Preparation of tetrahedral amorphous carbon films by filtered cathodic vacuum arc deposition

Tetrahedrally bonded amorphous carbon (ta-C) and nitrogen doped (ta-C:N) films were obtained at room temperature in a filtered cathodic vacuum arc (FCVA) system incorporating an off-plane double bend (S-bend) magnetic filter. The influence of the negative bias voltage applied to substrates (from −20 to −350 V) and the nitrogen background pressure (up to 10⁻³ Torr) on film properties was studied by scanning electron microscopy (SEM), electron energy loss spectroscopy (EELS), Raman spectroscopy, X-ray photoemission spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and X-ray reflectivity (XRR). The ta-C films showed sp³ fractions between 84% and 88%, and mass densities around 3.2 g/cm³ in the wide range of bias voltage studied. In contrast, the compressive stress showed a maximum value of 11 GPa for bias voltages around −90 V, whereas for lower and higher bias voltages the stress decreased to 6 GPa. As for the ta-C:N films grown at bias voltages below −200 V and with N contents up to 7%, it has been found that the N atoms were preferentially sp³ bonded to the carbon network with a reduction in stress below 8 GPa. Further increase in bias voltage or N content increased the sp² fraction, leading to a reduction in film density to 2.7 g/cm³.     

Surface energy of metal containing amorphous carbon films deposited by filtered cathodic vacuum arc

Metal containing amorphous carbon (a-C:Me) films including a-C:Al, a-C:Ti, a-C:Ni, a-C:Si were prepared by the filtered cathodic vacuum arc (FCVA) technique with metal-carbon (5 at.% metal) composite targets. The substrate bias ranging from floating to 1000 V was applied. The wettability of the films was examined using the VCA Optima system from AST Products, Inc. Three types of liquid with different polarities were used to study the surface energy changes of the films. X-ray photoelectron spectroscopy (XPS) was used to analyze the composition and chemical state of the films. Atomic force microscopy (AFM) was employed to characterize the morphology and roughness of the films. The contact angle of the a-C:Me films remains relatively constant with different substrate bias. The Al containing films show the highest contact angle with water, which reaches as high as 101°. The Si containing films show the lowest contact angle approximately 64°. The contact angles of Ni and Ti containing films are approximately 80°, 97°, respectively. The harmonic-mean method was used to calculate the polar and depressive component of the surface energy. The absorption of oxygen on the surface plays an important role on the polar component of the a-C:Me films. The formation of AlO and TiO bonds is responsible for their lower polar component. The metal state Ni results in higher polar component. However, the SiO bond is contributed to the high polar component of a-C:Si films. As all films are atomic scale smooth, the RMS roughness is below 0.5 nm, the roughness does not have obvious effect on the surface energy.     

Deposition of iron containing amorphous carbon films by filtered cathodic vacuum arc technique

Iron containing amorphous carbon (a-C:Fe) films have been deposited with an Fe/graphite composite target with different Fe content by filtered cathodic vacuum arc (FCVA) technique. X-Ray induced photoelectron spectroscopy (XPS) was used to analyze the Fe content in the films. Micro-Raman spectroscopy was employed to characterize the structural changes of a-C:Fe films. The properties of the a-C:Fe films such as the intrinsic stress, morphology and roughness investigated by the profiler, atomic force microscope (AFM). The XPS results show that there exists small amount of oxygen in the form of FeO in the films and the Fe fraction in the films is always larger than that in the target. Compared with pure amorphous carbon films the intrinsic stress was effectively reduced by incorporating Fe into the films, and decreases with increasing Fe content. As increasing the Fe content, the clusters in the films become finer and the roughness increases The studies of Raman spectra show that the positions of G peak and D peak shift to low and high wavenumbers, respectively, and the ratio of the intensity of D and G peaks increases with an increase in Fe content, that suggests that the sp²-bonded carbon and the size of the sp²-bonded cluster increases with an increase in the Fe content.     

