Structural characterization of dual-metal containing diamond-like carbon nanocomposite films by pulsed laser deposition

Two metal dopants were simultaneously added into a diamond-like carbon (DLC) matrix using a KrF pulsed laser system at room temperature with no post-processing. The nanometer thin films were fabricated from carbon source targets containing the two metals of interest, Ti and Ni, in atomic percentages 2.5%, 5%, 7.5% and 10% each. Films from carbon targets containing only 5% Ni or 5% Ti were also deposited for comparison against the dual-metal containing films. Microstructure analysis shows that each individual metal reacted independently and uniquely with carbon as confirmed by XPS and surface analysis shows the presence of TiC bonds and Ni⁰. Therefore, there was no reaction between Ti and Ni as metals confirmed by XPS. Through this independent interaction, a superposition of microstructural properties was obtained as if the metals were doped separately into DLC. The separate interactions of the two metals with carbon were important as they were able to play separate and different roles in enhancing the properties of DLC. In addition, TEM analysis confirmed a unique self-assembly state where the nickel ions converge into nanosized clusters of ～ 5 nm in diameter and predominantly oriented in a (200) direction. The resultant films were also extremely smooth with RMS roughness of about 0.1 nm, thus retaining the inherent smoothness of DLC films. The combined Ti/Ni films could be used as substrates to grow carbon nanotubes with controlled density which could be used as cold electron emitters. Thus, it is interesting to study the growth mechanism and microstructure of the composite films.     

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.     

Coating of DLC film by pulsed discharge plasma CVD

Diamond-like carbon (DLC) films were deposited onto Ti plate substrate by means of pulsed discharge (PD) plasma chemical vapor deposition (CVD) from gas mixture of methane and hydrogen, and their structures were investigated with transmission electron microscope (TEM). When the polarity of the substrate was negative, the DLC film was grown on the substrate. The transmission electron diffraction (TED) pattern of the deposited film, which was shaved with knife from the surface of the substrate, showed that both TiC and diamond structures were formed, showing that the DLC film can be coated with good adhesion by means of the formation of TiC interlayer. The coatings of DLC films onto a stainless steel plate and a drill of WC, on which Ti film were deposited previously, was also succeeded by the PD plasma CVD method with good adhesion.     

Field emission from metal-containing amorphous carbon composite films

Metal-containing (Co, Al and Ti) amorphous carbon composite films (a-C:Me) have been prepared by the filtered cathodic arc technique using metal-containing graphite targets at room temperature. Field emission properties of the heat-treated a-C:Me films were improved and were found to be dependent on the metal content and variety of metals. After heat-treatment at 550°C in a mixture of acetylene and nitrogen gases, the field emission properties of a-C:Co films were significantly improved, in which Co acted as catalysts to enhance graphitization as well as formation of carbon nanotubes during heat-treatment. A threshold electric field of less than 2 V/μm was obtained from the heat-treated a-C:Co composite films without conditioning. The heat-treated a-C:Al and a-C:Ti films, though the conditioning step could be avoided and relatively low threshold fields could be obtained, exhibited relatively low emission site densities, however. The a-C:Me films, which can be deposited with a high rate at room temperature and require a relatively low temperature, heat-treatment process to enhance electron emission, are promising for practical applications in field emission display.     

Me-DLC films as material for highly sensitive temperature compensated strain gauges

