Cathodic Vacuum Arc Technology Research Articles

Comparison of Corrosion Behavior of a-C Coatings Deposited by Cathode Vacuum Arc and Filter Cathode Vacuum Arc Techniques

This study explores the utilization of cathodic vacuum arc (CVA) technology to address the limitations of magnetron sputtering technology in preparing amorphous carbon (a-C) coatings, such as having a low ionization rate, low deposition rate, and insufficiently dense structure. Specifically, a-C coatings were prepared by the cathodic vacuum arc (CVA)and the filtered cathodic vacuum arc (FCVA) technology,, one with embedded carbon particles and one without, both having closely related carbon structures. Research is currently underway on bipolar plate coatings for fuel cells. The corrosion behavior of the prepared a-C coatings was examined through Tafel polarization analysis under simulated fuel cell operating conditions as well as potentiostatic analysis at 0.6 V under normal conditions and 1.6 V under start–stop conditions for 7200 s. The coatings before and after corrosion are characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, and infrared spectroscopy. The results reveal that the incorporation of conductive graphite-like particles in the coatings reduces their contact resistance. However, the gaps between these particles and the coatings act as pathways for corrosive solution, exacerbating the corrosion of the coatings. After corrosion at 0.6 V, both sets of coatings with sp2-hybridized carbon structures are contaminated by elements such as hydrogen and oxygen, leading to an increase in their contact resistance. Under high potential conditions (1.6 V), large corrosion pits and defects appear at the locations of graphite-like carbon particles. Furthermore, both sets of samples exhibit more severe oxygen contamination and a transformation of broken carbon bonds from sp3- to sp2-hybridized forms, irrespective of whether embedded graphite particles are present.

Enhanced tribological behavior and corrosion resistance in AlSiC-based coatings through varied carbon content

A series of AlSiC-based nanocomposite coatings with varying carbon concentrations were fabricated by filtered cathodic vacuum arc (FCVA) technology. These coatings featured an amorphous matrix with embedded Al4Si3C6 nanocrystals. With the increase in carbon content, the proportion of amorphous structure within the structure grew, which was accompanied by a rise in sp3 hybridized carbon bonds. This compositional change led to a significant enhancement in hardness and toughness. Notably, the AlSiC coating deposited at a flow rate of 50 sccm displayed exceptional mechanical properties, including a high hardness of approximately 23.2 GPa, toughness indices of H/E = 0.096 and H3/E2 = 0.216 GPa, a low friction coefficient around 0.18, a wear rate as low as ∼1.09 × 10−5 mm3 N−1 m−1, and a corrosion current density of approximately 1.08 × 10−9 A/cm2. The coating's superior tribological characteristics and corrosion resistance can be attributed to two main factors. The enhanced hardness and toughness indices (H/E and H3/E2) contributed to its improved deformability, which is essential for wear resistance. Secondly, the presence of a graphite layer formed during friction provided self-lubrication, further reducing wear. Additionally, the chemical inertness of both the amorphous SiC and the amorphous carbon phases within the nanocomposite structure significantly bolstered the coating's resistance to corrosion. The AlSiC nanocomposite coatings deposited by FCVA exhibit outstanding mechanical properties, tribological performance, and corrosion resistance, making them highly suitable for applications in environments where wear and corrosion are significant concerns.

Mechanical and corrosion properties of hydrogen-free DLC coatings prepared on degradable as-extruded WE43 alloy using FCVA technology

Magnesium alloys have great potential for medical applications. However, their rapid degradation has limited their development. Hydrogen-free DLC coatings were deposited on WE43 using filtered cathodic vacuum arc (FCVA) technology. The influence of different negative bias voltages on the microstructure and mechanical and corrosion properties of the coatings was systematically analyzed. The research demonstrated that application of a negative bias voltage altered the surface morphology of hydrogen-free DLC coatings with amorphous structures. In addition, the coatings exhibited a decrease in hardness and elastic modulus until the negative bias voltage reached −75 V, indicating that the increase may be attributed to the rise in sp2 cluster size and the fall in sp3 content. Furthermore, electrochemical experiments demonstrated that the coated samples exhibited superior anti-corrosion properties. The coatings deposited at −75 V displayed the highest corrosion resistance, as evidenced by their minimal corrosion current (4.53 μA·cm−2), maximal film resistance (2576 Ω·cm2), and charge transfer resistance (3171 Ω·cm2). Hydrogen evolution experiments indicated that the hydrogen-free DLC coatings effectively reduced WE43 corrosion and hydrogen gas production.

