Deuterium influence on optical gap of amorphous carbon diamond-like carbon (DLC) thin film

This present study aims to determine the hydrogen influence on the electrical gap of diamond-like carbon (DLC) film. DLC thin layers were deposited on silicon wafer by plasma enhanced chemical vapour deposition (PECVD). With this method we obtain a a-C:H film structure. To understand the mechanism of deposition, local structure and hydrogen effect in DLC we replace our methane plasma source by deuterated methane one. In this article, hydrogen rate is obtained by elastic recoil detection analysis (ERDA), electronic and bulk density is performed with X-ray reflectometry (XRR) and the determination of electrical gap is carried out using ultraviolet-visible absorption spectrometry. A specific attention is carried about the self-bias voltage and time variations to get different DLC and DDLC film compositions and also different electrical properties. We found that including deuterium in carbon increases the Tauc energy while keeping the same density. A comparison between these two sorts of film is expected to improve our understanding of the hydrogen role in the DLC films.     

Nano-mechanical properties and nano-tribological behaviors of nitrogen-doped diamond-like carbon (DLC) coatings

Diamond-like carbon (DLC) coatings doped with different nitrogen contents were prepared by an ECWR-CVD deposition technique, and their chemical compositions, nano-mechanical properties and nano-tribological behaviors were characterized using Auger Electron Spectrometer and Hysitron Triboindenter, respectively. The results have shown that, higher nitrogen contents in the N-doped DLC coatings can be obtained by increasing the N2 flow rate in the reactive gas mixture. The nitrogen addition in the DLC coatings decreases evidently the nano-mechanical properties, including nano-hardness and reduced modulus. In addition, the depths for the scratched tracks produced during the scratch testing depend heavily on the nitrogen content in the N-doped DLC coatings, and, at the same applied loads, the higher the doped nitrogen content, the deeper the resulting scratched tracks. For the DLC coatings doped with different nitrogen contents, however, the frictional coefficients (LF/INF) deduced from nano-scratch testing at same loads are similar, and, therefore, seem to be independent of the added nitrogen content.     

Optimised plasma enhanced chemical vapour deposition (PECVD) process for double layer diamond-like carbon (DLC) deposition on germanium substrates

Double layer DLC-films were deposited on germanium substrates by the PECVD-method, using ethyne as reactant gas during RF plasma excitation in a parallel plate reactor. The electric field distribution in the plasma chamber was simulated by FEM. The basic concept was the utilization of coatings with graded interfaces and without other materials.The bias voltage, working pressure and substrate temperature were changed stepwise to create an appropriate combination of an adhesive layer with improved elastic properties and a wear protective layer with increased hardness on the top.The layer thickness was determined by Scanning Electron Microscopy. Thickness data were used in combination with Infrared Spectroscopy to calculate the Refractive Index of the layer.Double layered DLC-films with Vickers hardness up to 3500 HV and a refractive index of around 2 were generated, which can be used as wear resistant optical layer on germanium substrates.     

基于LFM的类金刚石膜纳米摩擦现象研究

使用原子力显微镜(AFM)中的侧向力(LFM)模式对类金刚石膜纳米尺度的摩擦现象进行了研究,主要考察了载荷、微观形貌、粘附对类金刚石膜纳米摩擦性能的影响.首先结合粘附的影响提出了适用于外加载荷在100 nN以下类金刚石膜纳米摩擦力表征的修正Amonton公式.其次,试验发现摩擦过程中表面接触峰的斜率对薄膜的微观摩擦力的影响较大,微观摩擦系数与倾角θ成正比例关系,最后结合两者给出了综合考虑载荷、表面形貌、粘附且可用于类金刚石膜纳米尺度摩擦力表征的数学方法.     

Contact damage evolution in a diamond-like carbon (DLC) coating on a stainless steel substrate

A diamond-like carbon thin film was coated onto a stainless steel substrate using plasma assisted chemical vapour deposition (PACVD). Instrumented indentation and scratching were used, supported by focused ion beam (FIB) microscopy, to explore deformation and fracture behaviours of this coating system. The formation and growth of ring and radial cracks in the coating, as well as plastic flow in the ductile substrate, were observed to be the predominant deformation processes for this coating system. Lateral cracking occurred at the interface of the coating/substrate following indentation, but in the middle of the coating following scratching. No evidence of plastic flow within the coating was observed. Coating deformation is, therefore, controlled by its fracture energy. An indentation-energy-based model was applied to evaluate the fracture toughness of the coating.     

