩氧混合工作气体中含量及其沉积速率的关系。研究结果表明：RIBS制备的SiO2薄膜在0.63 μm处折射率n= 1.48,消光系数小于10-5;随着沉积速率的增加,薄膜的折射率和消光系数随之变大,当沉积速率超过0.3 nm/s,即使是在纯氧环境溅射,折射率值也不低于1.5;通过对红外透射光谱的主吸收峰位置研究得到沉积的SiO2薄膜为缺氧型,化学计量比不超过1.8,且红外吸收峰位置和SiO2折射率存在对应关系,因此在不加热衬底情况下使用RIBS制备SiO2薄膜时,会限制沉积速率的提高。     

Field emission, morphological and mechanical properties of variety of diamond-like carbon thin films

The effect of nitrogen incorporation and sandwich titanium and copper layers, on field emission, morphological and mechanical properties of diamond-like carbon (DLC) thin films is explored. The introduction of foreign element (N₂) and sandwich Cu and Ti layers changed the amorphous morphology to nanostructured, reduced the stress, enhanced the hardness (except N₂ incorporated DLC film) and improved the field emission (except Ti/DLC bilayer) of modified DLC films. The associated versatile electrical and mechanical properties of modified DLC film made it a material of great utility in the development of field emission display panels and also lead to its application as a hard and protective coating on cutting tools, automobile parts etc. It is important to mention that DLC-based electronic materials may replace currently used soft electronic materials (such as Si) due to their enhanced stability under high energy radiation.     

Room temperature pulsed laser deposition of Si x C thin films in different compositions

Amorphous silicon–carbon alloy films in different compositions were prepared by pulsed laser deposition from two-component targets containing pure silicon and carbon parts. The silicon–carbon ratio in the films was varied by adjusting the number of laser shots on the constituent silicon and carbon targets. The composition, optical properties, thickness, and bonding structure of the films were determined by backscattering spectrometry, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy, respectively. Backscattering spectrometry data were used to determine the deposition rate of silicon and carbon. This enabled the calculation of the number of the shots onto each target to reach a predefined composition. As the film composition changed from carbon to silicon, it was shown that the microscopic and macroscopic properties of the films also changed from a diamond-like carbon phase to an amorphous silicon phase via graphite- and silicon-carbide-like composite.     

The influence of the structures and compounds of DLC coatings on the barrier properties of PET bottles

To reduce the oxygen transmission rate through a polyethylene terephthalate (PET) bottle (an organic plastic) diamond-like carbon (DLC) coatings on the inner surface of the PET bottle were deposited by radio frequency plasma-enhanced chemical vapour deposition (RF-PECVD) technology with C₂H₂ as the source of carbon and Ar as the diluted gas. As the barrier layer to humidity and gas permeation, this paper analyses the DLC film structure, composition, morphology and barrier properties by Fourier transform infrared, atomic force microscopy, scanning electron microscopy and oxygen transmission rate in detail. From the spectrum, it is found that the DLC film mainly consists of sp³ bonds. The barrier property of the films is significantly relevant to the sp³ bond concentration in the coating, the film thickness and morphology. Additionally, it is found that DLC film deposited in an inductively coupled plasma enhanced capacitively coupled plasma source shows a compact, homogeneous and crack-free surface, which is beneficial for a good gas barrier property in PET bottles.     

Structure and hardness of a-C:H films prepared by middle frequency plasma chemical vapor deposition

a-C:H films were prepared by middle frequency plasma chemical vapor deposition (MF-PCVD) on silicon substrates from two hydrocarbon source gases, CH₄ and a mixture of C₂H₂ + H₂, at varying bias voltage amplitudes. Raman spectroscopy shows that the structure of the a-C:H films deposited from these two precursors is different. For the films deposited from CH₄, the G peak position around 1520 cm⁻¹ and the small intensity ratio of D peak to G peak (I(D)/I(G)) indicate that the C-C sp³ fraction in this film is about 20 at.%. These films are diamond-like a-C:H films. For the films deposited from C₂H₂ + H₂, the Raman results indicate that their structure is close to graphite-like amorphous carbon. The hardness and elastic modulus of the films deposited from CH₄ increase with increasing bias voltage, while a decrease of hardness and elastic modulus of the films deposited from a mixture of C₂H₂ + H₂ with increasing bias voltage is observed.     