Preparation and performance of Ti/Ti-DLC composite coatings for precision glass molding

Precision glass molding (PGM) is an efficient process used for batch manufacturing of high-precision glass optical elements. In this process, nickel phosphide (Ni–P) alloy is commonly utilized as a mold material due to its superior turning properties. However, the Ni–P mold suffers from issues such as diffusion of phosphorus elements, poor wear resistance, and easy peeling of the DLC coating during molding. To address these problems, the current study proposes enhancing the molding performance of mold by depositing a composite coating layer of Ti/Ti-DLC onto the surface of Ni–P using the filtered cathodic vacuum arc technology (FCVA). The effects of different flow rates of C2H2 on Ti-DLC coatings were analyzed in terms of composition, microstructure, mechanical, tribological, and molding properties. The results revealed that as the C2H2 flow rate increased, the Ti content of coatings decreased from 13.56 to 2.17 at.%. Additionally, the film microstructure transformed from TiC polycrystalline composite films to nanocrystalline amorphous composite films and finally to amorphous films. The Ti-DLC coatings with a nanocrystalline composite structure exhibited excellent overall performance when Ti content is 7.75 at.%. These coatings are suitable as protective coatings for microstructured array mold and demonstrate good stability at a molding temperature of 500 °C.

Co(OH)2 nanoneedles grown on Cu/NF current collector with high areal capacitance for supercapacitors

Despite the demand for high energy-density supercapacitors has been realized when transition metal hydroxides are used as electrode materials, the ion diffusion dynamics are still limited by its high impedance. In this work, Cu is deposited on nickel foam (NF) by filtered cathodic vacuum arc (FCVA) technology to serve as an ion-diffusion-favored surface state. Co(OH)2 synthesized hydrothermally on this Cu/NF exhibits remarkably enhanced electrochemical properties compared with Co(OH)2 grown on pristine NF. The resultant electrode can deliver a large area capacity of 0.772 C cm−2 at 1 mA cm−2 and retain 80.92% of initial capacitance after 4000 cycles. Moreover, an assembled asymmetric supercapacitor shows a high energy density of 0.086 mW cm−2 at 0.4 mWh cm−2 with a long lifespan (80.67% retention after 3000 cycles). Our strategy may provide a new insight to prepare electrodes for assembling high areal capacitance supercapacitors.

Structure control of high-quality TiAlN Monolithic and TiAlN/TiAl multilayer coatings based on filtered cathodic vacuum arc technique

Coating techniques are used to improve the surface properties of materials. The filtered cathodic vacuum arc (FCVA) technology is an effective method to obtain high-quality dense coatings. Through FCVA technology, the contradiction between large thickness (over 10 μm) and compactness of TiAlN ceramic coatings was resolved. In this study, a monolayer TiAlN coating with a thickness of 17.13 μm, which possess a hardness of 34.31 GPa was obtained by the FCVA technology. The toughness of the coating was improved by the multilayer structure design which consists of TiAlN/TiAl. The best H/E and H3/E2 value of multilayer coating reached 2.38 times and 4.83 times higher than that of monolayer coating, and the hardness was only decreased by 15.46% at the same time. The highest critical load of adhesion strength for multilayer coatings reached 89.56 N, which is 1.98 times higher than the monolayer coating (44.24 N). For multilayer coating, the mass loss rate in anti-sand erosion test at high angle with the speed of 90 m/s is as low as 0.537 × 10−4 g/g. The erosion resistance per unit thickness of the multilayer coating reaches 1.9 times higher than that of the monolayer coating. At the same time, the multilayer coating has super wear resistance under oil lubrication environment. There is no obvious wear loss in the harsh reciprocal tribological test for 300 min with a normal load of 20 N and a reciprocating friction frequency of 4 Hz. The TiAlN/TiAl multilayer coating with large thickness and high density has excellent crack resistance and has application prospects in high load environments.

