XPS表征类金刚石膜探讨

介绍X射线光电子能谱(XPS)分析类金刚石(DLC)膜的原理与方法,探讨分峰拟合计算时参量设定对分析结果的影响,改进拟合方法,拟合结果更准确,结果的一致性好。     

Friction of diamond-like carbon films in different atmospheres

Diamond-like carbon (DLC) films constitute a class of new materials with a wide range of compositions, properties, and performance. In particular, the tribological properties of these films are rather intriguing and can be strongly influenced by the test conditions and environment. In this paper, a series of model experiments are performed in high vacuum and with various added gases to elucidate the influence of different test environments on the tribological behavior of three DLC films. Specifically, the behavior of a hydrogen-free film produced by a cathodic arc process and two highly hydrogenated films produced by plasma-enhanced chemical-vapor deposition were studied. Flats and balls used in these experiments were coated with DLC and tested in a pin-on-disc machine under a load of 1 N and at constant rotational frequency. With a low background pressure, in the 10⁻⁶ Pa range, the highly hydrogenated films exhibited a friction coefficient of less than 0.01, whereas the hydrogen-free film gave a friction coefficient of approximately 0.6. Adding oxygen or hydrogen to the experimental environment changed the friction to some extent. However, admission of water vapor into the test chamber caused large changes: the friction coefficient decreased drastically for the hydrogen-free DLC film, whereas it increased slightly for one of the highly hydrogenated films. These results indicate that water molecules play a prominent role in the frictional behavior of DLC films—most notably for hydrogen-free films but also for highly hydrogenated films.     

类金刚石薄膜的光学性能的研究

利用脉冲真空电弧镀的方法,在硅基底上沉积类金刚石薄膜,研究薄膜的光学性能、光学常数和离子能量关系。结果表明:不同的离子能量可以得到不同折射率的薄膜,无氢类金刚石薄膜的折射率在2.5～2.7之间变化;通过改变工艺条件来制备不同折射率的薄膜,和不同折射率的基底材料相互匹配;折射率和光学能隙随离子能量具有相反的变化趋势,和理论预测的趋势相一致;对于硅、锗等红外材料,要求的薄膜应具有1.8～2.1左右的折射率,因此提出一种基于物理汽相沉积和化学汽相沉积两种相互结合的方法,来降低薄膜的折射率,以达到和硅、锗等材料的折射率匹配。     

The role of hydrogen on the friction mechanism of diamond-like carbon films

The structure, properties and tribological behavior of DLC films are dependent on the deposition process, the hydrogen concentration and chemical bondings in the films. The present paper reports selected tribological experiments on model DLC films with different hydrogen contents. The experiments were performed in ultrahigh vacuum or in an atmosphere of pure hydrogen or argon in order to elucidate various friction mechanisms. Two typical friction regimes are identified. High steady-state friction in UHV (friction coefficient of 0.6) is observed for the lowest hydrogenated and mostly sp²-bonded DLC film. Superlow steady-state friction (friction coefficient in the millirange) is observed both for the highest hydrogenated film in UHV, and for the lowest hydrogenated film in an atmosphere of hydrogen (10 hPa). The high steady-state friction in UHV, observed for the lowest hydrogenated film with a dominant sp² carbon hybridization, is associated with a –^* sub-band overlap responsible for an increased across-the-plane chemical bonding with a high shear strength similar to what is observed with unintercalated graphite in the same UHV conditions. Superlow friction is correlated with a hydrogen saturation across the shearing plane through weak van der Waals interactions between the polymer-like hydrocarbon top layers. This regime is observed during the steady-state period if the film contains enough hydrogen incorporated during deposition. If this condition is not satisfied (i.e., for the film with the lowest hydrogen content), the limited diffusion of hydrogen from the film network towards the sliding surfaces seems to be responsible for a superlow running-in period. The superlow friction level can be reached over longer time periods by suitable combinations of temperature and molecular hydrogen present in the surrounding atmosphere during friction.     