In technical applications strain gauges are widely used. Apart from conventional polymer foil based strain gauges that are glued to the work piece surface, sputtered strain gauges are already commercially used in special applications. Those sputter strain gauges are typically made of NiCr alloy and the sensor layer is as sensitive to strain as the ones used in the glued strain gauges with a gauge factor of 2, but neglecting problems of creeping and swelling of the involved polymer materials. Diamond-like carbon (DLC) films offer significantly higher strain sensitivity, but usually they are also very sensitive to temperature effects. Using metal doped diamond-like carbon (Me-DLC), higher strain sensitivity than conventional metal based systems, in combination with thermal compensation, is possible. The influence of different process parameters on the gauge factor and temperature coefficient of resistance (TCR) of DLC and Me-DLC films produced in industrial sputtering systems was investigated. Gauge factors up to 13 in combination with a high negative TCR in the range of a few thousand ppm/K were reached with sputtered DLC films. The substrate bias voltage in particular showed a strong influence on the resulting gauge factor of the films. For Me-DLC films different deposition methods (dc and rf sputtering) and various doping metals (Ag, Ni, Ti, and W) were investigated. Using dc sputtering of the Me-DLC films only Ni-DLC showed gauge factors slightly higher than 2. Furthermore, only for Ni-DLC zero crossing of the TCR was observed by variation of the metal content. Using rf excitation especially Ni-DLC films showed gauge factors exceeding values of 15 in combination with a TCR close to zero.     

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.     

Synthesis of rare earth containing single-phase multicomponent metal carbides via liquid polymer precursor route

Novel high-entropy carbide ceramics (HEC) containing rare earth metals, namely (Ti, Zr, Hf, Ta, La, Y)C, (Ti, Zr, Hf, Ta, Nb, La, Y)C, and (Ti, Zr, Hf, Ta, Nb, Mo, W, La)C were prepared with single-phase structure by polymer precursor method. Controlled co-hydrolysis and polycondensation of equiatomic metal-containing monomers were conducted successively, followed by blending allyl-functional novolac resin as carbon source, and the polymer precursors were obtained as clear viscous liquid solutions. The single-phase formation possibility was theoretically analyzed from the aspects of size-effect parameter δ of the designed compositions. All as-obtained ceramics possessed single face-centered-cubic structure of metal carbides and high-compositional uniformity from nanoscale to microscale. The (Ti, Zr, Hf, Ta, Nb, Mo, W, La)C ceramic powder pyrolyzed at 1800°C exhibited low-oxygen impurity content of 1.2 wt%. Thus, multicomponent high-entropy carbide nanoceramics with over five metal elements containing even rare earth element were firstly synthesized and characterized.     

生物医用氮化碳薄膜的力学性能比较研究

使用磁控溅射法在生物医用NiTi合金基体表面制备了Ti／TiN、Ti／DLC以及Ti／CNx梯度薄膜,利用扫描电镜研究了薄膜的截面形貌,并使用划痕仪及摩擦磨损仪研究比较了薄膜的力学性能。结果表明：薄膜均表面平整,与基底结合紧密。Ti／CNx薄膜与NiTi合金基底的结合力大于Ti／DLC薄膜,略低于Ti／TiN薄膜。3种梯度薄膜均能有效改善NiTi合金的耐磨损性能,其中,Ti／CNx薄膜拥有最低的摩擦系数和最完整的磨损表面,耐磨性最好。     

Ti(C,N)基金属陶瓷抗弯强度的价电子判据研究

利用固体分子经验电子理论,计算了金属陶瓷中三元复合陶瓷相（Ｔｉ,Ｍｏ,Ｗ）Ｃ,四元复合陶瓷相（Ｔｉ,Ｍｏ,Ｗ,Ｎｂ）Ｃ和（Ｔｉ,Ｍｏ,Ｗ,Ｔａ）Ｃ五元复合陶瓷相（Ｔｉ,Ｎｏ,Ｗ,Ｎｂ,Ｔａ）Ｃ的价电子结构,探讨陶瓷相的价电子结构与金属陶瓷抗弯强度关系,提出判据关系式,此外,还进行了抗弯强度的实验验证。     

Nanotribological study of PECVD DLC and reactively sputtered Ti containing carbon films