Corrosion resistance of AlN monolayer and Al/AlN multilayer deposited by filtered cathodic vacuum arc

The AlN monolayer and (Al/AlN)5 multilayer coatings were deposited on AZ31 magnesium alloys by filtered cathodic vacuum arc technology. The AlN monolayer showed a dense structure, but there were some holes at the coating/substrate interface. The (Al/AlN)5 multilayer showed a compact layered structure and the holes were interrupted by the Al/AlN interface. Both AlN monolayer and (Al/AlN)5 multilayer provided excellent corrosion resistance for magnesium alloys, with low corrosion current density of 1.91 × 10−6 and 1.11 × 10−6 A/cm2, respectively. Better corrosion resistance of the (Al/AlN)5 multilayer is attributed to its denser layered structure, better adhesion strength, better crack propagation resistance, and deformation coordination between coating and substrate during corrosion.

Effect of bias voltage on microstructure, mechanical and tribological properties of TiAlN coatings

TiAlN multilayer coatings composed of TiAl and TiAlN layers were deposited on ZL109 alloys using filtered cathodic vacuum arc (FCVA) technology. The effect of bias voltage on the microstructure and properties of the coating was systematically studied. The results show that the coating exhibits a multi-phase structure dominated by TiAlN phase. As the bias voltage increases, the orientation of TiAlN changes from (200) plane to (111) plane due to the increase of atomic mobility and lattice distortion. The hardness, elastic modulus and adhesion of the coating show the same trend of change, that is, first increase and then decrease. When the bias voltage is 75 V, the coating exhibits the highest hardness (~30.3 GPa), elastic modulus (~229.1 GPa), adhesion (HF 2) and the lowest wear rate (~4.44×10−5 mm3/(N·m)). Compared with bare ZL109 alloy, the mechanical and tribological properties of TiAlN coated alloy surface can effectively be improved.

Effect of annealing on the microstructure, mechanical and electrochemical properties of CrAlC coatings

The CrAlC coating has broad application prospects as a high temperature protective material due to its unique properties. However, it is difficult to control the properties of CrAlC coating due to the multiphase structure produced by thermally induced solid-reaction. In this paper, the CrAlC coating was prepared by filtered cathodic vacuum arc (FCVA) technology. In order to elucidate the relationship between the phase structure evolution and the properties, the structure, mechanical and electrochemical properties of the CrAlC coating before and after annealing were systematically investigated. The results illustrated that the CrAlC coating changed from amorphous structure to crystalline structure after annealing, and the phase composition varied with the increases of annealing temperature. As the annealing temperature increased from 700 °C to 800 °C, the content of Cr23C6 and Al4C3 increased. However, with further increasing the annealing temperature to 900 °C, the content of Al4C3 gradually decreased, and the Cr23C6 phase was transformed into Cr7C3 and Cr3C2 phases. In addition, the hardness and corrosion resistance of the coating first increased and then decreased with the increase of annealing temperature. When the annealing temperature was 800 °C, the CrAlC coating had the highest hardness (18.28 GPa) and the best corrosion resistance with the smallest corrosion current density (8.54 × 10-9 A/cm2).

Effect of self-ion with high-energy irradiation on the surface morphology, microstructure and mechanical properties of nanocrystalline TiAlN coating

TiAlN coating are used as nuclear reactor cladding protective materials due to their good corrosion resistance. However, long-term exposure to an extremely harsh nuclear environment will cause degradation, and the threshold irradiation fluence is not clear. In this work, a nanocrystalline TiAlN coating was successfully deposited on 304 L stainless steel and silicon wafers by filtered cathodic vacuum arc (FCVA) technology. The effects of different fluences of Al 3+ irradiation performed by the GIC4117 tandem accelerator on the structure and mechanical properties of TiAlN coatings were studied. After irradiation with a fluence of 4.0 × 10 14 ions/cm 2 , the refinement of grain size and columnar structure of nanocrystalline TiAlN coatings was confirmed, which improved the hardness. The irradiation fluence of 4.0 × 10 16 ions/cm 2 reduces all mechanical properties and can be taken as the threshold for the degradation of the TiAlN coating. These nanocrystalline TiAlN coatings have high surface integrity with no destruction, such as flacking, exfoliation and blistering, and good mechanical properties after irradiation. • Ultra-hardness (>40 GPa) was obtained by the formation of nanocrystalline structure and solid solution phase. • The crystallites refined from the average size of 23 ± 2 nm for the initial state up to a size of 18 ± 2 nm. • The hardening effect was confirmed under ion irradiation and the hardness increases from 42.5 ± 1.3 GPa to 46.4 ± 1.4 GPa. • The TiAlN coating with nano-polycrystalline structure exhibits structural integrity without blistering or flaking effects after irradiation.

