Adhesion Strength Of Diamond-like Carbon Films Research Articles

Effects of consecutive processing between cleaning and deposition on adhesion of diamond-like carbon prepared by plasma-based ion implantation and deposition

The effects of pretreatment on adhesion, which is the most important challenge of diamond-like carbon (DLC) films, were investigated. DLC films were prepared by changing pretreatment conditions on austenitic stainless steel (SUS304) substrates by hybrid process of plasma-based ion implantation and deposition (PBIID) using superimposed RF and negative high-voltage pulses. Although an oxide layer on a substrate surface was removed by Ar-plasma sputter cleaning, the substrate surface was immediately reoxidized when plasma was stopped for a moment between sputter cleaning and deposition. The DLC film on the oxide layer was poor adhesion strength less than approximately 50 MPa. Even if the oxide layer existed on the substrate surface, carbon ion implantation as an interface treatment in the PBIID process broke the oxide layer. As a result, the adhesion strength of DLC films was enhanced above the strength of epoxy resin (about 70 MPa). Furthermore, it was found that continuous generation of plasma after sputter cleaning was able to suppress reoxidation of the substrate surface. Consequently, the adhesion strength of DLC films prepared with no interface treatment was increased above 70 MPa, suggesting simplification of coating process and reduction in processing time for cost reduction.

Nitriding of high speed steel by bipolar PBII for improvement in adhesion strength of DLC films

In the present study, bipolar plasma based ion implantation and deposition (bipolar PBII) was used for plasma nitriding of high speed steel (SKH2), and the effects of the treatment parameters (positive pulse voltage, negative pulse voltage, treatment pressure, treatment time, and precursor gases) on the nitriding process were investigated. The hardness, roughness, and depth of nitride layer were also measured. The adhesion strength of diamond-like carbon (DLC) films coated on the nitride substrate was evaluated by carrying out Rockwell indentation and microscratch tests. Nitriding by bipolar PBII was achieved in the combining of two effects: nitrogen ion implantation by applying a high negative pulse voltage and thermal diffusion of nitrogen atoms under the application of a high positive pulse voltage. However, a very high voltage negative pulse caused surface roughening of the nitride layer. Application of a high positive pulse voltage during nitriding was found to be effective in promoting the thermal diffusion of the implanted nitrogen atoms. Effective nitriding could be achieved under the following conditions: high positive pulse voltage, low negative pulse voltage, high nitrogen gas pressure, and addition of hydrogen to the precursor gas. The adhesion strength of the DLC films on the SKH2 substrate was well improved after nitriding.

Comparative study between erbium and erbium oxide-doped diamondlike carbon films deposited by pulsed laser deposition technique

Diamondlike carbon (DLC) films doped with the same fraction of erbium and erbium oxide were prepared by using 248 nm KrF pulsed laser deposition system. The effects of erbium and erbium oxide on the surface morphology, microstructures, and mechanical property of DLC were investigated. Transmission electron microscopy showed that both erbium and erbium oxide retained their initial oxidation states while embedded as metal or metal-oxide nanoclusters in an amorphous matrix. Atomic force microscopy showed that erbium-doped and erbium oxide-doped DLC films were smooth with rms of less than 0.2 nm and closely resembled pure DLC film. The Raman analysis showed broad peaks centering around 1550 cm−1 on both samples. The deconvoluted Raman spectra showed that the ID/IG value of DLC film increased from 0.38 to ∼0.55 in the presence of erbium and erbium oxide, and the estimated sp3 content for the DLC nanocomposite films was ∼56%–57%. X-ray photoelectron spectroscopy (XPS) confirmed that the C 1s peaks for DLC nanocomposite were slightly shifted from 285.2 eV (diamond) to 284.5 eV (graphite). The deconvolution of XPS spectra further confirmed the amount of sp3 content and revealed the presence of a higher fraction of SiC bonding in erbium oxide-doped DLC film. Microscratch tester results showed that the presence of erbium oxide improved the adhesion strength of DLC film from ∼1.72 to ∼2.19 N, which was more effective than erbium at the same concentration (∼1.89 N). The coefficients of friction of the erbium-doped DLC and erbium oxide-doped DLC films were similar to that of pure DLC. Erbium and erbium oxide showed similar influence on the surface roughness, coefficient of friction, and sp3 content on DLC films, but improved adhesion strength, which was correlated with the SiC bonding states, was observed on erbium oxide-doped DLC.