负偏压对含氢类金刚石薄膜性能的影响

为了解决类金刚石(DLC)薄膜与金属基材间的界面结合强度问题,本研究采用直流等离子体增强化学气相沉积(DC-PECVD)技术,以等时长、不同偏压条件在45钢基材上沉积复合DLC薄膜.采用扫描电镜、原子力显微镜观察薄膜形貌;采用拉曼光谱仪分析薄膜成分;采用涂层附着力自动划痕仪测定膜基结合强度.结果表明:制备偏压从-600...     

Nanometre scale mechanical properties of extremely thin diamond-like carbon films

Abstract

Extremely thin diamond-like carbon (DLC) films are deposited by the filtered cathodic vacuum arc (FCVA) and plasma chemical vapour deposition (p-CVD) methods. The target thicknesses of the extremely thin protective DLC films deposited on a Si (100) surface by FCVA and p-CVD are 0·1, 0·4, 0·8, 1·0, 2·0, 5·0 and 100·0 nm. Nanoindentation hardness and nanowear resistance are evaluated by atomic force microscopy (AFM). The nanoindentation hardnesses of 100 nm thick DLC films deposited by FCVA and p-CVD are 57 and 25 GPa respectively. The nanowear test by AFM clarifies the mechanical properties of extremely thin DLC films. The wear depths of 1 and 2 nm thick FCVA-DLC films are extremely shallow. The wear depths of the 1·0 and 2·0 nm thick p-CVD-DLC films exceed the film thicknesses after five sliding cycles. These results reveal differences in the wear resistance of extremely thin DLC films and the superior mechanical properties of FCVA-DLC thin films.     

Preparation,characterization and investigation of molecular films coated on diamond-like carbon substrate

For the successful application of boundary lubrication, detailed investigations about the influence of preparation process on molecular films are needed. In this paper, a specially designed device was used for the film preparation. The scanning electron microscope (SEM) combined with atomic force microscope (AFM) was employed to characterize the surface morphology and nanotribological behavior of molecular films. After the liquid phase deposition, molecular films are randomly and densely distributed over Ti-doped diamond-like carbon (Ti-DLC) substrates. Through rigorous surface treatments, island-like molecular films were finally achieved on substrate surfaces. The surface friction of molecular films is obviously lower than that of Ti-DLC surfaces. Then, pin-on-disk tribotests were performed to study the macrofriction behavior of molecular films under different preparation parameters. Based on the orthogonal experiment, the effect of five preparation parameters (solution weight percent, smearing force and processing time of three smearing steps) on initial friction coefficient of molecular films was investigated. The results indicated that the order of significance levels is as follows: processing time of the second smearing step > solution weight percent > processing time of step 1 > processing time of step 3 > smearing force. For the purpose of friction reduction, the appropriate level ranges are 0.75% (Solution), 2.5 N–15 N (Force), 1 min–10 min (Step 1), 1 min–2 min (Step 2) and 1 min, 2 min, 5 min and 15 min (Step 3). The initial friction coefficient under the optimized conditions is around 0.112, and the equilibrium friction coefficient is around 0.162, which is lower than that of unlubricated Ti-DLC substrates.     

Senftleben-Beenakker thermal conductivity effect apparatus

An apparatus for measuring the influence of magnetic fields on the thermal conductivity of gases, the Senftleben-Beenakker effect, is described. Conventional 'cold finger type' cooling with appropriate cryogenic fluids is utilized with a helium exchange gas chamber to establish the general temperature level of the cell holder. Automatic temperature control of the trim heater maintains the desired temperature to +/-10(-3) degrees C in the 77-300 K range. A concentric cylinder cell adaptable for use with either conventional electromagnet or superconducting solenoid is described. The use of thin Mylar polyester film end seals minimizes cell 'end effect' corrections and provides a resolution of 5x10(-6) in gas thermal conductivity.     