Tribological Behaviors of Super-Hard TiAlN Coatings Deposited by Filtered Cathode Vacuum Arc Deposition.

High hardness improves the material’s load-bearing capacity, resulting in the enhancement of tribological properties. However, the high hardness is difficult to achieve for TiAlN coating due to the transformation of the close-packed structure from cubic to hexagonal and the increase in the grain size when the Al content is high. In the present study, the ultrahard TiAlN coatings (hardness > 40 GPa) are successfully developed by filtered cathodic vacuum arc technology to study the effect of nitrogen flux rate on tribological behaviors. The highest hardness of 46.39 GPa is obtained by tuning the nitrogen flux rate to achieve the regulation of Al content and the formation of nanocrystalline. The stable fcc TiAlN phase is formed via the solid-phase reaction under a high nitrogen concentration, and more aluminum atoms replace the titanium atoms in the (Ti, Al)N solid solution. The high Al content of the Ti0.35Al0.65N coating has a nanocrystalline structure and the average crystalline size is 16.52 nm. The TiAlN coating deposited at a nitrogen flux rate of 60 sccm exhibits the best properties of a combination of microhardness = 2972.91 Hv0.5, H = 46.39 GPa, E = 499.4 Gpa, ratio H/E* = 0.093 and ratio H3/E*2 = 0.403. Meanwhile, the TiAlN coating deposited at 60 sccm shows the lowest average friction coefficient of 0.43 and wear rate of 1.3 × 10−7 mm3 N−1 m−1 due to the best mechanical properties.

Development of irradiation-resistant enriched 12C targets for astrophysical [formula omitted] reaction measurements

The production of irradiation-resistant enriched 12C target is one of the key technologies in the direct measurement of the 12C(α,γ)16O reaction at energies of astrophysical interest. In this work, we produced the enriched Ti12C targets on Ta substrates via the filter cathodic vacuum arc (FCVA) technology. The target stability under the bombardment of a high-intensity 4He beam was investigated by monitoring the γ-ray yields of the 12C(p,γ)13N reaction regularly. A 25% deterioration of 12C in the target was observed after bombardment by a 740 keV, 500 μA 4He2+ beam with a charge of 280 C, which is stronger than the implanted targets developed before. Furthermore, the 13C/12C ratio in the Ti12C target was measured to be (1.1±0.3)×10−4, which can meet the requirement of the 12C(α,γ)16O measurement at the China JinPing underground Laboratory (CJPL).

Microstructure, mechanical and tribological properties of multilayer Ti-DLC thick films on Al alloys by filtered cathodic vacuum arc technology

Low hardness and poor wear resistance are major limitations of Al alloys, which hinder their application in several fields, especially automotive moving parts. DLC can effectively improve hardness and wear resistance of Al alloys, but high residual stress and poor adhesion limit the film thickness. Multilayer thick films (~10 μm) composed of alternating Ti and Ti-DLC layers were successfully deposited on Al alloys. The influence of Ti content on the microstructure, mechanical and tribological properties of the film was emphasized. As the Ti content decreased from 10.42 to 1.35 at.%, the microstructure evolved from a polycrystalline composite film to a nanocrystalline composite film, and then to an amorphous film. The mechanical and tribological properties of the film depended on the microstructure. The amorphous composite film (Ti >6.06 at.%) exhibited better wear resistance than the polycrystalline composite film (Ti <6.06 at.%) due to the higher H/E⁎ (>0.1), H3/E⁎2 (>0.2) and elastic recovery (>60%). When the doped Ti content was 6.06 at.%, the nanocrystalline composite multilayer film showed superior comprehensive performance of high hardness (~23 GPa), high elastic recovery (~69%), low friction coefficient (~0.13) and low wear rate (1.0 × 10−7 mm3/Nm).