The study on the effect of erbium on diamond-like carbon deposited by pulsed laser deposition technique

Diamond-like carbon (DLC) films doped with a small fraction of erbium (0.5–2.0 at. %, at 0.5 at. % interval) were prepared by using a 248 nm KrF pulsed laser deposition technique. The effects of erbium on the surface morphology, microstructure, chemical binding states, tribological property, and the adhesion strength of DLC films were investigated. Atomic force microscopy showed that the surface roughness of the films increased with the increasing of erbium fraction, but generally the nanocomposite films were smooth with rms below 1 nm. Raman analysis showed broad peaks centered at 1550 cm−1 on all the samples. The deconvoluted Raman spectra on DLC doped with different fractions of erbium showed that the ID/IG ratio increased with increasing erbium content, and the comparative percent of sp3 is between 50% and 58% for erbium fraction between 0.5 and 2.0 at. %. High resolution x-ray photoelectron spectroscopy confirmed that the C 1s peaks had slightly shifted away from 285.2 (diamond) to 284.5 eV (graphite). The deconvolution of the spectra further confirmed the influence of erbium to the sp3 contents and revealed the presence of SiC with the increasing of Er fraction. Microscratch tester results showed that the adhesion strength (critical load) of the films improved with the presence of SiC bonding at the interface. This hinted that the presence of the heavier erbium may force the impinging carbon ions to react more with the interface to form silicon carbide bonds, thus enhancing the adhesion strength. Although the presence of erbium increased the surface roughness of the films, the coefficients of friction of the erbium doped DLC films were still closely resembled to pure DLC, i.e., 0.11–0.12 compared to 0.10 for pure DLC.

Microstructure of interface for high-adhesion DLC film on metal substrates by plasma-based ion implantation

The diamond-like carbon (DLC) film was prepared on various metal substrates with a plasma-based ion implantation and deposition using superimposed RF and negative high-voltage pulses. The adhesion strength of DLC film was enhanced above the epoxy resin strength by implantation of carbon ions or mixed ions of carbon and silicon to the substrate surface before DLC deposition. In order to clarify the mechanism for improvement in adhesive strength, the microstructure of an interface between DLC film and substrate was examined in detail by transmission electron microscopy (TEM) observations in combination with EDS analysis. As a result, the enhancement in adhesion strength of DLC film by C ion implantation resulted from the formation of amorphous-like phase in the ion-implanted region of substrate, the production of carbon-component graded interface, the destruction of the oxide layer on the top surface of substrate, and the reduction of residual stress in DLC film by ion implantation during the deposition. The production of stress-free DLC film allowed us to demonstrate a supra-thick DLC film of more than 400 μm in thickness.

STEM observation of nano-interface between substrate and DLC film prepared by plasma-based ion implantation and deposition

This paper discusses the nano-interface between an aluminum alloy (A5052) substrate and diamond-like carbon (DLC) film prepared by a hybrid process of plasma-based ion implantation and deposition (PBIID) using superimposed RF and negative high-voltage pulses. Adhesion strength of DLC films were enhanced by carbon ion implantation to the substrate. The nano-interface between DLC film and substrate was observed by high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) and analyzed by energy dispersive X-ray spectroscopy (EDS). It was found that an unclear crystal structure damaged by ion implantation was formed in the carbon ion-implanted layer. Besides, the amorphous mixing layer of oxide and DLC was produced on the substrate surface. The formation of the mixing layer, the layer of unclear crystal structure and the destruction of oxide led to the enhancement in adhesion strength of DLC film.

Effect of a hard supra-thick interlayer on adhesion of DLC film prepared with PBIID process

Diamond-like carbon (DLC) films were prepared on aluminum alloy (A5052) and tungsten-carbide (WC) substrates with plasma-based ion implantation and deposition (PBIID) using hydrocarbon gas. Adhesion strength of DLC film was increased by the formation of interfacial mixing layer by carbon ion implantation and the production of SiCx nanolayer on the substrate prior to DLC deposition. As DLC films on the softer substrate were broken easily because of large deformation of substrate by local loads, the hard and supra-thick interlayer of plasma-sprayed tungsten-carbide (WC) with the thickness of 100–200μm was produced to protect the softer substrate between the DLC film and the substrate. The scratch testing evaluation showed that the supra-thick WC interlayer improved remarkably the adhesion of DLC films on the aluminum alloy substrate and the thicker WC interlayer was more effective for improvement of adhesion.

Measurement of Adhesion Strength of DLC Film Prepared by Utilizing Plasma-Based Ion Implantation

High-adhesion diamond-like carbon (DLC) film was prepared by a hybrid process of plasma-based ion implantation and deposition using superimposed RF and high-voltage pulses. The adhesion strength of DLC film on a stainless steel (SUS304) was enhanced by the carbon ion implantation to the substrate. Furthermore, ion implantation of mixed carbon and silicon led to considerable enhancement of adhesion strength above the resin glue strength. The adhesion strength of DLC film on the aluminum alloy (A-5052) was improved above the resin glue strength only by the carbon ion implantation to the substrate.