Architecture of superthick diamond-like carbon films with excellent high temperature wear resistance

A plasma-enhanced chemical vapor deposition system was used to deposit super thick diamond-like carbon (DLC)-based films ((Si_x-DLC/Si_y-DLC)_n). The aim of this work is to investigate the properties of super thick films to verify that increasing the thickness of DLC films offers the possibility of improving their properties at high temperatures. The investigation revealed that superthick (Si_x-DLC/Si_y-DLC)_n film exhibited excellent tribological property up to 500 °C. One reason is that a thin layer that consists of nanocrystals SiC is formed on the top of wear track. Another is that the stress mostly concentrates near the top surface.     

应用纳米压痕法测试类金刚石薄膜的力学性能

纳米压痕仪被称为材料机械性质微探针,它借助于加载-卸载过程中压痕对载荷和压入深度的敏感关系,使得测试始终在薄膜材料的弹性限度内,克服了维氏法和努氏法等传统方法引起压痕边缘模糊或者碎裂的缺点,从而正确地、可靠地测试出薄膜材料的硬度和弹性模量等纳米力学性能.试验用微波电子回旋共振等离子体增强化学气相沉积技术,在不同偏压条件下制备三种类金刚石薄膜(DLC膜),用纳米压痕仪测试不同载荷下薄膜的硬度和弹性模量值.试验结果表明,材料的纳米硬度和弹性模量随着载荷的增大而逐渐减小.     

飞秒脉冲激光沉积类金刚石膜实验研究

期望用类金刚石膜作为硅的红外保护/增透膜,采用波长为800nm,脉宽50fs,重复频率1KH z的T i:Sapph ire飞秒激光器及石墨靶材在单晶S i片上沉积了约0.7μm~1μm厚的类金刚石膜(d iam ond-like carbon film s,DLC),获得了光滑致密,硬度显著提高,红外透过率有一定增加的样品。通过对薄膜拉曼光谱和X射线光电子能谱等的测试,发现单脉冲能量在0.4m J~1.6m J范围内变动时,单脉冲能量0.8m J获得的类金刚石膜综合性能最佳,其对应的焦斑功率密度计算值为1.4×1014W/cm2。     

Microfrictional properties of diamond-like carbon films sliding against silicon, sapphire and steel

The low contact pressure characteristic of the microtribological regime relative to macro and nanosystems is suited for testing the microfrictional properties of different types of thin films. Motivated by macro as well as microsystem applications, this study investigates the microfrictional properties of different types of diamond-like carbon (DLC) films, prepared using low- and high-frequency plasma-assisted chemical vapor deposition (HF-PACVD) and the vacuum arc method. Testing was performed with a reciprocating precision microtribometer. Silicon, sapphire and steel balls were used as counterbodies. Friction-load curves suggest that, for applied forces in the μN to mN regime, two properties have a strong influence on the microfriction: first, the chemical composition plays a dominant role and second, the film roughness. With silicon and steel balls, the microfriction of hydrogen-free DLC films was greater than the hydrogen-containing films. With sapphire counterbodies, the results indicate that microfriction is inversely proportional to the film roughness. Also, for the films tested, microfriction was determined to be independent of the sliding velocity. For the force (pressure) regimes tested, mild wear was observed on silicon and some steel counterbodies, while no wear could be detected on any of the DLC films. These results illustrate the utility of implementing microtribological testing in comparative coating studies.     