Characteristics of nitrogen-incorporated silicon oxycarbide films and plasmas for plasma enhanced chemical vapor deposition with TMOS/N2/NH3

Plasma enhanced chemical vapor deposition of nitrogen-incorporated silicon oxycarbide thin films obtained from the gas mixture of TMOS (tetramethoxysilane), N₂, and NH₃ is studied. The effects of the TMOS to N₂ pressure ratio on the properties of the film and the plasma are investigated. The deposited films are analyzed by in situ ellipsometry, ex situ Fourier transform infrared spectroscopy (FTIR), and by X-ray photoelectron spectroscopy (XPS). The plasma is characterized by using optical emission spectroscopy (OES). The mass spectra of the constituents in the plasma are obtained by quadrupole mass spectroscopy. The correlation between the film properties and the plasma characteristics is explained wherever possible. As the partial pressure of N₂ is decreased, the refractive index begins to decrease, reaches a minimum, and then saturates. The FTIR absorption bands are observed from about 850 to 1000 cm⁻¹ and from 1000 to 1250 cm⁻¹, and can be attributed to the formation of a nitrogen-incorporated silicon oxycarbide thin film. The variation of the refractive index is discussed in relationship with the deposition rate, the OES spectra, the mass spectra of the plasma, the film composition obtained by XPS, and FTIR spectra.     

Defect effect on tribological behavior of diamond-like carbon films deposited with hydrogen diluted benzene gas in aqueous environment

This study examined the friction and wear behavior of diamond-like carbon (DLC) films deposited from a radio frequency glow discharge using a hydrogen diluted benzene gas mixture. The DLC films were deposited on Si (1 0 0) and polished stainless steel substrates by radio frequency plasma-assisted chemical vapor deposition (r.f.-PACVD) at hydrogen to benzene ratios, or the hydrogen dilution ratio, ranging from 0 to 2.0. The wear test was carried out in both ambient and aqueous environments using a homemade ball-on-disk type wear rig. The stability of the DLC coating in an aqueous environment was improved by diluting the benzene precursor gas with hydrogen, suggesting that hydrogen dilution during the deposition of DLC films suppressed the initiation of defects in the film and improved the adhesion of the coating to the interface.     

Microstructure, chemical bonds, and friction properties of nanocrystalline diamond films deposited in two different plasma media

Nanocrystalline diamond films with the properties dependent on the composition of the gaseous medium have been prepared using the microwave plasma enhanced chemical vapor deposition (MPECVD) method. A nanocrystalline film formed in the Ar/CH₄ plasma is characterized by a high crystallinity factor, a small grain size, a large fraction of sp ²-amorphous carbon, and, consequently, by an increase in the hardness and elastic modulus. The low value of the friction coefficient of this film is associated with the small grain size and large fraction of the sp ²-amorphous carbon boundary phase that ensures an easy sliding. The contact angle of the film is small (hydrophilic properties) in the case when the plasma consists of an Ar/CH₄ mixture. It has been shown that the wetting properties of the films are provided by a thin layer of carboxyl and hydroxyl functional groups passivating the dangling bonds at the surface that are responsible for the boundary lubrication mechanism. It has also been found that the friction coefficient of these films is inversely proportional to the contact pressure dependent on the diameter of the sliding counterbody ball.     

Ab initio study of electronic structure of strained

Micro-hardness and scratch adhesion testing are the most commonly used techniques for assessing the mechanical properties of thin films. Both of these testing methods utilize single-point contact and induce plastic deformation in the substrate and film. However, the influence of adhesion on the measured hardness has been seldom reported so far. In our experiments, diamond-like carbon (DLC) and silicon carbide (SiC) films deposited on silicon and nickel-based alloy substrates by pulsed laser ablation were indented and scratched by a Vickers micro-hardness tester and a diamond-cutter, respectively. It was found that the composite hardness decreased more rapidly for poor adhesion when increasing the indentation load. The result was explained by the elastic-plastic deformation mode of indentation and helped us to understand the physical meaning of one parameter commonly introduced in the models used to separate film hardness from the composite hardness. Received 30 June 1998