Metal-containing Diamond-like Carbon Films Research Articles

Surface Structuring of Diamond-Like Carbon Films by Chemical Etching of Zinc Inclusions

A diamond-like carbon (DLC) film with a nanostructured surface can be produced in a two-step process. At first, a metal-containing DLC film is deposited. Here, the combination of plasma source ion implantation using a hydrocarbon gas and magnetron sputtering of a zinc target was used. Next, the metal particles within the surface are dissolved by an etchant (HNO3:H2O solution in this case). Since Zn particles in the surface of Zn-DLC films have a diameter of 100–200 nm, the resulting surface structures possess the same dimensions, thus covering a range that is accessible neither by mask deposition techniques nor by etching of other metal-containing DLC films, such as Cu-DLC. The surface morphology of the etched Zn-DLC films depends on the initial metal content of the film. With a low zinc concentration of about 10 at.%, separate holes are produced within the surface. Higher zinc concentrations (40 at.% or above) lead to a surface with an intrinsic roughness.

Influences of Interfacial Carbonization on the Structure and Mechanical Properties of Multilayered Cr-Containing Diamond-Like Carbon Films

Regarding metal-containing diamond-like carbon (Me-DLC) multilayered films, current research has focused on the influences of macroelements in the transition layer on the mechanical properties. The understanding of influences of microinterfacial structures on the mechanical properties is far from enough. One example is the structure pattern due to carbonation around the layer-to-layer interfaces in the Me-DLC films. In this work, multilayered Cr-DLC films with three modulation periods (Λ) were deposited using midfrequency dual-magnetron sputtering, and the film microstructures and mechanical properties were investigated. Along with changes in Λ, interfacial carbonization induces microstructure changes, and the microstructures include carbon bond, phase compositions, and internal stresses. The microstructure changes affect the mechanical properties, including hardness, elastic modulus, fracture toughness, and adhesion. The results reveal that variation of mechanical properties is involved with the influenc...

Preparation of Metal-Containing Diamond-Like Carbon Films by Magnetron Sputtering and Plasma Source Ion Implantation and Their Properties

Metal-containing diamond-like carbon (Me-DLC) films were prepared by a combination of plasma source ion implantation (PSII) and reactive magnetron sputtering. Two metals were used that differ in their tendency to form carbide and possess a different sputter yield, that is, Cu with a relatively high sputter yield and Ti with a comparatively low one. The DLC film preparation was based on the hydrocarbon gas ethylene (C2H4). The preparation technique is described and the parameters influencing the metal content within the film are discussed. Film properties that are changed by the metal addition, such as structure, electrical resistivity, and friction coefficient, were evaluated and compared with those of pure DLC films as well as with literature values for Me-DLC films prepared with a different hydrocarbon gas or containing other metals.

Nanoparticles as a Metal Source in Plasma Processes

When a metal is added to a layer of diamond-like carbon (DLC), the resulting particle size of the metal within the film usually depends on the metal content. To be more flexible in influencing the size of the particles that result when using a plasma based preparation process two different approaches were tested: on the one hand the combination of a gaseous precursor with magnetron sputtering, where a nanostructured coating is applied on top of the sputter target in advance; on the other hand, the addition of preformed metallic nanoparticles to a liquid. In both cases, the nanoparticles or -structures were prepared by a wet chemical process, whereas the DLC layer was prepared by a plasma process. The produced metal-containing DLC films were characterized regarding their metal content and distribution as well as regarding possible contaminations from the chemical preparation process.

Characterization of Cr Doped Diamond-Like Carbon Films and Research on Mechanical Properties

Diamond-like carbon (DLC) films have been extensively studied for more than a decade due to their unique combination of properties. The internal compressive stress affects their adhesion and preventing wide usage of these films. Metal-containing DLC films are expected to relax internal stress. The present work focused on the synthesis, chemical bond and mechanical property characterization of Cr-containing DLC films. The films thickness, internal stress and composition were characterized by scanning electron microscopy, optical interferometry and X-ray photoelectron spectroscopy respectively. Incorporation of Cr into DLC causes an initial internal stress reduction and subsequent stabilization around 0.5 GPa. The hardness behavior was found to depend on Cr content. Films with less than 7.36 at.% Cr (no formation of C-Cr bond) showed a dramatically hardness reduction compared to pure DLC films. Above 7.36 at.% Cr (C-Cr bond formed) the hardness increases above 12 GPa.