Application of diamond-like Carbon (DLC) coatings for gravitational wave detectors

A laser interferometer gravitational wave detector requires an ultra high vacuum in the tubes in which the laser beams pass. To avoid noise due to scattered light from the surface of tubes, the surface should be treated with “black” coating without increasing the outgassing rate. We found that diamond-like Carbon (DLC) coatings are suitable for this aim. An outgassing rate of at was achieved for DLC coatings on SUS304 without baking. This rate was better than the surface of SUS316 with baking. The reflectivity of the DLC surface was 5% at minimum for a laser beam of Nd:YAG () which is used as a light source for the gravitational wave detector.     

Characterization and tribological application of diamond-like carbon (DLC) films prepared by radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique

Diamond-like carbon (DLC) films were successfully prepared on glass substrates and surfaces of selenium drums via radio frequency plasma enhanced chemical vapor deposition method. The microstructure, surface morphology, hardness, film adhesion, and tribological properties of the films were characterized and evaluated by X-ray photoelectron spectroscopy, atomic force microscopy, and micro-sclerometer and friction-wear spectrometer. The results showed that DLC films have smooth surfaces, homogeneous particle sizes, and excellent tribological properties, which can be used to improve the surface quality of the selenium drums and prolong their service life.     

Characterization and tribological application of diamond-like carbon (DLC) films prepared by radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique

Diamond-like carbon (DLC) films were successfully prepared on glass substrates and surfaces of selenium drums via radio frequency plasma enhanced chemical vapor deposition method. The microstructure, surface morphology, hardness, film adhesion, and tribological properties of the films were characterized and evaluated by X-ray photoelectron spectroscopy, atomic force microscopy, and micro-sclerometer and friction-wear spectrometer. The results showed that DLC films have smooth surfaces, homogeneous particle sizes, and excellent tribological properties, which can be used to improve the surface quality of the selenium drums and prolong their service life.     

Doping of rf plasma deposited diamond-like carbon films

Rf plasma deposited diamond-like carbon (DLC) films have been doped n-type with the addition of nitrogen as a feed gas to a magnetically confined rf plasma. Controlled amounts of nitrogen are added to the CH₄/He plasma and the films are characterised. The electronic properties together with the microstructure of the deposited films are examined. Activation energy studies show the Fermi level can be moved from 0.5 eV away from the valence band for the undoped DLC films, through a maximum activation energy of 0.9 eV corresponding to the midgap and to 0.45 eV away from the conduction band with maximum N incorporation. The optical band gap first increases, indicative of a reduction in the band-edge tail states, and then tends to a steady value of ˜2 eV. Activation energy studies together with the optical band gap data are used to analyse the density of states for the deposited films. The preferential doping configuration of the atomic nitrogen and the importance of the π-π* states for electronic conduction for DLC:N films is discussed in the light of the findings.     

Formation mechanisms of zinc,molybdenum, sulfur and phosphorus containing reaction layers on a diamond-like carbon (DLC) coating

Diamond-like carbon (DLC) coatings are nowadays successfully applied on industrial components like pistons, piston rings and bearings in lubricated tribological contacts due to friction and wear reducing effects. In contradiction thereto, todays lubricants and additives are designed for tribological steel/steel contacts, whereby the knowledge on tribochemical layer formation on steel surfaces is comprehensive in contrast to the physical-chemical interactions between diamond-like carbon coatings, lubricants and additives. Therefore the formation mechanisms of zinc, molybdenum, sulfur and phosphorus containing reaction layers on a zirconium modified diamond-like carbon coating a-C : H : Zr (ZrC_g) in lubricated tribological contacts were analyzed by means of pin-on-disc (PoD) tribometer by varying the distances from s = 200 m–3,000 m under boundary and mixed friction conditions at T = 90 °C and a contact pressure p = 1,300 MPa regarding the application of diamond-like carbon coatings on gears. The base lubricant poly-alpha-olefin (PAO) was formulated using the anti-wear (AW) and extreme pressure (EP) additive zinc dialkyldithiophosphate (ZnDTP) and the friction modifier (FM) additive molybdenum dialkyldithiophosphate (MoDTP). The chemical composition of the tribochemical reaction layers by means of and Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) as well as for the thickness differ significantly by varying the additivation.     

Oxygen plasma etching of silver-incorporated diamond-like carbon films

Diamond-like carbon (DLC) film as a solid lubricant coating represents an important area of investigation related to space devices. The environment for such devices involves high vacuum and high concentration of atomic oxygen. The purpose of this paper is to study the behavior of silver-incorporated DLC thin films against oxygen plasma etching. Silver nanoparticles were produced through an electrochemical process and incorporated into DLC bulk during the deposition process using plasma enhanced chemical vapor deposition technique. The presence of silver does not affect significantly DLC quality and reduces by more than 50% the oxygen plasma etching. Our results demonstrated that silver nanoparticles protect DLC films against etching process, which may increase their lifetime in low earth orbit environment.     

