Mechanical properties of alternating high-low sp3 content thick non-hydrogenated diamond-like amorphous carbon films

Thick non-hydrogenated DLC films (∼ 1μm), consisting of alternating sub-layers of high/low sp³ content, were deposited onto n++ Si substrates using the filtered cathodic vacuum arc method. These films were systematically studied to determine how the changes in composition of the sub-layers would affect the mechanical properties such as intrinsic stress, hardness, friction coefficient, wear rate and surface roughness. Variations of both the ratio of hard to soft layers (from 1:3 to 3:1) and thickness of individual layers (from 12.5nm to 75nm) were studied in detail. The stress of the film was sufficiently lowered (7.8GPa–2.4GPa) by the multilayer approach. The results indicated that although hardness has some correlations with the internal composition of the film, the reduced Young's modulus is largely not affected. Wear and frictional characterizations also showed that the multilayer was a good candidate for many mechanical applications.     

Mechanical and electrical properties of micron-thick nitrogen-doped tetrahedral amorphous carbon coatings

The effect of nitrogen doping on the mechanical and electrical performance of single-layer tetrahedral amorphous carbon (ta-C:N) coatings of up to 1 μm in thickness was investigated using a custom-made filtered cathode vacuum arc (FCVA). The results obtained revealed that the hardness and electrical resistance of the coatings decreased from 65 ± 4.8 GPa (3 kΩ/square) to 25 ± 2.4 GPa (10 Ω/square) with increasing nitrogen gas ratio, which indicates that nitrogen doping occurs through substitution in the sp² phase. Subsequent AES analysis showed that the N/C ratio in the ta-C:N thick-film coatings ranged from 0.03 to 0.29 and increased with the nitrogen flow rate. Variation in the G-peak positions and I(D)/I(G) ratio exhibit a similar trend. It is concluded from these results that micron-thick ta-C:N films have the potential to be used in a wide range of functional coating applications in electronics.     

Field emission properties from aligned carbon nanotube films with tetrahedral amorphous carbon coatings

Tetrahedral amorphous carbon (ta-C) film was coated on aligned carbon nanotube (CNT) films via filtered cathodic vacuum arc (FCVA) technique. Field electron emission properties of the CNT films and the ta-C/CNT films were measured in an ultra high vacuum system. The I–V measurements show that, with a thin ta-C film coating, the threshold electric field (E_thr) of CNTs can be significantly decreased from 5.74 V/μm to 2.94 V/μm, while thick ta-C film coating increased the E_thr of CNTs to around 8.20 V/μm. In addition, the field emission current density of CNT films reached 14.9 mA/cm² at 6 V/μm, while for CNTs film coated with thin ta-C film only 3.1 V/μm of applied electric field is required to reach equal amount of current density. It is suggested that different field emission mechanisms should be responsible for the distinction in field emission features of CNT films with different thickness of ta-C coating.     

Relationship between bonding structure and mechanical properties of amorphous carbon containing silicon

Unhydrogenated amorphous carbon films with different silicon concentrations were synthesized by magnetron sputtering, and the corresponding evolution of inter-atomic bonding configurations, surface roughness and mechanical properties like hardness, modulus and stress was analyzed. Introducing silicon into amorphous carbon not only reduced the sp²-hybridized carbon bonding, it also helped to reduce residual stress. Both the hardness and elastic modulus suffered degradation when the silicon concentration was low. But these properties recovered when silicon dosage increased. Surface roughness increased when silicon concentration was low, but decreased when the silicon dosage increased. Such changes in the mechanical properties were closely related to the carbon and silicon inter-atomic interaction. The amorphous carbon network was modified by silicon, and affected by deposition kinetics. The mismatch in the atomic size and bond length, and the alteration of the carbon hybridization were determined to be the basis for the changes in the mechanical properties.     

Nanotribological and nanomechanical properties of 5–80 nm tetrahedral amorphous carbon films on silicon

Nanoscratch testing has been used to investigate the tribological behaviour of 5, 20, 60 and 80 nm tetrahedral amorphous carbon (ta-C) thin films deposited on silicon by the filtered cathodic vacuum arc method. The nanoscratch behaviour of the films was found to depend on the film thickness, with 60 and 80 nm films undergoing border cracking and then at higher critical load a dramatic delamination event. 5 and 20 nm films have a lower critical load for onset of border cracks but do not undergo a clear dramatic failure, and instead are increasingly worn/ploughed through until film removal as confirmed by microscopic analysis. This is consistent with the thinner films having lower stress and reduced load-carrying ability. Nanoindentation confirms that the thicker films have enhanced load support and higher measured composite (film + substrate) hardness. The 80 nm film in particular can retain appreciable load support whilst deformed during indentation, as shown by its ability to alter the critical loads for contact-induced phase transformations in the Silicon substrate during unloading.     