Tribochemical reaction of hydrogenated diamond-like carbon films: a clue to understand the environmental dependence

Tribological behavior of hydrogenated diamond-like carbon (DLC) films and Si incorporated DLC (Si-DLC) films deposited on Si (100) wafer by r.f.-plasma assisted chemical vapor deposition were investigated by ball-on-disk type tribometry in various environments. The friction tests were performed in ambient air of relative humidity ranging from 0% to 90% or dry oxygen environment. We focused on the tribochemical reactions by analyzing chemical composition, chemical bond structure and agglomerated shape of the debris. High and unstable friction behavior was observed in both humid air and dry oxygen environments. In these environments, Auger spectrum analysis showed that the debris contained large amounts of Fe. Significant incorporation of Fe in the debris resulted from the wear of the steel ball, which might be enhanced by the surface oxidation of the ball. These results show that the humidity dependence of friction coefficient is not an inherent tribological property of DLC films but results from the surface reaction of the steel ball in humid environments. Two possible reasons for the Fe rich debris affecting the friction behavior are presented. Reduced dependence of the friction coefficient on the relative humidity observed for Si-DLC films is discussed in terms of the two possible reasons.     

Load-carrying capacity evaluation of coating/substrate systems for hydrogen-free and hydrogenated diamond-like carbon films

Diamond-like carbon (DLC) coatings have shown excellent tribological properties in laboratory tests. The coatings have also been introduced to several practical applications. However, the functional reliability of the coatings is often weakened by adhesion and load-carrying capacity related problems. In this study the load-carrying capacity of the coating/substrate system has been evaluated. The DLC coatings were deposited on stainless steel, alumina and cemented carbide with two different deposition techniques: the tetrahedral amorphous carbon (ta-C) coatings were deposited by a pulsed vacuum arc discharge deposition method and the hydrogenated carbon (a-C:H) films by radio frequency (r.f.) plasma deposition method. The load-carrying capacity of the coated systems was evaluated using a scratch test, Rockwell C-indentation test and ball-on-disc test. The effect of substrate material, substrate hardness, coating type and coating thickness was studied. An increase in substrate hardness increased the load-carrying capacity for the coated systems, as expected. The two coating types exhibited different performance under load due to their different physical and mechanical properties. For the load-carrying capacity evaluations the ball-on-disc configuration was found to be most suitable. This revised version was published online in July 2006 with corrections to the Cover Date.     

Wear of metal-containing diamond-like carbon coatings

Four commercial metal-containing DLC coatings were tested with a ball-on-disk tribomete to examine their modes of wear. Although all were sputter-deposited, the coatings differed in their compositions, thicknesses, and surface finish. The tests showed certain common wear modes. In each case the films wore away at constant rates until they were worn through. In this sense, interface adhesion was not an important issue. Since the nominal contact areas increased significantly during the course of the test, while the wear rates were constant, the wear rate was not controlled by the nominal average contact stress. Our data are consistent with the model of Greenwood and Williamson.     

Development of diamond-like carbon fibre wheel

The first author invented a unique diamond-like carbon (DLC) grinding wheel, in which the DLC fibres were made by rolling Al sheets coated with DLC films and aligned normally to the grinding wheel surface by laminating Al sheets together with DLC fibres [K. Yamaguchi, Y. Wei, M. Takeuchi, Development of DLC fibre grinding wheel, in: Proceedings of the Vernal Meeting of the JSPE, Tokyo, 16–18 March 1999, p. 260]. In this paper, the formation process of DLC fibres and the fabrication process of a DLC fibre wheel were investigated. Many grinding experiments were also carried out on a precision NC plane milling machine using a newly developed DLC wheel. Grinding of specimens of silicon wafers, optical glasses, quartz, granites and hardened die-steel SKD11 demonstrated the capabilities to nanometer surface finish. A smooth surface with a roughness value of Ra 2.5 nm (Ry 26 nm) was achieved.     

Methods for the measurement of thermal conductivity and thermal diffusivity of very thin films and foils

New methods for measuring the thermal conductivity λ, thermal diffusivity a and emissivity ε of very thin electrically conducting and insulating films and foils are described. Measurements are performed at bismuth films and cellulose acetate foils and results are represented. The methods permit measurements even for very small film thicknesses d down to a lower linit of λd ≈ 10⁻⁸ WK⁻¹. In comparison with publications known to us, this is more than one order of magnitude less than the lower limit reached up to now. Therefore, the methods described enable investigations of heat transport even on extreme thin films.     