Amorphous carbon film, also known as DLC film, is a promising material for tribological application. It is noted that properties relevant to tribological application change significantly depending on the method of preparation of these films. These properties are also altered by the compositions of these films. DLC films are well known for their self-lubricating properties, as well. In view of this, the objective of the present work is to compare the tribological properties of diamond like carbon (DLC) film obtained by plasma enhanced chemical vapour deposition (PECVD) with the Ti containing nanocrystalline carbon (Ti/a-C:H) film obtained by unbalanced magnetron sputter deposition (UMSD) in nN load range. Towards that purpose, DLC and Ti/a-C:H films are deposited on silicon substrate by PECVD and UMSD processes respectively. The microstructural features and the mechanical properties of these films are determined by scanning electron microscope (SEM), transmission electron microscope (TEM) and nano indenter. The surface topographies and the friction force surfaces of these films are evaluated by means of an atomic force microscope (AFM). The results show that although PECVD DLC film has higher elastic modulus and higher hardness than UMSD Ti/a-C:H film, the surface roughness and the friction coefficient of PECVD film is significantly higher than that of UMSD Ti/a-C:H film.     

A superhard diamond-like carbon film

A superhard hydrogen-free amorphous diamond-like carbon (DLC) film was deposited by pulsed arc discharge using a carbon source accelerator in a vacuum of 2×10⁻⁴ Pa. The growth rate was about 15 nm/min and the optimum ion-plasma energy was about 70 eV. The impact of doping elements (Cu, Zr, Ti, Al, F(Cl), N) on the characteristics of DLC films deposited on metal and silicon substrates was studied aiming at the choice of the optimum coating for low friction couples. The microhardness of thick (≥20 μm) DLC films was studied by Knoop and Vickers indentations, medium thick DLC films (1–3 μm) were investigated using a ‘Fischerscope’, and Young's module of thin films (20–70 nm) was studied by laser induced surface acoustic waves. The bonds in DLC films were investigated by electron energy loss spectroscopy (EELS), X-ray excited Auger electron spectroscopy (XAES), and X-ray photoelectron spectroscopy (XPS). The adhesion of DLC films was defined by the scratch test and Rockwell indentation. The coefficient of friction of the Patinor DLC film was measured by a rubbing cylinders test and by a pin-on-disk test in laboratory air at about 20% humidity and room temperature. The microhardness of the Patinor DLC film was up to 100 GPa and the density of the film was 3.43–3.65 g/cm³. The specific wear rate of the Patinor DLC film is comparable to that of other carbon films.     

Structural characterization and properties enhancement of diamond-like carbon films synthesized under low energy Ne bombardment

Diamond-like carbon (DLC) films were synthesized by Ar⁺ sputtering graphite with concurrent Ne⁺ bombardment. Transmission electron microscopy diffraction revealed that some diamond crystals were distributed in the amorphous matrix of DLC films synthesized under Ne⁺ bombardment at an energy of 200 eV and ion current density of 0.19 mA cm⁻². X-ray photo electron spectra showed that the valence band of the DLC films was similar to that of diamond, and the binding energy of electrons was 284.9 eV. The DLC films possessed a high hardness of 42.14 GPa and excellent wear resistance. It was confirmed that the wide atomic intermixed film-substrate interface meant that the DLC films would improve greatly the wear-resistant properties of AISI 52100 steel if the DLC films were coated on its surface.     

Mechanical and tribological properties of diamond-like carbon films prepared on steel by ECR-CVD process

Diamond-like carbon (DLC) films were prepared on AISI 440C steel substrates at room temperature by the electron cyclotron resonance chemical vapor deposition (ECR-CVD) process in C₂H₂/Ar plasma under different conditions. In order to prevent the inter-diffusion of carbon and improve the adhesion strength of DLC films, functionally gradient Ti/TiN/TiCN/TiC supporting underlayers were deposited on the steel substrates in advance. Using the designed interfacial transition layers, relatively thick DLC films (1–2 μm) were successfully prepared on the steel substrates without delamination. By optimizing the deposition parameters, DLC films with hardness up to 28 GPa and friction coefficients lower than 0.15 against the 100Cr6 steel ball were obtained. In addition, the specific wear rates of the films were found to be extremely low (∼10⁻¹⁷ m³/Nm). The friction-induced graphitization mechanism of DLC was confirmed by micro-Raman analysis.     