Nitrogenated carbon films deposited using filtered cathodic arc

Nitrogenated carbon films were deposited on various substrates using filtered cathodic arc. Non-uniformity of the film thickness was less than 5% over a 15 cm diameter area. Mechanical, optical (refraction index, extinction coefficient versus wavelength) and electrical properties were investigated as a function of nitrogen flow rate. Deposited coatings demonstrated high hardness of 40–65 GPa, Young's modulus 200–285 GPa, excellent elastic recovery, high critical pressure for scratch formation, and surface smoothness. While the hardness showed a relatively small decrease with nitrogen flow increase, the stress decrease was more significant (8–3.8 GPa). Extremely low wear rates were observed, even at high contact pressures, and no substantial debris was detected indicating that carbon is oxidized during wear. Clear correlation was found between transparency, electrical resistivity and stress of the films. Transparency and resistivity showed a significant rise with an increase of stress. An explanation of the film properties is based on the assumption that the basic characteristics of the deposited films were determined by the relative proportion of two three dimensional complementary type of bonds; the tetrahedral sp³ bonds leading to stiff networks, and the trigonal sp² arrangments close to fullerene-like, or nanotube-like, structures.     

Cathodoluminescence of fluorine doped amorphous carbon nanoparticles deposited by a filtered cathodic arc plasma system

The fluorine doped amorphous carbon nanoparticles (a-C:F NPs) films with sizes 50-100 nm were deposited on polyethylene terephthalate in an atmosphere of CF₄ by a 90°-bend magnetic filtered cathodic arc plasma system. The surface morphology of a-C:F NPs films was observed by field emission scanning electron microscope and atomic force microscope. The microstructure and chemical bonding nature of the a-C:F NPs films were investigated by Raman, X-ray diffraction and X-ray photoelectron spectroscopy. This work presents cathodoluminescence (CL) spectra of a-C:F NPs films obtained at 1.9-2.4 eV and verifies luminescence from a-C:F NPs films in the visible region. The incorporation of fluorine into the carbon network results in orange emission (∼2.03 eV) due to the transitions between fluorine-related electron levels and σ* states, and the red emission (∼1.97 eV) results from the recombination of carriers in the valence π and conduction π* states. The peak at ∼2.10 eV may result from the defects of the structures in a-C:F NPs films.     

Properties of tetrahedral amorphous carbon prepared by vacuum arc deposition

The structural, optical, electrical and physical properties of amorphous carbon deposited from the filtered plasma stream of a vacuum arc were investigated. The structure was determined by electron diffraction, neutron diffraction and energy loss spectroscopy and the tetrahedral coordination of the material was confirmed. The measurements gave a nearest neighbour distance of 1.53 Å, a bond angle of 110 and a coordination number of four. A model is proposed in which the compressive stress generated in the film by energetic ion impact produces pressure and temperature conditions lying well inside the region of the carbon phase diagram within which diamond is stable. The model is confirmed by measurements of stress and plasmon energy as a function of ion energy. The model also predicts the formation of sp²-rich materials on the surface owing to stress relaxation and this is confirmed by a study of the surface plasmon energy. Some nuclear magnetic resonance, infrared and optical properties are reported and the behaviour of diodes using tetrahedral amorphous carbon is discussed.     

Heat treatment of tetrahedral amorphous carbon films grown by filtered cathodic vacuum-arc technique

Tetrahedral amorphous carbon (ta-C) is a potential low-cost substitute for diamond in certain applications, but little is known of the temperature range over which its desirable properties are retained. The thermal stability of tetrahedral amorphous carbon (ta-C) films has been investigated by heat treatment of the films at temperatures from room temperature to 450°C in high vacuum, low vacuum and oxygen ambient. It was found that heat treatment in oxygen ambient leads to a much more prominent variation in film thickness, stress and hardness than in both low and high vacuum. Raman studies also show an increase of the G-band frequency to higher values, an increase of the integrated intensity ratio and a narrowing of the G bands for films annealed in oxygen ambient with increasing temperature. By contrast, ta-C films exhibit a high resistance to degradation during treatment in low and high vacuum. They sustain their structure, thickness, stress and hardness for temperatures up to 400°C.     

Techniques for filtering graphite macroparticles in the cathodic vacuum arc deposition of tetrahedral amorphous carbon films

Filtered cathodic vacuum arc (FCVA) deposition has been found to be a reliable technique for the production of high quality tetrahedral amorphous carbon films (ta-C). These coatings can be used as protective coatings for different applications ranging from cutting tools to human hip joint prosthesis. The FCVA technique is widely used in different laboratories around the world with somewhat different technical implementations. A serious disadvantage in the FCVA technique is the graphite particles that are emitted from the solid graphite cathode during the arc-discharge. A variety of different techniques exist to diminish their production and transport. However, some of the magnetic filtering designs that are used to reduce the macroparticle transport into the substrate do not work well with high melting point cathode materials such as graphite. Although the influence of graphite particles for the ta-C coating performance in some applications is controversial, many applications demand that the produced ta-C film is practically particle-free. This is especially important in corrosion resistance, electrical and optical applications. In this paper an introduction to different FCVA devices is presented. Different magnetic filtering designs together with control techniques for macroparticle generation have been reviewed and their advantages and disadvantages in the plasma transport and particle filtering efficiency have been discussed.     

