Properties Of Diamond-like Carbon Thin Films Research Articles

Correlation study of structural, optical, and hydrophobicity properties of diamond-like carbon films prepared by an anode layer source

Diamond- like carbon (DLC) thin films were deposited using anode layer source system on glass substrate at substrate temperature ranging from room temperature (RT) to 375 °C. An anode layer source is a specific ion gun, which can be fed with carbon precursors like propane to deposit hard and highly defect-free hydrogenated DLC thin films. The morphological, structural, optical, and hydrophobicity properties of DLC thin films were characterized by atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, UV- Vis spectrophotometer, and water contact angle (CA) measurement. The surface roughness was found to increase with substrate temperature. Disorder (D) and graphite (G) peak positions have been observed to respectively move toward 1400 cm−1 and 1546 cm−1, with substrate temperature, indicating a graphitization of DLC thin films, which may probably be ascribed to the sp2 cluster sites growth. The full width at half maximum (FWHM) of G peak increased upon increasing the substrate temperature. From the FWHM values of G peak, the clusters became more ordered with increasing the substrate temperature of DLC thin films. The G peak position changed by increasing the substrate temperature that in turn led to increment in the ID/IG ratio from 0.71 to 0.85, and also the graphite cluster size increased from 1.07 to 1.24 nm. Optical transmittance in UV and near infrared regions of the prepared DLC thin films found to decrease with the increase of substrate temperature. The refractive index (n) and extinction coefficient (k) of the films have been found to increase with substrate temperature. The CA of DLC thin films slightly increased with increasing substrate temperature from 80° at RT to 94° at 300 °C.

Effect of the Temperature on Diamond-Like Carbon (DLC) Thin Film Based on LIS

Diamond-like carbon (DLC) thin films were deposited on YG6 cemented carbide by an anode-layer linear ion source (LIS). The effect of different temperatures (20°C, 80°C, 115°C and 150°C) on DLC thin films was investigatedby using atomic force microscope (AFM), scanning electron microscope (SEM) and Raman spectroscopy. It was found thatthe surface roughness of the film decreased at first and then increased with the increase of the temperature, and reached the trough at 80°C. The intensity ratio (ID/IG) and the adhesion of the film increased at first and then decreased, and both of them reached the peak at 80°C. When the temperature was 80°C, the surface roughness was 6.9nm, the intensity ratio (ID/IG) was1.91 and the critical failure load was 107.23N. The results show that the temperatures have a great effect on the surface morphology and mechanism properties of DLC thin films. Consequently, this paperfurther studied the effect mechanism of different temperatures on DLC thin films based on the experiment.

Effect of titanium incorporation on the structural, mechanical and biocompatible properties of DLC thin films prepared by reactive-biased target ion beam deposition method

Amorphous diamond like carbon (DLC) and titanium incorporated diamond like carbon (Ti-DLC) thin films were deposited by using reactive-biased target ion beam deposition method. The effects of Ti incorporation and target bias voltage on the microstructure and mechanical properties of the as-deposited films were investigated by means of X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy and nano-indentation. It was found that the Ti content in Ti-DLC films gets increased with increasing target bias voltage. At about 4.2 at.% of Ti, uniform sized well dispersed nanocrystals were seen in the DLC matrix. Using FFT analysis, a facility available in the TEM, it was found that the nanocrystals are in cubic TiC phase. Though at the core, the incorporated Ti atoms react with carbon to form cubic TiC; most of the surface exposed Ti atoms were found to react with the atmospheric oxygen to form weakly bonded Ti–O. The presence of TiC nanocrystals greatly modified the sp 3/sp 2 hybridized bonding ratio and is reflected in mechanical hardness of Ti-DLC films. These films were then tested for their biocompatibility by an in vitro cell culturing test. Morphological observation and the cell proliferation test have demonstrated that the human osteoblast cells well attach and proliferate on the surface of Ti incorporated DLC films, suggesting possible applications in bone related implant coatings.