Piezoresistive properties of diamond like carbon films containing copper

In the present study diamond like carbon films containing copper (DLC:Cu) were deposited by reactive magnetron sputtering. Direct current (DC) sputtering and high power pulsed magnetron sputtering (HIPIMS) were used. The influence of the composition and structure on piezoresistive properties of DLC:Cu films was investigated. Structure of DLC:Cu films was investigated by Raman scattering spectroscopy and transmission electron microscopy (TEM). Chemical composition of the films was studied by using energy-dispersive X-ray spectrometry (EDS) and X-ray photoelectron spectroscopy (XPS). Particularly analysis of XPS O1s spectra revealed oxidation of Cu nanoparticles. Piezoresistive gauge factor of DLC:Cu films was in 3–6 range and decreased with the increase of copper atomic concentration. Tendency of the decrease of the gauge factor of DLC:Cu films with the increased D/G peak area ratio (decreased sp³/sp² carbon bond ratio) was observed. It was found that resistance (R) of DLC:Cu films decreased with the increase of Cu atomic concentration by logarithmic law. It is shown that a quasilinear increase of piezoresistive gauge factor with log(R) is in good accordance with percolation theory. Temperature coefficient of resistance (TCR) of DLC:Cu films was negative and decreased with copper amount in Cu atomic concentrations ranging up to ~ 40%. Very low TCR values (zero TCR) were observed only for DLC:Cu films with low gauge factor that was close to the gauge factor of the metallic strain gauges. Role of some possible mechanisms: copper amount as well as Cu cluster size on the value of gauge factor is discussed.     

Oxidation behavior of furan-resin-derived carbon alloyed with Ta or Ti

The effect of Ti, Nb and Ta on the anti-oxidation of furan-resin-derived carbons was investigated by thermogravimetric analysis combined with gas/mass spectroscopy, Hall coefficient and magnetoresistance measurements, transmission electron microscopy, and X-ray diffraction analysis. Hall coefficient and magnetoresistance measurements revealed that the electronic properties of carbons with the above metal elements, and thus their crystallinity, are similar to that of neat carbon. The oxidation rates of the carbons with a small amount of Ti or Ta are decreased up to 1000 °C compared to that of neat carbon. The number of working active sites in carbons with Ta or Ti is smaller than that in carbons with Nb or neat carbon. Ta or Ti terminates some active sites in the carbons, or somehow modifies the structures of the active sites and retards the formation of oxygen-carbon intermediate products (surface complexes) on the materials. Thus, the oxidation rate of the carbons is decreased.     

Structure and characterization of the multilayered Ti-DLC films by FCVA

This work presents a simple approach for the synthesis of multilayered titanium-diamond-like carbon (multilayered Ti-DLC) films on a Si substrate by a filtered cathodic vacuum arc (FCVA) system using Ti-coated graphite target to supply carbon as well as the dopant titanium. This study focuses on the characterization of microstructure, surface roughness, mechanical strength and electrical resistivity. The results indicated that the multilayered Ti-DLC films exhibit better mechanical properties than the Ti-free and Ti-implanted DLC films, and both multilayered Ti- and Ti-implanted DLC films have similar Ti atomic concentrations. The surface roughness of the multilayered Ti-DLC films shows a value much lower than the other films. The film microstructure consists in TiC nanocrystals precipitated in the amorphous carbon matrix with a multilayered structure. Because of the high hardness and low roughness, the multilayered Ti-DLC films can be used as biomedical, wear-resistant and solid lubricant coatings.     

