Diamond-like carbon (DLC) is a metastable amorphous film that exhibits unique properties. However, many limitations exist regarding the use of DLC, for example, its tribological characteristics at high temperature, as well as its limited thermal stability. In this study, silicon/oxygen and silicon/nitrogen co-incorporated diamond-like carbon (Si-O-DLC and SiN -DLC) films are studied, taking into account the thermal stability and tribological performance of these films compared with pure DLC. All the films were prepared on Si wafers, WC-Co materials, and aluminum foils using a plasma-based ion implantation (PBII) technique using acetylene (C 2 H 2), tetramethylsilane (TMS, Si(CH 3) 4), oxygen (O 2) and nitrogen (N 2) as plasma sources. The structure of the films was characterized using Raman spectroscopy. The thermal stability of the films was measured using thermogravimetric and differential thermal analysis (TG-DTA). The friction coefficient of the films was assessed using ball-on-disk friction testing. The results indicate that SiN -DLC films present better thermal stability due to the presence of Si-O networks in the films. The SiN -DLC (23 at.%Si, 8 at.%N) film was affected using thermal annealing in an air atmosphere with increasing temperature until 500˚C. The film can also resist thermal shock by cycling 10 times between the various temperatures and air atmosphere until 500˚C. Further, Si-O-DLC and SiN -DLC films exhibit excellent tribological performance, especially the SiN -DLC (23 at.%Si, 8 at.%N) film, which exhibits excellent tribological performance at 500˚C in an air atmosphere. It is concluded that Si-O-DLC and SiN -DLC films improve upon the thermal stability and tribological performance of DLC.

Abstract-Diamond-like carbon (DLC) thin films can be used in numerous industrial applications, including biomedical modified-surfaces with biocompatible and wetting properties. It is important to understand the surface properties of DLC thin films for these applications. In this study, oxygen (O 2 ) plasma treatment on DLC film surfaces is studied, taking into account the effects of radio frequency (RF) power and treatment time on wetting property. All the films were prepared on Si (100) wafers using a plasma-based ion implantation (PBII) technique using acetylene (C 2 H 2 ) as the plasma source. The deposited DLC films were then treated with oxygen plasma using various RF powers and treatment times in order to characterize the wettability, compared to as-deposited DLC film. The thickness and structure of the films were evaluated using stylus profilometer and Raman spectroscopy. The wettability of the films was assessed using a contact angle meter. The results indicate the oxygen plasma treatment on DLC film surfaces influenced to thickness change, but unaffected to structure of the films with various RF powers and treatment times. Further, oxygen plasma-treated DLC films exhibit a hydrophilic surface due to the introduction of some hydroxyl and carbonyl groups onto the DLC film surface. It is concluded that oxygen plasma treatment can be used to make hydrophilic DLC, making it a favorable wetting surface for biomedical applications.

Diamond-like carbon (DLC) is a metastable amorphous film that exhibits unique properties. However, a number of limitations exist regarding the use of DLC, for instance, its tribological characteristics. In this article, the fluorine and silicon incorporated diamond-like carbon (F-DLC and Si-DLC) films are studied, taking into account the tribological properties of these films compared with pure DLC. The structures of the films were characterized using Auger electron spectroscopy and Raman spectroscopy. The hardness and elastic modulus were evaluated by nanoindentation hardness testing. The friction behavior was assessed using ball-on-disk friction testing and optical microscopy. The results indicated that the deposited DLC films contained 0.6-2.1 at.% F and 26.7-38.4 at.% Si. A decrease in the hardness and elastic modulus was obtained as F increased in content, which was the opposite of the behavior observed in the Si-DLC films. This was due to the shifting in the G-peak position, which is related to the sp 3 bonding fraction in the film. When measured in ambient air, the addition of Si into the DLC film strongly influenced the friction coefficient, whereas doping with F only slightly influenced the films, as evidenced by their wear scars. In addition, only a 26.7 at.% Si-DLC film showed a very low friction coefficient when measured in dry air. This was attributed to the formation of silicon-rich transfer layer on the ball surfaces. Therefore, the addition of Si with 26.7 at.% content to a DLC film can be considered beneficial for improving tribological performance.

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Titanium and titanium alloys have found several applications in the biomedical field due to their unique biocompatibility. However, there are problems associated with these materials in applications in which there is direct contact with blood, for instance, thrombogenesis and protein adsorption. Surface modification is one of the effective methods used to improve the performance of Ti and Ti alloys in these circumstances. In this study, fluorinated diamond-like carbon (F-DLC) films are chosen to take into account the biocompatible properties compared with Ti alloys. F-DLC films were prepared on NiTi substrates by a plasma-based ion implantation (PBII) technique using acetylene (C2H2) and tetrafluoromethane (CF4) as plasma sources. The structure of the films was characterized by Raman spectroscopy. The contact angle and surface energy were also measured. Protein adsorption was performed by treating the films with bovine serum albumin and fibrinogen. The electrochemical corrosion behavior was investigated in Hanks’ solution by means of a potentiodynamic polarization technique. Cytotoxicity tests were performed using MTT assay and dyed fluorescence. The results indicate that F-DLC films present their hydrophobic surfaces due to a high contact angle and low surface energy. These films can support the higher albumin-to-fibrinogen ratio as compared to Ti alloys. They tend to suppress the platelet adhesion. Furthermore, F-DLC films exhibit better corrosion resistance and less cytotoxicity on their surfaces. It can be concluded that F-DLC films can improve the biocompatibility properties of Ti alloys.