Improved productivity on diamond-like carbon coating optical disk stamper

We report on a proposed process for depositing a diamond-like carbon (DLC) film on the back surface of a submaster stamper after a nickel electroforming process. This process could keep friction low and improve the productivity of an optical disk. Hydrogenated amorphous carbon films were deposited from a mixture of argon and acetylene by electron cyclotron resonance-chemical vapor deposition at pressures of about 5–9×10−3 mbar. In order to improve the adhesion strength of DLC films, functionally gradient Ti/TiN/TiCN supporting mutilayers were deposited on the stampers. The structural characteristics of DLC films were investigated by Raman spectroscopy. The properties of a DLC film coating on a stamper are summarized as follows: microhardness (five times improved), roughness less than 4 nm, excellent adhesion of 65 N, and coefficients of friction less than 0.1. The characteristics of the back surface coated by DLC film were improved, and the productivity of an optical disk per stamper is estimated at about 1.7 times more than obtained. Finally, the DLC submaster stamper could be used to overcome the barrier and dramatically improve the economics and yield of increased productivity of polymer compact disks.

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

Diamond-like carbon (DLC) films were prepared on AISI 440C steel substrates at room temperature by the electron cyclotron resonance chemical vapor deposition (ECR-CVD) process in C 2H 2/Ar plasma under different conditions. In order to prevent the inter-diffusion of carbon and improve the adhesion strength of DLC films, functionally gradient Ti/TiN/TiCN/TiC supporting underlayers were deposited on the steel substrates in advance. Using the designed interfacial transition layers, relatively thick DLC films (1–2 μm) were successfully prepared on the steel substrates without delamination. By optimizing the deposition parameters, DLC films with hardness up to 28 GPa and friction coefficients lower than 0.15 against the 100Cr6 steel ball were obtained. In addition, the specific wear rates of the films were found to be extremely low (∼10 −17 m 3/Nm). The friction-induced graphitization mechanism of DLC was confirmed by micro-Raman analysis.

Adhesion strength of DLC films on glass with mixing layer prepared by IBAD

The improvement of the adhesion of diamond-like carbon (DLC) films has been tried by ion beam assisted deposition (IBAD). The adhesion strength must be quantitatively evaluated and determined in order to confirm the improving effect of the adhesion of DLC films by IBAD. In this study, DLC films were prepared on a glass substrate with a mixing layer prepared by IBAD. For the samples, the scratch tests were carried out using a scratch tester with a CCD camera and two AE sensors. The detachment process of the DLC film during a scratch test was observed and the detachment area was measured. On the other hand, AE signals were detected corresponding to the detachment of the DLC film, and the force causing the detachment was determined by analyzing the signals. The adhesion strength of DLC films was calculated from the detachment area and the force. From that result, the adhesion strength of DLC films without a mixing layer was 3.2 MPa. When the mixing layer was formed by IBAD with a condition of Ar-30 kV and 2.1 μA/cm 2, the adhesion strength increased to 10.7 MPa. Furthermore, that increased up to 44 MPa in the case of 21.0 μA/cm 2. Therefore, it was realized that IBAD improved the adhesion of DLC films and the effects were made clear quantitatively.

Pulsed laser deposition of titanium nitride and diamond-like carbon films on polymers

We have investigated the deposition of titanium nitride (TiN) and diamond-like carbon (DLC ) films on polymethylmethacrylate (PMMA) substrates using pulsed laser deposition (PLD) technique. The TiN and diamond-like films were deposited by laser ablation (KrF excimer laser λ = 248 nm, pulse duration τ∼25 × 10−9 s, energy density ∼2−15J/cm2) of TiN and graphite targets, respectively, at room temperature. These films were characterized by transmission electron microscopy, scanning electron microscopy, x-ray diffraction, Auger electron spectroscopy, UV-visible absorption spectroscopy, and Raman spectroscopy. The TiN films were smooth and found to be polycrystalline with average grain size of 120A. The diamond-like carbon films were amorphous with a characteristic Raman peak at 1550 cm−1. The TiN films are highly adherent to the polymer substrates as compare to DLC films. The adhesion strength of DLC films on polymers was increased by interposing thin TiN layer (200A) on polymers byin-situ pulsed laser deposition. The DLC films were found to be amorphous with good adhesion to TiN/PMMA substrates.