Electrochemical and antimicrobial properties of diamondlike carbon-metal composite films

Implants containing antimicrobial metals may reduce morbidity, mortality, and healthcare costs associated with medical device-related infections. We have deposited diamondlike carbon–silver (DLC–Ag), diamondlike carbon–platinum (DLC–Pt), and diamondlike carbon–silver–platinum (DLC–AgPt) thin films using a multicomponent target pulsed laser deposition process. Transmission electron microscopy of the DLC–silver and DLC–platinum composite films revealed that the silver and platinum self-assemble into nanoparticle arrays within the diamondlike carbon matrix. The diamondlike carbon–silver film possessed hardness and Young’s modulus values of 37 GPa and 331 GPa, respectively. The diamondlike carbon-metal composite films exhibited passive behavior at open-circuit potentials. Low corrosion rates were observed during testing in a phosphate-buffered saline (PBS) electrolyte. In addition, the diamondlike carbon–metal composite films were found to be immune to localized corrosion below 1000 mV (SCE). DLC–silver–platinum films demonstrated exceptional antimicrobial properties against Staphylococcus bacteria. It is believed that a galvanic couple forms between platinum and silver, which accelerates silver ion release and provides more robust antimicrobial activity. Diamondlike carbon–silver–platinum films may provide unique biological functionalities and improved lifetimes for cardiovascular, orthopaedic, biosensor, and implantable microelectromechanical systems.     

掺硅类金刚石薄膜的制备及其微观机械性能研究

采用射频感应耦合离子源（ICP）在硅基底上沉积了DLC薄膜,并利用离子束溅射固体单晶石墨的方法掺入Si元素。通过原子力显微镜（AFM）和拉曼光谱对DLC薄膜的表面形貌及结构进行了分析表征。并用UTM-2摩擦磨损试验仪对薄膜进行了刻划测试,通过临界载荷的对比,分析了掺硅和纯DLC薄膜与基底的结合能力。结果表明,掺硅DLC薄膜具有良好的膜-基结合能力。     

Synthesis of cobalt/diamond-like carbon thin films by biased target ion beam deposition

Cobalt/diamond-like carbon (Co/DLC) composite thin films were synthesized on silicon wafers by biased target ion beam deposition (BTIBD) in which Co was deposited by sputtering a negatively biased Co target using an Ar ion beam and DLC was produced simultaneously by a second ion beam with CH₄ as carbon source. The surface morphology, chemical composition and binding states of the synthesised thin films were studied. The as-deposited Co/DLC films are continuous and smooth with a thickness of approximately 150 nm for an hour of deposition. The average roughness is 3.5 ± 0.3 Å and the root-mean squared roughness is 5.3 ± 1.1 Å. The films are low in contaminations and the mass concentration of Co is approximately 24%. Fourier transform infrared spectroscopy and Raman spectroscopy results indicate the Co did not react with C and barely changed the microstructure of DLC. X-ray photoelectron spectroscopy and synchrotron based near-edge X-ray absorption fine structure studies indicate that the Co is in metallic form in the as-deposited films. The preliminary results demonstrate the promise to synthesize high quality Co/DLC composite films by BTIBD.     

Compositional pathways and anisotropic thermal expansion of high-entropy transition metal diborides

The recent discovery of high entropy transition metal diborides (HEBs) has sparked renewed interest in ultra-high temperature ceramics (UHTCs). Presently, transition metal (Me) oxides based boro-carbo/thermal reduction (BCTR) syntheses show great promise as relatively cheap production methods, but also may present limits to attain single phase pure HEBs. Herein, by selectively tuning the concentration of boron and carbon, the reducing agents of Me oxide mixture (Me = Ti, Ta, Nb, Zr and Hf), and exploiting high-resolution synchrotron X-ray powder diffraction, we first identified and quantified the formation of intermediate phases during the BCTR synthesis, with the ultimate intent to achieve a full dense (Ti,Ta,Nb,Zr,Hf)B₂ solid solution (SS). Additional insight was obtained by temperature dependent diffraction, which highlighted, for the first time in this class of materials, anisotropic thermal expansion, most likely at the origin of the SS micro-cracking, as was also observed by electron microscopy.