Characterisation of electrodeposited Co-W-P amorphous coatings on carbon steel

Electrochemistry and nucleation mechanism of induced co-deposition of cobalt, tungsten and phosphorus from a citrate bath was investigated using voltammetry and chronoamperometry techniques. It was found that the induced co-deposition of the species occurred under diffusion control and followed instantaneous nucleation mechanism. Co-W-P coatings were electrodeposited potentiostatically on plain carbon steels from a citrate bath containing CoSO₄, Na₂WO₄ and NaH₂PO₂. X-ray diffraction studies of the coatings revealed that the as-deposited Co₈₁W₁₀P₉ coatings had amorphous structure. The formation of some stoichiometric compounds like Co₃W, Co₂P and WP₂, however, was observed upon annealing at 600 °C. The hardness of the Co-W-P coatings increased with annealing temperature which was possibly due to the formation of these inter-elemental compounds. The corrosion resistance of the Co-W-P coatings increased with increase in annealing temperature which might also be due to the formation of the stoichiometric compounds at elevated temperatures. A comparison between coating characteristics of Co-W-P and chromium showed that the Co-W-P coatings exhibited nobler corrosion potential than chromium coatings.     

Influence of oxygen plasma treatment parameters on the properties of carbon fiber

This study is focused on the impact of oxygen plasma treatment on properties of carbon fibers and interfacial adhesion behavior between the carbon fibers and epoxy resin. The influences of the main parameters of plasma treatment process, including duration, power, and flow rate of oxygen gas were studied in detail using interlaminar shear strength (ILSS) of carbon fiber composites. The ILSS of composites made of carbon fibers treated by oxygen plasma for 1 min, at power of 125 W, and oxygen flow rate of 100 sccm presented a maximum increase of 28% compared to composites made of untreated carbon fibers. Furthermore, carbon fibers were characterized by scanning electron microscopy (SEM), tensile strength test, attenuated total reflectance Fourier transform infrared (ATR-FTIR), and Raman spectroscopy analyses. It was found that the concentration of reactive functional groups on the fiber surface was increased after the plasma modification, as well the surface roughness, which finally improved the interfacial adhesion between carbon fibers and epoxy resin. However, high power and long exposure times could partly damage the surface of carbon fibers and decrease the tensile strength of filaments and ILSS of treated fiber composites.     

纳米碳纤维表面非晶态Ni-Fe-Ru-P合金镀层的制备与表征

在铁片试样上研究以次磷酸钠为还原剂的化学镀Ni-Fe-Ru-P合金镀层的工艺,考察了金属盐浓度对化学镀反应沉积速率的影响.利用优化的工艺配方在经过敏化,活化处理后的纳米碳纤维表面沉积Ni-Fe-_Ru-P合金镀层,分别利用EDS、XRD、SEM等手段对镀层的成分,结构,形貌进行了表征,并对其进行了热处理.结果表明,利用化学镀技术可以在纳米碳纤维表面获得连续、均匀的Ni-Fe-Ru-P合金镀层,且镀层为非晶态结构.在350℃以下热处理不会改变镀层的结构,在400℃以上热处理,镀层开始晶化.     

Nanotribology of silver and silicon doped carbon coatings

Amorphous hydrogenated carbon coatings a-C:H become very popular materials mainly because of their excellent properties such as low coefficient of friction, high hardness, good anti-wear and corrosion properties. More and more often are carried works aimed at improvement of biocompatibility and adhesion of bacterial cells by doping diamond-like carbon (DLC) coating with third element. Among them recently a great majority is devoted to carbon coatings doped with silver or silicon. The presence of silver in the coating ensures protection of the implant against the disadvantageous influence of bacteria and fungi causing biofilm associated infections, local inflammation and other implant-tissue reactions. Incorporation of silicon promotes osteointegration and leads to the enhancement of mechanical and tribological properties of the coating, which is beneficial for biomedical applications.Silver and silicon incorporated DLC coatings were prepared by a hybrid Radio Frequency Plasma Assisted Chemical Vapor Deposition/Magnetron Sputtering deposition technique on AISI316L substrates. Obtained coatings were characterized in terms of morphology, surface topography and mechanical properties. Tribological properties of the coatings were measured by lateral force microscopy and reciprocating sliding test using nanoindenter.     