Activation energy in metal-containing DLC films with various metals of various concentrations

The activation energy of (Co, Mo, W)-containing diamond-like carbon (DLC) films with different metal concentrations was investigated. The films were deposited onto silicon substrates by radio frequency discharged methane plasma and a co-sputtering of the metal target. The structure of the films was analyzed by Raman spectroscopy and using a transmission electron microscope. The results indicated that crystalline metal clusters are dispersed in amorphous carbon insulating matrix, and hence the metal-containing DLC films investigated can be classified as granular films. The temperature dependence of the resistance was also measured. From the temperature dependence, the activation energy was calculated numerically using σ = σ 0exp(− E / kT). The calculated activation energy rapidly decreases as the metal concentration increases. This is because of the increase in the average size of the metal clusters. A detailed discussion is presented in terms of the radius of the metal clusters inside the films.

Boundary Lubrication Characteristic of Metal-Containing Diamond-Like Carbon (DLC) Films with Poly Alpha Olefin (PAO) Lubricant

The effects of metals such as cobalt (Co), cerium (Ce), magnesium (Mg), nickel (Ni) and titanium (Ti) added to diamond-like carbon (DLC) films on boundary lubrication properties were investigated using a ball-on disk tribometer. The boundary lubrication properties of metal-containing DLC films are improved compared with those of DLC films without metal under poly alpha olefin (PAO) lubricant with and without glycerol mono-oleate (GMO) additives. Moreover, under boundary lubrication using PAO with GMO, DLC films with an appropriate quantity of Co-added show the lowest friction coefficient of μ= 0.02 among all the tested metal-containing DLC films. The friction product layers were formed on the sliding surface of Co-containing DLC films. Lower-nanofriction layers formed on the sliding surface were observed by force modulation methods of atomic force microscopy (AFM).

Self-assembled Ni nanoclusters in a diamond-like carbon matrix

Trace amounts (∼5 at%) of metal-containing diamond-like carbon films (DLC) have been deposited using a Off Plane Double Bend Filtered Cathodic Vacuum Arc (OPDB-FCVA) system. The films prepared this way resulted in amorphous thin films where the metal atoms are randomly mixed in a DLC matrix. These films are sometimes called carbon composites. In this paper, the observation of self-assembled Ni nanoclusters by high resolution TEM in a DLC matrix is reported. This phenomenon has only been observed in Ni and not in other metals such as Al, W etc. These Ni nanoclusters have a diameter of ∼2 nm and XRD measurements confirms a (111) orientation while XPS shows that no carbide formation occurs between Ni and DLC.

Metal-doped diamond-like carbon films synthesized by filter-arc deposition

Diamond-like carbon (DLC) thin films are extensively utilized in the semiconductor, electric and cutting machine industries owing to their high hardness, high elastic modulus, low friction coefficients and high chemical stability. DLC films are prepared by ion beam-assisted deposition (BAD), sputter deposition, plasma-enhanced chemical vapor deposition (PECVD), cathodic arc evaporation (CAE), and filter arc deposition (FAD). The major drawbacks of these methods are the degraded hardness associated with the low sp 3/sp 2 bonding ratio, the rough surface and poor adhesion caused by the presence of particles. In this study, a self-developed filter arc deposition (FAD) system was employed to prepare metal-containing DLC films with a low particle density. The relationships between the DLC film properties, such as film structure, surface morphology and mechanical behavior, with variation of substrate bias and target current, are examined. Experimental results demonstrate that FAD-DLC films have a lower ratio, suggesting that FAD-DLC films have a greater sp 3 bonding than the CAE-DLC films. FAD-DLC films also exhibit a low friction coefficient of 0.14 and half of the number of surface particles as in the CAE-DLC films. Introducing a CrN interfacial layer between the substrate and the DLC films enables the magnetic field strength of the filter to be controlled to improve the adhesion and effectively eliminate the contaminating particles. Accordingly, the FAD system improves the tribological properties of the DLC films.