超高分子量聚乙烯表面金属化及类金刚石薄膜沉积复合处理研究

采用超高分子量聚乙烯(UHMWPE)表面金属化及类金刚石薄膜沉积复合处理工艺,提高超高分子量聚乙烯的耐磨性.首先采用磁过滤阴极真空弧源沉积技术(FCVA)在UHMWPE表面制备约30nm钛金属层,使UHMWPE表面金属化,然后再沉积DLC薄膜,研究结果表明,UHMWPE表面金属化后,DLC薄膜沉积过程中,电荷累积效应消...     

CVD of hard DLC films in a radio frequency inductively coupled plasma source

Chemical vapor deposition (CVD) of hard diamond-like carbon (DLC) films on silicon (100) substrates from methane was successfully carried out using a radio frequency (r.f.) inductively coupled plasma source (ICPS). Different deposition parameters such as bias voltage, r.f. power, gas flow and pressure were involved. The structures of the films were characterized by Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The hardness of the DLC films was measured by a Knoop microhardness tester. The surface morphology of the films was characterized by atomic force microscope (AFM) and the surface roughness (R_a) was derived from the AFM data. The films are smooth with roughness less than 1.007 nm. Raman spectra shows that the films have typical diamond-like characteristics with a D line peak at 1331 cm⁻¹ and a G line peak at 1544 cm⁻¹, and the low intensity ratio of I_D/I_G indicate that the DLC films have a high ratio of sp³ to sp² bonding, which is also in accordance with the results of FTIR spectra. The films hardness can reach approximately 42 GPa at a comparatively low substrate bias voltage, which is much greater than that of DLC films deposited in a conventional r.f. capacitively coupled parallel-plate system. It is suggested that the high plasma density and the suitable deposition environment (such as the amount and ratio of hydrocarbon radicals to atomic or ionic hydrogen) obtained in the ICPS are important for depositing hard and high quality DLC films.     

Catalytic chemical vapor deposition of single-wall carbon nanotubes at low temperatures

We report surface-bound growth of single-wall carbon nanotubes (SWNTs) at temperatures as low as 350 degrees C by catalytic chemical vapor deposition from undiluted C2H2. NH3 or H2 exposure critically facilitates the nanostructuring and activation of sub-nanometer Fe and Al/Fe/Al multilayer catalyst films prior to growth, enabling the SWNT nucleation at lower temperatures. We suggest that carbon nanotube growth is governed by the catalyst surface without the necessity of catalyst liquefaction.     

DC electrical conductivity of poly(methyl methacrylate)/carbon black composites at low temperatures

The study deals with the dc electrical conduction of poly(methyl methacrylate)/carbon black composites of different carbon black (CB) filler concentrations (2, 6, 12 wt%). The dc electrical conductivity was studied as a function of filler concentration, and temperature in the range (20–290 K). It was found that the composites exhibit negative temperature coefficient of resistivity (NTCR) at low temperatures and enhancement in the dc electrical conductivity with both temperature and CB concentration. The observed increase of conductivity with CB concentration was interpreted through the percolation theory. The dependence of the electrical conductivity of the composites in low temperatures was analyzed in term of a formula in consistence with Mott variable rang hopping (VRH) mechanism. The observed overall mechanism of electrical conduction has been related to the transfer of electrons through the carbon black aggregations distributed in the polymer matrix.     

Surface plasmon characteristics of nanocrystalline gold/DLC composite films prepared by plasma CVD technique

Composite films containing gold nanoparticles embedded in diamond-like carbon (Au–DLC) matrix were deposited on glass and Si (1 0 0) substrates by using capacitatively coupled plasma (CCP) chemical vapour deposition technique (CVD). Particle size and metal volume fraction varied between 2.7–3.5 nm and 0.04–0.7, respectively with the amount of argon in the methane + argon gas mixture in the plasma. Bonding environment in these films were obtained from XPS, Raman and FTIR studies. Microstructural studies were carried out by SEM, XRD and TEM studies. Blue-shift of the surface plasmon resonance peak (located 540–561 nm) in the optical absorbance spectra of the films could be associated with the reduction of the particle size while red shift was associated with the increase in volume fraction of metal particles. The experimental results have been discussed in light of the core–shell model.     

Synthesis of graphitic carbon particle chains at low temperatures under microwave irradiation

Chains of graphitic carbon particles were formed by microwave irradiation of polyethylene glycol at temperatures between 160 and 220 °C for 40 min, in the absence of a catalyst. Chains were comprised of individual particles ranging in size from 340 to 620 nm; particle size increased with synthesis temperature. The D/G ratio measured by Raman spectroscopy was 0.91, indicative of a mixture of amorphous and graphitic material. SEM, TEM and TGA measurements confirmed this. Our experiments show that the chains are an intermediate product, which when heated further under hydrothermal conditions, produce MWNTs.