炭黑用量对不同聚丁二烯橡胶性能的影响

研究了低顺式聚丁二烯橡胶（BR3505）、低门尼顺丁橡胶（BR9002）和普通顺丁橡胶（BR9000）的硫化参数、拉伸性能和动态压缩性能。结果表明，与普通顺丁橡胶相比，聚丁二烯橡胶中反式结构含量较多（BR3505）时，芟联密度、断裂伸长率、压缩生热和压缩永久变形大，而硫化速度慢很多；且分子量分布变宽（BR9002）使其硫化速度稍快、断裂伸长率大、压缩生热稍低，同时低炭黑用量时的拉伸强度和伸长率较高，但是炭黑可填充量降低。     

Growth of carbon nanotube forests on carbon fibers with an amorphous silicon interface

Aligned multi-walled carbon nanotube forests were grown by chemical vapour deposition on carbon fibers by the use of an amorphous Si interface. The Si layer creates a barrier, hindering the Fe catalyst diffusion into the carbon fibers. This method provides a way to tailor the thermal, electrical and mechanical properties of the fiber-resin interface of a polymer composite.     

Influence of carbon content and particle dispersion on radiation properties of coal chars

Thermal radiation dominates the heat transfer in coal gasification or combustion furnaces operated at high temperatures. This study is to evaluate the radiation properties of coal char or ash particles, which are necessary to predict the behavior of heat transfer of a multiphase flow in the furnace. The monochromatic extinction of the sample particles dispersed in liquid paraffin wax was measured by the FT-IR spectroscopic analysis at a room temperature. Carbon containing in char particles influences significantly extinction efficiency as a radiation property. The normalized extinction efficiency was correlated by an exponential function of carbon content if the sample was prepared appropriately although the spectra depended on the preparation method of the samples.     

Ion beam deposition of amorphous hydrogenated carbon films on amorphous silicon interlayer: Experiment and simulation

A thick layer of amorphous silicon (a-Si) was deposited on industrial grade crystalline n-Si < 111 > substrate by means of electron beam evaporation. On top of a-Si layer, amorphous hydrogenated carbon (a-C:H) film was grown by direct ion beam deposition from acetylene precursor gas. In order to study on atomic level the a-C:H film growth on amorphous silicon, a theoretical model was developed in a form of reaction rate (kinetic) equations. Numerical simulation using this model has revealed that the ratio of sp³/sp² content in the film is heavily influenced by relaxation rate of the carbon atoms in a sub-surface region of the film that were activated by ion irradiation. The final structure of a-C:H film does not depend much on elemental composition and structure of amorphous Si coating, provided that deposition procedure is not terminated at its initial stage but continues for more than 60 s. It became evident, therefore, that the use of a-Si interlayer with a-C:H films could be particularly beneficial when a need arises to minimize or eliminate the effect of the substrate. As one of such cases, a poor adhesion of amorphous carbon on steel and other ferrous alloys could be mentioned.     

Disorder and optical properties of amorphous carbon

Tight-binding calculations shed light onto the link between disorder and optical properties in pure amorphous carbon films. It is shown that the Urbach energy E_U is an excellent probe of disorder in such films. Our striking finding is that E_U varies non-monotonically with sp³ fraction and optical gap, contrary to what is seen experimentally in hydrogenated samples. Firm evidence is provided, supported by experimental measurements, that in dense films the higher the sp³ fraction the lower the disorder. The Urbach energy has a value of ∼ 0.09 eV for the 100% sp³-bonded network, it reaches a maximum of ∼ 0.3 eV for 65% sp³ content, and it then declines to low values for low-sp³ content films. Analysis of cluster distributions and bond-angle and -length distortions reveals that the Urbach edge is associated to both topological and structural disorder. Another notable finding is that the edge is rather insensitive to the spin density due to unpaired sp² sites.     