An analysis of the nanotribological behaviour of Ti-containing hard carbon film

Diamondlike carbon (DLC) coatings are well known for their self-lubricating properties. Metal-containing DLC films exhibit reduced internal stress, improved adhesion and reduced sensitivity to humidity. Furthermore, Ti-containing DLC coatings are compatible with biological environments. In view of this, the primary aim of the present work was to evaluate and analyse the friction force behaviour of Ti-containing hard carbon films. This work is primarily intended for application to microelectromechanical systems. In order to achieve the above mentioned objective, a hard carbon layer containing 6 at.-%Ti was deposited using an unbalanced magnetron sputter system on a silicon substrate. The deposition rate of the film was monitored by a quartz microbalance. Using a stylus profilometer, the thickness of the film was found to be 1·67 μm. The hardness and the elastic modulus of the film were determined using a nanoindenter. The hardness and the elastic modulus were determined to be 1·7 GPa and 17·7 GPa, respectively. The pull-off force, topography and friction force surface of the film were characterised with the use of an atomic force microscope. The pull-off force and the friction force were found to be 165·9 nN and 1·7 nN, respectively. The surface roughness Ra was found to be 2·65 nm. The friction coefficient was evaluated as a ratio of the friction force and the summation of the pull-off force and the normal force. Using the topography, and lateral force image, the topography induced friction force surface and the adhesion induced friction force surface were evaluated. The influences of applied loads and scan speeds on friction coefficient and various friction force surfaces are described in detail.

Mo-containing diamond-like carbon films with blue emission

Molybdenum-containing diamond-like carbon (Mo-DLC) thin films were synthesized on silicon substrate using metal cathodic arc and acetylene dual plasma deposition. Microstructural observations show that fine γ-MoC nanocrystallites with sizes of 1–2 nm are embedded in amorphous carbon cross-linked structures. The Mo-DLC films were found to have a photoluminescence (PL) band in blue. Due to obvious PL spectral asymmetry, we Gaussian divided the PL peak into two bands with the peak positions at about 405 and 455 nm. Spectral analyses suggest that the two blue PL bands arise from sp 2 hybridized carbon clusters with different sizes and γ-MoC nanocrystallites. Our experimental results provide the understanding of the blue-emitting properties of metal-containing diamond-like carbon films.

Nickel-incorporated amorphous carbon film deposited by femtosecond pulsed laser ablation

Metal-containing diamond-like carbon films (Me-DLC), with metallic particles embedded in a DLC matrix, have become good candidates to improve many film properties (including mechanical properties and adhesion) and to enhance the tribological behavior in severe conditions. Previous studies on the properties of Me-DLC coatings have reported lower compressive stresses and higher wear resistance compared to undoped DLC. In many cases, the presence of metal inclusions enhances adhesion on metallic substrates. The present study investigates the composition and nanostructure of DLC coating alloyed with 50 at.% concentration of nickel. The film is deposited by femtosecond pulsed laser ablation (PLD) by ablating sequentially graphite and nickel targets. The chemical composition and the bonding characteristics of this film are determined by X-ray Photoelectron Spectroscopy (XPS), Near Edge X-ray Absorption Spectroscopy (NEXAFS) and Electron Energy Loss Spectroscopy (EELS) imaging. The chemical composition, the carbon hybridization and the morphology of the a-C:Ni film at the microscopic scale are discussed, in relation to the thermodynamic phase diagram of the Ni–C system.

Composition and morphology of metal-containing diamond-like carbon films obtained by reactive magnetron sputtering

The addition of metal atoms within the matrix of diamond-like carbon films leads to the improvement of their mechanical properties. The present paper discusses the relationship between the composition and morphology of metal-containing (W, Nb, Mo, Ti) diamond-like carbon thin films deposited at room temperature by reactive magnetron sputtering from a metal target in an argon and methane atmosphere. Composition was measured either by electron microprobe technique or by X-ray photoelectron spectroscopy and shows a smooth variation with relative methane flow. High relative methane flows lead to a bulk saturation of carbon atoms, which leads to a lack of homogeneity in the films as confirmed by secondary ion mass spectrometry. Cross-section micrographs were observed by transmission electron microscopy and revealed a structure strongly influenced by the metal inserted and its abundance. The surface pattern obtained by scanning electrochemical potential microscopy provided the metallicity distribution. These measurements were completed with atomic force microscopy of the surface. Selected area electron diffraction and X-ray diffraction measurements provided data of the crystalline structure along with nano-crystallite size. High-resolution transmission electron microscopy provided images of these crystallites.

Preparation and properties of metal-containing diamond-like carbon films by magnetron plasma source ion implantation

Fe-, Co-, Ni-, and Mo-containing diamond-like carbon (DLC) films were prepared on silicon wafer and glass substrates by a process combining reactive magnetron sputtering with plasma source ion implantation (PSII). Fe, Co, Ni, and Mo were used as targets for the sputter source. Ar/C 2H 2 mixed gas was introduced into the discharge chamber. A negative high-voltage pulse (−10 kV, 100 Hz, 100 μs) was applied to the substrate holder. The chemical composition of the films was determined using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The surface morphology was observed by scanning electron microscopy (SEM). The film structure was characterized by Raman spectroscopy and X-ray diffractometry (XRD). The sheet resistivity of the films was measured by a four-point probe method. Furthermore, a ball-on-disc test was employed to obtain information about the frictional properties and sliding wear resistance of the films. The structure of the films changed from metal-containing DLC to composites of metal-containing DLC and metal carbides with increasing metal content in the films. The sheet resistivity of the films decreased drastically with increasing metal content in the films. The tribological properties of the films were improved by Mo doping.