Corrosion and tribological properties of TiAlCN/TiAlN/TiAlcomposite system deposited by magneticfliter cathode vacuum arctechnique

The experiment is based on novel magnetic filtered cathodic vacuum arc (FCVA) technology, the effects of the structure and C contents of TiAlCN/TiAlN/TiAl composite coating on anticorrosion and wear resistance were studied. The macro/micro properties of the coatings were systematically characterized by SEM, XRD, XPS, electrochemical tests and friction equipment. The results show that, with the increase of C content,the form of C element in the coatings transforms from the TiAlCN solid solution to the coexistence of crystallized TiAlCN/amorphous carbon. The TiAlCN/TiAlN/TiAl coating with TiAlCNcrystallized/amorphous carbon nanocomposite structure demonstrated excellent performanceby combining the advantages of each layer, which the hardness reaches an ultrahigh leveland the amorphous carbonwith excellent self-lubricating effect exists in the coating structure. In 3.5% NaCl electrochemical corrosion test, &lt;i&gt;E&lt;/i&gt;&lt;sub&gt;corr&lt;/sub&gt; increased by 5.6 times to 0.271 V, &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;corr&lt;/sub&gt; decreased by 1/52 to 8.092 ×10&lt;sup&gt;–9&lt;/sup&gt; A·cm&lt;sup&gt;–2&lt;/sup&gt;. During the dry sliding, friction coefficient decreased by 1/3 to 0.43, and wear rate decreased by 1/1.4 to 1.13×10&lt;sup&gt;–5&lt;/sup&gt; mm&lt;sup&gt;3&lt;/sup&gt;·N&lt;sup&gt;–1&lt;/sup&gt;·m&lt;sup&gt;–1&lt;/sup&gt;.

Thick yet tough TiN coatings deposited by filter cathode vacuum arc technology

There are some high requirements for mechanical property to protective coatings of turbojet engine compressor blades as the appearance of extreme service conditions. The hard coating with high toughness, good adhesion, good wear resistance and excellent load carrying capacity is a potential coating for extreme service conditions in the future. Thick yet tough TiN hard coatings were successfully deposited on 304L stainless steel substrates by magnetic filtered cathodic vacuum arc technology. The morphology, structure and properties of the coatings were studied by SEM and XRD, etc.The results show that the continuous growth of TiN coatings attributed to periodic high energy ion bombardment which can suppress the large grain size and reduce the internal stress. The thickness of TiN coating can reach to 50 μm and the deposition rate was close to 0.2 μm/min. At the same time, the stable non stoichiometric TiN&lt;sub&gt;0.9&lt;/sub&gt; can be formed by controlling the constant N&lt;sub&gt;2&lt;/sub&gt; flow rate, which can improve the toughness of TiN coatings. All TiN ciatings belong to superhard coating and the max value of hardness and modulus of elasticity were 38.24 GPa and 386.53 GPa respectively. TiN coatings have good adhesion and excellent toughness.The highest &lt;i&gt; &lt;inline-formula&gt;&lt;tex-math id="Z-20200510122827-1"&gt;\begin{document}$ H/E^{*} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20200036_Z-20200510122827-1.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20200036_Z-20200510122827-1.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;&lt;/i&gt; and &lt;inline-formula&gt;&lt;tex-math id="Z-20200510122827-2"&gt;\begin{document}$ H^3/E^{*2} $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20200036_Z-20200510122827-2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="10-20200036_Z-20200510122827-2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;&lt;sup&gt; &lt;/sup&gt;rate of TiN coating can reach to 0.0989 and 0.3742. Thick yet tough TiN hard coatings have excellent wear resistance with the lowest friction coefficient of 0.26.

Effects of bilayer number and thickness ratio on structure and properties of (Cr, N)-DLC/DLC multilayer films

(Cr, N)-DLC/DLC multilayer films with different bilayer numbers and thickness ratios were prepared on cemented carbides and silicon wafers by cathodic vacuum arc technology. Surface and cross-section morphologies of multilayer films were observed by scanning electron microscope. Roughness, hardness, adhesion strength, friction coefficient and wear rates of the deposited films were investigated by surface profiler, nanoindentor, scratch tester, and ball-on-disk tribometer, respectively. Alternating stress field from adjacent sublayers benefited the mechanical properties while macroparticles piercing through interfaces between sublayers provided passages for cracks propagation and deteriorated films' mechanical properties. As bilayer numbers varied from 10 to 20 average friction coefficient and roughness of multilayer films had the same changing trend and wear rates increased linearly from 2.45 × 10−7 mm3/Nm to 3.81 × 10−7 mm3/Nm. Improving proportion of (Cr, N)-DLC layer in multilayer films increased quantity of macroparticles, leading to the rise of multilayer films' roughness, average friction coefficient and wear rates.

Effect of Ti Transition Layer Thickness on the Structure, Mechanical and Adhesion Properties of Ti-DLC Coatings on Aluminum Alloys.