Properties and tool performance of ta-C films deposited by double-bend filtered cathodic vacuum arc for micro drilling applications

This paper describes the results of the application of ta-C films to micro drilling operation for deep and small machining boreholes. Tetrahedral amorphous carbon (ta-C) films were successfully deposited on WC-Co substrates by a double-bend filtered cathodic vacuum arc (FCVA) system. The structure, mechanical and tribological properties of both pure ta-C and ta-C incorporated argon gas (ta-C:Ar-flow) films were systematically investigated. And then, high-speed through-hole drilling tests were performed on the PCB (printed circuit board) workpiece to investigate the machining performance of ta-C coated micro drills. The experimental results show that the ta-C:Ar-flow (2 sccm) coated micro drill has excellent microstructure, microhardness, and friction coefficient properties and represents the optimal coatings for micro drilling applications.     

Deposition of carbon nitride films by filtered cathodic vacuum arc combined with radio frequency ion beam source

Atomically smooth carbon nitride films were deposited by an off-plane double bend filtered cathodic vacuum arc (FCVA) technique. A radio frequency nitrogen ion source was used to supply active nitrogen species during the deposition of carbon nitride films. The films were characterized by atomic force microscopy (AFM), XPS and Raman spectroscopy. The internal stress was measured by the substrate bending method. The influence of nitrogen ion energy (0–1000 eV) on the composition, structure and properties of the carbon nitride films was studied. The nitrogen ion source greatly improves the incorporation of nitrogen in the films. The ratio of N/C atoms in the films increases to 0.40 with an increase in the ion beam energy to 100 eV. Further increase in the ion beam energy leads to a slight decrease in the N/C ratio. XPS results show that nitrogen atoms in the films are chemically bonded to carbon atoms as C---N, C=N, and CN bonds, but most of nitrogen atoms are bonded to sp² carbon. The increase in nitrogen ion energy leads to a decrease in the content of nitrogen atoms bonded to sp² carbon, and an increase in the content of nitrogen atoms bonded to sp³ and sp¹ carbon. Raman spectra indicate an increase in the sp² carbon phase in carbon nitride films with an increase in nitrogen ion energy. The increase in sp² carbon fraction is attributed to the decrease in internal stress with increasing nitrogen ion energy.     

Cathodoluminescence of the a-C:N films deposited by a filtered cathodic arc plasma system

Amorphous carbon nitride (a-C:N) films were successfully synthesized on silicon using a 90°-bend magnetic filtered cathodic arc plasma (FCAP) system. ESCA analysis demonstrated that the N/C ratios reached 1.08. Many investigations on photoluminescence (PL) spectra of diamondlike carbon films have been performed, but cathodoluminescence (CL) spectra have seldom been discussed. This work investigated a-C:N films using the CL spectra at 300 K. This work presents CL spectra of a-C:N films obtained at 1.5–3.5 eV and verifies luminescence from the a-C:N films in the visible region. The most prominent luminescence in the CL spectra from the a-C:N films has two peaks centered ∼2.67 eV (blue light) and ∼1.91 eV (red light), but the a-C film yielded only the band at ∼1.91 eV. These optical emissions are intrinsic and extrinsic to the a-C:N film and are sensitive to the content of nitrogen.     