硅源对无定形硅铝物化性能的影响

以硅溶胶和九水硅酸钠为硅源,九水硝酸铝为铝源,采用分步沉淀法制备一系列不同硅铝比的无定形硅铝,通过XRD、BET和NH₃-TPD等考察硅源对无定形硅铝物化性能的影响。结果表明,以九水硅酸钠为硅源制备的无定形硅铝比表面积和酸性均明显优于以硅溶胶为硅源制备的无定形硅铝;以九水硅酸钠为硅源,在SiO2质量分数为55%时,该无定形硅铝呈现出最大酸量和高的比表面积,作为性能优异的催化材料将具有良好的应用价值。     

Determining the oxygen content in partly oxidized silicon nitride

Conclusions The vacuum-extraction method is suitable for determining with adequate accuracy the content of oxygen (oxynitride) in partly oxidized silicon nitride and in silicon-carbide refractories with a nitride and silicon oxynitride bond.     

电沉积非晶态合金镀层磁性的控制

磁性元件薄膜化促进了磁性镀层的开发与应用。综述了镀液及镀层成分、电沉积工艺、镀层厚度及热处理对电沉积非晶态镀层性能的影响，以便在实际应用中控制非晶态合金镀层的磁性。     

Influence of oxygen content on structure and properties of pressurelessly sintered aluminum-nitride- and zirconium-boride-doped silicon-carbide ceramics

SiC is a widely used material. Understanding how oxygen content affects the SiC structure and properties is crucial. In this paper, heat treatment was used to prepare SiC powder samples with different oxygen contents, which were doped with AlN and ZrB₂ and were densified by pressureless sintering at 2050 °C. The effect of oxygen content on the sintered SiC structure was determined by X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy. The results indicated that the oxygen content influenced the SiC phase composition, grain boundaries, and densification. Additionally, the interaction between oxygen defects and AlN played an important role in sintering. The nanoindentation, alternating-current impedance, and thermal conductivity of the densified SiC specimens were also evaluated to elucidate the influence of the oxygen content on the densified-SiC functional properties. The results revealed that the oxygen content affected all the measured mechanical, electrical, and thermal properties. Furthermore, surface oxygen impurities suggested that oxygen content had similar critical effects on both the densified SiC structure and properties.     

Optical properties and new carbon forms of sputtered amorphous carbon films

Amorphous carbon films were deposited by r.f. magnetron sputtering at various bias voltages V_b applied on Si substrate. We studied the optical properties of the films using in situ spectroscopic ellipsometry (SE) measurements in the energy region 1.5–5.5 eV. From the SE data analysis the dielectric function ε(ω) of the a-C films was obtained, providing information about the electronic structure and the bonding configuration of a-C films. Based on the SE data the films are classified in three categories. In Category I and II belong the films developed with V_b≥0 V (rich in sp² bonds) and −100≤V_b<0 V (rich in sp³ bonds), respectively. The dielectric function of the films belonging in these two categories can be described with two Lorentz oscillators located in the energy range 2.5–5 eV (π–π^*) and 9–12 eV (σ–σ^*). A correlation was found between the oscillator strength and the sp² and sp³ contents. The latter were calculated by analyzing the ε(ω) with the Bruggeman effective medium theory. In films deposited with V_b<−100 V (Category III), the formation of a new and dense carbon phase was detected which exhibits a semi-metallic optical behavior and the ε(ω) can be described with two oscillators located at ∼1.2 and ∼5.5 eV.     

Effect of nitrogen content on high-temperature stability of hard and optically transparent amorphous Hf-Y-Si-B-C-N coatings

We study the effect of nitrogen content on functional properties, thermal stability and oxidation resistance of hard and optically transparent amorphous Hf-Y-Si-B-C-N coatings prepared by pulsed magnetron sputtering. Ab-initio simulations are performed to link the experimentally obtained properties with the atomic and electronic structures of the fabricated materials. It is shown that the content of N in the material, varied from subsaturation 46 at.% to saturation 51 at.%, is of significant importance for the optimization of thermal stability and tuning the refractive index and extinction coefficient. We identify an optimum N₂ content in the plasma and in turn N content in the coatings which outperform the previously introduced high-temperature material Hf₆Y₂Si₂₉B₁₂C₂N₄₅. The results constitute a progress in the efforts to combine multiple functional properties with exceptional (above 1300 °C) thermal stability and oxidation resistance.