Surface adsorption and wetting properties of amorphous diamond-like carbon thin films for biomedical applications

Diamond-like carbon (DLC) thin films have unique properties for biological and medical applications due to their excellent bio-compatibility, chemical inertness, and superior mechanical properties. It is important to understand the surface properties of DLC thin films for these applications. In this work, we showed that after DLC deposition, NiTi surfaces became much smoother by choosing suitable deposition conditions. Adsorption and wetting properties of DLC films were studied. The adsorption properties of DLC films were unusual in that a hysteresis was found in the adsorption/desorption isotherms, which cannot be interpreted using the conventional theory of capillary condensation in pores. The model proposed in this work for this unusual hysteresis characteristic is that the hysteresis results from the non-wetting property of DLC surfaces in the nano-scale. The nano-sized droplets formed on the DLC surfaces may require significantly higher energy to evaporate than the formation energy. Argon plasma treatment resulted in a small decrease of the contact angles. After oxygen plasma treatment, the wetting contact angles reduced significantly due to the increase of carbon–oxygen sites on the surfaces, suggesting that the low concentration of carbon–oxygen sites on the surfaces of DLC films contributed to the adsorption hysteresis observed in this work.

Properties of DLC thin films produced by RF PE−CVD from pyrrole monomer

This paper reports the properties of diamond like carbon (DLC) thin films obtained in a capacitively coupled, RF powered, plasma enhanced chemical vapor deposition (PE−CVD) system. A precursor used was pyrrole, one of the most known monomers for conductive polypyrrole polymer processing. The deposition rate of thin films was high: 74 nm/min at 50 W and 425 nm/min at 400 W input power. The hardness and elastic modulus of thin films reached the highest values of 16.5 and 148 GPa at 400 W and the surface morphology of the films did not suffer important changes in the interval of utilized input powers: RMS roughness decreased from 0.45 nm at 50 W to 0.20 nm at 400 W. All deposited films were transparent in the infrared range. Raman measurements revealed that the increase of the input power led to a decrease of the sp3 and an increase of sp2 bonded carbon atoms in thin films. The resistivity of DLC thin films was very high for low values of RF input power (ρ>107 kΩ cm) and decreased at higher values of input power (ρ≈55 kΩ cm at 400 W). By using nitrogen as a doping element the resistivity decreased to ρ≈3.5 kΩ cm at 400 W and 20 sccm N2.

Structure of diamond-like carbon films containing transition metals deposited by reactive magnetron sputtering

The addition of transition metal (Mo, Nb, Ti, W) atoms within the matrix of diamond-like carbon (DLC) films leads to the improving of their mechanical properties. In this work, we study the effects of the different metal induced structures on the electrical, optical and mechanical properties of DLC thin films. The samples were prepared at room temperature by pulsed-DC reactive magnetron sputtering, as a suitable way to vary their composition. X-ray photoelectron spectroscopy (XPS) evidenced a smooth variation of the composition with relative methane flow. Metal-DLC (Me-DLC) films are generally uniform in composition, as confirmed by secondary ion mass spectrometry (SIMS). Cross-section micrographs of the films, observed by transmission electron microscopy (TEM), showed relevant structural differences, which led to strong variations of physical properties. Among these variations, we can point to a better control of roughness, measured by atomic force microscopy (AFM), and stress. Indentation essays on W-DLC films have been performed in order to obtain the dependence of hardness with W concentration. Optical properties determined by UV–VIS spectroscopic ellipsometry evidenced the influence of methane dilution. The electrical measurements show a thermally activated conductivity, whose range of values and activation energy depend on the metal abundance. Me-DLC films suppose an advance in hard and wear-resistant coatings development.

Intrinsic mechanical properties of diamond-like carbon thin films deposited by filtered cathodic vacuum arc

The mechanical properties—Young’s modulus (E) and hardness (H)—of diamond-like carbon (DLC) thin films deposited on p2+ Si (100) by filtered cathodic vacuum arc with different substrate bias voltage have been studied by nanoindentation measurement, where the substrate effect is included. Their intrinsic properties [including E,H, and yield strength (Y)] without the substrate effect are then derived by finite element analysis. The results show that the intrinsic mechanical properties of the DLC thin films are not affected by the film thickness, but significantly affected by change of sp3 bonding fraction caused by varied substrate bias. An empirical relationship among E, Y, and H for DLC thin films has been built, where E, Y, and H are intrinsic properties of DLC thin films. It is also confirmed that, as an empirical rule, the measured H could be used to represent its intrinsic value when the indentation depth is limited to 10% of the film thickness. However, the measured E with the substrate effect does not observe this empirical rule.