Diamond-like carbon overcoat for TFMH using filtered cathodic arc system with Ar-assisted arc discharge

The deposition system described for sub-30 Å and thicker carbon (ta-C) overcoat that includes two RF ion beam guns and Filtered Cathodic Arc (FCA) module mounted on a single vacuum chamber. The system is capable of flattening the Thin Film Magnetic Heads (TFMH) surface by ion beam etching; smoothing scratches, trenches, steps on boundaries of different materials, and enhancing the adhesion by ion assisted ion beam sputtering. It provides the highly controllable deposition of carbon using an FCA module with Ar-assisted arc discharge. Low-level particulates are achieved on the deposited film surface (< 5/cm² ). It was shown that crucial impact on filtering the particles with size < 1 μm has the electrostatic field distribution across the plasma guide that can be controlled by duct bias. Mechanical and electrical properties, optical and Raman spectra of ta-C films were investigated as a function of Ar flow in the arc discharge area. At Ar flow rates 0–12 sccm, stress of the films was varied in a range 2.9–7.5 GPa while hardness and Young's Modulus stayed in ranges of 45–60 GPa, and 230–300 GPa, respectively. Density of the obtained films was greater than 2.8 g/cm³. Optical absorption and electrical conductivity of ta-C films showed a significant rise while stress came down with Ar flow. Raman G-peak was higher for ta-C films with lower stress and shifted to lower energy. The low stress films versus high stress films showed a few orders reduced electrical resistance and anisotropy of specific resistance with respect to substrate plane: ρ_⊥ ≫ ρ_∥. In situ ellipsometric control of growing film thickness was implemented on the system. Run-to-run standard deviation was less than 1 Å for 20–25 Å thick films. High corrosion resistance of FCA coatings was exhibited. The impact of Ar gas–carbon plasma interaction on the deposition conditions and microstructure of ta-C films was discussed.     

Surface,microstructure and optical properties of copper-doped diamond-like carbon coating deposited in pulsed cathodic arc plasma

Diamond-like carbon (DLC) coating doped with copper has been deposited on silicon substrate by pulsed cathodic arc plasma using a composite cathode made of graphite with inserted copper rods. The surface morphology, microstructure and distribution patterns of elements in the coating and substrate have been studied by atomic force microscopy, scanning electron microcopy, Raman spectroscopy and energy dispersive spectroscopy. The results show that the studied coating is very well-adhered to the silicon substrate, with no microcracks, microvoids, localized delaminations or other defects being observed at the coating/substrate interface. It is also shown that the studied coating has layered microstructure and its surface is very smooth, however containing a few of nano-sized particle-like projections of copper oxide that seems to be a specific feature of all the pulsed methods used for deposition of DLC coatings doped with metals. The distribution patterns of elements in the microstructure of the studied coating are discussed. The relationship between refractive index of the coatings, and the intensity ratio of D and G peaks in the Raman spectrum has been established.     

Bi-level surface modification of hard disk media by carbon using filtered cathodic vacuum arc: Reduced overcoat thickness without reduced corrosion performance

The corrosion performance of commercial hard disk media which was subjected to bi-level surface modification has been reported. The surface treatment was carried out by bombarding the surface of the magnetic media with C⁺ ions at 350 eV followed by 90 eV using filtered cathodic vacuum arc (FCVA). The energy and embedment depth of the impinging C⁺ ions were adjusted by applying an optimized bias to the substrate and simulated by a Stopping and Range of Ions in Matter (SRIM) code which predicted the formation of a graded atomically mixed layer at the carbon-media interface. Cross-section transmission electron microscopy (TEM) revealed the formation of a 1.8 nm dense nano-layered carbon overcoat structure on the surface of the media. Despite an ~ 33% reduction in the thickness, the bi-level surface modified disk showed corrosion performance similar to that of a commercially manufactured disk with a thicker carbon overcoat of 2.7 nm. This improvement in the corrosion/oxidation resistance per unit thickness can be attributed to the formation of a dense and highly sp³ bonded carbon layer, as revealed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. This study demonstrates the effectiveness of the bi-level surface modification technique in forming an ultra-thin yet protective overcoat for future hard disks with high areal densities.     

The carbon nitride films prepared at various substrate temperatures by vacuum cathodic arc method

Carbon nitride films have been grown by vacuum cathodic arc method in the substrate temperature range of 100–500 °C. The bonding structure of the films was investigated by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and infrared (IR) spectroscopy. With increasing substrate temperature, the films indicate various characteristics. At 100 °C, it can be described as a network similar to DLC in which aromatic sp²C phase is cross-linked by sp³C phase. Between 200 and 400 °C, with increasing substrate temperature the films become graphitized and the sp²CN phase increases, meanwhile the non-aromatic sp²CN phase appears at the edges of aromatic clusters in planar position as well as in out-of-planar regions. While at 500 °C the non-aromatic sp²CN phase almost comes to the same level as the aromatic sp²CN phase. So in the network of the film the aromatic sp²C phase is cross-linked by the non-aromatic sp²C phase. Based on the variation of the microstructure of the films, a comprehensive assignment pattern for the XPS C1s and N1s at different substrate temperature is proposed. In addition, the interpretation of p electron band in valence band spectra at various substrate temperatures is also discussed.     