Multilayers of Ti doped diamond-like carbon (Ti-DLC) coatings were deposited on aluminum alloys by filtered cathodic vacuum arc (FCVA) technology using C2H2 as a reactive gas. The effect of different Ti transition layer thicknesses on the structure, mechanical and adhesion properties of the coatings, was investigated by scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation and a scratch tester. The results showed that the Ti transition layer could improve interfacial transition between the coating and the substrate, which was beneficial in obtaining excellent adhesion of the coatings. The Ti transition layer thickness had no significant influence on the composition and structure of the coatings, whereas it affected the distortion of the sp2-C bond angle and length. Nanoindentation and scratch test results indicated that the mechanical and adhesion properties of the Ti-DLC coatings depended on the Ti transition layer thickness. The Ti transition layer proved favorable in decreasing the residual compressive stress of the coating. As the Ti transition layer thickness increased, the hardness value of the coating gradually decreased. However, its elastic modulus and adhesion exhibited an initial decrease followed by an increasing fluctuation. Among them, the Ti-DLC coating with a Ti transition layer thickness of 1.1 μm exhibited superior mechanical properties.

Effect of Bias Voltage on Microstructure and Mechanical Properties of Nanocomposite ZrCN Films Deposited by Filtered Cathodic Vacuum Arc**Supported by the National Natural Science Foundation of China under Grant No 51171028.

Nanocomposite ZrCN films consisting of nanocrystalline ZrCN grains embedded in nitrogen-doped amorphous carbon film are deposited by filtered cathodic vacuum arc technology under different bias voltages ranging from 50 to 400 V. The influence of bias voltage on the characterization and the mechanical properties of the ZrCN films are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and nano-indentation. The bias voltage has a subtle effect on the ZrCN grain size, which is around 9.5 nm and keeps almost constant. A slight increase of the bias voltage induces a relatively high sp3 fraction about 40% in N-doped amorphous C films but leads to the graphitization of the films under a higher voltage. The best mechanical property of the ZrCN film with the hardness of 41 GPa is obtained under the bias voltage of 200 V, indicating the positive effect of slight increase of ion bombardment on the hardness of the films.

Predicting multilayer film's residual stress from its monolayers

Multilayer film's residual stress was deduced from Stoney formula. A simple stress formula, which means that multilayer residual stress can be given by the weighted average of each monolayer's residual stress, was proposed and verified through experiments on gradient diamond-like carbon (DLC) and CrN/DLC multilayers prepared by cathodic vacuum arc technology. Typical stress formulas for alternating multilayers were also investigated on corresponding DLC multilayers. Multilayer samples, together with monolayers existed in multilayers, were prepared and studied. Surface profilometry and film stress tester were used to measure films' thicknesses and residual stresses, respectively. Cross-sectional morphologies of multilayers were observed by scanning electron microscope. Results showed that the proposed stress formula was correct and could provide useful instructions on multilayer design. The formula's accuracy of predicting multilayer's residual stress through its monolayers was also investigated. In the present paper, relative errors of theoretical values were in the range of 0.2% to 10.7%, which had a strong relationship with the substrate–film interfaces. In addition, as to alternating multilayer film, its residual stress is a constant value as the number of monolayers is even; while this number is odd, multilayers' residual stress gets close to the constant value gradually and monotonously.

Structural characteristics of surface-functionalized nitrogen-doped diamond-like carbon films and effective adjustment to cell attachment**Project supported by the National Natural Science Foundation of China (Grant Nos. 51272237, 51272231, and 51010002) and the China Postdoctoral Science Foundation (Grant Nos. 2012M520063, 2013T60587, and Bsh1201016).

Nitrogen-doped diamond-like carbon (DLC:N) films prepared by the filtered cathodic vacuum arc technology are functionalized with various chemical molecules including dopamine (DA), 3-Aminobenzeneboronic acid (APBA), and adenosine triphosphate (ATP), and the impacts of surface functionalities on the surface morphologies, compositions, microstructures, and cell compatibility of the DLC:N films are systematically investigated. We demonstrate that the surface groups of DLC:N have a significant effect on the surface and structural properties of the film. The activity of PC12 cells depends on the particular type of surface functional groups of DLC:N films regardless of surface roughness and wettability. Our research offers a novel way for designing functionalized carbon films as tailorable substrates for biosensors and biomedical engineering applications.