The effects of Si incorporation on the electrochemical and nanomechanical properties of DLC thin films

Silicon-doped diamond-like carbon (DLC) films with a Si content of up to 20.2 at.% were grown on Al2O3–TiC substrate by plasma-enhanced chemical vapour deposition. The influence of Si addition on the bonding structure, nanomechanical and corrosion behaviour of the DLC films was investigated by Raman and X-ray photoelectron (XPS) spectroscopy, nano-indentation, potentiodynamic and electrochemical impedance spectroscopy (EIS). Silicon addition promoted the formation of sp3 bonding and reduced the hardness. The deterioration of the nanomechanical properties is related to the increased hydrogen content in the films, leading to the formation of a polymeric sp3 CHn structure. The high hydrogen concentration in the Si-containing DLC samples was established by the increased Raman background slope. The EIS were analysed within the context of an equivalent circuit, which incorporated two time constants representing the DLC coating and the solution/Al2O3–TiC interface. Introduction of Si in the DLC led to significant improvements in the corrosion resistance of DLC, as revealed by increase in the charge transfer resistance and reduction in the anodic current of the polarisation curves. Films with a thickness of 20 nm remained intact after the polarisation scan when the Si concentration was increased above 11.8 at.%. The improvements in corrosion resistance are related to the formation of a passivation layer, which fills the pores present in the films.

The effects of Si incorporation on the microstructure andnanomechanical properties of DLC thin films

A small amount of silicon incorporation into diamond-like carbon (DLC) filmsprepared by plasma-enhanced chemical vapour deposition (PECVD) ontoAl2O3:TiC substrates was studied by a combination of surface analysisand nanomechanical measurement techniques, namely XPS, Raman spectroscopy,nanoindentation and nanoscratch methods. Addition of silicon to the DLC filmsleads to an increase in the fraction of sp3, as deduced from XPS analysis,and a decrease in the Raman band intensity ratio ID/IG. Although thecoated substrates exhibit better scratch resistance and lubricity, the filmsas deposited are softer than the Al2O3:TiC substrates. Upon siliconincorporation, the mechanical and tribological properties are degraded. Wearprotection of the Al2O3:TiC substrate by DLC coating corresponds to thecompetition between the reduction in friction coefficient and the softening ofthe films. It is suggested that, for such a PECVD process, the degradation ofthe mechanical properties is caused by the increased hydrogen content in thedeposits when silicon is incorporated, as is shown by the increased Ramanspectral background slope. These tendencies are attributable to thedevelopment of polymer-like chains, which can weaken the inter-molecularstructure of the films.

Fabrication and characterization of diamond-like carbon thin films by pulsed laser deposition

Diamond-like carbon (DLC) thin films have shown advantageous field emission properties due to a negative electron affinity (NEA) and low work function. The experiment was performed at substrate temperature in the range of room temperature to 600°C. The laser energy density used was in the range 6–20 J/cm 2. SEM, Raman, photoluminescence (PL), XPS and I– V measurement were used to investigate the microstructure and the field emission properties of DLC thin films. Deposition parameters, such as laser energy density and substrate temperature were optimized for the application of field emission properties. Good field emission properties were obtained with E th=5.03 V/μm at 300°C and 12 J/cm 2.

Thermal properties of DLC thin films bombarded with ion beams

We have studied the change in the thermal annealing properties of diamond-like carbon (DLC) films bombarded with ion beams. The carbon films were deposited on silicon wafers by evaporating a glassy carbon material. After the depositions, the carbon films were bombarded with argon, nitrogen or helium ions. The bombardments were performed with doses ranging from 5×10 15 to 5×10 17 ions cm −2at acceleration voltages ranging from 20 to 40 kV. The bombarded carbon films were annealed at 673 K, 773 K or 873 K in a vacuum. The chemical structure and mechanical properties were evaluated by measuring Raman spectra and microhardness testing, respectively. The results are as follows: 1. The carbon structure changes to a graphitic structure after annealing. Correspondingly the hardness of the films decreases. 2. Ion bombardment causes a decrease in the temperature at which the structure of the carbon films begins to become graphitic. 3. Bombardment with light ions, such as helium ions, makes the structure of carbon films change more to a graphitic structure than bombardment with heavier ions.