Temperature sensibility of amorphous diamond films prepared by filtered arc

The low temperature sensibility and the thermal stability in air of amorphous diamond (a-D) films deposited by filtered arc have been investigated with visible Raman spectroscopy. The films cooled in a range of room temperature to − 190 °C by a liquid nitrogen pump were in-situ measured on a Linkam stage. The films for thermal stability were heated in a furnace. It has been found that the films are thermally very stable in air. They can hold their hardness up to 400 °C and their structure up to 500 °C. However, complete material loss occurs if the temperature is continuously raised. Raman measurements show a shift of the G-peak frequency to higher values with increasing temperature. The films are not sensitive to low temperature and remain stable as temperature is decreased down to − 190 °C.     

Improved wear imbalance with multilayered nanocomposite nanocrystalline Cu and tetrahedral amorphous carbon coating

Tetrahedral amorphous carbon (ta-C) has a relatively high hardness, and it can be used to enhance film properties such as wear resistance. However, the high hardness of ta-C can adversely affect a counterpart and accelerate its wear, and the resulting wear imbalance between the film and its counterpart can cause vibrations. This issue may be resolved by improving the wear of the counterpart. This study aimed to reduce the hardness and improve the fracture toughness of ta-C films to enhance the durability of a tribosystem, which was achieved by toughening a composite and ductile phase. A multilayered nanocrystalline (nc)-Cu/ta-C nanocomposite film was fabricated that allowed for reductions in the wear of the film and its counterpart of more than 88% and 99%, respectively.     

Electron field emission from filtered arc deposited diamond-like carbon films using Au and Ti layers

In this work, tetrahedral diamond-like carbon (DLC) films are deposited on Si, Ti/Si and Au/Si substrates by a new plasma deposition technique — filtered arc deposition (FAD). Their electron field emission characteristics and fluorescent displays of the films are tested using a diode structure. It is shown that the substrate can markedly influence the emission behavior of DLC films. An emission current of 0.1 μA is detected at electric field E_DLC/Si=5.6 V/μm, E_DLC/Au/Si=14.3 V/μm, and E_DLC/Ti/Si=5.2 V/μm, respectively. At 14.3 V/μm, an emission current density J_DLC/Si=15.2 μA/cm², J_DLC/Au/Si=0.4 μA/cm², and J_DLC/Ti/Si=175 μA/cm² is achieved, respectively. It is believed that a thin TiC transition layer exists in the interface between the DLC film and Ti/Si substrate.     

Electrical properties of a-C: Mo films produced by dual-cathode filtered cathodic arc plasma deposition

Molybdenum-containing amorphous carbon (a-C:Mo) thin films were prepared using a dual-cathode filtered cathodic arc plasma source with a molybdenum and a carbon (graphite) cathode. The Mo content in the films was controlled by varying the deposition pulse ratio of Mo and C. Film sheet resistance was measured in situ at process temperature, which was close to room temperature, as well as ex situ as a function of temperature (300–515 K) in ambient air. Film resistivity and electrical activation energy were derived for different Mo and C ratios and substrate bias. Film thickness was in the range 8–28 nm. Film resistivity varied from 3.55 × 10^− 4 Ω m to 2.27 × 10^− 6 Ω m when the Mo/C pulse ratio was increased from 0.05 to 0.4, with no substrate bias applied. With carbon-selective bias, the film resistivity was in the range of 4.59 × 10^− 2 and 4.05 Ω m at a Mo/C pulse ratio of 0.05. The electrical activation energy decreased from 3.80 × 10^− 2 to 3.36 × 10^− 4 eV when the Mo/C pulse ratio was increased in the absence of bias, and from 0.19 to 0.14 eV for carbon-selective bias conditions. The resistivity of the film shifts systematically with the amounts of Mo and upon application of substrate bias voltage. The intensity ratio of the Raman D-peak and G-peak (I_D/I_G) correlated with the pre-exponential factor (σ₀) which included charge carrier density and density of states.