Visible and infrared ellipsometry applied to the study of metal-containing diamond-like carbon coatings

Metal-containing diamond-like carbon (Me-DLC) films were deposited by combining r.f. plasma-enhanced chemical vapour deposition (PECVD) and pulsed d.c. magnetron sputtering of several target materials (Mo, Nb, Ti and W) at different gas mixtures of methane and argon (relative methane flow ratios varying from 0 to 25%). Spectroscopic ellipsometric measurements from 1.5 to 4.1 eV were performed by a multichannel rotating analyser ellipsometer. It can detect a full spectrum in 20 ms at fixed positions of the analyser. IR ellipsometric spectra of the Me-DLC thin films as well as of the bare substrates were obtained from 900 to 3500 cm −1 with a FTIR phase-modulated ellipsometer that takes advantage of an optimized calibration method. The optical properties (refractive index and absorption) showed a clear dependence on concentration and type of metal on the film. When methane flow ratio increases, the size and concentration of nanocrystalline particles determine the variation from pure metal optical properties to typical DLC values. Optical results are discussed along with X-ray diffraction data and ellipsometry allows for a high sensitive analysis of Me-DLC films.

Preparation and properties of metal containing diamond-like carbon films by magnetron plasma source ion implantation

Metal-containing diamond-like carbon (DLC) films were prepared on silicon wafer substrate by a process combining reactive magnetron sputtering with plasma source ion implantation (PSII). Ti and Ta were deposited simultaneously by RF magnetron sputtering of metal target and PSII using hydrocarbon gas, respectively. Ar/C 2H 2 mixed gas was introduced into the discharge chamber. The negative high voltage pulse (typically 10 kV, 100 Hz, 100 μs) was applied to the substrate holder. The chemical composition of the films was determined using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The surface morphology was observed by scanning electron microscopy (SEM). The film structure was characterized by Raman spectroscopy and X-ray diffractometry. The sheet resistivity of the films was measured by a four-point probe method. Furthermore, a ball-on-disc test was employed to obtain information about the frictional properties and sliding wear resistance of the films. The structure of the films changed from metal containing DLC to composite of metal containing DLC and metal carbides with increasing in metal content in the films. The sheet resistivity of the films was decreased drastically with increasing metal content in the films. The tribological properties of the films were improved by metal elements doping.

Metal incorporation into diamond-like carbon films from single source metalorganic precursors

The incorporation of carbide forming metals into diamond-like carbon (DLC) can considerably increase the film adhesion to steel substrates due to the release of internal stress. The main advantages of DLC-films, e.g., hardness, low abrasive wear and low friction coefficient are maintained. We report about a method to deposit metal-containing DLC films in a plasma activated process using different iron- and cobalt-containing volatile precursors. In the case of ferrocene (FeCp 2; Cp: Cyclopentadienyl) and cyclooctatetraen iron-tricarbonyl, for example, we found surprisingly high deposition rates up to 60 μm/h. The used process is characterized by means of r.f.-power/potential measurements and the film composition of different precursors as a function of the r.f.-power is discussed. A steplike change of the metal-content in the film reflects the change of the deposition mechanism from direct ion-incorporation to an additional path via an incorporation of small radicals.

Deposition of metal-containing diamond-like carbon films from metal—organic precursors using a plasma activated r.f. process

Plasma activated chemical vapour deposition from ferrocene as metalorganic precursor was used to prepare Fe-C:H-films for different substrate temperatures. The films were analyzed with X-ray induced photoelectron spectroscopy. From the temperature dependent step-like change of the film-composition with r.f. power, we postulate two different deposition mechanisms. For low r.f. power, the films grow by direct incorporation of larger fragmentations, while for higher r.f. power the deposition mechanism includes a deposition via an adsorption-layer of CH3-radicals. By analyzing the Fe2p-states, we determined the reactivity of the iron-bonds in the films. Conclusions are drawn about the fragmentation and the impinging ions on the film surface.