Improvement of boundary lubrication properties of diamond-like carbon (DLC) films due to metal addition

The effects of added materials such as metals like titanium (Ti), molybdenum (Mo) and iron (Fe) diamond-like carbon (DLC) films on boundary lubrication and microtribological properties were investigated. The nanoindentation hardness and microwear resistance can be improved by adding the proper metal to DLC films, as evaluated by atomic force microscopy (AFM). Boundary lubrication properties of DLC films with metals are improved as comparing with DLC films without metal under lubricant with both MoDTC and ZDDP additives. Moreover, lower friction coefficient of μ=0.03 than carburized steel is exhibited with the appropriate quantity of Ti added. The tribochemical reactant was formed on the sliding surface of the Ti-containing DLC film like as carburized steel. Higher mechanical damping materials containing elements, such as Mo, Zn, P and S, formed tribochemical reactors as observed by X-ray photoemission spectroscopy (XPS) and AFM force modulation methods.     

Temperature effect on spreading of perfluoropolyethers on amorphous carbon films

The temperature effect on the spreading behavior of Fomblin Zdol and Z on amorphous carbon surfaces has been studied by scanning micro-ellipsometry. The temperature range explored in this study spans from 26 to 56°C under 0% relative humidity. The results show that while temperature in general accelerates surface diffusion, it has little effect on the surface conformation of the lubricants. The diffusion coefficient versus film thickness maintains the same shape, only the overall amplitude increases with increasing temperature. The activation energy E_a is found to be relatively insensitive to the lubricant coverage up to one monolayer. The average activation energy is around 37 kJ/mol for Zdol (M_n=2500 g/mol), and around 21 kJ/mol for Z of the same molecular weight. With increasing molecular weight the activation energy increases but the rate of increase is very moderate. More interestingly, the activation energy versus molecular weight curves for Zdol and Z are nearly parallel to each other, suggesting that the interactions between the main-chain and the carbon surface are essentially independent of the interactions between the end-groups and the carbon surface.     

Small amplitude reciprocating wear performance of diamond-like carbon films: dependence of film composition and counterface material

Small amplitude (50 μm) reciprocating wear of hydrogen-containing diamond-like carbon (DLC) films of different compositions has been examined against silicon nitride and polymethyl-methacrylate (PMMA) counter-surfaces, and compared with the performance of an uncoated steel substrate. Three films were studied: a DLC film of conventional composition, a fluorine-containing DLC film (F-DLC), and silicon-containing DLC film. The films were deposited on steel substrates from plasmas of organic precursor gases using the Plasma Immersion Ion Implantation and Deposition (PIIID) process, which allows for the non-line-of-sight deposition of films with tailored compositions. The amplitude of the resistive frictional force during the reciprocating wear experiments was monitored in situ, and the magnitude of film damage due to wear was evaluated using optical microscopy, optical profilometry, and atomic force microscopy. Wear debris was analyzed using scanning electron microscopy and energy dispersive spectroscopy. In terms of friction, the DLC and silicon-containing DLC films performed exceptionally well, showing friction coefficients less than 0.1 for both PMMA and silicon nitride counter-surfaces. DLC and silicon-containing DLC films also showed significant reductions in transfer of PMMA compared with the uncoated steel. The softer F-DLC film performed similarly well against PMMA, but against silicon nitride, friction displayed nearly periodic variations indicative of cyclic adhesion and release of worn film material during the wear process. The results demonstrate that the PIIID films achieve the well-known advantageous performance of other DLC films, and furthermore that the film performance can be significantly affected by the addition of dopants. In addition to the well-established reduction of friction and wear that DLC films generally provide, we show here that another property, low adhesiveness with PMMA, is another significant benefit in the use of DLC films.